1494
-2. TV. RALSTOS . W D D . S . EGGESBERGER
alkali soap gels in pinene. The per cent acceleration i h greater n-ith a stearate than a palmitate, and ciecrenv.; in the follon ing order for the cations: Ca
> 8r > Rii
and
1Ig
>
Zn
> C‘d > Hg
The per cent increase or tlrcieav in -etting time is related linearly t o the atomic n eights of the cation? in t!ie :~ddctl,mipi, :lid (lccreu~+11 itli increasing atomic n.eights. I1CFI,I1Ll C L Y (1) Da Fan-o, E . : Cioni. cliirn. inti. npplicata 11, 1%) (192!),; Itid. olii niinerali e grassi 9 ,
105 (1929). (2) HATTIASGIII, C . S . : J . Sci. Iiid. R c w a r c h (,Iritlixi 4, 489 (1946,. (.3) IIATTIASGIII, [;. S . : l’roc. Iiitiiari rlcntl. Sci. 27, 23 (1947). (4) HOIXIW,H. S . : J . l’!iys. C ‘ h ( ~ 1 n22, 510 (19181. (5) HOLMES, H . S., A N D ~ I A X S O 11. S . S.: Colloid Symposium Jlonograpli 6,287 (1928). (6) KLEXGIIRD, E. 3.: ~,ztbricnting G r e a s e s : Their jlnnirfucticre and 17se. Rrinhold Publishing Corporation, Se\v Torli (19373, ( 7 ) LAING,hl. E., ASD RICBAIS,J. W . : Kolloicl-Z, 36, 19 (1924). ( S ) LAWRENCE, A. S. C . : Trans. Faraday Soc. 34, 660 (1938). (9) LBWRESCE, A. S.c . : Trans. Faraday soc. 35, 702 (1939). (10) PALIT, S. R., A N D MCBAIN,J. W.:Oil&Soap23,58,72 (1916);24,190 (1947);Ind. Eng. Chcm. 18, 216, 711 (1946). ( 2 1 ) PRAS.411, AI., H A T T I A X G D I , (;. s.,.%SI) .kIIARKAR! s. P.: I’rOC. Indian .iCad. SCi. 22, 320
(1945). (12) PRAS.W, M.,
H . k w I . k s c ; n I , G . S., . ~ S D X~THL-R, II., Ha.rm.isc>i,I,C i . S., ASD VISFIT.~-.%TII, C . V.:I’roc. Indian Acad. Sci., 21, 56 (1945). (1-2) SMITH, G. H.: J. Am. Oil Chemists’ Soc. 24, 353 (1947). (15) VOLI),R . D.. A N D HATTIANGDI, G . S.: Communicated for publication.
THE ELECTRICAL BEHhVIOR OF DODECYLA.MJIONIUM CHLORIDE IX WATER-ORGASIC SOLTEST SYSTEMS’ ,4. W. RALSTOS
ASD
D. S.LGGESUERGER
Research Laboratory, 9 7 m o w and C o m p a n y , Chicago, Illznois Receiz3ed J w i e ?5,1948
Dodecylammonium chloride is a typical cationic colloidal electrolyte and the electrical behavior of its aqueous solutions has been the subject of several recent studies (9, 10, 13). Its critical concentration has been determined (2) by the dye method to be 1.27 X lo-? molar, which value is in substantial agreement with Presented a t the Symposium on Gel Formation, Dctcrgcncy, Emulsification and Film Forniation in Ton-Aqueous Colloidal Sjstcms which was held under the auspices of the Division of Colloid Chemistry and the Division of Petroleum Cheniistrl at the 113th Mreting of the -41nerican Chernical Socictv, Chicago, Illinois, .ipril, 1918
DODECYLAM?dOSIUN CHLORIDE IS WATER-ORGSKIC
SOLVEST SYSTEMS
1495
that of 1.30 x lo-? which had been preuiously obtained by the conductivity molar has been recently reported (11). method (14). A value of 1.44 X I t has been observed (15) that solutions of dodecylammonium chloride in pure ethanol do not exhibit evidences of micelle formation when investigated by the conductivity method. Additions of small amounts of ethanol to dilute aqueous solutions of dodecylammonium chloride are attended by an irregular decrease in equivalent conductance, whereas similar additions to more concentrated solutions bring about a significant rise. The critical concentration is slightly lowered upon adding a small amount of ethanol ; however, larger additions materially increase the concentration of colloidal electrolyte a t the critical point. The solubility (16) of dodecylammonium chloride is much greater in mixtures of
NUMBERS O N CURVES INDLCATE MOLE PER CENT OF ORGANIC SOLVENT
4NORMALITY OF AMINE SALT
FIG.1. The c~quivalciit c~ontluctivit\of tiodecvla~nmoiiiui~i clilor itlc in acctoiic-n atpr solution
