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Thiomercurimetric determination of carbon disulphide, carbonyl sulphide, thiols and hydrogen sulphide by use of 1,3-diaminopropane and tributyltin chloride
Tolanta. Vol. 22, pp 425-429
Pergamon
Press.
1975 Prmted m Great
Brntam
THIOMERCURIMETRIC DETERMINATION OF CARBON DISULPHIDE, CARBONYL SULPHIDE, THIOLS AND HYDROGEN SULPHIDE BY USE OF 1,3-DIAMINOPROPANE AND TRIBUTYLTIN CHLORIDE MIECZY~LAW WRONSKI Department of Chemical Technology, University of todi, Nowotki 18, Loti, Poland (Received 15 July 1974. Accepted 10 October 1974)
Summary-A new approach to the determination of carbon disulphide and carbonyl sulphide in the presence of each other is based on the reaction with 1,3_diaminopropane (DAP), and titration with o-hydroxymercurybenzoic acid (HMB) before and after the selective decomposition of the COS-derivative at pH 4. Determination of hydrogen sulphide, thiols, carbon disulphide and carbony1 sulphide in the presence of each other in hydrocarbon solvents involves four titrations with HMB, viz. of all compounds after conversion of CS2 and COS with DAP, of thiols plus H,S, of the thiols alone after removal of H2S by extractton, and of CS2 alone after removal of other compounds by shaking with aqueous alkali. For selective trapping of H,S, HCN, RSH, CO2 and CS2 + COS, the sample gas IS passed successively through a potassium antimony1 tartrate filter, a nickel carbonate filter, a tributyltin chloride filter, a bubbler containing 40% potassium hydroxide solution and a bubbler containing a benzene solution of DAP. The analysis is completed by titration with HMB with dithrzone or dithiofluorescem as indicator.
Rapid, simple and reproducible methods for determination of sulphur compounds occurring in gases and hydrocarbon solvents are of vital importance. Although the development of gas chromatography employing new types of detector for sulphur compounds has opened the way for interesting mvestigations, the practical difficulties in dealing with very complicated mixtures may appear formidable. In spite of a rather extensive literature on the determination of sulphur compounds,’ no one method deserves to be recommended for analysis of hydrocarbon solvents and fuel gases containing hydrogen sulphide, thiols, carbon disulphide and carbonyl sulphide. It is attempted in this paper to demonstrate the usefulness of a new approach to analysis of sulphur compounds, based on the application of the reagents, new for this purpose, 1,3-diaminopropane and tributyltin chloride. The former is soluble in aromatic and mixed hydrocarbons and reacts very rapidly with carbon disulphide and carbonyl sulphide to give the derivatives, 1-amino-3_propyldithiocarbamate and 1-amino-3-propylmonothiocarbamate, which can conveniently be determined by titration with o-hydroxymercurybenzoic acid (HMB). Taking into account that one mole of either carbon disulphide or carbonyl sulphide produces one mole of hydrogen sulphide, and that cyclic thioureas are indifferent towards HMB in alkaline solution2 the only possible course of the reactions is given by the equations
HPN(CH,),NHCSSH
+
H,N(CH,),
+
NHCOSH
20--H = ~-~;;o
+
2@i
+
=
o~;sO;;~
CHf::->CS
+ 2 “20
CHf::->CO
+ 2 Hz0
It has been found that in acid solution the derivative of COS is rapidly decomposed to COS and DAP, whereas the derivative of CS2 is relatively stable. In 5 min at 20” the COS derivative is 100,99*5 and 7% decomposed at pH 3*5,4 and 5, respectively. The corresponding values for the CS2 derivative are 0.6, 0.2 and O*O’/& Consequently the decomposition at pH 4 is the most suitable for the determination of both derivatives in the presence of each other. This approach has proved to be more convenient than methods based on 425
MIECZYSLAW WRO~KI
426
selective hydrolysis of carbonyl sulphide3 or on spectrophotometric determination of the derivatives.4 A benzene solution of DAP can be used for trapping carbon disulphide and carbonyl sulphide. The tributyltin chloride filter has been used with success for trapping thiols in absence of hydrogen sulphide and hydrogen cyanide, which must be removed beforehand. The thiols retained can be simply washed out and determined by titration with HMB. For trapping hydrogen sulphide a filter containing potassium antimony1 tartrate has proved the most suitable. The antimony1 sulphide formed can be dissolved in sodium hydroxide and titrated with HMB. For selective removal of hydrogen cyanide from H,S-free gas a nickel carbonate filter can be recommended.
