Sulfur dioxide, complexation with

Hexaruthenium carbonyl complexes have been used to prepare Ti02-supported mthenium catalysts for the sulfur dioxide reduction with hydrogen [112, 113], A catalyst derived from [Ru6C(CO)i6] showed higher activity in the production of elemental sulfur at low temperatures than that prepared from RUCI3 as precursor. This catalytic behavior is related with the formation of an amorphous ruthenium sulfide phase that takes place during the reaction over the ex-carbonyl catalyst [112]. 

Once sulfur dioxide has escaped into the atmosphere, it undergoes a series of reactions by which it is converted to sulfuric acid. Those reactions are somewhat complex and may follow at least three different courses. In the first of these reaction sequences, sulfur dioxide reacts with hydroxyl radicals in the atmosphere in the presence of some metallic catalyst (M) to form the bisulfite radical (HSO3 ) ... 

The complex (NH4),[Fe(S03)6] has been shown by an X-ray study to contain O-bonding as in (I4) 65 the Raman and IR spectra differ from those of S-bonded complexes, v, and v3 occurring at frequencies ca. 150 cm-1 lower.59 Sulfur dioxide reacts with [Co(NH3)5(OH)]2+ to give O-bonded [Co(NH3)5(S03)+ which slowly isomerizes to the S-bonded analogue.66... 

These methylene-bridged complexes III are extremely robust, air-stable substances. We have sought without success to effect insertions into the Pd-C bonds. The complexes are unreactive toward carbon monoxide (at 5 atm at 30°C) or sulfur dioxide. Reaction with methyl isocyanide or pyridine results in displacement of the terminal halide ions and produces cations that have been isolated as hexa-fluorophosphate salts [Pd2(dpm)2( -CH2)(CNCH3)2][PF6]2( (CN) = 2217 cm-1) and [Pd2(dpm)2(/Lt-CH2)(py)2][PF6]2. Treatment of III with fluoroboric or trifluoroacetic acid slowly results in the protonation of the methylene group which is converted into a terminal methyl group. The resulting brown complex, which has been isolated as its tetra-fluoroborate salt has been shown by H-l and P-31 NMR spectroscopy and X-ray crystallography to have Structure IV. 

Sulfur dioxide insertion with the aryl complexes also proceeds initially to the corresponding 0-sulfinates. A moderate p value of —4.3 is to be compared with p = —1.87 for SO2 insertion into the Sn—R bonds of MeaSnR (51,52). It reflects some stabilization by the substituent X of the positive charge developing on the ring during the reaction. A transition state approximating (X) (or a corresponding closed structure), similar to the classical a complex of electrophilic aromatic substitution reactions (103), seems reasonable on this basis. 

An excellent review entitled Sulfur Dioxide Complexes of the Platinum Metals has recently appeared which, in addition to the subject impUed by the title, addresses the electronic structure of SO2 and its bonding to metal complexes. The present work attempts a more comprehensive review of the structure and bonding of transition metal-SO2 complexes, with particular emphasis on results which have appeared since the previous review. 

Fig. 25. Ni(np3)(S02). (Reprinted, with permission, from Synthesis and Structural Characterization of a Sulfur Dioxide Complex of Nickel with Tris-(2-(d henylphosphino)ethyl)amine, Mealli, C. et al. Inorg. Chem. 17, 3021, Fig. 1, copyright, 1978, by the American Chemicd Society)...

Regeneration. The products formed by treating sulfur dioxide solutions with hydrogen sulfide depend in part on the pH. When hydrogen sulfide is added to a solution of sulfur dioxide in water, a complex mixture is formed that includes polythionic acids, thiosulfuric acid, and colloidal sulfur (in contrast to the crystalline sulfur obtained in the citrate process). This is known as Wackenroder s solution and has been extensively studied. The composition varies with the conditions used. With excess hydrogen sulfide the final product is ultimately approximately 100% sulfur (6). While the overall stoichiometry of the reaction is the same as the gas phase Claus reaction, the chemistry is more complex. 

Deoxygenation of sulfoxides. Sulfoxides are converted into sulfides in high yield when treated with 1 eq. of iodine and excess pyridine—sulfur dioxide complex in acetonitrile (80 ). If bromine is used, pyridine is omitted in order to... 

