Patent GB-685285-A (GB)
Title: Isolation and purification of penicillin g
IPC: C07D499/00
Filed: 1947-07-23
Abstract: Alkali and alkaline-earth metal salts of penicillin G are isolated by treating an organic solvent solution of penicillin acid with an organic solvent solution of an N-substituted heterocyclic amine to form an N-substituted heterocyclic amine salt of penicillin G (preferably as an insoluble precipitate by suitable choice of organic solvent), and then treating this salt with an alkali metal or alkaline-earth metal hydroxide in a mixture of water and an organic solvent to form the corresponding metal salt of penicillin G which is recovered from the aqueous phase.  Preferably the organic solvent solution of penicillin is prepared by extracting an aqueous solution of sodium penicillin, acidified with phosphoric acid, with amyl acetate.  Where the penicillin used as a starting material is of low potency, it may be given a preliminary treatment, by diluting an aqueous solution of the material with ether and adding pyridine, whereby the impurities are thrown out and form an oily layer which is removed. The N-substituted heterocyclic amine salt of penicillin G may be purified by dissolving in chloroform, washing with sodium chloride solution, concentrating to small volume, and either diluting with acetone to precipitate the salt, or adding butanol, evaporating the chloroform and precipitating the salt from the butanol solution. In examples (1) aqueous sodium penicillin is acidified and extracted into amyl acetate, the amyl acetate solution is treated with N-ethylpiperidine in acetone giving crystals of the N-ethylpiperidine salt of penicillin G, which are isolated, dissolved in chloroform, washed with saturated sodium chloride solution, concentrated in vacuo and diluted with acetone to precipitate the purified product or alternatively the crude N-ethylpiperidine salt of penicillin G may be purified by crystallization from chloroform and butanol, and in each case the product is converted to the alkali metal or alkaline-earth metal salt of penicillin G by dissolving in water, adding amyl acetate, treating with aqueous sodium hydroxide or calcium hydroxide and isolating the required salt from the aqueous layer by freeze drying, which is followed by crystallization from butanol in the case of the sodium salt; (2) low potency penicillin is extracted from aqueous solution into ether, treated with pyridine in ether and the ether layer is separated from the resultant oily layers of impurities by decanting, the ether solution is treated with N-ethylpiperidine and the resulting salt is separated and converted to the sodium or calcium salt of penicillin G; (3) the N-ethylpiperidine in (2) is replaced by N-methylpiperidine, and (4) by N-ethylmorpholine. Specification 604,563 is referred to.  The Specification as open to inspection under Sect. 91, comprises also the preparation of the N-substituted heterocyclic amine salts of penicillin G as an independent process, and contains an example of an alternative process of converting the N-ethylpiperidine salt to the sodium or calcium salt, involving intermediate liberation of penicillin acid. This subject-matter does not appear in the Specification as accepted.