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 −110 °C and the same solvents in a 4:1:1 ratio remain a liquid down to −120 °C. This solvent system retains a low viscosity until just before freezing and it allows a lower temperature reaction than pure THF, which melts at −108.4 °C. 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.
- Köbrich, G.; Trapp, H. (1966). "Darstellung und thermische Stabilität von 1-Chlor-2.2-diaryl-vinyllithium-Verbindungen ('The formation and thermal stability of 1-chloro-2,2-diaryl-vinyl lithium compounds')". Chem. Ber. 99 (2): 680. doi:10.1002/cber.19660990243.
- Eric K. Eisenhart, Bernard Bessieres "Vinyllithium" e-EROS Encyclopedia of Reagents for Organic Synthesis, 2001. doi:10.1002/047084289X.rv015.pub2.
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