LX-Salts of Thiocaq*Bamide. by AUGUSTUSEDWARD DIXON

View Article Online / Journal Homepage / Table of Contents for this issue 684 DIXON : SALTS OF THIOCARBAMIDE. LX-Salts of Thiocaq*bamide. By AUGUSTUSEDWARD DIXON. DURINGthe prosecutior of a certain research, some salts of thiocarbamide have been isolated. As very few of such compounds appear to be known, except the nitrate (Emerson Reynolds, Jozwn. Chem. SOC.,1869, 22, 5) and the hydrochloride (Stevens, T., 1902, 81, 80), mention may be made of those now obtained. From the fact that the solubility of thiocarb'amide in water is enhanced by the prewncei of strong acids, it is evident that salts are formed in solution. They are, however, markedly hydrolysed, and since, as a rule, they are freely soluble, whilst the parent base requires for dissolution at the ordinary temperature about nine times its o,wn weight of water, their isolation in the presence of this solvent is frequently impracticable. T hiocar bamid e Hydrochloride. To what Stevens (loc. cit.) has recorded in connetxion with this substance, the following may be added. Of the ready formed salt, 1-48 parts (= 1 part of thiocarbamide) required for dissolution 6.65 parts of water. When allowed to evaporate, the solution at first deposited thiocarbamide alone, this being accompanied later, when the bulk had considerably dimin- ished, by crystals of the hydrochloride. Also, when 1 part of thiocarbamide was treated with a prepared Published on 01 January 1917. Downloaded by Brown University 28/10/2014 09:55:04. solution of hydrochloric acid (really 0.5 per cent. weaker than had been intended) dissolution required 7.15 parts, consisting of 0.45 part of hydrogen chloride and 6.7 parts of water. Thus, in the direct and in the reversed experiments, the end-systems were respectively : (i) CSN,H, :HCI : H,O = 1 : 0.48 :6.65 and (ii) CSN,H, :Ha: H,O = 1 : 0.48 : 6.70. Obviously, these two were alike, the trifling excew of water in (ii) corresponding with the deficiency of hydrogen chloride in the prepared solntion of hydrochloric acid ; the action, therefore, is reversible. By operating as follows, a 75 per cent. yield may be obtained of a salt that is practically pure. To every 10 grams of t.hiocarbamide 9 C.C.are added of ordinary concentrated hydrochloric acid (D, 1.16) ; the thiocarbamide is dissolved by warming the mixture, and hydrogen chloride is passed in until distinct fuming is perceptible (during View Article Online DIXON : SALTS OF THIOCARBAMIDE. 685 the operation, a little hydrogen sulphide escapes). To prevent ‘‘ setting,” the solution, as it cools, should be well stirred; the crystals are now powdered if necessary, drained as far as po~~ible by the aid of the pump, thoroughly washed with chloroform, pressed in folds of bibulous paper, and dried over sulphuric acid. Analysis of two different preparations gave : Found : HC1= 32.40, 32-61. After recrystallisation from hydrochloric acid, 32.36. CH,N,S,HCl requires HCl= 32.44 per cent. It is possible, by reducing the proportion of concentrated hydrochloric acid, to increase the yield still further, but this is not desir- able, for even with 8 C.C.per 10 grams of base the liquid, on cooling, sets to a mass so hard that it cannot easily be freed from the mother liquor. In a dry atmosphere, at the ordinary pressure, the salt undergoes little change; a specimen kept for thirteen months ovelr sulphuric acid was found at the end of that time to have lost only 0.7 per cent. of hydrogen chloride. At 15O it is twice as soluble as thic- carbamide, 1 part of the saIt requiring about 4.5 parts of water; the solution, however, contains much of the total base as free thiocarbamide. Curiously, it is less soluble than the nitrate, this seem- ing paradox depending on the fact that it is more hydrolysed than the latter; hence, a larger amount of water is necessary to dimolve the resultant free thiocarbamide. Fusion, which took place at about 136-13‘i0, with the evolution of a trace of gas, was preceded by distinct softening; after recrystallisation from highly concentrated hydrochloric acid, the same behaviour was shown, except that the melting point was now Published on 01 January 1917. Downloaded by Brown University 28/10/2014 09:55:04. 