Temperature of maximum density of aqueous solutions of aliphatic amines

Abstract

Temperature of maximum density (TMDs) in water at low concentrations for the seven amines: rnethyl-, ethyl-, <em>n</em>-propyl-, <em>n</em>-butyl-, <em>t</em>-butyl-, dimethyl-, and trimethyl amines have been measured and analyzed by applying hydrolysis correction to evaluate the structural part of the change in TMD (<img src='http://www.niscair.res.in/jinfo/delta.gif' border=0>&theta;_str) for the unhydrolysed amine molecules. A correction procedure is described for which additional experimental data on TMDs of corresponding amine hydrochlorides have been obtained. The results of amines studied in this work do not fit in the conventional straight line relation (<img src='http://www.niscair.res.in/jinfo/delta.gif' border=0>&theta;_str/x₂) = a + bx₂, which is obeyed by other non-electrolytes, like alcohols, which show positive intercepts (<em>a</em>) and negative slopes (<em>b</em>)<em>. </em>The slopes of such plots for arnines are positive at low concentrations and negative at higher concentrations showing a broad maxima in between. The intercepts <em>a </em>which indicate the structure strengthening property of the solute are large negative for MeNH₂ and EtNH₂, slightly negative for <em>n-&nbsp;</em>PrNH₂, and positive for the rest of the amines. Comparison of <em>a </em>values of alcohols and amines indicate the difference in the amine-water and alcohol-water interactions.