Carbon Disulphide, CS₂

Carbon Disulphide, CS₂, is formed when carbon and sulphur are heated together and is consequently produced when coal containing iron pyrites is distilled. It was discovered accidentally in this way by Lampadius in 1796 and rediscovered in 1802 by Clement and Desormes. Besides occurring in small quantity in crude coal gas, from which it is usually eliminated, carbon disulphide is also found in crude petroleum and in mustard oil.

Carbon disulphide is prepared by passing sulphur vapour over red hot charcoal. The preparation may be carried out on a small scale by heating pieces of charcoal in a combustion tube placed in a furnace slightly tilted, a Liebig potash bulb, immersed in ice, being attached to the lower end of the tube, and small pieces of sulphur introduced into the upper end of the tube which is then closed with a cork. Sulphur vapour passes over the red-hot charcoal and impure carbon disulphide containing sulphur in solution is gradually formed and collects in the cooled receiver.

Manufacture of Carbon Disulphide by the action of sulphur.

The reversible reaction

C + 2S ⇔ CS₂

has been studied at 800° to 1100° C. by Koref. It has been suggested that the formation of carbon disulphide is preceded by that of a solid sulphur-carbon complex, just as the oxidation of carbon is believed to be preceded by the formation of a complex C_xO_y.

For the manufacture of carbon disulphide on the large scale, the charcoal is contained in a large vertical cast-iron cylinder, ten to twelve feet high and from one to two feet in diameter. This cylinder is surrounded by brickwork and heated by a fire beneath. The sulphur is introduced through a hopper connected with a side tube at the base of the cylinder. The carbon disulphide vapour is led away from the top of the cylinder through a pipe, the end of which dips under water, where most of the product condenses. Beyond the water condenser is a series of tubes in which condensation is completed. Hydrogen sulphide, one of the impurities, escapes condensation and passes on, being subsequently absorbed in slaked lime.

Instead of an iron cylinder furnace, retorts made of refractory material are sometimes employed. The water condensers may be of the open tank type, a layer of about six inches of water on top of the disulphide affording a thoroughly efficient seal. The liquid may be purified from dissolved sulphur by steam distillation. A modern method for the final rectification of the carbon disulphide consists in the continuous distillation of the crude liquid in two similar fractionating columns fitted with reflux condensers. The first column is maintained at a temperature just above the melting-point of sulphur and fed with crude carbon disulphide from above, whilst the second is kept at a temperature slightly above the boiling-point of pure carbon disulphide and fed at the top with the purified liquid from the first column. Condensation of the vapours leaving the lower end of the second column yields pure carbon disulphide. The waste gases (hydrogen sulphide, etc.) escape from the reflux condensers and are condensed by further cooling, any carbon disulphide obtained being passed back to the first column. The sulphur which separates is drawn off as liquid from the still of the first column.

Electric Furnace for the Production of Carbon Disulphide.

A thermo-electrical process for the production of carbon disulphide from its elements is also largely employed, especially in America. The type of furnace generally employed is shown diagrammatically in fig. The heat emanated from the electrodes E₁ and E₂ melts and ultimately vaporises the sulphur, which then passes up through the tower of charcoal. The furnace is self-regulating in that if it becomes too hot, the sulphur, melting at a more rapid rate than it volatilises, rises up over the electrodes, thus reducing or cutting off the current. Two-phase alternating current is employed, and the efficiency exceeds 40 per cent.

The sulphur may be evaporated and superheated either in the reaction chamber itself or in an attached chamber before it is brought into contact with the charcoal.

Carbon disulphide may also be formed by the action of sulphur dioxide on carbon. When sulphur dioxide is led over red-hot charcoal which has previously been freed from hydrogen by heating it in a current of chlorine, the following reactions can occur:-

1. 2SO₂ + C = 2CO₂ + S₂,
2. S₂ + C ⇔ CS₂,
3. CO₂ + C ⇔ 2CO,
4. S₂ + 2CO₂ ⇔ COS + CO + SO₂,
5. S₂ + 2CO ⇔ 2COS,
6. CS₂ + CO₂ ⇔ 2CO + S₂ ⇔ 2COS,
7. 2SO₂ + 4C ⇔ 4CO + S₂.