witer and ethanol than in eithcr of the components of such mixtures. The addition of alcohols such as butanol and pentanol greatly lowers the critical concentration. That many of these effects can he attributed to the colloidal nature of dodecylammonium chloride has been shon-n by the facts that thr. solubility of hex-ylammonium chloride, which does not function as a colloidal electrolyte, is regularly reduced by the addition of ethanol to its aqueous solutions (16) and that the conductivity is uniformly lowered (15). I n view of the previously observed behavior of dodecplammonium chloride in mixtures of water and ethanol it wab decided t o extend this work to inchide other water-organic solvent systems and also t o repeat the conductometric 1% ork with ethanol-water mixtures. This present paper is, therefore, concerned with the conductivity behavior of dodecylammonium chloride in acetone, acetonitrile, methanol, a n d cthanol, and in aqueous mixtures of these solvents.
1496
A . W. RALSTOS AND D. X. EGGESBEHGER
EXPERI4IENT.AL
The preparation and properties of the dodecylammoniuni chloride used in this investigation have been previously described (1G). Conductance measurement:: showed none of the organic solvents employed to contain appreciable amounts of electrolytes. Density determinations were made upon the absolute ethanol and methanol and corrections \\-ere made for their water contents. The acetone used was Baker’s C.P. quality. Some difficulty was experienced in obtaining acetonitrile with a sufficiently lor\ conductance. C.P. acetonitrile was shaken with phosphorus pentoside and filtered. The filtrate vas then shaken Tvith anhydrous potassium carbonate and distilled through a p lass-helices-packed fractionating column. It was necessary t o repeat the latter operation before the conductivity was satisfactory. The water employed had a conductarwe of about 1X lop6mhos. The solutions \rere prepared by dissolving the amine salt in the water-orgnnic solvent mixture. Dilute solutions were obtained by adding the appropriate solvent mi.uture to more concentrated solutions. The electrical conductivities were determined in the manner and with the equipment previously described (17). RESULTS A S D DISCI SSIOS
Aiceto~ie-watprsolutions Figure 1 shows the equivalent conductance of dodecylammonium chloride plotted against x/L/-yv in pure water and in wrious niivtures of acetone and water. The solubility of this salt in pure acetone is so small that a conductivity curve could not be obtained. It is apparent that when the solvent contains more than 9.5 mole per cent acetone the curves are no longer typical of those of colloidal electrolytes. I n dilute solutions, below the critical concentration, progressive additions of acetone result in lowered conductivities. The curve obtained for the amine salt in 49.5 mole per cent acetonr appears to be an exception to this statement a t very lon- concentrations of the amine salt. The addition of acetone increases the concentration of dodecylammonium chloride at the critical point. Thus, the value of 0.0144 S in pure water increases t o 0.0177 I\; in 2.65 mole per cent acetone and to 0.0300 -1-in 5.77 mole per cent acetone. This increase in the critical concentration may be attributed to two causes: the decreased number of free ions occasioned by the n-eaker ionizing properties of the solvent and n lessened tendency of the free ions t o associate in the mixed solvent. This lessened tendency towards association may result from the decreased dielectric properties of the solvent, which decrease magnifies the effectiveness of the repulsion of similarly charged ions. The effect of acetone upon the critical concentration is the opposite of that produced by the addition of salts, since the presence of salts materially lowers the critical concentration (6, 7, 19, 20). It has been stated (4) that the position of the critical point is affected by the concentration of the salt ion opposite in charge to that on the colloidal aggregate and is independent of the nature and concentration of the other ion. The effect of various salts and acids upon the electrical conductance
