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Some aliphatic amines have been titrated enthalpimetrically. The heats of neutralization have been calculated from the results and correlated with the basicity of the amines and the number of hydroxyl and amine groups present. The titration curves were all plotted on Cartesian coordinates and again on oblique coordinates to eliminate secondary thermal effects. The order of basicity is ethylamine < ethanolamine, and ethylamine < diethylamine > triethylamine, the last because of steric factors reducing the basicity of the tertiary amine. The low basicity of ethanolamine relative to ethylamine is atttributed to the inductive effect of the hydroxyl group. Ethylenediamine contains two amino groups, one of which is hydrated in solution and the other protonated; the existence of the protonated group together with the electron-withdrawing power of the hydroxyl group accounts for the lower second dissociation. The ethanolamines are more feeble bases than di- and triethylamine, because of the presence of the hydroxyl group. A steric factor further reduces the basicity of triethanolamine. These facts are confirmed by the experimental heats of neutralization.
Popper
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Laboratoire de Chimie Analytique de l'Institut de Médicine et de Pharmacie, Cluj, Roumanie.
Roman
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Marcu
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