Determination of Sulfuric Anhydride in Sulfonated Oils and Other Products New Direct Gravimetric Method RALPHHART,Hart Products Corporation, 1440 Broadway, New York, N. Y.
I
N T H E analysis of sulfonated (sulfated) oils for organically combined sulfuric anhydride by the present direct method (1) or the sulfuric acid titration method, the sample is boiled with sulfuric acid and the increase in acidity, which corresponds to the organically combined sulfur, is determined volumetrically in the presence of methyl orange indicator. The method is rapid and reliable, and has replaced to a considerable extent, in this country as well as abroad, the old gravimetric method consisting of two barium sulfate determinations. The method, however, fails in the presence of titratable salts, such as sodium acetate, that do not give a sharp end point with indicators. Moreover, the titration method as well as the old gravimetric method is not applicable to oils of the true sulfonic type which are not hydrolyzed by acids. I n connection with an investigation of sulfonated oils by a committee, of which the writer is chairman, appointed by the American Association of Textile Chemists and Colorists, a new direct gravimetric method has been developed by the writer-the ash-gravimetric method-which seems applicable to all types of sulfonated oils, including those containing troublesome titratable salts. The ash-gravimetric method consists essentially in isolating the sulfonated compound free from inorganic salts and determining the ash of the purified product. The method is direct in the sense that it requires only one determination and the inorganic sulfate present in the oil need not be determined separately. Preliminary tests have indicated that the new method will determine the combined sulfur not only in sulfonated oils of the usual kind-i. e. ester type-but in special sulfonated products, such as sulfonated mineral oils, sulfonated saponifiable oils of the true sulfonic type, sulfonated aromatic hydrocarbons, and sulfonated fatty alcohols, esters, and other compounds which have recently appeared on the market (Nekal, Gardinol, Igepon etc.) as substitutes for soap and wetting-out agents. The only requirement in the successful application of the method is that the product may be completely extracted by solvents over a saturated solution of sodium chloride or sulfate. It was found that the ash of the pure sulfonated product consists of sodium sulfate and represents just half of the organically combined sulfuric anhydride. The reaction during ignition is as follows, where R sthnds for the organic radical : 2R-S04Na -+ NazSOl SO8 etc. or 2R-SOsNa +NasSOc SO8 etc. ,
when dissolved in ether it forms emulsions with saturated salt solutions.
A. REGULAR PROCEDURE. Weigh 10 grams of the sample into a 250-cc. pear-shaped separatory funnel containing 50 cc. of 25 per cent sodium chloride solution. Add 5 dro s of a 0.1 per cent solution of methyl orange and 75 to 100 cc. orether, and acidify with approximately normal sulfuric acid until the lower layer is distinctly pink (about 0.2 cc. excess). Add solid sodium chloride equal t o one-third of the acid added, shake vigorously until the salt is practically dissolved, and allow the layers to separate. Draw off the lower layer into another separatory funnel and wash the ether layer with 25 cc. of the salt solution. Combine the salt layers and extract twice with 20-cc. portions of ether. Combine the ether layers and, after carefully removing any water that may settle, shake well for 3 t o 5 minutes with 10 cc. of 25 per cent sodium sulfate solution, at 50" C. Separate the lower layer as completely as possible, warming it in warm water or with steam to keep the salt from crystallizing. After the water layer is removed, however, crystallization of any salt that may be dissolved in the ether layer should be induced by cooling to about 15" C. and, if necessary, by scratching the wall of the funnel with a glass rod. Filter into a dry 250-cc. beaker, washing the funnel and crystals, if any, with three 10-cc. portions of ether or until all the fatty matter has been transferred. Cool the filtered ether solution in ice water for 15 minutes, warm to 25" to 30' C., filter againinto a dry 300-cc. flask and wash the beaker and filter paper with three 10-cc. portions 01 chilled ether. The filtered solution when again chilled to 0" C. and warmed to 25" to 30" C. should remain perfectly clear. A flocculent precipitate during chilling that does not clear upon warming indicates insufficient solvent to keep the fat in solution a t that temperature, in which case more solvent should be added. Distill off the ether until the volume has been reduced to about 20 cc. and transfer to a tared 50-cc. crucible (high form), which is allowed t o float in a 100-cc. beaker