Patent GB-611303-A (GB)
Title: Improvements in or relating to the production of olefinic nitriles
Filed: 1945-08-03
Abstract: <PICT:0611303/III/1> Olefinic nitriles are prepared by dehydration of the corresponding alkylene cyanohydrins by continuously introducing the cyanohydrin into the top of a heated column 11 containing a specified catalyst supported on an inert material 13 (see Group IV (b)), while vapours of an inert organic compound, which is liquid at the dehydration temperature and has a boiling point not above 260 DEG C., supplied from a heated vessel 19, are passed through the column; the issuing vapours enter a fractionating condenser 22 whereby the inert organic compound and any unchanged cyanohydrin are refluxed back to the column and the remaining vapours of nitrile and water are condensed in a condenser 23 and collected in vessel 24 forming two layers.  The upper wet layer of nitrile may be subjected to azeotropic distillation, for removal of water as its azeotrope with the nitrile, to leave a residue of anhydrous nitrile.ALSO:<PICT:0611303/IV(b)/1> <PICT:0611303/IV(b)/2> Olefinic nitriles are prepared by heating the corresponding alkylene cyanohydrins to a temperature of at least 155 DEG  C. in the presence of a solid inorganic compound having an alkaline reaction which acts as a catalyst so as to cause dehydration of the alkylene cyanohydrin. The dehydration may be carried out in the presence of an inert organic compound which is liquid at the dehydration temperature and has a boiling point not above 260 DEG  C. Fig. 1 illustrates a pot-still method wherein alkylene cyanohydrin and catalyst are heated in reaction vessel 1 under a reflux condenser 2, unchanged cyanohydrin flowing back into the vessel whilst vapours of nitrile and water formed in the reaction pass upwards into a condenser 6. The condensed nitrile and water are collected in separate layers in vessel 8.  The process may be made continuous by introducing cyanohydrin into the reaction vessel via funnel 4 at a suitable rate. The pot-still method is illustrated by examples in which ethylene cyanohydrin is converted into acrylonitrile, the catalysts being calcium oxide, calcium hydroxide, magnesium oxide, sodium borate and sodium carbonate with or without a petroleum fraction present as the inert organic compound; further examples describe the preparation of a mixture of cis- and transbetamethylacrylonitrile from propylene-cyanohydrin with sodium borate or trisodium phosphate as catalyst and of b  : b -dimethylacrylonitrile from isobutylene cyanohydrin using sodium borate as catalyst.  Fig. 2 illustrates a reflux-tower continuous method, wherein a distilling column 11 contains the catalyst supported on an inert material 13 such as chips of brick, pumice, coke, porcelain and the like, preferably retained by a metal basket 14, the column being heated to dehydration temperature by an electrical heating element 16.  The cyanohydrin is introduced via a funnel 15.  A suitable inert organic compound is boiled in vessel 19, the vapours refluxing in the column and serving to clean the catalyst of polymers and to supply heat to remove the nitrile and water as formed.  The issuing vapours pass to a fractionating condenser 22, whereby the inert carrier and unchanged cyanohydrin are returned to the column whilst the nitrile and water vapours pass through a condenser 23 and the condensate is collected as two layers in vessel 24.  The process may be effected in absence of the inert organic compound. The wet nitrile layer obtained may be dried by distilling off the water as an azeotrope with the nitrile. The water layer may be extracted, for example, with toluene or xylene for recovery of any dissolved nitrile.  Examples illustrate this method applied to the dehydration of ethylene cyanohydrin using supported calcium oxide or hydroxide or sodium carbonate in conjunction with diphenyl ether or naphthalene as inert organic compound.  Potassium carbonate is also specified as a catalyst.  The Specification as open to inspection under Sect. 91 is not restricted as regards the temperature of dehydration and includes the use of any compound having an alkaline reaction as catalyst. This subject-matter does not appear in the Specification as accepted.