Conductances of Solutions of Several Alkyl Sulfates and

662

F. D. HAFFNER, Q. A, PICCIONE, AND C. ROSENBLUM

Downloaded by NEW YORK UNIV on September 7, 2015 | http://pubs.acs.org Publication Date: June 1, 1942 | doi: 10.1021/j150420a008

REFERENCES (1) KASSEL,L.: Chem. Rev. 18, 277 (1936). (2) LANDOLT-B~RNSTEIN: Physikalish-chemische Tabellen, 5th edition, 1st Erg., p. 702. J . Springer, Berlin (1927). (3) NERNST, W.:Die theoretischen und etperimentellen Crundlagen de8 neuen Wdrmesatzes. W. Knapp, Halle (1918). (4) NEWMAN, F. W.: Trans. Cambridge Phil. SOC.13, 146 (1883); 14, 237 (1883).

COKDUCTANCES OF SOLUTIONS OF SEVERAL ALKYL ‘SULFBTES AND SULFOSUCCINATES FREDERICK D . HAFFNER, GARY A. PICCIONE, AND CHARLES ROSENBLUM’ Frick Chemical Laboratory, Princeton University, Princeton, New Jersey Received April 10, 1042

Para&-chain salts display a remarkable tendency to concentrate a t interfaces, because they contain groups which differ greatly in polarity. This is demonstrated in a striking manner by their surface activity in water (14,18, 24,25, 27, 30,31)and at interfaces between water and organic liquids (14,18, 25, 27,30, 31). In addition to being wetting agents, many of them are detergents and emulsifying agents, properties which suggest that these substances are capable not only of collecting in a two-dimensional 6lm as at a surface, but also of forming three-dimensional aggregates even in fairly dilute solutions. The solubilities (27,30, 31) of these substances, as well as viscosity (11, 34) and denpity (2,4, 11, 34) measurements of their solutions, indicate the occurrence of aggregation above a certain “critical concentration for micelles” (5). This conclusion is supported further by their effect on the electrophoretic velocity (26) of certain colloids, by minima which occur in surface tension os. concentration curves (18,24, 25, 31), by electromotive-force (17,22, 28) and freezing-point (16,21) data, and by changes in slope which appear in curves of diffusion coefficients (9, 15), transference numbers (8),and conductances (5,12, 16,17,20, 23,27,31,32,33)as a function of concentration. Furthermore, the existence of micelles in dilute solutions of para&-chain compounds has been verified by x-ray examination (10,11, 29). The work cited above is concerned primarily with substances contributing normal-paraifin-chain ions to solution, and the question arises (7) as to whether micelle formation would be displayed by compounds with a more complicated disposition and structure of the paraifin groups. This can be tested by comparing the electrolytic conductance of solutions of normal-paraifin-chain salts, such as alkyl sulfates, with those of d i e l sulfosuccinates. The latter class of electrolytes has two hydrocarbon residues separated by a succinic acid radical; and derivatives containing branched paraffin chains are available. 1 Present

address: Merck & Co., Inc., Rahwsy, New Jersey.

CONDUCTANCES OF SOLUTIONS OF ALKYL SULFATES

663

Conductances were measured because one of the consequences of aggregation in paraffin-chain electrolytes is a marked decrease in the equivalent conductance of solutions a t a characteristic “critical concentration for micelles” (5). Thus the existence of such a break in the conductivity curves of the sulfosuccinates would be construed as evidence of micelle formation.


