Patent GB-653377-A (GB)
Title: Improvements in or relating to refining penicillin x
IPC: C07D499/18
Filed: 1946-09-02
Abstract: Penicillin X is purified in the form of its ammonium salt by preparing a solution of ammonium penicillins (including X), in a primary aliphatic monohydric alcohol having 4-6 carbon atoms in the molecule, the solution being saturated or supersaturated with respect to ammonium penicillin X; the saturated solution is then cooled or allowed to evaporate and crystalline ammonium penicillin X separates on standing; if the solution is supersaturated, the salt crystallizes on merely allowing to stand.  Penicillin G may or may not be present, and in the former case, the solution is below the concentration of ammonium penicillin G necessary to saturate it.  The purification process takes place in 4 steps: (1) extraction of crude penicillin from the culture medium into an organic solvent; (2) purification of the organic solution; (3) transfer to the alcohol used for crystallizing; (4) crystallization; various alternative procedures are described for each step.  Step 1: The culture medium is filtered and acidified, and the crude penicillin extracted with a water-immiscible organic solvent such as butyl acetate, amyl acetate, or other ester, methyl isobutyl ketone or n-butaonol; a preliminary extraction with chloroform helps to remove penicillin G and other forms.  The filtered culture medium may, if desired, be purified with active carbon and the penicillin eluted therefrom with an aqueous organic solvent; the organic solvent is then removed.  In cases where the culture medium is relatively free from organic impurities, steps 2 and 3 may be omitted and the extraction in step 1 is then effected with the alcohol used for crystallization in Step 4.  Step 2: The organic penicillin solution is extracted with an aqueous alkaline solution and the resulting salt solution separated and acidified, the penicillin being then transferred back into an organic solvent.  This procedure may be supplemented or replaced by purification by means of a decolorizing agent such as active charcoal or magnesium silicate followed by elution. Step 3: The organic solution of penicillin acid may be converted into the alcoholic solution of ammonium penicillin in various ways: (A) dehydration by distillation or treatment with sodium sulphate, precipitation with dry ammonia (pure gas, diluted with nitrogen, or in an inert organic solvent), separation of the precipitate and dissolution in the alcohol; (B) extraction with an aqueous solution of an alkaline ammonium compound, distillation to dryness (preferably below 40 DEG  C.) and dissolution in the alcohol; (C) conversion to aqueous solution as before, addition of the alcohol and dehydration by distillation (preferably below about 40 DEG  C.); (D) as in (C) but separating the solvent layers without dehydration; (E) conversion to aqueous solution of salt and salting out as in Specification 642,369; (F) conversion to aqueous solution of salt, acidification, extraction with an organic solvent and neutralization with an alkaline ammonium compound; (G) conversion to aqueous solution of salt and salting out after acidification as in Specification 642,370.  The organic solvent used for (F) and (G) may be the alcohol used in step 4 or may be another lower-boiling solvent which is subsequently removed by azeotropic distillation when the alcohol has been added.  The extraction with aqueous alkaline solutions is preferably carried out at pH 6-8, and the acidification effected (preferably with phosphoric acid) to pH 2-4.  Ammonium hydroxide, carbonate and bicarbonate are suitable for neutralization, phosphates leading to contamination of the product.  They may be added in aqueous solution, preferably with the addition of an organic solvent to minimize the addition of excessive quantities of water. At any stage, the water-content of the organic solutions may be reduced by distillation at low temperatures and pressures.  Step 4: The alcoholic solution of ammonium penicillins is dehydrated and concentrated by distillation at low temperature and pressure, the concentrate being neutralized if the pH changes, pH values of 4-8.5 being suitable for crystallization.  Seeding with crystals of ammonium penicillin X is desirable.  Specified alcohols for step 4 are n- and iso-butanols, n-amyl alcohol, isopentyl alcohol, 2-methyl-1-butanol, t-butyl-carbinol and n-hexanol.  In the examples, ammonium penicillin X is crystallized from (1) n-butanol after purification via steps 1 and 3(A); (2) n-butanol after steps 1 and 3 (E); and (3) isopentyl alcohol after steps 2 and 3(A). Specifications 628,251, 642,371 and 642,372 also are referred to.  According to the Specification as open to inspection under Sect. 91, the process is applicable to starting materials containing comparatively large proportions of penicillin G.  The product does not then consist of pure ammonium penicillin X, but the latter has been freed at least in part from non-penicillin organic and inorganic impurities and from penicillins F and K.  This subject-matter does not appear in the Specification as accepted.