GB731458A - Improvements in the production of pure adipic acid dinitrile - Google Patents

Abstract

A process for the purification of adipic acid dinitrile containing as impurity 1-cyano-2-iminocyclopentane comprises treating it at from ordinary temperature up to about 120 DEG C. with at least equivalent amounts, with reference to the amount of 1-cyano-2-iminocyclopentane present, of acids which do not form stable addition compounds with ketones or nitriles and which form salts with imino compounds in the absence of water, or split up the imino compound in the presence of water into 1-cyanocyclopentanone-2 and the ammonium salt of the acid used, and fractionally distilling the product. Crude adipic acid dinitrile may be saturated with water and allowed to flow over acid ion exchange resins until the imino compound is split up into cyclopantanone-2 and ammonium ions. Acids mentioned include sulphuric, phosphoric, hydrochloric, hydrobromic and formic acids, chlorinated carboxylic acids such as mono- or trichloracetic acetic acid, glycolic, tartaric, oxalic, succinic, adipic, benzoic, salicyclic, phthalic, terephthalic, benzene-or toluene-sulphonic and propane-1,3-disulphonic acids. In examples, pure adipic acid dinitrile is obtained by treating the impure dinitrile containing 1-cyano-2-iminocyclopentane with concentrated sulphuric acid, filtering off the sulphates crystallized and fractionating the filtrate, 1-cyanocyclopentanone-2 being obtained as first runnings (1); in similar process phosphoric acid (3); and aqueous hydrochloric acid or tartaric acid (4) are employed; the impure dinitrile is heated with benzoic, salicylic, formic, succinic or trichloracetic acid and the product fractionated (5); or the impure nitrile is saturated with water and passed at elevated temperature through a resinous product obtained by the condensation of benzaldehyde disulphonic acid, resorcinol and formaldehyde or other acid ion exchange resin and fractionated (2).