404 WERNER RESEARCHES ON CHROM-ORGA NIC ACIDS. XXXT1.-Researches o n Ch-om-organic Acids. Part 11. Certain C h ~ o nz oxalat es. Bed lSer ies. B*y EMrL A WERNER Assistant in the Chemical Laboratory Trinity College University of Dublin. Tim first member of the red series of chromoxalates was discovered by Crofts in 1842 (Ph;Z. Mag. 21 197) but has hitherto been little studied. Salts of this series are in all cases constant products of the reduction of dichromates by oxalic acid the compounds of the blue series which are formed under conditions described in the first part of this paper (Trans. 51 383) being the result of the direct addition of oxalic acid or an oxalate to the red salt. Regarded as anhydrous compounds the salts of the blue and red series are represented respectively by the formultx M’&h,( C,O,) and 31 ,Cl*,(C,O,), WERNER RESEARCHES ON CHROM-ORGANIC ACIDS.405 The potassium salt was prepared by the interaction of potaasium dichromate (1 mol.) and oxalic acid (7 mols.) both in aqueous solution ; tbe composition of the purple-red crystals which separate from the concentrated liquid and to which Crofts assigned the formuia K,Cr,(C20~)d,12H20 I find to be correctly represented by the formula KzCr,(C204)4,10H,0. The method of analysis was the same as that adopted in the case of the blue chromoxalates. Pound. 7-7 Theory. I. 11. K2 . . . . . 10.92 p. C. 11.08 p. C. 11.26 p. C. Cr . . . . . . . . 14.56 , 14.19 , 14.34 ,, (CZO4)i . . . . 49.29 , 49.17 , 49.21 ,, (HzO),o . . . . 25.21 , 22.72 , 25.19 (by diff.).-99.98 97.06 100~00 The apparent deficiency in the water-determination of the first analysis-the result of direct experiment-is due to the fact that the last 2 mols. HzO in this salt are only expelled a t an exceptionally high temperature. The behaviour of the water in this salt has such an important bearing on its constitution that I append the experi-mental results obtained during the dehydration of the compound. TVeig7~t taken 1.153 gram. Time. 2 hrs. ,* 9 4 hrs. > 150" 2 hrs. Y 180 2 hrs. Y 7 4 hrs. ) 200-235 2 1113. > 9 4 hre. Heated to 110-120" C. , 180-200" C. 2 lirs. H,O. Loss = 0 *1865 grain = 16 e l 7 , = 0.1865 , - ,, NO further loss -Loss = 0 *2145 gram = 18.60 , = 0.2255 , = 19.55 , = 0.2415 , = 20.94 , = 0'2535 , = 21-98 , = 0.2621 , = 22.72 -Molecules.6 -33 Y ? -'7 '37 7 9 4 8 *29 8 -70 8.99 The loss of the first 6 mols. H,O is accompanied by a change of colour from red to bluish-grey and after 8 mols. have been lost the salt commences to become green ; at the time that the above analyses were made the appearance of the latter colour mas thought to be due to decomposition but I have since found that the salt may be heated to a temperature approaching 300" without decomposition. 0943 gram heated cautiously until the whole mass assumed a deep green colour lost 0.062 gram = 25.51 per cent. of total water. Calc. 25.21 per cent. When strongly ignited with access of air this compound leaves a, ' O L . L I t I . 2 406 WERNER RESEARCHES ON CHROM-ORGANIC ACLDS.residue of chromic oxide and potassium chromate the decomposition taking place according to the equation-2K,Cr2(C201)4,10H20 + 110 = 2KzCr04 + Cr203 + 10H20 + 16C02. which represents a residue = 37.81 per cent. or 36 per cent. if the salt contained 12H20 ; 0.4897 gram left residue = 0.1848 gram, corresponding with 37.72 per cent. My formula therefore is the correct one. When the decahydrated salt is exposed over sulphuric acid in a desiccator it continues to lose water for several weeks but the loss ceases when the compound has the composition K2Cr2( C2OJ4,4H,O. This also represents the composition of the salt dried at 110-120" ; if however the aqueous solution of the salt is evaporated to dryness on the water-bath it leaves a green amorphous residue which has the composition K2Cr2 ( C2O,),,2H,0.Crofts considered this compound to be a double salt of potassium oxalate and chromic oxalate thus K2C,04 + Cr2(C,04)3 differing simply from Gregory's compound by 2 mols. KaCZO4 since on boiling its solution with the latter Gregory's blue salt is produced thus :-K2Cr2(C204)4 4- 2K2C204 = I(6cr2(c20~)6. This view of the constitution of these salts as I have already pointed out is quite untenable and its inconsistency with their peculiar properties is particularly recognised in this somewhat rern arkable compound. With the exception that their solutions are not precipitated by either calcic