How can we add a methoxy group to a benzoic acid? At the meta position.
My thought process:
Use friedel craft alkylation and add a CHO and then convert to hydroxyl and use CH3-I to get methoxy, but then theres an extra carbon at the meta position...
To add a methoxy group (-OCH3) at the meta position of a benzoic acid, we can follow the following steps:
Step 1: Protect the carboxylic acid group
Since benzoic acid contains a carboxylic acid group (-COOH) and we want to add the methoxy group to the aromatic ring, we need to protect the carboxylic acid group to avoid unwanted reactions with the reagents. One common way to protect a carboxylic acid is by converting it to its corresponding ester. In this case, we can convert benzoic acid to its methyl ester by reacting it with methanol in the presence of an acid catalyst (e.g., sulfuric acid):
Benzoic acid + Methanol → Methyl benzoate + Water
Step 2: Perform Friedel-Crafts alkylation
Now that the carboxylic acid group is protected, we can proceed with the introduction of the methoxy group through Friedel-Crafts alkylation. This reaction involves the reaction of an alkyl halide with an aromatic compound in the presence of a Lewis acid catalyst, such as aluminum chloride (AlCl3).
For the meta position, we need to use a methylating agent that can react selectively at that position. One option is to use dimethyl sulfate (CH3)2SO4:
Methyl benzoate + (CH3)2SO4 → Meta-methyl benzoate + Dimethyl sulfate by Friedel-Crafts alkylation
Step 3: Hydrolysis
Now, we need to convert the methyl benzoate to benzoic acid to remove the protection from the carboxylic acid group. This can be accomplished by hydrolysis, which involves the reaction of the ester with an aqueous acid or base. In this case, we can use dilute hydrochloric acid (HCl):
Meta-methyl benzoate + HCl(aq) → Meta-benzoic acid + Methanol + Water
Step 4: Convert carboxylic acid to methoxy group
Finally, we need to convert the carboxylic acid group of meta-benzoic acid to the methoxy group. This can be achieved by using suitable reagents such as diazomethane (CH2N2) or the Schiemann reaction:
Meta-benzoic acid + Diazomethane (or Schiemann reaction) → Meta-methoxybenzoic acid
By following these steps, we can successfully add a methoxy group to the meta position of benzoic acid.