Question

An alkene (A) on ozonolysis gives propanone and aldehyde (B). When (B) is oxidised (C) is obtained. (C) is treated with Br₂/P gives (D) which on hydrolysis gives (E). When propanone is treated with HCN followed by hydrolysis gives (E). Identify A, B, C, D and E.

Answer 1

1. 2-methyl-but-2-ene (A) on ozonolysis gives propanone and acetaldehyde (B)

\[\begin{array}{cc}
\ce{CH3}\phantom{............................}\\
|\phantom{...............................}\\
\ce{\underset{\underset{(A)}{(2-methyl-but-2-ene)}}{CH3 - CH = C - CH3} ->[O3][Zn/H2O] \underset{\underset{(B)}{(Acetaldehyde)}}{CH3CHO} + CH3 - C - CH3}\\
\phantom{............................................}||\\
\phantom{............................................}\ce{\underset{(Propanone)}{O}}
\end{array}\]

2. Acetaldehyde (B) is oxidised to give acetic acid (C), which on further treated with Br₂/P give monobromo acetyl bromide (D) which on hydrolysis gives monobromo acetic acid (E).

\[\begin{array}{cc}
\ce{\underset{\underset{(B)}{(Acetaldehyde)}}{CH3CHO} ->[H^+/K2Cr2O7][(O)] \underset{\underset{(C)}{(Acetic acid)}}{CH3COOH} ->[Br2/P][Excess] CH2COBr}\\
\phantom{.................................}|\\
\phantom{...................................}\ce{\underset{\underset{(D)}{(Monobromo acetyl bromide)}}{Br}}
\end{array}\]

3. Propanone is treated with HCN followed by hydrolysis to gives 2-methyl-2-hydorxy propanoic acid (E)

\[\begin{array}{cc}
\ce{COOH}\\
|\\
\ce{CH3 - C - CH3 ->[(i) HCN][(ii) H^+/H2O] CH3 - C - CH3}\\
\phantom{.}||\phantom{...........................}|\phantom{.}\\
\phantom{...........}\ce{\underset{(Propanone)}{O}}\phantom{............}\ce{\underset{\underset{(E)}{(2-methyl-2-hydorxy propanoic acid)}}{OH}}\phantom{}
\end{array}\]

A	\[\begin{array}{cc} \ce{CH3 - CH = C - CH3}\\ \phantom{.......}|\\ \phantom{........}\ce{CH} \end{array}\]	2-methyl-but-2-ene
B	CH3CHO	Acetaldehyde
C	CH3COOH	Acetic acid
D	Br – CH2 – COBr	Monobromo acetyl bromide
E	CH3C(OH) (COOH) CH3	2-methyl-2-hydorxy propanoic acid