The Trapp mixture is a specific mixture of organic solvents that allows chemical reactions to take place at very low temperatures. It is made up of THF:diethyl ether:pentane in a 4:4:1 ratio which remains liquid down to âÂÂ110 ðC and the same solvents in a 4:1:1 ratio remain a liquid down to âÂÂ120 ðC. This solvent system retains a low viscosity until just before freezing and it allows a lower temperature reaction than pure THF, which melts at âÂÂ108.4 ðC. An illustrative application of Trapp solvent is the preparation of vinyllithium by lithium halogen exchange from vinyl bromide and tert-butyllithium. The low temperatures suppress the reaction of the strongly basic organolithium reagent with the THF.