Determination of Sulfuric Anhydride in Sulfonated Oils New Titration Met hod RALPHHART,The H a r t Products Corp., 1440 Broadway, New York, N. Y. mole 801. This relationship, inNE of the most imporA new titration method is outlined, based upon stead Of two ~ O l e of s potassium tant determinations in the absorption of alkali when the sulfonated oil hydroxide being equivalent to the Of sulfois ashed. It is more rapid than the old acidone mole of sulfate, holds true nated oils is the amount of orboiling titration method, Particularly where many since the sulfuric acid in the oil ganically combined sulfuric anhydride. This may be in the analyses are to be run at the same time. The is already half neutralized. form of a s u l f a t e - t h a t is, a new method yields better check results and rePROCEDURE Sulfonic acid ester-or a t~~~ quires fewer reagents. The values for organic Two determinations are reacid* The former is sulfur are higher, indicating either more comquired: akalinity,”, and characterized by the f o r m u l a decomposition or the presence 0. true sui“decrease in a l k a l i n i t y after R-0-SO3H and the latter by R-S03H, where R r e p r e s e n t s fonic acids. The method, however, does not ashing.” the fatty r a d i c a l . An essendetermine the organic sulfur in sulfonated FIXEDA L K A L I N I T Y(AFJ. mineral oils or other nonsaponifiable oils or This r e f e r s to the nonvolatile tial difference between the two alkali and, in the a b s e n c e of is the fact that the salts. It is suggested that it m a y also be used ammonia or other volatilealkali, sulfonic a c i d esters split off sulfuric acid when heated with as a qualitative test for sulfonation. it is determined as follows: Ten grams of the oil are d i s s o l v e d mineral acids, whereas the true in 50 cc. of water in a 250-cc. Erlenmeyer flask, 50 cc. of 25 sulfonic acids are stable under such conditions. The writer (3) in 1917 proposed a volumetric method, now per cent neutral salt solution added, and the mixture titrated widely used in practice, for the determination of organically to an approximate end point in the presence of 5 drops of combined sulfate in sulfonated oils of the ester type, which methyl orange (1 per cent solution, dissolved hot, cooled, and eliminated two barium sulfate determinations required in the decanted). The contents are transferred to a separatory old gravimetric method. It is based upon the principle that funnel, the flask rinsed with 3- to 15-cc. portions of ether, when the oil is boiled with mineral acids, one molecule of the which are added to the separatory funnel, and the mixture neutralized sulfonated oil liberates one molecule of sodium made distinctly acid with standardized solution. After shaking and separating, the lower layer is drawn off into a acid sulfate, according to this formula: R-0-SO8Na HzO -+ ROH NaHS04. The method consists in heating 250-cc. beaker. The ether layer is washed with 15-cc. porthe oil with a given quantity of standardized sulfuric acid and tions of the salt solution until the wash water is neutral to determining the increase in acidity after boiling. Some ob. methyl orange, first rinsing the flask with them. The comjections have been raised against the method because of the bined water layers are warmed to expel ether, two drops of difficulty in observing the end point, since the titrations are methyl orange are added, and the titration completed, apmade in the presence of oil. It has also been stated that the proaching the end point with acid. The result is calculated results are somewhat low when compared with the acid gravi- to milligrams of potassium hydroxide per gram of sample and metric method, owing to incomplete decomposition. Finally denoted by AP. I n the presence of ammonia, the fixed alkalinity is deterit is claimed that the method is inapplicable in the presence of sodium acetate since all the sodium is not completely titrable mined in the following manner: Five grams of the oil are dissolved in 100 cc. of water in a 400-cc. beaker, 25 cc. of in presence of methyl orange, the indicator used. 0.5 N sodium hydroxide are added, and the solution boiled A new titration method, hereafter called “ash-titration” method, is outlined below which is based upon the principle until wet litmus paper no longer indicates ammonia. The rest that when the completely neutralized sulfonated oil is ashed, of the procedure is according to the above. The fixed a b the organically combined sulfate is quantitatively converted kalinity in this case is given by the difference in the alkalinity after boiling and the amount of alkali added, and is readily into sodium sulfate. The reaction is as follows: calculated according to the following formula (acid and alkali R--SO4Na --f NazSO4 etc. used in titration, in milligrams of potassium hydroxide): bOONa Fixed alkalinity (Ap), mg. KOH per gram = It will be noticed that one mole of sodium hydroxide or its total acid - total alkali equivalent combined with the carboxyl group corresponds to sample one mole of sodium sulfate. Since the former can be acTn this connection it is to be observed that the change in the curately determined, it