Sulfur dioxide decomposition

This is an exothermic, reversible, homogeneous reaction taking place in a single liquid phase. The liquid butadiene feed contains 0.5 percent normal butane as an impurity. The sulfur dioxide is essentially pure. The mole ratio of sulfur dioxide to butadiene must be kept above 1 to prevent unwanted polymerization reactions. A value of 1.2 is assumed. The temperature in the process must be kept above 65°C to prevent crystallization of the butadiene sulfone but below lOO C to prevent its decomposition. The product must contain less than 0.5 wt% butadiene and less thM 0.3 wt% sulfur dioxide. 

C. Further warming to 65°C forms white iron sulfate monohydrate [17375-41 -6], FeSO H2O, which is stable to 300°C. Strong beating results in decomposition with loss of sulfur dioxide. Solutions of iron(II) sulfate reduce nitrate and nitrite to nitric oxide, whereupon the highly colored [Fe(H20) (N0)] ion is formed. This reaction is the basis of the brown ring text for the quaUtative deterrnination of nitrate or nitrite. 

PPS dust should be treated as a nuisance particulate. The OSHA permissible exposure limit for respirable dust is 5 mg/m for dust containing no asbestos and less than 1% siUca. The principal decomposition products released during mol ding of PPS and their permissible exposure limits are given in Table 10. Sulfur dioxide and carbonyl sulfide are the most significant off-gases for production of mucous membrane irritation. 

Ammonium sulfate [7783-20-2], (NH 2 U4, is a white, soluble, crystalline salt having a formula wt of 132.14. The crystals have a rhombic stmcture d is 1.769. An important factor in the crystallization of ammonium sulfate is the sensitivity of its crystal habit and size to the presence of other components in the crystallizing solution. If heated in a closed system ammonium sulfate melts at 513 2° C (14) if heated in an open system, the salt begins to decompose at 100°C, giving ammonia and ammonium bisulfate [7803-63-6], NH HSO, which melts at 146.9°C. Above 300°C, decomposition becomes more extensive giving sulfur dioxide, sulfur trioxide, water, and nitrogen, in addition to ammonia. 

Inorganic Reactions. Thermal decomposition of Hquid sulfamic acid begins at 209°C. At 260°C, sulfur dioxide, sulfur trioxide, nitrogen, water, and traces of other products, chiefly nitrogen compounds, result. 

Chemical Properties. The chemistry of the sulfur chlorides has been reviewed (141,142). Sulfur monochloride is stable at ambient temperature but undergoes exchange with dissolved sulfur at 100°C, indicating reversible dissociation. When distilled at its atmospheric boiling point, it undergoes some decomposition to the dichloride, but decomposition is avoided with distillation at ca 6.7 kPa (50 mm Hg). At above 300°C, substantial dissociation to S2 and CI2 occurs. Sulfur monochloride is noncombustible at ambient temperature, but at elevated temperatures it decomposes to chlorine and sulfur (137). The sulfur then is capable of burning to sulfur dioxide and a small proportion of sulfur trioxide. 

Chemical Properties. Anhydrous sodium sulfite is stable in dry air at ambient temperatures or at 100°C, but in moist air it undergoes rapid oxidation to sodium sulfate [7757-82-6]. On heating to 600°C, sodium sulfite disproportionates to sodium sulfate and sodium sulfide [1313-82-2]. Above 900°C, the decomposition products are sodium oxide and sulfur dioxide. At 600°C, it forms sodium sulfide upon reduction with carbon (332). 

Manufacture. Aqueous sodium hydroxide, sodium bicarbonate, sodium carbonate, or sodium sulfite solution are treated with sulfur dioxide to produce sodium metabisulfite solution. In one operation, the mother Hquor from the previous batch is reinforced with additional sodium carbonate, which need not be totally in solution, and then is treated with sulfur dioxide (341,342). In some plants, the reaction is conducted in a series of two or more stainless steel vessels or columns in which the sulfur dioxide is passed countercurrent to the alkaH. The solution is cooled and the sodium metabisulfite is removed by centrifuging or filtration. Rapid drying, eg, in a stream-heated shelf dryer or a flash dryer, avoids excessive decomposition or oxidation to which moist sodium metabisulfite is susceptible. 

Chemical Properties. Anhydrous sodium dithionite is combustible and can decompose exothermically if subjected to moisture. Sulfur dioxide is given off violentiy if the dry salt is heated above 190°C. At room temperature, in the absence of oxygen, alkaline (pH 9—12) aqueous solutions of dithionite decompose slowly over a matter of days. Increased temperature dramatically increases the decomposition rate. A representation of the decomposition chemistry is as follows ... 

