[C:ONTRIBCTIOK FROM THE
RESEARCHLABORATORY O F ARMOURAND COMPANY]
SOLUBILITIES OF DODECYL- AND OCTADECYL-TRIMETHYLAMMONIUM CHLORIDES IN ORGANIC SOLVENTS R . A. RECK, €1. J. HARWOOD,
AND
A . W.RALSTON
Received Ft?bruary lY, 194Y
The quaternary ammonium salts which contain at least one long-chain hydrocarbon group are rapidly becoming an jmportant class of compounds, many representatives of which have been synthesized within recent years. Such compounds function as cationic colloidal electrolytes when dissolved in water and the electrical conductivities of aqueous solutions of the alkyltrimethylammonium bromides have been studied in detail (1). On the other hand, the literature upon the solubilities of the long-chain quaternary ammonium compounds in organic solvents has been fragmentary and largely confined to qualitative statements concerning specific compounds. When Krafft and Moye (2) first described hexadecyltriethylammonium iodide they reported it to be soluble in warm water and ethanol but insoluble in ether. Later. Reychler (3) observed this compound to be soluble in warm water but almost insoluble in cold water, soluble in ethyl acetate and in ethanol, and insoluble in ether. Recently, Shelton and coworkers (4)have prepared a number of quaternary ammonium salts containing a long-chain hydrocarbon group and have stated that, in general, they are soluble in water and ethanol, sparingly soluble in acetone, and nearly insoluble in diethyl ether. In an attempt to obtain a broader understanding of the solubility behavior of the long-chain quaternary ammonium salts we have determined the solubilities of two representative compounds of this class, namely, dodecyltrimethylammonium chloride and octadecyltrimethylammonium chloride, in a variety of organic solvents. EXPERIMEiVTAL
Preparafzon of dodecyltrimethylummonium chloride. T o a mixture of 0.1 mole (18.5 9.) of dodecylamine (f.p. 28.2S0), 12 cc. of water, and 200 cc. of ethanol was slowly added 13.7 cc. of 85% formic acid. After cooling to about W", 20 cc. of 36% forinaldehyde was added and the reaction was allowed t o proceed for two hours a t 60-80". When the evolution of carbon dioxide stopped, the solution n-as made alkaline with sodium hydroxide and the amine was separated and dried over sodium carbonate. The amine w m then fractionated through a two-foot Stedman-packed column. Seven fractions were taken and a freezing point was determined on each fraction. Fractions 2-5 inclusive had the freezing point -20.30" and were combined. The over-all yield was So$$. The quaternary ammonium salt was prepared by adding methyl chloride t o the tertiary amine, mixed with 50 cc. of Skellysolve A (b.p. 35-40'), in a bomb and heating for two hours a t 60". The bomb was opened slowly t o permit the gradual escape of methyl chloride and solvent. The product was removed and recrystallized several times from 200 cc. of benzene to which just enough ethanol was added t o effect solution. The quaternary amnoniuni salt was dried and stored in a desiccator. I t is slightly hygroscopic. Preparation of octadecy1trimethyZammoniur.t chloride. A procedure similar t o the above was employed. The octadecylamine used had the freezing point 52.86" and the di5L7
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RECK, HARWOOD, A N D RALSTON
methyloctadecylamine the freezing point 22.89'. The quaternary ammonium salt is not hygroscopic. The freezing points of the amines were determined by previously described methods (5). The quaternary ammonium chlorides do not possess definite melting points. They begin t o soften a t 70" and decompose at 180". The solubilities of the quaternary ammonium salts were determined in sealed tubes by the method and with the apparatus previously described (6, 7,8,9). RESULTS AND DISCUSSIONS
Since both dodecyl- and octadecyl-trimethylammonium chlorides are true salts one would expect them to be difficultIy soluble in the non-polar and in the slightly polar solvents. This study, which comprises the solubility determinations of these two salts in a series of organic solvents of varying polarities, broadly confirms this generalization. Notable exceptions are the appreciable solubility of these quaternary ammonium chlorides in the two chlorinated solvents investigated, chloroform and carbon tetrachloride. The high solubilities in chloroform may possibly be explained by hydrogen bonding between the solute and
G.
SALT
30'
40'
1.21 -
34.2
- I-
-DodecylOctadecyl-
-
PEE 100 G. SOLVENT
soo
45"
102
-
~
1
gel
-
550 60" 65' ___ --
0.402
5.04
36.2
solvent molecules. Solvation may account for the appreciable solubilities of these salts in carbon tetrachloride, although this phenomenon is most frequently encountered when both solute and solvent are polar substances. Saturated solutions of dodecyltrimethylammonium chloride in carbon tetrachloride form gels above 4 5 O , and this salt could not be induced to crystallize from chloroform since it forms gels a t all the concentrations investigated. The solubility of octadecyltrimethylammonium chloride in chloroform is shown in Curve C, Figure 1, and the solubilities of the two quaternary ammonium chlorides in carbon tetrachloride are shown in Table I. Both dodecyl- and octadecyl-trimethylammonium chlorides are essentially insoluble in n-hexane, cyclohexane, benzene, and ethyl acetate. No attempts were made to determine their actual solubilities in these solvents; however, the following observations confirm their limited solubilities. The solubility of dodecyltrimethylammonium chloride is < 0.2g. in 100 g. of n-hexane,
