oxidation of alcohols experiment

This page will also refer constantly to . Follow this link if you haven't come across these compounds before.

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The electron-half-equation for this reaction is

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Primary alcohols can be oxidised to either aldehydes or carboxylic acids depending on the reaction conditions. In the case of the formation of carboxylic acids, the alcohol is first oxidised to an aldehyde which is then oxidised further to the acid.

You get an aldehyde if you use an excess of the alcohol, and distil off the aldehyde as soon as it forms.

The excess of the alcohol means that there isn't enough oxidising agent present to carry out the second stage. Removing the aldehyde as soon as it is formed means that it doesn't hang around waiting to be oxidised anyway!

If you used ethanol as a typical primary alcohol, you would produce the aldehyde ethanal, CH CHO.

The full equation for this reaction is fairly complicated, and you need to understand about electron-half-equations in order to work it out.

In organic chemistry, simplified versions are often used which concentrate on what is happening to the organic substances. To do that, oxygen from an oxidising agent is represented as [O]. That would produce the much simpler equation:

It also helps in remembering what happens. You can draw simple structures to show the relationship between the primary alcohol and the aldehyde formed.

If you are in the UK A level system (or its equivalent), it is highly likely that your examiners will accept equations involving [O]. To be sure, consult your . If you are studying a UK-based syllabus and haven't got any of these things, follow this link to find out how to get them.

You need to use an excess of the oxidising agent and make sure that the aldehyde formed as the half-way product stays in the mixture.

The alcohol is heated under reflux with an excess of the oxidising agent. When the reaction is complete, the carboxylic acid is distilled off.

The full equation for the oxidation of ethanol to ethanoic acid is:

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Alternatively, you could write separate equations for the two stages of the reaction - the formation of ethanal and then its subsequent oxidation.

This is what is happening in the second stage:

Secondary alcohols are oxidised to ketones - and that's it. For example, if you heat the secondary alcohol propan-2-ol with sodium or potassium dichromate(VI) solution acidified with dilute sulphuric acid, you get propanone formed.

Playing around with the reaction conditions makes no difference whatsoever to the product.

Using the simple version of the equation and showing the relationship between the structures:

If you look back at the second stage of the primary alcohol reaction, you will see that an oxygen "slotted in" between the carbon and the hydrogen in the aldehyde group to produce the carboxylic acid. In this case, there is no such hydrogen - and the reaction has nowhere further to go.

Tertiary alcohols aren't oxidised by acidified sodium or potassium dichromate(VI) solution. There is no reaction whatsoever.

If you look at what is happening with primary and secondary alcohols, you will see that the oxidising agent is removing the hydrogen from the -OH group, and a hydrogen from the carbon atom attached to the -OH. Tertiary alcohols don't have a hydrogen atom attached to that carbon.

You need to be able to remove those two particular hydrogen atoms in order to set up the carbon-oxygen double bond.

First you have to be sure that you have actually got an alcohol by testing for the -OH group. You would need to show that it was a neutral liquid, free of water and that it reacted with solid phosphorus(V) chloride to produce a burst of acidic steamy hydrogen chloride fumes.

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In the case of a primary or secondary alcohol, the orange solution turns green. With a tertiary alcohol there is no colour change.

After heating:

You need to produce enough of the aldehyde (from oxidation of a primary alcohol) or ketone (from a secondary alcohol) to be able to test them. There are various things which aldehydes do which ketones don't. These include the reactions with Tollens' reagent, Fehling's solution and Benedict's solution, and are covered on a separate page.

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Schiff's reagent is a fuchsin dye decolourised by passing sulphur dioxide through it. In the presence of even small amounts of an aldehyde, it turns bright magenta.

It must, however, be used absolutely cold, because ketones react with it very slowly to give the same colour. If you heat it, obviously the change is faster - and potentially confusing.

While you are warming the reaction mixture in the hot water bath, you can pass any vapours produced through some Schiff's reagent.

Because of the colour change to the acidified potassium dichromate(VI) solution, you must therefore have a secondary alcohol.

You should check the result as soon as the potassium dichromate(VI) solution turns green - if you leave it too long, the Schiff's reagent might start to change colour in the secondary alcohol case as well.

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© Jim Clark 2003 (modified October 2015)

Home / Demystifying The Mechanisms of Alcohol Oxidations

Alcohols, Epoxides and Ethers

By James Ashenhurst

• Demystifying The Mechanisms of Alcohol Oxidations

Last updated: August 5th, 2023 |

Alcohol Oxidation Mechanisms, Demystified

• The mechanisms for the oxidation of alcohols generally involve putting a good leaving group  on oxygen, followed by deprotonation of an adjacent C-H bond that results in elimination to give a new C-O pi bond.

• In this sense it greatly resembles an E2 mechanism.

• Oxidation of aldehydes to carboxylic acids usually involves addition of water to the aldehyde first (formation of a hydrate ) which then undergoes elimination with base.

Table of Contents

• E2: The Familiar Key Step At The Heart of (Almost) All Oxidation Reactions
• Oxidants Are Essentially Fancy Reagents For Attaching Leaving Groups To Oxygen
• What About Oxidation of Aldehydes  To Carboxylic Acids? ( Spoiler: Yes, that too )
• Why Don’t Ketones Oxidize Further?
• Summary:  Alcohol Oxidation Mechanisms

(Advanced) References and Further Reading

1. e2: the familiar key step at the heart of (almost) all alcohol oxidation reactions.

When I was learning organic chemistry I remember the reagents for oxidation reactions completely coming out of left field.

KMnO 4 , K 2 Cr 2 O 7 , PCC, CrO 3 , Swern, Dess—Martin ? Hold on. Where did these reagents come from? How do they work? Why chromium? What’s the mechanism?

In my course, the details of these reactions were completely glossed over. “ Don’t worry about the mechanism! No time to go through this! “ the instructor said. I was left with the impression that there was something deeply mysterious about alcohol oxidation.

Only later did I learn that it’s not mysterious at all. In fact the key mechanism is very familiar.

Let me show you what I mean.

Here’s a reaction we’ve seen before. Elimination of alkyl halides to give alkenes through an E2 mechanism . Base removes hydrogen, we break C-H, form C-C (π) and break C-LG. The result is an alkene.

Now imagine a slightly different E2 reaction, except one where the good leaving group is on oxygen. We’ll leave it vague, as “LG” for now.

See how we  break C-H, form C-O (π), and break O-LG, forming a new C-O π bond in the process. Since we’ve formed a new C-O bond at the expense of a C-H bond, an oxidation has occurred.

Believe it or not, most oxidation reactions of alcohols proceed exactly this way!  [Note 1 ]

I wish I’d known this when I was learning organic chemistry because it would have made alcohol oxidation seem a lot less mysterious.

2. Oxidants Are Essentially Just Fancy Reagents For Attaching Good “Leaving Groups” Directly To Oxygen

Hold on, you might say. It can’t possibly be that simple. Why do we have so many different types of oxidizing agents? And why do the mechanisms (like the Jones oxidation  here for example) seem so complicated?

Yes, there are a lot of steps in a typical oxidation reaction. However, most of these steps consist of:

• activating the oxidant (such as in the Swern oxidation, where oxalyl chloride converts DMSO to an electrophilic sulfur species, or in chromate oxidations, where strong acid converts chromate (such as K 2 Cr 2 O 7 ) to the active oxidant [H 2 CrO 4 ]
• coordination of the alcohol to the oxidant , followed by proton transfer(s) (seen in the mechanisms of most chromium oxidants, and Dess-Martin periodinane).

These steps are important, of course, but only in a supporting role. If you’ll excuse the analogy, they’re just foreplay that precedes the main event.

The effect of these beginning steps is simply to install a good leaving group on oxygen . That “good leaving group” can take many forms. It’s illustrated here with each oxidant, in green. There are, of course, many, many more oxidizing agents for alcohols than those depicted, but almost all of them essentially work the same way.

Treatment of each of these substrates with base then results in breakage of C-H, formation of C-O (π) and breakage of O-LG.

Each of these “leaving groups” accepts the pair of electrons from the bond to oxygen, reducing its oxidation state by 2 in the process. [remember – the oxidant is reduced,  the substrate is oxidized]

3. What About Oxidation Of Aldehydes To Carboxylic Acids?

So if oxidation of alcohols to aldehydes and ketones is essentially an E2 reaction, how do we explain oxidation of aldehydes to carboxylic acids?

See, given what we’ve just shown, you might initially think it works something like this:

That’s actually not what happens. [Why not? Because the aldehyde carbon is a good electrophile, and any species basic enough to remove the C-H is more likely to add to the aldehyde C ]

It actually follows the same type of process as with alcohols! However, there’s a trick.

There’s a missing ingredient not mentioned in the diagram above. Water.

What happens is that water adds to the aldehyde, forming a hydrate . [If this looks unfamiliar, you’ll see MANY variations of this type of mechanism in your upcoming chapter on aldehydes and ketones. This is a sneak preview]

NOW, the oxidant attaches to one of the hydroxyl groups of the hydrate. The E2 from here is much easier to visualize.

