SOLUBILITY O F ALKALI
DIXONYLNAPHTHALENESULFONATES
3453
The Solubility of Alkali Dinonylnapthalenesulfonates in Different Solvents and a Theory for the Solubility of Oil-Soluble Soaps
by R. C. Little and C. R. Singleterry U.S. Naval Research Laboratory, Washington, D. C. 20890 (Received March $6, 1964)
The solubility of the alkali metal dinonylnaphthalenesulfonates parallels that of dinonylnaphthalene in low polarity solvents. In sulfonate-solvent systems showing limited solubility, the equilibrium is characteristic of a liquid-liquid pair having a critical solution temperature, the condensed soap phase behaving as an extremely viscous liquid. Micelle size in low polarity solvents decreases as the solubility parameter increases, probably because such a variation improves the match in solubility parameter between micelle and solvent by exposing more of the polar core. I n moderately polar solvents, the sulfonate is freely soluble as an equilibrium mixture of monomer, dimer, and possibly higher units. Pure crystalline alkali metal carboxylates do not show high solubility in hydrocarbons unless they are heated to a temperature at which they pass over into a liquid-like phase; noncrystalline carboxylates, or mixtures of many different branched chain carboxylate species, have high or unlimiteld solubilities and appear to behave as liquid-liquid systems in much the same way as the (alkali metal sulfonates.
Introduction The behavior of the dinonylnaphthalenesulfonates has been well studied in benzene,’p2 and this report is an extension of that work into other solvent systems with a view toward determining the influence of cation and solvent upon the apparent soap solubility (defined as the total solubility of associated and nonassociated sulfonate-derived species which are in thermodynamic equilibrium). The published data on the solubility of soaps in various solvent environments are often difficult to interpret, each soap-solvent system appearing to have its own individual character.3-lo Winsorll has attempted to clarify and classify some of this work. His theory, however, refers primarily to solutions containing water as an important component and is most readily exemplified in systems of high soap content. The need for a more comprehensive theory of soalp behavior in nonaqueous systems continues to exist.
(abbreviated LiDNNS, NaDNNS, and CsDKNS, respectively) were prepared by neutralization of an aqueous alcoholic solution of the acid by the appropriate base. The soaps were then lyophilized and stored in a desiccator over PZO, until used. This acid and its salts have been described previous1y.l All of the solvents used were ACS grade or better except for the 0.65, 1, 2, and 10 centistoke silicones, which were commercial samples. All solvents were passed through Linde molecular sieve materials and Florisil in order to remove water and polar contami~
~-
(1) 6. Kaufnian and C. R. Singleterry, J. Colloid Sci., 10, 139 (1955).
Experimental
(2) S. Kaufman and C. R. Singleterry, ibid., 12, 465 (1957). (3) S. S. Marsden, Jr., and J. W. McBain, J . Chem. Phys., 16, 633 (1948). (4) S. R. Palit and J. W. McBain, Ind. Eng. Chem., 38, 741 (1946). (5) G . H. Smith and J. W. McBain, J. Phys. Colloid Chem., 51, 1189 (1947). (6) P. N. Cheremisinoff, J . Am. Oil Chemists’ Soc., 28, 278 (1951). (7) A. Bondi, J. Colloid Sci., 5, 458 (1950). (8) S. M. Nelson and R. C. Pink, J . Chem. SOC.,1744 (1952). (9) H. Kambe, bull. Chem. Soc. Japan, 35, 265 (1962).
The lithium, sodium, and cesium salts of a special grade of dinonylnaphthalenesulfonic acid (HDNNS)
(10) I. Satake and R. Matuura. Kolloid-Z., 176, 31 (1961). (11) P. A. Winsor, “Solvent Properties of Amphiphilic Compounds,” Butterworth and Co., Lhd., London, 1954.
Volume 68, Number 18 December, 196’4
R. C. LITTLEAXD C. R. SINGLETERRY
3454
nants. A check on the efficiency of the percolations was made, in the case of dioxane, by means of a Karl Fischer titration. No water could be detected within the precision of the method. The cyclohexane used was of very high purity (99.92 mole %) and was obtained by fractional crystallization. The dimethylsiloxanes were specially prepared monodisperse species available from the Dow-Corning Corp. The nitroparaffins were fractionally distilled from the best available grade of Eastman Kodak solvents. Their boiling points and refractive indices corresponded closely to the literature values. The preparation and purification of the fluoro compounds have been described.12 All solvents were stored over molecular sieve pellets in glass-stoppered bottles and were used as soon as possible after percolation. Benzil (used for calibrating the osmometer) was twice crystallized from anhydrous ethanol, dried a t 50", and stored in a vacuum desiccator over Pz05until used.