EXPERIMENTAL Reagents The preparation of the solution of HMB in 50% v/v aqueous propyl alcohol, and of the solutions of dithiofluorescein and dithizone is described in an earlier paper.5 1,3-Diaminopropane and tributyltin chloride were supplied by EGA Chemie KG (7924 Steinheim bei Heidenheim/Brenz, West Germany). Solution A is 0.05M in potassium carbonate and 0.025M in borax in saturated sodium chloride solution, The extraction coefficient for the system tohiene-sohttion A 1s 0074 for H,S, 72 for ‘CH,SH, and 40 for thiophenol. Solution B is M in phosphoric acid and 0.5M in tartaric acid. Reagents for impregnating
filters
Filter A for trapping hydrogen sulphide. Whatman CF 11 cellulose (10 g) mixed with 12 ml of a solution containing 30 g of potassium antimony1 tartrate, 50 g of disodium tartrate, 10 g of disodium EDTA and 4 g of potassium carbonate per Iitre. Filter B for trapping hydrogen cyanide. Solutions of 25 g of nickel chloride hexahydrate in 7.5 ml of water and 1.5 g of potassium carbonate m 2.5 ml of water are mixed and added to 10 g of cellulose. Filter C for trapping thiols. Tributyltin chloride (10 ml of 0.5M solution in 2-ethylhexanol) mixed with 0.4 ml of triethanolamine and 10 g of cellulose. Filter D for trapping carbon dlsulphide and carbonyl sulphide. Tributyltin chloride (1 ml), 1,3-diaminopropane (3 ml) and 2-ethylhexanol(l0 ml) are mixed with 10 g of Woelm column-chromatography polyamide. Analysis of solvents Determination of carbon disulphide and carbonyl sulphide, procedure 1 a. Place in a dry 15-mm diameter test-tube 0.05 ml of DAP, add 2 ml of sample solvent, placing the jet of the pipette at the bottom m order to avoid any loss of COS, wait 2 min, add 2 ml of propanol, @15 ml of 2M potassium hydroxide and titrate with 10m3M HMB, using dithiofluorescein as indicator. Wait 3-5 min and titrate to the final end-point. During the titration add ethanol in amounts just enough to clear the emulsion produced. The method is directly applicable to aromatic hydrocarbons; aliphatic hydrocarbons should first be diluted 1: 1 with sulphur-free benzene. With alcohols as samples the reaction is not so rapid; a wait of about 10 min is needed before the titration. Procedure 1 b. Place 0.05 ml of DAP in a separatmg funnel and add slowly, keeping the jet of the pipette at the bottom 10 ml of the sample, mix, wait 2 min, add 2 ml of 0.3M potassium hydroxide containing 1 g of EDTA per litre, shake for 5 min, let the phases separate, take 1.5 ml of the aqueous phase, add 2 ml of ethanol and 0.1 ml of 4M potassium hydroxide, and titrate m a test-tube with 10-4-10-3M HMB, using dithlzone as indicator. to a permanent purple colour. Dithiofluorescein can be used as well but dithizone is preferable. In titration with lo-“M HMB a blank comparison solution containing dithizone and HMB must be used, the titration being continued until the colours of the both solutions match. The result multiplied by the ratio 2.05/1,5 (because DAP increases the volume of the aqueous phase) corresponds to the whole sample. If an aliquot of the aqueous phase is titrated after 5 min decomposition at pH 4, as described later, the COS and CS2 content can be calculated. Procedure lb can be used for analysis of aromatic hydrocarbons. aliphatic hydrocarbons diluted with benzene and for halogen derivatives such as carbon tetrachloride. Procedure 1 c. This applies to determination of CS, and COS in water. In this case the use of ethylenediamme is preferable. Heat in a test-tube 0.5 ml of ethylenediamme and add slowly l-5 ml of water sample, keeping the jet of the pipette at the bottom. Do not mix. The ethylenediamine should form an upper layer, Place the test-tube in boiling water for 2 min, then mix and titrate with IO-‘M HMB in the presence of dithiofluorescem. Procedure 2. This applies to determination of hydrogen sulphide and thiols in the presence of carbon disulphide and carbonyl sulphide. Carbonyl sulphide interferes with the titration in alkalme solution but does not in slight alkaline solution. On the other hand a remarkable loss of hydrogen sulphide can be observed during titration in slight alkaline solution. Good results can, however, be obtained by using a reverse titration: a definite volume of HMB is diluted with ethanol and titrated with the sample, added from a graduated pipette with the jet kept at the bottom of the HMB solution, in the presence of dithiofluorescein as indicator, until the solution turns blue. The content of CS2 and COS can be calculated by difference from the results of this procedure (H,S + RSH) and of procedure la (H2S + RSH + CSZ + COS). Procedure 3. This applies to determination of small amounts of thtols m the presence of an excess of hydrogen sulphide, carbon disulphide and carbonyl sulphide. Place 10 ml of sample in a separating funnel and extract four times with 4 ml of solution A and finally with 2 ml of water. Add 5 ml of propanol and titrate the thiols remaining in the organic phase with 10e3M HMB in the presence of dithiofluorescein.