Reaction with sulfur dioxide yields a o--allylic rhodium-sulfur dioxide complex (1). 

The complex [RuCl(NH3)4(S02)]Cl was reported in 1936 it was prepared by the reaction of HCl upon [Ru(HS03)2(NH3)4]. However, another 30 years had elapsed before an extensive series of sulfur dioxide complexes was synthesized and investigated by spectroscopic and X-ray crystallographic studies. " The compound [RuCl(NH3)4(S02)]Cl was shown by X-ray crystal analysis to be octahedral with the SOj and Cl ligands mutually trans and the Ru—S distance 2.07 A. The related pentaammine complexes [Ru(NH3)5(S02)]X2 = Cl, Br, I) are known and the iodide has been prepared by the reaction of [Ru(NH3)5(H20)]l2 with S02- ... 

The reactions of chlorine gas with either dry sulfur dioxide, or with carbon monoxide are remarkably slow. In both cases reaction only occurs at high temperature, and by a complex process involving free chlorine atoms (Bamford and Tipper 22)). Simple concerted mechanisms can be imagined in both cases. 

Olah, G.A. and YD. Vankar. 1978. Synthetic methods and reactions. 52. Preparation of nitriles from aldoximes via dehydration with trimethylamine/sulfur dioxide complex. Synthesis 9 702-703. 

Another important example of a redox titration for inorganic analytes, which is important in industrial labs, is the determination of water in nonaqueous solvents. The titrant for this analysis is known as the Karl Fischer reagent and consists of a mixture of iodine, sulfur dioxide, pyridine, and methanol. The concentration of pyridine is sufficiently large so that b and SO2 are complexed with the pyridine (py) as py b and py SO2. When added to a sample containing water, b is reduced to U, and SO2 is oxidized to SO3. 

Whereas sulfolane is relatively stable to about 220°C, above that temperature it starts to break down, presumably to sulfur dioxide and a polymeric material. Sulfolane, also stable in the presence of various chemical substances as shown in Table 2 (2), is relatively inert except toward sulfur and aluminum chloride. Despite this relative chemical inertness, sulfolane does undergo certain reactions, for example, halogenations, ting cleavage by alkah metals, ring additions catalyzed by alkah metals, reaction with Grignard reagents, and formation of weak chemical complexes. 

Lewis Acid Complexes. Sulfolane complexes with Lewis acids, such as boron trifluoride or phosphoms pentafluoride (17). For example, at room temperature, sulfolane and boron trifluoride combine in a 1 1 mole ratio with the evolution of heat to give a white, hygroscopic soHd which melts at 37°C. The reaction of sulfolane with methyl fluoride and antimony pentafluoride inhquid sulfur dioxide gives crystalline tetrahydro-l-methoxythiophenium-l-oxidehexafluoroantimonate, the first example of an alkoxysulfoxonium salt (18). 

A method suitable for analysis of sulfur dioxide in ambient air and sensitive to 0.003—5 ppm involves aspirating a measured air sample through a solution of potassium or sodium tetrachloromercurate, with the resultant formation of a dichlorosulfitomercurate. Ethylenediaminetetraacetic acid (EDTA) disodium salt is added to this solution to complex heavy metals which can interfere by oxidation of the sulfur dioxide. The sample is also treated with 0.6 wt % sulfamic acid to destroy any nitrite anions. Then the sample is treated with formaldehyde and specially purified acid-bleached rosaniline containing phosphoric acid to control pH. This reacts with the dichlorosulfitomercurate to form an intensely colored rosaniline—methanesulfonic acid. The pH of the solution is adjusted to 1.6 0.1 with phosphoric acid, and the absorbance is read spectrophotometricaHy at 548 nm (273). 

R Tl compounds react readily with acids, halocarbons, or sulfur dioxide to form R2TIX. They also form neutral complexes (R3TI L) with Lewis bases (L), eg, amines and phosphines, in a similar manner as the gaHium and indium analogues. 

Acidification of thiosulfate with strong acid invariably leads to decomposition with the formation of colloidal sulfur and sulfur dioxide. The mechanism of this reaction is complex and depends on the thiosulfate concentration and the pH (14). The following reaction explains the formation of the main products ... 

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