Convenient procedures have been developed to convert secondary alcohols into ketones in excellent yield and high epimeric purity utilizing oxidation of the alcohol in diethyl ether with aqueous chromic acid. In one procedure (procedure A) the stoichiometric amount of sodium dichromate and sulfuric acid in water is added to the diethyl ether solution of alcohol at 25-30°and the reaction is continued for 2 hr. In the second procedure (procedure B), especially applicable to strained bicyclic alcohols, a 100% excess of the oxidation agent is used. In this case the reaction is complete in 15 min at 0°. These procedures offer especial promise for the preparation of ketones without accompanying epimerization or loss of isotopic purity.arising from further oxidation of the ketone product.
Rate constants of solvolysis of a-tert-butyl(2-naphthyl)methyl chloride (1), 9-fluorenyl chloride (2) and a series of monosubstituted benzhydryl chlorides (3) in a wide range of solvents were measured. Grunwald-Winsteintype correlation analysis of log k for 2 and 3 against Y BnCl , with or without nucleophilicity N, yielded less satisfactory linear correlations than that against log k(1). A new scale of solvent ionizing power, Y xBnCl , for the correlation of solvolytic reactivities of benzylic chlorides with extended charge delocalization based on log k(1) was developed. Application to the mechanistic study suggested the solvolysis of 2 and 4-nitrobenzhydryl chloride were non-limiting. Hammett plots against ' constants exhibited more negative r values in less nucleophilic solvents. In a benzhydryl chloride containing a strong deactivating substituent, such as 4-nitro, the positive charge delocalizes mainly over the unsubstituted ring in the cationic transition state. The uneven charge distribution was also confirmed by Mulliken population analysis at the level of the RHF/6-31G * //RHF/3-21G
Solvolysis rate constants for a number of tertiary benzylic p-nitrobenzoate esters in a wide range of solvents were measured. New scales of solvent ionizing power for Grunwald-Winstein-type correlation analyses, Y BnOPNB from 2-phenyl-2-adamantyl p-nitrobenzoate and Y xBnOPNB from 2-(6-methoxy-2-naphthyl)-2-adamantyl p-nitrobenzoate, were developed for the mechanistic study of solvent effects on the solvolytic reactivity of benzylic p-nitrobenzoates. The excellent linear log k -Y BnOPNB plot for 2-(4-methylphenyl)-2-propyl p-nitrobenzoate indicated a limiting S N 1 mechanism. The solvolytic transition state for 9-phenyl-9-fluorenyl p-nitrobenzoate and that for 1,1-diphenylethyl p-nitrobenzoate were considered to involve extended positive charge delocalizations from the observation of linear relationships between log k and Y xBnOPNB . The ambiguity in the case of 2, 2-dimethyl-1-(4-methoxyphenyl)-1-phenyl-1-propyl p-nitrobenzoate is discussed.
The solvolysis of 4-methoxybenzyl chloride (1) and bromide (3), and 1-(4-methoxyphenyl)ethyl chloride (4) in a variety of solvents were carried out. The observation of linear correlation using the dualparameter Grunwald-Winstein equation, and the positive azide salt effect indicate significant nucleophilic solvent participation for 1 and 3. A smaller deviation of log k (in 100% 2,2,2-trifluoroethanol) for the bromide 3 than chloride 1 in the log k ؊ Y BnX plots reveals a lesser extent of nucleophilic participation and is also in harmony with the greater nucleofugality of the bromide ion. The use of a low k Br /k Cl ratio as evidence for the presence of solvent participation is discussed. The observed -deuterium kinetic isotope effect of 1.08 to 1.21 measured for 1 and 3 is inconsistent with the magnitude generally considered for a concerted mechanism.
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