Determination of carbon disulphide
421
Procedure 4. This applies to determination of small amounts of carbon disulphide in the presence of an excess of hydrogen sulphide, carbonyl sulphide and thiols. Remove the interfering compounds by shaking 10 ml of sample twice for 1 min with 5 ml of 2M potassium hydroxide, for 30 min with another 5 ml (to complete the hydrolysis of carbonyl sulphide) and finally twice for 1 min with 2 ml portions of alkali. Determine the carbon disulphide remaining, according to procedure lb. Only about 0.1% CSz is lost by hydrolysis. Analysis of gases
For preparation of the filters use lO-mm diameter lOO-mm long tubes, packed for a length of 052 cm with slight pressure from a glass rod. On both sides of the packing place wads of cotton-wool, (except for filter D). The gas or an sample is aspirated at a rate of @l l./min through the trapping filters and solutions in the following order, l-cm filter A, 05-cm filter B, l.S-cm filter C, lo-mm diameter U-tube containing 10 ml of 40”%w/w potassmm hydroxide solution (to remove carbon dioxide which at high concentration interferes with trapping of carbon drsulphide and carbonyl sulphide), 20-ml conical gas bubbler containing 4 ml of 2.5% v/v solution of DAP in benzene or toluene. When only the CS2 and COS content are to be determined the gas is passed through 40% potassium hydroxide solution and the DAP bubbler. When no distinction between CSz and COS is necessary, filter D may be used instead of the DAP bubbler. After the sample, pass a stream of pure inert gas or air for 5 min and determine the separated constituents as described below. Determination of hydrogen sulphide. Place in a 14-mm diameter 180-mm long test-tube a glass rod of 8-mm diameter and 140-mm long, push out filter A onto it and wash the filter (in a vertical position) with 2 ml of IM sodium hydroxide and 2 ml of water, using air pressure on the upper part of the filter tube to accelerate the flow. The solution passes the filter and flows down along the glass rod to the bottom of the test-tube. Remove the filter and glass rod (rinsed with a few drops of water) and titrate the solution with 10-4-10-3M HMB in the presence of dithizone. Determimtzon of thiols. Wash filter C twice with 2 ml of ethanol as described above, add dithiofluorescein and 1M sodium hydroxide dropwise till the solution just turns blue. Titrate with 10m3M HMB until the blue colour disappears. Determination of carbon disulphide and carbonyl sulphide. Add to the DAP bubbler 4 ml of 0.3M potassium hydroxide (containing 1 g of EDTA per litre) and stir vigorously with an air stream for 5 min to transfer the product into the aqueous phase. Let the phases separate, and take 1 ml of the aqueous phase, add 0.2 ml of 4M potassium hydroxide, dilute with.ethanol and titrate with 10-4-10-3M HMB, usmg dithizone as indicator, (VI ml). In another bubbler (prepared from a test-tube) place 2 ml of the aqueous phase and add enough of solution B (as determined in a blank test) to make the pH 3.ti.0, or add solution B dropwise till Methyl Red added as indicator just changes to red. Pass an an-stream for 5 mm to remove the carbonyl sulphide produced, add the same volume of 4M potassium hydroxide as of solution B, dilute with ethanol and titrate with 10e3M HMB in the presence of dithizone as indicator, (V, ml). Calculate the concentration (mg/l.) as follows:
CCW = [COS] =
38 x 1.05 x 2.05 x V, x MHMB V,
1~05(4~1OV, - 2.05V,)30MnMB
v, where V, 1s the volume of gas taken and 1.05 is an empirical coefficient. Another approach is based on using filter D. After trappmg of CSI and COS by a 2cm filter D, the filter is pushed out into a test-tube, ethanol and @2 ml of 4M potassium hydroxide are added and the sample is titrated with HMB. with dithizone as indicator. RESULTS
AND
DISCUSSION
Samples containing known amounts of test substances were prepared or produced as follows. Carbon disulphide solutions were prepared by weighing and gas mixture by acid decomposition of an aqueous solution of sodium diethyldithiocarbamate, the concentration of Table 1. Determination of carbon disulphide and carbonyl sulphide in benzene and in water Procedure
la la la la la lb lb lb lb lb lc * Without correction.
