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REYNOLD C. MERRILL
Under the 1.5-kv. potential in the suspension, the slides were coated much more densely, as indicated by the greater interference value by the barium carbonate having the smallest average particle size (column 2 of table 4),while the suspension prepared from ammonium carbonate produced a coating which was less dense than even the control (column 4).The negative effect shown in this last case seems to confirm the validity of figure 2, in which the use of barium carbonate (precipitated with ammonium carbonate) decreases the conductivity of the resulting suspension. At this point the direction for future work is indicated. A more complex but parallel study of double- and triple-carbonate suspensions should be made so that the mechanism of cataphoresis may be more adequately related to the mode of precipitation and, equally important, to the alkali impurity, while the other operative factors such as concentration, viscosity, and size and shape of electrodes are held constant. CONCLUSIONS
The conductivity of dilute suspensions of single alkaline earth carbonates in nitrocellulose lacquer media shows a dependence on the history of the precipitation of the powders. This dependence is a function of both particle size and sodium-ion impurity. Furthermore, characteristic conductivity-particle size curves obtained for the barium, strontium, and calcium carbonate systems indicate that the conductivity of the calcium carbonate is affected by its crystalline nature in somewhat different manner than is the conductivity of the noncrystalline barium and strontium carbonate suspensions. In the case of the barium carbonate suspensions studied, such factors as the sodium-ion impurity and particle size, which in turn determine the conductivity of their suspensions, are shown to affect the cataphoretic velocity. REFERENCE (1) CHAMOT, E. hl., AND MASOK,C. W.: Handbook of Chemical Microscopy, 2nd edition, Val. 11, pp. 102-4. John Wiley and Sons, Inc., New York (1940).
SOLUBILIZATION AND COSOLVENT EFFECTS WITH SODIUM STEARATE REYNOLD C. MERRILL Philadelphia Quartz C o m p a n y , Philadelphia, Pennsylvania Received M a y 11, 1949
The ability of aqueous solutions of detergents to solubilize otherwise waterinsoluble dyes and organic liquids is now well known and has been extensively studied (e.g., 3, 5, 7, 8, 15, 21, 22). Less extensive study has been given to the solubilization of high-molecular-weight soaps and detergents, such as sodium stearate, which are practically insoluble in water at ordinary room temperatures. Phase diagrams of sodium palmitate-sodium laurate mixtures (6, 13 ; cf. also 11)
SOLUBILIZATION A S D COSOLVENT EFFECTS WITH SODIUM STEARATE
483
and of soaps from oils and fats containing mixt'ures of fatty acids (10) indicate that the solubility of mixtures of soaps ie greater than that expected on an additivity basis, owing t o solubilization of the less soluble soaps by the more soluble ones. Despite the interest in the solubilization of organic liquids by soaps, the effect of these organic liquids on the solubility and other properties of the soap itself has been studied systematically by relatively few investigators. That such organic additives as cresol, cyclohexanol, and pine oil are soluble in soap solutions and that they increase the solubility of soaps, particularly in hard waters, has long been recognized by the soap industry. For example, Woodman (24) showed that the solubility of sodium oleate in water at 25°C. is 10.4 per cent, whereas in a 2.14 per cent phenol solution it is 12.6 per cent. Angelescu and Popescu (1) showed that the solubilization of cresols by soap solutions was accompanied by an increase and then a decrease in the viscosity, and that at the yiscosity minimum the electrical conductivity was a maximum. This suggests that the micelles in the presence of cresols are smaller and less hydrated. This paper reports the solubilization of sodium stearate by potassium stearate, sodium laurate, and several modern synthetic organic detergents. Data showing the effect of such organic additiws as cresol, cyclohexanol, cyclohexylamine, and tertiary butyl alcohol on the solubility of sodium stearate are also included. EXPERIMEKTAL
The sodium stearate used in the xork with t,he synthetic detergents was made from Eastman Kodak Company's best stearic acid after recrystallization from acetonitrile. It had an equivalent weight of 284.5, in agreement with the theoretical yalue. An alcoholic solution of the acid was neutralized to the phenolphthalein end point with sodium methoxide and the precipitated soap washed with alcohol and dried at 105'C. It then contained 0.05 per cent excess sodium hydroxide. The sodium stearate used in the work with organic liquids and the potassium stearate were made from another sample of the Eastman acid without recrystallization. The former contained about 4 mole per cent excess sodium hydroxide to minimize hydrolysis (cf. 9). The sodium laurate was prepared similarly from a recrystallized Eastman lauric acid. The acid had an equivalent weight determined by titration of 202.4 (theory, 200.3) and the soap contained 0.057 per cent excess sodium hydroxide. The sodium lauryl sulfate was a commercial