EXPERIMENTAL

Materials Pure samples of octyl, decyl, and dodecyl sodium sulfates (C,HZ,+SOJa) were made available through the extreme kindness of Dr. S. Lenher of the Fine (Organic) Chemicals Division of E. I. du Pont de Nemours and Co. They were prepared by esterification and neutralization of carefully fractionated alcohols. As a check on their purity, sodium was determined by ignition, sulfuric acid treatment, and final weighing as anhydrous sodium sulfate. These analyses showed 9.85 per cent sodium in the C8, 8.79 per cent sodium in the CIO,and 7.95 per cent sodium in the CU alkyl sulfate as compared with the respective theoretical percentages of 9.90 per cent, 8.83 per cent, and 7.97 per cent. The sodium sulfosuccinates studied were the diisobutyl, the di(methylamyl),2 di-n-octyl, and the di(2-ethylhexyl) esters. They have the general structure NaSOsFHCOOR I

CHtCOOR and will be referred to respectively as IB, MA2, OT-IC, and OT, which are their common trade designations. These materials were commercial products generously provided by Mr. C. A. Sluhan of the American Cyanamid and Chemical Corporation. They were all subjected to further purification. The IB, MA, and OT were salted out of aqueous solution, and the wetting agent separated from salt by repeated solution in acetone, filtration, and evaporation. This was continued until all salt was eliminated. The OT-N was crystallized by adding 95 per cent alcohol to its warm concentrated aqueous solution. The sodium content of the treated products, determined as described above, agreed with the theoretical values to about 99 per cent. All compounds were dried to constant weight by standing a t room temperature in sulfuric acid or phosphorus pentoside desiccators. Potassium chloride used for determining cell constants was obtained from reagent-grade salt in the usual manner, which involves precipitation from concentrated solution by addition of strong hydrochloric acid solution, filtration, alcohol washing, and fusion in platinum. Distilled water with a specific conductance of about 2.5 X 1o-B reciprocal ohms was used in all the more concentrated solutions. For the preparation of solutions more dilute than 0.005 M , this water was distilled first from acid permanganate and then from alkaline permanganate through a block-tin condenser, and finally stored in paraffined containers. The specific conductance of

* This radical is 1-methylisoamyl.

66664

F. D. HAFFNER, G. A. PICCIONE, AND C. ROSENBLUBI

thewwater was cut in half thereby. Only in solutions less concentrated than 0.003 Jf was the specific conductance of the water 1 per cent or more of the total conductance.


AppaTatus and

PTOCedUTe

Conductivity measurements were performed using a simple Wheatstone bridge arrangement in the manner conventional for electrolyte solutions (3). KO attempt was made to achieve great precision, since the purpose of the investigation was to detect gross changes in the slope of conductivity-concentration curves. High-frequency alternating current (1000 cycles) was supplied by a microphone hummer, and telephonic headphones were used to detect the balance point. A Leeds and Northrup Kohlrausch-type drum-wound slide-wire served &s the variable resistance ratio of the bridge. Two resistance boxes made of manganin wire were employed as the fixed resistance of the bridge. One had a resistance as high as 100,OOO ohms and was used for measuring the specific conductance of the water samples; and the second, which went up to 11,OOO ohms, was used for the salt solutions. Two conductivity cells were used for the solutions of unknown resistance. One contained electrodes fixed in a vertical position and supported by horizontal leads, while the second was a “dip” cell provided with horizontal electrodes. The cell constants were about 0.25 and 0.13, respectively. In both cells the circular electrodes and supports were of platinum, the electrodes being platinized before use. Measurements were made in a mineral-oil thermostat maintained at 25°C. 0.1” by means of a two-bulb toluene regulator, a vacuum-tube relay, and a knife-type immersion heater. Cell constants were determined at frequent intervals, using standard potassium chloride solutions (0.1 and 0.01 D)prepared according to the directions of Jones and Bradshaw (13). More than half of the paraffin-chain salt solutions were prepared by direct weighing of the solid (correcting to vacuum by assuming unit density) into calibrated volumetric flasks. The remainder were obtained by dilution. All solutions were stored in Pyrex Erlenmeyer flasks stoppered by corks wrapped in tin foil. Cells were always flushed at least four times between each measurement. The conductance of each solution was measured at least twice. The reproducibility of the equivalent conductances recorded below was usually better than h0.2 unit, except at concentrations of 0.001 M or below. RESULTS

