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Ozonolysis: Reductive vs. Oxidative

Reaction of Alkenes with Ozone ($O_3$) followed by different work-up conditions.

By chemca Team • Updated Jan 2026

Ozonolysis is a powerful method for cleaving double and triple bonds. The reaction involves the formation of an Ozonide intermediate, which is then decomposed. The nature of the final products depends entirely on the reagent used for decomposition (work-up).

1. Reductive Ozonolysis ($Zn/H_2O$)

Preserving the Carbonyl

Reagents: Ozone ($O_3$) followed by Zinc dust and water ($Zn/H_2O$) or Dimethyl Sulfide ($Me_2S$).

Function: Zinc acts as a reducing agent. It destroys the $H_2O_2$ produced during the reaction ($Zn + H_2O_2 \rightarrow ZnO + H_2O$), preventing further oxidation of aldehydes.

Products:

• Carbon-Carbon double bonds are cleaved.
• An Oxygen atom is added to each carbon.
• Aldehydes and Ketones are the final products.

$$ R-CH=C(R')_2 \xrightarrow{1. O_3, 2. Zn/H_2O} \underset{\text{Aldehyde}}{R-CHO} + \underset{\text{Ketone}}{O=C(R')_2} $$

2. Oxidative Ozonolysis ($H_2O$ or $H_2O_2$)

Oxidation to Acids

Reagents: Ozone ($O_3$) followed by Water ($H_2O$) alone or Hydrogen Peroxide ($H_2O_2$).

Function: In the absence of Zinc, the decomposition of ozonide generates $H_2O_2$ in situ, which acts as a strong oxidizing agent.

Products:

• Ketones remain unaffected (they resist oxidation).
• Aldehydes are oxidized to Carboxylic Acids.
• Terminal $=CH_2$ groups are fully oxidized to $CO_2 + H_2O$ (via Formic acid).

$$ R-CH=C(R')_2 \xrightarrow{1. O_3, 2. H_2O_2} \underset{\text{Carboxylic Acid}}{R-COOH} + \underset{\text{Ketone}}{O=C(R')_2} $$

3. Comparison: Product Analysis

Substrate	Reductive ($Zn/H_2O$)	Oxidative ($H_2O_2$)
$R-CH=CH-R$	2 Aldehydes ($2 RCHO$)	2 Acids ($2 RCOOH$)
$R_2C=CR_2$	2 Ketones ($2 R_2CO$)	2 Ketones ($2 R_2CO$)
$R-CH=CH_2$ (Terminal)	Aldehyde + Methanal ($HCHO$)	Acid + $CO_2 + H_2O$

4. Ozonolysis of Alkynes

Alkynes are less reactive toward ozone than alkenes, but cleavage still occurs.

A. Reductive ($Zn/H_2O$): Yields 1,2-Dicarbonyls (Diketones or Glyoxals). The bond is not completely cleaved; the sigma bond may remain initially but hydrolysis usually breaks it.

$$ R-C \equiv C-R \xrightarrow{1. O_3, 2. Zn/H_2O} R-CO-CO-R $$

B. Oxidative ($H_2O_2$): Complete cleavage to Carboxylic Acids.

$$ R-C \equiv C-R \xrightarrow{1. O_3, 2. H_2O_2} 2 R-COOH $$

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