Quantitative Determination of Organic Disulfides RETHEL L. HUBBARD, WILLIAM E. HAINES, and JOHN S. BALL Petroleum and Oil-Shale Experiment Sfation,
U. S.
,Few published methods for determination of disulfides in petroleum and its products have been tested on a variety of disulfides. The availability of disulfides of known purity allowed comparison of three typical chemical methods; none was suitable for all types of disulfides. The acid-reflux method gave the best over-all recoveries but poor recovery of disulfides of lower molecular weight. Because of its rapidity, an acid-stirring method can be recommended for routine work where tertiary compounds are not a factor. Polarography is unsatisfactory for a wide range of disulfides.
of the two tertiary disulfides, recovery data indicate purities greater than 95%. Even though the tertiary disulfides may be of lower purity, comparative recovery data are useful. All recovery figures are based on the assumption of 100% purity of disulfides. As no disulfides with secondary linkages were available, compounds 8, 9, and 10 were synthesized by the general procedure of McAllan and associates ( 7 ), and purified by distillation. Freezing point determinations showed that the first two disulfides had purities of 99+ mole %. The purity of the third could not be determined because it formed a glass. Polarographic Equipment and Solutions. The polarographic studies were made with a Sargent-Heyrovsk9 Polarograph, Model XII. An Htype electrolysis cell was used with a Beckman sleeve-type saturated calomel electrode immersed in tetra-nbutylammonium chloride solution as the reference electrode. The dropping mercury electrode had a rate of flow, m, of 0.975 mg. of mercury per second and a drop time, 1, of 5.0 seconds a t -1.75 volts im*ls t 1 / 6 = 1.285 mg.2/3 sec.-l/J. The basic electrolyte solvent was prepared by mixing 404 ml. of 2propanol, 83.5 ml. of distilled water, and 12.5 ml. of 1 M tetra-n-butylammonium hydroxide. Chemicals. Reagent-grade glacial acetic acid, potassium hydroxide, silver nitrate, sodium acetate trihydrate, methanol, absolute ethanol, 2,2,4-trimethylpentane, benzene, 2-
M
procedures for the determination of disulfides have been proposed, but most have been tested only superficially. Few data are available regarding their efficiency toward disulfides of varied structures. As exploratory work showed that structural differences caused significant differences in recovery. a program was designed to compare the procedures, on 15 disulfides available through API Research Project 48 on the synthesis and purification of sulfur compounds. Three chemical reduction procedures and a polarographic method were tested. The chemical procedures, selected as representative of the many proposed, were: acid-reflux, acid-stirring, and alkali methods. The first two involve reduction of the disulfides with zinc and acetic acid, the first a t elevated temperatures and the second a t room temperature. The third method depends on alkali reduction. Of the several techniques used to determine the thiol resulting from the reduction, all were satisfactory and one was chosen for use with all three procedures. ANY
APPARATUS AND REAGENTS
Test Solutions. A solution of each disulfide was prepared to contain about 0.02 weight yo sulfur. A weighed amount of each compound, except one, n-as dissolved in sulfur-free 2,2,4-trimethylpentane. Benzene was used as the solvent for lJ4-diphenyl2,3-dithiabutane because of its low solubility in 2,2,4-trimethylpentane. Freezing point purity determinations were not possible on many commercial samples because of the small quantity of material available. Others formed glasses when crystallization was attempted. However, with the exception
Bureau o f Mines, laramie, Wyo.
