Question

How will you convert ethanol into the following compounds? Write chemical equation only.
(i) 3-Hydroxybutanol (ii) But-2-enal

Hint:

From ethanol, go via acetaldehyde: aldol addition gives 3-hydroxybutanal; \(-\mathrm{H_2O}\) \(\Rightarrow\) crotonaldehyde, while reduction of the aldehyde group \(\Rightarrow\) 1,3-butanediol (3-hydroxybutanol).

Answer 1

(i) 3-Hydroxybutanol (3-hydroxybutan-1-ol \(\equiv\) 1,3-butanediol) from ethanol
\[ \mathrm{CH_3CH_2OH} \xrightarrow{[O]} \mathrm{CH_3CHO} $\Rightarrow$ 2\,\mathrm{CH_3CHO} \xrightarrow[\text{aldol}]{\text{dil.\ NaOH}} \mathrm{CH_3\!-\!CH(OH)\!-\!CH_2\!-\!CHO} \xrightarrow{\mathrm{NaBH_4\ (or)\ H_2/Ni}} \boxed{\mathrm{HO\!-\!CH_2\!-\!CH(OH)\!-\!CH_2\!-\!CH_3}} \] (ii) But-2-enal (crotonaldehyde) from ethanol
\[ \mathrm{CH_3CH_2OH} \xrightarrow{[O]} \mathrm{CH_3CHO} $\Rightarrow$ 2\,\mathrm{CH_3CHO} \xrightarrow[\text{aldol}]{\text{dil.\ NaOH}} \mathrm{CH_3\!-\!CH(OH)\!-\!CH_2\!-\!CHO} \xrightarrow[\,-\mathrm{H_2O}\,]{\Delta} \boxed{\mathrm{CH_3\!-\!CH{=}CH\!-\!CHO}} \]