Determination of Sulfur in Surface-Active Agents

Determination of Sulfur in Surface-Active. Agents. RALPH HART, The Hart Products Corp., 1440 Broadway, New York, '.Y. ONE of the. best criteria of the...
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Determination of Sulfur in Surface-Active Agents RALPH HART. The Hart Products Corp., 1440 Rroaduaj. Ueu korh.

S E of the best crkeria of the quality of any detergent or wetting-out agent) of the sulfuric acid ester or sulfonic acid type is the content of organically conibined sulfuric anhydride. The methods available for this determination are ( a ) the Herbig method (6) in which the sample is decomposed with hydrochloric acid anti the sulfate is determined in the water layer after extracting the fat \\-it11 ether; in another sample, the inorganic sulfate is determined by washing the oil layer, dissolved in solvents, with concentrated sodium chloride solution and determining the alkali sulfate in the wash waters. ( b ) The Ilerbig method has been mostly superseded by the acid-titration method ( 4 ) , in which the sample is decomposed with a known quantity of sulfuric acid and the organically combined sulfuric anhydride is calculated from the increase in acidity. (c) The last and most recent method is the ash-gravimetric method (e),which has been adopt8edas provisional by the American Association of Textile Chemists and Colorists ( I ) , the American Oil Chemists' Society ( 2 ) ,and the American Society for Testing Materials ( 3 ) . According to this method the pure sulfonated product is first isolated by extracting with solvents over a concentrated solution of salt and then ashed; from the Teiglit of the ash the conibined sulfuric anhydride may be calculaterl. The first t w o iiiethock evidently caniiot be user1 in tlie case of triie sulfonates) which are not decomposed 17y acids under the conditions of the methods. Furtherinow. in the case of highly sulfated sulfuric acid esters, theqe methods are inconrenient, as it takes a long time for complete hydrolysis-sounetiIiies over 10 hours. The ash or third method may be iisctl for sulfoiiated as Tyell as sulfated products and is sat,isfactory for t,he ordinary type of sulfat'ed oils. Unfortunately i n the case of highly sulfated oils or the ne~ver sulfonated detergents, such as t'he sulfated alcohols, sulfonated fat,ty acid amides, etc. (particularly if it, is necessary to use alcohol as one of the solvents in extraction), the extract carries over with it in solution a large amount of salt, which vitiates the results. Every effort to reinore t'he salt from the solvent b y filtering, freezing, or dehydrating ha.< ileen nnsuccessful. The rrietliod proposed in this paper is applicable t o every type of sulfated or sulfonated organic compound, provided it may be quantitatively extracted with a solvent over concentrated salt solutions. This was true of every such compound investigat,ed tha,t possessed detergency or surface activity. The sodium salt of /3-naphthalenesulfonic acid could not be analyzed by this method, since it was soluble in the salt solution and could not be extracted with solvents, but this compound has no value as a detergent and probably very little value, if any, as a wetting-out agent. T h e new method is convenient and comparatively rapid, and the results are of good precision and accuracy. It is based upon the observation t h a t the sodium or potassium salt of the sulfonated or sulfat,ed product when shaken with a concentrated solution of ammonium chloride or sulfate is quantitatively conrerted into its aiiiinoninm salt and, conrersely, the latter is converted iiito the sodium or pot,aesimn salt when shaken with a concent,ratetl snliition of the respective chloride or wlfat'e.

Procedure Shake the saliiple, dissolved in the proper solvent or solvents, repeatedly with a concentrated solution of ammonium chloride until the conversion is complete-about five portions, Wash the solvent layer 6imilarly 1%-itha concentrated solution of sodium



