Synthesis of Highly Purified Tetramethylammonium Hydroxide Solution

Abstract

Tetramethylammonium hydroxide (TMAH) solution free from Cl ion was synthesized by electrolysis of the corresponding formate and hydrogencarbonate salts in an electrolytic cell with a cation exchange membrane. As formate salt was used as intermediate of TMAH synthesis, the TMAH solution was contaminated by a small amount of formic acid, while the high-purity TMAH solution was obtained as hydrogencarbonate salt was used as intermediate. Reaction of trimethylamine and dimethyl carbonate in equivalent molecule ratio suggested that one of the two methyl groups of dimethyl carbonate was incorporated into methyl carbonate salt. By electrolysis of the hydrogencarbonate salt which was free from methanol by hydrolysis of methyl carbonate salt, the TMAH solution was prepared at high current efficiency. The sufficient current efficiency was obtained as hydrogencarbonate salts were used as counter anions of tetramethylammonium salts. The important factor dominating the current efficiency was pH of anolyte. 18 refs., 5 figs., 4 tabs.