Taken, pceq cos CS2 23.5 235 4.55 2.35 042 0.74 004 8.70
202 4.04 2.02
Rel. std. devn. %
Mean recovery* (6 titrations), %
0.3 0.5 0.5 0.6 0.8 0.8 41 3.3 13 0.6 0.7
99.1 964 91.2 96.8 97.6 98.4 94.3 97.0 93.6 97.5 983
428
MIECZYZAWWRO~~SKI Table 2. Determination of methanethiol in benzene in the presence of hydrogen sulphide, carbon disulphide and carbonyl sulphide (100 peq of each) (procedure 3)
Table 3. Determination of carbon disulphide in benzene in the presence of methanethiol, hydrogen sulphide and carbonyl sulphide (100 pq of each) (procedure 4)
Taken, pceq
Found, pey
Taken, peq
Found, pq
1.02 2.04 3.06
0.98,@99,0.99 2.01, 1.98,2.00 3.00.3.05, 3.03
1.50 3.00
1.47, 1.54, 1.48 3.02.2.96. 2.99
which was determined via BaSO,. Known amounts of carbonyl sulphide, hydrogen sulphide and methanethiol were produced by acid decomposition, in a stream of nitrogen, of aqueous solutions of DAP-COS, of soluble starch-zinc sulphide6 and of a solution of methanethiol in 2M potassium hydroxide. The solutions were analysed by titration with HMB, and decomposed by 1M sulphuric acid.
Table 4. Determmation of hydrogen sulphide and methanethrol in the presence of each other m nitrogen, by using filters A. B and C Taken, peq CH$H
Found, peq
H2S 044
1.76 0.044
1.30 3.90 3.90
CH,SH
H*S 0~44,0~43.0~41 1.73. 1.75, 1.70 0~040.0~041
1.25. 1.27, 1.25 3.88, 3.90. 3.92 3.88. 3.86
As shown by Tables l-5, the results are satisfactory and the suggested methods can be recommended for general use. Method lb has a lower limit of 0.1 ppm and is very suitable for trace determination of carbon disulphide in such solvents as benzene or carbon tetrachloride. By use of procedures la, 2, 3 and 4, a solvent containing carbon disulphide, carbony1 sulphide, hydrogen sulphide and thiols can easily be analysed. The results are not influenced by thioethers and disulphides, but free sulphur interferes with the procedures for CS2 and COS. In the presence of hydrogen cyanide a few drops of 5% formaldehyde solution must be added. Table 5. Determination of carbon disulphide and carbonyl sulphide in the presence of each other in nitrogen after passage through filters A. E, C and potassium hydroxide bubbler. Results are corrected by a factor of 1.05 Taken. peq cos CS,
Found, peq cos cs2
1.16 55.8 11.6 6.10 6.10 0
1.15 56.0 11.3 5.90 5.95 0.05
42.5 2.18 4.25 0 1.80 7.25
41.7 2.22 4.23 0.10 1.84 7.10
The use of filters A and C for trapping hydrogen and thiols and of filter D for trapping carbon disulphide can be recommended for air analysis as the products are very resistant to air oxidation. In order to make a correction for low recovery of CS, and for loss of COS during passage through the 40% potassium hydroxide solution, the use of an empirical coefficient, 1.05, is suggested. The average CS2 and COS content in the town gas in todz, as determined by the suggested method, amounted to 0.077 and 0.103 mg/l. respectively.
Determination of carbon disulphide
429
REFERENCES 1. J. H. Karchmer, ed., The Analyfical Chemistry ofSu&v and its Compounds, Vols. I and II. Wiley, New York, 1972. 2. M. Wroriski, Gem. Anat. (Warsaw). 1961,6,865,969; 1969,14,83. 3. L. A. Pursglove and H. W. Wainwright, Anal. Chem., 1954,26, 1835. 4. F. J. O’Hara, W. M. Keely and H. W. Fleming, ibid., 1956,28, 466. 5. M. Wroriski, Talanta, 1974,22,347. 6. Idem., 2. Anal. Chem., 1971,253,24.