The free sulphur in the issuing gas may be removed by condensation and filtration through glass wool. Carbon disulphide vapour may be absorbed in ethereal triethylphosphine. The maximum formation of the disulphide is at 850° to 900° C., the sulphur from the sulphur dioxide then being distributed as follows:-

Carbon disulphide	35 %
Carbonyl sulphide	55 %
Free sulphur	10 %

This process is useless as a technical method of making carbon disulphide.

Crude carbon disulphide has a very offensive odour due to the presence of organic sulphur compounds; sulphur is also contained in solution and is left behind on redistillation. Organic impurities may be eliminated by distilling over fat, which retains them. Contact with mercury, fuming nitric acid, corrosive sublimate or solid potassium permanganate serves the same purpose. Commercial carbon disulphide may be freed from hydrocarbons by shaking for twenty-four hours at 35° to 40° C. with a saturated solution of sodium sulphide. The solution of sodium thiocarbonate obtained is treated with the calculated amount of copper sulphate solution, the resulting copper thiocarbonate being decomposed with steam. The product is dried over phosphorus pentoxide.

When sulphur is heated with acetylene at temperatures up to 650° C. and the products condensed, a brown oil is obtained which contains 77 to 83 per cent, of carbon disulphide, with some thiophen and thiophten. The optimum temperature for producing the latter compounds is 500° C.

When calcium carbide and sulphur are heated together at 270° C. carbon disulphide in about 20 per cent, yield and considerable quantities of carbon are produced. At higher temperatures the amount of carbon disulphide diminishes, only traces being detected at 500° C.

Pure carbon disulphide is a colourless, mobile, highly refractive liquid with a pleasant odour resembling that of chloroform. Its density at 0° C. according to Thorpe is 1.2923; according to Wullner the density at t° C. can be calculated from the formula

D^t₀ = 1.29366 - 0.001506t.

Carbon disulphide vapour appears to be associated to a small extent. When the vapour and ether vapour are mixed at constant volume at 80° C. under atmospheric pressure, the increase of pressure observed indicates previous association of the carbon disulphide to the extent of 0.14 per cent., whilst vapour density determinations by Dumas' method give results corresponding with 2 per cent, association.

The boiling-point at 760 mm. pressure is 46.25° C. According to Regnault the vapour pressures at different temperatures are as follows:-

Temp., °C.	Vapour Pressure, mm.
-20	47.3
-10	79.44
0	127.91
10	198.46
20	298.03
30	434.62
40	617.53
50	857.07
60	1164.51
70	1552.09
80	2032.53
90	2619.08
100	3325.15
110	4164.06
120	5148.79
130	6291.60
140	7603.96
150	9095.94

The constants for van der Waals' equation are a = 0.02166, b = 0.003209, and the critical temperature and pressure are, respectively, 277.68° C. and 78.14 atmospheres.

At very low temperatures carbon disulphide solidifies to a crystalline mass which melts at -112.97° C. The crystallisation may be accompanied by the emission of small sparks. At -185° C. the crystals are tetragonal. The heat of fusion, deduced from determinations of the freezing-points of dilute solutions in certain organic solvents, is 660 calories. The fusion curve showing the connection between pressure and melting-point has been determined.

The total heat of vaporisation (λ) of carbon disulphide at 0° C. into vapour at t° C. is given by the expression

λ = 89.5 + 0.16993t – 0.0010161t² + 0.0000033245t³ calories per kilogram, whilst the latent heat of vaporisation (l) of liquid at t° C. into vapour at t° C. is given by

l = 89.5 – 0.065302 – 0.00109792t² + 0.00000342452t³ calories per kilogram.

The constant, K, for the molecular elevation of the boiling-point of carbon disulphide is 23.7. The specific heat, C, of liquid carbon disulphide is given by

C_liq. = 0.2352 + 0.000162t,

and for the vapour at 86° to 190° C. is 0.1596, whilst the ratio at C_p/C_v at 99.7° C. is 1.234.