Conductances as a function of concentration are reported numerically in tables 1 and 2 and depicted graphically in figures 1 to 3. The tables show the concentration (normality) of paraffin-chain salts followed by the corresponding equivalent conductance, while in the figures conductance is plotted against the square root of the normality in order to compress the abscissae. Figure 1 concerns the three alkyl sulfates. The Cusalt was included among the sulfates as & check on the experimental method, since the conductances of its aqueous solutions have been measured. In each case, there occurred a decrease in conductance indicative of micelle formation, the break being increasingly abrupt

665


the longer the aliphatic chain. The critical concentrationsa for micelle formation are approximately 0.13 N , 0.031 N , and 0.0081 N for the CS,CIO,and C I ~


TABLE 1 Equivalent conductance of solutions of alkyl sulfates

N

A

N

A

0 .c ” 9 9 0. ooo998 0.002995 0.006988

75.9 73.5 71.4 70.1 68.0 66.2 64.5 58.2 52.7 46.4 41.7 38.4 39.1 39.9

0.000193 0.000985 0. 003002 0.005003 0.008005 0.01001 0.01737 0.03474

76.1 71.3 69.3 68.4 66.8 59.8 45.2 35.1

71 1 70 5 68 3 666

0.0099&1 0.01997 0.02995 0.04992 0.07987 0.09984 0.1520 0.2000 0.2995 0.5503 0 6648

648 62 3 60 7

~

j

1

0 OM996 0 009607 0 01999 002903 0 03997 0 04996 0 06995

TABLE 2 Equivalent conductances of solutions of alkul sulfosuccinates

I1

MA I1____

IB

OT-N

OT

_ _ _ ~ _ _ _ _ 0 0 0 0

000503 001006 002991 001986 0 007076 0 009971 0 01651

77 72 67 67 65 64 64

3 8 9

1 5 7 9

I 0 0 0 0 0 0 0

I

000545 001089 003024 005MO 008064 01008 02969

71.3 68.5 67.0 65.8 64.3 63.9 60.4

O.OCO41.1 0.000943 0.001798 0.002876 0.005137 0.006280 0.009302

75.6 75.0 71.1 67.5 60.2 57.9 52.5 45 8

Y

1.

0m o 4 0 001011 0 001607 0 002026 0 003014 0 004045 0 005057 0 006027 0 008090 0 009991 0 01618 0 02023 0 02526 0 03236

69.4 67.5 67.1 66.4 66.3 66.1 65.9 65.1 62.7 6! .1 57.5 55.7 53.9 51.3

compounds, respectively. The value for dodecyl sulfate agrees with the conductivity findings (0.0074.008N ) of Lottermoser and Puschel (17) and Howell These are averages of various Ncr,values obtained from plots of equivalent conductance N , W S , and N’j3, and from specific conductance us. N curves (33) for each compound except for the octyl sulfate, in which case the K-N curve gave a value of 0.07 N . Such a discrepancy has already been noted in the literature (16). 3

us.

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F. D. HAFFNER, Q. A. PICCIONE, AND C. ROSENBLUM


and Robinson (12) for this compound, and is the same critical concentration (approximately 0.008 N ) as was observed with dodecylsulfuric acid (17). It is of interest to note that for the free sulfonic acid (16) Ncr.is approximately 0.008 N , although the values obtained by different methods for the corresponding sodium sulfonate (", 30, 33) are somewhat higher. The critical concentra-

FIG.1. Equivalent conductance of solutions of sodium octyl sulfate, sodium decpl sulfate. and sodium dodecyl sulfate.

eo(

I

m-

50

#

I

I

ISOBUTYL

1

2-ETHYL HEXYL

-

rn

I

40

0

0.1

0.2

0.3

I

I

0.4

0.5

FIG.2. Equivalent conductance of solutions of sodium diisobutyl sulfosuccinate and sodium di(2-ethylhexyl) sulfosuccinate.