filled with warm water. Rinse the flask with two 10-cc. and two 5-cc. portions of ether, respectively, or until all the oil has been transferred to the crucible, each addition being made only after the ether of the previous portion has practically evaporated. Care should be taken during the evaporation t o prevent loss of oil by creeping; this may be avoided and the eva oration hastened by constant stirring with a glass rod, whicl&is ultimately wiped clean with ashless filter paper that is added to the crucible. After the ether is evaporated, burn the oil gently and ignite to constant weight. To complete the oxidation of any remaining carbon or traces of sulfide that may be formed, moisten the ash with a few drops of 30 per cent hydrogen peroxide and again carefully ignite to constant weight. B. PROCEDURE IN PRESENCE OF AMMONIA. Dissolve 10 grams of the sample in 80 cc. of water in a 300-cc. beaker, add 10 cc. of 0.5 N sodium hydroxide, and boil the solution gently until wet litmus paper no longer indicates ammonia. Cool and transfer into a 300-cc. pear-shaped separatory funnel and add about 33 grams of solid sodium chloride, or enough to make finally a 25 per cent salt solution. Add 5 drops of a 0.1 per cent solution of I n the calculation it is assumed that the ash consists of so- methyl orange and proceed with the neutralization and extraction dium sulfate rather than potassium or other metal sulfate. as directed in A. This assumption applies to nearly all commercial oils, since C. PROCEDURE IN CASE EMULSIONS FORM. Dissolve the the sulfonic (or sulfate) group is almost completely neutralized sample in 50 cc. of water and transfer carefully to a separatory during the washing, which is usually done with a solution of funnel. Add 100 cc. of ether and enough solid sodium chloride to saturate the water layer and leave some solid salt in excess. either sodium chloride or sulfate. Shake well, add methyl orange indicator, and acidify as directed under regular procedure. If emulsions form, add 2 cc. of alcohol at a time until the emulsion breaks, mixing gently but not shaking PROCEDURE after each addition of the alcohol. Proceed then following proThe procedure is varied somewhat, depending upon whether cedure A, except that whenever emulsions are formed, break or not the product contains ammonia, and whether or not them with alcohol as outlined. 413
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ANALYTICAL EDITION
414
DISCUSSION According to Nishizawa and Winokuti (2), sulfonated oil is least soluble as its monosodium compound-i. e., free from soap-and in that form it is entirely insoluble in, or may be completely extracted from, saturated solutions of either sodium chloride or sodium sulfate. Hence in the procedure enough acid is added to the sample before extracting just to decompose the soap. A very slight excess of acid is permissible. Sodium chloride rather than sulfate is used for the first few washes because it gives a much sharper color change with methyl orange and because the salt does not tend to crystallize. The purpose of the final wash with sodium SUIfate is to dehydrate the ether extract as much as possible. The addition of caustic soda to samples of sulfonated oil containing ammonia is required only where the combined S03H group is partly or wholly neutralized by the ammonia. In that case unless converted into the sodium salt there would be a loss of combined sulfate due to the volatilization of the ammonium salt upon being ignited. Ammonium soaps, however, do not interfere with the regular procedure. In the presence of sodium acetate, the acidification as outlined probably decomposes the acetate incompletely into acetic acid, which is partly extracted by the ether. This does not interfere with the method, since during ignition the acetic acid is entirely volatilized. The ether layer probably becomes contaminated also with some of the undecomposed sodium acetate which, however, is removed together with other foreign inorganic salts by the Glauber's salt wash and during the chilling process.
greatest differences were 0.35 and 0.14 per cent, and the for average samples deviations and B-l. were 0.09 and 0.05 per cent, respectively,
coMsINED sULFURrC A~~~~~~~~
gravimetric method. The results are given in Table I. Sample B was a highly concentrated sulfonated (sulfated) castor oil and sample B-1 was a mixture of equal parts of sample B and a 5 per cent solution of anhydrous sodium acetate. I n the case of sample B-1 the committee reported unanimously that accurate end points were impossible; hence, no data are listed under the sulfuric acid titration method. O F COMBINED SULFURIC ANHYDRIDE TABLE I. DETERMINATION IN SULFONATED OILSBY NEWAND OLD METHODS
SAMPLE B ABH-QRAVIMETRIC MlTHOD
AN^^^^^ 1 2 3 5 6 7 8
a
I %
I1
%
5 37 5 37
d4V
Av.
