Patent GB-700856-A (GB)
Title: Production of omega-cyano-carboxylic acids
Filed: 1950-10-04
Abstract: In a process for the production of aliphatic o -cyanocarboxylic acids a diamide of an aliphatic o , o 1-dicarboxylic acid is heated in the presence of free mono- or di-carboxylic acid or boric and/or phosphoric acid to a temperature above 150 DEG  C. preferably above 200 DEG  C.  In a modification of the process an aliphatic o -cyano-carboxylic acid amide is reacted with a mono- or di-carboxylic acid.  The diamide and the acid may be brought together or a dicarboxylic acid may be partially converted to the corresponding diamide by ammonia or another substance which forms ammonia.  The dicarboxylic acid may be mixed with another of the above defined organic or inorganic acids and then reacted with ammonia.  The reaction may be promoted by adding one or more of molybdenic acid, tungstic acid and derivatives thereof, e.g. the anhydrides, boron phosphate and tricresyl phosphate.  The reaction may be carried out under vacuum when the reaction products may be removed by distillation.  The aliphatic o -cyano-carboxylic acid amide employed in the modified process may be isolated from, or present in, a reaction mixture.  When the free acid employed is the same aliphatic dicarboxylic acid as that from which the o -cyano-carboxylic acid monoamide is derived the reaction takes place in two stages an o -cyano-carboxylic acid and a half amide of the dicarboxylic acid being formed.  The conversion of the latter to the o -cyano-carboxylic acid is only partially complete.  When the free acid is a monocarboxylic acid the amide of that acid is formed intermediately in addition to the desired o -cyanocarboxylic acid and dehydrates to the nitrile which can be separated from the desired product.  The reaction products may be extracted with selective solvents or separated by distillation. 5-Cyanovaleric and 9-cyanononylic acid are mentioned as products. The o -cyano-carboxylic acids produced by this process are shown by molecular weight determinations to be dimeric.  The dimeric products may be polymerized by heating at high temperatures and on distillation the polymers disproportionate into the corresponding dinitriles and dicarboxylic acids. o -Cyanocarboxylic acids may be produced continuously by passing a mixture of the diamide of an aliphatic dicarboxylic acid preferably in large excess and the free acid through a heated reaction chamber and removing the product at such a rate that the dinitrile is not formed.  The diamide may be formed by passing ammonia and the free discarboxylic acid into the chamber. By-product diamide may be recycled with free dicarboxylic acid with proportionate reduction in the ammonia supply or increase in the free dicarboxylic acid supply.  Molten or crystalline dicarboxylic acid may be introduced into the heated reactor filled, if desired, with a dehydration catalyst and ammonia allowed to flow upwards through the melt.  The reaction product is removed from the reactor floor so as to leave a constant level in the reactor.  Excess ammonia together with water produced in the reaction is driven out of the reactor and the former is recycled after drying.  Introduction of the starting materials at too rapid or too slow a rate leads to incomplete reaction with diamide formation or extensive dehydration with dinitrile formation respectively.  By applying vacuum to the reactor the cyano-carboxylic acid produced is at once vaporized and withdrawn continuously and after condensation entrained ammonia is withdrawn and recycled.  The use of a soluble catalyst such as tricresyl phosphate is advantageous in this embodiment of the process.  A reactor filled with Raschig rings only is then employed and the catalyst is introduced in admixture with the soluble catalyst. The products may be hydrogenated and the resulting amines separated.  With separately prepared diamides the corresponding free acids are frequently used.  In examples: 5-cyanovaleric acid is separated from the products including the dinitrile are obtained by heating adipic acid diamide with adipic acid and tricresyl phosphate by distilling in vacuo (1); 9-cyanononylic acid is similarly obtained from sebacic acid diamide and sebacic acid (2); 5-cyanovaleric acid and the dinitrile are obtained by heating adipic acid diamide with orthophosphoric acid (3); 5-cyanovaleric acid is obtained by heating the amide thereof with adipic acid (4); adipic acid diamide is heated in a reactor with adipic acid and boron phosphate catalyst, the reaction product is siphoned off automatically as starting materials are introduced, water and liberated ammonia are removed overhead and 5-cyanovaleric acid is obtained with the dinitrile by fractionation (5); molten adipic acid is dropped into a heated reactor containing boron phosphate whilst ammonia is introduced liquid is withdrawn as in (5), extracted with an alcohol-benzene mixture, residual diamide is recycled and 5-cyanovaleric acid and the dinitrile are obtained on distillation of the extract (6); an analogous process is carried out using molten adipic acid containing o-tricresyl phosphate and a Raschig ring filled chamber (7) and sebacic acid is reacted with ammonia in a manner analogous to (6) when 9-cyano-nonylic acid is obtained.