This also helps to explain one key observation made tangentially in the last post. The reagent CrO 3 /pyridine (Collins’ reagent) will oxidize primary alcohols to aldehydes and stop there.

However, if water is present, this oxidation will go all the way to carboxylic acids. That’s because the water will form a hydrate with the aldehyde, allowing for further oxidation.

No hydrate, no further oxidation.

4. Why Don’t Ketones Oxidize Further?

This also explains why ketones don’t oxidize further. There’s no hydrogen that can be removed in an E2-type process that will lead to a new double bond!

It’s similar to the old question of why this alkyl halide (below) doesn’t undergo elimination. There’s no hydrogen on the “beta” carbon (i.e. on the carbon adjacent to the carbon bearing the good leaving group) that can be removed, so no elimination occurs.

The same could be said for why tertiary alcohols don’t oxidize.

5. Summary: Alcohol Oxidation Mechanisms

So the bottom line for alcohol oxidation is the following.

• Pretty much every alcohol oxidation reaction you’ll encounter has the same key step: an E2-like deprotonation of C-H that results in formation of a new C-O pi bond and breakage of a transient leaving group.
• Aldehydes oxidize to carboxylic acids after formation of a hydrate .
• Ketones don’t oxidize further because there’s no C-H bond that can be broken that would result in a new C-O pi bond.

In the next post we’ll move to something completely different: intramolecular reactions of alcohols , a perennial subject of organic chemistry exams.

Next Post – Intramolecular Reactions Of Alcohols And Ethers

Related Articles

• Intramolecular Reactions of Alcohols and Ethers
• The E2 Mechanism
• Alcohol Oxidation: “Strong” and “Weak” Oxidants
• Hydrates, Hemiacetals, and Acetals
• Oxidation of secondary alcohols to ketones using PCC (MOC Reaction Guide)
• Oxidation of Primary Alcohols to Aldehydes using PCC (MOC Reaction Gudie)

Note 1. The main exception you’ll encounter is KMnO4, which likely proceeds through a C-H abstraction/internal return type mechanism followed by collapse of the hydrate to give the new carbonyl. That mechanism is mentioned in exactly zero introductory textbooks, so you likely don’t “need” to know this unless you are exceptionally curious about organic chemistry. [ back to post ]

Dess-Martin Periodinane:

• A useful 12-I-5 triacetoxyperiodinane (the Dess-Martin periodinane) for the selective oxidation of primary or secondary alcohols and a variety of related 12-I-5 species Daniel B. Dess and J. C. Martin Journal of the American Chemical Society 1991, 113 (19), 7277-7287 DOI: 1021/ja00019a027
• Oxidation of fluoroalkyl-substituted carbinols by the Dess-Martin reagent Russell J. Linderman and David M. Graves The Journal of Organic Chemistry 1989, 54 (3), 661-668 DOI : 10.1021/jo00264a029 #1 is by the developers of the eponymous ‘Dess-Martin Periodinane’, a hypervalent I(V) compound that has found widespread use as a mild oxidant in organic synthesis. Prof. J. C. Martin spent most of his career at University of Illinois Urbana-Champaign and ended his career at Vanderbilt University. During his career he contributed a lot towards our understanding of hypervalent main-group chemistry, preparing many S(IV), S(VI), Br(III), I(III), I(V), and I(VII) compounds, among others. Ref #2 extends the substrate scope to fluorinated alcohols, and the use of fluorine also enables mechanistic studies of the oxidation via 19 F NMR.Swern oxidation:
• Structure of the dimethyl sulfoxide-oxalyl chloride reaction product. Oxidation of heteroaromatic and diverse alcohols to carbonyl compounds Mancuso, A. J.; Brownfain, D. S.; Swern, D. J. Org. Chem. 1979, 44 (23): 4148–4150 DOI: 10.1021/jo01337a028
• Mechanisms of dimethylsulfoxide oxidations Kurt Torssell Tetrahedron Letters 1966 7 (37), 4445-4451 DOI: 1016/S0040-4039(00)70057-8 These papers are on what is now commonly called the “Swern oxidation” after its developer, Daniel Swern. This method is rather mild and uses DMSO, a common solvent, as the oxidant. However, this also results in the formation of dimethyl sulfide (which is notoriously stinky) as the product of the reaction, one of its noteworthy characteristics.Corey-Kim oxidation:
• New and highly effective method for the oxidation of primary and secondary alcohols to carbonyl compounds E. J. Corey; C. U. Kim Journal of the American Chemical Society 1972 , 94 (21): 7586–7587 DOI : 10.1021/ja00776a056.
• A method for the oxidation of sec,tert-1,2-diols to α-hydroxy ketones without carbon-carbon cleavage E. J. Corey; C. U. Kim Tetrahedron Letters 1974 , 15 (3): 287–290 DOI : 10.1016/S0040-4039(01)82195-X These papers by Nobel Laureate Prof. E. J. Corey (Harvard) are on the development of what is now known as the “Corey-Kim” oxidation. This is very similar to the Swern oxidation in that DMSO is used as the oxidant, except that here NCS (N-chlorosuccinimide) is used instead of oxalyl chloride. The advantage with this procedure is that temperatures above –25 °C can be used, and the disadvantage is that substrates susceptible to chlorination by NCS cannot be used.KMnO 4 oxidation:
• Oxidations with Manganese Dioxide P. Papadopoulos, A. Jarrar, and C. H. Issidorides The Journal of Organic Chemistry 1966 , 31 (2), 615-616 DOI: 10.1021/jo01340a520 As this paper shows, MnO 2 can also be used for oxidation of secondary alcohols.
• Synthesis of a model depsipeptide segment of Luzopeptins (BBM 928), potent antitumor and antiretroviral antibiotics Marco A. Ciufolini and Shankar Swaminathan Tetrahedron Letters Volume 30, Issue 23, 1989 , Pages 3027-3028 DOI: 1016/S0040-4039(00)99393-6 Step f in the synthesis ( Scheme 1 ) is an oxidation of a primary alcohol to carboxylic acid using KMnO 4 .
• Stereocontrolled addition to a penaldic acid equivalent: an asymmetric of -β-hydroxy-L-glutamic acid Philip Garner Tetrahedron Letters Volume 25, Issue 51, 1984 , 5855-5858 DOI : 10.1016/S0040-4039(01)81703-2 The final step ( g , 6 -> 7) in the synthesis in this paper is an oxidation of a primary alcohol to a carboxylic acid using KMnO 4 .PCC (pyridinium chlorochromate) oxidation:
• Pyridinium Chlorochromate: A Versatile Oxidant in Organic Synthesis Piancatelli, A. Scettri, M. D’Auria Synthesis 1982 ; 1982 (4): 245-258 DOI: 10.1055/s-1982-29766 Review on the applications of PCC in organic synthesis. Includes a discussion on the mechanism.
• Kinetics and Mechanism of the Oxidation of Alcohols by Pyridinium Chlorochromate Banerji Kalyan K. Bull. Chem. Soc. Jpn. 1978 , 51 (9), 2732 DOI: 10.1246/bcsj.51.2732 A nice mechanistic study of PCC oxidation, and includes a probable mechanism of the reaction.
• Stoichiometry of the oxidation of primary alcohols with pyridinium chlorochromate. Evidence for a two-electron change Herbert C. Brown, C. Gundu Rao, and Surendra U. Kulkarni The Journal of Organic Chemistry 1979 44 (15), 2809-2810 DOI: 1021/jo01329a051 In this paper, Nobel Laureate H. C. Brown proves that PCC oxidations involve a transfer of 2 electrons from the Cr to the substrate. Therefore, one does not need to use an excess of PCC – 1 equivalent works fine. The Jones oxidation, which uses chromic acid (CrO 3 in H 2 SO 4 ) is a common method for the oxidation of primary alcohols to carboxylic acids. The drawback is of course the production of stoichiometric amounts of chromium waste.
• Researches on acetylenic compounds. Part XIV. A study of the reactions of the readily available ethynyl-ethylenic alchohol, pent-2-en-4-yn-1-ol Sir Ian Heilbron, E. R. H. Jones and F. Sondheimer J. Chem. Soc., 1947, 1586-1590 DOI: 10.1039/JR9470001586
• An Improved Procedure for the Oxidation of Alkynols to Alkynoic Acids C. Holland and N. W. Gilman Synth. Commun. 1974 , 4 , 203-210 DOI: 10.1080/00397917408062073 Oxidation with PDC (pyridinium dichromate):
• Useful procedures for the oxidation of alcohols involving pyridinium dichromate in aprotic media E. J. Corey, Greg Schmidt Tetrahedron Letters Volume 20, Issue 5, 1979 , 399-402 DOI : 10.1016/S0040-4039(01)93515-4 Nobel Laureate Prof. E. J. Corey (Harvard) shows that PDC (pyridinium dichromate) in DMF can be used for the oxidation of primary alcohols to carboxylic acids.

