oxidation of aldehyde and ketone and mechanism

oxidation of aldehyde and ketone

1. TOPIC:-OXIDATION
ALDEHYDE AND KETONE
NAME :-FAIZ SIDDIQUI
CLASS:-M.sc-I
Roll no:-78

2. ➢General Mechanism of Aldehyde Oxidation
➢Step 1: Nucleophilic Attack on the Carbonyl Carbon
➢The oxidation process begins with the attack of a nucleophile (such as a hydroxide
ion, OH⁻) on the electrophilic carbonyl carbon of the aldehyde group.
➢The carbonyl carbon is highly electrophilic due to the polarization of the C=O bond,
where the oxygen is more electronegative, pulling electron density away from the
carbon.
➢Reaction:
➢R−CHO+OH−→R−C(OH)HOR-CHO + OH⁻ → R-C(OH)HOR−CHO+OH−→R−C(OH)HOIn
this step, the hydroxide nucleophile attacks the carbonyl carbon, and the oxygen
from the carbonyl accepts an electron pair, forming a tetrahedral intermediate.

3. General Mechanism of Ketone Oxidation
Step 1: Nucleophilic Attack on the Carbonyl Carbon
•The mechanism begins with the nucleophilic attack on the electrophilic carbonyl carbon of
the ketone by a nucleophile (often water or hydroxide ion, OH⁻).
•The carbonyl carbon is polarized, making it susceptible to nucleophilic attack.
•Reaction:
•R2C=O+OH−→R2C(OH)R′R_2C=O + OH⁻ \rightarrowR_2C(OH)R'R2​C=O+OH−→R2​C(OH)R′In
this step, the nucleophile attacks the carbonyl carbon, forming a tetrahedral intermediate.
Step 2: Formation of a Geminal Diol (Hydrate)
•The tetrahedral intermediate rearranges to form a geminal diol. This involves the
protonation of one of the oxygen atoms while the other oxygen remains as a hydroxyl
group.
•Reaction:
•R2C(OH)R′(geminaldiol)R_2C(OH)R' \quad \text{(geminal diol)}R2​C(OH)R′(geminaldiol)
Step 3: Oxidation Step
•The oxidation of the geminal diol involves the removal of electrons (oxidation) and
typically occurs through the involvement of an oxidizing agent.
•Depending on the strength of the oxidizing agent and the conditions, the geminal diol can
be oxidized to a carboxylic acid or can simply revert to a ketone.
•For strong oxidizing agents, ketones can sometimes be oxidized to carboxylic acids.

4. Example: Oxidation of Acetone (CH₃COCH₃)
1.Step 1: A hydroxide ion attacks the carbonyl carbon of acetone, forming a tetrahedral
intermediate.
2.CH3C(=O)CH3+OH−→CH3C(OH)(R)CH3CH₃C(=O)CH₃ + OH⁻ \rightarrow
CH₃C(OH)(R)CH₃CH3​C(=O)CH3​+OH−→CH3​C(OH)(R)CH3​
3.Step 2: The intermediate rearranges to form a geminal diol (hydrate).
4.CH3C(OH)(R)CH3(geminaldiol)CH₃C(OH)(R)CH₃ \quad \text{(geminal
diol)}CH3​C(OH)(R)CH3​(geminaldiol)
5.Step 3: The geminal diol undergoes oxidation.
6.CH3C(OH)(R)CH3+[O]→CH3C(O)OH+R′OHCH₃C(OH)(R)CH₃ + [O] \rightarrow
CH₃C(O)OH + R'OHCH3​C(OH)(R)CH3​+[O]→CH3​C(O)OH+R′OH

5. OxidationofAldehydes/Ketones
1)H
2O
2/NaOH(DakinOxidation)
➢TheDakinoxidationisanorganicredoxreactioninwhicharomaticaldehydeorketonescontaining
orthoorparahydroxyl.
➢or amino group as substituents in alkaline H2 O2 are converts into catechol or hydroquinol.

