Sulfur dioxide redox reactions

Reasonable NO conversion can be achieved using n-decane as reductant. In the absence of sulfur dioxide, the catalytic activity is roughly related to the r ucibility of the Cu phase of Cu ions in zeolites the reaction temperature needed to reach 20% NO conversion parallels that of the TPR peak (Table 7). This relation also practically holds for Cu on simple oxides, therefore a redox mechanism in which reduction of Cu + cations is the slow step could account for the results. 

Hydrogen peroxide plays an important role in many processes in the atmosphere and in natural aqueous systems. It affects numerous redox reactions, which in turn influence the stability and transport of other chemical substances, e.g., pollutants. In the atmosphere, hydrogen peroxide is believed to be involved in several important oxidation reactions, e.g., conversion of sulfur dioxide to sulfuric acid... 

O Nickel and copper are both very important to the Ontario economy. Before they can be refined by electrolysis, they must be extracted from their ores. Both metals can be extracted from a sulfide ore, NiS or CU2S. The sulfide is roasted to form an oxide, and then the oxide is reduced to the metal. Research the extraction processes for both nickel and copper, and write balanced equations for the redox reactions involved. One product of each extraction process is sulfur dioxide. Research the environmental effects of this compound. Describe any steps taken to decrease these effects. 

Recently Bogolytsin and co-authors (62) found that the associations of sulfur dioxide and other inorganic sulfur derivatives interact with the aromatic nuclei of lignins, and strongly influence their reaction and redox behavior. This association effect also forms a selective pre-association state in the sulfonation reaction in wood pulping. It is evident that a wide range of similar association effects may be present, but they remain to be detected and studied. 

Unstabilized chrome yellow pigments have poor lightfastness, and darken due to redox reactions. Recent developments have led to improvements in the fastness properties of chrome yellow pigments, especially toward sulfur dioxide and temperature. This has been achieved by coating the pigment particles with compounds of titanium, cerium, aluminum, antimony, and silicon [3.134] — [3.142]. 

Almost all of the reactions that the practicing inotganic chemist observes in the laboratory take place in solution. Although water is the best-known solvent, it is not the only one of importance to the chemist. The organic chemist often uses nonpolar solvents sud) as carbon tetrachloride and benzene to dissolve nonpolar compounds. These are also of interest to Ihe inoiganic chemist and, in addition, polar solvents such as liquid ammonia, sulfuric acid, glacial acetic acid, sulfur dioxide, and various nonmctal halides have been studied extensively. The study of solution chemistry is intimately connected with acid-base theory, and the separation of this material into a separate chapter is merely a matter of convenience. For example, nonaqueous solvents are often interpreted in terms of the solvent system concept, the formation of solvates involve acid-base interactions, and even redox reactions may be included within the (Jsanovich definition of acid-base reactions. 

The elements with a lone pair of electrons and very rich redox chemistry, have certainly been well exploited in ionic reactions. We decided to study the radical chain reactions based on acyl derivatives of thiohydroxamates and incorporating compounds of group V or VI elements in a unique fashion. In these very highly disciplined and efficient chain reactions (if properly designed and administered) the basic concept is one of valence shell expansion.11 The general philosophy of this series of reactions developed by us is depicted in Scheme 31. A simple illustration of this concept is the use of sulfur dioxide as a radical trap in conjunction with an o-acyl thiohydroxamate leading to the formation of S-pyridyl alkylthiosulfonates 117.84 For practical reasons this reaction is carried out at —10 °C in a mixture of dichloromethane and liquid S02. The sulfur atom undergoes a valence shell expansion from S(IV) to S(VI). 

The reaction of gaseous SO2 with molecular oxygen in the contact process seems to proceed over two independent mechanisms [13] one of which is the direct oxidation of a vanadium pentoxide-sulfur dioxide adduct by oxygen and the other proceedings via a redox cycle involving V4+ and V3+ intermediate species [13-15]. 

Centi and Perathoner [139] have discussed the benefits of small amounts of sulfur dioxide in the reaction feed. The SO2 is thought to adsorb on the surface to form stable VOSO4, blocking the redox activity of surface sites (considered to be responsible for over-oxidation). This results in an increase in selectivity to maleic anhydride, particularly at high conversions. 

