Enthalpies of fusion and solid-to-solid transition, entropies of fusion for urea and twelve alkylureas

Abstract

Enthalpies and temperatures of fusion have been measured by differential scanning calorimetry for urea and a number of its mono- and di-alkyl derivatives. Enthalpies obtained are: urea, 14.79 kj mol −1; monomethylurea, 15.75 kJ mol −1 ; monoethylurea, 13.94 kJ mol −1 ; monopropylurea, 14.63 kJ mol −1 ; monoisopropylurea, 17.40 kJ mol −1 ; monobutylurea, 14.55 kJ mol −1 ; monotertbutylurea, 33.13 kJ mol −1 ; dimethyl-1,1 urea, 29.61 kJ mol −1 ; dimethyl-1,3 urea, 13.62 kJ mol −1; diethyl-1,1 urea, 16/78 kJ mol −1 ; diethyl-1,3 urea, 12.46 kJ mol −1 ; dibutyl-1,3 urea, 14.87 kJ mol −1; trimethyl-1,1,3 urea, 14.30 kJ mol −1. Entropies of fusion have been derived from the experimental results. By temperature scanning starting from r.t. some solid-to-solid transitions for four alkylureas have also been detected, all hitherto unreported. Temperatures and enthalpies of transition are: for monoisopropylurea, 375.5 K and 2.31 kJ mol −1 ; for monobutylurea (two transitions), 313.1 K and 7.02 kJ mol −1 , 344.9 K and 0.88 kJ mol −1 ; for diethyl-1,3 urea, 339.4 K and 1.87 kJ mol −1 ; for dibutyl-1,3 urea, 311.5 K and 11.10 kJ mol −1.