Elsevier

Fluid Phase Equilibria

Volume 293, Issue 2, 25 June 2010, Pages 137-140
Fluid Phase Equilibria

Static permittivity and molecular interactions in binary mixtures of ethanolamine with alcohols and amides

https://doi.org/10.1016/j.fluid.2010.02.038Get rights and content

Abstract

The relative static permittivity at 1 MHz and high frequency limit permittivity at wavelength of sodium-D line of the binary mixtures of ethanolamine (2-aminoethanol) with alcohols (ethyl alcohol, ethylene glycol and glycerol) and amides (formamide, N,N-dimethylformamide and N,N-dimethylacetamide) have been investigated over the entire concentration range at 30 °C. The excess permittivity and Kirkwood correlation factor of the binary mixtures were determined to explore the hydrogen-bonded hetero-molecular interactions and their dependence on the number of hydroxyl groups of alcohols molecules and the extent of substitution in amides molecules. Results confirm that ethanolamine form weak H-bond interactions with alcohols, N,N-dimethylformamide and N,N-dimethylacetamide, but the dipolar alignments in these mixtures vary with number of hydroxyl group of alcohols and their molecular size. Comparatively strong H-bond interactions were found between ethanolamine and formamide molecules with reduce in number of parallel aligned effective dipoles.

Introduction

Alcohols, amides and amines are important biological, pharmaceutical, analytical, and industrial solvents. The molecules of these solvents form H-bonded linear polymeric chain structures in dynamical equilibrium [1], [2], [3], [4], [5]. Chemical and physical properties of alcohols are mainly governed by the number of carbon atoms and hydroxyl groups, and their position in the molecular structures [1]. Amides have large range liquid state and possess the donor–acceptor –CO–NH– peptide bond and their molecular dynamics changes on passing from unsubstituted amide to di-substituted N,N-dialkylamide [2], [3]. Amines molecules have the combined physical and chemical characteristics of both the alcohols and amides, and hence it is interesting to study the H-bond interaction behaviour of amines mixed with alcohols and amides over the entire concentration range by static permittivity (dielectric constant) measurements.

The relative static permittivity of a material is a fundamental property and its measurement is a highly interdisciplinary field of physics, chemistry, bio-chemistry, pharmaceutical and soft material sciences. Investigation of static permittivity of binary mixtures is important in design of mixed solvents of required solvating power for the suitable solubility and chemical stability of the solute in the solution [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. The concentration dependent excess permittivity of the mixed solvent provides the quantitative information about the strength of hetero-molecular H-bond interactions, H-bonded dipolar ordering and molar ratio of stable adduct [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. Earlier, authors have studied the concentration dependent permittivity and molecular interactions behaviour in alcohols–alcohols mixtures [12], [13] and amides–polar solvents mixtures [16], [17], [18], [19], [20], [21] for their molecular conformations.

Recently, authors have investigated the static permittivity and H-bond molecular association in binary mixtures of N,N-dimethylethanolamine (2-dimethylaminoethanol) (DMEA) with alcohols and amides [20]. In continuation, the present paper deals with the study of H-bond molecular interactions of ethanolamine (2-aminoethanol) with alcohols and amides over the entire mixing range by precise static permittivity measurements. The objective of the paper is to provide the precise static permittivity values of these mixed solvents for design of their required solvating power and to confirm the effect of number of hydroxyl groups of alcohols molecules and substitution of amide molecules on the H-bond interactions with ethanolamine molecules.

Section snippets

Materials

Analytical grade ethanolamine (2-aminoethanol) (AE), alcohols (ethyl alcohol (EA), ethylene glycol (EG), glycerol (Gly)) and amides (formamide (FA), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA)) were purchased from E. Merck, Himedia laboratories, Qualigens ExcelaR and Loba Chemie of India. The mass fraction purities of these samples as reported by the manufactures are: AE > 0.99, FA > 0.99, DMF > 0.99, DMA > 0.995, EA > 0.999, EG > 0.995 and Gly > 0.995. Binary mixtures of AE with alcohols and

Results and discussion

The measured ɛr values of alcohols, amides and amine in their pure liquid state recorded in Table 1 were found in good agreement with the literature values (EA: 23.87, EG: 39.84, Gly: 41.17, FA: 106.14, DMF: 36.55, DMA: 37.72, AE: 31.46) [1], [2], [3], [4], [5], [6], [12], [13], [16], [22], [23]. The evaluated Kirkwood correlation factor g values using Eq. (2) for AE, EA, EG, Gly, FA, DMF and DMA in pure liquids state are 2.06, 2.73, 2.35, 2.61, 2.22, 1.01 and 1.50, respectively, which confirms

Conclusions

This paper presents the precisely measured relative static permittivity values of ethanolamine mixed with alcohols and amides over the entire concentration range, which is useful in the design of these mixed solvents of required solvating power. The magnitude of excess permittivity of the mixtures revealed the formation of weak hetero-molecular H-bond interactions of ethanolamine with EA, EG, Gly, DMF and DMA molecules whereas FA form strong H-bond interactions with ethanolamine. The

Acknowledgements

The authors thank the University Grants Commission, New Delhi, for a project grant (F. No. 33-15/2007 (SR)) under which the work was carried out. The Department of Science and Technology, Government of India, New Delhi, is kindly acknowledged for providing experimental facilities through the project (SR/S2/CMP-09/2002). One of the authors SS is grateful to the CSIR, New Delhi for providing the RA fellowship and SC is thankful to the UGC, New Delhi for the award of RFSMS fellowship.

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