chloride or ammonia the salts of the red series differ remarkably in their properties from the blue ; they do not yield cor-responding salts by double decomposition.The only oiher compounds of the series hitherto described are the complete sodium and ammonium salts (Warington Phil. >lag. 21,202). I have succeeded in producing the potassium ammonium compound, K(NH4) Cr2( C,O,)JOH,O, by the following reaction :-KNH4Cr207 + 7H,Cz0 = K(NH,)Cr,(C2OJ4 + 6C0 + i H 2 0 . This salt is of interest in proving that the simplest formula for these compounds must. contain at least 2 atoms of chromium. This com-pound forms small pnrple-red monoclinic prisms ; they are more freely soluble in water than the potassium salt itself which in every other respect they resemble closely. A remarkable property of the salts of this series is the readines WERNER RESEARCHES ON CHROM-ORGANIC ACIDS.407 with which they form addition products. With ammonium oxalate Croft's salt yields the compound K,(NH,)4,Cr,(C,04)6,6H20 ; it also combines with the oxalates OE the different types of organic bases, yielding in some cases beautifully crystallised compounds. The com-binations of these red salts are not restricted to oxalates but extend also to salts of certain other organic acids yielding i n each case products in which the new acid radicle can no longer be detected by the m u d reagents. The effect of alkalis and particularly of ammonia on the red salt' is very peculiar if t o the rich red solution of the latter an alkali be added the colour of the liquid will immediately change t o green ; on adding an acid in excess the original red colour of the liquid is restored.This colour change is very delicate the green solution being sensitive even to carbonic acid. I n the case of the fixed alkalis, decomposition of the green liquid with separation of chromic hydr-oxide takes place after 5 to 6 mols. of alkali have been added for each mol. of the red salt. In an experiment 7.14 grams of the red salt required at the boiling temperature 2-20 grams NaOH for decom-position corresponding to 5.5 mols. This behaviour with alkali seemed entirely in favour of a view regarding the constitution of the red salt which had already been suggested to me by Dr. Emerson Reynolds on his consideration of my results obtained on heating the compound to the very high temperature at which it lost the last 2 mols. of HzO; namely that in this compound there were at least two but more probably four hydroxyl-groups in the molecule.Looking upon it as a derivative of chromic hydroxide the constitu-tion of Croft's salt may be expressed by the following structural formula :-These compounds will be described in another paper. i n which the hydrogen-atoms of four of the hydroxyls have been displaced. According to this formula the componnds would contain the hydroxyls in two distinct positions whereby two would be basic and two acidic tending to neutralisation; as a matter of fact the acidic property predominates in the red salt as the feeble basic powers of chromic hydroxide? would naturally indicats. The existence of the compound K,Cr,( C,OJ,(OH), obtained in the following way is strong evidence in favour of the above constitution ascribed to the red salt.A quantity of the latter in aqueous solution was mixed with 3 mols. of caustic potash and the greenish-red solution precipitated with alcohol ; the mixture was then warmed on the water-bath which caused the precipitate to quickly coagulate and attach itself to the sides and bottom of the flask from which afte 405 TTERNER RESEARCHES ON CHROBI-ORGANIC ACIDS. decanting the mother-liquor and heating in the air-bath it was easily removed. When dry it forms a dull greenish-red dichroic powder which on heating a t 110" to expel H,O gave the following results on analysis :-0.3854 gram gave 0.091 gram Crz03. 0.3854 gram gave 0.206 gram &SO,. (I) 0.346 gram gave 0.188 0.2399 gram (C2O4).gram (Cz04) ; (11) 0.441 gram gave From which the following percentage composition is obtained. Found. 7- -7 Theory. I. 11. - Kd 24.14 p. C. 24.00 p. c. C r 2 . 16.10 , 16.22 ,, (C,O,)a. . 