IJUP08 - Universidade do Porto

Thermochemical studies of two cyclic ureas: Imidazolinone and
N,N'-Trimethyleneurea
V. Freitas 1 , M. Roux 2 , J. Elguero 3 , M. Ribeiro da Silva 1
1 CIQ-UP, Department of Chemistry, Faculty of Science, University of Porto, Portugal.
2 Instituto de Química Física "Rocasolano", C.S.I.C., Serrano, 119, E-28006 Madrid, Spain.
3 Instituto de Química Médica, CSIC, Juan de la Cierva, 3, E-28006 Madrid, Spain.
Due to the significance of urea derivatives both as drugs and as materials, its importance does
not need to be stressed too much [1,2]. Some of us have studied abiotic receptors designed for
interacting with ureas [3,4]. To discuss the reactivity of the compounds where those molecular
units are present, we feel useful to know their thermodynamic properties, althougt we
discovered that almost none was known about cyclic ureas. Thus efforts of our Research
Groups were joint to determine some gaseous enthalpies of formation, following previous
studies for other class of relevant nitrogen heterocyclic molecules. A survey of the literature on
thermochemical properties of cyclic ureas yield only one hit and it concerns the recently
published study of benzimidazolinone [5].
H
N
N
H
a)
O
Figure 1. Structural formula for a) N,N´-ethyleneurea (2-imidazolidone) and b) N,N´-propyleneurea (N,N´-
trimethyleneurea)
We will report now the experimental results of the energy of combustion and enthalpy of
sublimation obtained for imidazolinone and N,N'-trimethyleneurea (represented in Fig. 1),
using static bomb calorimetry and Knudsen effusion technique, respectively. These data allow
to derive the values of the standard molar enthalpies of formation, in the gaseous state, for
both compounds. The results are discussed in terms of structural contributions.
[1] http://en.wikipedia.org/wiki/Urea
[2] Bagley, M. C. et al., Org. Biomol. Chem. 2006, 4, 4158.
[3] Claramunt, R. M. et al., Biosens. Bioelectron. 2004, 20, 1242.
[4] Herranz F., et al., Tetrahedron Lett. 2006, 47, 9017; and references cited therein.
[5] Morais, V. M. F., et al., Mol. Phys. 2006, 104, 325.
NH
NH
b)
O
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