|
|
Bibliographic Information
Effect of solvent on rate of base-catalyzed proton abstraction from carbon. Cram, Donald J.; Rickborn, Bruce; Knox, Graham R. Univ. of California, Los Angeles, Journal of the American Chemical Society (1960), 82 6412-13. CODEN: JACSAT ISSN: 0002-7863. Journal language unavailable. CAN 56:30969 AN 1962:30969 CAPLUS
Abstract
cf. CA 54,4471d. Racemization of 2-methyl-3-phenylpropionitrile (I) in mixts. of MeOH and Me2SO with a metal methoxide as base was described. Rates in 76.5% and higher Me2SO were obtained by direct polarimetric measurement, at lower concn. by the ampul technique, and the rate consts. extrapolated to 25? Relative rates of racemization of I were given [solvent system (% by weight), base, and relative rate (25? given]: 100 MeOH-O Me2SO, MeOM (M = Li, Na, K), 1; 75 MeOH-25Me2SO, MeONa, 32; 49.6 MeOH-50.4 Me2SO, MeONa, 160; 23.5 MeOH-76.5 Me2SO, MeOLi, 4900; 10 MeOH-90 Me2SO, MeOM, 1.3 ?105; 3 MeOH-97 Me2SO, MeOM, 1.4 ?106; 1.5 MeOH-98.5 Me2SO, MeOK, .apprx.1.05 ?107, 0 MeOH-100 Me2SO, MeOK, ?09 (estd.); and 100 Me3COH, Me3COK, 4.1 ?106. Rates of racemization of optically active PhCHMeOMe in Me2SO at 49?and 75?and in Me3COH at 173?were measured, and the rate in Me2SO extrapolated to 173?gave a value >106 greater than in Me3COH. Preliminary expts. indicated that (CH2)4SO also enhanced the catalytic activity of alkoxide ions, but less than Me2SO. Substitution of Me2SO for the usual hydroxylic solvents with Me3COK gave 86% conversion of PhBr to PhOCMe3 (II) at 25?(15 hrs.) and 35% yield in Me3COH at 175?(9 hrs.). PhF in Me2SO also gave II, but at 1/25 the rate. Me2SO at 100?converted o-MeC6H4F to o-MeC6H4OH (<3% meta), and o-MeC6H4Br to a 4:1 mixt. of m- and o-MeC6H4OH. Presumably, aryl bromides gave aryne intermediates, which added Me3COH to give aryl ethers as initial products, converted to the resp. phenol during vapor phase analysis of the products. Aryl fluorides underwent direct substitution |
|
回复此楼