IJUP08 - Universidade do Porto

Molecular Energetics of Hydroxybenzaldehyde Isomers
Mariana Vidinha, Manuel J. S. Monte, Maria D. M. C. Ribeiro da Silva
Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências,
Universidade do Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal.
The thermochemical study of different classes of aromatic compounds has been carried out
in our Research Group (CIQ-UP) in order to correlate molecular energetic data with the
structural characteristics of the molecules. Some of our attention has been particularly
devoted to Schiff bases derived from ketones or aldehydes with diamines, which being
molecules whose role is well known on the development of agrochemical and
pharmaceutical industries, particularly in the context of catalysis, have motivated our
interest.
In this context, during the development of the energetic study of some Schiff bases,
derived from salicylaldehyde (2-hydroxybenzaldehyde) with aliphatic and cyclic diamines,
we detected the lack of the relevant thermochemical data for that phenol derivative. The
need of the knowledge of such parameters led us to study that compound [1]. Considering
that thermochemical data for phenols with carbon-bonded substituents containing the acyl
group are scarce, as it is reported by Slayden and Liebman [2], we decided to extend the
study to the other two isomers of the salicylaldehyde (3-hydroxybenzaldehyde and 4hydroxybenzaldehyde,
Fig. 1), which we present in this work.
O
C
H
OH
O
C
OH
(a) (b)
Figure 1: Structural formula for (a) 3-hydroxybenzaldehyde and (b) 4-hydroxybenzaldehyde.
The standard (pº = 0.1 MPa) molar enthalpies of formation, in gaseous phase, at T = 298.15
K, for 3- and 4- hydroxybenzaldehyde were derived from measurements of standard molar
energies of combustion, using a static bomb calorimeter, and from the standard molar
enthalpies of sublimation, determined by Knudsen method effusion experiments.
These results allow the derivation of the values of the enthalpies of formation of the two
hydroxybenzaldehyde isomers and, consequently, to establish structural correlations with
these energetic data.
[1] - Ribeiro da Silva, M. D. M. C., Araújo, N. R.M. (2007), J. Chem. Thermodynamics 39, 1372 –
1376.
[2] – Slayden, S. W., Liebman, J. F. (2003), Therchemistry of Phenols and Related Arenols, in: Z.
Rappoport (Ed.), The Chemistry of Phenols, Wiley, Chichester, (Chapter 3).
H
125