Identification of Anionic Surface Active Agents by Infrared Absorption of the Barium Salts J. W. JENKINS and K. 0. KELLENBACH Research and Development Departmenf, Colgafe-Palmolive Co., 7 05 Hudson St., Jersey City, N. J.
b The barium salts of 10 organic sulfates and sulfonates, of the types commonly used as detergents, have been prepared. The infrared curves of these water-insoluble salts serve as a means of identification. Details of preparation, ashing of salts, and infrared procedure are presented. The infrared curves are correlated.
S
acids and organic sulfates have been identified by means of their 8-benzylthiuronium derivatives (4-7) and by reaction with aryl amines such as p-toluidine ( 1 ) to give solid crystalline compounds. Determination of the molecular n eight by the benzidine method is useful in characterizing sulfates and sulfonates (9), but does not itself constitute a positive identification. The use of infrared techniques has been applied to the identification of fatty acids and soaps (8). Barium salts of lignosulfonic acids have been prepared and barium and sulfur have been determined after ion exchange ( 3 ) . Organic sulfates and sulfonates of the type commonly used as surface active agents form n ater-insoluble barium salts. The barium salts yield distinct infrared spectra which serve as a means of identification. The insolubility of these salts in water makes possible their removal from solutions containing TI ater-soluble impurities and their insolubility in hydrocarbon solvents allows them to be washed free of fatty contaminants. The infrared spectrum is obtained on the dried sample ULFOKIC
Table I.
and identification is based on the comparison with spectra of authentic compounds. Structural assignments are based on literature references found in Bellamy ( 2 ) . Interferences result from inorganic and organic anions such as sulfate, phosphate, and fatty acid. Coprecipitation of these anions is prevented by prior removal. The neutral inorganic sulfate and phosphate salts are insoluble in alcohol, while the organic sulfates and sulfonates are soluble. Removal of matter insoluble in alcohol beforc preparation of the barium salt eliminates these interferences. Soap or free fatty acid may be removed by acidification and extraction prior to the formation of the barium salt. The barium salts of the sulfates and sulfonates may be ashed to yield barium sulfate, thus providing a convenient method of estimating the molecular neight of the original sample. The compounds used in this study n ere from two general sources. Igepon T C and the e s t u sulfates and sulfonates n ere obtained from commercial sources. The alkyl aryl sulfonate, alkyl sulfonate, and alkyl sulfates were prepared in the Research and Development Laboratories of the Colgate-Palmolive Co. EXPERIMENTAL
Preparation of Barium Salt. A sample containing 200 t o 400 mg. of sulfate or sulfonate is dissolved in 150 ml. of n-ater and heated t o 40" t o 50" C. Twenty-five milliliters of a 10% solution of barium chloride di-
Ash of Barium Salts
Barium dodecane-1-sulfate Tetradecane-1-sulfate Hexadecane-1-sulfate Tridecane-2-sulfate Dodecane-1-sulfonate Monoglyceride sulfonate derived from coconut fatty acid Monoglyceride sulfate derived from hydrogenated coconut fatty acid S-Methvl-A'-acyl taurine sulfonate derived from coconut fatty acid" Igepon TC.
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ANALYTICAL CHEMISTRY
Ash, 7c 36.11 32.71 30.56 33.91 36.53
Jlolecular Weight Based on Based benzidine on ash method 277 5 286 4 311 2 315 1 336 2 345 5 298 5 297 1 273 8 279 0
hydrate are added n i t h stirring. The solution is allowed t o stand with occasional stirring until t h e supernat a n t liquid is clear. The precipitated barium salt is collected b y filtration and n-ashed n i t h water. It is then air-dried on a porous plate. The dried preciptate is slurried with 100 ml. of n-pentane, collected by filtration, air-dried, and finally dried a t 80" C. for one hour. Ashing of Barium Salts. A sample of dried barium salt u-eighing 50 t o 100 nig. is placed in a previously ignited and tared platinum thimble of 5-ml. capacity. The salt is charred slowly over a hIeker burner, until t h e organic matter is destroyed, then the thimble is heated t o a cherry red. iifter cooling, 4 drops of concentrated sulfuric acid are added and t h e acid is volatilized on a hot plate. The crucible is again heated to a cherry-red color and cooled, and 1 drop of concentrated sulfuric acid added. This sulfuric acid is removed on the hot plate and the crucible again is heated with the burner, cooled, and weighed. Results of the ashing of the barium salts are presented in Table I. The molecular weight obtained by the benzidine method (6) is included for cornparison. Preparation of Sample for Infrared. The infrared spectra are recorded in the solid state, t h e potassium bromide pelleting technique being used. I n a 2-inch porcelain mortar 10 mg. of t h e barium salt are mixed n-ith 1.2 grams of 325-mesh potassium bromide and with sufficient chloroform t o make intimate mixing possible. T h e chloroform is evaporated in a current of air, leaving a fine, dry powder. A Baird potassium bromide pelleting die with vacuum attachment is used to prepare the 4.5 X 22 mm. rectangular pellet. The 0.031 spacer is used. The die is assembled and evacuated and the pellet is pressed for 30 seconds with a total force of 18,000 pounds, which corresponds to approximately 118,000 p.s.i. of applied pressure. The samples are mounted with the aid of two small magnets on the frame of a demountable cell. A PerkinElmer Model 21 double-beam spectrophotometer with sodium chloride prism
28.04
370 5
370 1
25.71
408 2
400 9
b
28.65
361 7
355 1
Figure 1 . Infrared spectra for four sulfates and one sulfonate
WAVE LENGTH, MICRONS
VOL. 3 1 , NO. 6 , JUNE 1 9 5 9
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W A V E LENGTH, MICRONS
Figure 2.