Methods The apparatus used for the determination of the apparent soap solubility in various solvents consisted of a stationary NBS certified 0.1-deg. thermometer upon which was mounted a baffle to promote agitation. A rotator turned a solution cell within an air space surrounded by a bath of controlled temperature. A magnetic stirrer provided agitation of the bath while a copper heat exchange coil permitted easy change of temperature conditions by means of the thermostated reservoir. A solubility determination was made by preparing a sulfonate solution of known molality a t a higher temperature and allowing it to cool a t a rate of O.l"/min. in the vicinity of the temperature a t which precipitation would occur. Rates of cooling from 0.05 to 0.2"/min. gave the same results within the experimental error of h0.2". The point at which precipitation occurred was determined by visual observation of the turbidity in a concentrated light beam directed at a right angle to the observer. It should be n o k d that the separating phase in the solvent-rich systems was soap saturated with solvent. The possibility of undercooling in these systems was explored by comparing the temperature for disappearance of turbidity upon warming with that for its appearance upon cooling. An undercooling no greater than 0.2" was observed and is considered to be within the precision of the solubility determinations. Vapor pressure lowering data were obtained by means of a commercial thermoelectric device-the I\Zechrolab Model 301A osmometer. I n all cases, a drying agent-Linde molecular sieves-was added to the solvent cup The Journal of Physical Chemistry
in order to maintain a water-free solvent atmosphere in the measuring chamber. Some difficulty was experienced with the osmometer in measuring solutions containing significant concentrations of ions. This was due to the fact that the thermistor leads of the nonaqueous type probe support are not insulated. Substitution of a matched pair of glass probe-type thermistors for the glass bead type furnished with the commercial unit eliminated this difficulty, which was apparently due to ionic conductaiice between the thermistor leads. Liquid crystal systems were detected by means of crossed Polaroid sheets. Conductivity measurements were made with a portable conductivity bridge, Industrial Instruments, Inc., Type RC16Bl. Measurements were made at 35.02 rt 0.02" in a cell protected from atmospheric humidity by means of molecular sieve materials. The cell was surrounded by an oil bath.
Results I n order to facilitate discussion of the experimental results the sulfonate-solvent systems have been divided into four rather arbitrary classes based upon their experimental behavior (see Table I). T y p e I . Sulfonate i s Miscible with the Solvent in All Proportions; Micellar Size I s Constant in a Given Solvent. Figure 1 presents the data obtained from vapor pressure lowering measurements in terms of osmotic coefficient us. concentration. Two generalizations may be made which are consistent with results previously obtained by Kaufman and Singleterry2 on benzene solutions of lithium and sodium dinonyl04
-
SOLID POINTS t i DNNS OPEN POlNTS HALF SOLID POWTS
q
0
Eh DNNS
* Ce WNL
t %
02
5 CHLOROFORM lL1,Ndl: BENZENE (-1 BENZENE
IL,,N a l ( EClr ma1
CICLOHEYANE Ol
d N-HEPTANE 0 DIMETHYL SILOXANE DIMER
6 . 2
0 os
010
1
I
I
015 MOLMIY
020
o e5
Figure 1. Osmotic coefficient us. concentration for sulfonates in low polarity solvents (35"). (12) P. D. Faurote, C. M.Henderson, C. M. Murphy, J. G. O'Rear, and H. Ravner, Ind. Eng. Chem., 48, 445 (1956).
SOLUBILITY OF ALKALIDISONYLXAPHTIHALENESULFONATES
3455
Table I : Solubility of Sodium Dinonylnaphthalenesulfonate in Different Solvents Solvent
NrsDNNS, 1 m soh. a t 2 5 O
Dielectric constant
Type I solvents 1.924 (25") 2.01 (25') 2.2 (25") 2.21 (25") 2.24 (25") 2.27 (25") 4.81 (25")
%-Heptane Cyclohexane Siloxane dimer Dioxane Carbon tetrachloride ]Benzene Chloroform
Siloxane nonoamer Siloxane octamer Siloxane heptamer Bis( $ '-heptyl) P-methylglutarate Ethyl perfluorobutyrate Bis( $'-amyl) diphenate Bis( $'-propyl) diphenate (,'-Amyl alcohol Nitroethane Nitromethane Acetonitrile Water
m
m
m
m
m
fb m
0)
m
f
m
m
f f f
m
m
f m
m
f f
m
f
m
f
m
m
m
m
m
m
m
m
0.12
m
m
0.20 0.30 S 0 IO001 0.0001 0,001 0.01 0.04 >1
