932 JONES AND ROBINSON: NICKELO- AND

XCI V.-Nickelo- and Pa I lad io-dit hio - oxalic acids. By HUMPHREY OWEN JONES and CHARLES STANLEY ROBINSON.

XN a former paper (this VOI., p. 62) the preparation and properties of a number of highly coloured salts derived from the complex nickel* and palladio-dithio-oxalic acids were described. The salts were found to be derived from dibasic acids, M”(COS),H,, dilute aqueous solutions of which had a higher electrical conductivity than equivalent solutions of sulphuric acid. The solutions when hea.ted decomposed and lost their colour; attempb t o evaporate the solvent under diminished pressure in the cold also resulted in partial decomposition. Finally, however, these difficulties were overcome, both acids were isolated in well-defined crystals, and their properties have been studied.

Nickelodit hio-o x d i c A cid, Ni(C0 S),H,,4H20.

The barium salt, Ni(COS),Ba,4H,O, in quantities of about 1 gram a t a time was finely powdered and stirred with the calcu- lated quantity of a 3N-solution of sulphuric acid, the solution was filtered through a Gooch crucible, placed in a flat dish in a vacuum desiccator over quicklime, and allowed to remain until most of the solvent had evaporated. Long, lustrous, black prisms, often exceeding 1 centimetre in length, were thus obtained:

0.4031 gave 0.1900 CO, and 0.0920 H,O. 0.3320 ,, 0.8305 BaSO,. S=34*6.

Ni(COS),H2,4H,O requires C = 12.87; H =2*68; S=34.3 per cent. !I he acid dissolves readily in water, giving the characteristic, deep

magenta-coloured solution like the metallic salts previously described. The solution is strongly acid; on addition of barium chloride the barium salt is precipitated, and on addition of ammonium carbonate the ammonium salt is precipitated and carbon dioxide is evolved. On heating the solution of the acid, the colour disappears, hydrogen sulphide and carbon monoxide are evolved, a green precipitate of nickel oxalate separates, and the solution was found to contain oxalic acid.

Quantitative experiments showed that on boiling the solution 1 gram-molecule of the acid gave 4 gram-molecules of hydrogen sulphide and 1 gram-molecule of nickel oxalate, but that the relative quantities of oxalic acid and carbon monoxide were variable. In solutions of about normal strength 1 gram-molecule of acid gave 0.5 gram-molecule of oxalic acid and 0.5 gram- molecule of carbon monoxide ; but in approximately decinormal

C= 12.85 ; H = 2-54.

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PALLAD10-DITH10-OXALIC ACIDS. 933

solution the decomposition was much less rapid, and the proportion of oxalic acid rose to about 0-7 gram-molecule and the carbon monoxide fell to about 0-3 gram-molecule.

The following experiments illustrate the kind of result obtained :

0.8945 Gram of the barium salt (molecular weight 508), when heated with the calculated quantity of N / 10-sulphuric acid, gave 9.0 C.C. of carbon monoxide at 17O and 770 mm. measured over potassium hydroxide solution ; that is, 6-34 litres per gram-molecule. The oxalic acid required 23.3 C.C. of potasaium permanganate solution (1 C.C. =0*00353 gram), and the nickel oxalate required 31.2 C.C. of the same solution fo r oxidation.

Hence the free oxalic acid is 66.6 grams and the oxalic acid as nickel oxalate is 89.1 grams per gram-molecule of salt.

The sum of the carbon monoxide and the oxalic acid is, there- fore, 1-02 gram-molecules per gram-molecule of salt.

A similar experiment gave 0-315 gram-molecule of carbon mon- oxide, 0.703 gram-molecule of oxalic acid, and 90.3 grams of oxalic acid as nickel oxalate.

Two experiments in which the calculated quantity of N-sulphuric acid was used gave 0.482 and 0.509 gram-molecule of carbon monoxide with 0-55 and 0.51 gram-niolecule of oxalic acid respec- tively, whilst both gave practically 1 gram-molecule of nickel oxalate. The sum of the carbon monoxide and oxalic acid is therefore practically 1 gram-molecule in each case.

Two experiments gave as a mean 4.1 gram-molecules of hydrogen sulphide from 1 gram-molecule of salt.

