Abstract
The heat of adsorption of alkylmonosulfonic acids (CnH2n+1SO3H, n=1_??_4) on polyamide was measured by the flow method at 30° and 40°C. Observed values of heat of adsorption are influenced considerably by the measured temperature and concentration of acid similarly to the case of hydrohalogenic acids (HX). From the heat of adsorption at saturated adsorption and -Δμ°I (obtained from adsorption isotherm), the entropy change of adsorption(ΔS°C•I) was calculated. The value of decrease with increasing alkyl group in acid, and all these values are smaller than those of HX. A parameter which is concerned with the state of hydration of these acids in the aqueous solution was obtained from the measurement of NMR absorption spectra, and the relationship between ΔS°C•I and Δδ is discussed. Plots of ΔS°C•I against Δδ show a straight line.
Differences in and Δδ between these acids except buthansulfonic acid correspond to those in enthalpies and entropy changes for the transfer of normal aliphatic hydrocarbons (CnH2n+2, n=1_??_3) from the liquid state to the aqueous solution at 25°C, respectively.
From these results, it is assumed that the process of dehydration of these acid anions is an important factor for the adsorption of alkylsulfonic acids on polyamide similarly to the case of HX, and in these cases, differences in ΔS°C•I correspond with those in the interaction of alkyl group in acid anions with water. It is also assumed that ΔS°C•I of these acids are positively larger than those of HX and decrease by the decrease of the structure of water with dehydration of alkyl group.