tion of 0.031 N for the Cl0 compound is slightly below the values (27, 30, 33) (approximately 0.04 N ) found for the sulfonic acid derivative, while the Nor.= 0.13 of the octyl sulfate is the same aa was found for sodium octyl sulfonate (27). The decyl sulfate curve exhibits a minimum conductance in 0.22 N solution, while the conductance of the octyl compound seems to approach a minimum at

667


about 0.6 N , though the exact position of the latter minimum cannot be determined from the data. The sulfosuccinates also show evidence of micelle formation, judging from figures 2 and 3. Gradual breaks in the conductance curves of the diisobutyl and the di(methylamy1) derivatives occur at approximately 0.014N and 0.03N , respectively. The di(2-ethylhexyl) compound shows a distinct drop a t 0.0055 N . For the di-n-octyl sulfosuccinate, the critical concentration must occur a t about or below O.OOO9 N.' Downloaded by NEW YORK UNIV on September 7, 2015 | http://pubs.acs.org Publication Date: June 1, 1942 | doi: 10.1021/j150420a008

80

I

70

-

60

-

50

-

I

0

0.1

I

1

METHYL AMYL

1

N-CCTYL

F ,

I

40

I

02

03

I

0.4

05

FIQ.3. Equivalent conductance of solutions of sodium di(methylamy1) sulfosuccinate and sodium di-n-octyl sulfosuccinate.

TABLE 3 Limiting equivalent conductance COYHlDND

Octyl sulfate.. ................................... Decyl sulfate.. .................................... Dodecyl sulfate.. ..................................

79 76

IB ................................................

M A . ..............................................

74 75

OT................................................

73 70

29 26 24 25 23 20

Below their critical concentrations, paraffin-chain salts exhibit approximately normal electrolyte behavior, so that it is possible to estimate the conductances of most of these salts at infinite dilution merely by extrapolating the A-Nl'? or A-N''3 curves to zero concentration. The data in tables 1 and 2 gave fairly good linear plots, using the cube root of concentration aa abscissae, if all points below 0.001 N were ignored in these extrapolations. For the isobutyl sulfosuccinate and the octyl sulfate the 0.001N solutions were also disregarded; of Although only one concentration was measured below this point, it must be approximately correct, because the absence of such a critical concentration would yield an abnormally high extrapolated conductance at infinite dilution.


668

F. D. HAFFNER, G. A. PICCIONE, AND C. ROSENBLUM

these two compounds the octyl sulfate was the least satisfactory in that deviations from linearity persisted to 0.003 N . If these omissions are allowed, then linear extrapolations lead to the figures for equivalent conductance a t infinite dilution (Ap) recorded in table 3; and if 50.1 is taken as the mobility (19) of the sodium ion at 25"C., we have the accompanying approximate mobilities (Lon) of the corresponding paraffin-chain anion. An insufficient number of low concentrations were examined with the di-n-octyl sulfosuccinate to allow a reliable estimate of A,. However, judging from the two lowest points this quantity cannot exceed 77. It should be noted that the A , obtained from these measurements for sodium dodecyl sulfate is in substantial agreement with the values of Lottermoser and Puschel (17) ( A , = 75 at 25OC.) and Ward (32) ( A , = 65.5 a t 20°C.) for the same compound. The Zanion for the corresponding sulfonate (16) is 22 (at 25OC.). DISCUSSION