00 General Chemistry Review

• Lewis Structures
• Ionic and Covalent Bonding
• Chemical Kinetics
• Chemical Equilibria
• Valence Electrons of the First Row Elements
• How Concepts Build Up In Org 1 ("The Pyramid")

01 Bonding, Structure, and Resonance

• How Do We Know Methane (CH4) Is Tetrahedral?
• Hybrid Orbitals and Hybridization
• How To Determine Hybridization: A Shortcut
• Orbital Hybridization And Bond Strengths
• Sigma bonds come in six varieties: Pi bonds come in one
• A Key Skill: How to Calculate Formal Charge
• The Four Intermolecular Forces and How They Affect Boiling Points
• 3 Trends That Affect Boiling Points
• How To Use Electronegativity To Determine Electron Density (and why NOT to trust formal charge)
• Introduction to Resonance
• How To Use Curved Arrows To Interchange Resonance Forms
• Evaluating Resonance Forms (1) - The Rule of Least Charges
• How To Find The Best Resonance Structure By Applying Electronegativity
• Evaluating Resonance Structures With Negative Charges
• Evaluating Resonance Structures With Positive Charge
• Exploring Resonance: Pi-Donation
• Exploring Resonance: Pi-acceptors
• In Summary: Evaluating Resonance Structures
• Drawing Resonance Structures: 3 Common Mistakes To Avoid
• How to apply electronegativity and resonance to understand reactivity
• Bond Hybridization Practice
• Structure and Bonding Practice Quizzes
• Resonance Structures Practice

02 Acid Base Reactions

• Introduction to Acid-Base Reactions
• Acid Base Reactions In Organic Chemistry
• The Stronger The Acid, The Weaker The Conjugate Base
• Walkthrough of Acid-Base Reactions (3) - Acidity Trends
• Five Key Factors That Influence Acidity
• Acid-Base Reactions: Introducing Ka and pKa
• How to Use a pKa Table
• The pKa Table Is Your Friend
• A Handy Rule of Thumb for Acid-Base Reactions
• Acid Base Reactions Are Fast
• pKa Values Span 60 Orders Of Magnitude
• How Protonation and Deprotonation Affect Reactivity
• Acid Base Practice Problems

03 Alkanes and Nomenclature

• Meet the (Most Important) Functional Groups
• Condensed Formulas: Deciphering What the Brackets Mean
• Hidden Hydrogens, Hidden Lone Pairs, Hidden Counterions
• Don't Be Futyl, Learn The Butyls
• Primary, Secondary, Tertiary, Quaternary In Organic Chemistry
• Branching, and Its Affect On Melting and Boiling Points
• The Many, Many Ways of Drawing Butane
• Wedge And Dash Convention For Tetrahedral Carbon
• Common Mistakes in Organic Chemistry: Pentavalent Carbon
• Table of Functional Group Priorities for Nomenclature
• Summary Sheet - Alkane Nomenclature
• Organic Chemistry IUPAC Nomenclature Demystified With A Simple Puzzle Piece Approach
• Boiling Point Quizzes
• Organic Chemistry Nomenclature Quizzes

04 Conformations and Cycloalkanes

• Staggered vs Eclipsed Conformations of Ethane
• Conformational Isomers of Propane
• Newman Projection of Butane (and Gauche Conformation)
• Introduction to Cycloalkanes (1)
• Geometric Isomers In Small Rings: Cis And Trans Cycloalkanes
• Calculation of Ring Strain In Cycloalkanes
• Cycloalkanes - Ring Strain In Cyclopropane And Cyclobutane
• Cyclohexane Conformations
• Cyclohexane Chair Conformation: An Aerial Tour
• How To Draw The Cyclohexane Chair Conformation
• The Cyclohexane Chair Flip
• The Cyclohexane Chair Flip - Energy Diagram
• Substituted Cyclohexanes - Axial vs Equatorial
• Ranking The Bulkiness Of Substituents On Cyclohexanes: "A-Values"
• Cyclohexane Chair Conformation Stability: Which One Is Lower Energy?
• Fused Rings - Cis-Decalin and Trans-Decalin
• Naming Bicyclic Compounds - Fused, Bridged, and Spiro
• Bredt's Rule (And Summary of Cycloalkanes)
• Newman Projection Practice
• Cycloalkanes Practice Problems

05 A Primer On Organic Reactions

• The Most Important Question To Ask When Learning a New Reaction
• Learning New Reactions: How Do The Electrons Move?
• The Third Most Important Question to Ask When Learning A New Reaction
• 7 Factors that stabilize negative charge in organic chemistry
• 7 Factors That Stabilize Positive Charge in Organic Chemistry
• Nucleophiles and Electrophiles
• Curved Arrows (for reactions)
• Curved Arrows (2): Initial Tails and Final Heads
• Nucleophilicity vs. Basicity
• The Three Classes of Nucleophiles
• What Makes A Good Nucleophile?
• What makes a good leaving group?
• 3 Factors That Stabilize Carbocations
• Equilibrium and Energy Relationships
• What's a Transition State?
• Hammond's Postulate
• Learning Organic Chemistry Reactions: A Checklist (PDF)
• Introduction to Free Radical Substitution Reactions
• Introduction to Oxidative Cleavage Reactions

06 Free Radical Reactions

• Bond Dissociation Energies = Homolytic Cleavage
• Free Radical Reactions
• 3 Factors That Stabilize Free Radicals
• What Factors Destabilize Free Radicals?
• Bond Strengths And Radical Stability
• Free Radical Initiation: Why Is "Light" Or "Heat" Required?
• Initiation, Propagation, Termination
• Monochlorination Products Of Propane, Pentane, And Other Alkanes
• Selectivity In Free Radical Reactions
• Selectivity in Free Radical Reactions: Bromination vs. Chlorination
• Halogenation At Tiffany's
• Allylic Bromination
• Bonus Topic: Allylic Rearrangements
• In Summary: Free Radicals
• Synthesis (2) - Reactions of Alkanes
• Free Radicals Practice Quizzes

07 Stereochemistry and Chirality

• Types of Isomers: Constitutional Isomers, Stereoisomers, Enantiomers, and Diastereomers
• How To Draw The Enantiomer Of A Chiral Molecule
• How To Draw A Bond Rotation
• Introduction to Assigning (R) and (S): The Cahn-Ingold-Prelog Rules
• Assigning Cahn-Ingold-Prelog (CIP) Priorities (2) - The Method of Dots
• Enantiomers vs Diastereomers vs The Same? Two Methods For Solving Problems
• Assigning R/S To Newman Projections (And Converting Newman To Line Diagrams)
• How To Determine R and S Configurations On A Fischer Projection
• The Meso Trap
• Optical Rotation, Optical Activity, and Specific Rotation
• Optical Purity and Enantiomeric Excess
• What's a Racemic Mixture?
• Chiral Allenes And Chiral Axes
• Stereochemistry Practice Problems and Quizzes

08 Substitution Reactions

• Introduction to Nucleophilic Substitution Reactions
• Walkthrough of Substitution Reactions (1) - Introduction
• Two Types of Nucleophilic Substitution Reactions
• The SN2 Mechanism
• Why the SN2 Reaction Is Powerful
• The SN1 Mechanism
• The Conjugate Acid Is A Better Leaving Group
• Comparing the SN1 and SN2 Reactions
• Polar Protic? Polar Aprotic? Nonpolar? All About Solvents
• Steric Hindrance is Like a Fat Goalie
• Common Blind Spot: Intramolecular Reactions
• The Conjugate Base is Always a Stronger Nucleophile
• Substitution Practice - SN1
• Substitution Practice - SN2

09 Elimination Reactions

• Elimination Reactions (1): Introduction And The Key Pattern
• Elimination Reactions (2): The Zaitsev Rule
• Elimination Reactions Are Favored By Heat
• Two Elimination Reaction Patterns
• The E1 Reaction
• E1 vs E2: Comparing the E1 and E2 Reactions
• Antiperiplanar Relationships: The E2 Reaction and Cyclohexane Rings
• Bulky Bases in Elimination Reactions
• Comparing the E1 vs SN1 Reactions
• Elimination (E1) Reactions With Rearrangements
• E1cB - Elimination (Unimolecular) Conjugate Base
• Elimination (E1) Practice Problems And Solutions
• Elimination (E2) Practice Problems and Solutions

10 Rearrangements

• Introduction to Rearrangement Reactions
• Rearrangement Reactions (1) - Hydride Shifts
• Carbocation Rearrangement Reactions (2) - Alkyl Shifts
• Pinacol Rearrangement
• The SN1, E1, and Alkene Addition Reactions All Pass Through A Carbocation Intermediate

11 SN1/SN2/E1/E2 Decision

• Identifying Where Substitution and Elimination Reactions Happen
• Deciding SN1/SN2/E1/E2 (1) - The Substrate
• Deciding SN1/SN2/E1/E2 (2) - The Nucleophile/Base
• SN1 vs E1 and SN2 vs E2 : The Temperature
• Deciding SN1/SN2/E1/E2 - The Solvent
• Wrapup: The Key Factors For Determining SN1/SN2/E1/E2
• Alkyl Halide Reaction Map And Summary
• SN1 SN2 E1 E2 Practice Problems

