Chapter 11, Problem 44P

Interpretation Introduction

Interpretation:

The steps involved in the synthesis of 2,4-dichlorophenoxyacetic acid from phenol and chloroacetic acid are to be outlined.

Concept introduction:

Electrophiles are electron deficient species that have positive or partially positive charge. Lewis acids are electrophiles that accept electron pair.

Nucleophiles are electron rich species that have negative or partially negative charge. Lewis bases are nucleophiles that donate electron pair.

Free radical is an atom, molecule, or ion that has unpaired electrons, which makes it highly chemically reactive.

Substitution reaction: A reaction in which one of the hydrogen atoms of a hydrocarbon or a functional group is substituted by any other functional group is called substitution reaction.

Elimination reaction: A reaction in which two substituent groups are detached and a double bond is formed is called elimination reaction.

Addition reaction: It is the reaction in which unsaturated bonds are converted to saturated molecules by the addition of molecules.

Addition reaction: It is a reaction in which unsaturated bonds are converted into saturated molecules by the addition of molecules

If a compound has more than one functional group, then, to carry out some specific synthetic protocols, one of the functional groups is often blocked. After the required reaction, the functional group has to be unblocked using suitable reagents. If the carboxylic acid is sufficiently active in nature, it has to be esterified to carry out reactions in the carbon skeleton. After the completion of the reaction, the functionality of ester is hydrolyzed to deprotect the acid.

Phenol is chlorinated using chlorine in the presence of a Lewis acid catalyst. If the dichloride product is the required synthon, an excess amount of chlorine is required.

The carboxylic acid group of α-chloro acetic acid is blocked by esterification, which is done by using ethanol, in the presence of catalytic sulfuric acid.

When 2, 4-dichlorophenol is treated with sodium carbonate, the considerably-acidic phenol is deprotonated and the phenoxide anion acts as the nucleophile to substitute the chlorine atom from the α-chloro ester. If the reaction is carried out prior to protecting the carboxylic acid group, there would be the probability of esterification.

The deprotection is carried out by the hydrolysis of the ester in an alkaline medium and the acidification of the carboxylate salt.