Animated Solution for Chemistry - Organic Chemistry: The major product of the following reaction is [2019, 10 Jan Shift-II]

The reaction proceeds in two steps: first with dilute $HCl$ and heat, and then with oxalic acid ($(COOH{)}_2$) under polymerisation conditions.

Ether Cleavage When $p$-methoxyphenol is heated with dilute $HCl$, the ether linkage undergoes cleavage. The acidic medium protonates the ether oxygen, making it a good leaving group. Water then attacks the methyl group, resulting in the formation of hydroquinone (benzene-1,4-diol) and methanol. The phenolic $-OH$ group remains unaffected under these conditions.

Condensation Polymerisation The intermediate, hydroquinone, is a diol. It reacts with oxalic acid, which is a dicarboxylic acid. This is a classic condensation polymerisation reaction where the $-OH$ groups of the diol react with the $-COOH$ groups of the dicarboxylic acid, eliminating water molecules to form ester linkages. The resulting polymer is a linear polyester with alternating hydroquinone and oxalate units.