Question

The most suitable reagent used for converting ethanoic acid to ethanol is
(A) $LiAl{H_4}$
(B) $B{H_3}$
(C) $PC{l_3}$
(D) ${K_2}C{r_2}{O_7}/{H^ + }$

Answer 1

Hint: The reaction of obtaining ethanol from ethanoic acid is a reduction reaction. A good hydride donor can do the reaction efficiently. A suitable reducing agent is required in this reaction to achieve this conversion. We will check for every reagent what their reaction products are to get the correct answer.

Complete step by step solution: We have been given the conversion of ethanol to ethanoic acid which is a reduction reaction. The following conversion is taking place and it is as follows-

$C{H_3}COOH \to C{H_3}C{H_2}OH$

We will see at the reagents whether they will be able to achieve this conversion or not –
-$LiAl{H_4}$- It is commonly known as lithium aluminium hydride. As it is a hydride donor it can reduce the double and triple bond of carbon. It is a very strong reducing agent and can easily reduce the carboxylic acid into alcohol. So this reagent can give this conversion.
So when ethanoic acid is treated with lithium aluminium hydride it yields ethanol as a product.
-$B{H_3}$- It is called borane. It is used in hydroboration reactions.
-$PC{l_3}$- Phosphorus pentachloride as a chlorinating agent. It is also used as chlorine to the hydroxyl group of carboxylic acid. It converts carboxylic acid to acid chlorides and alcohols to alkyl halides. So this reagent cannot be used for the conversion.
-${K_2}C{r_2}{O_7}/{H^ + }$- It is a very strong oxidising agent which oxidises every functional group. It produces chromic acid on reaction with acid. So it cannot be used for the conversion of ethanoic acid to alcohol.
So the reagent which can give the conversion of ethanoic acid to ethanol is lithium aluminium hydride ( $LiAl{H_4}$)

Hence the correct answer is option A.

Note: It should be noted that here this conversion can be given by a relatively less strong reducing agent such as sodium borohydride( $NaB{H_4}$). Lithium aluminium hydride ( $LiAl{H_4}$) is used in the reduction of esters, nitriles etc.