The "critical" concentrations for the alkyl sulfates seem to be normal, inasmuch as Ncr,is greater for shorter chain lengths. It is interesting to find that the sulfosuccinate diesters also exhibit a range of concentrations, more or less restricted, where the equivalent conductance diminishes, thereby indicating that aggregation of molecules takes place. Although no break was evident in the OT-N conductance curve, a critical concentration probably would have been observed had the measurements been continued to sufficiently low concentrations. This becomes evident if one realizes that otherwise the limiting equivalent conductance of the OT-N would be 92, which is abnormally high by far for a large univalent organic anion. Obviously, aggregation begins a t or below the lowest concentrations studied. It seems clear that the property of aggregation to form micelles is characteristic of the diester type of paraffinchain salt, even though the aliphatic residue is a branched chain; but in view of the complexity of molecular structure of the sulfosuccinates, it is doubtful that the aggregates can be simply spherical in shape. At first glance there does not seem to be any simple relationship between the N,, 's of the sulfosuccinates and the total number of carbon atoms in the alkyl radicals. However, if the number of carbons is counted for the longest straightchain portion of the radicals, exclusive of branches, it follows that MA is equivalent to a ten-carbon-atom compound, OT represents a twelve-carbon-atom compound, and OT-N corresponds to a paraffin-chain electrolyte containing sixteen carbon atoms in the non-polar portions of the molecule. With this revision in mind, we find that the Ncr.N 0.03 M for MA compares favorably with the decyl sulfate value of 0.031 M ; the 0,0055 M value for OT approaches the range (0.007-0.00S M ) reported for sodium dodecyl sulfate; and the maximum Ncr,of O.OOO9 M of the OT-N is close to the critical concentrations established (1, 6, 12, 17, 25) for other hexadecyl paraffin-chain compounds of the anionic type. The Nor.of diisobutyl sulfosuccinate is definitely out of line with this generali-



669

zation. However, this compound behaves abnormally, in that above 0.02 M its solutions became turbid. This turbidity obviously masks the phenomenon under investigation, and the Ncr. obtained in this system probably bears no relationship to the critical concentration being sought. Solutions of the methyl amyl derivate are also turbid, but this turbidity is evident a t all concentrations and varies regularly with concentration. As regards the mobilities of the paraffin-chain anions, i t is of interest to note the decreasing mobilities of the alkyl sulfates with increasing chain length. Furthermore, the mobilities of the sulfosuccinate anions are lower than those of the alkyl sulfates, owing to the larger size and more complicated structure of the former group of compounds. SUMMARY

1. The conductances of solutions of several alkyl sulfates and sulfosuccinates have been measured a t a number of concentrations. 2. The course of the conductivity curves indicates that aggregation occurs with sulfosuccinates just as with the alkyl sulfates. 3. From these data, “critical concentrations” for micelle formation and equivalent conductances at infinite dilution were estimated.

The authors are greatly indebted to Dr. S. Lenher and Mr. C. A. Sluhan for providing the paraffn-chain salts. They wish to thank Dr. L. B. Rogers of this laboratory and Dr. R. P. Chapman of the American Cyanamid Stamford Laboratory for extended corroborative analyses of certain of the products employed in this investigation. REFERENCES

(1) ADAMSAND SHUTE:Trans. Faraday SOC. 34, 758 (1938). (2) BURYAND PARRY: J. Chem. SOC. 1936, 626. (3) DANIELS,M.4THEWS, AND WILLIAMS: Ezpmimental Physical Chemistry, 2nd edition, Chap. X and XXV. McGraw-Hill Book Company, Inc., New York (1934). (4) DAVIESAND PARRY:J. Chem. SOC.1930,2263. Aqueous Solutions of Parafin-chain Salts. Hermann et Cie, Paris (1936). (5) HARTLEY: (6) HARTLEY: J. Am. Chem. SOC.68,2347 (1936). Trans. Faraday SOC.37, 130 (1941). (7) HARTLEY: (8) HARTLEY, COLLIE,AND SAMIS:.Trans. Faraday SOC.32,799 (1936). AND RUNNICLES: Proc. Roy. SOC.(London) Al68,420 (1938). (9) HARTLEY (10) HESSAXD GUNDERYAN: Ber. 70, 1800 (1937). (11) HESS,PHILIPOFF, AND KIESSIG:Kolloid-Z. 88,40 (1939). AND ROBINSON: Proc. Roy. SOC. (London) Al66, 386 (1936). (12) HOWELL AND BR.4DSHAW: J. Am. Chem. soo. 66,1780 (1933). (13) JONES AND JATKAR: J. Indian Inst. Sci. 2lA, Pt. 34,395 (1938). (14) KULKARNI Proc. Roy. SOC. (London) Al70, 415 (1939). (15) LAING-MCBAIN: DYE,AND JOHNSTON: J. Am. Chem. SOC.61, 3210 (1939). (16) LAINQ-MCBAIN, (17) LOTTERMOSER AND PUSCHEL: Kolloid-Z. 63, 175 (1933). AND STOLL:Kolloid-Z. 69.49 (1933). (18) LOITERMOSER (19) MACINNES, SBEDLOVSKY, A N D LONGSWORTH: J. Am. Chem. SOC.64,2758 (1932). (a)MCBAINAND BETZ:5. Am. Chem. SOC.67.1905 (1935). (21) MCBAIN AIVD BETZ:J. Am. Chem. SOC.67, 1909 (1935).


