Sulfur in Organic Compounds Containing Nitrogen and Halogen

Acidimetric Microdetermination EDWIN L. BREWSTER, J. T. Baker Chemical Co., Phillipsburg, N. J.

AND WM. RIETlIAN, 111, Rutgers University, New Brunswick, N. J.

r HE disadrantages of the gravimetric microdetermination r o f sulfur in organic substances are so well known that

many investigators (1-4) have sought, more or less success- fully, to develop a volumetric procedure to replace it.

In the case of a sample containing only carbon, hydrogen, oxy- gen, and sulfur, the problem is simple: The sulfuric acid resultin from the combustion in oxygen can be titrated with standar! sodium hydroxide (5) . If the sample contains nitrogen or halo- gen, the problem is more difficult. The nitric or halogen acid must be evaporated without loss of sulfuric acid (S), or the sulfate must be titrated with barium chloride with tetrahydroxyquinone as indicator ( 4 ) . Although the latter method has some staunch supporters, many analysts find the end point difficult. Friedrich and Watzlaweck (9) state that simple evaporation on a steam bath will not serve to separate nitric and halogen acids from sulfuric acid. They recommend a complicated system of titrations and countertitrations designed to hold the sulfuric acid back as sodium bisulfate while the nitric and halogen acids are evaporated.

The authors have found that the low results obtained on simple evaporation of a solution of sulfuric acid are not en-

n

I I I tireiy due to volatilization of that acid, but that neutraliza- tion of the sulfuric acid bv ammonia from the laboratorv air

FIGURE 1

accounts for part of the apparent loss. B y evaporation in a stream of purified air under uniform conditions, nitric and halogen acids can be completely separated from sulfuric acid with only a small, constant loss of the latter.

Air was purified

Apparatus The combustion spiral

tube is of the customary design (5) , except that it must be made of transpar- ent silica. Glass tubes are slightly decomposed a t the temperature of combustion with resultant liberation of alkali that neutralizes some of the sulfuric acid. Opaque silica is too porous to per- mit satisfactory washing, The spiral of the combus- tion tube and the test tube used to cover the end may be of Pyrex.

T h e e v a p o r a t i n g dish must also be of transpar- ent silica. Dishes 3.75 cm. (1.5 inches) tall and 5.6 cm. (2.25 inches) in di- ameter, holding 65 ml., were used in this work.

The evaporation occurred in an air conditioner illus- trated in Figure 1. The evaporating dish rested on a porcelain ring supported by a beaker, which served as a steam bath. A funnel was inverted over the dish.

by passage through concen- TABLE I. RESULTS OBTAISED FROM RIARCH 13 TO JUNE 21, 1940 trated sodium hydroxide, concentrated sulfuric

acid, and a large bottle serving as a settling vessel for droplets of sulfuric acid, and was

Sulfur Sulfur Mean Deria- finally led into the stem of the funnel a t a rate Compound Formula Theory Found Error tion of 9 liters Der minute. (Rates of 5 to 20 liters

(Blank correction = + 107 sulfur) Mean

Benzyl sulfide Sulfanilic acid Imuure diuhenvlthio- . .

urea 2.4 - Dichlorouhenvl- - . ~

4-to1rienesu1fbnati 2,4 - Dichlorophenyl-

3,4-dichlorobenzene- sulfonate

Bromorrrsoi purple

CiiHiaS CsH;OaNS

CiaHizNzS

CiaHloOsCInS

CinHsOaClrS CnHlsOsBrzS

% 14.97 18.51

14.040

10.11

8 . 6 1 5.96

7% 14.92 18.65

14.83

10.17

8.62 5.85

% -0.05 $0.14

+0.03

$0.06

+0.01 -0 .11

70 0.18 0.06

0.08

0 . 0 1

0 . 0 7 0 .08

2,4,6-Tribrornophenyl- p-toluenrsulfonate CiaHDOaBrsS 6.61 6.79 $0.18 0 .01

4 - Ivitrr,chli,robenzene- 2-sulforiic acid dihy- drate CsI-14OsNC1S.2HzO 11.71 11.49 -0.22 0.02 a Impure compound. Mean of several macrodeterminations with a Parr peroxide bomb

wa6 14.80% sulfur.

