Rapid Determination of Hydrolyzable Sulfur in Organic Compounds SIR: X h e n compounds containing CS, S-S, SCS, or SCN groups are heated with o-hydroxymercuribenzoic acid in the presence of sodium hydroxide solution, they readily split u p the total sulfur or its sulfide component, which form complexes with o-hydroxyniercuribenzoic acid. Numerous compounds have been successfully determined from the consumption of o-hydroxymercuribenzoic acid. The procedure used for titration of sulfides m+ith o-hydroxymercuribenzoic acid solution using dithizone or thiofluorescein as indicator ( 1 , 2) can be applied to the determination of hydrolyzable sulfur in organic compounds. “Hydrolyzable sulfur” in this paper relates to sulfur that forms sulfide after boiling with o-hydroxymercuribenzoic acid. It has been stated that the numerous bivalent sulfur-containing compounds undergo rapid hydrolysis when heated with o-hydroxyniercuribenzoic acid in alkaline solution, rrhich produces the sulfide complexes. T h e back-titration of unconsumed o-hydroxymercuribenzoic acid represents a simple method for the determination of hydrolyzable sulfur,
ammonium hydroxide) solution to 15 ml. of 0.038 o-hydroxymercuribenzoic acid solution, dilute to 100 ml., and titrate with thioglycolic acid in the presence of 1 ml. of 0.02% thiofluorescein solution to a permanent blue color. Thioglycolic acid solution loses about 0.1% of its titer per day. SODIUM SULFIDE SOLUTION. Dissolve 6 grams of sodium sulfide nonahydrate in 1 liter of solution containing 0.2N sodium hydroxide and 20 grams of sodium sulfite. For standardizing add 5 ml. of 1N sodium hydroxide t o 10 ml. of this solution, dilute to 100 ml., and titrate with o-hydroxymtrcuribenzoic acid in the presence of 0.5 ml. of O.lyodithizone solution until the color changes sharply from yellow to purple. The solution of sodium sulfide loses about 0.2% of its titer per day. PROCEDURE
Add 5 ml. of 1 S sodium hydroxide solution and 20 ml. (excess) of 0.03N o-hydrosymercuribenzoic acid solution, in a n Erlenmeyer flask, t o the sample which contains less than 10 mg. of hydrolyzabk sulfur, dissolved in alcohol or water. Heat to a gentle boil on a hot plate and boil for 5 minutes. Volatile compounds must be boiled under reflux with 10 ml. of alcohol REAGENTS added. After the solution is cool, o-Hydroxymer c u r i b e n z o i c Acid dilute t o 100 ml. with cold water and Solution. Dissolve 10 t o 16 grams of determine the unconsumed o-hydroxyo-niercuribenaoic acid anhydride in mercuribenzoic acid by one of the follow200 ml. of I N sodium hydroxide. ing methods. After 2 t o 3 days filter a n d dilute t o Add 10 ml. of 0.02yo thiofluorescein 1 liter. solution in dilute ammonium hvdroxide Standardization of o-Hydroxymerand titrate with thioglycolic azid solucuribenzoic Acid Solution. STAKD- tion until a permanent blue color apARDIZING WITH STANDARDTHIO- pears. SULFATE SOLCTION.Dilute 5 t o 10 Add 5 ml. (escess) of sodium sulfide ml. of 0.1‘)- thiosulfate solution t o solution and 0.5 ml. of dithizone solu80 ml., add 20 ml. of t h e solution contion and titrate with o-hydroxymercuritaining 0.LV acetic acid plus O.5N benzoic acid solution until the color sodium acetate and 1 ml. of 0.2y0 changes from yellow t o purple. Dediphenylcarbazone solution as intermine separately the consumption of dicator, and titrate with 0.03 t o o-hydroxymercuribenzoic acid for the 0.05.V o-hydrosymercuribenzoic acid sodium sulfide added and subtract it solution to the first permanent blue from the result of the first titration. tinge. Thiosulfate and o-hydroxyEach milliliter of 0.03N o-hydroxymercuribenzoic acid react as folio\\ s: mercuribenzoic acid solution corresponds to 0.4809 mg. of hydrolyzable RHgOH 4 SeOa-’ CHaCOOH = sulfur. RHgS203 CH3COOH?O Although the hydrolysis of the STANDIRDIZIKG WITH ARSENIOUS SULmajority of compounds is complete FIDE. Dissolve 10 to 20 mg. of pure after 2 minutes of boiling, for some even AS& dried a t 105’ C. in 5 ml. of I S 5 minutes of boiling are insufficientsodium hydroxide, and dilute t o 100 e.g., ethyl xanthate and diethyldithioml. Titrate with o-hydroxymercuribenzoic acid solution in the presence of carbamate. 