Towards light, carbon disulphide possesses high refractive and dispersive powers, and in these properties is exceeded only by methylene iodide, bromonaphthalene and phenyl mustard oil. On this account it is used for filling hollow glass prisms for the production of spectra.

The following are the refractive indices for lines of different wavelengths of the visible spectrum at 0° C. and 20° C.:

Wave-length. μμ (D)	Refractive Index at 0° C.	Refractive Index at 20° C.
589.31	1.64362	1.62761
533.85	1.65508	1.63877
480.01	1.67131	1.65466
441.59	1.68850	1.67135
394.41	1.71989	1.70180

Carbon disulphide is an endothermic compound, its heats of formation as vapour from rhombic sulphur and amorphous carbon or diamond being, respectively, -25,430 calories or -26,000 calories:

C(amorphous) + 2S = CS₂(vap.) -25,430 calories.

C(diamond) + 2S = CS₂(vap.) -26,000 calories.

Carbon disulphide is an excellent solvent for fats and resins; it is employed technically for the extraction of vegetable fats and oils and for removing fats from wool. It dissolves rubber, camphor and other organic substances, as well as iodine, sulphur, phosphorus and aluminium bromide.

The disulphide is slightly soluble in water, the solubility diminishing with rising temperature like that of a gas. One hundred cubic centimetres of water dissolve the following quantities of carbon disulphide at the temperatures indicated:

Temp., ° C.	0	10	20	30	40	49
Grams CS2	0.204	0.194	0.179	0.155	0.111	0.014

Clear aqueous solutions of considerable concentration may, however, be obtained, and are produced commercially, by the addition of soap and an alcohol; thus a solution containing 5 per cent, of carbon disulphide, 2.3 per cent, of soap and 4.2 per cent, of butyl alcohol is stable. Amyl alcohol may also be used. 100 c.c. of carbon disulphide dissolve 0.974 c.c. of water at 22° C.

Carbon disulphide absorbs ultra-violet rays, a maximum absorption being reached when λ is approximately 3250 Å. The "chemical constant" is given by Nernst as 3.1.

Carbon disulphide is not easily decomposed by heat and no change is observed when it is passed through a tube at 400° C. Decomposition may be started by detonation with mercury fulminate, but it is not propagated through the vapour. Under the influence of sunlight the disulphide may be decomposed into sulphur and a lower sulphide of carbon. According to Berthelot this decomposition is partially due to the oxygen of the air and is not produced by diffused light. Dissociation to carbon and sulphur or lower sulphides, which is considerable at high temperatures, is promoted by the presence of metals or gases with which the sulphur can combine. Decomposition also occurs under the influence of the electric arc, electric sparks or the silent electric discharge.

Carbon disulphide burns in air with a blue flame, producing carbon dioxide and sulphur dioxide. Moisture is not necessary for the combustion. It inflames at a lower temperature than ether.

When a stream of air or oxygen laden with carbon disulphide vapour is passed through a tube heated to about 200° C., a gentle phosphorescent combustion is observed and a reddish-brown deposit, carbon monosulphide, separates, sulphur dioxide also being formed. The transition from this state to actual rapid combustion is not sharp, so that no definite ignition-point can be assigned to such mixtures. There is little difference between the spectrum of the cool phosphorescent flame and that of the normal flame of carbon disulphide, except in the distribution of intensity, but a group of closely spaced bands between 3400 and 2900 Å present in the normal flame are not evident in the low temperature flame. The flame of carbon disulphide is strongly actinic.

Carbon disulphide vapour mixed with hydrogen and directed on to heated platinum reacts to form carbon and hydrogen sulphide. Carbon disulphide inflames in the cold in contact with fluorine, and under varying conditions it reacts with chlorine, bromine and iodine.

The production of thiophen when acetylene interacts with sulphur vapour has already been mentioned. That this product is not the result of a secondary reaction between acetylene and carbon disulphide follows from the fact that thiophen is only produced in quantity from these two reactants at a considerably higher temperature than that required when sulphur is used. Acetylene saturated with carbon disulphide vapour and passed through an electrically heated tube containing broken porous pot, yields a condensate which at the optimum temperature of 700° C. contains about 10 per cent, by volume of thiophen and 10 per cent, of hydrocarbons.