12 Alkene Reactions

• E and Z Notation For Alkenes (+ Cis/Trans)
• Alkene Stability
• Alkene Addition Reactions: "Regioselectivity" and "Stereoselectivity" (Syn/Anti)
• Stereoselective and Stereospecific Reactions
• Hydrohalogenation of Alkenes and Markovnikov's Rule
• Hydration of Alkenes With Aqueous Acid
• Rearrangements in Alkene Addition Reactions
• Halogenation of Alkenes and Halohydrin Formation
• Oxymercuration Demercuration of Alkenes
• Hydroboration Oxidation of Alkenes
• m-CPBA (meta-chloroperoxybenzoic acid)
• OsO4 (Osmium Tetroxide) for Dihydroxylation of Alkenes
• Palladium on Carbon (Pd/C) for Catalytic Hydrogenation of Alkenes
• Cyclopropanation of Alkenes
• A Fourth Alkene Addition Pattern - Free Radical Addition
• Alkene Reactions: Ozonolysis
• Summary: Three Key Families Of Alkene Reaction Mechanisms
• Synthesis (4) - Alkene Reaction Map, Including Alkyl Halide Reactions
• Alkene Reactions Practice Problems

13 Alkyne Reactions

• Acetylides from Alkynes, And Substitution Reactions of Acetylides
• Partial Reduction of Alkynes With Lindlar's Catalyst
• Partial Reduction of Alkynes With Na/NH3 To Obtain Trans Alkenes
• Alkyne Hydroboration With "R2BH"
• Hydration and Oxymercuration of Alkynes
• Hydrohalogenation of Alkynes
• Alkyne Halogenation: Bromination, Chlorination, and Iodination of Alkynes
• Alkyne Reactions - The "Concerted" Pathway
• Alkenes To Alkynes Via Halogenation And Elimination Reactions
• Alkynes Are A Blank Canvas
• Synthesis (5) - Reactions of Alkynes
• Alkyne Reactions Practice Problems With Answers

14 Alcohols, Epoxides and Ethers

• Alcohols - Nomenclature and Properties
• Alcohols Can Act As Acids Or Bases (And Why It Matters)
• Alcohols - Acidity and Basicity
• The Williamson Ether Synthesis
• Ethers From Alkenes, Tertiary Alkyl Halides and Alkoxymercuration
• Alcohols To Ethers via Acid Catalysis
• Cleavage Of Ethers With Acid
• Epoxides - The Outlier Of The Ether Family
• Opening of Epoxides With Acid
• Epoxide Ring Opening With Base
• Making Alkyl Halides From Alcohols
• Tosylates And Mesylates
• PBr3 and SOCl2
• Elimination Reactions of Alcohols
• Elimination of Alcohols To Alkenes With POCl3
• Alcohol Oxidation: "Strong" and "Weak" Oxidants
• Protecting Groups For Alcohols
• Thiols And Thioethers
• Calculating the oxidation state of a carbon
• Oxidation and Reduction in Organic Chemistry
• Oxidation Ladders
• SOCl2 Mechanism For Alcohols To Alkyl Halides: SN2 versus SNi
• Alcohol Reactions Roadmap (PDF)
• Alcohol Reaction Practice Problems
• Epoxide Reaction Quizzes
• Oxidation and Reduction Practice Quizzes

15 Organometallics

• What's An Organometallic?
• Formation of Grignard and Organolithium Reagents
• Organometallics Are Strong Bases
• Reactions of Grignard Reagents
• Protecting Groups In Grignard Reactions
• Synthesis Problems Involving Grignard Reagents
• Grignard Reactions And Synthesis (2)
• Organocuprates (Gilman Reagents): How They're Made
• Gilman Reagents (Organocuprates): What They're Used For
• The Heck, Suzuki, and Olefin Metathesis Reactions (And Why They Don't Belong In Most Introductory Organic Chemistry Courses)
• Reaction Map: Reactions of Organometallics
• Grignard Practice Problems

16 Spectroscopy

• Degrees of Unsaturation (or IHD, Index of Hydrogen Deficiency)
• Conjugation And Color (+ How Bleach Works)
• Introduction To UV-Vis Spectroscopy
• UV-Vis Spectroscopy: Absorbance of Carbonyls
• UV-Vis Spectroscopy: Practice Questions
• Bond Vibrations, Infrared Spectroscopy, and the "Ball and Spring" Model
• Infrared Spectroscopy: A Quick Primer On Interpreting Spectra
• IR Spectroscopy: 4 Practice Problems
• 1H NMR: How Many Signals?
• Homotopic, Enantiotopic, Diastereotopic
• Diastereotopic Protons in 1H NMR Spectroscopy: Examples
• C13 NMR - How Many Signals
• Liquid Gold: Pheromones In Doe Urine
• Natural Product Isolation (1) - Extraction
• Natural Product Isolation (2) - Purification Techniques, An Overview
• Structure Determination Case Study: Deer Tarsal Gland Pheromone

17 Dienes and MO Theory

• What To Expect In Organic Chemistry 2
• Are these molecules conjugated?
• Conjugation And Resonance In Organic Chemistry
• Bonding And Antibonding Pi Orbitals
• Molecular Orbitals of The Allyl Cation, Allyl Radical, and Allyl Anion
• Pi Molecular Orbitals of Butadiene
• Reactions of Dienes: 1,2 and 1,4 Addition
• Thermodynamic and Kinetic Products
• More On 1,2 and 1,4 Additions To Dienes
• s-cis and s-trans
• The Diels-Alder Reaction
• Cyclic Dienes and Dienophiles in the Diels-Alder Reaction
• Stereochemistry of the Diels-Alder Reaction
• Exo vs Endo Products In The Diels Alder: How To Tell Them Apart
• HOMO and LUMO In the Diels Alder Reaction
• Why Are Endo vs Exo Products Favored in the Diels-Alder Reaction?
• Diels-Alder Reaction: Kinetic and Thermodynamic Control
• The Retro Diels-Alder Reaction
• The Intramolecular Diels Alder Reaction
• Regiochemistry In The Diels-Alder Reaction
• The Cope and Claisen Rearrangements
• Electrocyclic Reactions
• Electrocyclic Ring Opening And Closure (2) - Six (or Eight) Pi Electrons
• Diels Alder Practice Problems
• Molecular Orbital Theory Practice

18 Aromaticity

• Introduction To Aromaticity
• Rules For Aromaticity
• Huckel's Rule: What Does 4n+2 Mean?
• Aromatic, Non-Aromatic, or Antiaromatic? Some Practice Problems
• Antiaromatic Compounds and Antiaromaticity
• The Pi Molecular Orbitals of Benzene
• The Pi Molecular Orbitals of Cyclobutadiene
• Frost Circles
• Aromaticity Practice Quizzes

19 Reactions of Aromatic Molecules

• Electrophilic Aromatic Substitution: Introduction
• Activating and Deactivating Groups In Electrophilic Aromatic Substitution
• Electrophilic Aromatic Substitution - The Mechanism
• Ortho-, Para- and Meta- Directors in Electrophilic Aromatic Substitution
• Understanding Ortho, Para, and Meta Directors
• Why are halogens ortho- para- directors?
• Disubstituted Benzenes: The Strongest Electron-Donor "Wins"
• Electrophilic Aromatic Substitutions (1) - Halogenation of Benzene
• Electrophilic Aromatic Substitutions (2) - Nitration and Sulfonation
• EAS Reactions (3) - Friedel-Crafts Acylation and Friedel-Crafts Alkylation
• Intramolecular Friedel-Crafts Reactions
• Nucleophilic Aromatic Substitution (NAS)
• Nucleophilic Aromatic Substitution (2) - The Benzyne Mechanism
• Reactions on the "Benzylic" Carbon: Bromination And Oxidation
• The Wolff-Kishner, Clemmensen, And Other Carbonyl Reductions
• More Reactions on the Aromatic Sidechain: Reduction of Nitro Groups and the Baeyer Villiger
• Aromatic Synthesis (1) - "Order Of Operations"
• Synthesis of Benzene Derivatives (2) - Polarity Reversal
• Aromatic Synthesis (3) - Sulfonyl Blocking Groups
• Birch Reduction
• Synthesis (7): Reaction Map of Benzene and Related Aromatic Compounds
• Aromatic Reactions and Synthesis Practice
• Electrophilic Aromatic Substitution Practice Problems

20 Aldehydes and Ketones

• What's The Alpha Carbon In Carbonyl Compounds?
• Nucleophilic Addition To Carbonyls
• Aldehydes and Ketones: 14 Reactions With The Same Mechanism
• Sodium Borohydride (NaBH4) Reduction of Aldehydes and Ketones
• Grignard Reagents For Addition To Aldehydes and Ketones
• Wittig Reaction
• Imines - Properties, Formation, Reactions, and Mechanisms
• All About Enamines
• Breaking Down Carbonyl Reaction Mechanisms: Reactions of Anionic Nucleophiles (Part 2)
• Aldehydes Ketones Reaction Practice

