Reactions of Alcohols and Phenols
Cleavage of O-H Bond
Alcohols react with carboxylic acid in the presence of conc. H2SO4 or dry HCl to form esters.
Due to resonance, phenols do not undergo this reaction.
Alcohols react with acid chlorides (R−COCl) and acid anhydrides [(R−CO)2O] to form esters.
If the acid chloride or acid anhydride used is acetyl chloride (CH3COCl) or acetic anhydride [(CH3CO)2O] , the reaction is usually termed as acetylation. However, if benzoyl chloride (C6H5COCl) is used, the reaction is termed as benzoylation.
Phenols also undergo the reaction in the presence of base catalyst such as pyridine.
In case of acetic anhydride, either acids (conc. H2SO4) or base (pyridine etc.) are used as catalysts.
Phenols react with benzoyl chloride in the presence of aqueous NaOH to form phenylesters. This reaction is called Schotten-Baumann reaction.
Reaction with Grignard reagents
Both alcohols and phenols react with Grignard reagents to form alkanes. The alkane thus formed corresponds to the alkyl group of the Grignard reagents.
Question : Show how are the following alcohols prepared by the reaction of a suitable Grignard reagent on methanl?
Answer : The reaction of methanal — HCHO or CH2O — with Grignard reagents is carried out as given below:
Thus, to identify the reagent, we need to look for the part other than -CH2OH.
- Isopropyl magnesium halide is used.
- Cyclohexyl magnesium halide is used.