Benzaldehyde phenylhydrazone formation, like semicarbazone, thiosemiearbazone, oxime, and Schiff base formation, occurs with rate-determining attack of the nucleophilic reagent under slightly acidic conditions and with rate-determining dehydration of the carbinolamine intermediate under neutral and basic conditions. The attack of phenylhydrazine on -chloro-, unsubstituted, -methoxy-, and p-hydroxybenzaldehyde is subject to general acid catalysis by carboxylic acids and the conjugate acid of the nucleophile while that on p-nitrobenzaldehyde is subject to catalysis by carboxylic acids and apparent inhibition by carboxylate ions. Rate constants for the hydrated proton, chloroacetic acid, acetic acid, phenylhydrazinium ion, and wrater as catalysts for the attack of phenylhydrazine on a series of substituted benzaldehydes are well correlated by the + substituent constants. The derived values of p + increase linearly with increasing pKa of the catalyst. The dehydration of the carbinolamines derived from phenylhydrazine and benzaldehydes exhibits both acid-catalyzed and pH-independent reactions and, in the case of that derived from p-nitrobenzaldehyde, a base-catalyzed reaction as well.

ibid., 54, 2469 (1971).(22) (a) G. H. Whitham and M. Wright, J. Chem. SOC. C, 883 (1971); (b) ibid., 886 (1971): (c) ibid., 891 (1971). (23) The conformational barriers in the interconversion between the two diastereoisomers of cyclic Eallylic alcohols seem to resemble those to the racemization of optically active € cycloalkenes, except for the effect of the C,-hydroxyl substituent in the former. Some kinetic parameters for the racemization rates of (0-cyclooctene and (0-cyclononene, reported by Cope et al., are summarized in Table XI ((a) , J. Am. Chem. Soc., 87, 3644 (1965); (b) A. C. Cope and B. A. Pawson, ibid., 87, 3649 (1965)). Recently Whitham and Wright (ref 22) obtained the activation energy AH* = 35 kcal/mol at 170 OC for the thermal interconversion between the diastereoisomeric (l+cyclooct-2-en-1-yI acetates. This value is compatible with the value = 35.6 kcal/mol at 155 OC for the racemization of (0-cyclooctene. One can see also from Table XI that the longer is the methylene loop of cyclic Eallylic alcohols, the lower becomes the con-35 (1975). (28) The oxidation of secondary alcohols by the dioxovanadium (VO,' ) species In acidic aqueous solution is well known (W(1969), and references cited therein. (30) J. H.-H. Chan and 8. Rickborn, J. Am. Chem. SOC., 90, 6406 (1968).(31) The separation between u:p and u : ? (= Au) was also used as a measure of the length of the hydrogen bond for a series of cis and trans cyclic 1,Pdiols (L. P. Kuhn, J. Am. Chem. Soc., 76, 4323 (1954)). (32) Upon the magnetic anisotropic effect by oxirane ring; see, e.g., D. Lavie. Y. Kashman, and E. Glotter, Tetrahedron, 22, 1103 (1966). (33) It is well known that in the chair conformation of the cyclohexane ring, an axial proton resonances at higher field than the corresponding equatorial proton owing to the anisotropic effect exerted by the neighboring C-C single bond (L. The higher erythro-threo selectivity in the vanadium-catalyzed epoxidation Of acyclic allylic alcohols than in peroxy acid reactions also seems to be rationalized in terms of our transition state models, 111 and IV (cf. ref 7). (26) A. 0. .Abstract: Kinetic n secondar! deuterium isotope effects. k o / k H , for f o r m y l group transfer f r o m either the 4-methoxyphenql or 4-nitrophenyl esters, o r both, of formic and deuterioforinic acids to a variety o f oxygen acceptors have been measured at 25 O C i n aqueous solution: hydroperoxide ion. 1.12; 2-propynol anion, I . 13: hexafluoropropan-2-01 anion, 1.14; and water. I .22. I n addition, corresponding isotope effects have been obtained for general-base-catalyzed f o r m y l group transfer f r o m the same substrates t o acetate, I .21, formate. 1.23, and trimethylamine N-oxide, I .20.The n secondary deuterium isotope effect for acid-catalyzed hqdrolqsis o f both esters has been determined to be I .24. These data are interpreted to reflect considerable. and perhaps complete. carbon-oxygen bond formation i n the transition state for addition of oxygen nucleophiles to phenql formates. Finally. corresponding ...

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Kinetic secondary deuterium isotope effects, kfkK, for the water-catalyzed addition of semicarbazide to a series of substituted benzaldehydes are near 1.30 and are independent of the nature of the polar substituent; corresponding values for the same reaction catalyzed by the hydrated proton and other acids are near 1.21. Values of ko/kR for the water-catalyzed addition of phenylhydrazine to substituted benzaldehydes decrease from 1.28 to 1.16 as the nature of the polar substituent is varied from p-methoxy to p-nitro. The corresponding values for the same reaction catalyzed by the hydrated proton decrease from 1.21 to 1.13 for the same substituents. These results indicate that the extent of carbon-nitrogen bond formation in the transition state for addition of nucleophiles to the carbonyl group is a function of the reactivity of substrate, nucleophilic reagent, and the strength of the catalyzing acid. The secondary deuterium isotope effect on the equilibrium constant for carbinolamine formation from benzaldehyde and hydroxylamine is near 1.36, larger than the largest of the kinetic effects observed. Under conditions in which carbinolamine dehydration is rate determining, values of kn/ku for the overall rate of semicarbazone formation from benzaldehydes decrease from 1.31 to 1.20 as the nature of the polar substituent varies from hydrogen to p-nitro. This result demonstrates that the extent of carbon-oxygen bond cleavage in the transition state for carbinolamine dehydration is a function of the nature of the polar substituent of the substrate. Moreover, for those substituents which are not strongly electron withdrawing, the transition state closely resembles the carbinolamine itself.

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