21 Carboxylic Acid Derivatives

• Nucleophilic Acyl Substitution (With Negatively Charged Nucleophiles)
• Addition-Elimination Mechanisms With Neutral Nucleophiles (Including Acid Catalysis)
• Basic Hydrolysis of Esters - Saponification
• Transesterification
• Proton Transfer
• Fischer Esterification - Carboxylic Acid to Ester Under Acidic Conditions
• Lithium Aluminum Hydride (LiAlH4) For Reduction of Carboxylic Acid Derivatives
• LiAlH[Ot-Bu]3 For The Reduction of Acid Halides To Aldehydes
• Di-isobutyl Aluminum Hydride (DIBAL) For The Partial Reduction of Esters and Nitriles
• Amide Hydrolysis
• Thionyl Chloride (SOCl2)
• Diazomethane (CH2N2)
• Carbonyl Chemistry: Learn Six Mechanisms For the Price Of One
• Making Music With Mechanisms (PADPED)
• Carboxylic Acid Derivatives Practice Questions

22 Enols and Enolates

• Keto-Enol Tautomerism
• Enolates - Formation, Stability, and Simple Reactions
• Kinetic Versus Thermodynamic Enolates
• Aldol Addition and Condensation Reactions
• Reactions of Enols - Acid-Catalyzed Aldol, Halogenation, and Mannich Reactions
• Claisen Condensation and Dieckmann Condensation
• Decarboxylation
• The Malonic Ester and Acetoacetic Ester Synthesis
• The Michael Addition Reaction and Conjugate Addition
• The Robinson Annulation
• Haloform Reaction
• The Hell–Volhard–Zelinsky Reaction
• Enols and Enolates Practice Quizzes
• The Amide Functional Group: Properties, Synthesis, and Nomenclature
• Basicity of Amines And pKaH
• 5 Key Basicity Trends of Amines
• The Mesomeric Effect And Aromatic Amines
• Nucleophilicity of Amines
• Alkylation of Amines (Sucks!)
• Reductive Amination
• The Gabriel Synthesis
• Some Reactions of Azides
• The Hofmann Elimination
• The Hofmann and Curtius Rearrangements
• The Cope Elimination
• Protecting Groups for Amines - Carbamates
• The Strecker Synthesis of Amino Acids
• Introduction to Peptide Synthesis
• Reactions of Diazonium Salts: Sandmeyer and Related Reactions
• Amine Practice Questions

24 Carbohydrates

• D and L Notation For Sugars
• Pyranoses and Furanoses: Ring-Chain Tautomerism In Sugars
• What is Mutarotation?
• Reducing Sugars
• The Big Damn Post Of Carbohydrate-Related Chemistry Definitions
• The Haworth Projection
• Converting a Fischer Projection To A Haworth (And Vice Versa)
• Reactions of Sugars: Glycosylation and Protection
• The Ruff Degradation and Kiliani-Fischer Synthesis
• Isoelectric Points of Amino Acids (and How To Calculate Them)
• Carbohydrates Practice
• Amino Acid Quizzes

25 Fun and Miscellaneous

• A Gallery of Some Interesting Molecules From Nature
• Screw Organic Chemistry, I'm Just Going To Write About Cats
• On Cats, Part 1: Conformations and Configurations
• On Cats, Part 2: Cat Line Diagrams
• On Cats, Part 4: Enantiocats
• On Cats, Part 6: Stereocenters
• Organic Chemistry Is Shit
• The Organic Chemistry Behind "The Pill"
• Maybe they should call them, "Formal Wins" ?
• Why Do Organic Chemists Use Kilocalories?
• The Principle of Least Effort
• Organic Chemistry GIFS - Resonance Forms
• Reproducibility In Organic Chemistry
• What Holds The Nucleus Together?
• How Reactions Are Like Music
• Organic Chemistry and the New MCAT

26 Organic Chemistry Tips and Tricks

• Common Mistakes: Formal Charges Can Mislead
• Partial Charges Give Clues About Electron Flow
• Draw The Ugly Version First
• Organic Chemistry Study Tips: Learn the Trends
• The 8 Types of Arrows In Organic Chemistry, Explained
• Top 10 Skills To Master Before An Organic Chemistry 2 Final
• Common Mistakes with Carbonyls: Carboxylic Acids... Are Acids!
• Planning Organic Synthesis With "Reaction Maps"
• Alkene Addition Pattern #1: The "Carbocation Pathway"
• Alkene Addition Pattern #2: The "Three-Membered Ring" Pathway
• Alkene Addition Pattern #3: The "Concerted" Pathway
• Number Your Carbons!
• The 4 Major Classes of Reactions in Org 1
• How (and why) electrons flow
• Grossman's Rule
• Three Exam Tips
• A 3-Step Method For Thinking Through Synthesis Problems
• Putting It Together
• Putting Diels-Alder Products in Perspective
• The Ups and Downs of Cyclohexanes
• The Most Annoying Exceptions in Org 1 (Part 1)
• The Most Annoying Exceptions in Org 1 (Part 2)
• The Marriage May Be Bad, But the Divorce Still Costs Money
• 9 Nomenclature Conventions To Know
• Nucleophile attacks Electrophile

27 Case Studies of Successful O-Chem Students

• Success Stories: How Corina Got The The "Hard" Professor - And Got An A+ Anyway
• How Helena Aced Organic Chemistry
• From a "Drop" To B+ in Org 2 – How A Hard Working Student Turned It Around
• How Serge Aced Organic Chemistry
• Success Stories: How Zach Aced Organic Chemistry 1
• Success Stories: How Kari Went From C– to B+
• How Esther Bounced Back From a "C" To Get A's In Organic Chemistry 1 And 2
• How Tyrell Got The Highest Grade In Her Organic Chemistry Course
• This Is Why Students Use Flashcards
• Success Stories: How Stu Aced Organic Chemistry
• How John Pulled Up His Organic Chemistry Exam Grades
• Success Stories: How Nathan Aced Organic Chemistry (Without It Taking Over His Life)
• How Chris Aced Org 1 and Org 2
• Interview: How Jay Got an A+ In Organic Chemistry
• How to Do Well in Organic Chemistry: One Student's Advice
• "America's Top TA" Shares His Secrets For Teaching O-Chem
• "Organic Chemistry Is Like..." - A Few Metaphors
• How To Do Well In Organic Chemistry: Advice From A Tutor
• Guest post: "I went from being afraid of tests to actually looking forward to them".

Comment section

17 thoughts on “ demystifying the mechanisms of alcohol oxidations ”.

Why do some reactant like Collins reagent stop their oxidation at the aldehyde level? Is it just the absence of water?

Question: If the hydrate happens BEFORE the actual attachment of the leaving group, why do we have different outcome with different leaving group?

Paragraph 2: “2. Oxidants Are Essentially Just Fancy Reagents For Attaching Good “Leaving Groups” Directly To Oxygen”

Just fabulous

Hi, will there be a major product if a molecule with both primary and secondary alcohol is oxidized? I mean, is there a preference for oxidizing primary or secondary?

There are some reagents that will preferentially oxidize primary over secondary, and vice-versa. You usually don’t learn about such details in introductory organic, but an example of the first type (primary over secondary) is TEMPO, and an example of the second type is Bobbitt’s reagent (among others) See this super useful handout. http://hwpi.harvard.edu/files/myers/files/6-oxidation.pdf

I was wondering if the prof could give a quick answer on NAD+ as a leaving group. Nicotinamide Adenine Dinucleotide acts as a leaving group in the same way? Probably a weak oxidant?

Hi! I loved your site! You explain very well! I have a doubt… How can I convert secondary alcohols into aldehydes? it’s possible?

Not without breaking a C-C bond somehow.

Which book covers the KMnO4 oxidation mechanism correctly?

Good luck. It’s complicated. Start with March’s advanced organic chemistry and dig in there.

You’ve mislabeled the ketone as aldehyde in the second last diagram.

Yes – thank you, finally fixed!

Hey, I have a doubt. Can ketones be oxidised to carboxylic acids in the presence of H2O?

Not under any conventional conditions we cover, because a C-C bond would need to break.

Non-conventionally though, and by a completely novel mechanism, methyl ketones can be oxidized to carboxylic acids in the haloform reaction. :)

Excellent post, makes a lot of things clearer even for me. One minor observation: in the hydrate formation image, in the first reaction it looks like the water molecules attacks the C=O bond; please shift the arrow tip a bit to the left.

Will fix. Thanks for your suggestions, as always. James

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Oxidation of Alcohols by Chromium(VI)

Oxidation of ethanol by chromium(vi).

