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