DODECTL.IMUOSIUJ1 CHLORIDE IS IV~ITEI2-OHG.IXIC SOLVEST SYSTEMS
1497
of aqueous solutions of dodecylammonium chloride has been recently investigated, and it has been shown that whereas metallic ions have a decided effect, hydrogen ions are essentially without influence upon the position of the critical point. Such results are explainable on the basis of the decreased solubility of the hydrocarbon portion of the long-chain ions in the presence of salts. It has been shown (18) that the salting-out properties of salts have little connection with the valences of the salt ions. Since acetone increases the critical concentration, it is quite probable that its presence must increase the ability of the solvent t o hold long-chain ions in solution and thus decreases their tendency towards association. It will be noted that the conductivities of solutions of dodecylammonium chloride in 2.65, 5.77,9.50, and 14.04 mole per cent acetone, beyond the critics 100
*
NUMBERS ON CURVES INDICATE NORMALITY OF AMINE SALT
cl
2
IV 3 0
z 0 V
I-
50
z w
-4 4:
L3 0
w
0
0
20 40 MOLE PER CENT ACETONE
1:1(:.2 . T h e ctfcct of acctoiic upon equivalent conductivity of clodccj lammonium chloridc
point, are higher than those in pure water. Solutions in 26.9 mole per cent acetone show a higher conductivity only over a limited concentration range, whereas those in 49.5 mole per cent acetone have a l o w r conductivity over the entire concentration range. It i., therefore, apparent that the effect of the addition of acetone upon the conductance of aqueous solutions of dodecylammonium chloride varies with the concentration of the amine salt. Figure 2 shows the equivalent conductance of various concentration5 of dodecylammonium chloride plotted against the mole per cent of acetone in the solvent. The addition of acetone to dilute solutions of dodecylammonium chloride produces ,z significant reduction in the conductivity. This effect ib reversed with concentration of amine salt higher than the critical point, since increase in the percentage of acetone produces a decided increase in the conductance values. This increase is such that the condiictance reaches a maximum a t from 3 t o 10 mole per cent of acetone. The occurrence of these maxima is undoubtedly dependent upon the colloidal properties of the colloidal electrolyter,
1498
A . TV. RALYTOX AND D. S . EGGESBERGER
since they do not occur with non-colloids. *kt concentrations beyond the critical point it has been postulated (10) that the colloidal particle consists of associated ions which have solubilized the undissociated molecules of the colloidal electrolytes. The solubilized moleciiles greatly reduce the mobility of the colloidal aggregate and impart t o it an abnormal transference number. d reduction in either the size or the number of the micelles will reduce the solubilization of the undissociated molecules. If this results in an increased number of free ions or an enhanced mobility of the micelleh, the caonductitnce of the system will rise. The maxima in the conductivity curveb represent those points at which reduced nhsociation combined with the ionizing properties of the solvent gives maximum values. On the water side of these maxima the conductivity drops because of
A IO NUMBERS ON CURVES INDICATE MOLE PER CENT
t
e z
k0
3 0
OF ORGANIC SOLVENT -
z 0
0
P
5
50-
-I
a ?