propanol (98%) , zinc dust, and granulated (20-mesh) zinc were used as required. Tetra-n-butylammonium hydroxide and tetra-n-butylammonium chloride as 1M aqueous solutions were purchased from Southwestern Analytical Chemicals. Mercury was redistilled before use. PROCEDURES
Thiol Titrations. The thiols resulting from the three chemical methods were titrated potentiometrically with 0.01N silver nitrate, using a Precision-Dow Titrometer. The method of Tamele and Ryland (10) was followed, except that silver-silver sulfide and glass electrodes (6) were used. The titrant was prepared daily by exact dilution of a 0.1N solution. Titrations of known thiol solutions, including tertiary, showed quantitative thiol recovery. Acid-Reflux Method. A method suggested by Ball ( 1 ) was slightly modified. Fifty milliliters of disulfide test solution, 10 grams of granulated zinc, and 50 ml. of glacial acetic acid were placed in a red-glass (nonactinic) flask fitted with a reflux condenser. A trap cooled in an ice-salt mixture and containing 50 ml. of titration solvent was connected to the reflux condenser. Titration solvent was as efficient a trap as silver nitrate and much more convenient t o handle, because the titration could be done directly without additional solutions. After the mixture had refluxed for 3 to 4 hours, the
Disulfides Tested
1. 2.
3.
4. 5. 6. 7. 8.
9.
10. 11.
Compound 2,3-Dithiabutane (methyl disulfide)= 3,4Dithiahexane (ethyl disulfide)^ 4,5-Dithiaoctane (n-propyl disulfide)" 5,6-Dithiadecane (n-butyl disulfide) 6,7-Dithiadodecane(n-amyl disulfide) 9,lO-Dithiaoctadecane(n-octyl disulfide) 11,12-Dithiadocosane (n-decyl disulfide) 2,5-Dimethyl-3,Pdithiahexane (isopropyl disulfide) 3,6-Dimethyl-4,5-dithiaoctane (sec-butyl disulfide) 1,2-Dicyclopentyl-l,2-dithiaethane (cyclopentyl disulfide) 2,2,5,5-Tetramethyl-3,4-dithiahexane(tertbutyl disulfide)
Source APIRP 48 APIRP 48 APIRP 48 Eastman Kodak Co. Eastman Kodak Co. Connecticut Hard Rubber Co. Connecticut Hard Rubber Co. Synthesized from 2-propanethiol Synthesized from 2-butanethiol Synthesized from cyclopentanethiol Phillips Petroleum Co.
12. 3,3,6,6-Tetramethyl-4,5-dithiaoctane(tertamyl disulfide) 13. 1,2-Diphenyl-1 2-dit hiaethane (phenyl di-
Eastman Kodak Co.
sulfide) 14. 1,4Diphenyl-2,3-dithiabutane (benzyl di-
Eastman Kodak Co.
~
sulfide) 15. 1,2- Di - (4-methylphenyl)- 1,2- dithiaethane (p-tolyl disulfide) Purities >99.9 mole 7,.
Phillips Petroleum Co.
Eastman Kokak Co.
VOL. 30, NO. 1, JANUARY 1958
0
91
reaction flask was cooled with ice-salt mixture; the reflux condenser was rinsed with cold, distilled water and the sample-acid mixture diluted t o 250 ml. with cold, distilled water in a separatory funnel. The water layer was separated, and a 10-ml. aliquot of the oil layer was diluted with 100 ml. of titration solvent for potentiometric titration with silver nitrate. Acid-Stirring Method. Several authors (4,5,8)have suggested reduction of disulfides a t 20" to 50' C., with and without stirring. Investigation of these methods led to the following procedure. A IO-ml. portion of test solution was placed in a 125-ml. Erlenmeyer flask with 25 ml. of methanol, 1 ml. of glacial acetic acid, and approximately 0.5 gram of powdered zinc. A mechanical stirrer was introduced through a one-hole stopper and the mixture was stirred at room temperature for 30 minutes, then filtered quickly by decantation into the titration beaker. The reaction flask and filter paper were rinsed with 100 ml. of titration solvent. The combined filtrate and washings were titrated with silver nitrate.
c-s-5-c-
5-s-
Figure 1 . Polarographic data for 16 disulfides
CFS-S-Cz-@
-
35;
30
t
o c - s - 5 -
c
/ @ a
c - s-s-c
c,s-c:
rp/"
c -s-s-c
LEGEND NORMAL
% I
15I I
=
=
-
lI/ll1 &$
IS0 SECONDARY TERTIARY AROMATIC
c c c- t-s-s-t-c
I or I
5c
c-c-c-s-s-bc-c F C , t ,c
I
a
8
Rosenwald (9), which involves room Toble 1.