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ANALYTlCAL CHEMISTRY
Infrared curves for two sulfates and three sulfonates
Table II.
Infrared Absorption Data Sulfates, Phenyl Sulfonates,
c-c
Compound Alkyl sulfates Barium dodecane-1-sulfate
OH
...
StretchCarbonyl ing CH,
...
...
7.30
Tetradecane-1-sulfate
...
...
7.30
Hexadecane-1-sulf ate
. . .
.
,
V.K.
.
7.21
Tridecane-2-sulfate Alkyl and alkyl aryl sulfonates Barium dodecane-1-sulfonate Barium p-phenyldodecane sulfonate Ester sulfates Barium salt monoglyceride sulfate derived from coconut fatty acid Derived from hydrogenated coconut fatty acid Ester sulfonate Barium salt monoglyceride sulfonate derived from coconut fatty acid Amide and sulfonate Barium salt N-methyl-N-acyl taurine sulfonate derived from coconut fatty acidc a Ester. * Disubstituted amide. e Igepon TC.
... 2.95 H10
c-0
Ester Stretching 7.86, 8.06, 8 . 2 1 max., 8 . 3 8 7.85, 8.08, 8.21 mas., 8.38 7 . 8 1 , 8.08, 8.20 max., 8.38 7.72) 7 9 5 , 8.10, 8.38 max., 8.59
Peaks CharacHydroxyl teristic Stretchfor ing Compound
C-0,
...
9.30-12.15
...
9.28-12.15
. . .
9.30-12.15
. .
9.32-10.53
...
9.44, 9.60, 12.60
...
8.25, 8 . 6 8 max.
. .
9.49-9.84
2.90
5.81U
. . .
.. .
7 . 5 7 , 8.10max., 8.40
8.90 Second.
9.32-12.38
2 90
5 . 80a
...
.
7.55, 8.10 max., 8.33
8.88 Second.
9.28-12.35
3 00
5 . 76a
.. .
. .
8.00, 8.28, 8.508 . 60 mas.
9.02 Second.
9.58-13.16
...
6.11b
...
7.28
7.90, 8.05, 8.40 max., 8.58
...
9.40-13.10
was used in this study. T h e spectra were recorded between 2 and 15.5 microns. DISCUSSION
The infrared spectral data presented in Table I1 may be divided into five classifications: sulfates, sulfonates, ester sulfates, ester sulfonates, and amide sulfonates. The sulfates show primary sulfate absorption a t 7.85, 8.08, 8.20, and 8.38 microns, the maximum being at 8.20 microns. The secondary sulfate, 2tridecane, displays a shift toward longer wave length a t 7.95, 8.10, 8.38, and 8.59 microns, the maximum being at 8.38 microns. The methyl absorption at 7.24 microns is stronger in the sccondarp sulfate than in the primary sulfate. The “fingerprint” region, between 9 and 12 microns, is characteristic for each compound and distinguishes the primary alcohol sulfates from one another. The primary aliphatic sulfonate s h o w
.
sulfonate absorption at 8.25 and 8.68 microns. The aromatic sulfonate, barium p-phenyldodecane, has sulfonate absorption a t 8.30, 8.52, and 8.80 microns. The phenyl absorption is observed at 6.24, 6.35, and 6.65 microns. The absorption seen at 11.88 and 12.27 microns is indicative of a primary benzene sulfonate substituted in the para position. The hydroxyl component in the monoglyceride sulfates s h o w absorption a t 2.90 and 8.90 microns due to secondary C-0 stretching vibration. The ester peaks are at 5.80 and 8.30 microns. The sulfate group absorbs a t 8.10 and 8.40 microns. The sulfonate, barium monoglyceride derived from coconut fatty acid, has hydroxyl absorption at 3.00 and 9.02 microns. Ester absorptions are seen a t 5.76 and 8.30 microns. The sulfonate peak is identified a t 8.2 to 8.3 and 8.5 to 8.6 microns. The barium salt of Igepon T C shows characteristic amide carbonyl absorption a t 6.11 microns. The peaks a t
Phenyl Ring Substitution
...
11.88, 13.27 para, 5.20 overtone para
8.39 and 8.58 microns are sulfonate absorptions. The methyl absorption at 7.28 microns is relatively strong. Peaks a t 9.40 and 13.10 microns are characteristic for this compound. LITERATURE CITED
(1) Barton, A. D., Young, L., J . Am. Chem. SOC.6 5 , 294 (1943). ( 2 ) Bellamy, L.. J., “Infrared Spectra of Complex RIolecules,” 2nd ed., Methuen and Co.. London. 1958. (3) Brauns, F‘. E., Hlava, J. B., Seiles, H., ANAL.CHEM.26, 607 (1954). (4) Chambers, E., Watt, G. W., J. Ore. Chem. 6,376 (1941). ( 5 ) Chambers, R. F., Scherer, P. C., Znd. Eng. Chem. 16, 1272 (1924). (6) Compaigne, E., Suter, C. M., J . Am. Chem. SOC.64, 3040 (1942). (7) Donleavy, J., Ibid., 58, 1004 (1936). (8) Meiklejohn, R. A., Meyer, R. J., Arnovics, S. Rf., Schuette H. A,, Rleloche, V. W., ANAL. HEM. 29, 329 (1957). (9) Shiraeff, D. il.,Am. DyestuflReptr. 36, 313 (1947).
RECEIVEDfor review June 30, 1958. Accepted January 26, 1959.
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