Esterfication of 2,2,2-triphenylethanoic acid
Disclaimer: The question has pretty much been answered in the comments. I'm just making it substantial.



The triphenylacetic acid is dehydrated in the presence of concentrated sulfuric acid to give an acylium ion, namely triphenylacetylium cation, which is stabilized by resonance.

Then, the triphenylacetylium cation undergoes decarbonylation (removal of carbon monoxide) to give triphenylmethyl cation, which is stabilized by the three phenyl groups.

The oxygen in methanol acts as a nucleophile to attack the carbocation, and is deprotonated to give our desired product triphenylmethyl methyl ether.

It is noted that this reaction should be done in a well-ventilated area because of the evolution of toxic carbon monoxide gas.