Adapted by J. M. McCormick

Last Update: January 17, 2012

Introduction

In acidic solution the dichromate ion will oxidize primary alcohols to aldehydes, which can be further oxidized in the presence of excess dichromate to carboxylic acids.  Under the same conditions secondary alcohols are oxidized to ketones, which are not susceptible to oxidation by dichromate. 1   Westheimer first proposed the mechanism shown in Fig. 1 for the oxidation of alcohols by dichromate ion in 1949. 2,3   In the first step the dichromate ion is protonated to form chromic acid in a rapidly established equilibrium.  The chromic acid then undergoes a rapid, reversible reaction with the alcohol to form a chromate ester, which then decomposes in the rate-determining step to form H 2 CrO 3 and the aldehyde or ketone. There are subsequent steps in which H 2 CrO 3 and various other chromium species react with the resulting carbonyl compound until all of the chromium is in the 3+ oxidation state.  Fortunately, these reactions are fast, and will not complicate the kinetics that we wish to study.

Figure 1. Proposed mechanism for the oxidation of alcohols to aldehydes (or ketones). 2-4

In this exercise you will test the proposed mechanism by determining the rate law for the oxidation of ethanol by dichromate ion in acidic solution.  The isolation method will be used with the alcohol’s concentration being much larger than the [Cr 2 O 7 2- ].  However, by varying the ethanol’s concentration you will be able to determine the order of the reaction with respect to ethanol. This is similar to the kinetics exercise you did in CHEM 120, and you are referred there for more information.  One problem that must be overcome in this exercise is that both Cr 2 O 7 2- (yellow) and the Cr 3+ (green) strongly absorb light in the visible portion of the spectrum.  Therefore, you will need to choose a wavelength at which the Cr 2 O 7 2- absorbs, but the Cr 3+ does not.  Even then you will need to measure the absorbance at an infinite time (A 8 ) to correct for any residual absorbance at this wavelength.

Experimental

Prepare a stock solution of 3.9 M H 2 SO 4 from concentrated H 2 SO 4 .  Precisely prepare a 0.0196 M K 2 Cr 2 O 7 solution from the solid using distilled water.  When preparing the latter solution, take into account how much of it you will use for this exercise and minimize the amount of waste. CAUTION! Concentrated sulfuric acid can cause severe burns and chromium(VI) is a known carcinogen.

Kinetics data will be obtained by measuring the decrease in the chromium(VI) species’ absorbance as a function of time.  The instrument that will be used is an Ocean Optics USB2000 Vis-NIR spectrometer with a water-jacketed cell holder so that the sample’s temperature may be held constant by means of an external water bath.  Allow sufficient time for the spectrometer to warm up and the water bath to attain equilibrium before proceeding with a kinetics run.  Be sure that you know how to take wavelength scans and perform kinetics measurements with the spectrometer before coming to lab.  Note that, by convention, kinetics data are obtained at 25 °C.  Therefore, set the water bath to 25 °C initially and be sure water is circulating through the jacketed cell holder.

Prepare a solution of the dichromate solution by transferring 1 mL of the 0.0196 M K 2 Cr 2 O 7 solution into 10 mL of the 3.9 M H 2 SO 4 solution.  Mix well and obtain the absorption spectrum of this solution (save it for later use).  Prepare a solution of CrCl 3 ·6H 2 O of approximately the same concentration in 3.9 M H 2 SO 4 , obtain its spectrum (save it, too).  Determine the wavelength at which you will follow the reaction and record the absorbance of the dichromate solution at this wavelength (A 0 ). Set up the spectrometer’s kinetics routine to obtain data at least once a minute at this wavelength for 10 min.  Don’t forget to set a delay time to account for mixing of the reagents (1 min, or less, should be appropriate).  You may find that these initial settings are not adequate, and you may change these parameters as needed to optimize data collection.

To start a kinetics run prepare the chromic acid solution by mixing 1 mL of the 0.0196 M dichromate solution and 10 mL of the 3.9 M H 2 SO 4 solution in a small beaker.  Add to this 10.0 µ L of absolute ethanol, starting the count down on the spectrometer at the same time.  Swirl the solution in the beaker to assure complete mixing, transfer the solution to a cuvette and place the cuvette in the spectrometer.  Once the data collection has stopped, remove the solution from the cuvette and place it in a safe place.  After an hour, measure the absorbance at the same wavelength that you monitored for the kinetics run (this is A 8 ).  As you prepare for the second run,  graph the data from your first run using the integrated rate laws (at this point don’t worry about A 8 ) and critically evaluate the acquisition parameters.  Change the acquisition parameters as needed.

While you are waiting for the infinite time on the first run, repeat the kinetics runs twice more (you may need to arrange with the instructor how you will obtain A 8 for your last run) examining the data from the previous run while the next data is being acquired.  Be sure that your data is consistent and makes sense.  Is A 8 so small that it may be ignored?

With the data from the first run and the integrated rate laws, determine the order of the oxidation with respect to dichromate.

Once you have determined the order with respect to dichromate, vary the ethanol concentration.  From these data determine the order with respect ethanol and the rate constant for the reaction.

Determine the activation energy for the slow step of the reaction by varying the temperature with whichever reactant concentrations gave you the best results.  Note that at least three runs must be made at each temperature and that data at a minimum of three additional temperatures must be obtained.

Derive the rate law from the mechanism shown in Fig. 1.

You will need to present an example of each of the integrated rate law graphs demonstrating the order with respect to Cr 2 O 7 2- (i. e., a zeroth order graph and a first order graph and a second order graph), and the graph that you prepared to demonstrate the order with respect to the ethanol.  Include the Arrhenius plot from which you determined the activation energy.  Don’t forget to calculate uncertainties on the rate constant and the activation energy.

Conclusions

Discuss whether your results are consistent with the proposed mechanism and with the previously reported results.

1. Pavia, D. L.; Lampman, G. M.; Kriz, Jr., G. S. Introduction to Organic Laboratory Techniques: a Contemporary Approach, 2 nd Ed. ; Saunders: Philadelphia, PA; 1982, pp. 194-200.

2. Westheimer, F. H. Chem. Rev. 1949 , 45 , 419. Click here to obtain this article as a PDF file (Truman addresses and Chem. Rev. subscribers only).

3. Westheimer, F. H. and Nicolaides, N. J. Am. Chem. Soc. 1949 , 71 , 25. Click here to obtain this article as a PDF file (Truman addresses and J. Am. Chem. Soc. subscribers only).

4. Lanes, R. M.; Lee, D. G. J. Chem. Educ. 1968 , 45 , 269.  Click here to obtain this article as a PDF file (Truman addresses and J. Chem. Educ. subscribers only).

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The properties of alcohols

In association with Nuffield Foundation

• No comments

Ethanol and propan-1-ol are tested for pH, reaction with sodium, combustion and oxidation with acidified dichromate(VI) solution

This experiment can be done completely by advanced students if the use of sodium is closely supervised. With intermediate students, the sodium reaction and possibly the reaction with acidified dichromate should be demonstrated by the teacher. The experiments will take about 45 minutes.

• Eye protection: goggles
• Test tubes x2
• Boiling tubes x2
• Beakers (100 cm 3 ) x2 (note 2)
• Wooden splint
• Heat resistant mat
• Bunsen burner
• Boiling tube holder
• Dropping pipette (for water)
• Universal indicator paper (full range, pH 1–14)
• Forceps for sodium
• Filter paper for sodium
• Ethanol (HIGHLY FLAMMABLE) or Industrial denatured alcohol, IDA (HIGHLY FLAMMABLE, HARMFUL)
• Propan-1-ol (IRRITANT, HIGHLY FLAMMABLE)
• Sodium or potassium  dichromate(VI) solution, 0.1 M (TOXIC)
• Sulfuric acid, 1 M (IRRITANT) (note 3)
• Sodium (HIGHLY FLAMMABLE, CORROSIVE), small pieces (note 1)

Equipment notes

• Prepare the small pieces of sodium in advance of the lesson. Using forceps, remove a large piece of sodium (HIGHLY FLAMMABLE, CORROSIVE) from the oil, and place on a tile. Ensure that conditions are dry. Using a scalpel or sharp knife, cut some of the sodium into a few small pieces no larger than 2 x 2 x 2 mm. Place these small pieces in a separate bottle of oil. Return the larger piece to its bottle.
• Dispose of any small pieces of unused sodium by dissolving them in propan-2-ol until all trace has disappeared and the fizzing has stopped. Then pour the solution down the sink with plenty of water. See CLEAPSS Hazcard HC084a for more detailed disposal information. The teacher must supervise the use of sodium by students. The beakers must be absolutely dry.
• Remove all sodium from the bench (including bottles and spills) before issuing sulfuric acid. Alternatively, a technician should prepare acidified dichromate solution (correctly labelled) in advance to avoid the need for 1 M sulfuric acid solution to be used by students.

