SOLUBILITIES OF QUATERNARY AMMONIUM SALTS IN ORGANICSOLVUNTS
and encouragement throughout this work. It is also noted that the expense of this research has
been defrayed partially from the Grant in Aid for Fundamental Scientific Research.
SOLUBILITIES OF QUATERNARY AMMONIUM SALTS I N CEltTAIN ORGANIC SOLVENTS BY VINCENTL. HUGHES~ AND ARTHUR A. VERNON Il’he Hayden Memorial Laboratories, Northeastern University, Boston 16, Massachusetls Received Janzlarv 66,I962
Solubilities are reported for tetramethylammonium iodide and tetrapropylammonium iodide in methanol-benzene mixtures; for tetraethylammonium iodide, tetraethylammonium bromide, tetrapropylammonium iodide and tetrabutylammonium iodide in ethanol-benzene mixtures; for tetraethylammonium iodide and tetrapropylammonium iodide in methanolnitrobenzene mixtures; for tetraethylammonium bromide, tetrapropylammonium bromide and tetrabutylammonium iodide in ethanol-nitrobenzene mixtures. The ethanol-benzene and ethanol-nitrobenzene solutions all show a maximum in the solubility-mole fraction plot. It is suggested that this may be due to (I combination of solute-solvent interaction.
Introduction Goldberg and Vernon2 reported the solubility of tetraethylammonium iodide in methanol-benzene mixtures and found that the solubility increased with the mole fraction of methyl alcohol with a maximum value at about 0.8 methanol. Therefore, it was decided to study other solutes and solvent mixtures to determine whether a similar effect was present. Experimental
Results The results of the measurements are plotted in Figs. 1, 2, 3 and 4 in which the solubility values are the averages of from three to five determinations. Eight of the values of solubility have average deviations from the mean from 1 to 1.5%; the rest are considerably less than 1%. Discussion The additional data obtained for the solvent pair methanol-benzene do not lead to a consistent beMaterials.-Tetraethylammonium iodide, prepared by havior when added to the information reported by the method reported by Vernon and Sheard,3 analyzed 49.3% iodine compared to the theoretical value of 49.4%. Goldberg and Vernon.2 If the maximum is due to The other salts were Eastman Kodak materials prepared by methanol interaction with the iodide ions, it would recrystallization. Tetramethylammonium iodide was crya- seem that the effect should be more pronounced for tallized from a 50% water-methyl alcohol mixture to give an iodine content of 68.1% compared to the theoretical 68.2%. the tetrapropylammonium iodide since the large Tetrapropylammonium iodide was dissolved in hot methyl cation should favor anion-methanol interaction. The ethanol-benzene and ethanol-nitrobenzene alcohol, the solution cooled for crystallization, and precipitation completed by the addition of ether. The salt curves present a more consistent picture although was dried at 70” to give an iodine content of 40.4% compared it seems evident that other studies than solubility to the theoretical 40.5%. Tetrabutylammonium iodide was crystallized from ben- would have to be made to establish a theoretical zene and dried in a vacuum desiccator to give an iodine anal- explanation of the behavior found. However, ysis of 34.4% compared to the theoretical 34.3%. Tetra- the following comments seem justified as a preethylammonium bromide was crystallized from absolute ethyl liminary proposal. The behavior of the solute is alcohol and dried in a vacuum oven at 70”. The salt analyzed approximately the same in both liquid pairs with 38.1oJ, bromine compared to the theoretical 38.170. Anhydrous methyl alcohol and benzene were purified as the maximum lying between methanol mole fracdescribed by Goldberg and Vernon.a The methyl alcohol tions of 0.7 and 0.85. It is interesting that in had a refractive index of 1.3271 a t 25” compared to the “In- ethanol-benzene both tetraethylammonium iodide ternational Critical Tables” value of 1.32773. The benzene refractive index was 1.4977 at 25” compared to the and tetraethylammonium bromide show a maxi“International Critical Tables” value of 1.49779. mum since Goldberg and Vernon2found that tetra95% ethyl alcohol was refluxed and distilled off calcium ethylammonium bromide gave no maximum in oxlde and in turn off silver oxide. The solvent was then methanol-benzene mixtures. dried over calcium hydride and distilled. Copenhafer and Kraus4 showed that many Nitrobenzene was shaken with sulfuric acid and then with sodium carbonate solution. After a further shaking with quaternary ammonium salts are highly associated distilled water, the solvent wm stored over activated alu- in benzene solutions. Further, they found that the mina for three days, filtered and stored over calcium hydride association numbers went through a maximum at for two weeks. Procedure.-The method of saturation and solution re- different concentrations for different salts-usually moval was the same as that described by Goldberg and between about 0.1 and 0.3 molal. If such an effect Vernon .* The analyses’ of the methanol-benzene solutions were the cause of the behavior in the systems here were made by a modified Volhard analysis as described by the same authors. The solutions containing nitrobenzene reported it would be likely that the association were usually analyzed by adding ethyl alcohol, titrating with would be decreased by increase in dielectric consilver nitrate, and digesting on a steam-bath for 20 minutes. stant and if such decrease took place, the solubility After adding an equal volume of hot distilled water, the should drop. However, it is doiibt,ful if this can precipitate settled to leave a clear supernatant liquid. be the cause of the solubility behavior since maxima Further titrations could be performed to a sharp end-point . are more consistently obtained with ethanol than (1) Clark University, Worcester, Massachusetts. with methanol which has the higher dielectric (2) G. M. Goldberg and A. A. Vernon, J . A m . Chem. Soc., 73, 2845 constant of the two alcohols. (1951). (31 A. A. Vernon and J . L Slleard, ibid
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(4) I). T. Cogcnhafer and C. A. Iiiaub. ibid., 73, 4257 (1951).
VINCENT L. HUGHES AND ARTHUR A. VERNON
2a 1.4 c 0
2 c3 3.0.6 n
0 0.4 0.8 Mole fraction of methanol. Fig. 1.-Solubility in methanol-benzene mixtures: 1, tetramethylammonium iodide x 102; 2, tetraethylammonium iodide from Goldberg and Vernon; 3, tetrapropylammonium iodide.
0 0.4 0.8 Mole fraction methanol. Fig. 3.Solubility in methanol-nitrobenzene mixtures: 1, tetrapropylammonium iodide; 2, tetraethylammonium iodide.
d Fi I I )
3 0.8 C
F 3 .r(
Mole fraction of ethanol. Fig. 2.Solubility in ethanol-benzene mixtures a t 25": 1, tetraethylammonium bromide: 2, tetrabutylammonium iodide; 3, tetrapropylammonlum iodide; 4, tetraethylammoniumiodide X 10.
Sadek and FUOSS~ cited evidence of solventsolute interaction with tetrabutylammonium bromide in methanol-nitrobenzene mixtures. It seems likely that such effects are present in the systems here reported. Apparently the nitrobenzene negative dipole interaction is less important than the ( 5 ) H. Sadek and
R. M. Fuoss.
J . Am. Chem. Soc., 72, 301 (1950).
Mole fraction ethanol. Fig. 4.-Solubility in ethanol-nitrobenzene mixtures a t 25': 1, tetraethylammonium bromide; 2, tetrabutylammonium iodide; 3, tetrapropylam~qoniumiodide.
ethanol dipole interaction since the ethanolnitrobenzene curves are not greatly different from the ethanol-benzene curves. The ethanol interaction seems to be stronger than the methanol interaction since maxima are more predominate with ethanol-benzene mixtures than with those of met hanol-benzen e. The authors express their appreciation to the Research Corporation which supported this work.