The decomposition of dithionite in aqueous solution is accelerated by thiosulfate, polysulfide, and acids. The addition of mineral acid to a dithionite solution produces first a red color which turns yellow on standing subsequentiy, sulfur precipitates and evolution of sulfur dioxide takes place (346). Sodium dithionite is stabilized by sodium polyphosphate, sodium carbonate, and sodium salts of organic acids (347). 

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 ... 

Ammonium bisulfite can be used in place of the sulfur dioxide. The solution is treated with activated carbon and filtered to remove traces of sulfur. Excess ammonia is added and the solution evaporated if the anhydrous crystalline form is desired. The crystals ate dried at low temperature in the presence of ammonia to prevent decomposition (61—63). 

Strong dehydrating agents such as phosphorous pentoxide or sulfur trioxide convert chlorosulfuric acid to its anhydride, pyrosulfuryl chloride [7791-27-7] S20 Cl2. Analogous trisulfuryl compounds have been identified in mixtures with sulfur trioxide (3,19). When boiled in the presence of mercury salts or other catalysts, chlorosulfuric acid decomposes quantitatively to sulfuryl chloride and sulfuric acid. The reverse reaction has been claimed as a preparative method (20), but it appears to proceed only under special conditions. Noncatalytic decomposition at temperatures at and above the boiling point also generates sulfuryl chloride, chlorine, sulfur dioxide, and other compounds. 

The decomposition of sulfuryl chloride, SO U, to sulfur dioxide and chlorine gases is a first-order reaction. 

To a stirred solution of 5.70g (21.1 mmol) of 4,4.5,5-tetramethyl-2[(5)-(A)-3-(trimethylsilyloxy)-l-bulenyl]-l, 3,2-dioxaborolane in 130 mL of petroleum ether (bp 40-60 C) are added ca. 20 mg of cobalt(II) nitrate hexahydrale followed immediately by 2.75 g (23.1 mmol) of freshly distilled thionyl chloride. Slow evolution of sulfur dioxide ceases after 4h. The mixture is then filtered and concentrated in vacuo at r.t. to give crude 15, which is taken up in 50 mL of petroleum ether and washed with 30-mL portions of buffer (pH 5) until the pH is constant. 100 mL of brine are added to the organic phase and the pH is adjusted to 7 by addition of sat. aq NaHCO,. The pH should not exceed 7, otherwise decomposition ensues. The phases are separated and the organic phase is dried with MgS04 and concentrated at r.t. to give 15 yield 4.39 g (96%) Contact of 15 with metal surfaces should be avoided. 

Ammonia, hydrogen sulfide, and sulfur dioxide may result from the decomposition of chemical treatments (although in large boiler plants, ammonia is often deliberately added to raise the boiler, steam, or condensate system pH). 

It is highly probable that the lesser stability of thiirene dioxides compared with that of the thiirene oxides simply reflects the more facile extrusion of sulfur dioxide relative to that of sulfur monoxide. In fact, the same effect is probably operative in the case of the cis- and trans-diphenylthiirane oxides (16g,h)110 compared with cis- and trans-diphenylthiirane dioxides (17d,e)99 the former were found to be more stable toward thermal decomposition than the latter. 

Satisfactory sebacoyl chloride can be purchased from the Eastman Kodak Co., Rochester, New York. The submitters prepared it as follows. A mixture of 150 g. (0.74 mole) of sebacic acid and 150 ml. of thionyl chloride is heated in a water bath at 60°. The acid gradually goes into solution with evolution of sulfur dioxide and hydrogen chloride. When gas evolution ceases, the mixture is distilled as rapidly as possible under reduced pressure. The yield of sebacoyl chloride, b.p. 171-175°/15 mm., is about 140 g. (79%). Caution1 Toward the end of the distillation, spontaneous decomposition of the residue with formation of a voluminous black foam frequently occurs. 

Sulfur forms several oxides that in atmospheric chemistry are referred to collectively as SOx (read sox ). The most important oxides and oxoacids of sulfur are the dioxide and trioxide and the corresponding sulfurous and sulfuric acids. Sulfur burns in air to form sulfur dioxide, S02 (11), a colorless, choking, poisonous gas (recall Fig. C.1). About 7 X 1010 kg of sulfur dioxide is produced annually from the decomposition of vegetation and from volcanic emissions. In addition, approximately 1 X 1011 kg of naturally occurring hydrogen sulfide is oxidized each year to the dioxide by atmospheric oxygen ... 

