Aug.,
1920
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
THE DETERMINATION OF SULFATE IN SULFONATED
OILS’ By Erwin J. Kern 161 CONCORDIA AVE., MILWAUKEE, WISCONSIN
During a recent visit t o the author’s laboratory Prof. A. W. Thomas showed t h a t sulfuric acid can be extracted quantitatively from leather by means of a solution of monosodium phosphate. The writer has found t h a t with a sulfonated oil this solution causes a practically complete separation of oil from solution in a remarkably short time and t h a t the solution contains all of the free and none of the combined sulfates of the original oil. It was a t once apparent t h a t this phosphate solution possessed real advantages over the saturated sodium chloride solution and ether used in the ordinary method of determining uncombined sulfates in sulfonated oils. F R E E SULFATE
The usual procedure for free sulfate is t o dissolve 4 or j g. of the oil in ether, shake out several times with saturated salt solution, combine these washings, dilute, filter, and precipitate the sulfate with barium chloride. The use of ether is necessary in this method because the salt solution when used alone does not readily cause a clear separation of oil and solution; in fact, it, not only fails t o give a sharp separation, but i t extracts only a small portion of the free sulfate, giving in one case only 0 . 0 6 per cent when 0 . 2 0 per cent was actually present. On the other hand, the phosphate solution, without the addition of an organic solvent, extracts all the free sulfate and produces a sharp separation in less time than when sodium chloride and ether are used. A 2 5 per cent phosphate solution gives a sharp separation in about 5 min., but for general work a I O per cent solution is quite satisfactory. When the ordinary method is used with oils containing much water, the salt solution becomes so dilute t h a t i t fails t o give a clear separation, in which case it has been found necessary t o add dry salt and shake vigorously until the solution became nearly saturated. N o difficulty from this source has been found with the I O per cent phosphate solution, even with oils containing as high as 3 j per cent water. I n a series of tests i t was proved t h a t one extraction with a I O per cent phosphate solution is quite as effective in removing the free sulfates from an oil as t h e customary three with brine and ether. Comparative results for four typical oils are given in Table I. TABLEI-PER
CENT OF
FREESULFATE (SOa)
............ ...........
Brine and ether (3 extractions). Phosphate solution ( 1 extraction).
IN
(1) 0.10 0.12
FOUR TYPICAL OILS (2) 0.20 0.21
(3) 0.33 0.33
(4) 0.18 0.20
I n order t o test the completeness of the extraction, definite amounts of anhydrous sodium sulfate were added t o portions of an oil containing only 0.04 per cent of free sulfate and these samples were then extracted four times with I O per cent phosphate solution. The results in Table I1 show t h a t the bulk of the sulfate is removed in the first extraction and the remainder in the second extraction. 1 Presented before the Section of Leather Chemistry at the 59th Meeting of the American Chemical Society, St. Louis, Mo., April 12 t o 16, 1920.
TABLE11-PER Per cent Free SO3 Actually Present 0.27 0.57 0.98
CENT SO3
1st Extraction 0.21 0.53 0.93
78s
EXTRACTED BY P H O S P H A SOLUTION T~ 2nd Extraction 0.03 0.06 0.06
3rd Extraction Trace Trace Trace
4th Extraction None None None
Where the amount of water in the oil is known, complete separation of the solution from the oil is unnecessary. Five samples, of known sulfate content, were prepared, measured amounts of phosphate solution were added, the mixtures were shaken and allowed t o separate, and aliquot portions of the solution were taken for analysis. Dilution caused by the water in the oil is allowed for in the calculation. This method of procedure is extremely rapid and the results in Table I11 show t h a t i t is quite accurate. If the aliquot portion is taken before the solution is quite clear, t h e oil must be filtered off before boiling with the barium chloride solution. Per cent Free SOs Actually Present 0.10 0.20 0.27 0.57 0.98
TABLE111 Per cent so3 Found by Taking Aliquot Portion of the Phosphate Solution 0.12 0.21 0.26 0.57 0.97
TOTAL SULFATE
A common method of estimating the amount of total sulfate in sulfonated oils is t o boil with hydrochloric acid solution to liberate the combined sulfate, cool, add petrol t o dissolve the oil, wash in a separatory funnel several times with water, combine t h e washings, and precipitate the sulfate with barium chloride. The organic solvent can be dispensed with, just as in the determination of free sulfate, by using the I O per cent phosphate solution. Two extractions with the phosphate solution proved sufficient t o extract all of the sulfate. A comparison of the two methods is given in Table IV, along with determinations made by a fusion method. I n boiling the oil with hydrochloric acid we have always experienced difficulties due t o the bumping of the mixture. We have consequently found i t preferable t o use a fusion method, which consists of evaporating the oil with sodium carbonate, igniting, fusing, dissolving the residue and boiling with sodium peroxide, acidifying, and precipitating as usual with barium chloride. TABLE IV-TOTAL so3
DIFFERENTMETHODS Per cent Total so3 Found in Sulfonated Sulfonated Castor Oil Neat’s-foot Oil Extraction with water, using petrol., 3.39 2.78 Extraction with phosphate solution alone, . . . . . 3 . 4 4 2.80 B y the fusion method.. 3.31 2.88 BY
.......... ......................
RECOMMENDED METHOD
For the determination of uncombined sulfate in any ordinary oil, we recommend the following procedure: Weigh from 2 0 t o 40 g. of oil into a separatory funnel, add I O O cc. of a I O per cent solution of monosodium phosphate, shake, allow the oil and solution t o separate, draw off the major portion of solution, and filter free from any oil particles, acidify 50 cc. of the filtrate, and precipitate the sulfate with barium chloride. I n calculating the per cent of free sulfate in the original oil, make allowance for the dilution of the solution by the water of the oil.
