Synthesis of Highly Purified Tetramethylammonium Hydroxide Solution by Electrolysis of Its Hydrogencarbonate

Abstract

Tetramethylammonium hydroxide (TMAH) (1) solution which was free from chloride ion was synthesized by electrolyzing its hydrogencarbonate (11) in an electrolytic cell with a cation exchange membrane. Trimethylamine (2) and dimethyl carbonate (8) reacted in an equivalent molecular ratio, suggesting that one of the two methyl groups of (8) was incorporated into methyl carbonate salt (10) (Scheme 3). 482 g (2.25 mol) of the hydrogencarbonate solution (63.0%), which was free from methanol by hydrolyzing of methyl carbonate salt (10), was placed in the electrolytic cell with a cation exchange membrane (Du Pont Nafion 324) as a diaphragm and was electrolyzed by impressing 20 V for 12 h. 626 g of 30.7% TMAH solution was obtained with a high current efficiency. Current efficiency was changed by the variation in the anion of tetramethylammonium salts and sufficient result was obtained with hydrogencarbonate among sulfate, chloride, and formate salts (Fig. 2). The decrease in current efficiency was more prominent with the stronger acid in the anolyte. It was suggested that the important factor affecting current efficiency was the pH of the anolyte. All containments of metallic ions were less than 10 ppb, and the concentration of carbon dioxide was less than 10 ppm. © 1995, The Chemical Society of Japan. All rights reserved.