GB570532A - Preparation of heptamethylenediamine - Google Patents

Abstract

Heptamethylene diamine is prepared by a process which comprises passing the lactone of 4-hydroxypimelic acid or an ester thereof, together with ammonia in excess of the molecular proportion required, over a dehydration catalyst at a temperature of 325 DEG -550 DEG C., and catalytically hydrogenating the so-formed heptendioic nitrile in the liquid phase at a temperature of 50 DEG to 175 DEG C. and under a hydrogen pressure of at least one atmosphere and advantageously in the presence of ammonia. More specifically, in converting the lactone to the nitrile, the vaporized lactone is passed over a boron phosphate catalyst such as is described in Specification 535,187, at a temperature of 350 DEG to 400 DEG C. with a substantial excess of ammonia, preferably in a molecular ratio of ammonia to lactone of 8 : 1, and with a contact time of 4 to 6 seconds. The conversion is carried out at atmospheric pressures though it is possible to use higher or lower pressures. The catalyst may be in the solid form, broken up or compressed into tablets, or may be formed on a support such as kieselguhr. Other dehydrating catalysts specified are the oxides of aluminium, thorium, zirconium and silicon. Suitable esters of the lactone of 4-hydroxy-pimelic acid are the monomethyl, -ethyl, and -butyl esters. Although the nitrile may be hydrogenated in the complete absence of ammonia it is preferred to operate in the presence of ammonia and to maintain a pressure higher and a temperature lower than the corresponding critical values for ammonia in order to keep the ammonia in the liquid phase. Pressure ranging from 1 to 500 atmospheres may be employed in the hydrogenation but preferably pressures of 100 to 175 atmospheres are used. Specified hydrogenation catalysts are a Raney cobalt catalyst, pyrophoric or stabilized nickel catalysts either in the massive state or supported on kieselguhr or pumice and metals selected from the base metals of the eighth group of the Periodic Table. However, hydrogenation catalysts in general may be used including hydrogenating metals, oxides, and salts of platinum, copper and silver. The hydrogenation may be carried out in the presence of an inert organic solvent such as alcohol, ether or a hydrocarbon solvent. Examples are given.