Trapp mixture

{{Short description|Low-melting mixture of organic solvents}}

{{Use dmy dates|date=March 2024}}

The Trapp mixture is a specific mixture of organic solvents that allows chemical reactions to take place at very low temperatures.{{cite journal | url=https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cber.19660990243| author1=G. Köbrich |author2=H. Trapp | journal = Chem. Ber. | date = February 1966 | volume = 99 | issue = 2 | pages = 680 | doi = 10.1002/cber.19660990243 | title = 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')| accessdate = 10 March 2024| url-access = subscription }} 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.{{Cite journal|url=https://onlinelibrary.wiley.com/doi/10.1002/047084289X.rv015.pub2| author1 = Eric K. Eisenhart| author2 = Bernard Bessieres | title= "Vinyllithium" | work = e-EROS Encyclopedia of Reagents for Organic Synthesis| date = 17 September 2007| doi=10.1002/047084289X.rv015.pub2| accessdate = 10 March 2024| url-access = subscription}} The low temperatures suppress the reaction of the strongly basic organolithium reagent with the THF.