Tetramethylammonium chloride is a phase transfer catalyst in organic synthesis. Its catalytic activity is stronger than that of triphenylphosphorus and triethylamine. It is a white crystalline powder at room temperature. It is volatile, irritating, easy to absorb moisture, soluble in methanol, water and hot ethanol, insoluble in ether and chloroform. When heated above 230 ℃, it is decomposed into trimethylamine and methyl chloride. Median lethal dose (mice, abdominal cavity) 25mg / kg. It is also used in the synthesis of liquid crystalline epoxy compounds, polarographic and pop analysis, electronic industry, etc.