6. Oxidation of Aldehydes/Ketones Dakin oxidation

7. Oxidation of Aldehydes/Ketones Peroxy acid (Baeyer Villiger Oxidation)
Baeyer-Villiger oxidation is the oxidation of a ketone to a carboxylic acid ester or lactones using a peroxyacid as the oxidizing
agent
Mechanism
Migration order = 3
0
alkyl > 2
0
alkyl > aryl >1
0
alkyl > methyl

8. Baeyer Villiger Oxidation

10. Baeyer–Villiger Oxidations
When diphenylmethanone (benzophenone) is treated with a peroxyacid (RCO3H) such as meta-chloroperbenzoic acid (MCPBA),
phenyl benzoate is produced. This is an example of a Baeyer–Villiger oxidation, named after the German chemist Adolf von
Baeyer (1835–1917) and the Swiss chemist Victor Villiger (1868–1934).

11. Peroxy acid (Baeyer Villiger Oxidation)
The oxidation of acyclic Ketones or cyclic ketones with peroxyacids gives esters or lactones.
Eg.perbenzoic acid, peracetic acid trifluroacetic acid, and meta-chloroperbenzoic acid (mCPBA).
Epoxidation of Alkenes

12. Reduction
Reductive process of the organic molecules fall into three categories
i.e the removal of oxygen or the addition hydrogen or the gain of electrons.
Reduction of carbonyl group ( –CO-) to methylene group(-CH
2-) in Aldehydes and Ketones.
1) Zn/HCl (Clemmensen Reduction)
The reduction of a carbonyl group to a methylene group by zinc amalgam, Zn(Hg), in dilute hydrochloric acid
HCl is the source of the protons that form bonds to the carbonyl C.
The zinc metal acts as a reducing agent in what is called a dissolving metal reduction, where by the metal dissolves in solution.
Zinc loses two electrons (it is oxidized) on going from elemental Zn to Zn
+2
(represented by ZnCl
2 )whereas the carbonyl C is
reduced because it loses the double bond to O and gains two bonds to H.

13. The Clemmensen reduction requires the use of concentrated HCl, it cannot be used to reduce a carbonyl group in a molecule
that also contains acid sensitive groups, such as a tertiary alcohol that might undergo dehydration, or an acetal that is
hydrolyzed so that its resulting carbonyl group is also reduced.
The Clemmensen reduction is used when the molecule is stable to strong acid, and the Wolff-Kishner reduction is used when
the molecule is stable to strong base.
In the above reaction, along with the reduction of carbonyl
group, the -OH group is substituted by the -Cl group (side
reaction). However this side reaction can be avoided by
employing Wolff-Kishner method
But the phenol group is not affected in Clemmensen reduction.
(Why? Ans: Nucleophilic substitution is not easy on sp2 carbon
of benzene ring!)

14. Reduction of carbonyl group ( –CO-) to methylene group(-CH
2-) in Aldehydes and Ketones.
1) Zn/HCl (Clemmensen Reduction)
The Clemmensen reduction reaction condition consider to be
vigorous and is not suitable for the reduction of polyfunctional
molecules such as 1,3 or 1,4- diketones or of sensitive compounds.

15. Wolff-Kishner reduction
➢In Wolff-Kishner reduction, the carbonyl compounds which are stable to strongly basic conditions can
be reduced conveniently
➢to alkanes. The C=O group is converted to CH
2 group.
➢The carbonyl compound is first treated with excess of hydrazine to get the corresponding hydrazone
which upon heating, in
➢presence of a base, furnishes the hydrocarbon
➢A high-boiling hydroxylic solvent, such as diethylene glycol (DEG), is commonly used to achieve the
temperatures needed
➢The Wolff-Kishner reduction is complementary to Clemmensen reduction, which is used to
reduce base sensitive compounds.
➢In the following example, the alcohol group is not
affected during the reduction.
➢The halogen group undergoes
dehydrohalogenation under strongly basic
conditions
➢This side reaction can be avoided by using Clemmensen reduction.

17. The Wolff–Kishner reduction should be avoided if there is a
functional group present that is susceptible to reaction under basic
conditions or with strong nucleophiles.
The Clemmensen reduction
should be avoided if there is a
functional group present that is
susceptible to reaction under
acidic conditions.