Vaporization, fusion and sublimation enthalpies of the dicarboxylic acids from C4 to C14 and C16

The fusion  enthalpies  of the series butanedioic acid through to tetradecanedioic acid and hexadecanedioic acids have been measured by DSC. In addition to fusion, a number of  solid–solid phase transitions  have also been detected in these diacids. The vaporization enthalpies of these compounds have been measured by correlation  gas chromatography  using the vaporization enthalpies of butanedioic, hexanedioic and decanedioic acids as standards. The vaporization enthalpies of the diacids from C 4  to C 10  correlated linearly with the number of  methylene groups  present. Above C 10 , the vaporization enthalpies of C 11 –C 14  and C 16  begin to deviate from linearity. The vaporization enthalpies for these compounds are dependent on the temperature of the GC column used. Similar departure from linearity has also been observed previously in the  sublimation  enthalpies for these compounds. The results are discussed in terms of formation of a cyclic intramolecular hydrogen bonded network in the gas phase similar to the bimolecular association observed in smaller  mono-carboxylic acids  at ambient temperatures.