In crossed cannizzaro reactions between formaldehyde and Benzaldehyde the alcohol formed is only benzyl alcohol and methanol. Give reason.

In a crossed Cannizzaro reaction involving formaldehyde and benzaldehyde, only benzyl alcohol and methanol are formed as the products. This outcome can be explained by considering the reaction mechanism and the relative reactivity of the two aldehydes.

The Cannizzaro reaction is a disproportionation reaction in which one molecule of an aldehyde is oxidized to its corresponding carboxylic acid, while another molecule of the same or a different aldehyde is simultaneously reduced to an alcohol. In the case of formaldehyde and benzaldehyde, the reaction proceeds as follows:

Formaldehyde (HCHO) is both a strong reducing agent and a strong oxidizing agent. When it undergoes the Cannizzaro reaction, one molecule of formaldehyde is reduced to methanol (CH3OH), and the other molecule is oxidized to formic acid (HCOOH).

Benzaldehyde (C6H5CHO) is less reactive compared to formaldehyde in the Cannizzaro reaction due to the presence of the electron-withdrawing benzene ring. The benzaldehyde molecule is reduced to form benzyl alcohol (C6H5CH2OH) and oxidized to benzoic acid (C6H5COOH).

The reason why only benzyl alcohol and methanol are formed as products in the crossed Cannizzaro reaction is because of the difference in reactivity between the two aldehydes. Formaldehyde is more reactive than benzaldehyde due to its simpler structure and higher electrophilic nature. As a result, formaldehyde preferentially undergoes reduction to methanol, while benzaldehyde undergoes reduction to benzyl alcohol.

The relative reactivity of the aldehydes determines the products formed in the crossed Cannizzaro reaction. Since formaldehyde is more reactive, it gets reduced to methanol before benzaldehyde can react with it. Likewise, benzaldehyde gets reduced to benzyl alcohol, and the oxidation products (formic acid and benzoic acid) are not observed in significant amounts in this reaction due to the selective reduction pathways followed by the aldehydes.