Question

Propose a synthesis of triphenylmethane from benzene, the only source of aromatic rings, and any other necessary reagents.

Short answer

Answer: The key steps in synthesizing triphenylmethane from benzene are: 1. Converting benzene to phenyl bromide (bromobenzene) using bromine and iron bromide catalyst, 2. Converting phenyl bromide to benzophenone through Grignard reagent formation and Clemmensen reduction, 3. Converting benzophenone to triphenylmethanol by alkoxylation of the carbonyl group with phenylmagnesium bromide, and 4. Converting triphenylmethanol to triphenylmethane using an acid-catalyzed dehydration reaction with concentrated sulfuric acid.

Step-by-step solution

Convert benzene to phenyl bromide (bromobenzene)

To accomplish the first step, benzene should be treated with bromine (Br2) and iron (III) bromide (FeBr3) catalyst. This will lead to an electrophilic aromatic substitution reaction, replacing one of the hydrogens with a bromine atom to create bromobenzene.

Convert phenyl bromide to benzophenone

In this step, the bromobenzene can be transformed into benzophenone. This can be done by treating bromobenzene with magnesium turnings in a dry ether environment. This will form the Grignard reagent, phenylmagnesium bromide. Next, treat the phenylmagnesium bromide with carbon dioxide (CO2) and then acidify with hydrochloric acid (HCl). This forms benzoic acid which is then reduced with Clemmensen reduction using zinc amalgam and HCl. This step will yield benzophenone. Reaction: 1. Mg, dry ether 2. CO2 3. HCl 4. Clemmensen reduction (Zn-Hg, HCl)

Convert benzophenone to triphenylmethanol

Now, benzophenone is treated with phenyl magnesium bromide (the Grignard reagent previously formed from bromobenzene), and then, treated with hydrochloric acid (HCl) or any other acid. This causes the alkoxylation of the carbonyl group resulting in triphenylmethanol. Reaction: 1. Phenylmagnesium bromide 2. HCl

Convert triphenylmethanol to triphenylmethane

Finally, to obtain the desired triphenylmethane, we must remove the hydroxyl group in triphenylmethanol. To do this, perform an acid-catalyzed dehydration using concentrated sulfuric acid (H2SO4). This eliminates water from the molecule, leaving the triphenylmethane structure. Reaction: 1. H2SO4 Overall, the synthesis of triphenylmethane is accomplished through sequential electrophilic aromatic substitution, formation of Grignard reagent, carbonyl alkylation, and dehydration reactions.