Pergamon
Press.
1975 Prmted m Great
Brntam
THIOMERCURIMETRIC DETERMINATION OF CARBON DISULPHIDE, CARBONYL SULPHIDE, THIOLS AND HYDROGEN SULPHIDE BY USE OF 1,3-DIAMINOPROPANE AND TRIBUTYLTIN CHLORIDE MIECZY~LAW WRONSKI Department of Chemical Technology, University of todi, Nowotki 18, Loti, Poland (Received 15 July 1974. Accepted 10 October 1974)
Summary-A new approach to the determination of carbon disulphide and carbonyl sulphide in the presence of each other is based on the reaction with 1,3_diaminopropane (DAP), and titration with o-hydroxymercurybenzoic acid (HMB) before and after the selective decomposition of the COS-derivative at pH 4. Determination of hydrogen sulphide, thiols, carbon disulphide and carbony1 sulphide in the presence of each other in hydrocarbon solvents involves four titrations with HMB, viz. of all compounds after conversion of CS2 and COS with DAP, of thiols plus H,S, of the thiols alone after removal of H2S by extractton, and of CS2 alone after removal of other compounds by shaking with aqueous alkali. For selective trapping of H,S, HCN, RSH, CO2 and CS2 + COS, the sample gas IS passed successively through a potassium antimony1 tartrate filter, a nickel carbonate filter, a tributyltin chloride filter, a bubbler containing 40% potassium hydroxide solution and a bubbler containing a benzene solution of DAP. The analysis is completed by titration with HMB with dithrzone or dithiofluorescem as indicator.
Rapid, simple and reproducible methods for determination of sulphur compounds occurring in gases and hydrocarbon solvents are of vital importance. Although the development of gas chromatography employing new types of detector for sulphur compounds has opened the way for interesting mvestigations, the practical difficulties in dealing with very complicated mixtures may appear formidable. In spite of a rather extensive literature on the determination of sulphur compounds,’ no one method deserves to be recommended for analysis of hydrocarbon solvents and fuel gases containing hydrogen sulphide, thiols, carbon disulphide and carbonyl sulphide. It is attempted in this paper to demonstrate the usefulness of a new approach to analysis of sulphur compounds, based on the application of the reagents, new for this purpose, 1,3-diaminopropane and tributyltin chloride. The former is soluble in aromatic and mixed hydrocarbons and reacts very rapidly with carbon disulphide and carbonyl sulphide to give the derivatives, 1-amino-3_propyldithiocarbamate and 1-amino-3-propylmonothiocarbamate, which can conveniently be determined by titration with o-hydroxymercurybenzoic acid (HMB). Taking into account that one mole of either carbon disulphide or carbonyl sulphide produces one mole of hydrogen sulphide, and that cyclic thioureas are indifferent towards HMB in alkaline solution2 the only possible course of the reactions is given by the equations
HPN(CH,),NHCSSH
+
H,N(CH,),
+
NHCOSH
20--H = ~-~;;o
+
2@i
+
=
o~;sO;;~
CHf::->CS
+ 2 “20
CHf::->CO
+ 2 Hz0
It has been found that in acid solution the derivative of COS is rapidly decomposed to COS and DAP, whereas the derivative of CS2 is relatively stable. In 5 min at 20” the COS derivative is 100,99*5 and 7% decomposed at pH 3*5,4 and 5, respectively. The corresponding values for the CS2 derivative are 0.6, 0.2 and O*O’/& Consequently the decomposition at pH 4 is the most suitable for the determination of both derivatives in the presence of each other. This approach has proved to be more convenient than methods based on 425
MIECZYSLAW WRO~KI
426
selective hydrolysis of carbonyl sulphide3 or on spectrophotometric determination of the derivatives.4 A benzene solution of DAP can be used for trapping carbon disulphide and carbonyl sulphide. The tributyltin chloride filter has been used with success for trapping thiols in absence of hydrogen sulphide and hydrogen cyanide, which must be removed beforehand. The thiols retained can be simply washed out and determined by titration with HMB. For trapping hydrogen sulphide a filter containing potassium antimony1 tartrate has proved the most suitable. The antimony1 sulphide formed can be dissolved in sodium hydroxide and titrated with HMB. For selective removal of hydrogen cyanide from H,S-free gas a nickel carbonate filter can be recommended.