Carbon disulphide readily undergoes oxidation and reduction. With alkalis it reacts to form a series of thio- or sulpho-salts.

Hypochlorite solution converts carbon disulphide into carbonate and sulphate, thus:

CS₂ + 8KOCl + 6KOH = 2K₂SO₄ + K₂CO₃ + 8KCl + 3H₂O.

In the absence of alkali, oxidation, as for instance by permanganate solution, bromine water, or nitric or iodic acid, involves the separation of sulphur. Water and aqueous alkalis hydrolyse carbon disulphide at 150° C., thus:

CS₂ + 2H₂O = CO₂ + 2H₂S.

Heated with baryta water in an atmosphere of nitrogen, carbon disulphide yields barium hydrosulphide, which is subsequently converted into sulphate by contact with the air:

CS₂ + 2Ba(OH)₂ = BaCO₃ + Ba(SH)₂ + H₂O.

In alcohol solution, potassium hydroxide forms the xanthate.

Carbon disulphide interacts with dry ammonia, but the reaction has not yet been fully investigated; the gas is slowly absorbed and a dark brown liquid results, which probably contains ammonium thiocarbonate and thiocyanate. An alcohol solution of ammonia readily dissolves carbon disulphide, the foregoing products being formed.

Carbon disulphide reacts additively with primary and secondary aliphatic amines to form alkylammonium salts of alkyldithiocarbamic acids. The products obtained with dimethylamine, diethylamine and piperidine, also certain derivatives of these products, are manufactured on a large scale for use as accelerators in the vulcanisation of rubber. With aromatic amines the disulphide reacts with elimination of hydrogen sulphide and formation of substituted thio-ureas, e.g. thiocarbanilide.

Carbon disulphide also combines with tertiary amines and phosphines, forming crystalline substances, the most important of which is a scarlet compound with triethylphosphine, CS₂.P(C₂H₅)₃, to which the constitution is attributed. This substance is formed immediately the reactants meet, and may be used to detect carbon disulphide in coal gas.

Carbon disulphide may be detected by means of the red, crystalline compound which it forms with triethylphosphine and the white compound with phenylhydrazine. Minute quantities can also be detected by producing one of the dithiotrimercuric salts of the type HgX₂.2HgS, which form characteristic crystalline precipitates when dilute aqueous solutions of mercuric salts are heated on a water-bath with carbon disulphide.

Determination of the specific gravity of benzene before and after extraction of carbon disulphide with alcoholic potash gives a fairly accurate estimation of the quantity of carbon disulphide present, the error being less than 0.03 per cent. The following table shows experimental results obtained on shaking benzene containing 0.4 per cent, by volume of carbon disulphide for two hours with alcoholic potash (10 per cent.) containing varying concentrations of alcohol.

	Per cent. Alcohol by Volume.	Vol. of Benzene. / Vol. of Alcoholic Potash.	Sp. Gr. of Benzene + 0.4 per cent. CS2.	Sp. Gr. after Treatment.	Sp. Gr. when free from CS2.	Per cent. CS2 in Total Mixture.
1	96.1	2	0.8861	0.8844	0.8844	0.45
2	89.6	2	0.8861	0.8845	0.8844	0.4
3	85.6	2	0.8861	0.8845	0.8844	0.4
4	77.5	2	0.8861	0.8845	0.8844	0.4
5	69.6	2	0.8861	0.8846	0.8844	0.4
6	49.8	2	0.8862	0.8848	0.8844	0.35
7	35.8	2	0.8862	0.8852	0.8844	0.25

Oxidation of the alkaline extract with bromine and subsequent estimation of the resulting sulphate also yields trustworthy results.

Estimation of carbon disulphide by solution in alcoholic potash, with formation of the xanthate, followed by titration with standard copper sulphate, iodine, or permanganate solution which oxidises the xanthate to sulphate, according to Spielmann and Jones yields less trustworthy results.