,
IO I2 14 E I-VOLTS) vs S C E
16
Sulfur in Organic Disulfides
Sulfur
Structure
Added, TVt. 7 0 0.032
3,4-Dithiahexane
c-s-S-c c2-S--s-c?
4,SDithiaoctane
C3-S-S-C3
0 023
5,6-Dithiadecane
c,-s-s-c, cj-S-S-cs Ca--S-s--C8 ela--S-s-clo
0.024
6,7-Dithiadodecane 'J,l0-Dithiaoctadecane 11.1%-Dithiadocosane
0 025
0 023
0.028 0.024
92
ANALYTICAL CHEMISTRY
Sulfur Determined, Rt. % ' AcidAlkali stirring Reflux 0 027 0.032 0.012 0 027 0.032 0.012 0 023 0.024 0.015 0 023 0.025 0.015 0 024 0.024 0 . e19 0 023 0.024 0.020 0 023 0,024 0.023 0 023 0.024 0.023 0 022 0.022 0.022 0 022 0.023 0.022 0 029 0.029 0,029 0 028 0.029 0.028 0 026 0.025 0.024 0 018 0.026 0.025 0.030 0.028
0 018 0 022
0 . 026
0.024 0.025
0 021 0 021
0.025
0.024 0.024
0.027 0.026 0.026 0.025
0.024
0,020
0,019
0.003 0.003
0 003 0 003
c-c-c-s-s-c-c-c I
0.024
0,017
0.015
0.004 0.004
0 004 0 003
C C C,-S-S-(73;
0 026
0,023
0.022 0.022
0 022 0 022
a 4 - s - s - c - a
0.018
CH~-C,-S-S-OCH~
0,022
C
c
/c-c \c-c
0 022 0 020
C
I
1,2-Di(4methylphenyl)-l,2-dithiaethane
20
0,023 0.023
C
lJ4-Diphenyl-2,3-dithiabutane
1 18
0.030
c-c, c-S-s-c c-c/ c C c-c-s-s-c-c
1,2-Diphenyl-1,2-dithiaethane
>
5
2 5c
Alkali Method. The method of
Compound 2,3-Dithiabutane
Size of circle represents estimated precision of measurement
I
0.023 0.017 0.017 0.020 0.021
0.018
0.018 0.021 0.021
0.017
0 019 0 019 0 020
temperature reaction with zinc dust and Claisen alkali in methanol, was followed. Ten milliliters of test solution was required. Polarographic Method. Methods for determining disulfides polarographically by reduction a t the dropping mercury electrode have been suggested by Gerber (W) and Hall ( 3 ) . The techniques suggested by Hall were used to obtain polarograms of 16 disulfides. The test solutions were diluted 1 to 5 with the solvent electrolyte, andpolarograms were obtained a t 25” =t 1°C. Satisfactory curves were obtained for all compounds except the three secondary disulfides. No plateau was detectable for the secondary disulfides before breakdown of the electrolyte; interpretable inflections were observed when a greater dilution (2 t o 25) was used. RESULTS
Acid-Reflux Method. D a t a for the disulfide determination by the acidreflux method on the 15 compounds are given in Table I. This method is satisfactory for determining the normal and secondary disulfides and aromatic disulfides of high molecular weight. With the tertiary disulfides, recoveries of 62 to 83y0were obtained. Results were low with disulfides t h a t ieduce to volatile thiols of low molecular weight. These thiols may remain as gases in the apparatus or 10 to 307, may be lost in the wash water. Acid-Stirring Method. Good recoveries were obtained by this method
with all the normal and secondary disulfides (Table I). Except for 1,2-diphenyl-1,2-dithiaethane,recoveries greater than 95% were obtained with aromatic compounds. Low results (13 to 17%) were obtained with tertiary disulfides. The use of zinc amalgam (6) did not improve recoveries. Alkali Method. Except for the first two compounds, recoveries above 95yo ryere obtained for the normal disulfides (Table I). Low results were obtained for the secondary, tertiary, and aromatic disulfides. Results on duplicate determinations were often erratic. The use of air pressure to facilitate filtering probably contributes to the low piecision of this method, causing loss of thiols by ovidation and increased evaporation. Polarographic Method. Polaro. graphic data on the 16 disulfides are shown in Figure 1. (One