3 0
w
-
I
I
0.2
I
I
0.4
I
I
0.6
1
I
0.8
I
I .o
qNORMALlTY OF AMINE SALT
FIG.3 . The equivalent conductivity of dodecylammonium chloride in acetonitrile-water solution.
association attended by soluhilization, n-hereas on the acetone side it drops because of the weaker ionizing properties of the solvent media. Acetonitrile-water solutions The equivalent conductances of dodecylammonium chloride plotted against Z / N , in pure water and in mixtures of mater and acetonitrile up t o and including 66.0 mole per cent of acetonitrile are shown in figure 3. Solutions containing more than 66.0 mole per cent of acetonitrile were not investigated because of the limited solubility of the amine salt in such solvents. The curve for this salt in 3.66 mole per cent acetonitrile is characteristic of a colloidal electrolyte, the conductance decreasing linearly until the critical point and then dropping abruptly. The critical concentration is slightly increased. The presence of 7.89 mole per cent or more of acetonitrile in the solvent brings about a profound
DODECYL.4hIMOXIL31 CHLORIDE IS \YATER-ORGAXIC
SOLVENT SYSTEMS
1499
change in the shape of the curves. Instead of an abrupt drop a t the critical point the curves for 7.89 and also 12.8 mole per cent acetonitrile actually show a slight rise followed by a gradual drop. X similar phenomenon has been recently reported ( 5 ) in the equivalent conductance curves of octadecylpyridinium chloride in methanol-water mixtures, the conductances showing maximum values at concentrations materially remote from infinite dilution. Maxima in equivalent conductance curves are not confined to solutions in mixed solvents, since they have been observed in aqueous solutions of methylene blue (8), hexadecyl- and octadecylpyridinium iodides (1), and in certain quaternary ammonium compounds which contain two long-chain alkyl groups, such as didodecyldimethyl-
w
-
NUMBERS ON CURVES INDICATE NORMALITY OF AMINE SALT
I
I
I
I
I
I
I
ammonium chloride (12). In the latter instance the presence of the maxima was attributed to a retarded solubilization of the undissociated molecules of the quaternary ammonium salts. When the solvent contains more than 12.8 mole per cent acetonitrile the conductance curves fall linearly with concentration. At high dilutions the conductance of dodecylammonium chloride in 66.0 mole per cent acetonitrile is higher than in the other acetonitrile-water mixtures investigated. The effect of the addition of acetonitrile upon the equivalent conductance of various concentrations of dodecylammonium chloride is shown in figure 4. The similarity of these curves to those obtained for the acetone-water mixtures is apparent. Beyond the critical concentration, the addition of small amounts of acetonitrile is attended by an abrupt rise in the conductance values. Lynpublished observations indicate that the cationic transference numbers of dodecylammonium chloride at concentrations higher than the critical point are
1500
A . I\-. RALSTON Ah-D D. S. EGGESBERGER
materially lowered by the addition of acetonitrile. These results are explainable on the basis of a decreased association tendency attended by an increased number of free ions. It is of interest t o note that these maxima occur a t approximately that mole per cent of acetonitrile which represents a transition of the amine salt from a colloidal to an ordinary electrolyte.
IIIethanol-water solutions Figure 5 shows the equivalent conductances of dodecylammonium chloride in pure water, pure methanol, and in various mixtures of water and methanol. The critical concentration of this salt increases from 0.0114 ,V in pure water t o 0.0164 in 4.82 mole per cent methanol and 0.0250 in 12.71 mole per cent
>
100
t 2
NUMBERS ON CURVES INDICATE MOLE PER CENT
t 0
a a
OF ORGANIC SOLVENT
z 0
0 I-
50
J
a >
-
3 0 W
I
I
02
I
I
0.4
NORMALITY
1 I 0.6 OF AMINE SALT
I
I
0.e
I
I
ID
FIG.5 . The equivalent conductivity of clodec~lamnloniu~n chloritic i n iiic,tliariol-n-atc’!’ solution.