From CS2 solution S7O2 is obtained as intensely orange colored crystals which on heating spontaneously decompose at 60-62 °C with evolution of sulfur dioxide. S7O2 is far less soluble in CS2 (ca. 1 g at 0 °C) than S7O. The solution decomposes within 1 h to a mixture of sulfur homocycles and SO2. Solid S7O2 decomposes at 25 °C within minutes and quantitatively within 2 h, even in the dark. Heating in a high vacuum to 50-60 °C produces S2O and elemental sulfur. The El mass spectrum therefore exhibits peaks due to these decomposition products only [67]. 

Roasting pyrite, an iron ore composed of iron sulfide, results in the oxidation and decomposition of this compound to volatile sulfur dioxide and the formation of iron oxide, which can be smelted with relative ease into iron ... 

The chemistry involved in this explosively unstable system is reviewed [1]. The mechanism of the trigger reactions that initiate the exothermic decomposition of chlorate-sulfur mixtures has been studied. Mixtures containing 1-30% of sulfur can decompose well below the m.p. of sulfur, and addition of sulfur dioxide, the suspected chemical trigger, causes immediate onset of the reaction [2], Autoignition of stoichiometric mixtures can be as low as 115°C, with frictional sensitivity at 5N, the lowest load the test apparatus permitted. Both were dependent upon the history of the sulphur used [3],... 

Reaction to give tetrafluorooxathietane 2,2-dioxide (tetrafluoroethane sultone) had been used industrially and uneventfully, but reaction with excess sulfur trioxide may cause explosive decomposition to carbonyl fluoride and sulfur dioxide [1]. An incident involving the same explosion hazard was reported 11 years later [2], Use of inert gas to prevent explosion has been patented [3],... 

Scale formation in the scrubber can lead to sodium carbonate as an additional dry sorbent in the scrubber. Alternatively, limestone is also introduced into combustion chambers to treat sulfur dioxide emissions. Decomposition of CaC03 into CaO and CO2 occurs in the combustion chamber, and the resulting CaO combines with S02 to produce calcium sulfite. Notice that this process produced another potentially environmentally harmful pollutant (CO2) as it gets rid of a definite environmentally harmful pollutant (SO2). 

The sulfonyl radical is unstable and dissociates via C—S bond back to the alkyl radical and sulfur dioxide. The rate constant of this reaction for the cyclohexylsulfonyl radical was calculated from the kinetic data on the chain decomposition of cyclohexylsulfonyl chloride [2]. This decay of cyclohexylsulfonyl chloride initiated by DCHP occurs according to the following chain mechanism [29,31] ... 

The reactions of sulfides with ROOH give rise to products that catalyze the decomposition of hydroperoxides [31,38-47]. The decomposition is acid-catalyzed, as can be seen from the analysis of the resulting products cumyl hydroperoxide gives rise to phenol and acetone, while 1,1-dimethylethyl hydroperoxide gives rise to 1,1-dimethylethyl peroxide, where all the three are the products of acid-catalyzed decomposition [46-49]. It is generally accepted that the intermediate catalyst is sulfur dioxide, which reacts with ROOH as an acid [31,46-50]. 

The resulting products, such as sulfenic acid or sulfur dioxide, are reactive and induce an acid-catalyzed breakdown of hydroperoxides. The important role of intermediate molecular sulfur has been reported [68-72]. Zinc (or other metal) forms a precipitate composed of ZnO and ZnS04. The decomposition of ROOH by dialkyl thiophosphates is an autocata-lytic process. The interaction of ROOH with zinc dialkyl thiophosphate gives rise to free radicals, due to which this reaction accelerates oxidation of hydrocarbons, excites CL during oxidation of ethylbenzene, and intensifies the consumption of acceptors, e.g., stable nitroxyl radicals [68], The induction period is often absent because of the rapid formation of intermediates, and the kinetics of decomposition is described by a simple bimolecular kinetic equation... 

Cyanide blood agents are relatively unstable and tend to polymerize on standing. Polymers can be explosive. Stabilizers or solvents can be added to inhibit decomposition. Stabilizers include phosphoric acid, sulfuric acid, powdered sodium pyrophosphate, and sulfur dioxide. Although cyanide blood agents react with metals, they can be stored in steel or other common containers if stabilized. 

---