EXPERIMENTAL Reagents The preparation of the solution of HMB in 50% v/v aqueous propyl alcohol, and of the solutions of dithiofluorescein and dithizone is described in an earlier paper.5 1,3-Diaminopropane and tributyltin chloride were supplied by EGA Chemie KG (7924 Steinheim bei Heidenheim/Brenz, West Germany). Solution A is 0.05M in potassium carbonate and 0.025M in borax in saturated sodium chloride solution, The extraction coefficient for the system tohiene-sohttion A 1s 0074 for H,S, 72 for ‘CH,SH, and 40 for thiophenol. Solution B is M in phosphoric acid and 0.5M in tartaric acid. Reagents for impregnating
filters
Filter A for trapping hydrogen sulphide. Whatman CF 11 cellulose (10 g) mixed with 12 ml of a solution containing 30 g of potassium antimony1 tartrate, 50 g of disodium tartrate, 10 g of disodium EDTA and 4 g of potassium carbonate per Iitre. Filter B for trapping hydrogen cyanide. Solutions of 25 g of nickel chloride hexahydrate in 7.5 ml of water and 1.5 g of potassium carbonate m 2.5 ml of water are mixed and added to 10 g of cellulose. Filter C for trapping thiols. Tributyltin chloride (10 ml of 0.5M solution in 2-ethylhexanol) mixed with 0.4 ml of triethanolamine and 10 g of cellulose. Filter D for trapping carbon dlsulphide and carbonyl sulphide. Tributyltin chloride (1 ml), 1,3-diaminopropane (3 ml) and 2-ethylhexanol(l0 ml) are mixed with 10 g of Woelm column-chromatography polyamide. Analysis of solvents Determination of carbon disulphide and carbonyl sulphide, procedure 1 a. Place in a dry 15-mm diameter test-tube 0.05 ml of DAP, add 2 ml of sample solvent, placing the jet of the pipette at the bottom m order to avoid any loss of COS, wait 2 min, add 2 ml of propanol, @15 ml of 2M potassium hydroxide and titrate with 10m3M HMB, using dithiofluorescein as indicator. Wait 3-5 min and titrate to the final end-point. During the titration add ethanol in amounts just enough to clear the emulsion produced. The method is directly applicable to aromatic hydrocarbons; aliphatic hydrocarbons should first be diluted 1: 1 with sulphur-free benzene. With alcohols as samples the reaction is not so rapid; a wait of about 10 min is needed before the titration. Procedure 1 b. Place 0.05 ml of DAP in a separatmg funnel and add slowly, keeping the jet of the pipette at the bottom 10 ml of the sample, mix, wait 2 min, add 2 ml of 0.3M potassium hydroxide containing 1 g of EDTA per litre, shake for 5 min, let the phases separate, take 1.5 ml of the aqueous phase, add 2 ml of ethanol and 0.1 ml of 4M potassium hydroxide, and titrate m a test-tube with 10-4-10-3M HMB, using dithlzone as indicator. to a permanent purple colour. Dithiofluorescein can be used as well but dithizone is preferable. In titration with lo-“M HMB a blank comparison solution containing dithizone and HMB must be used, the titration being continued until the colours of the both solutions match. The result multiplied by the ratio 2.05/1,5 (because DAP increases the volume of the aqueous phase) corresponds to the whole sample. If an aliquot of the aqueous phase is titrated after 5 min decomposition at pH 4, as described later, the COS and CS2 content can be calculated. Procedure lb can be used for analysis of aromatic hydrocarbons. aliphatic hydrocarbons diluted with benzene and for halogen derivatives such as carbon tetrachloride. Procedure 1 c. This applies to determination of CS, and COS in water. In this case the use of ethylenediamme is preferable. Heat in a test-tube 0.5 ml of ethylenediamme and add slowly l-5 ml of water sample, keeping the jet of the pipette at the bottom. Do not mix. The ethylenediamine should form an upper layer, Place the test-tube in boiling water for 2 min, then mix and titrate with IO-‘M HMB in the presence of dithiofluorescem. Procedure 2. This applies to determination of hydrogen sulphide and thiols in the presence of carbon disulphide and carbonyl sulphide. Carbonyl sulphide interferes with the titration in alkalme solution but does not in slight alkaline solution. On the other hand a remarkable loss of hydrogen sulphide can be observed during titration in slight alkaline solution. Good results can, however, be obtained by using a reverse titration: a definite volume of HMB is diluted with ethanol and titrated with the sample, added from a graduated pipette with the jet kept at the bottom of the HMB solution, in the presence of dithiofluorescein as indicator, until the solution turns blue. The content of CS2 and COS can be calculated by difference from the results of this procedure (H,S + RSH) and of procedure la (H2S + RSH + CSZ + COS). Procedure 3. This applies to determination of small amounts of thtols m the presence of an excess of hydrogen sulphide, carbon disulphide and carbonyl sulphide. Place 10 ml of sample in a separating funnel and extract four times with 4 ml of solution A and finally with 2 ml of water. Add 5 ml of propanol and titrate the thiols remaining in the organic phase with 10e3M HMB in the presence of dithiofluorescein.