methanol. Those solutionb which contain 30.8 mole per cent or mole of methanol show no discontinuities in their conductance c111vw. ‘l’hc high conductanc~s of dilute solutions of this salt in pure methanol u r note\vorthy. ~ The equivalent conductances of various concent ixtions of t1odecyl:immunium chloride plotted against the mole percentage of mt~thnnolin the -ol!*eiit arc sho~vnin figure 6. At concentrations lower than the critical point the equivalent conductance is a t a minimum at approximately 40 niolc per cent meth:inol, the values then rising smoothly as the composition of thc wlycnt mixture approache5 either pure component. At concentrations some\\ hat beyond the critical point the addition of methanol is attended by a slight drop i n equivalent conductance values. This drop is then followed by an appreciable ri.;e. These curve:, differ from those obtained for acetone-water and acetonitrile-water mixtures in that the maxima orcur a t higher concentrations of the organic addend. The ability
DODECTLAJIJIOSIU~I CHLORIDE IX \V'STER-ORG.kTIC
SOLVEST SYSTEMS
1501
of methanol t o reduce association is, therefore, less than that of acetone or acetonitrile, as evidenced by the initial drop in conductance and also by the larger amounts required to produce a maximum value. The conductance of certain concentration\ of thiq amine salt, beyond the critical point, is actually sonieTvhat greater in pure methanol than in pure water. This accounts for the relative flatnesq of the curves.
Ethanol-water solutions The electrical conductance of solutions of dodecylammonium chloride in aqueous ethanol has been previously investigated (1G) ; however, because of n later correction (11) of the equivalent conductance curve for this amine salt in pure water, it appeared advisable to repeat this Tvork. The equivalent con-
100
NUMBERS ON CURVES INDICATE NORMALITY OF AMINE SALT
>-
z! 1 t 0
3 0
z
0 0
t-
5 50
-I
a
L
3
0
w
0
0
20
40 60 MOLE PER CENT METHANOL
00
100
FIG.6. The effect of inethanol upon cquivalcnt conductivitj- of dodccylammoiiiurn chloride
cluctances of solutions of dodecylammoniuqi chloride in pure water, pure ethanol, and in mixtures of ethanol and m t e r are shon-n in figure 7. The presence of 3.2'7 mole per cent of ethanol in the solvent lowers the critical point slightly, the 1-alue of 0.0144 S in pure water being reduced t o 0.0130 S in this solvent. Corrin and Harltins (3) have studied the effect of ethanol addition upon the critical concentration of dodecylammonium chloride, using dichloroflriorescein as the indicator. Their results shoJved an abrupt drop in the critical concentration of this amine salt attending successive additions of ethanol up to 1: per cent ethanol. Our results indicate a reversal of this effect, since 7.06 mole per cent ethanol gives a slightly higher critical point than that obtained in pure water. The addition of 9.93 mole per cent ethanol increases the critical concentration to 0.0454 S,whereas 16.2 or higher mole per cent shows smooth curves for this salt. The equivalent conductance of dilute solutions of dodecyl-
1502
A. I\*. RALHTOX AKD D. N. EGGENBERGER
ammonium chloride regularly decreases upon the addition of ethanol ; however, the conductance of more concentrated solutions is perceptibly increased.
* 100 t L !-
NUMBERS ON CURVES INDICATE MOLE PER CENT OF OROANIC SOLVENT
0 =J
0
t
0 0
c 50 A
s
= i
0 W
0 0
02
0.4
NORMALITY
0.6
0.8
1.0
OF AMINE SALT
FIG.7 . Tlic equivalent conductivity of tlodecylammoriiuni cliloride in ethanol-water solution.
