Tetrabutylammonium bromide (TBAB) is produced commercially in high yield by the straightforward reaction of tributylamine and butyl bromide when performed in the right solvent. From time to time, users of quaternary ammonium phase-transfer catalysts consider producing the quat salts themselves since the quaternization of the trialkylamine with an alkyl bromide or chloride is usually simple and reliable.
The challenge is obtaining the trialkylamine because not many producers are willing or have the capability to produce the trialkylamine that usually uses a toxic nickel catalyst. In the case of tributylamine, n-butyl alcohol and ammonia can react under the action of a catalyst to prepare tri-n-butylamine. According to the inventors of the patent CN116023269A (Shandong Tongcheng Medicine Co Ltd), the product of the method to produce tributylamine contains n-butylamine, di-n-butylamine and tri-n-butylamine, and the selectivity of the tri-n-butylamine is not as good as desired. If n-butyraldehyde and di-n-butylamine are adopted to react to generate enamine, and then reductive amination is carried out to obtain tri-n-butylamine, the problem of low selectivity of the tri-n-butylamine can be avoided, and the obtained product tri-n-butylamine has high yield and high purity.
The reductive amination is still not trivial to perform because it uses nickel tetracarbonyl as the catalyst, and hydrogen at 20-25 ATM (2.0-2.5 MPa). The solvent is toluene. The yield and selectivity are very good.
The abstract of the patent is as follows: “The invention discloses a synthesis method of tetrabutylammonium bromide, which takes n-butyraldehyde, di-n-butylamine and n-bromobutane as raw materials, hydrogen as a reducing agent and nickel tetracarbonyl as a catalyst, and sequentially performs serial reactions of enamine, reductive amination and quaternary amination, so that tetrabutylammonium bromide is generated by a one-pot method, the yield is 93-98%, and the product purity is 99.7-99.9%. The method has the advantages of convenient operation, simple raw materials and reagents, easy separation and purification of products and higher reaction yield.”
