Improvements in process for manufacturing dicyanobutene

摘要

An improvement in the manufacture of 1,4-dicyano-2-butene by the reaction of dichlorbutenes, e.g. either 1,4-dichloro-2-butene or 3,4-dichloro-1-butene or mixtures thereof, with hydrogen cyanide formed in situ from sodium cyanide in a liquid aqueous acidic medium containing a dissolved cuprous compound as catalyst, comprises removing ferrocyanide iron from a liquid aqueous copper-containing phase, which constitutes the catalyst recycle stream, by lowering the pH of the aqueous phase to such a level that substantially all of the ferrocyanide iron is precipitated with resultant slurry, admixing at least a part of the slurry with sufficient alkali metal cyanide to dissolve cuprous cyanide leaving part of the ferrocyanide iron undissolved, and thereafter separating the liquid phase from the remaining slurry. Preferably the pH of the aqueous phase is lowered to between 1.0 and 2.5 preferably 1.7, the slurry of copper-containing compound thus produced is concentrated by removal of liquid component therefrom, and is admixed with only enough aqueous sodium cyanide to produce a pH of 4.0 to 4.5, whereby cuprous cyanide goes into solution and part of the ferrocyanide remains undissolved, the liquid phase is separated from the remaining slurry and recycled to the reaction vessel in which the reaction between HCN and dichlorobutenes takes place. The concentrated product may be further treated with manganese, cadmium, cupric or ferric ions as in Specification 732,863 for a final purging of ferrocyanide ions. Alternatively, Mn ions can be introduced into the mixture immediately prior to removal of the liquid phase from the slurry at a pH of 4.0 to 4.5. The optimum temperature, in the absence of manganese, is 50 DEG to 80 DEG C., but in the presence of manganese, temperature in the range 0 DEG to 100 DEG C. may be used, preferably 20 DEG to 40 DEG C. In examples (1) the pH of an aqueous raffinate, produced by benzene extraction of the products obtained by reaction between dichlorobutenes and HCN, is lowered to 1.7 to precipitate cuprous cyanide and cuprous ferrocyanide which are then filtered. NaCN is added to the slurry to give a pH of 4.5 and the undissolved ferrocyanide iron is removed by settling. The remaining liquid containing dissolved copper may be used in the cyanation process. When NaCN is added to give a pH of 10, all the ferrocyanide dissolves; (2) NaCN is added to the slurry as in (1) to produce a pH of 4.5 and aqueous manganese chloride was added to precipitate further ferrocyanide. Specification 639,438 also is referred to.