The first widely used herbicide for the control of weeds was 2,4 -dichlorophenoxyacetic acid (2,4-D). Show how this compound might be synthesized from phenol and chloroacetic acid by way of the given chlorinated phenol intermediate.

The reactants in this synthesis are phenol and chloroacetic acid. The target product is 2,4-dichlorophenoxyacetic acid (2,4-D). The chlorinated phenol intermediate will be formed during the synthesis.

The first step in the synthesis is the chlorination of phenol to form the chlorinated phenol intermediate. This can be done using a chlorinating agent, such as chlorine gas, in the presence of a catalyst like iron(III) chloride (FeCl3). The reaction proceeds as follows: Phenol + Cl2 + FeCl3 -> 2,4-Dichlorophenol + HCl where Phenol is C6H5OH, Cl2 is chlorine gas, and 2,4-Dichlorophenol is the chlorinated phenol intermediate (C6H3Cl2OH).

The next step is to react the 2,4-dichlorophenol with chloroacetic acid to form an ester intermediate. This reaction can be done by heating the reactants in the presence of sulfuric acid (H2SO4) as a catalyst. The reaction proceeds as follows: 2,4-Dichlorophenol + ClCH2COOH -> 2,4-Dichlorophenyl chloroacetate + H2O where ClCH2COOH is chloroacetic acid and 2,4-Dichlorophenyl chloroacetate (C6H3Cl2OCOCH2Cl) is the ester intermediate.

The final step in the synthesis is the hydrolysis of the ester intermediate to form 2,4-dichlorophenoxyacetic acid (2,4-D). This can be done by reacting the ester intermediate with a strong base (such as NaOH) or water under acidic conditions. The reaction proceeds as follows: 2,4-Dichlorophenyl chloroacetate + NaOH -> 2,4-Dichlorophenoxyacetic acid (2,4-D) + NaCl or 2,4-Dichlorophenyl chloroacetate + H2O (acidic conditions) -> 2,4-Dichlorophenoxyacetic acid (2,4-D) + HCl In both cases, the 2,4-dichlorophenoxyacetic acid (2,4-D) is formed as the final product. In summary, the synthesis of 2,4-dichlorophenoxyacetic acid (2,4-D) from phenol and chloroacetic acid involves three main steps: chlorination of phenol, formation of an ester intermediate, and hydrolysis of the ester intermediate. These steps are described in detail above.