A further method for the estimation of carbon disulphide depends upon the fact that when heated with alcoholic ammonia at 60° C. under pressure, the disulphide is converted into a mixture of hydrosulphide and thiocyanate, thus:



The hydrosulphide may then be titrated with ammoniacal zinc solution.

Carbon disulphide may be estimated gravimetrically by treatment with baryta water, whereby barium sulphide is produced, which is then oxidised and weighed as sulphate.

Besides its employment as a solvent, carbon disulphide is used extensively in the manufacture of viscose silk. Viscose is a solution of the sodium salt of the cellulose ester of thiolthioncarbonic acid in water or dilute aqueous sodium hydroxide, or it may be described as an aqueous solution of the sodium salt of cellulose xanthic acid. For its production cellulose is steeped in concentrated sodium hydroxide solution and then pressed, the product being called alkali-cellulose and the formula C₆H₁₀O₅.NaOH assigned to it. This is converted into viscose by treatment with carbon disulphide, when the colour changes to golden yellow:



This product, after keeping for four or five days, is pressed through a "rose" perforated with small holes into a coagulating bath containing, for example, aqueous sulphuric acid (10 per cent.), when hydrated cellulose is precipitated in solid threads, which after purification and washing constitute viscose silk.

Much carbon disulphide is used in the rubber industry, particularly as a solvent for sulphur chloride in vulcanisation by the "cold" process or "vapour" process. It is also employed in the manufacture of numerous organic compounds used for the acceleration of vulcanisation, for example thiocarbanilide, alkyl xanthates (particularly zinc alkyl xanthates) and substituted dithiocarbamates. Many other compounds, such as ammonium thiocyanate and certain organic dyes containing sulphur, also require the use of carbon disulphide in their preparation.

The disulphide is used as an insecticide.

Carbon disulphide has a powerful toxic effect, producing headache, sickness, giddiness, a general weakening of the senses and muscular forces, and finally death.

Just as by the reducing action of hydrogen on carbon dioxide formic acid, formaldehyde, methyl alcohol and methane may be directly or indirectly obtained, so from the analogous disulphide the following products should result:

dithioformic Acid

Thioformaldehyde

H3C.SH Methyl mercaptan

H4C Methane

Dithioformic Acid has been obtained by the addition of dilute hydrochloric acid to an alcohol solution of the potassium salt (see the following) cooled in ice. It separates as a white solid and there is a slight evolution of hydrogen sulphide during the reaction. The precipitate after filtering is washed with alcohol and ether. It is insoluble in the common solvents. On heating it melts at 55° to 60° C. with partial decomposition, which proceeds further at higher temperatures, the products being hydrogen sulphide, carbon disulphide, carbon and sulphur. Potassium dithioformate is obtained by treating chloroform with potassium sulphide in alcohol solution:

CHCl₃ + 2K₂S = H.CS₂K + 3KCl.

It forms golden-yellow crystals which melt to a red liquid at 193° C., undergoing decomposition as in the case of the free acid. Ammonium dithioformate cannot be obtained from chloroform and the sulphide, but it is formed on titration of the acid with ammonia. It decomposes on keeping, thus:

2H.CS₂NH₄ = 2NH₃ + H₂S + (HCS)₂S.

The monosulphide produced by this decomposition is also formed by the interaction of the potassium salt with cyanogen bromide:

2H.CS₂K + BrCN = KCNS + (HCS)₂S + KBr.

A disulphide, [(HCS)₂S₂]_x, is formed as a yellowish-red precipitate when potassium dithioformate in alcohol solution is cautiously oxidised by the addition of iodine. It decomposes similarly to the acid above 200° C. Both sulphides are insoluble in the common solvents. Dithioformates of silver, lead, zinc and cobalt have also been described.

From molecular weight determinations by cryoscopic methods, the esters of dithioformic acid appear to have a trimeric constitution, for example, (H.CS₂Me)₃, and it is suggested that the molecule of the acid is similarly constituted and possesses a cyclic structure with alternating carbon and sulphur atoms.