BIMOLECULAR FORMATION OF RADICALS BY HYDROGEN-TRANSFER - 14 - THE UNCATALYZED TRANSFER HYDROGENATION OF ALPHA-METHYLSTYRENE BY 2,6-DISUBSTITUTED 9,10-DIHYDROANTHRACENES

Citation
F. Keller et C. Ruchardt, BIMOLECULAR FORMATION OF RADICALS BY HYDROGEN-TRANSFER - 14 - THE UNCATALYZED TRANSFER HYDROGENATION OF ALPHA-METHYLSTYRENE BY 2,6-DISUBSTITUTED 9,10-DIHYDROANTHRACENES, Journal fur praktische Chemie, Chemiker-Zeitung, 340(7), 1998, pp. 642-648
Citations number
24
Categorie Soggetti
Chemistry,"Chemistry Applied
ISSN journal
09411216
Volume
340
Issue
7
Year of publication
1998
Pages
642 - 648
Database
ISI
SICI code
0941-1216(1998)340:7<642:BFORBH>2.0.ZU;2-3
Abstract
2,6-Dimethoxy-(4a), 2,6-bis(dimethylamino)- (4b), 2,6-dichloro- (4c) a nd 2,6-dimethoxycarbonyl-9,10-dihydroanthracene (4d) were prepared by conventional methods and used as hydrogen transfer donors to alpha-met hylstyrene (5) between 290-350 degrees C. The mechanism followed secon d order kinetics and the rate constants were only slightly influenced by the solvent polarity and the type of substituents introduced. The a ctivation parameters are also closely similar in the series with Delta S-not equal values between -21 and -28 cal/mol K. These results, toge ther with the observation of a large isotope effect (k(H)/k(D) = 1.4- 2.0 at 310-350 degrees C), suggest that the mechanism involves a prima ry kinetic H-atom-transfer from the donors to alpha-methylstyrene (5) in the rate determining step. The compounds 4a-4d constitute a new pro be for investigating polar effects on H-transfer reactions.