5 37
5.24 5 39 5 18 5 26 5 10 5 16 5.17 5 25 5 19 5 22 0 29 0 06
%
5 05
4 98
5 02
5 04 5 26 5 22 5 20 5.27
5 6 5 5 5
5 07
10 18 17 24
BULFURIC ACID TITRATION METHOD
5 22 5 20 9 5.22 10 29 5 28 Mean 5 20 Greatest difference 0 35 Average deviation 0 09 By calculation, 2 60
SAMPLE B-1
ABH-QRAVIMETRIC METHOD
I %
%
3 4 5 6 7 8 9 10
I1
%
51 2 , 5 8 2.52 2 52 2 50 2 61 2 57 2 . 6 5 2 54 2 63 2 . 6 4 2 67 2 61 2 50 2 54 2 46 2 . 5 7 2 48
Av.
%
2.65 2 50 2.51 2 54 2 60 2.64 2.64 2 52 2 51 2 56* 0 05 14
It will be noticed that the mean for sample B by the new and old methods was 5.20 and 5.22 per cent, respectively; also that for sample B-1 the mean by the new method was 2.56 per cent with 2.60 per cent by calculation. It will also be observed that the different analysts obtained good agreement in the results by the new method; thus the
IN
coMnlERCIA
SULFONATED COMPOUSDS
SulfOnated Products of different types were analyzed in the writer's laboratory by the new method and the results are listed in Table 11. Where the method could be used, results by the sulfuric acid titration method are also given. Where it was not possible to compare the two methods, the combined salt water washes by the new method were further extracted with ether or ether-alcohol, but in all cases the residues in the extracts were found to be negligible. Furthermore, the ash invariably gave a negative test for chloride, indicating the probability that the ether extracts were free from Glauber's salt. Because of troublesome emulsions with samples 4, 5, 6, and 7 , the combined sulfuric anhydride in these products was determined by procedure C. TABLE11. DETERMINATION OF ORGANICALLY COMBINED FURIC ANHYDRIDE IN SULFONATED COMPOUNDS ASH-
GRAVI-
SUL-
SELFURIC ACID
TITRATION METHOD METHOD % % METRIC
SAMPLE
DEBCRIPTION
a
1 Sulfated castor oil 2 Sulfated castor oila 3 Sulfated olive oilc 4 Sulfonated oild 5 Sulfated fatty alcohol 6 Sulfonated fatty ester0 7 Sulfonated aromatic hydrocarbon1 Sulfonated mineral oil 8 9 Sulfonated mineral oile Equal parts of sample 1 and 5 per cent solution
d
Saponifiable, true sulfonic acid type.
ANALYSIS OF SAMPLES
To test the possibilities of the new method in the case of the ordinary commercial sulfonated oils and similar products containing sodium acetate, the commit tee was requested to analyze two samples of sulfonated oils, samples B and B-1, by both the sulfuric acid titration method and the new ash-
Vol. 5 , No. 6
g;;t;;;io,n,,",ea9;lmonia,
~ ' , 8 . 0 { t $ ~ ~~ ~~ ~ ~~ ~ ~~ ~ ~~ e~
5 23 5 19 2 58b 3 90 3182 3.00 0.00 16.18 15.80 6.25 0.00 10 70 0.00 14.21 0.00 4 88h 0.00 of sodium acetate
l ~ ; f i ~ ~
u One part of sample 8 and two parts of 25% solution of NasSO4 h
By calculation 4.74.
SUMMARY A new gravimetric method, called the "ash-gravimetric" method, is outlined for the determination of organically combined sulfuric anhydride in sulfonated oils. The method is direct and seems to be applicable to all types of sulfonated oils, including: the sulfate or ester type, with or without titrable salts; sulfonated saponifiable oils (true sulfonic type) ; sulfonated mineral oils; sulfonated aromatic hydrocarbons; and sulfonated or sulfated fatty alcohols and esters -the last two being soap substitutes recently brought on the market. In many of these cases the present sulfuric acid titration method is not applicable. I n the new method only one sample is required for analysis, compared with two by the other methods. The manipulations are comparatively simple, check results are easily obtained, and the concordance among different analysts is very satisfactory. ACKNOWLEDGMENT The writer wishes to express his appreciation to M. B. Hart of this laboratory for assistance with the analytical work, and to L. A. Olney, chairman of the Research Committee of the American Association of Textile Chemists and Colorists, under whose guidance the subcommittee on sulfonated oils is working. LITERATURE CITED (1) Hart, R., J. IND. ENG.CHEM.,9,850(1917). (2) Nishizawa, K., and Winokuti, K., Chem. Umschau Fette, o l e , Wachse Harze, 38, 1 (1931). RBCEIVED May 27, 1933.
