Iron cyanates

Organosulfur Compounds. These compounds, Hsted in Table 8, are used in a variety of appHcations, including cooling water, paint, and metalworking. Methylenebisthiocyanate hydroly2es rapidly at a pH above 8 to cyanate ion which complexes with ferric iron to poison the cytochrome systems (36). 

In the presence of a trace of iron or nickel oxide, rapid oxidation occurs when cyanide is heated in air, first to cyanate and then to carbonate ... 

Note Iron(III) cations also react and give the well known deep red iron(III) isothii cyanate. 

The term organic chemistry was first used by the Swedish chemist Berzelius in 1807 (Larsson, 1981). He coined the name to describe the chemistry of substances derived from living matter. Berzelius was a staunch believer in the vis vitalis theory, which held that such substances were endowed with a mystical vital force that precluded their synthesis in the laboratory from materials of mineral origin. Ironically, it was a student of Berzelius, Wohler, who heralded the demise of vitalism with his synthesis of urea from ammonium cyanate (Wohler, 1928). In a letter to Berzelius in 1828, Wohler wrote I must tell you that I can make urea without requiring kidneys, or even an animal, whether a human being or a dog . 

Tris (triphenylphosphine) nickel, tris (tri-p-tolylphosphine) nickel, and bis (1,3-diphenylphosphinepropane) nickel proved to be good catalysts, the first being slightly more effective. The tricyclohexylphosphine complex was a very poor catalyst, and bis (cyclooctadiene) nickel did not catalyze cyanation. Cyanation of several substituted aromatic halides in the presence of Ni[P(C6H5)3]3 prepared by reducing dichlorobis (triphenylphosphine) nickel (II) 2 with a powdered manganese iron (80 20) alloy (Reaction 3) is reported in Table II. 

Table II. Cyanation of Aromatic Halides in the Presence of a Catalyst Prepared in situ from Nickel(II) Salt6 and Manganese—Iron Alloy...

Sodium cyanide solution dissolves certain metals (I) with absorption of oxygen, e.g.. gold, silver, mercury, lead, and (2) with evolution of hydrogen, e.g.. copper, nickel, iron. zinc, aluminum, magnesium and solid sodium cyanide, when heated with certain oxides, e.g.. lead monoxide PhO. stannic oxide SnO.. yields the metal of the oxide, e.g.. lead. tin. respectively. and sodium cyanate NaCNO. Two classes of esters arc known, cyanides or nitriles, and isocyanides, isonitriles or carbylatnincs. the latter being very poisonous and of marked nauseating odor... 

The oxidation of free cyanide ion yields cyanogen or cyanate, never fulminate. It might seem that when the carbon atom is attached to hydrogen or a metal, addition of oxygen to the nitrogen atom should be possible, but there is no record of such an oxidation ever having been achieved. The reverse process, conversion of combined fulminate into combined cyanide, has, however, been demonstrated for platinum(II) and iron(ll) complexes. 

The iron-catalyzed [3 + 2]-cycloaddition (Huisgen reaction) of nitriles and carbonyl compounds as reported by Itoh et al. is one of the rare examples reported where an iron reagent can be utilized for the synthesis of 1,2,4-oxadiazoles (Scheme 9.35) [93]. In this reaction, methyl ketones are nitrated at the a-position by Fe(N03)3 to generate an a-nitro ketone. This intermediate rearranges to an acyl cyanate, which reacts further with the nitrile to give the heterocyclic product 48 in good to excellent yields (R1 = Ph, R2 = CH3 95% yield). 

Chem. 29 (1967), pp. 1637-1642. Spectroscopic studies of die reaction of hexa-cyanoferrate(III) in water and ethanol. 3.3x 10 4 M Fe(NC>3)3 were exposed with a cyanide excess of likewise 3.3x10 mol l"1. With pH values of approximately 10, all the Fe2[Fe(CN)6] was converted into Iron Blue within 48 hours. Cyanate, die anticipated product of die oxidation of die CN-, could not, however, be proven. Perhaps this is further oxidized directly into C02. If this mechanism is assumed, die result, purely stoichiometrically, is that an alkaline environment must be favorable. This finding is supported by die known fact that hexacyan-oferrate(III) is a strong oxidation agent in alkaline medium and is even able to oxidize divalent chrome to hexavalent, therefore, that is, CN ions must have oxidized very quickly J.C. Bailar, Comprehensive Inorganic Chemistry, Vol. 3, Pergamon Press, Oxford 1973, p. 1047. An overly alkaline environment would, however, disturb die complexing of the Fe3+- ion by cyanide, which is then displaced by OH- (Fe(OH)3 then occurs as a by-product) and/or the latter can hardly be displaced from die iron. 

Cyanotrimethylsilane, (CH3)3SiCN. This silane is present in solution in part as the isocyanide isomer, (CH3)3SiNC. And indeed it is more useful than NaCN for cyanation of the iron complex l2 to provide 2 and 3, intermediates in a projected synthesis of tridachione. 

The scope of this chapter is based on the analogous one by Naso and Marchese published in 19831. Since the time of their review, the focus of work in this area has shifted somewhat, and sections have been added or omitted to reflect that focus. New sections covering chromium(II)-mediated reactions of halides and covering cobalt-mediated radical reactions of halides have been added. In view of the relatively mature nature of the areas, sections dealing with 7c-allylnickel complexes, iron oxyallyl cations and cyanation reactions have been omitted. 

George SJ, Cui Z, Razavet M, Pickett CJ (2002) The di-Iron subsite of all-iron hydrogenase mechanism of cyanation of a synthetic 2Fe3S -carbonyl assembly. Chem. Eur. J. 8 4037 1046... 

Alternatively, the complex cyanides may be eliminated from the mixture by fusing with an equal weight of sodium or potassium carbonate in a porcelain crucible. Soluble cyanates and cyanides are formed, which may be extracted with water the residual metallic iron may be dissolved in dilute hydrochloric acid. 

A similar reaction yielding alkyl selenocyanates occurs between trialkylboranes and sodium selenoiso-cyanate in the presence of iron(ni) ions. There is a strong preference for the transfer of secondary or tertiary as compared to primary alkyl groups. This allows selective transfer reactions to be carried out in yields of 57-68% (equation 71) and 67-78% (equation 72). ... 

Nucleophilic attack on ( -alkene)Fp+ cations may be effected by heteroatom nucleophiles including amines, azide ion, cyanate ion (through N), alcohols, and thiols (Scheme 39). Carbon-based nucleophiles, such as the anions of active methylene compounds (malonic esters, /3-keto esters, cyanoac-etate), enamines, cyanide, cuprates, Grignard reagents, and ( l -allyl)Fe(Cp)(CO)2 complexes react similarly. In addition, several hydride sources, most notably NaBHsCN, deliver hydride ion to Fp(jj -alkene)+ complexes. Subjecting complexes of type (79) to Nal or NaBr in acetone, however, does not give nncleophilic attack, but instead results rehably in the displacement of the alkene from the iron residue. Cyclohexanone enolates or silyl enol ethers also may be added, and the iron alkyl complexes thus produced can give Robinson annulation-type products (Scheme 40). Vinyl ether-cationic Fp complexes as the electrophiles are nseful as vinyl cation equivalents. ... 

Now let me come back to primary substitutions at the ferrocene nucleus. Together with Vil chevskaya, we phosphorylated ferrocene and its derivatives to triferrocenylphosphine oxides [263, 264). An unusual reaction, discovered in collaboration with Perevalova and Yur eva, was the direct cyanation of ferrocene with hydrocyanic acid in the presence of ferric chloride [265,272). Initially, cyanide attacks the iron atom of the ferricinium cation, then the cyanide group transfers to the ring while the iron is simultaneously reduced. The reaction was termed by us as the ricochet (from the metal to the nucleus) substitution it may be applied to many substituted ferrocenes and to the ruthenocenium cation [273), and it is now the simplest route to ferrocene carboxylic acids through their nitriles. Further, ferrocene was studied in acid-medium reactions with oxo compounds. With aldehydes [274), the reaction was complicated by the transformation of ferro-cenylalkyl carbinol formed Initially via the carbonium ion, followed by transformation to a radical which, in its turn, was coupled to 1,2-bis-(ferrocenylalkyl)ethane (27.5). The reaction with acetone led to 2,2-di-ferrocenylpropane (276). 

This same substitution of sulphur for oxygen occurs in the case of cyanic acid and its salts, e.g., potassium thio-cyanate and ammonium thiocyanate used as reagents in testing for ferric iron. 

With ferric salts in solution either of these reagents forms the cherry red ferric thio-cyanate and is the basis of qualitative tests for iron and the use of the thio-cyanate as an indicator in volumetric titrations. Potassium thio-cyanate may be prepared by heating potassium cyanide with sulphur or ammonium sulphide. Ammonium thio-cyanate may be prepared by heating together carbon disulphide and ammonia in the presence of alcohol. 

---