sulfate; all the ammoilia bound to the organically combined auiiate or sulfonate is quantitatively converted into ammonium sulfate, which passes into the water layer. The latter also contains a11 the ammonium chloride with which the solvent layer may have been contaminated. The water layer is now analyzcd for total ammonia by distillation with excess alkali and for ammonia due to ammonium chloride by analyzing the same solution or an aliquot portion of it for chloride, an analysis which is most conveniently determined volumetrically. The difference represents the ammonia bound by the organic compound; from these data the organically combined sulfuric anhydride may readily be calculated. A duplicate analysis may be made within 3 hours, regardless of the complexity of the sample. SALTWMHISGS. To a mixture of 50 ml. of a concentrated neutral solution of ammonium chloride (about 30 per cent containing some solid salt) and 50 ml. of ether in a 250-nil. separatory funnel, add enough of the sample t o yield about 0.5 gram of organically combined sulfur trioxide and shake vigorously until the sample is completely dissolved. If the sample is a solid, it may more conveniently first be dissolved in water, to which the proper amount of ammonium chloride is then added. Add 5 drops of methyl orange indicator and sufficient 0.5 N hydrochloric acid until the water layer after settling is faintly pink. Draw off the l o m r layer and repeat the washing with four 25ml. portions of the ammonium chloride solution or until conversion into the organic ammonium salt is complete. shaking vigorously each time for about 1minute. With unknown samples, a duplicate analysis is made and when the ash of the oil layer upon ignition is negligible, complete conversion has taken place. If an emulsion forms during the washings, add 3 ml. of alcohol a t a time, mixing gently after each addition, until the emulsion breaks comparatively rapidly and forms t\vo clear, sharp layers. With certain highly sulfonated oils, three layers may form; in that case, either add enough alcohol to cause the niiddle layer t o combirie with the ether layer or dran- off only tlie lower water layer. Combine the mashes and extract n-it,lione or more portions of 25 ml. of ethyl ether (or with equal parts of alcohol and ether where three layers are formed); discard the water layer and wash the solvent layer with two IO-mi. portions of tlie ammonium chloride solution. Combine the solvent layers and similarly wash with a neutral 25 per cent solution of sodium sulfate (about 35" C,) free from chlorides and containing some solid salt--or until all of the ammonia is transferred to the water layer. (To test for complete conversion at this stage, the wash water i;. trsted for ammonia in the usual via?..) Combine the sodium sulfate washes, extract once n-ith 25 ml. of ethyl ether, and viash the latter ivith t\vo 10-ml. portions of the sulfate solutions which are combined with the other washes. Total ammonia and ammonia as chloride are determined in the combined sodium sulfate washes, as follonx: TOTAL A m r o ~ a . Dilute the sulfate washes exactly to 500 ml. and determine the ammonia by distilling an aliquot portion or 200 ml. in a Kjeldahl flask with about 35 ml. of N sodium hydroxide solution, absorbing the liberated ammonia in 25 ml. of N sulfuric acid, and determining the loss of acidity of the latter with 0.5 A\r sodium hydroxide solution, using methyl orange as the indicator. To prevent foaming, pumice stone and 20 to 30 ml. of octyl alcohol may be added to the solution before distillation. Total ammonia is given by the following formula, expressed as milligrams of potassium hydroxide: Total ammonia. as mg. of KOH =


- (ml. of H2S04 X


- ml. of



where t l and tl represent the titers of the acid and alkali, respectively, in milligrams of potassium hydroxide per ml., and a is t.he fraction of the solution taken for analysis. AMMOXIA .IS CHLORIDE.To another 200-ml. portion of the solution, add 0.1 W or 0.25 N silver nitrate solution, depending upon whether the extract is more or less contaminated with ammonium chloride (if alcohol was used in the extraction, considerable amounts of ammonium chloride will usually be present), until present in some excess (about 5 ml. of 0.1 N ) , stir continually for about I O minutes or until the precipitate has coagulated well, filter, and \msh the filter free from silver nitrate. Bdd 2 ml. of nitric acid (4 parts of strong nitric acid and 1 part of xvater, boiled until colorless), 5 ml. of ferric ammonium chloride (saturated solution), and titrate with 0.1 N ammonium thiocyanate olution to a definite brown. Standardize the silver nitrate olution again~t standardized hydrochloric acid, folloning a?


DECEhlBER 15. 1938



Organically Combined SOIAmmonia or S e w .-icid-Volumetric Method Method I I1 Av. I I1 .I\..



70 Sulfated oleic acid Sulfated castor oil Sulfated tallow Sulfated blended oii’ Highly sulfated castor oil Sulfated f a t t y alcohol a Used i n spinning rayon

3 88 3.92 2.53 3.42 6 68 6 13

3 3 2 3 6 fi

65 98 48 51

58 24



3 87 3 95 2 51 3 47 6 63 6 19

3 90 4.26 2.54 3.54 6.92 6 01

% 3 4 2 3

9s 22 60 61


6 16

% 3 4 2 3 6 6

94 24 5; 58 98 09

closely as possible the actual test-namely, in the presence of about 200 ml. of a 10 per cent solution of sodium sulfate. The Rmmonia bound as chloride is calculated as follows: d m m o n i a bound as chloride, i n mg. of KOH =

1 (ml. of



mi. of t S H ‘ S C S X Eitr

where E represents the equivalent of the thiocyanate in terms of the silver nitrate (standardized in a 10 per cent sodium sulfate solution) and t: equals the titer of the silver nitrate, expressed in milligrams of potassium hydroxide.

ORGANICALLY COMBINEDSULFURIC ASHYDRIDE. It is evident, from t h e formulas for t h e ammonium salts of sulfuric acid esters and sulfonic acids (ROS03NH4 and RS03NH4), t h a t one mole of ammonia is equivalent t o one mole of combined sulfuric anhydride. Hence, the organically combined sulfuric anhydride is readily calculated from the previous d a t a as follows (the ammonia results are given in milligrams of potassium hydroxide) : Oreanicallv combined SOa, as ester or sulfonic acid, per cent =