135-136O. No sign of change was perceptible when the salt was put into the apparatus at 103O. Stevens found the substance to be fusible below looo. To remove the mechanically adherent acid, he had washed the crystals with alcohol, a procedure likely to cause hydrolysis. On this point the following experiment was made: a quantity of the salt, having a primary melting point of 136--137O, was washed very rapidly, by the aid of the pump, with just enough strong alcohol to cover it; a portion, A, of the residue having been withdrawn, the remainder was again rapidly washed as before, leaving a twice washed mate- rial, B, the duration of each washing being about five seconds. Portion A softened gradually from 60° on, changing at 75O to an opaque paste which, by 112O, was transparent; portion B, placed in the apparatiis at 85O, melted at once to a turbid liquid, becoming clear at 98O. Although the melting point is so strongly affected, the extent of hydrolysis caused by rapid washing cannot be very View Article Online 686 DIXON : SALTS OF THIOCARBAMIDE. gre'at; for Stevens, who made several analyses, obtained quite satis- factory figures. Another portion of the salt was heated at the fusion temperature for half-an-hour. The escaping gas consisted of hydrogen chloride, with a trace of hydrogen sulphide ; the residue, entirely soluble in water, consisted principally of free thiocarbamide, togethelr with a little unchanged hydrochloride and enough ammonium thio- cyanate (see Reynolds and Werner, T., 1903, 83, 4) to give a well- marked reddelning with ferric chloride. No indication was detected in the residue of the presence of an imino-base, NH,*C( :NH)*SH. Although thiocarbamide is a diacidic base, yielding (see below) the salts CSN,H,,H,SO, and CSN,H,,H,C,O,, no evidence has been found that it can afford corresponding salts with monobasic acids; for example, the dihydrochloride, CSN,H4,2HC1, is not pro- ducible-or, at all events, was not detected-even in the presence of a large excess of free hydrogen chloride. On the other hand, no sulphate, (CSN,H,),,H,SO,, could be isolated. Thiocarbamide and Sdphuric Acid. When sulphuric acid was mixed with a saturated solution of thiocarbamide in amtone, a colourless oil was precipitated, changing, when kept over sulphuric acid in a vacuum, to a white, crystal- line substance, rapidly attracting moisture from the air. Found (by titration) : H2S04= 55.0. CH,N,S,H,SO, requires H2S04= 56.3 per cent. This rather low figure was the best obtained, other preparations giving lower values, the lowest of which was about 52 per cent. Published on 01 January 1917. Downloaded by Brown University 28/10/2014 09:55:04. When thiocarbamide was treated with enough 98 per cent. sulphuric acid to afford 1 molecular proportion of the acid, the base soon dissolved, yielding a spup, possibly the solution of the salh in the small quantity of water present. This was at 20°; on cooling to go, the! syrup changed to a white solid. Thiocarbamide sulphate is soluble) in glacial acetic acid, from which it is precipitated by acetone or by chloroform in oily droplets, wh icli presently crys tallise. Thiocarb arnide Nitrate . Between the solubility of ready-f ormed thiocarbamide nitrate in water and that of thiocarbamide in a dilute nitric acid having about the concentration calculated from that solubility a disagree- ment was found, she weights of water (for 1 part of thiocarbamide) being 6.8 parts and 6-3 parts respectively. The variance is probably View Article Online DIXON : SALTS OF THIOCARBAMIDE. 687 due to a partial oxidation of the salt, during the process of drying, into the dinitrate of f ormamidine disulphide, C,S2N,H6,2HNO3, a sparingly soluble compound, which decomposes rather easily, with the production of free sulphur. The nitric acid used in preparing tlie nitrate was previ'ously swept by a current of air, and in these circumstances tlie salt-except as mentioned above-seemed toler- ably stable. Curiously enough, when the nitric acid was previously boiled with carbhamide, to remove every trace of nitrous acid, the nitrate prepared from it, as soon as it became dry in the desiccator, exploded. Emerson Reynolds, the first to produce thiocarbamide and its nitrate (loc. cit.), records the tendency of the latter to de- compose spontaneously, or even to explode. Thiocarbamide and Oxalic Acid. By reason of the sparing solubility of both substances iii cold water, it could be foreseen that hydrolysis would defeat the isolation of any but a nearly insoluble salt; and when cold, saturated solutions were mixed and evaporated, this proved to be tlie case. A mixture of oxalic acid and thiocarbamide, in molecular proportions, was dissolved in the minimum amount of hot water; from this also, on cooling, a mixture of the components was deposited. No better rasult was obtained by evaporating a cold solution in acetone. But when molecular proportions of thiocarbamide and of crystallised oxalic acid were together dissolved in about the minimum quantity of boiling acetone, a solid separated on cooling; when recrystallid from acetone, nearly saturated, in the cold, with oxalic acid, it formed small, white prisms melting at 73-74O and consisting of the' anhydrous oxalate.

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