Cystostatic agents. III. Mechanism of reduction of Schiff bases by activated aluminum

Abstract

cf. Schoenenberger, et al., CA 62, 6992f, 7664a, 13163g. The mechanism of redn. was investigated of benzylidenealkyl- and benzylidenearylamine-type Schiff bases with activated Al, to form mono- and dimeric secondary amines. Redn. of PhCH:NBu (I) in abs. EtOH with Al-Hg gave yields of benzylbutylamine (II) and N,N'-dibutyl-alpha ,alpha '-diphenylethylenediamine (III) (in meso- and racemic forms) which varied with the amt. of EtOH. HgCl2 (200 mg.) was dissolved in abs. EtOH (12.5-400 ml.), the soln. heated to boiling (78 Deg) under reflux, and 2 g. Al foil (0.1 mm. thick) added. After 5 min., 4 g. I in 20 ml. abs. EtOH was added to the 78 Deg mixt. with vigorous stirring. The reaction was continued at 78 Deg until the metals dissolved (.apprx.2 hrs.). Concd. HCl (40 ml.) was added to the gelatinous mixt.; the soln. was evapd. almost to dryness on a 100 Deg bath. The green residue was mixed with small vols. of 30% NaOH until the soln. was alk.; the mixt. was extd. with an equal vol. of CHCl3 (3 times), and the combined CHCl3 exts. dried over anhyd. Na2SO4. The dried CHCl3 soln. was satd. with HCl gas, and the CHCl3 distd. The residue (mainly II.HCl + III.HCl) was extd. in a Craig 34 stage countercurrent extn. app., using 40:12:28 CHCl3-MeOH-2% HCl solvent. The compn., and no., of the sepd. fractions are: (A) racemic III, 1-5; (B) meso-III, 6-21; (C) II, 22-34, resp. The av. yields of II, racemic III and meso-III, using first vols. of 12.5, 25, 50, 100, 200, 300, and 400 ml. of abs. EtOH in the redns. of I, are 10.0, 45.1, 45.4; 15.9, 41.5, 42.7; 27.2, 36.1, 36.8; 41.0, 29.0, 30.1; 59.0, 20.2, 20.8; 67.9, 15.7, 16.4; and 71.9, 13.3, 14.9%, resp. Cf. Arzneimittel-Forsch, 15(1), 30-6(1965).