SALTING AND SOLUBILIZATION BEHAVIOUR OF SOME POLAR AROMATIC COMPOUNDS

Abstract

The activity coefficients of nonelectrolytes in aqueous solutions are influenced by the presence of salts. Salt effect studies can provide considerable information of theoretical importance as to the complex interactions of ions and neutral molecules in water and have application to such related problems as kinetic salt effects and mechanisms of reactions. They have a practical bearing on the separation of nonelectrolytes from water solutions by salting-out processes. Solubilization or the formation of a thermodynamic ally stable isotropic solution of a substrate, normally insoluble or only slightly soluble in a given solvent, by the addition of a surfactant have been utilized in several fields to enhance the solubility of organic compounds. Tne nature of the substrate (solubilizate) as well as that of solubilizer (surfactant), the solvent, the presence of additional polar or non-polar substrates, and the temperature are the complex parameters which influence solubilization. Salting out studies of nonpolar nonelectrolytes have been studied with varying degrees of success. In salt solutions of polar non-electrolytes, as in o,u,vr» c/-a.^sceo , tthhep mmoolleecular interactions are .ore complex ana thus the pattern of the solubility behaviour Is less comprehensible, and more experimental data Is desired. *. have stadied the salting out behaviour of the naphthols and aTew substituted phenols. We have also carried out solubilization Sadies of these solutes in cationic, anionic (ii) and nonionic surfactants. Refractive index and ultrasound velocity measurements of ternary solutions (water-salt-solute) have been done. The motivation for these studies comes from their rele vance to efficient extraction of the phenolics from the petro leum fractions. The entire work has been divided into five chapters which are: (I) General Introduction : An overview of the structure of liquid mixtures and especially of solutions of nonelectrolytes has been given. A brief history of previous studies carried out, their advantages and disadvantages have also been.discussed, and various terms like salting-out, sal ting-in, solubilization, etc. have been defined. At the end of the chapter, the present problem and its scope have been given. (II) Salting Studies of Some Polar Aromatic Compounds : Detailed investigation of the salting studies of two naphthols, 6 substituted phenols viz. p-ni trophenol, 3,5-dinitro- and 5- nitrosalicylic acids and p-chloro-, p-bromo-, and p-amino phenols in presence of various salts(such as NaCl, Na^O^, NaCIO, , KSCN etc.) and solvents have been carried out. These have been carried out at three temperatures by extraction method in most cases and by solubility method in a few cases. The salting out coefficients and various thermodynamic proper ties associated with transfer from water to salt solutions have been evaluated. (iii) (III) Solubilization Studies of Some Polar Aromatic Compounds; Solubilization studies of all the solutes mentioned earlier have been carried out. An attempt has been made to find the solubilization sites of these solutes and the extent of solu bilization and binding to the micelles have been discussed. (IV) Ultrasonic and Refractometric Studies of Ternary Solutions: This includes refractometric studies and ultrasonic velocity measurements of ternary systems i.e.water-salt-solute systems. Refractive index measurements have been used to calculate the molar refractivity of solutions. The deviation from the mixture rule are explained in terms of plausible intermolecular inter actions. The ultrasonic velocity (u) measurements have been utilized to calculate the compressibility which depends solely on the structure of solutions. Another quantity ^ g^- ) is found to be additive for such ternary mixtures and is correlated to changes in compressibility of the hydration sphere of ions with and without nonelectrolytes. (V) Conclusions t Various theoretical approaches have been used to explain our results. The extent of solute aggregation taking place in the organic and aqueous phase have been evaluated in case of each solute in different solvents. The effect of substituents on the salting parameters have been elucidated. The surface area created by a solute in a solution have been calcu lated and these have been used to find out the partial molar volume of the solute. The applicability of the scaled particle theory to our systemshas been critically assessed. Different thermodynamic parameters have been obtained, compared and interpreted with valid reasons. (iv) ACKNOWLEDGEMENT The author sincerely expresses her heartfelt gratitude for the invaluable guidance rendered by Dr. Ratna Ghosh through the working of this thesis. Her supervision and constructive criticism in the case of the present investi gation have successfully led to the completion of the work. The author expresses her thanks to Dr. S.P. Srivastava, Head of the Chemistry Department for providing the necessary research facilities. Thanks are also due to Prof. W.U. Malik, former Head, now Vice-Chancellor of Kashmir University, Srinagar, and all the teaching staff of the department for their suggestions and encouragement during the period of work. The author is indebted to Dr. A.R. Das of IACS, Calcutta, for the necessary facilities rendered for carrying out Ultra sonic velocity measurements at Jadavpur. The libraries at the IACS and Indian Institute of Technology at Delhi and Kharagpur have been of immense help to the author. The author is thankful to Uma Goyal and Mala Tyagi, research scholars, for their help in compilation of the thesis, and to her colleagues for helpful suggestions. Thanks are also to Mr. L.S. Chauhan for technical assistance and to Mr. Darshan Lai for typing the thesis. The author takes this opportunity to pay her heartfelt regards to her most respected and loving parents and to thank them and her sisters and brother who were a constant source of encouragement at each and every stage of the work. The financial assistance from GSIR, New Delhi, India is gratefully acknowledged.