ISSN:
1572-8927
Keywords:
Alkylamines
;
enthalpy of solution
;
enthalpy of protonation
;
calorimetry
;
elevated temperatures
;
amine basicity
;
hydrophobic hydration
;
thermodynamics of hydration
;
temperature dependence
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The enthalpies of solution ofn-hexyl- and cyclohexylamine have been determined at temperatures up to 125°C, of di-n-propylamine up to 100°C, and of triethylamine up to 75°C from reaction-solution calorimetric experiments. Quadratic polynomials were found to give good representations of the experimental values, implying a linear variation with temperature of the heatcapacity changes. The enthalpies of protonation of the aqueous amines have been determined in the same temperature range. Linear expressions give satisfactory representations of the protonation enthalpies of the hexylamines and dipropylamine, whereas a quadratic expression is required to represent the triethylamine values. The calorimetric results are used together with reported pK a values at 25°C to calculate the dissociation constants of the corresponding ammonium ions between 0 and 200°C. At 0°C triethylamine was found to be the weakest base, the relative base strengths being triethyl〈cyclohexyl〈n-hexyl〈dipropyl, whereas above 60°C triethylamine was the strongest base, the order of the other amines being unchanged.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00643377
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