product (obtained from Eimer and Amend) which was completely soluble in alcohol. Ultran-et K is an alkyl aryl type of synthetic detergent made by the iltlant,ic Refining Company; it contains about 15 per cent sodium sulfate. Santomerse No. 3, produced by the Monsanto Chemical Company, is essentially sodium dodecylbenzenesulfonate and is free from inorganic salt. Rohm and Haas' Triton X-100 is a condensation product of one molecule of diisobutylphenol with about nine or ten ethylene oxide molecules (4). Renex, obtained from the Atlas Powder Company, is a condensation product of rosin and fatty acids with ethylene oxide. Their Tween 80 is described as sorbitan monooleate. Butyl cellosolve was obtained from the Carbide and Carbon Company, hydroabietyl alcohol from the Hercules Powder Company, and cyclohexylamine
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from the Monsanto Chemical Company. The cresol mas a U.S.P. grade commercial product. The other organic materials were Eastman Kodak Company products. All experimental data were obtained by the synthetic method. Weighed amounts of soap, detergent, or organic additive and water were added to narrowneck tubes made from 13 x 100 mm. Pyrex test tubes. These were sealed to prevent changes in composition and their contents heated until they formed a homogeneous isotropic solution. On cooling to room temperature all of the systems studiedcontainedwhite opaque solid crystalline soap. The solution temperature, T,, was determined by heating slowly in a water bath until the last trace of opaque white solid had just disappeared to complete the formation of an isotropic or anisotropic solution. The T , values are precise to i l " C . or less. Sodium
X
DLTEROLNT
FIG.1. Solution temperatures, T,, for soap mixtures I
0 0
0
__--
Sodium stearate 50 per cent sodium stearate 50 per cent potassium stearate 1 50 per cent sodium stearate 50 per cent sodium laurate Potassium stearate (data of McBain and Sierichs (9)) Sodium laurate (data of McBain, Brock, Vold, and Vold (14)) I
+ +
~
stearate systems dissolve t o isotropic solution up to a concentration of about 20 per cent soap. Above this concentration the transition is from white solid to liquid crystalline (anisotropic) soap. Systems containing a synthetic detergent or an organic additive seemed to require a somewhat higher soap concentration before liquid crystal was formed, but this was not particularly studied. RESULTS
Solution temperatures for various concentrations of sodium stearate alone and mixed with equal weights of potassium stearate, sodium laurate, and four modern synthetic organic detergents are shown in figures 1 and 2. Our data on sodium stearate are in good agreement with those of McBain, Vold, and Frick (12). The solution temperatures for mixtures containing 77 per cent sodium stearate and 23 per cent Ultravet K , Tween 80, Renex, sodium laurate, and
SOLUBILIZATION A S D COSOLVEKT EFFECTS W I T H SODIUM STEBRATE
485
Triton X-100 decrease in that order at comparable concentrations, but the T , values for even the most soluble mixture are only 4" or 5" below those of an equal weight of sodium stearate. Figure 1 s h o w that the solution temperatures of mixtures with the shorter chain sodium laurate are lower than those with the potassium stearate. Similarly, sodium laurate itself is more soluble than potassium stearate (9, 14). Solution temperatures for the mixtures are closer to those of the less soluble component than to those of the more soluble. Mixtures of sodium stearate with sodium lauryl sulfate have a lower solution temperature below a concentration of 15 per cent but a higher T , above this concentration. Santomerse S o . 3, which is essentially sodium dodecylbenzenesulfonate, lowers the solution temperatures more than Ultrawet K, which also is an alkyl aryl sulfonate type of detergent but contains 15 per cent sodium sul-
0 0
0
50 per cent sodium stearate 50 per cent sodium stearate 50 per cent sodium stearate
+ 50 per cent sodium lauryl sulfate + 50 per cent Ultramet K + 50 per cent Santomerse S o . 3
fate. Triton X-100 lowers the solution temperatures more than the other synthetic detergents. The lowering is greater than with sodium laurate below about 7 per cent total detergent, although somewhat higher above this concentration. All of the synthetic detergents are readily soluble. For example, the solution temperature T , for a 23.2 per cent Ultranet K solution is 51°C. Solution temperatures for various concentrations of mixtures of sodium stearate with several organic additives are given in table 1. The more extensive data with cresol, cyclohexanol, cyclohexylamine, and tertiary butyl alcohol are summarized only in figure 3. Solution temperatures for sodium stearate with butyl cellosolve, 1-octanol, and 2-ethylhexanol are lower than those for the stearate alone at concentrations from about 0.5 per cent to approximately 4, 3, and 5 per cent, respectively. At higher concentrations the solution temperatures rise rapidly to above 100°C. They appeared to consist of a milky emulsion of organic liquid in
486
REYNOLD C. MERRILL
TABLE 1 Solution temperatures, T,, f o r s o d i u m stearate-organic additive systems OPOANIC ADDITIYE
SODIUM STEARATE.
per ccnl
Butyl cellosolve
TC "C.
