AROMATIC SUBSTITUTION .21. KINETICS OF NUCLEOPHILIC SUBSTITUTION OF SOME BROMOPYRIDINES AND -PICOLINES WITH THIOPHENOXIDE ION . NATURE OF ACTIVATION BY ORTHO-METHYL GROUPS

被引:23
作者
ABRAMOVI.RA
HELMER, F
LIVERIS, M
机构
[1] Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
关键词
D O I
10.1021/jo01258a044
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
The rates and activation parameters were determined for the reaction of potassium thiophenoxide in methanol with 2-bromo-, 2-bromo-3-methyl-, 2-bromo-5-methyl-, 2,3-dibromo-, and 2,5-dibromopyridine. An o-methyl group accelerated the reaction, probably due to the combined effects of London forces and ion-dipole interactions. At 110°, ko-CH2/kp-CH2 = 5.0, while ke-Br/kp-Br = 2.5. These results were compared with those obtained with methoxide ion in methanol. Substitutions with thiophenoxide ion in dimethyl sulfoxide were also studied. The increase in rate on going to this solvent was not as great as expected and is discussed. Thiophenol itself reacted faster in methanol than did the thiophenoxide ion due to a fast acid-base preequilibrium in which the bromopyridine was protonated and allowed to react as such with the thiophenoxide ion formed. © 1969, American Chemical Society. All rights reserved.
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页码:1730 / +
页数:1
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