Health, safety and technical notes

• Read our standard health and safety guidance
• Wear goggles throughout. 
• Ethanol (HIGHLY FLAMMABLE) or Industrial denatured alcohol, IDA (HIGHLY FLAMMABLE, HARMFUL), C 2 H 5 OH(l) – see CLEAPSS Hazcard HC040a .
• Propan-1-ol, C 3 H 7 OH(l), (IRRITANT, HIGHLY FLAMMABLE) – see CLEAPSS Hazcard HC084a . 
• Sodium or potassium dichromate(VI) solution, Na 2 Cr 2 O 7 (aq), (TOXIC) – see CLEAPSS Hazcard HC078c and CLEAPSS Recipe Book.
• Dilute sulfuric acid, H 2 SO 4 (aq), (IRRITANT) – see CLEAPSS Hazcard HC098a and CLEAPSS Recipe Book RB070. 
• Sodium, Na(s), (HIGHLY FLAMMABLE, CORROSIVE) – see CLEAPSS Hazcard HC088 . 

Carry out each of these tests firstly with ethanol and then propan-1-ol:

• Place a few drops of the alcohol in a test-tube and add an equal number of drops of water. Do the liquids mix fully?
• Place a drop of the alcohol on a piece of full-range indicator paper. Note the pH.
• Place a few drops of alcohol on a tin lid on a heat resistant mat. Ignite the alcohol with a lit splint and observe the flame.
• Using forceps, take two small pieces of sodium and place them on a piece of filter paper. Dab the pieces of sodium with the filter paper to remove any excess oil.
• Place about 0.5 cm depth of each of the alcohols in a separate dry 100 cm 3  beakers. To each, add a small piece of sodium (using forceps) and observe the reaction.
• Put 5 cm 3  (about 2 cm depth) of dilute sulfuric acid in a boiling tube. Add five drops of potassium dichromate(VI) solution. Now add two drops of alcohol and a few anti-bumping granules and heat the mixture until it just boils. Is there any sign of a reaction? Is there any change of smell that could come from a new compound? Make sure all sodium is removed from the bench (including bottles and spills) before issuing the sulfuric acid, or prepare the acidified dichromate solution (correctly labelled) in advance to avoid the need for 1 M sulfuric acid solution to be used by students.

Teaching notes

Both alcohols are fully miscible with water. This is because the –OH groups hydrogen bond with the water. Higher alcohols are less soluble since the hydrocarbon chain starts to break an appreciable number of hydrogen bonds in water.

The pH of both alcohols will show as neutral. Note that, if indicator solution is used, ethanol at least will give an acid colour. This is because ethanol is the solvent used to prepare the indicator solution, and diluting the dyes puts the mixture out of balance. The RO –  anion is very unstable in aqueous solution, so virtually none of the reaction ROH + H 2 O ↔ RO –  + H 3 O + occurs.

Both alcohols will burn with a fairly clean, blue flame. C 2 H 5 OH + 3O 2  → 2CO 2  + 3H 2 O C 3 H 7 OH + 4½O 2  → 3CO 2  + 4H 2 O

Both alcohols will fizz with sodium to form hydrogen. C 2 H 5 OH + Na → C 2 H 5 ONa (sodium ethoxide) + ½H 2 C 3 H 7 OH + Na → C 3 H 7 ONa (sodium propoxide) + ½H 2

Both alcohols are oxidised to aldehydes, which have a sour but fruity smell. C 2 H 5 OH + [O] → CH 3 CHO (ethanal) + H 2 O C 3 H 7 OH + [O] → CH 3 CH 2 CHO (propanal) + H 2 O

These experiments show that alcohols react similarly in all these reactions. They make clear the concept of functional group in organic chemistry. The –OH functional group behaves in the same way whether it is attached to C 2 H 5  or C 3 H 7 . Further oxidation turns primary alcohols into acids, while secondary alcohols are only oxidised to ketones under these conditions. However, tertiary alcohols are not oxidised under these conditions but can be oxidised by stronger oxidising agents, resulting in C–C bond breaking.

Additional information

This is a resource from the Practical Chemistry project, developed by the Nuffield Foundation and the Royal Society of Chemistry. 

Practical Chemistry activities accompany Practical Physics and Practical Biology .

© Nuffield Foundation and the Royal Society of Chemistry

• 14-16 years
• 16-18 years
• Practical experiments
• Acids and bases
• Organic chemistry
• Functional groups
• Reactions and synthesis

Specification

• Alcohols: structure and nomenclature up to C-4 (primary and secondary alcohols only). Physical properties [physical state, solubility (qualitive only) in water and non-polar solvents].
• (d) Redox reactions: Alcohols:
• (e) Reactions as acids: Reactions of alcohols with sodium.
• Hydroxyl groups make alcohols polar and this gives rise to hydrogen bonding. Hydrogen bonding can be used to explain the properties of alcohols, including boiling points, melting points, viscosity and solubility/miscibility in water.
• (e) oxidation of primary alcohols to aldehydes/carboxylic acids and secondary alcohols to ketones
• (f) dichromate(VI) test for primary/secondary alcohols and sodium hydrogencarbonate test for carboxylic acids
• (t) the use of potassium dichromate(VI) in testing for alcohols
• 2.5.21 describe the complete and incomplete combustion of alcohols;
• 2.5.22 describe the complete and incomplete combustion of alcohols;
• 2.5.24 recall the oxidation of alcohols when exposed to air and by the reaction with acidified potassium dichromate solution (equations are not required) and demonstrate understanding that methanol, ethanol and propan-1-ol are oxidised to the…
• 2.6.4 describe the complete and incomplete combustion of alcohols and their use as an alternative fuel;
• 2.6.5 describe the reaction of alcohols with sodium, hydrogen bromide and phosphorus pentachloride;
• 2.6.6 describe the oxidation of alcohols using acidified potassium dichromate(VI), with reference to formation of aldehydes and carboxylic acids from primary alcohols, formation of ketones from secondary alcohols and resistance to oxidation of…

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• Alcohols, Phenols and Ethers
• Identification Of Alcohols

Oxidation of Alcohols

What are alcohols.

“Alcohols are a group of compounds containing one, two or more hydroxyl (-OH) groups that are attached to the alkane of a single bond. These compounds have a general formula -of ROH.” 

The alcohols are converted to aldehydes and ketones by the process of oxidation. This is one of the most important reactions in the field of organic chemistry.

Table of Contents

Oxidation of alcohols to aldehydes and ketones, what are the different types of alcohol, identification of alcohols, related videos, frequently asked questions – faqs.

Alcohols are a group of compounds containing one, two or more hydroxyl (-OH) groups that are attached to the alkane of a single bond. These compounds have a general formula -of ROH. They have primary importance in the field of organic chemistry as they can be changed or converted to different types of compounds such as Aldehydes and Ketones, etc. The reactions with alcohol are of two different categories. These Reactions can leave the R-O bond or even they can leave O-H bond.

Oxidizing alcohols to aldehydes and ketones are one of the vital reactions in the field of synthetic organic chemistry. These reactions occur in the presence of catalysts and the best oxidants required for these conversions have high valent ruthenium acting as the catalyst for this kind of reaction. It is very much important to have complete knowledge and also understanding the factors and mechanisms of the oxidation reactions influencing them.

1. Mechanism of conversion Alcohols into Aldehydes and Ketones

The catalytic conversion of the primary type of alcohols into aldehydes and the secondary form of alcohols into ketones are important in the preparation of various synthetic intermediates in organic chemistry.

The result of the oxidation reaction of the alcohols depends on the types of substituents used on the carbonyl carbon. For the oxidation reaction to take place, a hydrogen atom needs to be present on the carbonyl carbon.

The oxidizing agents or the catalysts used in these types of reactions are normally the solutions of sodium or also potassium dichromate(VI) which is acidified with the dilute sulphuric acid. In the process of oxidation, the orange solution which contains ions of dichromate(VI) is reduced to the green solution which contains chromium(III) ions.

2. Making of Aldehydes

The preparation of Aldehydes is by oxidizing the primary alcohols. The aldehyde which is produced can be oxidized further to the carboxylic acids by the use of acidified potassium dichromate(VI) solution that is used as an oxidizing agent. The net effect occurs as the oxygen atom of the oxidizing agent eliminates the hydrogen atom from the hydroxyl (-OH) group of alcohol and also one carbon atom attached to it.

Here, R and R’ are the alkyl groups or hydrogen. If these groups contain the hydrogen atom, you will get the aldehyde. These aldehydes are obtained from the primary alcohols.

3. Making of Ketones

The preparation of Ketones is done by the oxidation of secondary alcohols. Consider, for example, heating the secondary alcohol propan-2-ol with the sodium or even potassium dichromate(VI) solution which is acidified with the dilute sulphuric acid, then the ketone called propanone is formed.

The occurring reaction is as shown below-

The Ketones obtained cannot be further oxidized because this reaction would involve the breaking up of C–C bond, requiring too much energy.

On the basis of chemical groups attached to the carbon atom, alcohols are divided into three categories:

• Primary alcohol:   When the carbon atom attached to the hydroxyl group is bonded to only one carbon atom such type of alcohol is known as primary alcohol .
• Secondary alcohol:   When it is bonded to two carbon atoms such type of alcohol is known as secondary alcohol .
• Tertiary alcohol:   When it is bonded to three carbon atoms such type of alcohol is known as  tertiary alcohol.

