Standard sublimation enthalpies of some dichlorophenoxy acids and their methyl esters.

The standard sublimation enthalpies of 2,4-dichlorophenoxy acetic acid, 2,4-dichlorophenoxy propionic acid, and 2,4-dichlorophenoxy butyric acid and their methyl esters 2,4-dichlorophenoxy acetic methyl ester and 2,4-dichlorophenoxy butyric methyl ester were determined by direct differential scanning calorimetry (DSC) measurements along with the Langmuir and torsion effusion methods. For 2,4-dichlorophenoxy acetic acid, 2,4-dichlorophenoxy propionic acid, and 2,4-dichlorophenoxy butyric acid, the values Delta(sub)H degrees(298 K) = {(122 +/- 5), (127 +/- 8), and (137 +/- 10)} kJ center dot mol(-1), respectively, were selected. For 2,4-dichlorophenoxy acetic acid methyl ester and 2,4-dichlorophenoxy butyric acid methyl ester, the Delta(sub)H degrees(298 K) final values 89 kJ center dot mol(-1) and 100 kJ center dot mol(-1), respectively, were selected with an estimated error of 10 kJ center dot mol(-1). From torsion data, the standard sublimation entropies for 2,4-dichlorophenoxy acetic acid, 2,4-dichlorophenoxy propionic acid, and 2,4-dichlorophenoxy butyric acid equal to Delta(sub)S degrees(298 K) = (239, 263, and 294) J center dot K(-1)center dot mol(-1), respectively, were derived, with an error of 4 J center dot K-1-mol(-1) for all compounds.