Sulphur Dioxide Insertion

An alternative mechanism might operate with organocobaloximes, and possibly other systems as well. Evidence is given for a radical-chain mechanism with initiation by C—Co rupture or adventitious Co fi impurities with the following propagation steps  

The transfer of alkyl groups between metal atoms was established in mixed Co and Rh systems. The insertion reaction is markedly photocatalysed, the rates are variable, there are induction periods, and Co catalyses the reaction. These observations support the radical nature of the reaction. 

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Reactions of carbon subsulphide and of elementary phosphorus, sulphur and selenium with complexes of the platinum metals Sulphur dioxide insertion reactions of transition metal alkyls and related complexes... 

Sulphur Dioxide. The observed products and high rates of insertion of sulphur dioxide into tin-carbon bonds in organotin allenes and alkynes have been interpreted in terms of an electrophilic cleavage mechanism. Such a mechanism is also proposed for sulphur dioxide insertion into mercury-carbon and into lead-carbon bonds. The mechanism of sulphur dioxide insertion into transition metal (Mo, W, or Mn)-carbon bonds is again similar. ... 

CO>2] and [Cp(CO)2M CH(NR)N(CO)R ] from [Cp(CO),MCl] (M=Cr, Mo, or W), Sulphur dioxide insertion into 2-alkenyl derivatives (16) leads to two main product types [equation (10)]. The effects of varying R, R, and R were studied, and a mechanism was proposed which involves formation of a metaH -alkenesulphinate zwitterion, a 1,3-rearrangement via internal return of the alkenesulphinate anion, and a recombination of the rearranged (or unrearranged) anion with the metal cation. 

The stereochemistry of iron-carbon bond cleavage by electrophilic attack by mercury(n) chloride or bromine, or by carbon monoxide or sulphur dioxide insertion, has been probed by n.m.r. studies of products derived from /Areo-[Mc3C CHD-CHD-Fe(CO)2(A -C5H5)]. Predominant retention occurs in the reaction with mercury(n) chloride, predominant inversion in the reactions with sulphur dioxide or bromine. It is this last result which is of the most interest, for it affects discussions of the stereochemical course of oxidative additions... 

Sulphur Dioxide.—Insertion reactions of sulphur dioxide into transition-metal-alkyl bonds and into metal-carbon bonds have been the subject of review articles. 

Sulphur dioxide inserts into palladium-oxygen bonds. When a solution of palladium chloride in an alcohol is treated with sulphur dioxide, a sulphinato-complex is produced, presumably by insertion into a palladium-alkoxide bond. The reaction of sulphur dioxide with molecular oxygen complexes of platinum and of iridium, producing sulphato-complexes, involves insertion of sulphur dioxide into one of the metal-oxygen links, as shown in Scheme 5. ... 

The first kinetic study of sulphur dioxide insertion into a transition-metal-carbon bond, mentioned above, indicated an electrophilic mechanism. Such a mechanism is also indicated by the first kinetic study of sulphur dioxide insertion into tin-carbon bonds. For insertion into the substituted phenyltrimethyltin compounds (26), the variation of second-order rate constant with the nature of the substituent Y gave a reasonable Hammett... 

Elimination of sulphur dioxide from an S-bonded sulphinate complex is a process related to sulphur dioxide insertion. Kinetic studies on the rearrangement of the five-co-ordinate sulphinato-complexes (20) to the sulphur dioxide complexes (21) show that if the organic group R contains electron-withdrawing... 

Insertion reactions of sulphur dioxide and nitric oxide have also been observed with [(7i-Cp)2Zr(Cl)Me] and [(rc-CplaZrlCp)]." ... 

Because atmospheric humidity must be avoided, the reaction flask is isolated from the atmosphere with drying tubes. Moreover, since the solvent is rarely perfectly anhydrous and will contain traces of water due to its hygroscopic nature, its water content must be measured prior to the determination. The equivalence point of the titration reaction is detected by an electrical method instead of a visual method. The current intensity that passes between two platinum electrodes inserted in the reaction medium is measured (see Fig. 19.10). The reagent, which is a mixture of sulphur dioxide, iodine and a base, is characterised by the number of mg of water that can be neutralised by 1 cm3 of this reagent. This is referred to as the equivalent mass concentration of water, or the titre T of the reagent. 