0.29 0.58 3.55 5.30
> 100
Hydroabietyl alcohol . . . . . . . . . . . . . . . . . . . . . . . . ,
1.13
>100
1-Octanol . . . . . . . . . . . . . . . . , . . . . . . , . . . , , , , , . , . . .
0.42 1.44 2.05 3.61
56
2-Ethylhexanol
Urea
73
65 64
57 61 > 100
0.77 1.72 3.57 4.51 6.90
>100
0.27 1.94 4.57 5.82
65 72 76 >100
58 59 60 61
* I n all cases except for hvdroabietvl alcohol t weight of the organic a itive was 30 per cent of the weight of the soap. The weight of hydroabietyl alcohol was 40 per cent of the weight of the soap.
Y)-
a
STE~RATE
FIG.3. Solution temperatures, T., for sodium stearate in aqueous solutions containing 30 per cent as much organic liquid as soap. a 0
A
A
Sodium stearate Sodium stearate ' Sodium stearate Sodium stearate ~
I
+ cresol + cyclohexanol + cyclohexylamine + 30 per cent tertiary butyl alcohol
SOLUBILIZATION AKD COSOLVENT EFFECTS W I T H SODIUM STEARATE
487
the soap solution. Urea increases the solution temperatures at all soap concentrations. The lowering of the solution temperatures of sodium stearate by amounts of cyclohexylamine, cresol, and cyclohexanol corresponding to 30 per cent by weight of the soap is shown clearly in figure 3. Below a concentration of 2 per cent sodium stearate the solution temperatures increase in the presence of cresol and cyclohexanol. Unless there is about 4 mole per cent excess sodium hydroxide present a similar increase in T , occurs for soaps alone in distilled water (9). This increase in T , is attributable to hydrolysis and formation of the less soluble acid soaps. Hydrolysis is apparently increased by the addition of the essentially neutral cyclohexanol as well as by the acidic cresol but not by the alkaline cyclohexylamine. Similarly, Fryling and Harrington found that the pH of sodium myristate and oleate solutions decreased on the addition of acrylonitrile, styrene, methyl methacrylate, isoprene, benzene, and methyl ethyl ketone ( 2 ) . Sodium stearate is less soluble in the tertiary butyl alcohol solutions than in distilled water. DISCUSSIOK
Sodium palmitate and stearate, the main constituents of tallow soaps, are practically insoluble at room temperature and only become readily soluble at temperatures above 5 5 T . (9). It is therefore customary to add coconut oil, containing a high proportion of the shorter chain lauric acid which forms the more soluble sodium laurate, to tallow in order to obtain a mixed soap readily soluble a t temperatures of practical use. Since coconut oil is more expensive and must be imported, it may be an advantage to replace the coconut oil soap with a cheaper synthetic detergent produced from petroleum or other resources in this country. Such a product itas extensively used by the Army and Navy in World War 11. Our data confirm their experience that a mixture of a soap from a high-titer fat such as tallow with a suitable synthetic detergent has solubility properties similar to those of tallow-coconut oil soaps. Practical experience has indicated that it is sometimes difficult to incorporate the large amount of sodium silicate builders justified on the basis of detergent value into a tallow soap, although this is readily done with a mixed tallowcoconut oil soap. The solubility and the emulsifying and detergent (6. 16) properties of mixtures of sodium stearate (a main ingredient of tallow soaps) and synthetic detergents are similar to those of sodium stearate-laurate (chief ingredient of coconut oil soaps) mixtures. It therefore seems likely that the addition of synthetic detergent to a tallow soap should aid in the incorporation of relatively large amounts of sodium silicate builders. That the solution temperature of sodium stearate is lowered to about the same extent by 30 per cent of the cosolvents cresol, cyclohexanol, and cyclohexylamine as by 100 per cent of the solubilizing, more soluble soaps and synthetic detergents is interesting and theoretically significant. Both mechanisms probably involve the formation of smaller, less heavily hydrated micelles containing both constituents of the solution. When more experimental data are available, it seems likely that a theory of cosolvent effects for water-organic additive solutions can be developed, involving considerations of van der Waals forces, polar and dipolar
