SYNTHESIS OF HIGHLY PURIFIED TETRAMETHYLAMMONIUM HYDROXIDE SOLUTION

Tetramethylammonium hydroxide (TMAH) solution, which was free from chl oride ion, Has synthesized by electrolysis of the corresponding format and hydrogencarbonate salts in an electrolytic cell with a cation exc hange membrane. When the formate salt was used as an intermediate of T MAH synthesis, the TMAH solution was contaminated by a small amount of formic acid. More purified TMAH solution was obtained, upon using the hydrogencarbonate salt as an intermediate. Reaction of trimethylamine and dimethyl carbonate reacted in an equivalent molecular ratio sugge sted that one of the two methyl groups of dimethyl carbonate was incor porated into the methyl carbonate salt. Electrolysis of the hydrogenca rbonate solution which was free from methanol by hydrolysis of the met hyl carbonate salt provided the corresponding TMAH solution with a hig h current efficiency in the electrolytic cell with a cation exchange m embrane as a diaphragm. Counter anions of tetramethylammonium salts af fected current efficiency, and a sufficient result was obtained with h ydrogencarbonate among such anions examined as sulfate, chloride, and formate salts. The current efficiency decreased more prominent with st ronger acids in the anolyte. It was suggested that the important facto r to affect the current efficiency was pH of the anolyte. All contamin ants of metallic ions were less than 10 ppb, and the concentration of carbon dioxide was less than 10 ppm.