Show how you would use an acid chloride as an intermediate to synthesize
(b) phenyl propionate (CH₃CH₂COOPh) from propionic acid and phenol.

Verified step by step guidance

Step 1: Convert propionic acid (CH3CH2COOH) into propionyl chloride (CH3CH2COCl) using thionyl chloride (SOCl2) or oxalyl chloride ((COCl)2). This reaction replaces the hydroxyl group (-OH) of the carboxylic acid with a chlorine atom, forming the acid chloride. The reaction mechanism involves nucleophilic substitution.

Step 2: Prepare phenol (PhOH) for the esterification reaction. Phenol acts as the nucleophile in the next step, attacking the electrophilic carbon of the acid chloride.

Step 3: React propionyl chloride (CH3CH2COCl) with phenol (PhOH) in the presence of a base, such as pyridine or triethylamine, to neutralize the HCl byproduct. The base ensures the reaction proceeds efficiently by removing the acidic byproduct and stabilizing the intermediate.

Step 4: During the reaction, phenol's oxygen atom attacks the carbonyl carbon of the acid chloride, forming a tetrahedral intermediate. This intermediate collapses, releasing the chloride ion and forming the ester bond.

Step 5: Isolate and purify the product, phenyl propionate (CH3CH2COOPh), using techniques such as distillation or recrystallization, depending on the physical properties of the product.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acid Chlorides

Acid chlorides, also known as acyl chlorides, are derivatives of carboxylic acids where the hydroxyl group is replaced by a chlorine atom. They are highly reactive compounds that can be used as intermediates in organic synthesis, particularly in the formation of esters and amides. Their reactivity allows them to easily react with alcohols or phenols to form esters, making them valuable in synthetic pathways.

Esterification Reaction

Esterification is a chemical reaction that forms an ester from an alcohol and a carboxylic acid, typically in the presence of an acid catalyst. In this context, the reaction between an acid chloride and a phenol leads to the formation of an ester, specifically phenyl propionate. This reaction is characterized by the nucleophilic attack of the alcohol on the carbonyl carbon of the acid chloride, resulting in the release of hydrochloric acid.

Nucleophilic Acyl Substitution

Nucleophilic acyl substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks the electrophilic carbon of a carbonyl group, leading to the substitution of a leaving group. In the case of acid chlorides, the chlorine atom acts as a good leaving group, facilitating the formation of new bonds with nucleophiles such as phenols. This mechanism is crucial for understanding how acid chlorides can be transformed into esters and other derivatives.

Show how you would use an acid chloride as an intermediate to synthesize (b) phenyl propionate (CH3CH2COOPh) from propionic acid and phenol.