3-Alkylpyridine measurements

McKillop and associates have examined the electrophoretic separation of alkylpyridines by CZE. Separations were carried out using either 50-pm or 75-pm inner diameter capillaries, with a total length of 57 cm and a length of 50 cm from the point of injection to the detector. The run buffer was a pH 2.5 lithium phosphate buffer. Separations were achieved using an applied voltage of 15 kV. The electroosmotic flow velocity, as measured using a neutral marker, was found to be 6.398 X 10 cm s k The diffusion coefficient,... 

The main feature of the reactivity of alkylpyridines is deprotonation of the alkyl group at the carbon adjacent to the ring. Measurements of side-chain-exchange in methanolic sodium methoxide, 4 2 3, 1800 130 1, and of pK values in tetrahydrofuran each have the 7-isomer more acidic than the a-isomer, both being much more acidic than the / -isomer, though the actual carbanion produced in competitive situations can depend on both the counterion and the solvent. Alkyllithiums selectively deprotonate an a-methyl where amide bases produce the... 

The main feature of the reactivity of alkylpyridines is deprotonation of the alkyl group at the carbon adjacent to the ring. Measurements of side-chain-exchange in methanolic sodium methoxide, 4 2 3, 1800 130 and of pK values... 

Earlier data have indicated that 3-pyridinol is a weaker base than pyridine. A reexamination of these basicities suggests that the reverse is true and that the 3-hydroxyl group is electron releasing here and its introduction increases the basicity of the nitrogen of pyridine and alkylpyridines. pM values for the individual acid dissociation steps for pyridoxamine, pyridoxal, 3-hydroxypyridine-4-carboxaldehyde, and 3-hydroxypyridine-2-carboxaldehyde have been obtained by NMR measurements in Dq 0 solution. ... 

The acidity is, of course, increased when R and R in (17) are electron-attracting, and when the nitrogen atom is protonated or quaternized. Some comparative data are available for phenyl-substituted compounds in the last conditionii2 xhe system of ionic and tautomeric equilibria shown occurs with, for example, a 4-alkylpyridine. Ka has, of course, been measured in many cases, and Kt is commonly very large in favour of the NM (alkyl-pyridine) form rather than the Z (methide) form (pp. 137, 154). The remaining constants Kiy Kz and Kz are unknown. K can be approximated by the equivalent constant for the quaternary system ... 

The alkyl substituent effect on the CpNiCA of 12 alkylpyridines has been measured by the kinetic method [144]. Unfortunately, the CpNiCB of unsubstituted pyridine has not yet... 

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