Determination of carbon disulphide
421
Procedure 4. This applies to determination of small amounts of carbon disulphide in the presence of an excess of hydrogen sulphide, carbonyl sulphide and thiols. Remove the interfering compounds by shaking 10 ml of sample twice for 1 min with 5 ml of 2M potassium hydroxide, for 30 min with another 5 ml (to complete the hydrolysis of carbonyl sulphide) and finally twice for 1 min with 2 ml portions of alkali. Determine the carbon disulphide remaining, according to procedure lb. Only about 0.1% CSz is lost by hydrolysis. Analysis of gases
For preparation of the filters use lO-mm diameter lOO-mm long tubes, packed for a length of 052 cm with slight pressure from a glass rod. On both sides of the packing place wads of cotton-wool, (except for filter D). The gas or an sample is aspirated at a rate of @l l./min through the trapping filters and solutions in the following order, l-cm filter A, 05-cm filter B, l.S-cm filter C, lo-mm diameter U-tube containing 10 ml of 40”%w/w potassmm hydroxide solution (to remove carbon dioxide which at high concentration interferes with trapping of carbon drsulphide and carbonyl sulphide), 20-ml conical gas bubbler containing 4 ml of 2.5% v/v solution of DAP in benzene or toluene. When only the CS2 and COS content are to be determined the gas is passed through 40% potassium hydroxide solution and the DAP bubbler. When no distinction between CSz and COS is necessary, filter D may be used instead of the DAP bubbler. After the sample, pass a stream of pure inert gas or air for 5 min and determine the separated constituents as described below. Determination of hydrogen sulphide. Place in a 14-mm diameter 180-mm long test-tube a glass rod of 8-mm diameter and 140-mm long, push out filter A onto it and wash the filter (in a vertical position) with 2 ml of IM sodium hydroxide and 2 ml of water, using air pressure on the upper part of the filter tube to accelerate the flow. The solution passes the filter and flows down along the glass rod to the bottom of the test-tube. Remove the filter and glass rod (rinsed with a few drops of water) and titrate the solution with 10-4-10-3M HMB in the presence of dithizone. Determimtzon of thiols. Wash filter C twice with 2 ml of ethanol as described above, add dithiofluorescein and 1M sodium hydroxide dropwise till the solution just turns blue. Titrate with 10m3M HMB until the blue colour disappears. Determination of carbon disulphide and carbonyl sulphide. Add to the DAP bubbler 4 ml of 0.3M potassium hydroxide (containing 1 g of EDTA per litre) and stir vigorously with an air stream for 5 min to transfer the product into the aqueous phase. Let the phases separate, and take 1 ml of the aqueous phase, add 0.2 ml of 4M potassium hydroxide, dilute with.ethanol and titrate with 10-4-10-3M HMB, usmg dithizone as indicator, (VI ml). In another bubbler (prepared from a test-tube) place 2 ml of the aqueous phase and add enough of solution B (as determined in a blank test) to make the pH 3.ti.0, or add solution B dropwise till Methyl Red added as indicator just changes to red. Pass an an-stream for 5 mm to remove the carbonyl sulphide produced, add the same volume of 4M potassium hydroxide as of solution B, dilute with ethanol and titrate with 10e3M HMB in the presence of dithizone as indicator, (V, ml). Calculate the concentration (mg/l.) as follows:
CCW = [COS] =
38 x 1.05 x 2.05 x V, x MHMB V,
1~05(4~1OV, - 2.05V,)30MnMB
v, where V, 1s the volume of gas taken and 1.05 is an empirical coefficient. Another approach is based on using filter D. After trappmg of CSI and COS by a 2cm filter D, the filter is pushed out into a test-tube, ethanol and @2 ml of 4M potassium hydroxide are added and the sample is titrated with HMB. with dithizone as indicator. RESULTS
AND
DISCUSSION
Samples containing known amounts of test substances were prepared or produced as follows. Carbon disulphide solutions were prepared by weighing and gas mixture by acid decomposition of an aqueous solution of sodium diethyldithiocarbamate, the concentration of Table 1. Determination of carbon disulphide and carbonyl sulphide in benzene and in water Procedure
la la la la la lb lb lb lb lb lc * Without correction.
