Self-Neutralizing in Situ Acid Catalysis for Single-Pot Synthesis of Iodobenzene and Methyl Yellow in CO₂-Expanded Methanol

Despite widespread use, homogeneous acid catalysis has the drawback of requiring downstream neutralization, resulting in salt waste. Methylcarbonic acid is a self-neutralizing acid that forms in situ in methanol/CO₂ systems at mild pressures (10−47 bar) and then decomposes by depressurization. In the work presented here, methylcarbonic acid catalyzes the diazotization of aniline, which is either coupled with N,N-dimethyl aniline to form methyl yellow or reacted with iodide to form iodobenzene. The syntheses of methyl yellow and iodobenzene represent a class of industrially important reactions.