Question

Complete the following equations and identify A, B, C, D and E.
i) \(\mathrm{CH_3COCH_3}\ \xrightarrow[\text{distillation}]{\text{conc. } H_2SO_4}\ (A)\)
ii) \(\mathrm{CH_3COCH_3}\ \xrightarrow[\text{Heat}]{I_2 + NaOH}\ (B)\)
iii) \(\mathrm{CH_3CHO}\ \xrightarrow{\text{dil.\ } NaOH}\ (C)\ \xrightarrow{\text{Heat}}\ (D)\)
iv) \(\mathrm{HCHO}\ \xrightarrow{Ca(OH)_2}\ (E)\)

Hint:

Acetone shows iodoform test \(\rightarrow\) \(\mathrm{CHI_3}\). Acetaldehyde gives aldol \(\rightarrow\) dehydration to \(\alpha,\beta\)-unsaturated aldehyde. Formaldehyde undergoes Cannizzaro with bases to give formate salt \(+\) methanol.

Answer 1

i) Acetone + conc.\ \(H_2SO_4\) (distillation):
Self-condensation and aromatization give mesitylene.
\[ 3\,\mathrm{CH_3COCH_3}\ \xrightarrow[\text{distill.}]{\text{conc. } H_2SO_4}\ \mathrm{C_6H_3(CH_3)_3}\ (A)\ +\ 3\,\mathrm{H_2O} \]
\(A=\) Mesitylene (1,3,5-trimethylbenzene), formula \(\mathrm{C_9H_{12}}\).
ii) Iodoform reaction of acetone (NaOH, \(I_2\), heat):
\[ \mathrm{CH_3COCH_3}+3\,I_2+4\,NaOH \rightarrow \underbrace{\mathrm{CHI_3}}_{(B)}+ \mathrm{CH_3COONa}+3\,\mathrm{NaI}+3\,\mathrm{H_2O} \]
\(B=\) Iodoform, formula \(\mathrm{CHI_3}\) (yellow ppt.).
iii) Aldol reaction of acetaldehyde then dehydration:
\[ 2\,\mathrm{CH_3CHO}\ \xrightarrow{\text{dil.\ } NaOH}\ \mathrm{CH_3CH(OH)CH_2CHO}\ (C) \]
\[ \mathrm{CH_3CH(OH)CH_2CHO}\ \xrightarrow{\text{Heat}}\ \mathrm{CH_3CH{=}CHCHO}\ (D)+\mathrm{H_2O} \]
\(C=\) 3-Hydroxybutanal (aldol), formula \(\mathrm{C_4H_8O_2}\).
\(D=\) Crotonaldehyde (but-2-enal), formula \(\mathrm{C_4H_6O}\).
iv) Formaldehyde with \(Ca(OH)_2\) (Cannizzaro):
\[ 2\,\mathrm{HCHO}+Ca(OH)_2 \rightarrow \underbrace{(HCOO)_2Ca}_{(E)}+\mathrm{CH_3OH} \]
\(E=\) Calcium formate, formula \((\mathrm{HCOO})_2\mathrm{Ca}\).