Heats of Immersion of Metaphosphates in Aromatic Hydrocarbons
نویسندگان
چکیده
Heats of immersion of alkali and alkaline earth metaphosphates in some aromatic hydrocarbons were measured with a twin microcalorimeter to investigate the interaction of the interfaces between the phosphates and the hydrocarbons. The heats of immersion in benzene for the phosphates with long chains were lower than those for the phosphates with short chains. The dependence of heat of immersion on chain lengh is attributed to the change in the concentration of the hydroxyl groups, which can interact with ƒÎ-electron of benzene, with an increase of chain length. The heats of immersion in benzene increased with an increase in polarizing power, z+/r+2 (where z+ is the number of positive charge and r+ the ionic radius), of the cations of the phosphates. This variation is considered to be interpreted in terms of the polariz ing effect of the phosphate surface on benzene molecules. The relatively high values , especially of lithium metaphosphate, suggest that the acid-base interaction between the surfaces of the phosphates and benzene may contribute to the heat of immersion. In order to examine the effect of substitution of methyl group, the heats of immer sion of lithium and sodium metaphosphates in benzene, toluene and p-xylene were me asured. The heat decreased with an increase of the number of the substituent. It is not clear at the present stage that which the predominant factor is, the electron donor strength or the steric factor of the aromatic hydrocarbon.
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