Q.(a) Grignard reagents are important class of organometallic compounds used to prepare alcohols. Identify the compounds A and B and write the formula.

Grignard reagents add across a carbonyl group and, after hydrolysis, give an alcohol whose class (1°, 2°, or 3°) depends on the starting carbonyl compound; and the acetylation of salicylic acid's phenolic –OH with acetic anhydride is the industrial synthesis of aspirin.

1. Identifying A and B Grignard reagents (RMgX) add to the carbonyl group of aldehydes/ketones; hydrolysis of the resulting magnesium alkoxide gives an alcohol.
   1. HCHO (methanal/formaldehyde) + CH3MgBr --(1) dry ether (2) H2O--> A + Mg(OH)Br Formaldehyde (the only aldehyde with no carbon substituent) always gives a PRIMARY alcohol with a Grignard reagent: HCHO + CH3MgBr → CH3–CH2–OMgBr --(H2O)--> CH3CH2OH + Mg(OH)Br So A = CH3CH2OH (ethanol).
   2. B + CH3MgBr --(1) dry ether (2) H2O--> CH3–CH(CH3)–OH + Mg(OH)Br The product CH3–CH(CH3)–OH is (CH3)2CHOH, propan-2-ol — a SECONDARY alcohol, which forms when CH3MgBr adds to an aldehyde (other than formaldehyde). Working backwards, B must be ethanal (acetaldehyde): CH3CHO + CH3MgBr → CH3–CH(OMgBr)–CH3 --(H2O)--> CH3CH(OH)CH3 + Mg(OH)Br So B = CH3CHO (ethanal / acetaldehyde).
2. Reaction of salicylic acid with acetic anhydride …