Toluene hydrogen-deuterium exchange reactions

Data from competitive hydrogen deuterium exchange reactions of toluene and benzene over DHY (66)... 

Fio. 20. Plot of log pt and selectivity factor, Sf. data from competitive hydrogen deuterium exchange reactions of toluene and benzene over DHY (7f) O, data from competitive ethylation reactions of toluene and benzene over REX (12S). 

Some experimental observations on hydrogen-deuterium exchange are summarized below. The reactions were carried out in toluene solution (10 M) (one at. ) was used in large excess, and the products were isolated and characterized as pure deuteride complexes. 

Cinneide and Clarke (770) have studied the activity of Pd-Au films for the deuteration and exchange of benzene and the hydrogenation of p-xylene. The authors report that the activity for the exchange reaction between benzene and deuterium persists to the palladium-lean compositions, which is in agreement with results obtained by Honex et al. (Ill) in a study of the exchange of toluene over alloys of the same kind. The rates are much reduced (by 102 to 103) compared to those found with palladium-rich films. 

It is interesting to note that C-H activation on ruthenium NHC complexes is not limited to intramolecular protons located in the N-sidechain of the carbene, but occurs inter-molecularly as well. Leimer et al. reacted [MesIRuH PCyj] with toluene-dg at ambient temperature and observed a rapid H/D exchange reaction involving the four hydride hydrogen atoms on ruthenium, the methyl protons of the mesityl substituents of the carbene ligand and the deuterium atoms on the meta positions of toluene-dg. The ortho-, para- and methyl-deuterium atoms of the solvent did not participate [145]. 

The cationic rhenium complexes [Re(NO)2(PR3)2] (R = Cy, Pr) [50] indeed show great potential for hydrolytic activation of dihydrogen. When [Re(NO)2(PR3)2l is treated with a mixture of H2 and D2 in toluene or chlorobenzene, hydrogen-deuterium scrambling is observed, and HD can be traced in the NMR spectrum of the reaction mixture [51]. The proposed mechanism for this catalytic exchange is illustrated in Scheme 4. 

Yakushin and Shatenshtein (1960) and Yakushin et al. (1959) have determined the ratio of the rate constants for tritium and deuterium replacement by protium in ammonia solutions of fluorene and methyl 2-naphthyl ketone at 25°. Yakushin has obtained data for these reactions in anhydrous methylamine. Streitwieser et al. (1960, 1962b) have measured the ratio fcD/ T for the hydrogen exchange of ethylbenzene and toluene catalysed by a solution of lithium cyclohexylamide in cyclohexylamine at 49-9°. 

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