The data strongly suggest the formation of benzyne from o-sulphobenzoic anhydride—from the products of its reaction with benzene by 1,2- and 1,4-addition (naphthalene, phenylnaphthalene) and insertion (biphenyl, about four times as much by weight as from benzene alone). The uncondensed gases from the reaction were a 1 1 mixture of sulphur dioxide and carbon dioxide. This, in addition to the other products, indicates that the first step of Path 2, loss of sulphur dioxide, is the dominant primary process. However, the resulting zwitterion, unlike its cationic counterpart in the mass spectrometer, does not go on to lose carbon monoxide it stabilizes itself more easily by losing carbon dioxide... 

Insertion of sulphur dioxide and 41 sulphur trioxide into metal- (77) carbon bonds... 

Sulphur dioxide (free and total) Wines GD UV—Vis 2.0-40, 25—250 mg L 1 Sequential injection system p-rosaniline plus formaldehyde solution as the acceptor stream sample alkalinisation prior to its insertion [552]... 

Sulphur dioxide gas. This gas is available commercially in a liquefied state in aluminium canisters, from which it can be taken. Alternatively it can be produced from sodium sulphite and 8m sulphuric acid. The solid reagent should be placed into a round-bottomed flask, which can be heated. The acid is kept in a funnel with a stopcock, inserted into one opening of the flask. By adding some sulphuric acid to the solid and by gentle heating, sulphur dioxide gas comes through the second opening of the flask and can be washed in concentrated sulphuric acid. 

Preparation.—Few examples of insertion of SO3 into organometallic compounds have been reported, > in contrast with corresponding reactions of sulphur dioxide recent examples are the formation of RS03Re(C0)s (R = Me, Ph, or p-tolyl) and MeHgS03Me from HgMe2 and SO3 at — 70 °C, further reaction giving methylmercuric methanedisulphonate, MeHgSaOgMe. ... 

The formation of chloroformates and chlorosulphates via insertion of carbon monoxide and sulphur dioxide, respectively, into the O—Cl bonds of per- or poly-fluoroalkyl hypochlorites (sec Vol. 1, p. 150) has formed the subject of some new patent literature. Perfluoroalkyl hypochlorites have also been used to prepare perfluoro-[(iV-chloro)methylethylamine [CjFj NiCFt-f CFa-OCl (CF3)(C F,)NC1 + COF2] (see p. 212), AW-dichloro(chloro-... 

Cleavage of the iron-carbon bond in reactions of sulphur dioxide with complexes of the type [FeR( j -C5H6)(CO)2] is an electrophilic process which proceeds with a large and negative entropy of activation and with inversion of configuration at the a-carbon. The inversion of stereochemistry observed on insertion of sulphur dioxide... 

R = CH2CM63. Reactions involving frontside attack usually have comparable rates for neopentyl and methyl complexes. Insertion reactions with dilute solutions of sulphur dioxide may therefore well proceed via a different mechanism to those occurring in liquid sulphur dioxide. It is suggested that under these conditions reaction occurs via a bimolecular electrophilic process of Se2 retention or iSEi inversion (Scheme 6) rather than St2 inversion proposed for insertion in liquid sulphur dioxide. ... 

Although reactions of sulphur dioxide with [Fe(CHDCHDCMe3)( / -C5H5)(CO)2] proceed with inversion in organic solvents the concentrations of sulphur dioxide are apparently higher than those used in the kinetic studies described above where a different mechanism may operate. Similarly the report that [Fe(Me)( -l-Me-3-Ph-CsHaXCOXPPhg)] inserts sulphur dioxide with high stereospecificity at iron (probably retention) both in liquid sulphur dioxide and in methylene chloride solution does not resolve this problem. ... 

The insertion of sulphur dioxide into organosilanes is difficult. 

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