Sulfur dioxide retention

Hexavalent chromium reduction through the use of sulfur dioxide and sodium metabisulfite has found the widest application in the metal finishing industry. It is not truly a treatment step, but a conversion process in which the hexavalent chromium is converted to trivalent chromium. The hexavalent chromium is reduced through the addition of the reductant at a pH in the range of 2.5-3 with a retention time of approximately 30-40 min (Figure 9.7). 

Chlorosulfate groups can be readily removed to give the corresponding hydroxyl groups, with retention of configuration, by treatment of a solution of the carbohydrate chlorosulfate in methanol with sodium iodide in aqueous methanol24 immediate liberation of iodine and evolution of sulfur dioxide occur.34 A possible mechanism for the dechlorosulfation reaction involves displacement by iodide at the chlorine atom the initially formed iodine monochloride would react with iodide ion to give iodine and chloride ion. Alternatively, an unstable iodosulfate could be formed as an intermediate.35... 

Sulfur dioxide readily inserts into metal-carbon tr bonds (136, 137). The reaction is stereospecific with respect to the configuration at the a-carbon atom of the alkyl group (138) and proceeds with inversion of configuration at the a-carbon atom (139-142). The stereospecificity of the S02 insertion with respect to the metal center was demonstrated with diastereoisomeric pairs of enantiomers of Fe compounds (143-146). Also, the stereochemistry of the S02 insertion at the iron atom was studied by starting with the optically active iron alkyl derivative 26a (see Scheme 18). Retention of configuration was concluded from the similarity in the... 

At carbon, most leaving groups are good in SN2 reactions these go with inversion. At carbon, most leaving groups are poor in SE2 reactions these go with retention. As for the SNi reaction, this is usually strongly assisted, e.g. in (129) and (130) by the formation of sulfur dioxide (Mackenzie, 1964 de la Mare, 1963). The stereo-... 

Balchum, O.J., J.Dybicki, and G.R.Meneely. 1960a. The dynamics of sulfur dioxide inhalation, absorption, distribution and retention. Arch. Ind. Health 21 564-569. 

Derivatives of phosphonic acids, RP==O(0H)2, can be prepared by several different oxidative methods. Primary phosphines RPH2 are oxidized to phosphonic acids by hydrogen peroxide or by sulfur dioxide thus, phenylphosphine gave benzenephosphonic acid (96%) on reaction with sulfur dioxide at room temperature in a sealed tube. Phosphinic acids, RI sO(OH)H, can also be oxidized to the corresponding phosphonic acids with hydrogen peroxide. Ozone oxidized the dioxaphosphorane (54) to the phosphonic ester in 73% yield. Ozone is also capable of stereospecific oxidation of phosphite esters to phosphates. For example, the cyclic phosphite (SS) was oxidized to the phosphate (56) with retention of configuration. Peroxy acids and selenium dioxide are other common oxidants for phosphite esters. 

It (1 ) deals with the derivation of relations giving the particle size distribution in the bed, overflow, and carryover streams and their respective weights. This theory will be extended to include the effects of particle growth or shrinkage (Z>1 or Z<1). For typical combustion of char containing sulfur followed by sulfur dioxide absorption by limestone, relations will be derived to determine the extent of sulfur retention. The reaction, carryover, and overflow rates will be evaluated with particular attention to their dependence on Z. 

The development of mathematical models to describe the thermochemical process occurring in a fluidized bed involves setting up the material and energy balance equations. The total process is represented in terms of a set of independent equations which are solved simultaneously to obtain such quantities as combustion efficiency, sulfur retention, oxygen utilization, oxygen and sulfur dioxide concentration profiles in the bed, etc. 

On the other hand, t/ireo-Fe(f7 -C5H5)(CHDCHDCMe3)(CO)2 reacts with sulfur dioxide with > 95% inversion of configuration at carbon. Thus, sulfur dioxide insertion into the iron-carbon bond proceeds differently from carbon monoxide insertion, which is characterized by retention of configuration at carbon" . 

Sulfur dioxide inserts into alkyltin bonds to give stannylsulfinates, R3Sn0-S(0)R,46 but the reactivity falls off in the sequence R = allyl allenyl propargyl > phenyl > benzyl > methyl. Insertion into a vinyl-tin bond occurs with retention of configuration. The reaction with aryl and benzyl compounds is cleanly first order in each of the two reactants, and is rather insensitive to the nature of any substituents in the benzyl ring. 

In the reactor system, designed for 5-min retention time or less in each of the three reactors, sulfur dioxide is reduced to sulfur and citrate solution is regenerated. Sulfur slurry is pumped to a sulfur slurry surge drum and then to the sulfur separation system. Various alternative units... 

The aporphine alkaloids can be N-demethylated and thus converted into N-noraporphine alkaloids (retention of the chirality at C-6a) with hydrogen peroxide and following treatment with liquid sulfur dioxide (yield ca. 35%)... 

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