Bis(trichloromethyl)carbonate (BTC, Triphosgene): A Safer Alternative to Phosgene?

Abstract

Bis(trichloromethyl)carbonate (BTC, triphosgene) is a versatile compound that enables highly efficient syntheses. In addition, because of its solid state, it is a very convenient compound for small-scale phosgenations. Consequently, this compound is favored as a phosgene substitute in research and development and in small-scale production. Although BTC is highly toxic, safe handling is possible as long as the properties and chemical reactivity of this compound are understood and considered. However, branding as "safe phosgene" or "safer phosgene" is misleading. The solid state of BTC leads to the misconception that there is no significant exposure. However, the vapor pressure is sufficiently high to easily result in toxic concentrations. In addition, proper monitoring is not yet possible. Proper use of BTC could be more complex than the handling of phosgene itself. However, handling of BTC is normally always associated with phosgene and has its own toxicity. Therefore, the use of BTC will become more regulated in the future, which will directly increase responsibility in route selection during process development. A stringent safety concept for phosgenations using BTC is necessary. Because of the interconnection with phosgene, the safety concept for BTC will likely be an extended version of the safety concept for phosgene.