HYDROTROPIC SOLUBILITIES Solubilities in Aqueous Sodium Arylsulfonate Solutions HAROLD SIL\IIMONS BOOTH AND HOWARD E. EVERSON' Western Reserve University, Cleveland 6 , Ohio study was made of the solubility of t e n selecte3 solutes in several concentrations of aqueous sodium benzenesul-
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fonate, sodium p-cymenesulfonate, sodium toluenesulfonate, and sodium xylenesulfonate solutions at 25.0" and 60.0" C., with the object of determining the relative effectiveness of these salt solutions as hydrotropic solvents. The results indicate that, in general, the aqueous sodium xylenesulfonate solutions are most effective as solvents for the solutes studied.
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N 4 previous article ( I ) the authors reviewed earlier investigations of others and discussed their own work on hydrotropic solubilities in 40% sodium xylenesulfonate. Initially their studies on hydrotropic solubilities were focused on the solubilizing effect of commercial aqueous sodium xylenesulfonate solutions on many slightly water-soluble or -insoluble materials ( I ) . The object of the present part of the investigation was t o determine the relative effectiveness of other salts similar to sodium xylenesulfonate in hydrotropic action. Therefore sodium xylenesulfonate was compared with sodium benxenesulfonate, sodium p-cymenesulfonate, and sodium toluenesulfonate a t several concentrations in aqueous solutions a t 25.0"and 60.0" C. Ten solutes were selected for this study which exhibited solubilities in the-initial study ( I ) from very soluble to insoluble. These solutes were: acetophenone, aniline, benzaldehyde, benzene, carbon tetrachloride, cottonseed oil, o-cresol, cyclohexanol, ethyl acetate, and n-hexane. All the solutes used were either C.P. or highest grade commercial samples purchased expressly for this study. The hydrotropic salts were furnished by The Wyandotte Chemicals Corporation of Wyandotte, Mich., in the form of aqueous solutions and are listed in Table I together with their properties. The different concentrations of solutions used for these determinations were made from the stock solutions by dilution with distilled water or by evaporation where necessary. EXPERIMENTAL PROCEDURE
of o-cresol were measured a t 31.0 * 0.5" C., as the freezing point of this material is but slightly below this value. The constant temperatures were maintained by the use of mercury bulb-type thermoregulators immersed in constant temperature water baths. Mercury bulb thermometers calibrated against a U. S. Bureau of Standards thermometer were used to check the temperatures throughout the solubility determinations. As w~tspointed out in the initial study, the solubiliiy of a liquid solute can be determined well within 0.1 ml. of solute for a given volume of solvent. Howww, with o-cresol and cyclohexanol in some of the intermediate concentrations of hydrotropic salts, this degree of accuracy is not attained as it is difficult to observe the appearance of a second phase when solute is added t o solvent. In some cases, such as o-cresol in aqueous 10.0% sodium p cymenesulfonate, it is not possible to make a satisfactory solubility determination by the method used. One factor involved is the similarity in density of the two phases which makes separation next t o impossible. Another factor is the ease with which these materials form colloidaI solutions. RESULTS
The results of the solubility determinations are shown in Tables 11, 111, IV, and V. These results are expressed in milliliters of solute dissolved in 100 ml. of solvent. No attempt was made to determine the solubility when it was greater than 400 ml. of solute per 100 ml. of solvent. The maximum concentration of hydrotropic salt used for the determinations in the
AND CHARACTERISTICS O F STOCK SOLUTIONS TABLE I. ANALYSES
OF
HYDROTROPIC SOLVENTS
Total solids % SO^-- a s % COa as NaaCOa, p H a t 25.0' C. (glass electrode) Density,at 25.0' C., g./ml. Alcohol-insoluble, %
NLSO~ %
Sodium Sodium Sodium Benzene- p-Cymene- Toluenesulfonate sulfonate sulfonate 32.00 35.10 38.20 0.02 0.49 0.62 0.005 0.02 0.17
Sodium Xylenesulfonate 41.70 0.37 0.12
7.54 7.00 8.05 8.05 The methods used for the solubility determinations were those 1.149 1.120 1.164 1.165 employed in the previous study ( 1 ) . ... ... 0.80 0.45 However. in the -present stud; the solute-solvent mixtures wvere not centriTABLE11. SOLUBILITIES IN AQUEOUSSODIUMBENZENESULFONATE SOLUTIONS fuged to cause separation of excess Soly M1. Solute/Ml. Solvent solute. Temp., Sodiim beneenesuifonate, % ' Separation was accomplished by gentle Solute O C. 0.0 5.0 10.0 1 5 . 0 20.0 22.0 25.0 32.0 rotation of the solubility tubes while Acetophenone 25 0.54 0.60 0.80 .. 1.30 .. . . . 2 . 6 5 0.97 .. 1.62 .. .... .. 3.56 60 0.80 0.83 they were immersed in the constant~ ~ i l i ~ ~ 25 3.80 3.88 4.29 .. 6.92 .. 34.0 60 4.90 5.00 5.30 . . 8.82 .. ,.. 29.6 temperature bath. This procedure is 25 0.40 0.60 0.70 .. 1.05 .. .. .. ,. 2.53 much slower than the use of a oentri60 0.96 1.10 1.16 .. 1.89 .. 3.81