These results are in agreement with the following equations for the decomposition of the acid:

H,(COS),Ni + 4H,O = 4H2S + H,CgO, + NiGO,. H,(COS),Ni + 3H,O = 4IX-3 -i- GO + CO, + NiC,O,.

The two modes of decomposition take place in different propor- tions according to the concentration of the solution.

It is probable that the decomposition of the radicle of dithio- oxalic acid takes place, giving different proportions of oxalic acid and its decomposition products-carbon monoxide and carbon dioxide-according t o the concentration.

T.he decomposition of the acid by heat was examined by heating the acid to about 180-200° in a vacuous bulb, and collecting the gas evolved by means of a Topler pump.

The following experiment is typical:

0-0960 Gram gave 28.6 C.C. of gas at 17O and 766 mm. (= 106 litres per gram-molecule), of which 12.0 C.C. remained after treat-

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934 NICKELO- AND PALLADIO-DITHIO-OXALIC ACIDS.

ment with potassium hydroxide solution (= 43.7 litres per gram- molecule).

The decomposition may therefore be represented by the equation :

Ni(COS),H,4H20 = NiS + 2CO -i 3COS + H2S + 4H,O, which differs slightly from that which represents the decomposition 'of the aniline salt (loc. c i t . , p. 70).

The electrical conductivity of a solution of this acid was measured, and found to be slightly greater than that already recorded (Zoc. c i t . , p. il) from solution prepared by mixing equiva- lent solutions of the barium salt and sulphuric acid. This is prob- ably to be attributed to the presence of small quantities of oxalic acid in the free acid; the values previously given are therefore to be regarded as the more trustworthy, and show that this acid is probably stronger than sulphuric acid.

Several attempts were made to prepare the ester of tFe acid by the interaction of the potassium salt and methyl sulphate. On heating the two substances together in the presence of water, nickel sulphate, hydrogen sulphide, and dimethyl dithio-oxalate were obtained. On warming the dry potassium salt with methyl sulphate in a sealed tube, a deep blue-coloured mass was obtained, from which dry acetone extracted a coloured substance mixed with some dimethyl dithieoxalate, and much unchanged potassium salt was left; heating for a longer time resulted in decomposition with loss of the colour.

Methyl sulphate was found to react slowly with the dry potassium salt in the cold, but even after keeping for six months in a sealed tube the reaction was incomplete. The excess of methyl sulphate was removed by means of dry ether, and the residue was extracted repeatedly with dry acetone. On evaporating the acetone in the cold, deep indigo-blue, feathery needles were deposited, mixed with a few red octahedra of the potassium salt. Analysis gave results approximating to the composition of the half ester, Ni(@OS),KMe,. but no method of separating this from the unchanged potassium salt has been found.

This substance when heated evolved dimethyl dithio-oxalate.

PalZadiodit~~Lio-oealic d cid, Pd(COS),H2,3H,0.

This acid is more soluble in water than the corresponding nickel0 acid, but the same method served for its preparation. Crystals of oxalic acid were sometimes observed mixed with the crystals of the acid if the evaporation had not been carried out rapidly enough. The acid separates from its solution in small, dark brown plates:

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JONES A N 0 ROBIN'SOS : DITHIOMALOSATES. 935

0.3155 gave 0.1390 CO, and 0.0545 H,O. C= 12.0; H = 1.92. 0'3090 ,, 0'1361 60, ,, 0.0531 H,O. C=12.0; H=1*87. 0.2160 ,, 0.5053 BaSO, rand 0.0585 Pd. S=32*1; Pd=27*0.

Pd(COS),&,3&O requires C=11.94; H=1-98; S=31-84; Pd = 26-4 per cent.

The solution of the acid in water is dark brown in colour, strongly acid to indicators, gives a precipitate of the barium salt with barium chloride, and liberates carbon dioxide from ammonium carbonate with precipitation of the ammonium salt.

On heating, the solution gradually becomes colourless, hydrogen sulphide and carbon monoxide are evolved together with some carbon dioxide, and the residue consists mainly of palladium.

The expenses of this work were partly defrayed by a grant from the Government Grant Committee of the Royal -Society, for which we are glad to make this grateful acknowledgment.

UNIVEESITY CHEMICAL LABORATORY, C A i f BRI DG E .

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