MOLE PER C E N T ETHANOL
FIG.8. Thc ei’frct of ethanol upon cyuivaleiit conductivitv of t l o d c ~ ~ ~ l a r n m o ~ cliluritlc iiuni
Figure 8 shows the effect of ethanol upon the equivalent conductances of rarious concentrations of dodecylammonium chloride. The effect of ethanol is qualitatively similar t o those of the other three addends investigated. Thebe
DODECYLAM?dONIUAf CHLORIDE IN WATER-ORGAKIC
S O L V E h T SYSTEMS
1503
results, combined wit'h the previously observed lowering of the cationic transference number (15) in the presence of ethanol, indicate a decreased tendency towards association of dodecylammonium chloride in the solvent mixture a s compared t o pure water. The addition of organic addends to aqueous solutions of dodecylammonium chloride brings about a progressive decrease in colloidal properties. This results in a transition of the amine salt from a colloidal to an ordinary electrolyte and maximum values in the equivalent conductances occur in the neighborhood of this transition point. Further experiments upon the effect of organic addends upon the electrical conductances of cationic colloidal electrolytes are now in progress. STJMM.4RY
The equivalent conductance of dodecylammonium chloride has been det,ermined in aqueous solutions of acetone, acetonitrile, niet'hanol, and ethanol. The concentration of dodecylammonium chloride a t the critical point is materially increased by the addition of acetone, acet'onitrile, or methanol. Small additions of ethanol decrease the critical concentrat,ion; however, larger additions bring about a substanttial increase. The addition of these solvent's to aqueous solutions of dodecylammonium chloride a t roncentratioiis beloiv the critical point of t'he amine salt lowers t,he critical conductance. Additions to concentrations beyond the critical point materially raise the equivalent conductance, maximum values being attained. The positions of these maxima are dependent on the concentration of amine salt and the nature of the organic addend. These results have been interpreted as evidencing a transition of t'he dodecylammonium chloride from a colloidal t o an ordinary electrolyte. REFER E S CE S (1) & t o w s , GRIEGER, ].:V.F.HS, A S I ) I ~ R A U SJ. : Am. Chcm. 8or. 69, 1835 (1947). (2) ('ormi?; ASD HARKISS: .J. Akni.Chem. Sac. 69,679 (1947)j J . ('hem. Phys. 14,641 (19Xi). (3) C~ORRIN ?LXDHARKISS:J . Chem. l'hys. 14,640 (1946). (4) CORRISA N D HARKISS:J . A m . Chcm. Sac. 69,683 (1947). (5) EVERS, GRIEGER,. ~ S DKRAUS:J . Ani. Chem. Soc. 68, 1137 (1946). (6) IIARTLEY: J. Chem. Soc. 1938,1968. (7) 3 I c B . u ~ASD BRAI)Y:J. i l m . Chem. Soc. 66, 2072 (1943). (8) M o I L n m ~COLIJE,ROBIXSOS, ASI) HARTLEY: Trans. Faraday 8oc. 31,120 (193.5). (9) RAISTOSASD EGGESBEGGER: J. Am. Chem. Sac. 70,980 (194s). (10) R A L S ~ O .4su S EGGESBERGER: J. Ani. Chem. Sac. 70,083 (1948). ASD EGGESBERCER: J . ilm. Chem. Sac. 70,436 (1948). (11) RALSTOS (12) RALSTOS ASD EGGESBERGER: J. A m . Chem. soc. 70,977 (194s). (13) RALSTOS ASD HOERR: J . Ani. Chcm. SOC.69, 883 (1947). (14) R.41,STOs .4SD HOERR:J. Am. Chem. S O C . 64, 772 (1942). (15) RALSTON ASD HOERR: J. Am. Chem. Soc. 68,2460 (1946). (16) RALSTOS . ~ S D HOERR: 3. d m . Chem. SOC.68,851 (1916). (17) RALSTOX, HOERR, . 4 S D HOFF : J. Am. Chem. Soc.64,97(1942). ASD FAILEY: Chem. Revs. 4,285 (1927). (18) RASDALL (19) TARTAR ASD CADLE:J. Phys. Chem. 43, 1173 (1939). (20) \$'RIGHT, ABBOTT, SIVERTZ, A S D TARTAR: J. h i . Che111. S O P . 61, 553 (1939).