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J. L. HENDERSON AND E. A. YOUNG

(22) MCBAIN AND BETZ:J . Am.Chem. SOC.67, 1913 (1935). (23) MCBAIN,LAXNO, AND TITLEY: J. Chem. SOC.116,1279 (1919). (24) MCBAINAND MILLS:Reports on Progress in Physics 6,30 (1939). (26) POWNEY AND ADDISON:Trans. Faraday 800. 83, 1243 (1937);a,356 (1938). (26) POWNEYAND WOODS:Trans. Faraday SOC.88,57,420 (1940). (27) REEDAND TARTAR: J. Am. Chem. Soc. 68,322 (1936). (28) STAUFF: Z. physik. Chem. Ala, 65 (1938). (29) STAUXF: Naturwissenschaften 27,213 (1939). (30)TARTAR AND WRIQHT: J. Am. Chem. 800. 61, 539 (1939). : Grundlagen det Teztilueredlung, Chap. 14. J. Springer, Ber(31) V A L S ~Kolloidchemische lin (1937). (32) WARD:J. Chem. Soc. 1999, 522. (33) WRIQAT,ABBOTT,SIVERTS AND TARTAR: J. Am. Chem. SOC.61,550 (1939). (34) WRIOETAND TARTAR: J. Am. Chem. Soc. 61, 544 (1939).

SOME ASPECTS OF T H E RATE OF REACTION OF OLEIC ACID WITH OXYGEN J. L. HENDERSON Division of Dairy Industry, College of Agriculture, University of California, Davis, California AND

H. A. YOUNG Division of Chemistrb; College of Agriculture, University of California, Davis, California Received February 86, 19.48

Investigators in the field of fat deterioration usually agree with Powick (12) : “The oleic acid radical (in the glyceride) is the point of attack in the development of rancidity (oxidative), and a study of the chemistry of rancidity should begin with a study of oleic acid.” The literature gives few data on studies of the uncatalyzed oxidation of oleic acid. Taufel and Suess (15) studied the absorption of oxygen by oleic acid in a Warburg apparatus. Their oleic acid, however, had a melting point of 6.8-8.0”C. and undoubtedly contained appreciable amounts of more unsaturated acids, probably linoleic acid. More recently, Hamilton and Olcott (9) have reported the absorption of oxygen by purer preparations of oleic acid. An attempt was made to assign the oxygen absorbed to the different products formed, in the manner used by Almquist and Branch (1) for the autoxidation of benzaldehyde. Deatherage and Mattill ( 6 ) continued the work of Hamilton and Olcott, using an apparatus with traps filled with dehydrite, traps filled with ascarite, and Dewar flasks filled with alcohol and solid carbon dioxide to collect the products of oxidation. Their experiments, as well as those of Powick (12), Hamilton and Olcott (9),and others, indicate the complexity of the reaction and the many products formed, especially after the initial stages of the reaction. The literature furnished no data regarding experiments on the rate of reaction

Conductances of Solutions of Several Alkyl Sulfates and

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