Carbon Dioxide → 1,2,3,4-Tetrafluorobenzene

Participants

Reaction Steps

19.4 g (0.1 mol) of 2,3,4,5-tetrafluorobenzoic acid are dissolved in 40 g of water, 20 g of a mixture of trialkylamines having 6 to 14 carbon atoms (Hostarex A 327; a commercial product of Hoechst AG) and 0.2 g of copper(I) oxide are added and the pH is adjusted to 7 by addition of 30% strength aqueous sodium hydroxide solution. The decarboxylation is carried out in an autoclave at 155° C. within a period of 4 hours, the evolved carbon dioxide at a pressure of 12 bar being depressurized via a pressure cooler and the distillate passing overhead in this case being collected (cold trap -78° C.). After termination of the reaction, the autoclave is cooled and the 1,2,3,4-tetrafluorobenzene is distilled off by steam at 100° C. and 1.5 l of distillate are obtained, which distillate is combined with the distillate collected previously. The combined distillates are extracted by means of dichloromethane, the organic phase is separated off, dried over magnesium sulfate, filtered and the solvent is removed in vacuo. 10.5 g of crude, slightly yellowish 1,2,3,4-tetrafluorobenzene are obtained, which can be brought to a very high purity by fractional distillation.

Provenance & Evidence