54.48 , 54.39 , 54.42 p. c. (0H)z 5.26 , 5.39 (by diff.) --- -99.98 100~00 This compound as indicated by its constitution possesses a feeble alkali~ze reaction. When ignited it leaves a residue of potassium chromate the decom-position taking place according to the equation-K4Cr2(C204)4(0H)2 + 7 0 = 2K,Cr04 + 8C02 + H,O, which requires a residue = 60.06 per cent. ; 0.3854 gram ignited with free access of air left a residue = 0.931 gram corresponding to 59.93 per cent. Heated to a temperature approaching :-lOOo this compound loscs its reddish tint leaving a pure green residue of the corresponding anhydride thus :-(OH) Cr( O*C,Oz*OK) Cl*( O*C202*OK), I = O/I + HZO.(OH) Cr(O*C,O,*OK)2 'Cr(O-C,02*0K), In t'he same way the original red salt near 300" yields its corre-sponding anhydride by loss of 2 mols. H,O. With ammonia the chromoxalates of the red series react in a peculiar manner ; when it is added to the red solution of the potash salt WERNER RESEARCHES ON CHROX-ORGANIC ACIDS. 409 a deep-green liquid is formed as in the case of the fixed alkalis and when all free ammonia has been expelled by boiling 2 mols. are still retained for each mol. of red salt employed corresponding to the compound K,(NH&,Cr2(C20&. If ammonia gas be passed to saturation into the green solution or better if the finely-powdered red salt be treated with strong aqueous ammonia it dissolves after a short time yielding an intense claret-coloured liquid which on boiling becomes green.Alcohol added in excess to the red ammoniacal liquid throws down a dull red crystalline precipitate which after drying by a gentle heat gave results on analysis which lead to the formula KzCr2 ( G O ) J 6NH3,6Hz0. (I) 0.4535 gram gave 0.0629 gram NH ; (11) 0.334 gram gave 0.043 gram NH,. 0.328 gram gave 0.15417 gram (C,OJ radicle. (I) 0.3472 gram gave 0.0865 gram K,SOI; (11) 0.3175 gram gave 0-0774 K,SO,. 0.3175 gram gave 0.0636 gram Crz03. Calculated percentage composition :-Found. r-J- 7 Theory. I. 11. 10.48 p. c. Cr, . . . . . . 13.97 ). 13.75 , -(C,Oi)r . . . . 47.31 ) 47.00 ,) -R .. . . . . . . 11-04 p. c. 10.82 p. c. (NH3)G . . 13.71 , 13.87 , 13-88 ,, (H,0)6 14.51 :7 14.34 (by diff.) -99-98 100~00 It readily loses ammonia on heating. chromic oxide thus :-When ignited it leaves a residue of potassium chromate and 2KzCr2(CzOr)~,6NRS,6H20 + 130 = 2K,Cr04 + Cr,03 + 16C02 + 12NH + 12Hz0, corresponding to 36.29 per cent. ; 0.1715 gram left a residue weighing 0.063 gram = 36.67 per cent. If the salt (NH,),H2Cr2(C,04)r(OH)2* be treated with ammonia solution in place of Croft’s salt alcohol precipitates the compound Cr,(CzOa)a,6NH3,6H10 ; as deduced from the following analysis :-* Warington’s ammonium salt represmted as a hydroxyl compound. VOL. LIII. 2 ‘4 1 O WERNER RESEARCHES ON CHROM-ORGANIC ACIDS. 0.2372 gram gave 0.0546 gram CrzOs; 0.2267 gram gave 0.0351 0.396 gram gave 0.2087 gram (C204) radicle.gram NH,. Theory. Found. (NH,),. . 15.31 p. c. 15.49 p. c. Cr 15.61 , 15.81 ,, (C,O,)j. 52.85 , 52-77 ,) (H,O) . 16.21 15.93 (by diff.) - -99.98 100*00 When heated this compound readily loses part of its ammonia. On ignition it leaves a residue of chromic oxide; 0.2372 gram left a residue weighing 0.0546 gram = 23.01 per cent. Theory 22.82 per cent. The addition of calcic chloride to solutions of these compounds produces an immediate precipitate of calcium oxalate ; hydrochloric acid added to warm concentrated solutions causes the separation of osalic acid on cooling together with small red crystals of the corre-sponding chloride. From these reactions it will be seen that these two compounds are no longer chromoxalates but appear to be the oxalates of a peculiar class of chromammonium base.In an experiment with a view to displace the two hydroxylic hydrogen-atoms in the compound K,Cr,( CZO4),( OH) by potassium by the direct action of potash (4 mols.) on the red salt, and precipitation of the solution with alcohol a compound was obtained belonging to st new class of chromoxalates containing 4 atoms of chromium in the niolecule apparently resulting from the condensation of 2 mols. of the di-hydroxyl compound with elimination of oxalic acid. The nature of this reaction has not yet been sufficiently studied for inter-pretation and is being investigated. I here take the opportunity of acknowledging the receipt of a paper from Professor F. W. Clarke containing a communication made t o the American Chemical Society some years ago on the blue series of chromoxalates. In this paper Professor Clarke has assigned to these compounds a constitution similar to that independently adopted by me in my former paper. Professor Clarke’s paper completely escaped my notice a t the time. University Laboratory, Trinity Cbllege Dublin