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forces, hydrogen bonding, resonance effects, and steric effects similar to that developed for mixtures of nonaqueous solvents (17). The effect of the three polar cyclic compounds cresol. cyclohexanol, and cyclohexylamine may be attributed to a strong tendency t o combine with the carboxyl group of the stearate, thus decreasing its tendency to crystallize into the usual lattice arrangements. Another possibility is that a small amount of a sparingly soluble organic liquid may increase the extent of micelle formation, resulting in greater solubility of the soap. Recent patents have disclosed the use of long-chain amides, nitriles, and other polar derivatives as builders for synthetic detergents (18, 19, 23). A study of their effect on solubility would be of interest, particularly in view of the recent claim (20) that dicyanodiamide increases the solubility of synthetic detergents. SUMMARY
Solution temperatures of various concentrations of sodium stearate are decreased by potassium stearate, to a greater extent by sodium laurate and also by six modern synthetic anionic and nonionic detergents. Cresol, cyclohexanol, and cyclohexylamine also decrease the solution temperatures of sodium stearate, whereas other organic additives have variable effects. REFERENCES AKGELESCU, E., AND POPESCU, D. M.: Kolloid-Z. 61, 247, 336 (1930). FRYLING, C. F., AND HARRINQTON, E . W.: Ind. Eng. Chem. 36, 114 (1944). KOLTHOFF, I. M., AND STRICKS, W.: J. Phys. & Colloid Chem. 63, 424 (1949). MARSDEN, S. S., JR., AND MCBAIK,J. W.: J. Phys. & Colloid Chem. 62, 110 (1948). MCBAIN,J. W.: In Advances in Colloid Science, Vol. I , pp. 99-142. Interscience Publishers, Inc., Kew York (1942). (6) McBAIx, J . W., A N D JOHNSTOX, S.A . : J. Am. Chem. SOC.63, 875 (1941). (7) MCBAIN,J . W., A N D MERRILL,R . C.: Ind. Eng. Chem. 34, 915 (1942). (8) MCBAIN,J . W., AND RICHARDS, P. H . : Ind. Eng. Chem. 38, 642 (1946). (9) MCBAIN,J . W., AND SIERICHS, W. C . : J. Am. Oil Chemists’ SOC.26, 221 (1948). (10) MCBAIN,J . W., ELFORD, W. J . , AXD VOLD,R . D.: J. SOC. Chem. Ind. 69, 243 (1940). (11) MCBAIS,J . W., LAZARUS, L. H . , AKD PITTER, A. V . : Z. physik. Chem. 147A, 87 (1930). (12) MCBAIN,J. W., VOLD,R. D., AND FRICK, 31.:J. Phys. Chem. 44, 1013 (1940). (13) MCBAIN,J. W., VOLD,R. D.. AND JAMESON, W. T.: J. Am. Chem. SOC.61, 30 (1939). (14) MCBAIX,J . W., BROCK,G. C., VOLD,R . D., A N D VOLD,hl. J . : J. Am. Chem. SOC.60, 1870 (1938). (15) MERRILL,R . C., AND MCBAIS,J. W.: J. Phys. Chem. 46, 10 (1942). (16) MORRISROE, J. J., AXD KEWHALL, R . G.: Ind. Eng. Chem. 41, 423 (1949). (17) PALIT,S. R., AND MCBAIN,J. W . : Ind. Eng. Chem. 38,741 (1946). (18) RICHARDSON, A. S.:U. S. patent 2,383,527 (August 25, 1945). (19) RICHARDSON, A. S.,A N D MCALLISTER, W. H . : U . S.patent 2,383,738 (August 28, 1945). (20) SHEPARD, Tu’. A , : U . S. patent 2,445,975 (July27, 1948). (21) SMITH,E. L.: J . Phys. Chem. 36, 1401,2455 (1932). (22) STEARNS, R . S., OPPENHEIMER, H . , SIMON,E., AND HARKINS, W. D.: J. Chem. Phys. 16, 496 (1947). (23) TUCKER,N . B . : U.S. patents 2,383,525-6 (August 25, 1945); U. S. patents 2,383,739-40 (August 28, 1945). (24) WOODMAN, R . M.: J. SOC. Chem. Ind. 62, 185 (1933). (1) (2) (3) (4) (5)