follows that the organically combined sulfate can readily be estimated. The method consists in presence of methyl orange at the neutral point when titrating ashing a mixture of the oil and excess standardized caustic, with acid is from a yellow color to a faint orange. The followand finding the loss in titrable alkali after ignition. The loss ing method for noting this change accurately is suggested: in alkalinity-i. e., the difference between the alkali added Titrate to an approximate end point, leaving the solution plus the fixed alkalinity of the sample and the alkali found slightly but distinctly on the alkaline side, and transfer abou% after ignition-is calculated to organically combined sulfate 30 cc. into a 100-cc. beaker (beaker 1). Continue with the according to the following formula: one mole KOH == one titration in the original beaker, adding one or two drops of
0
+
+
+
411
ANALYTICAL EDITION
412
d.
the acid a t a time, and transfer after each addition 30 cc. of the solution into another 100-cc. beaker (beaker 2). If upon comparing beakers 1and 2 there is no change in color, contents of the latter are poured back into the original beakei and the titration continued until a change is just noted. Beaker 1 is now carefully titrated until it just matches beaker 2. Very slight change in the color of the solution is readily detected by this procedure, whereas over-titration is likely by the usual method. DECREASE IN ALKALINITY AFTER ASHING. Five grams of the oil in a 30-cc. platinum or porcelain evaporating dish are mixed with an equal quantity of 1 N sodium hydroxide, using a small glass rod for stirring. The solution is evaporated to dryness either in an oven or over a free flame, the residue heated until it catches fire, allowed to burn gently, and the ash ignited for about 10 minutes, or until the carbon is nearly consumed. The stirring rod is now removed and wiped with moistened ashless filter paper, the latter is added to the oil, and the stirring rod is put in the beaker in which the titration is to be made. The residue is again heated until the filter paper is ashed, and then oxidized with 3 to 5 drops of 30 per cent neutral hydrogen peroxide. The ash is now heated to a dull red heat, covering the dish to prevent loss by spattering. If not practically free from carbon, the treatment with peroxide is repeated. After cooling, the dish is covered with water in a 250-cc. beaker and brought to a boil, It is now titrated in the presence of methyl orange with 0.5 N sulfuric acid, then about 0.5 cc. excess added, and boiled about 5 minutes to expel carbon dioxide. Half normal caustic is now added until slightly but distinctly alkaline, the dish and small stirring rod removed, and the titration finished as given under Fixed Alkalinity. The combined sulfate is given by the following formula, where AZ represents total milligrams of alkali and Ac the amount of acid added or used during the titration: Combined SOa, % = A1 - AC -!r A F ) 56.1 8
(-
DISCUSSION Where the fatty acids in the oil have been neutralized with ammonia only, the oil will evidently contain no titrable fixed alkali. Moreover, part or all of the organically combined sulfate may have been neutralized with ammonia. I n that case, upon boiling with caustic soda the ammonium sulfonate is converted into the sodium salt, with the liberation of ammonia and absorption of fixed alkali that can no longer be determined by titration, The fact that the fixed alkali is absorbed by the sulfonic group in this manner is indicated by a negative result obtained by means of the alkalinity formula, which should be carefully retained for use in subsequent calculations. The writer finds that sodium acetate may be titrated with a fair degree of accuracy with thymol blue as the indicatar. The pH ( I ) of 0.2 molal sodium acetate is 8.3, the same concentration of acetic acid is 2.86, and the color change of thymol blue is 1.2 to 2.8 (red to yellow). Since the pH of acetic acid is above the pH of the color change of thymol blue, it can exert only a very slight effect on the indicator. Hence NaAc may be titrated with thymol blue the same way as soap is titrated in the presence of methyl orange. However, the end point in the former case is not so sharp as might be desired. The least accurate factor in the method is the titration, which may vary by as much as 0.1 cc. of half normal solution, or 2.8 mg. This affects the result on a one-gram sample by 2.8 X 8/56.1, or 0.4 per cent sulfate. By increasing the size of the sample taken for analysis, the error is correspondingly reduced. With a 5-gram sample, the accuracy of the method
VOl. 4, No. 4
is. approximately 0.1 per cent sulfate, which is about the variation found in the data given below. It must also be evident that errors due to mechanical losses are smaller the less the excess of alkali added to the oil, the losses being a minimum or zero where there is no excess alkali present at all. It seems that excess alkali is not required in order to get accurate results. A number of tests were made with excess alkali varying from zero to an amount equivalent to twice the sulfate content, with practically identical results.
