Sulfite methods

Cu +-catalyzed sodium sulfite oxidation had already been studied in the 193O s and was used by Cooper et al. in 1944 [84] to determine the absorption rate in stirred tanks. 

Linek [328] proved experimentally in work of fundamental importance, that there are significant differences between Cu - and Co -catalyzed sodium sulfite oxidations. When Cu is used, a pure physical absorption is involved at c = 0. If it is catalysed by 3 x 10 mol C0S04/I at pH = 7.9, it proceeds by chemisorption in the phase boundary. Hence, measurements under these conditions permit the determination of the interfacial area. 

Waal and Okeson [568] came to the same conclusion at about the same time. 

They established that the oxidation with oxygen was a first-order reaction and the reaction rate constant could be varied between 50 and 10,000 s by changing the concentration at pH = 8.0 and T = 15-25°C. An activation energy of 50 kJ/ 

The kinetics of the Co + heterogeneously catalysed oxidation of sodium sulfite were measured by Sawicki and Barron [480] in a falling-film column. In contrast with [568] the reaction imder such conditions was found to be of second-order with respect to oxygen concentration and 0.5-order with respect to Co + concentration. 

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Procedures for determining the quaUty of formaldehyde solutions ate outlined by ASTM (120). Analytical methods relevant to Table 5 foUow formaldehyde by the sodium sulfite method (D2194) methanol by specific gravity (D2380) acidity as formic acid by titration with sodium hydroxide (D2379) iron by colorimetry (D2087) and color (APHA) by comparison to platinum—cobalt color standards (D1209). 

Unreacted free sulfur can be determined to ISO 7269 1995 — Rubber — Determination of free sulfur. Three methods for the determination of free sulfur in vulcanized rubber are detailed two versions of the copper spiral method and the sodium sulfite method. The copper spiral methods are also applicable, subject to limitations, to unvulcanised rubber. The technique of DSC can detect non-reacted rubber curatives such as residual peroxides. 

The sulfite method is a chemical method which is based on the reaction between sodium sulfite and oxygen [Eq. (8.36)]. 

Usually, iodine is not detected as its usual brown form but as a blue inclusion complex (cage complex) with starch. The sulfite method, besides being labor-intensive, has the disadvantage of yielding accurate data in cell-free systems only, as living cells interfere with the processes in Eqs. (8.36)—(8.38) necessary for the analysis. 

There are several modifications of the sulfite method which are designated according to the pH of the cooking liquor (Table 7-1). For the production of chemical pulps, delignification is allowed to proceed until most of the lignin in the middle lamella is removed after which the fibers can be readily separated from each other. Semichemical pulps are often produced by the neutral sodium sulfite method followed by mechanical fiberization of the partially delignified wood. 

Fig. 7-3. UV absorbance (222 nm, 0.5 p,m section thickness) by various morphological regions of spruce fibers delignified to various lignin contents by the kraft and acid sulfite method (Wood and Goring, 1973). S, secondary wall P, primary wall CCP, primary wall at the cell corner.

During acid sulfite pulping, lignin may also condense with reactive phenolic extractives. Pinosylvin and its monomethyl ether, present in pine heartwood, are examples of phenolic extractives of this type. Dual condensation of pinosylvin with lignin generates harmful cross-links. Consequently, pine heartwood cannot be delignified by the conventional acid sulfite method. 

Assay Determine as directed in the Neutral Sulfite Method under Aldehydes and Ketones, Appendix VI. 

The sulfite method resolves some of the limitations of the traditional methodology in the synthesis of some dialkyl sulfoxides with high ee. The method is particularly suitable for the synthesis of tert-butyl sulfoxides. 

The sulfite method is an ideal diastereoselective route to o.p. sulfoxides, especially when group permutation is possible. Thus, a single intermediate is used in an enantiodivergent approach to both, sulfoxides. 

The rates of reduction of the osmate esters vary considerably. We found that although the sulfite method (in the past we have also used sodium bisulfite) would reduce osmate esters from monosubstituted and 1,2-disubstituted olefins, however, osmate esters derived from trisubsti-tuted and 1,1-disubstituted olefins were more inert to this treatment. Sodium borohydride reduces even these more hindered osmate esters rapidly at room temperature. 

Steam distillation of 1,4-dinitronaphthalene is very slow. However, the cupro-cupri sulfite method is a general one for the replacement of the diazonium group by the nitro group, and steam distillation is preferable whenever the product is readily volatile. 

A considerable disadvantage of the sulfite method is that the liquid contains much salt, making the gas bubble coalescence not comparable with those in material systems with low salt contents (see Section 4.10). This disadvantage first attracted attention in studies of the absorption behavior in gassing devices for biological systems and for waste water purification and was the reason for looking for an alternative. This was found in the hydrazine method [624]. 

A direct proportionality is expected between k a and e for monodisperse bubble populations in coalescence-inhibited material systems. In fact it was found [617] for three differently sized bubble columns of D = 96 200 300 mm with a perforated plate as sparger (boreholes 0.5 mm in diameter) in the material system 1 N sodium sulfite solution (Cu -catalyzed sulfite method for kbU determination) that ... 

Resazurln was purchased from Aldrich Chemical Co., Milwaukee, Wisconsin. Formaldehyde stock solution was prepared by diluting 2.7 ml of 37% formaldehyde solution to 1 liter with deionized water and standardized using the sulfite method (3,9). This solution remained stable for several months. Formaldeh e solution was ACS reagent grade and obtained from Fisher Scientific, Pittsburgh, Pennsylvania. Formaldehyde standard solutions for the calibration were prepared dally from the stock solution. Other chemicals for formaldehyde standardization and buffer preparations were all analytical reagents and were used without further purification. 

Tin(n) chloride has often been used for reduction of arenediazonium salts in acid solution, a procedure that usually gives the tin double salt of the arylhydrazine hydrochloride, these salts being readily decomposed by alkali. This process is simpler than the sulfite method and is very suitable for laboratory purposes the reduction occurs at a low temperature (about 0°), but it fails with diazonium salts of the anthraquinone series, with / -nitrobenzene-diazonium chloride, and with o-benzenetetrazonium dichloride. Victor Meyer exemplifies the use of tin(n) chloride by the reduction of benzenediazonium chloride to phenylhydrazine.12... 

Methods of formaldehyde analysis include the iodometric, sulfite [31], and mercurimetric [32,33] methods. The sulfite method measures only the formaldehyde present, whereas the iodometric method can also estimate the methylol groups. Another method is based on the partition of formaldehyde between water and isoamyl alcohol [34]. Estimation of the formaldehyde in the alcohol phase of a mixture of an aqueous solution of the resin and isoamyl alcohol allows deduction of the amount of free formaldehyde. This procedure has the advantage that no risk of reaction arises between free formaldehyde and the resin components. 

The interfacial area can be measured in specific systems using chemical reactions in which the absorption rate kinetics are a known function of the gas-liquid interfacial area. For example, Vasquez et al. (2000) compared three different chemical methods (i) Danckwerts method using the absorption of CO2 in sodium or potassium carbonate buffer solutions, (ii) the sodium sulfite method involving the oxidation of sulfite ions, and (iii) the sodium dithionite method involving the oxidation of dithionite ions. All three methods were shown to produce similar interfacial area measurements. 

In order to estimate the efficiency of the mass transfer in gas-liquid flows, a sulfite method [22], based on the catalytic oxidation of sodium sulfite by atmospheric oxygen, was used ... 

Aldehydes and ketones. Bisulfite method, neutral sulfite method, phenylhy-drazine method, hydroxylamine method. 

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