additional disulfide, 2,7-dimethyl-4.5-dithia-o~tane, was added t o shon- the effect of branching.) The diffusion current constant, K, measured a t 25’* 1’ C., is expressed as I d / C where I d is the observed diffusion current in microamperes and C is the concentration of the disulfide in millimoles per liter. Half-wave potentials are reported in reference to the saturated calomel electrode. Internal resistance corrections, which would be high because of the high resistance of the electrode, have not been applied to the half-wave potentials. However, the data are internally consistent because measurements were made a t approxi-
mately equal current. The precision for the secondary and tertiary conipounds was less than for the other conipounds because of interference of the electrolvte. LITERATURE CITED
(1) Ball, J. S., Bur. Mines Rept. In-
vest 3591 (1941). (2) Gerber, M. I., Shusharina, 4. D., Zhur. Anal. Khim. 5 , 262-71 (1950). (3) Hall, M. E., ANAL.CHEM.25,556-61 (1953). (4) Harnish, D. P., Tarbell, D. S., Ibid., 21,968-9 (1949). (5) Kolthoff, I. M., May, D. R., Morgan, Perry, Laitinen, H. A., O’Brien, A. S., IND.ENG.CHEM.,ANAL.ED. 18.442 (1946). (6) Lykken, Louis,’ Tuemmler, F. D., Ibid.. 14, 67-9 (1942). ( 7 ) McAllan, .D. T.; Cullum, T. V., Dean, R. A., Fidler. F. A., J. A m . Chem. SOC.73,3627-32 (1951). (8) McCoy, R. N., Weiss, F. T., ~ X A L . CHEM.26, 1928 (1954). (9) ~, Rosenwald, R. H., Petroleum Processing 6,’973 (1951). (10) Tamele, M. W , Ryland, L. B., IND.ENG.CHELI.,ANAL. ED. 8, 16-19 (1936). RECEIVEDfor review June 11, 1956. Accepted August 26, 1957. Group session, Refining Division, American Petroleum Institute, Montreal, Quebec, May 14, 1956. Part of the work, of American Petroleum Research Project 48A on “Production, Isolation, and Purification of Sulfur Compounds and Measurement of Their Properties,” which Bureau of Mines conducts a t Bartlesville, Okla., and Laramie, Wyo.
Fluorometric and Colorimetric Estimation of Cyanide and Sulfide by Demasking Reactions of Palladium Chelates JACOB S. HANKER, ALAN GELBERG, and BENJAMIN WITTEN Chemical Research Division, Chemical Warfare laboratories, Army Chemical Center, Md.
b Rapid, sensitive, fluorometric and colorimetric methods have been developed for the estimation of microgram amounts of sulfide and cyanide. The methods are based on demasking reactions of palladium chelates. By the fluorometric procedure 0.02 7 of cyanide per ml. of solution may be estimated; the sensitivity to sulfide is 0.2 7 per ml. of solution. The colorimetric method is sensitive to 1 of sulfide or cyanide ion per ml.
T
of cyanide by demasking reactions has been reported by Feigl and Feigl ( I ) and Feigl and Heisig ( 2 ) . The former reported a colorimetric detection procedure in which the demasking of dimethylglyoxime by the action of cyanide ion on palladium(I1) dimethylglyoximate permits nickel ion present to form the red nickel dimethylglyoximate. Feigl and Heisig reported the detection of 2.5 y of cyanide by the demasking of oxine HE DETECTIOS
(8-quinolinol) from copper(I1) oxinate, which permits aluminum ion present to form the fluorescent aluminum(II1) oxinate. This work describes demasking reactions for the detection and estimation of cyanide which are more sensitive and more readily adaptable to quantitative instrumental analysis than the methods mentioned above. The fluorometric method depends upon the demasking of 8-hydroxy-5VOL. 30,
NO. 1,
JANUARY 1958
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