T.4BLE 11. RESULTS OBTAINED FRO31 JULY 11 TO JULY 18, 1941 (Blank correction = +21r sulfur)

Compound

7 - Iodo - 8 - hydroxy- quinoline - 5 - sul- fonic acid

8 - Methyl - 2,2' - di- ethylthiocarbocya- nine iodide

Methylbensothiazole- ethiodide

Ethylphenylthiohy- dantoin

Mean Sulfur Sulfur Mean Devia-

Formula Theory Found Error tion % % % %

CpHsOiINS 9.13 9.22 +0.09 0.07

CzzHnIXnS, 12.66 12.56 -0.10 0.06

CioHizINS 10.51 10.59 $0.08 0.03

CiiHuONnS 14.55 14.49 -0.06 0 . 0 1

per minute' were found satisfactory.) When the air stream impinged directly on the surface of the evaporating solution, excessive loss of sul- furic acid was incurred. This was avoided by employing an ordinary crucible cover as a baffle. The cover was suspended by string which was held in place by the rubber tubing over the end of the funnel.

Procedure A sample of 4 to 6 mg. is weighed in a platinum

boat and subjected to the usual combustion in the spiral tube (6). After combustion, the con- tents of the spiral tube are rinsed into the evapo- rating dish by five 2-ml. portions of water. If the tube is clamped vertically and the water added quickly, complete transference is achieved with this volume of wash water. Each portion of wash water is caught in the Pyrex test tube and then transferred t o the dish.

The dish is then set on the steam bath (Figure 1) for 45 minutes. The evaporation appears to be complete in 30 minutes, but 40 to 45 minutes are required to drive off nitric acid completely.

After cooling, the contents of the dish are titrated with standard 0.01 N sodium hydroxide to the methyl red end point. The sodium hy- droxide may be conveniently standardized against potassium biniodate or sulfamic acid with the same indicator.

a20

October 15, 1942 A N A L Y T I C A L E D I T I O N 82 1

BLANK. A blank determination is performed as follows: The combustion tube is heated just as in a combustion, but no sample is taken. The tube is rinsed into the evaporating dish, and a measured volume of standard sulfuric acid (usually 2 ml. of 0.01 N solution) is added. The evaporation is conducted for 45 min- utes, and the contents are titrated with sodium hydroxide as usual. Any difference between the sulfuric acid taken and that found by the titration is added to or subtracted from-as the case mag require-the sulfur found in an actual determination.

The blank corrects for acids in the hydrogen peroxide, alkali acquired from the glass spiral, volatilization of sulfuric acid, and neutralization of sulfuric acid by ammonia from the air. The blank correction increases slightly with continued use of the com- bustion tube. This phenomenon, which is illustrated by a com- parison of the blank correction of Table I with that of Table 11, is probably due to a slow deterioration of the glass spiral during the combustion.

Results

Some typical results obtained by this method are given in Tables I and 11. Each entry in the table is the mean of two or more determinations.

Discussion

This method yields accurate results in the presence of large amounts of nitrogen, chlorine, bromine, and iodine. It requires less time than the method of Friedrich and Katzla-

weck (3) and gives a much sharper end point than the method of Hallet and Kuipers ( d ) , but is not applicable to metal or- ganic compounds. I n such cases some of the sulfur is retained in the boat as metallic sulfate.

An attempt was made to apply the evaporation and titra- tion of sulfuric acid to the determination of sulfur, following an oxidationof the organic sample by the micro-Carius method. This was not successful because alkali is extracted from the glass bomb during the oxidation. Furthermore, a longer period of evaporation is necessary to remove the large quan- tity of nitric acid.

Acknowledgment

The authors wish to express their indebtedness to E. B. Middleton of the Du Pont Film Manufacturing Corporation, Parlin, N. J. , for several of the samples used in the analyses.

