Enthalpy of cooperative hydrogen bonding in complexes of tertiary amines with aliphatic alcohols: Calorimetric study Ksenia V. Zaitseva, Mikhail A. Varfolomeev ⇑ , Vladimir B. Novikov, Boris N. Solomonov Chemical Institute, Kazan (Volga region) Federal University, Kremlevskaya 18, Kazan 420008, Russia article info Article history: Received 10 November 2010 Received in revised form 18 February 2011 Accepted 21 February 2011 Available online 26 February 2011 Keywords: Solution calorimetry Hydrogen bond Aliphatic alcohol Amine Cooperativity Reorganization Associated solvent abstract The work is devoted to the investigation of thermodynamics of specific interaction of the tertiary ali- phatic and aromatic amines with associated solvents as which aliphatic alcohols were taken. Solution enthalpies of aliphatic alcohols in amines (tri-n-propylamine, 2-methylpyridine, 3-methylpyridine, N- methylimidazole) as well as amines in alcohols were measured at infinite dilution. The enthalpies of spe- cific interaction (H-bonding) in systems studied were determined based on experimental data. The enthalpies of specific interaction of amines in aliphatic alcohols significantly lower than the enthalpies of hydrogen bonding in complexes amine–alcohol of 1:1 composition determined in base media due to the reorganization of aliphatic alcohols as solvents. The determination of solvent reorganization contri- bution makes possible to define the hydrogen bonding enthalpies of amines with clusters of alcohols. Obtained enthalpies of hydrogen bonding in multi-particle complexes are sensitive to the influence of cooperative effect. It was shown, that hydrogen bond cooperativity factors in multi-particle complexes of alcohols with amines are approximately equal for all alcohols when pyridines and N-methylimidazole as solutes are used. At the same time, H-bonding cooperativity factors in complexes of trialkylamines with associative species of alcohols decrease with increasing of alkyl radical length in alcohol and amine molecules. This work shows that the thermodynamic functions of specific interaction of solutes with associated solvents cannot be described using the H-bond parameters for the complexes of 1:1 composition. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction A great part of research literature on hydrogen bonding con- cerns the self-associated liquids. Such liquids can be considered as a mixture containing complexes with various structure (linear, branched, cyclic) and composition (monomer, dimer, tetramer, etc.), which are in equilibrium with each other. Formation of hydrogen bonds in these liquids significantly affects their physical and chemical properties [1,2]. The simplest self-associated solvents are aliphatic alcohols. This type of solvents is widely used in organ- ic synthesis and industry. It should be noted, that various pro- cesses, which occur in aliphatic alcohols, greatly depend on the hydrogen bonding with the solvent. Therefore, quantification of the thermodynamic parameters of formation of hydrogen bonds in them has a great practical interest. Studies of hydrogen bond formation in aliphatic alcohols have been carried out with different experimental methods, for exam- ple, vapor pressure [3,4] and calorimetric measurements [5–8], infrared (FTIR) spectroscopy [9–14] and nuclear magnetic reso- nance (NMR) [15–19] techniques. The authors attempted to solve two major tasks in these studies. The first one was to determine the structure of associative species of alcohol and to describe ther- modynamic parameters of their formation. Usually obtained experimental data were interpreted with a variety of statistical and empirical models postulating the specified association way in aliphatic alcohols [20]. Second, more complicated task, concerning non-covalent inter- actions in solutions of aliphatic alcohols, is the determination of hydrogen bond energy of solute molecule with associated solvent. Hydrogen bonding with solvent may significantly influence on the properties and reactivity of solutes. One should take into account two important peculiarities of associated liquids for analysis of hydrogen bonding in alcohols solution. The first one is the phe- nomenon of cooperativity. The concept of cooperativity implies that the hydrogen bonding energy in multi-particle complex is not equal to the sum of energies of pair-wise interactions [21]. The cause of the cooperative effect as follows from [22,23] is a change in the basicity and acidity of alcohols associative species in comparison with free molecules. Luck et al. [24] revealed by FTIR-spectroscopy, that in ternary complex (ROH) 2 B (B – proton acceptor) both hydrogen bonds are strengthened and the value of 0021-9614/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2011.02.019 ⇑ Corresponding author. Tel.: +7 843 2337606; fax: +7 843 2315416. E-mail addresses: zaitseva.ksenia@gmail.com (K.V. Zaitseva), vma.ksu@gmail.com (M.A. Varfolomeev), vladimir.novikov@ksu.ru (V.B. Novikov), boris.solomonov@ksu.ru (B.N. Solomonov). J. Chem. Thermodynamics 43 (2011) 1083–1090 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct