PHYSICO-CHEMICAL STUDIES ON THE INTERACTION OF ORGANIC COMPOUNDS WITH CYANOGEN COMPLEXES WITH SPECIAL REFERENCE TO THEIR INTER ACTION WITH NITROSOBENZENE, PYRIDINE, 8-HYDROXY-QUINOLINE 5-SULPHONIC ACID AND GLYCINE.

Abstract

Complex metal oyanides of atleast twenty eight heavy metals (in between Ti (22) and U (92)) in their various oxidation states are reported in the existing literature (l). Majority of these compounds are hexa oo-ordinated (octahedral), although quite a few exist as tetra co-ordinated (e.g., copper, zinc, palladium, nickel, mercury, platinum, gold etc.) oyanides (tetrahedral or square planar) or in the form of trieyano (planar) or dicyano (linear) complexes. Others of particular Interest are cyano complexes of Mo, Wand Re of co-ordination number eight (dodeeahedral) with tendency to expand their co-ordinating sphere to ten and a series of *mixed cyanide complexes*, accomodating NO, OH, HgO, CO, NH3 etc. in the co-ordinating sphere, e.g., Fe(CH)g »0~"\ KRe(CR)a(C0)4, W(CN)7(H30) , Cr04(CH)a(RH3f\ | Comprehensive Investigations on the chemistry of metal cyanides have more or less remained limited to those of iron. Valuable information on the synthetic, thermodynamic, electrochemical, analytical and kinetic aspects is available on the basis of these investigations Similar approaches are being made towards the study of octaeyano complexes in recent years. Before Introducing the problem it would be worthwhile to give a brief review of the work done on the complex cyanides of iron. -2- SrathqUqi Information on this aspect deals with the preparation of simple and mixed metal cyanides, salts of metal cyanides with organic bases and the characterisation of these compounds. Baglnlng with the preparation of Iron blues. The synthetic aspects covered the preperation of such difficult compounds as the salts of hydroferrocyanic aoid with a large number of organic bases, e.g., aniline, o-toluidine, dimethylaniline, pyridine, benzidine, isoquinoline etc. and basic dyestuffs, e.g. Bismark brown, auramine, malachite green, methyl violet, acriflavine ete.(2)| mixed complex cyanidea (3-10) of Fe(II)i Fe(CK)6(H20)3" Fe(CH)5 (H0)S-, Fe(CH)5(Ho2)4', Fe^UaGg)4-. re(CH)5(303) , Fe(C!f)6(C0)3*, Fe(CK)5(RSo4), Fe(CH)6(NH3)3-f Fe(CH)2(CH3Ha)4, Fe(CH)2(Phen)2, Fa(CH)2(dipy);, Fe(CK)4(Phen)^, Fo(CH)4(dipy)2- and Fe(CN)g(COg)(Py) andFe(in)t Fe(CH)5 H203", Fe(CH)6 (MH3)a", Fe(CH)5(R0g)3- and Fe(CH)5(N0)3". Studies on the structure of these complexes date back to 1930 have been investigated. The constitution of Prussion and Tumbulls blues was studied by keggin and Mites (11) with the help of x-rays (more refined and accurate x-ray diffraction now makes it possible to make a distinction between the C and R attached to metal ion). These studies were extended by Weiser, Milligan and Bates (12) and later -3- by Reganontic (13) to give useful information about the structure and chemical constants of a number of metal ferrooyanides. Investigations of the later author showed the existence of complex anions of the type MFe(CS)J" with interstitial structures In thin films of copper ferrocyanlde* The techniques of absorption (visible, infra red and ultraviolet regions) spectra and magnetic susceptibility when applied to the dispersed pre cipitate of Iron blues lent support to the theory of super complex formation and formulae! Fe Fe(FeCK-) and Fe ?e(FeCNQ)3 were assigned to Prussian and Turnbull blues respectively* Recently magnetic (14), cryscopic (15) and Studies Vpolorographic (l6-l7)/to investigate the structure of mixed complexes of Fe(II) and Fe(III)i>k>a- c^IouaoL fioUvJLIftl •ProgaxtJ.fts.t Investigations on this property can be divided under fewo sub-headst one dealing with the properties of metal ferrocyanlde colloids, the other dealing with the composition and stability of colloidal precipitates of some less familiar metal cyanogen complexes. Viscosity data of Ghosh and Dhar (18), Malik and Bhattacharya (19) offered strong evidence for the adsorption of the reacting ions, Fe3% FeCHg4". FeCKg on Prussian and Turnbull s blues* The -4- latter authors also studied the composition, adsorptlve, hydrolytic and colloidal properties of sine, manganese, nickel and cobalt ferrocyanides. Other colloidal aspects studied were changes in conductivity, pH, seta potential (20-21) of copper ferrocyanlde, permeabllity( 22-24) of metal ferrocyanlde (cobalt, nickel, silver, chromium etc.) membranes and their sol-gel transformation. Malik (25) for the first time reported the existence of a number of soluble complexes of Cr(lll) | Be (II) * MoUll and VI). TiUlI and IV) etc. and studied their composition and stability by the spectrophotcmetrlc method (26-27). The flr (III) and Cr(Il) complexes were isolated and composition confirmed by chemical analysis, ffl^fttroaetrlc and analytical StttfllflMl With the more frequent use of physico-chemical methods, especially the electrometric ones, precise information not only about the composition of these complexes but *bout the use of hexaoyanoferrate (II and IH) as analytical reagent^. In this connection worth mentioning is the contributions of Kolthoff (28-29) who for the first time successfully employed conductometric and potentiometrlc methods in studying the metal cyanide reactions and, at the same time, demonstrated the importance of potassium ferrocyanlde as a reagent for the estimation of metal ions, specially sine (the use of conductivity titrations in precipitation analysis was employed)* Kolthoff*s work was followed by extensive investigations on the use of potassium ferro and ferricyan!dee in quantitative analysis by other workers and a number of papers on this aspect of the problem appeared from 1922 to 1929* These include the eleotrometrle titrations of ferricyanide with titanous sulphate (30-31), Vanadate hydrosul] hits (32) and eerie ions (33). The effect of alkali on the titrations of certain metal ions (Cd**, Fe**, Pb** a«\ Mc** «tc.) with ferrocyanlde (34)tocx/> cJUl&caji$>S«x» Extensive use of eleotrometrle technique was made from 1940 onwards to study the compositions of the metal ferrocyanogen complexes. The complexes studied were cadmium ferrocyanlde copper ferro and ferricyanides, Prussian and Turnbull blues, sine ferricyanlde, Prussian green, mercuric and uranyl ferrocyanides, nickel ferrlcyanldes (35-37). The studies on metal ferrocyanogen complexes during this period was not limited to the use of eonductometrlc and potentlometric methods alone. The comparatively new technique of amperometry was also employed for the elucidation of the composition of these complexes. Kolthoff (38) for the first time used amperometric titrations to show that the end point in the ferrocyanlde titration of lead correspon ded to the precipitation of FbgFeCHg. Later on -6- Ghounyk and Kleibs (39) Zuman (40) Khosla and Oaur (41) Amore (42) used amperometric titrations In studying copper ferrocyanlde, ferric-ferro cyanides of manganese, cadmium and silver* Zolotavin and Kuznetova (43) carried out polarographle titrations with vanadyl sulphate* Of the other recent techniques employed, besides amperoraetry and polaregraphy are the ooloumetrio titrations and ion exchange methods. Hartley and Llngane (44) had described a method for the eoloumetric titrations of Tl* in strongly alkaline 3- solution by means of Fe(CH)6 generated by anodic 4- oxidation of Fe(CK)s at platinum anode* The accuracy of the method was found to be within 0.2 per cent. In connection with the attempts to use hexaoyanoferrate (II) as the analytical reagent it is worthwhile to mention the work of Deshmukh and Fujita. Deshmukh (46) carried out determination of ferrocynide with lead nitrate and also the volumetric determination of cadmium and cerium by potassium ferrocyanlde. Cadmium and cerium were estimated by titrating excess of potassium ferro cyanlde after the complete precipitation of the respective metal ferrocyanides, while in case of lead a saturated solution of diphenyl oabasone was used as an Indicator. Fujlta <47) estimated lead, silver manganese, nickel cobalt, cadmium and mercury -7- volumetrlcally. He used starch-iodine (silver, manganese, nickel, cobalt), phenol red (lead) potassium ehromate (mercury and cadmium) as Internal indicators for the titrations of metal Ions. More recent studies of Boyland and Mery (48) reveal the possibility of using hexaoyanoferrate (III) as a colorimetric reagent for the estimation of arylhydroxylamines and nitrones or its use as an oxidising agent for reducing sugars (49). Dolezal and zyka (SO) studied analytical use of hexaoyano ferrate (III) in the determinations of qulnones in presence of sine salts as reaction accelerators. Thermodynamical measurements, which would include measurement of formation constants, enthalpies and entropies of formation in solutions, have been very little studied so far* Even for most stable complexes, 4— *a_ ••B.f Fe(CR)g and Fe(CR)^ no stepwise formation constant has been successfully reported* Hepler, Sweet (51) and Jesser had reported heat of solution in water of K3?e(CH)6, K4Fe(CN)9 and the heat of oxidation of Fe(CR)9 by liquid Bra. Stephenson and Morrow (82) had measured tha heat capacities of potassium ferrieyanide and potassium cobalticyanide. These studies revealed a gradual transition, magnetic in nature, occurlng at 131°K in the paramagnetic potassium ferrieyanide* Other investigations, worth mentioning, on thermodynamic properties are those of Asperger (53) EmsehwUler (54) on the hydrolytic decomposition of hexaoyanoferrate (II). More recent work in this direction is due to Breck (55) and Vernon (56) who Investigated entropy differences between correspond ing ferrate (III) and force constants and vibrations of, in relation to leostructural hexaoyanoferrate