Question

An unknown compound X is one of the four compounds listed in the table below. A mixture of X with o-toluic acid melts at 100 degrees Celsius, a mixture of X with benzoic acid melts at 112 degrees Celsius, a mixture of X with phenyl succinate melts at 110 degrees Celsius, and a mixture of X with m-aminophenol melts at 115 degrees Celsius. Give the identity of X and explain your reasoning.

Compound, melting point:
o-toluic acid, 102 degrees Celsius
benzoic acid, 121 degrees Celsius
phenyl succinate, 121 degrees Celsius
m-aminophenol, 122 degrees Celsius