Equilibrium constants for the dissociation of thiourea adducts of dialkylaphthalenes

摘要

Various 2,6-dialkylnaphthalenes,2,3-dimethylnaphthalene,and 2-methyl-7-t-butylnaphthalene adducts with thiourea were formed to determine the equilibrium constants at temperatures of 273.2 to 303.2K.No adducts of thiourea with 2,6-dimethylnaphthalene,2-methyl-6-ethylnaphtahalene,and 2-methyl-6-isopropyl-naphthalene were detected at these temperaures.Equilibrium constants of dialkylnaphthalene-thiourea systems,expcept for the 2-methyl-7-t-butylnaphthalene-thiourea system,were greater than those of the hexadecane-urea system and less than those of isopraaffin-or naphtene-thiourea systems,indicating that stability of dialkylnaphthalene-thiourea adducts is relatively high,whereas n-paraffinurea adducts are more stable than thiourea adducts with various adducts is relatively high,whereas n-paraffin-urea adducts are more stable than thiourea adducts with various guest molecules.The order of adduct formation was as follows:2,6-di-t-butylnaphthalene>2,3-dimethylnaphthalene>2,6-diisopropylnaphthalene approx 2,6-diethylnaphthalene>2-methyl-6-t-butylnaphthalene>2-methyl-7-t-butylnaphthalene.The olar ratios of thiourea to substrate were in the range of 5.0 to 6.7,depending on the size of thedialkylnaphthalenes or bulkiness of the alkyl groups. The formation of the thiourea adducts was exothermic and were favored at lower temperatures.The heats of formation were between 28 and 37 kJ mol~(-1),which are of the same order of magnitude as those of other thiourea adducts with branched paraffins or cycloparaffins.Deviations were correlated with m,suggesting that the structure of thiourea adducts is more flexible than that of urea adducts.