Chemical examination of calabar beans / by Arthur H. Salway.

  • Salway, Arthur H. (Arthur Henry)
Date:
[1911?]
Catalogue details

Licence: In copyright

Credit: Chemical examination of calabar beans / by Arthur H. Salway. Source: Wellcome Collection.

    6/16 (page 2151)
    ing with ether, and subjecting the ethereal solution to the same process as that described above. The total crude salicylate thus obtained amounted to 330 grams, representing 219'7 grams of physostigmine, which is equivalent to O'179 per cent, of the material employed in the investigation. In order to ascertain whether this crude salicylate was homogeneous or not, a considerable portion of the compound was subjected to systematic fractional crystallisation from alcohol. The fractions were found to be uniform in character, crystallising in stout, colourless prisms, melting at 180—181°, and were therefore homogeneous. (Found, C = 64T; H = 6'6; N = 10'2. Calc., C-=63'9; H = 6'5; N = 10*2 per cent.) It is evident that the above compound consisted of physostigmine salicylate. The free base was obtained from the latter by agitation with aqueous sodium carbonate in the presence of ether. The ethereal solution of physostigmine thus obtained was dried, and the solvent removed. The pale brown, viscid residue wras dissolved in benzene, and the solution allowed to evaporate slowly at the ordinary temperature in a vacuum desiccator over sulphuric acid. After sometime there was deposited a mass of crystals, which was collected and recrystallised several times from a mixture of benzene and petroleum. The physostigmine separated from this solvent in stout prisms, which melted at 86—87°. (Found, C = 65'l; H = 7'9. Calc., 0=65'5; H = 7'6 per cent.) 0'2659, made up to 20 c.c. with chloroform, gave aD — 20!7 in a 2-dcm. tube, whence [a]D — 75'8°. The above specimen of physostigmine does not agree in melting point with the physostigmine obtained by Pictet and Polonowsky {Bull Soc., chim., 1893, [iii], 9, 1008), who state that the alkaloid melts at 105—106°. A commercial sample of physostigmine was therefore procured, and this also melted at 105—106°. It was then found that the alkaloid is dimorphous, since the modification melting at 86—87° could be readily converted into the substance melting at 105—106° by recrystallisation in the presence of a crystal of the latter. The optical rotation of the compound melting at 105—106° was determined, and found to be identical with that of the modification melting at 86—87°, as recorded above: O'3062, made up to 20 c.c. with chloroform, gave aD — 2°19/ in a 2-dcm. tube, whence [a]D — 75'8°. Pictet and Polonowsky (loc. cit.) ascribe to physostigmine an optical rotation, [a]D — 82°, which is somewhat higher than the results obtained above. Physostigmine does not yield any definite aurichloride or platino- chloride, but a well-defined picrale was obtained, which crystallises