Literature Cited (1) Brewster, doctor’s thesis, Rutgers University, 1912. (2) Friedrich and h‘iandl, Mikrochemie, 22, 14 (1937). (3) Friedrich and Watzlaweck, 2. anal. Chem., 89, 401 (1932). (4) Hallet and Kuipers, IND. ENG. CHEM., A x . i L . ED., 12, 360 (1940). ( 5 ) Niederl and Niederl, “.Micromethods of Quantitative Organic

Elementary Analysis”, 2nd ecl., p. 188, New York, John Wiley & Sons. 1942.

Adaptation of an Indirect Method for Potassium to the Photoelectric Colorimeter

C. P. SIDERIS, Pineapple Research Institute of Hawaii, Honolulu, 1’. H.

The determination of potassium as po- tassium sodium cobaltinitrite with nitroso R salt (disodium salt of 1-nitroso-2-hy- droxy-3,6-naphthalenedisulfonic acid) can be made with much greater precision using a photoelectric colorimeter with appro- priate light filters instead of an optical colorimeter. The range of concentrations best suited is from 0.5 to 15 micrograms.

N APPRECIABLE iniprovement was found by using a A photoelectric instead of an optical colorimeter in con- nection with the colorimetric method of the author (4) for cobalt and potassium within a range of concentrations from 0.5 to 15 micrograms of potassium or from 1.0 to 30 niicro- grams of cobalt.

Potassium is precipitated as potassium sodium cobaltini- t’rite as in the original method. The precipitate is dissolved and its potassium content’ is determined indirectly by measur- ing colorinietrically with a photoelectric colorimet’er (Klett or other type) the coloi intensities of the wine-red pigment of nitroso It salt with different amount’s of cobalt whic,h are directly proportional to those of potassium in the sodium potassiuni cobaltinitrite precipitat,e.

Reagents SITROSO R SALT.

SoDImf A A ~ ~ ~ ~ k ~ ~ .

Dissolve 1 gram of nitroso R salt in 70 ml. of

Place 544.3 grams of sodium acetate tri- water and then add 30 ml. of iron-free acetone.

hydrate in a 1000-ml. volumetric flask, add water to complete volume, heat over a steam bath, and filter.

Dissolve 12.5 grams in 100 ml. of water and filter. Only immediately before using, portions of this reagent should be mixed with equal volumes of 95 per cent alcohol because the mixture is not very stable after mixing and should not be prepared in greater amounts than those needed immediately.

Dissolve 3.043 grams of cobalt chloride hexahydrate in water, add 5 ml. of 5 -11 hydrochloric acid, and dilute with water to 1 liter. One milliliter of this solu- tion contains 0.7537 mg. of cobalt, which is equivalent to 1.000 mg. of potassium. This standard is relatively concentrated and aliquots taken for comparisons must be diluted from 100 to 500 times.

Place 400 grams of sodium hydroxide in a 1000-ml. volumetric flask and make to volume with water.

SODIUM COBBLTINITRITE.

STANDARD COBALT SOLUTION.

10 SODIUM HYDROXIDE.

Procedure A4sh a quantity of plant tissues (0.5 to 1.0 gram) containing 0.04

to 0.10 mg. of potassium in a platinum crucible, and dissolve the ash in 5 ml. of 1 per cent hydrochloric acid. If analyses for other elements are to be made in the same material, filter to remove silica and other precipitates, and take an aliquot for the deter- mination. If not, make the entire volume of the solution alkaline to phenolphthalein by adding a few drops of a 40 per cent solution of sodium hydroxide. Warm on a hot plate to effect flocculation of iron and of vanadium which interfere with the potassium and cobalt determinations and then either centrifuge or filter to re- move the precipitate. Make to 100 ml. with water.

Take an aliquot of the centrifugate or filtrate, either 5 or 10 ml., and place in a 50-ml. beaker. Xeutralize and make decidedlj- acid with 1 ml. of 1 per cent hydrochloric acid. Place the beaker over a steam bath and evaporate to dryness until all fumes of hydrochloric acid have disappeared. Add t o the beaker after cooling about 0.5 ml. of water and then 10 ml. of the sodium cobaltinitrite-alcohol reagent. Place the mixture in a refrigera- tor for 2 to 4 hours and cover it t o protect it from ammonia fumes. Filter through a fritted-glass crucible (Corning S o . F)