The correct answer is (2) Pseudo first-order reaction.
The hydrolysis of methyl acetate (\(CH_3COOCH_3\)) in an acidic medium is a common reaction in organic chemistry. This reaction involves the cleavage of the ester bond in methyl acetate in the presence of an acid, typically a strong acid like hydrochloric acid (\(HCl\)) or sulfuric acid (\(H_2SO_4\)).
The overall reaction can be represented as follows:
\[ CH_3COOCH_3 + H_2O \rightarrow CH_3COOH + CH_3OH \]
This reaction proceeds via a nucleophilic acyl substitution mechanism, where water acts as a nucleophile attacking the electrophilic carbon in the carbonyl group of the ester.
Now, let's discuss the order of the reaction kinetics:
1. Pseudo-First-Order Kinetics:
The hydrolysis of methyl acetate in an acidic medium is often considered to follow pseudo-first-order kinetics.
The term "pseudo" is used because the reaction appears to be first order, even though it involves more than one reactant.
The concentration of water (\(H_2O\)) is usually present in excess, so its concentration remains approximately constant throughout the reaction.
As a result, the rate of the reaction becomes dependent on the concentration of the ester (methyl acetate), making the reaction effectively a first-order reaction with respect to the ester.
2. Reaction Mechanism:
The nucleophilic acyl substitution mechanism involves the attack of the water molecule on the carbonyl carbon of the ester.
The protonation of the carbonyl oxygen by the acid facilitates the nucleophilic attack by water.
The reaction produces acetic acid (\(CH_3COOH\)) and methanol (\(CH_3OH\)) as products.
3. Rate Equation:
The rate equation for the pseudo-first-order reaction can be written as follows:
\[ \text{Rate} = k [CH_3COOCH_3] \]
where \(k\) is the rate constant and \([CH_3COOCH_3]\) is the concentration of methyl acetate.
In summary, the hydrolysis of methyl acetate in an acidic medium is a pseudo-first-order reaction because the concentration of water, which is in excess, remains constant throughout the reaction. The reaction proceeds via a nucleophilic acyl substitution mechanism, and the rate equation reflects the first-order dependence on the concentration of methyl acetate. |