The arsenic and antimony pentahalides EX5 (E group 15 element As or Sb X = F or Cl) are strong, irreversible oxidants the gas AsFs has little been used, but SbCF and SbFs are commercially available, very air-sensitive liquids which are used in dry and deoxygenated dichloromethane and liquid sulfur dioxide respectively. SbCls is easier to handle than SbFs which gives the dangerous HF by reaction with moist air. Moreover, SbCls is conveniently used in dichloromethane whereas SbFs is best used in liquid SO2. On the other hand, the side products (halogenation) are more frequently encountered with SbCls than with SbFs. The redox process follows ... 

Oxidation-reduction reactions are among the most important in chemistry, biochemistry, and industry. Combustion of coal, natural gas, and gasoline for heat and power are redox reactions, as are the recovery of metals such as iron and aluminum from their oxide ores and the production of chemicals such as sulfuric acid from sulfur, air, and water. The human body metabolizes sugars through redox reactions to obtain energy the reaction products are liquid water and gaseous carbon dioxide. 

During the thermally driven differentiation of the Earth into core-mantle-crust, numerous reactions would have produced oxidized forms of iron, sulfur and carbon. These would have contributed to the redox chemistry in the early planet development. Volcanic and hydrothermal emission of sulfur dioxide, SO2, delivered oxidants to the oceans and atmosphere. Photodissociation of water vapor in the atmosphere have undoubtedly provided a small but significant source of molecular oxygen. Furthermore, UV-driven ferrous iron oxidation could have been coupled to the reduction of a variety of reactants, for instance, CO2 (Figure 16). 

The generation of free radicals at such low temperatures can be conveniently accomplished by redox reaction between organic hydroperoxides and sulfur dioxide. This is an effective method for initiation at temperatures as low as -80 C (2, 2)- A plausible mechanism for radical formation is given below (4) ... 

So-called Raffo or LaMer sulfur sols are used most frequently. These can be prepared by dropwise addition of aqueous sodium thiosulfate to concentrated sulfuric acid followed by coohng and precipitation of the hydrophilic sol by a saturated solution of sodium chloride. The sol originates from the spontaneous decomposition of the primary product thiosulfuric acid (H2S2O3) which disproportionates in a series of complex redox reactions producing elemental sulfur, hydrogen sulfide, sulfur dioxide and polythionic acids ... 

In the presence of water, iodine reacts with sulfur dioxide through a redox reaction that is specific to these three compounds ... 

When the calcium carbonate, CaC03, in limestone is heated to a high temperature, it decomposes into calcium oxide (called lime or quick lime) and carbon dioxide. Lime was used by tbe early Romans, Greeks, and Egyptians to make cement and is used today to make over 150 different chemicals. In another reaction, calcium oxide and water form calcium hydroxide, Ca(OH)2 (called slaked lime), used to remove the sulfur dioxide from smoke stacks above power plants burning bigb-sulflir coal. The equations for all these reactions are below. Determine the oxidation number for each atom in the equation and identify whether the reactions are redox reaction or not. For each redox reaction, identify what is oxidized and what is reduced. 

Write a balanced equation for the redox reaction of solid copper(II) sulfide with oxygen gas to form solid copper(II) oxide and sulfur dioxide gas. 

This work shows that oxygen-free sulfite in lime/limestone slurries, exposed to sulfur dioxide, slowly decomposes under process conditions. In fact, auto-redox reactions of sulfur oxyacids can occur in all coal desulfurization systems, including coal-gasification systems and impurities present in commercial flue gas systems are capable of catalyzing the reaction under process conditions. Our experiments indicate that any large-scale coal utilization will depend on appropriate control of the autoredox reactions of sulfur species. 

Another characteristic of 02 is its ability to act as a moderate one-electron reducing agent. For example, combination of 02 with 3,5-di-r-butylquinone (DTBQ) in DMF yields the semiquinone anion radical DTBSQ as the major product. The relevant redox potentials in DMF are 02/02 , E° = —0.60 V versus NHE, and DTBQ/DTBSQ , ° = —0.25 V versus NHE, which indicate that the equilibrium constant K for the reaction of O2 with DTBQ has a value of 0.8 x 10 (equation 148). Electrochemical studies of sulfur dioxide (S02/S02 , ° = —0.58 V vs. NHE) and of molecular oxygen in DMF indicate that the equilibrium constant K) for the reaction of SO2 with 02 has a value of 1.1 (equation 149). 

When an aqueous solution of iron(III) ions is reacted with sulfur dioxide gas (this forms an acid solution), aqueous iron(II) ions and the sulfate ion (SO ) are produced. Write a balanced overall redox equation for the reaction. 

---