2021 H2 Chem P1 Q20 — Carboxylic Acid Solution

DOTP is the diester of terephthalic acid (benzene-1,4-dicarboxylic acid) with the primary alcohol 2-ethylhexan-1-ol, so it is made by esterifying that acid with that alcohol.

A ✗: The 2-ethylhexyl group is supplied as a carboxylic acid and the ring as a diacyl chloride, so both partners are acid derivatives and the ester of DOTP cannot form.

B ✗: This pairs 2-ethylhexanoyl chloride with benzene-1,4-diol, giving an ester with the connectivity reversed (an aryl ester), not DOTP.

C ✓: 2-ethylhexan-1-ol reacts with terephthalic acid by esterification, forming the two \(\text{R-O-CO-}\) ester linkages of DOTP.

D ✗: The alcohol has the wrong carbon skeleton (a secondary alcohol rather than 2-ethylhexan-1-ol), so the terephthalate ester produced is not DOTP.