Experimental and computational thermochemical study of 3-hydroxypropanenitrile

Dedicated to Professor J. Simões Redinha on the occasion of his 80th birthday
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Abstract

This paper reports the values of the standard (p = 0.1 MPa) molar enthalpy of formation in the gas phase, at T = 298.15 K, for 3-hydroxypropanenitrile derived from the respective enthalpy of combustion in oxygen, measured by static bomb combustion calorimetry and the standard molar enthalpy of vaporization, at T = 298.15 K, determined using the transference (transpiration) method in a saturated N2 stream, the value of the gas-phase enthalpy of formation being ΔfHm(g)=-(91.2±1.4)kJ·mol-1.

Furthermore, we have performed high-level ab initio molecular orbital calculations at the G3 level. Four different conformations corresponding to local minima of the potential energy surface have been found for 3-hydroxypropanenitrile. The optimised molecular and electronic structure of the most stable conformer of 3-hydroxypropanenitrile shows a gauche arrangement with a weak intramolecular hydrogen bond from OH hydrogen to the π-bond charge cloud of the nitrile group. The calculated values for the enthalpy of formation of the most stable conformer using atomization and isodesmic bond separation reactions, −94.7 and −95.0 kJ · mol−1, respectively, are in very good agreement with the experimental value.

Introduction

The structure and energetics of molecules are fundamental concepts in Chemistry, the energy associated with a particular structure being related to the constituent atoms, and the corresponding bond and angles that form the molecular framework [1]. Thermodynamic data such as the enthalpies of formation are often helpful in the understanding of the structural, conformational, and reactivity trends exhibited by the molecules. They are needed to estimate the amount of energy released or absorbed in a chemical reaction, to calculate other thermodynamic functions and, more importantly, to asses the stability of a molecule. One of the purposes of thermochemistry is to derive the enthalpies of formation of compounds from their elements, and to relate them to structure and chemical binding [1], [2], [3].

We are presently involved in a study of the thermochemistry of β-hydroxy compounds in order to analyse and evaluate the energy of the structural effects produced by different groups in this family of compounds. Experimental and/or theoretical studies of the thermolysis reaction of β-hydroxy derivatives [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], and specially β-hydroxynitriles [5], [9] have been carried out for some of us. In a recent work [16], we have published the results obtained from a calorimetric and computational study of the thermochemistry of 3-buten-1-ol and 3-butyn-1-ol concluding that the weak intramolecular hydrogen bond from the OH hydrogen to the π-bond charge cloud that exists in both compounds has not significant influence on the enthalpy of formation of these species. Very recently, a similar intramolecular SH⋯π hydrogen bonding interaction has been reported for a thiol analogue, 3-butyn-1-thiol, in a study of its microwave spectrum [17].

In this work, we have carried out the experimental determination of the enthalpy of formation in the gas phase of 3-hydroxypropanenitrile. The standard (p = 0.1 MPa) molar enthalpy of combustion for the liquid compound has been measured by static bomb combustion calorimetry. The standard molar enthalpy of vaporization was determined using the transference (transpiration) method in a saturated N2 stream. Furthermore, we have also carried out high-level ab initio molecular orbital calculations at the G3 level.

Section snippets

Material and purity control

The 3-hydroxypropanenitrile was commercially available from Aldrich (mass fraction purity 0.99). It was distilled twice. Determination of purities, assessed by gas chromatography and mass spectrometry indicated that the mole fraction of organic impurities was less than 0.001. The content of water, 1.0792%, was assessed by mass spectrometry and Karl–Fisher analysis.

Combustion calorimetry

An isoperibol calorimeter equipped with a static combustion bomb was used for the measurements of the energy of combustion. The

Results and discussion

The results of combustion experiments of 3-hydroxypropanenitrile are given in table 2. The experimental values have been derived as in reference [32]. The massic energy of combustion is referenced to the final temperature of 298.15 K. The energy of solution of carbon dioxide in water at T = 298.15 K, ΔsolU(CO2), was taken as −17.09 kJ · mol−1, and the solubility constant, K(CO2), as 0.03440 mol · dm−3 · atm−1 at T = 298.15 K [20].

Table 3 gives the molar energies and enthalpies of combustion derived from the

Acknowledgements

The support of the Spanish MEC/DGI under Projects CTQ2006-12745 and FIS2004-02954-C03-01 and the Colombian DIME, Dirección General de Investigaciones Medellı´n, Sede Medellı´n under Project 030802749 and Vicerrectoria de Investigación, Universidad Nacional de Colombia, Convocatoria Nacional de Investigacion, Modalidad 1, is gratefully acknowledged. M.T. thanks MEC/SEUI, FPU AP2002-0603, Spain, for financial support. A.G. thanks CSIC, I3PCPG-06-00062 for financial support.

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