(168a) Risk Mitigation in Process Scale up of Aminopropyl Silicone Intermediates

Within silicones, access to terminal aminopropyl silicone polymers has been limited due to the difficulties in synthetic methods of aminopropyl silicone endblocking intermediates. Bis-aminopropyl disiloxane is generally used to build terminal primary aminosiloxanes via a silicone equilibration process. However, this intermediate requires multiple synthetic steps and raw materials making production costly. In addition, the production chemistry requires based-catalyzed equilibration with dimethyl silicone followed by neutralization and filtration. An alternative synthetic method involves the primary amino, 2,2,4-trimethyl-1- aza- 2- silacyclopentane (CAS: 661492-94-0) or N-[(3-Aminopropyl)dimethylsilyl]-2,2-dimethyl-1-aza-2-silacyclopentane (CAS: 388606-32-4) as a direct reaction with silanol terminated silicones. However, synthetic yields have been low or a catalyst was required for the silanol capping reaction. Another route that was not previously investigated involves the use of cyclic-siloxazanes, specifically 2, 2, 7, 7- tetramethyl-1- oxa- 3- aza- 2, 7- disilacycloheptane. The cyclic siloxazane readily ring opens at the Si-N bond when combined with silanols to add a disiloxy-propylamine unit. This will occur at ambient temperature and free of catalyst. Prior to the work reported in this paper, the process to make the cyclic-siloxazane (GE Silicones) was plagued by low-volume efficiency and a hazardous, untenable process in a manufacturing setting. Attempts by GE to reduce excessive use of allylamine led to disastrous results—a runaway reaction. As it will be shown in this presentation, the large exotherm was likely a result of an accumulation of SiH and olefin functionalities in the mixture concurrent with the reduction of free allylamine, which is known to act as a hydrosilylation inhibitor. In this work, we show that the cyclic siloxazane can be successfully and safely synthesized through new process controlled methods. The scale up from a glove box to a 1L fume hood reactor with batch distillation was successfully demonstrated for the production of cyclic siloxazane endblocker. There are four key technologies specific to the hydrosilylation of olefinic amines in this example that are required and enable the sensitive chemistry. These include pulsed feed of tetramethyldisiloxane, use of a hydrosilylation promoter, ammonium sulfate catalyzed rearrangement, and batch distillation of the lights and product. Proper implementation of these methods can result in volume yields ~89% at >99% purity.