1578
NOTES
bhat of malonic acid.8 Evidence for the validity of this assumption is found by comparing lines 1, 2, 5 and 6 of Table 11. For the decomposition of oxalic acid in methylaniline and in dimethylaniline the differences in the entropy of activation and the enthalpy of activation exactly parallel those for the decomposition of malonic acid in these game solvents. Such a parallelism strongly suggests that the mechanism is the same for both acids. Acknowledgment.-The financial support of this research by the Raskob Foundation for Catholic Activities, Wilmington, Delaware, is gratefully acknowledged. SOLUBILITY O F LAURYL ALCOHOL I N AQUEOUS SOLUTIONS OF SODIUM LAURYL SULFATE BY M. B. EPSTEIN AND J. Ross Colgate Palmolive Company, Jersey City, New Jersey Received April 69,1967
Vol. 61
viously thicker. Below the observed break the bands are uniform and the films are clear and undistorted and the transition temperatures are presumed to correspond to homogeneous solutions unsaturated with respect to LOH. If this view is taken, then a solubility curve may be constructed. It will be a curve of solubility of LOH at maximum transition temperature versus concentration of SLS. The values above the CMC are essentially at one temperature, 33", but for the values below the CMC there is a different temperature for each concentration of SLS. I n Fig. 1, it is seen that above the CMC a line typical of solubility isotherms for similar systems is obtained. Below the CMC the slope is far less than that over the micellar region. An accurate value for the solubility of LOH in water is not available, but it must be exceedingly small. Sporck2 extrapolated solubilities for the lower alcohols and gave an estimate of 0.00019% mole/l.). Addison and Hutchinsona by a similar approach derived an equation for the solubility of the fatty alcohols in water which gives the value 0.000370for LOH. It is apparent from Fig. 1 that the solubility of LOH in water is markedly enhanced by the presence of SLS below as well as above the CMC.
It appears possible to obtain quantitative data for the solubility of lauryl alcohol (LOH) in aqueous solutions of sodium lauryl sulfate (SLS) from film drainage transition temperature data. When plotted as tt function of the amount of LOH in the sys(2) C. R. Sporck, J . Amer. Oil Chem. SOC.,$0, 190 (1953). tem a t any particular concentration of SLS, these (3) C. C. Addison and 8. K. Hutchinson, J . Chem. Boc., 3387 transition temperatures rise to a limit and then do (1949). not increase much upon addition of even large amounts of LOH. Below the critical micelle concentration (CMC) this effect is apparent from a NATURE OF THE METHANOL-METHYL direct plot of transition temperatures against the BORATE AZEOTROPE1 concentration of LOH at constant SLS. Above BY THOMAS J. TULLY~ AND PHOEBUS M. CHRIS TOP HER^ the CMC, it is preferable to use a function logarithmic in LOH. Contribution from the Departmen2 of Chemistry Newark College of Engineering, Newark 6, N . ' J . The observed break we interpret as being due to Received June 10, 1967 the limit of solubility of the LOH at the given concentration of SLS. Indeed it is observed that beMethanol and methyl borate form an azeotrope yond this break the films are visibly different. The that boils between 53 and 55". This is lower than interference colors are not always horizontal but the boiling point of any other mixture of the two often distorted by the superposition of local areas compounds. Due to the fact that the composition often showing a large number of bands and ob- of the azeotrope is very close to an equimolar ratio of the two components, it is generally believed that solutions of methyl borate in methanol contain a complex alkoxo acid formed by the reaction
The tetraalkoxo acid itself has not been isolated but stable salts of the acid have been prepared and characterized. 3-6 Mixtures of the two components give an acidic color with brom thymol green, showing that some reaction must occur. The acidity must be due to the formation of the methyloxonium ion, CH30H2+, since neither component by itself produces an acid color with the indicator. The present work comprises a study of the prop1.0 1.5 2.0 SLS, g./100 g. soh. of LOH in SLS from surface transition temperatures.
0.5
Fig. 1.-Solubility
( 1 ) M. B. Epstein, A. Wilson, C. W. Jakob. L. E. Conroy and J. Ross, THISJOURNAL, 68, 8GO (1954).
(1) Presented before the Physical Chemistry group of the North Jersey Section of the American Chemical Society Meeting-in-Miniature, January 30, 1956. (2) Department of Chemistry, Newark College of Engineering, Newark 2, N. J. (3) H.Cooaux. Comnt. rend.. 127. 719 (1898). (4j L. Cambi, Atti n'sndi.. 2S, I, 244 (1914): (5) H.Meerwein, Ann., 466, 227 (1927). (6) 11. Meerwein and T. Bersin, ibid., 476, 113 (1929).
