Synthesis, characterization and thermochemical properties of N-acyl-N ',N '-diethylthioureas

Three N-acyl-N',N'-diethylthioureas, RCONHCSNEt2. R = Pr-1, Bu-1, Bu-1, hav e been prepared and characterised. The standard (p(o) = 0.1 MPa) molar enth alpies of combustion in oxygen of the three crystalline compounds, at T = 2 98.15 K. have been measured by rotating bomb-combustion calorimetry. and th e standard molar enthalpies of sublimation of the compounds by microcalorim etry. These values were used to derive the standard molar enthalpies of for mation of the compounds in their crystalline and gaseous phases, respective ly. The derived standard molar enthalpies of formation in the gaseous state are discussed comparatively. Acid constants and some complex stabilities h ave been measured pH-potentiometrically in dioxane-water mixture. The cryst al structure of N,N-diethyl-N'-isovaleroyl-thiourea is presented and shows a delocalization of the pi electrons of the C=S group over the carbon-amine nitrogen bond. CS-NEt2 stabilising the molecule, in accordance with the th ermochemical results.