Question

Complete the following reactions and write the names and formulae of A, B, C, D and E.
i) \((\mathrm{HCOO})_2\mathrm{Ca}\ \xrightarrow[\text{Dry distillation}]{}\ (A)\ \xrightarrow[\text{NaOH}]{}\ (B) + \mathrm{CH_3OH}\)
ii) \((\mathrm{CH_3COO})_2\mathrm{Ca} + (\mathrm{HCOO})_2\mathrm{Ca}\ \xrightarrow[\text{Dry distillation}]{}\ (C)\ \xrightarrow[\ \mathrm{HCN}\ ]{}\ (D)\ \xrightarrow[\ \mathrm{H_2O}\ ]{}\ (E)\)

Hint:

Dry distillation of calcium salts: acetate \(\rightarrow\) ketone; formate + acetate (mixed) \(\rightarrow\) corresponding aldehyde. Carbonyl + HCN gives cyanohydrin, which on hydrolysis \(\rightarrow\) \(\alpha\)-hydroxy acid.

Answer 1

(i) Identification and equations:
Dry distillation of calcium formate gives formaldehyde.
\((\mathrm{HCOO})_2\mathrm{Ca} \ \xrightarrow[\Delta]{\text{dry dist.}} \ \mathrm{HCHO}\ (A) \ +\ \mathrm{CaCO_3}\)
Formaldehyde undergoes Cannizzaro reaction with NaOH to give sodium formate and methanol.
\(2\,\mathrm{HCHO}\ (A) + \mathrm{NaOH} \rightarrow \mathrm{HCOONa}\ (B) + \mathrm{CH_3OH}\)
Therefore:
\(A =\) Formaldehyde, formula \(\mathrm{HCHO}\).
\(B =\) Sodium formate, formula \(\mathrm{HCOONa}\).
(ii) Identification and equations:
Dry distillation of mixed calcium acetate and calcium formate gives acetaldehyde.
\((\mathrm{CH_3COO})_2\mathrm{Ca} + (\mathrm{HCOO})_2\mathrm{Ca} \ \xrightarrow[\Delta]{\text{dry dist.}} \ \mathrm{CH_3CHO}\ (C) + \text{(by-product(s) } \mathrm{CaCO_3})\)
Addition of HCN to acetaldehyde gives its cyanohydrin (lactonitrile).
\(\mathrm{CH_3CHO}\ (C) + \mathrm{HCN} \rightarrow \mathrm{CH_3CH(OH)CN}\ (D)\)
Hydrolysis of the nitrile yields lactic acid (2-hydroxypropanoic acid).
\(\mathrm{CH_3CH(OH)CN}\ (D) \xrightarrow{\mathrm{H_2O}/\text{hydrolysis}} \ \mathrm{CH_3CH(OH)COOH}\ (E)\)
Therefore:
\(C =\) Acetaldehyde, formula \(\mathrm{CH_3CHO}\).
\(D =\) Acetaldehyde cyanohydrin (lactonitrile), formula \(\mathrm{CH_3CH(OH)CN}\).
\(E =\) Lactic acid (2-hydroxypropanoic acid), formula \(\mathrm{CH_3CH(OH)COOH}\).