Each of the three types of alcohol (primary, secondary and tertiary alcohol) exhibits different physical and chemical properties.

Certain tests are carried out for the identification of primary, secondary and tertiary alcohols. Some of these tests are:

1. Lucas Test

Lucas test is based on the difference in reactivity of primary, secondary and tertiary alcohols with hydrogen chloride. In the Lucas test , the alcohol is treated with Lucas reagent (concentrated HCl and ZnCl 2 ). Turbidity is produced as halides of the substituted alcohol are immiscible in Lucas reagent. The time taken to achieve turbidity is noted and the following observations are made:

• In the case of a  primary alcohol , turbidity is not produced at room temperature. However, on heating, an oily layer is formed.
• In the case of a  secondary alcohol , an oily layer is produced in 5-6 minutes. Thus, the reaction takes some time to produce turbidity.
• In the case of tertiary alcohol , turbidity is immediately produced as halides are easily formed.

Thus, the rate of formation of turbidity upon the reaction of an alcohol with Lucas reagent helps us in the identification of primary, secondary and tertiary alcohol.

2. Oxidation Test

In the oxidation test, the alcohols are oxidized with sodium dichromate (Na 2 Cr 2 O 7 ). The rate of oxidation varies between primary, secondary and tertiary alcohol. On the basis of their oxidation rates, alcohols can be distinguished as:

• Primary alcohol gets easily oxidized to an aldehyde and can further be oxidized to carboxylic acids too.
• Secondary alcohol gets easily oxidized to ketone but further oxidation is not possible.
• Tertiary alcohol doesn’t get oxidized in the presence of sodium dichromate.

Thus, the rate of oxidation upon oxidation with sodium dichromate helps us in the identification of primary, secondary and tertiary alcohol.

What is oxidation of ethanol?

Alcohol oxidation is oxidation with respect to the conversion of hydrogen. The alcohol is oxidised as a result of hydrogen degradation. In hydrocarbon chemistry, oxidation and reduction in hydrogen transfer are common. Ethanol is oxidised to form the aldehyde ethanal by sodium dichromate (Na2Cr2O7) acidified in dilute sulphuric acid.

Why are tertiary alcohols not oxidised?

Acidified sodium or potassium dichromate(VI) solution does not oxidise tertiary alcohols. No reaction whatsoever occurs. There’s no hydrogen atom bound to the carbon in tertiary alcohols. In order to set up the carbon-oxygen double bond, you need to be able to eliminate those two unique hydrogen atoms.

What do secondary alcohols oxidised to?

A significant oxidation reaction in organic chemistry is the oxidation of secondary alcohols to ketones. It is converted to a ketone as a secondary alcohol is oxidised. Along with the hydrogen bound to the second carbon, the hydrogen from the hydroxyl group is lost.

Can alcohols be oxidized?

In organic chemistry, the oxidation of alcohol is an important reaction. To form aldehydes and carboxylic acids, primary alcohols can be oxidised; secondary alcohols can be oxidised to deliver ketones. Tertiary alcohol, on the other hand, can not be oxidised without breaking the C-C bonds of the molecule.

How does oxidation of alcohols work?

Depending on the reaction conditions, primary alcohols may be oxidised into either aldehydes or carboxylic acids. As carboxylic acids are formed, the alcohol is first oxidised into an aldehyde and then further oxidised into the acid.

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A direct oxidative esterification of aldehydes with alcohols mediated by photochemical C–H bromination †

First published on 30th August 2024

The photochemical direct esterification of aldehydes with alcohols via in situ -generated acyl-bromides presented in this report is an attractive complementary addition to hitherto reported methods, as these are usually carried out in a two-step, one-pot procedure in order to avoid side reactions such as the oxidation of alcohols by halogen sources.

Oxidative esterifications via acyl halides represent a highly useful method in organic chemistry to generate functionalized esters ( Scheme 1(b) ). Recently, Kim and coworkers have reported an oxidative esterification with dibromoisocyanuric acid (DBI) via acyl bromides. 3 Furthermore, photochemical esterifications with halogen sources such as N -bromosuccinimide (NBS) or N -chlorosuccinimide (NCS) have also been developed. 4 Despite these advances, these reactions are usually carried out in a two-step, one-pot procedure in order to avoid side reactions such as the oxidation of alcohols by halogen sources. 5 Thus, the development of more efficient methods, such as direct esterifications, still remains desirable.

Our group has developed various visible-light-induced photochemical reactions. 6 During our investigations, we have discovered an unexpected photochemical esterification of an aldehyde with an alcohol, which prompted us to investigate the direct photochemical esterification of aldehydes. Here, we report the esterification of aldehydes with alcohols mediated by a photochemical C–H bromination.

We initially investigated the optimization of the reaction conditions for the photochemical esterification of benzaldehyde ( 1a ) with 1-butanol ( 2a ) ( Table 1 ). When the reaction was carried out under irradiation from blue LEDs ( λ ex = 425 nm), the desired ester ( 3a ) was obtained in low yield ( Table 1 , entry 1). In contrast, under irradiation from purple LEDs ( λ ex = 380 nm), the product yield was increased to 75% ( Table 1 , entry 2), suggesting that the Br–C bond of BrCCl 3 is efficiently cleaved under these conditions. Ultraviolet light ( λ ex = 365 nm) can also be used for this reaction ( Table 1 , entry 3). Typical solvents such as toluene, CH 3 CN, and hexane furnished the product in low to moderate yields ( Table 1 , entries 4–6). Although CBr 4 can be used instead of BrCCl 3 , CCl 4 is not suitable, suggesting that the presence of a bromo group is important for the reaction to proceed ( Table 1 , entries 7 and 8). Reducing the amount of BrCCl 3 used resulted in a lower product yield ( Table 1 , entry 9). When the reaction was carried out for 36 h in the presence of MS3 Å, the desired product was obtained in high yield due to the reduced formation of benzoic acid ( Table 1 , entry 10). Control experiments, wherein BrCCl 3 or the light source were omitted, did not proceed, and it can therefore be concluded that both elements are crucial for the reaction to proceed ( Table 1 , entries 11 and 12).

With the optimal conditions in hand, we subsequently screened the photochemical esterification using various alcohols and aldehydes ( Table 2 ). Both electron-rich and -deficient aromatic systems are compatible with the applied reaction conditions ( 3b–g ), and heteroaromatic aldehydes ( 1h–1i ) are also tolerated. Cinnamaldehyde ( 1j ) is a good substrate for this reaction. Furthermore, aliphatic aldehydes ( 1k–1o ) are well tolerated, in particular those with more sterically congested groups, such as an adamantyl group ( 1o ), which furnished the desired ester ( 3o ) in excellent yield. Although aliphatic aldehydes have higher acyl-C–H bond dissociation energies relative to arylaldehydes, these reactions smoothly proceed to give the corresponding esters in good yields. 7 Moreover, the reaction could be applied to multi-substituted aldehydes to give the corresponding esters ( 3p–3r ) in moderate yields. Since these multi-substituted esters are found in functional materials, 8 the present reaction constitutes a promising tool for the synthesis of these useful compounds. Notably, the current reaction allows for the synthesis of trisubstituted esters such as 3r , 9 for which there are so far only a few examples. 10 A variety of aliphatic alcohols, including primary and secondary alcohols, furnished the desired esters ( 3a–3y ) in moderate to high yields. While direct esterification reactions mediated by other halogen sources such as NBS are difficult due to side reactions between the halogen sources and the alcohols, 3–5 the present reaction with BrCCl 3 can be effectively applied to alcohols 1a–1y . In fact, when the reactions of 1t or 1x were carried out with NBS, the desired products were not obtained. 11

To examine the reaction mechanism, we used a radical scavenger in the reaction ( Scheme 2 ). When the reaction was performed with TEMPO, the product yield decreased effectively. In addition, an acyl radical was trapped by TEMPO and detected as 4a using mass spectrometry. Thus, the reaction may produce an acyl radical via a radical reaction.

A feasible reaction mechanism is proposed in Scheme 3 . Homolytic cleavage of BrCCl 3 under irradiation from purple LEDs affords a trichloromethyl radical and a bromo radical. 12 The bromo group is important for the reaction to proceed, as evident from the result obtained when using CCl 4 ( Table 1 , entry 8). According to Scheme 2 , the trichloromethyl radical can dissociate the C–H bond of benzaldehyde to form acyl radical A , which reacts with BrCCl 3 to form acyl bromide B . 3,4,13 This hypothesis is supported by the detection of benzoyl bromide using 1 H and 13 C NMR spectroscopy. 14 Finally, the alcohol can react with acyl bromide B to furnish the desired ester.

Conclusions

Data availability.

The data that support the findings of this study are available from the corresponding author, Kenta Tanaka, upon reasonable request.

Conflicts of interest

Acknowledgements.

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