EXPERIMENTAL RESULTS
A number of analyses for organically combined sulfate in commercial sulfonated products by the old and new titration methods are given in Table I, TABLE I. SAMPL~
ORQANICALLY COMBINED SULFATE IN SOMECOMMERCIAL SULFONATED OILS AND SALTS
DESCRIPTION
ORGANICALLY COMRINED SOa Old method New method
%
%
Sulf. olive oil 4.90 5.28 Sulf. castor oil 5.09 6.41 Sulf. castor oil” 3.30 3.41 Sulf. neat’s-fobt oilb 1.87 2.0s Sulf. cod oil0 3.44 3.61 6 Sulf. oi!d 8.92 9.48 7 S11k finishing oil 4.82 5 08 8 Silk soaking oil 1.97 2.10 9 Sulf. mineral oil6 Neg. 10 Isobutyl naphthalene sodium sulfonatee .. Neg. a Completely neutralized with caustio soda. b Contained 0 88Y NHs. mostly as ammonium sulfonate. c Contained 1 . 4 6 d “a, mostly as ammonium sulfonate d Highly sulfonated oil of foreign manufacture. 8 Large amounts of sulfide formed on ashing. 1
2 3 4 5
..
% 6.29 6.47 3.39 2.01 3.49 9.48 6.00 2.14
Neg
Neg
ADVANTAGES OF THE NEW METHOD The ash-titration method offers the following advantages over the old acid-boiling titration method: It is more rapid, particularly where many such analyses are made simultaneously, gives better check results, and requires fewer reagents. Moreover, the results are consistently higher, indicating either more complete decomposition than by the acid-boiling methods (titration and gravimetric), or the presence of true sulfonic acids. In this connection it is interesting to note that De Groote, Keiser, Wirtel, and Monson (2) report that the values for organically combined sulfate determined by the Parr bomb were much greater in some cases than results obtained by any method depending on decomposition by boiling, even for excessive periods, with mineral acid, such as concentrated hydrochloric acid. A sample of a true sulfonic acid of a saponifiable oil not being available a t short notice, this phase was not further investigated It was found, however, that the new method is not applicable to sulfonic acids that are not saponifiable, for example, sulfonated mineral oils, naphthalene sulfonic acid, etc. By taking a small sample for analysis, such as one gram, the method is sufficiently rapid to be used as a qualitative test for organically combined sulfate. ACKNOWLEDGMENT The writer is greatly indebted for samples of oil to the following: W. H. Cotton of the General Dyestuff Corp.; F. W. Breth of L. Sonneborn Sons, Inc.; and L. Collins of E. I. du Pont de Nemours & Company; also to E. I. Birnbaum of this laboratory for assistance with the analytical work. LITERATURE CITED (1) Britton, H. T. S., “Hydrogen Ions,” p. BO, Chapman and Hall, 1929. (2) D e Groote, M., Keiser, B . , Wirtel, A. F., and Monson, L. T., I N D .ENQ.CHEM.,Anal. Ed., 3, 243 (1931). (3) Hart, R., J. IND.ENG.CHEM.,9, 850 (1917).
RECEIVED June 11, 1932.
