Hydrogen abstraction from diarylamines (4-X-C(6)H(4))(2)NH [X = H, CH(3), C(8)H(17), CH(3)O, and Br] by the 2-methyl-2-phenylpropyl radical in n-dodecane solution was investigated by thermolysis of 3-methyl-3-phenylbutanoyl peroxide in the presence of various concentrations of the amines. The reaction is a non-chain process in which the 2-methyl-2-phenylpropyl radical and its rearrangement product, the 2-benzylpropan-2-yl radical, abstract hydrogen from both the solvent and the amine. Cross-disproportionation reactions of the rearranged radical led to the formation of significant amounts of beta,beta-dimethylstyrene. Rate constants for hydrogen abstraction by the unrearranged, primary alkyl radical from n-dodecane (k(373K) = 3.5 x 10(3) M(-)(1) s(-)(1)), diphenylamine (k(373K) = 1.3 x 10(6) M(-)(1) s(-)(1)), and the substituted diarylamines were determined from the product yields and the known rate constant for the radical rearrangement. From kinetic experiments with N-deuteriodiphenylamine the deuterium kinetic isotope effect,k(NH)/k(ND), was found to be 2.3 at 373 K.
The nitration and hydrogen exchange in the 4-position of the title compounds and corresponding N-methyl cations are studied kinetically. Criteria previously developed to distinguish between reaction on the free-base or conjugate-acid forms of six-membered heterocyclic aromatic compounds are applied. Both hydrogen-exchange and nitration occur on the free-base form of 3.5-dimethylisoxazole. For 1,3,5-trimethylpyrazole and 3.5-dimethylisothiazole, nitration occurs on the conjugate acids, while hydrogen-exchange undergoes a changeover from free-base to conjugate-acid reaction as the acidity is increased.The kinetic rates are compared with those for related compounds and the influence of N, 0, S. and NMe atomic groupings discussed.
3-Methyl-5-phenylisoxazole undergoes nitration as the conjugate acid at the para-position of the phenyl group. 5-Methyl-3-phenylisoxazole undergoes nitration as the conjugate acid at the rneta-position and also as the free base at the para-position of the phenyl group. Standard ratesfor nitration at 25 "C and H,, -6.6 are calculated and the influence of the charged and neutra I isoxazolyl substituents is discussed.WHEREAS alkylisoxazoles undergo nitration at the 4position of the heterocyclic ring, phenylisoxazoles are frequently substituted in the benzene ring. The precise orientation of such nitrations has been a matter of some controversy : Kochetkov and Khomutova reported that 5-phenylisoxazole (1) with H2S04-HNO, yields both 5-fi-nitrophenyl-(2) and 4-nitro-5-phenyl-isoxazole (3), but Lynch and Shiu claim3 that (2) is the sole mononitro-product and that is further nitrated to (4). 3,5-Diphenylisoxazole is reported to yield the para,para' dinitro-derivative. 3-Phenylisoxazole was first stated to yield the para-nitro-derivative, but reinvestigation 5a indicated that a mixture of 3-metn-and S-$ara-nitrophenyl derivatives was formed with H2S0,-HNO, but the 4-nitro-compound with HNO,-Ac,O.Recently the nitration of 3,5-diphenylisoxazole has been reinvesti-gated5b and found to give the 5-fi-nitrophenyl and the 3-m-nitrophenyl-5-fi-nitrophenyl analogues in mixed acid but the 4-nitro-derivative in acetic anhydride.Following our work 011 the nitration of 3,5-dimethylisoxazole,G we have now investigated preparatively and kinetically the nitration of 3-niethyl-5-phenylisoxazole ( 5 ) , 5-methyl-3-phenylisoxazole (6), and the corresyonding N-methyl cations (8) and (10) which serve as models for the protonated species (7) and (9), respectively. The methylphenylisoxazoles (5) and (6) were prepared by standard methods ; the methoperchlorates (8), (la), (lo),
The nitration of 2-pyridone yields largely the 3-nitro-derivative in low acidity media and largely the 5-nitro-compound in high acidity media. However, both reactions occur on the free base species. This behaviour is compared with similar phenomena in the literature.
Norwich NOR 88CRECENTLY, we studied the kinetics for the nitration of 3-methyl-2-pyridone in the 5-position and for 5-methyl-2pyridone in the 3-position: the rate constants for these two nitrations showed significantly different dependence on the acidity of the nitration medium. Raising the acidity appeared to increase the relative rate of nitration at the 5-position. In connection with other workJ3 we found that the proportion of the 3-and 5-nitro-derivatives formed in the mono-nitration of 4-methyl-2pyridone did indeed vary considerably with the condi-
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