Acetic acid (an important constituent of vinegar) reacts with red phosphorus and bromine in the Hell-Volhard-Zelinsky reaction to give compound B (a monobromoderivative), which on reaction with excess ammonia gives compound C (a white solid amino acid). Separately, acetaldehyde undergoes S

Question

Acetic acid (an important constituent of vinegar) reacts with red phosphorus and bromine in the Hell-Volhard-Zelinsky reaction to give compound B (a monobromoderivative), which on reaction with excess ammonia gives compound C (a white solid amino acid). Separately, acetaldehyde undergoes Strecker synthesis (reaction with HCN in presence of NH3, followed by acidic hydrolysis) to give compound D (a high-melting amino acid). If x = total number of optical isomers of C, y = total number of optical isomers of D, then find x + y.

Accepted Answer

3. Acetic acid (CH3COOH) + red P + Br2 gives bromoacetic acid BrCH2COOH (compound B). B + excess NH3 gives glycine NH2CH2COOH (compound C). Glycine has no stereocentre (alpha carbon has two H atoms), so x = 1. Acetaldehyde (CH3CHO) + HCN + NH3 then H3O+ hydrolysis gives alanine CH3CH(NH2)COOH (compound D) via Strecker synthesis. Alanine has one stereocentre (alpha carbon bonded to CH3, NH2, COOH, H), giving 2 optical isomers (L-alanine and D-alanine), so y = 2. Therefore x + y = 1 + 2 = 3.

Solution

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