Taken, pceq cos CS2 23.5 235 4.55 2.35 042 0.74 004 8.70
202 4.04 2.02
Rel. std. devn. %
Mean recovery* (6 titrations), %
0.3 0.5 0.5 0.6 0.8 0.8 41 3.3 13 0.6 0.7
99.1 964 91.2 96.8 97.6 98.4 94.3 97.0 93.6 97.5 983
428
MIECZYZAWWRO~~SKI Table 2. Determination of methanethiol in benzene in the presence of hydrogen sulphide, carbon disulphide and carbonyl sulphide (100 peq of each) (procedure 3)
Table 3. Determination of carbon disulphide in benzene in the presence of methanethiol, hydrogen sulphide and carbonyl sulphide (100 pq of each) (procedure 4)
Taken, pceq
Found, pey
Taken, peq
Found, pq
1.02 2.04 3.06
0.98,@99,0.99 2.01, 1.98,2.00 3.00.3.05, 3.03
1.50 3.00
1.47, 1.54, 1.48 3.02.2.96. 2.99
which was determined via BaSO,. Known amounts of carbonyl sulphide, hydrogen sulphide and methanethiol were produced by acid decomposition, in a stream of nitrogen, of aqueous solutions of DAP-COS, of soluble starch-zinc sulphide6 and of a solution of methanethiol in 2M potassium hydroxide. The solutions were analysed by titration with HMB, and decomposed by 1M sulphuric acid.
Table 4. Determmation of hydrogen sulphide and methanethrol in the presence of each other m nitrogen, by using filters A. B and C Taken, peq CH$H
Found, peq
H2S 044
1.76 0.044
1.30 3.90 3.90
CH,SH
H*S 0~44,0~43.0~41 1.73. 1.75, 1.70 0~040.0~041
1.25. 1.27, 1.25 3.88, 3.90. 3.92 3.88. 3.86
As shown by Tables l-5, the results are satisfactory and the suggested methods can be recommended for general use. Method lb has a lower limit of 0.1 ppm and is very suitable for trace determination of carbon disulphide in such solvents as benzene or carbon tetrachloride. By use of procedures la, 2, 3 and 4, a solvent containing carbon disulphide, carbony1 sulphide, hydrogen sulphide and thiols can easily be analysed. The results are not influenced by thioethers and disulphides, but free sulphur interferes with the procedures for CS2 and COS. In the presence of hydrogen cyanide a few drops of 5% formaldehyde solution must be added. Table 5. Determination of carbon disulphide and carbonyl sulphide in the presence of each other in nitrogen after passage through filters A. E, C and potassium hydroxide bubbler. Results are corrected by a factor of 1.05 Taken. peq cos CS,
Found, peq cos cs2
1.16 55.8 11.6 6.10 6.10 0
1.15 56.0 11.3 5.90 5.95 0.05
42.5 2.18 4.25 0 1.80 7.25
41.7 2.22 4.23 0.10 1.84 7.10
The use of filters A and C for trapping hydrogen and thiols and of filter D for trapping carbon disulphide can be recommended for air analysis as the products are very resistant to air oxidation. In order to make a correction for low recovery of CS, and for loss of COS during passage through the 40% potassium hydroxide solution, the use of an empirical coefficient, 1.05, is suggested. The average CS2 and COS content in the town gas in todz, as determined by the suggested method, amounted to 0.077 and 0.103 mg/l. respectively.
Determination of carbon disulphide
429
REFERENCES 1. J. H. Karchmer, ed., The Analyfical Chemistry ofSu&v and its Compounds, Vols. I and II. Wiley, New York, 1972. 2. M. Wroriski, Gem. Anat. (Warsaw). 1961,6,865,969; 1969,14,83. 3. L. A. Pursglove and H. W. Wainwright, Anal. Chem., 1954,26, 1835. 4. F. J. O’Hara, W. M. Keely and H. W. Fleming, ibid., 1956,28, 466. 5. M. Wroriski, Talanta, 1974,22,347. 6. Idem., 2. Anal. Chem., 1971,253,24.