The 2-reaction sequence shown in the diagram is interesting.
The second step is likely a solid-liquid PTC reaction.
In the first step, tetrabutylammonium chloride (TBAC) serves as a source of organic-soluble chloride ion to catalyze the opening of the epoxide and subsequent attack of the alkoxide on the phosgene that regenerates the chloride anion as leaving group. The glycidyl ether starting material and the chloromethyl chloroformate intermediate are liquids (oil). The intermediate is not isolated other than being stripped with dry argon to remove excess phosgene. This means that the tetrabutylammonium cation was not separated from the intermediate.
For the second step, acetonitrile is added to the crude intermediate and the mixture is cooled to 0 deg C. To the reaction mixture is added solid sodium sulfide at a rate that maintains the temperature below 5 deg C. While a very small amount of the sodium sulfide might dissolve in acetonitrile, it may be reasonable to assume that the tetrabutylammonium cation, that was not separated from the intermediate after the first step, transfers the sulfide anion into the acetonitrile phase and therefore acts as a phase-transfer catalyst.
In other words, we speculate that the second reaction is a solid-liquid phase-transfer catalyzed sulfide SN2 reaction to form the cyclic thiocarbonate product.
It should be noted that trimethoxysilanes are very sensitive to hydrolysis, much more so than triethoxysilanes. For that reason, it is important to avoid the use of water and the role of the quaternary ammonium phase-transfer catalyst may have been crucial in the thiocarbonate formation reaction.
When your company needs to develop low-cost high-performance green chemistry reactions using phase-transfer catalysis, now contact Marc Halpern of PTC Organics to assure resource efficient PTC process development.
About Marc Halpern
Dr. Halpern is founder and president of PTC Organics, Inc., the only company dedicated exclusively to developing low-cost high-performance green chemistry processes for the manufacture of organic chemicals using Phase Transfer Catalysis. Dr. Halpern has innovated PTC breakthroughs for pharmaceuticals, agrochemicals, petrochemicals, monomers, polymers, flavors & fragrances, dyes & pigments and solvents. Dr. Halpern has provided PTC services on-site at more than 260 industrial process R&D departments in 37 countries and has helped chemical companies save > $200 million. Dr. Halpern co-authored five books including the best-selling “Phase-Transfer Catalysis: Fundamentals, Applications and Industrial Perspectives” and has presented the 2-day course “Practical Phase-Transfer Catalysis” at 50 locations in the US, Europe and Asia.
Dr. Halpern founded the journal “Industrial Phase-Transfer Catalysis” and “The PTC Tip of the Month” enjoyed by 2,100 qualified subscribers, now beyond 130 issues. In 2014, Dr. Halpern is celebrating his 30th year in the chemical industry, including serving as a process chemist at Dow Chemical, a supervisor of process chemistry at ICI, Director of R&D at Sybron Chemicals and founder and president of PTC Organics Inc. (15 years) and PTC Communications Inc. (20 years). Dr. Halpern also co-founded PTC Interface Inc. in 1989 and PTC Value Recovery Inc. in 1999. His academic breakthroughs include the PTC pKa Guidelines, the q-value for quat accessibility and he has achieved industrial PTC breakthroughs for a dozen strong base reactions as well as esterifications, transesterifications, epoxidations and chloromethylations plus contributed to more than 100 other industrial PTC process development projects.
Dr. Halpern has dedicated his adult life to his family and to phase-transfer catalysis (in that order!).