1 ml. of 0.0270 thiofluorescein solution The presence of thiosulfate, sulfite, until the blue color sharply disappears. and thiocyanate does not interfere The total sulfur content of arsenious with the titration of sulfide with sulfide reacts as sodium sulfide. o-hydroxymercuribenzoic acid in the THIOGLYCOLIC ACID SOLUTIO?;.Dispresence of dithizone or thiofluorescein solve 5 grams of thioglycolic acid in 1 as indicator. or with the determination liter of solution containing 0 . 2 5 soof hydrolyzable sulfur, although thiodium hydroxide and 20 grams of sodium sulfate can be titrated in acid solution sulfite. For standardizing add 5 ml. of 1S sodium hydroxide (or 5 ml. of with o-hydroxymercuribenzoic acid in
+
+
+
Table 1. Repeatability of Hydrolyzable Sulfur Determination
Thioacetamide,
Hydrolyzable Sulfur,
Mg. 8.41 16.82 25.23
Mg. 3.52, 3.56 7.18, 7.14 10.72, 10.70
Table II. Total and Hydrolyzable Sulfur in Organic Compounds
Compound Sodium trithiocarbonate Sodium methylxanthate Sodium cellulosexanthate Thiourea DiDhenvlthiourea Ammoiium ethyldithiocarbamate Ammonium phenyldithiocarbamate Ammonium dithiocarbamate Phenyl isothiocyanate
Sulfur in Sample, Mg. HydroTotal lyzable 7 ,92 6.75 7.12 7.44 5.85
7 .90 6.71 7.16 7.42 5.77
7 .17 7.14 9.84 9 . 7 6 8 . 4 6 4.20 5.06 4.98
Table 111. Consumption of o-Hydroxymercuribenzoic Acid as a Function of Weight of Wool
o-Hydroxymercuribenzoic, Mmole
Sheep FF-ool, Mg.
0.040 0,090 0.155 0.195 0.268
17.6 45.0 79.2 106 158
the presence of diphenylcarbazone as indicator. During boiling, the complex of ohydroxymercuribenzoic acid with sulfide undergoes the follo-cving reaction 2 RHgSHgR = RHgR
+ RHgSHgSHgR
and forms a new yellow complex. However, this reaction has no influence on the hydrolyzable sulfur determination because there is no change in the o-hydroxymercuribenzoic acid consumption after boiling with sulfide. Addition of sodium sulfide to the alkaline solution containing mercury(I1) salts and o-hydroxymercuribenzoic acid does not induce the precipitation of mercury sulfide because the RHgSHgSHgR and RHgSHgS- complexes are formed. The back-titration of excess sulfide with o-hydroxymercuribenzoic acid in the presence of dithizone can be successfully applied to the rapid accurate determination of mercuric ion. RESULTS AND DISCUSSION
The repeatability of hydrolyzable VOL. 32, NO. 1, JANUARY 1960
133
sulfur determination in thioacetamide is shown in Table I. The average results from three determinations of hydrolyzable sulfur appear in Table 11. The total sulfur was known from the composition. For compounds which cannot be obtained in a pure state, total sulfur was found by analysis. I t can be seen from Table I1 that the hydrolyzable sulfur of the compounds listed is equal to their total sulfur content, except for ammonium dithiocarbamate which decomposes according to the reaction SHICSS-
+ 2 OHCSS-
+ S-’+ 2 HzO
The method described in this paper
can be applied for such conipounds as rubianic acid, rhodanine. cystine, organic aiid inorganic polysulfides, and organic thiocyanate. Reliable results can be obtained when o-hydroxymercuribenzoic acid solution is standardized under the conditions of the determination. In some cases-e.g., polysulfide-the course of hydrolysis depends on o-hydroxymmxribenaoic acid and sodium hydroside concentration. For the determination of such compounds the calibration curve giving the consumption of o-hytlrosymercuribenzoic acid as a function of quantity of the compound tinder the conditions of determination may be recommended. This method can be applied to the rapid determination of wool (Table 111).
The sample containing less than 180 nig. of wool, dried at 105” C., is heated with 10 nil. of 0.04-V o-hydrosymercuribenzoic acid, 5 1111. of 1N sodium hydroside, and 25 nil. of m-ater for 15 minutes. and the excess of o-hydrolymercuribenzoic acid is backtitrated n i t h thioglycolic acid as described a h o w . LITERATURE CITED
(1) W-roriski, >I., l n d y s t 83, 314-5 (1908). ( 2 ) Wroriski, SI.,Zeszyly .\-a,tk. C., r n i v . Lodz 11, XO.4 , 181-93 11958). ~IIECZY‘T x w \TRO
