Sodium Sulfite Oxidation Method

The sodium sulfite oxidation method (Cooper et al., 1944) is based on the oxidation of sodium sulfite to sodium sulfate in the presence of catalyst (Cu++ or Co++) as 

This reaction has following characteristics to be qualified for the measurement of the oxygen-transfer rate  

The rate of this reaction is independent of the concentration of sodium sulfite within the range of 0.04 to 1 N. 

The rate of reaction is much faster than the oxygen transfer rate therefore, the rate of oxidation is controlled by the rate of mass transfer alone. 

To measure the oxygen-transfer rate in a fermenter, fill the fermenter with a 1 N sodium sulfite solution containing at least 0.003 M Cu++ ion. Turn on the air and start a timer when the first bubbles of air emerge from the sparger. Allow the oxidation to continue for 

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Oxygen transfer rate (OTR) was determined using the sodium sulfite oxidation method [12]. OTRs were measured for standard Erlenmeyer flasks of 500-mL flask, 200-mL flask, 100-mL flask, 100-mL serum flask, and 100-mL serum flask filled with nitrogen, containing 100 mL of medium, respectively, shaken at 150 rpm at 37 °C. The OTRs of different oxygen-limited conditions were 12.6, 8.4, 5.1, 3.3, and 0 mmol/L h, respectively. 

The effective area can be measured directly by the sodium sulfite oxidation method. 

Measurement of the absorption rate of carbon dioxide in aqueous solutions of sodium hydroxide has been used in some of the more recent work on mass-transfer rate in gas-liquid dispersions (D6, N3, R4, R5, V5, W2, W4, Y3). Although this absorption has a disadvantage because of the high solubility of C02 as compared to 02, it has several advantages over the sulfite-oxidation method. For example, it is relatively insensitive to impurities, and the physical properties of the liquid can be altered by the addition of other liquids without appreciably affecting the chemical kinetics. Yoshida and... 

In 1960, Yoshida et al. (Y4), working with a geometrically similar system and with the sulfite-oxidation method, confirmed the results reported by Cooper et al. They also showed that the gas film does not offer any resistance to the mass transfer of oxygen from air to the sodium sulfite solution. In addition, they found that the mass-transfer coefficient per unit area was equal for water and for aqueous sodium sulfite. 

Sulfite Oxidation Method The sulfite oxidation method is a classical, but still useful, technique for measuring /cgfl (or [4]. The method is based on the air oxidation of an aqueous solution of sodium sulfite (Na SOg) to sodium sulfate (Na.,SO ) with a cupric ion (Cu " ") or cobaltous ion (Co ) catalyst. With appropriate concentrations of sodium sulfite (about 1 N) or cupric ions (>10 inolH ), the value of k for the rate of oxygen absorption into sulfite solution, which can be determined by chemical analysis, is practically equal to Zr, for the physical oxygen absorption into sulfate solution in other words, the enhancement factor E, as defined by Equation 6.20, is essentially equal to unity. 

It is possible to influence the size of the dispersion spots in liquid-gas systems (specific phase contact surface) and therefore, the mass transfer efficiency, by changing the method of reactant introduction. During the motion of the gas-liquid flows in tubular turbulent reactors, an increase of the gas supply branch pipe diameter results in a slight decrease of the sulfite number of the reactor (Table 4.4), which can be seen from the decrease of the phase contact surface as d 2 grows by 15%. Similarly, with the decrease of the coaxial liquid-phase supply branch pipe diameter from 10 to 5 mm, SuR equals 13.5 and 14 g02/h, respectively. Thus, there is almost no dependence of the rate of sodium sulfite oxidation in aqueous solution, by atmospheric oxygen, on the method of reactant introduction. This is related to the fact that changes in the method of the liquid- and gas-phase introduction, in particular, the diameters of the feeding branch pipes, do not influence the mass delivery coefficient in the liquid phase. 

Another method employed is the treatment of aqueous solutions of aminophenols with activated carbon (81,82). During this procedure, sodium sulfite, sodium dithionite, or disodium ethylenediaminotetraacetate (82) is added to increase the quaUty and stabiUty of the products and to chelate heavy-metal ions that would catalyze oxidation. Addition of sodium dithionite, hydrazine (82), or sodium hydrosulfite (83) also is recommended during precipitation or crystallization of aminophenols. 

Analytical Methods. A classical and stiU widely employed analytical method is iodimetric titration. This is suitable for determination of sodium sulfite, for example, in boiler water. Standard potassium iodate—potassium iodide solution is commonly used as the titrant with a starch or starch-substitute indicator. Sodium bisulfite occurring as an impurity in sodium sulfite can be determined by addition of hydrogen peroxide to oxidize the bisulfite to bisulfate, followed by titration with standard sodium hydroxide (279). 

Mass-transfer rates have been determined by measuring the absorption rate of a pure gas or of a component of a gas mixture as a function of the several operating variables involved. The basic requirement of the evaluation method is that the rate step for the physical absorption should be controlling, not the chemical reaction rate. The experimental method that has gained the widest acceptance involves the oxidation of sodium sulfite, although in some of the more recent work, the rate of carbon dioxide absorption in various media has been used to determine mass-transfer rates and interfacial areas. 

This method involves measurement of the oxidation rate of an aqueous sodium sulfite solution catalyzed by cupric or cobaltous ions. The oxygen absorbed reacts with the sulfite according to the equation ... 

Measurements Using Liquid-Phase Reactions. Liquid-phase reactions, and the oxidation of sodium sulfite to sodium sulfate in particular, are sometimes used to determine kiAi. As for the transient method, the system is batch with respect to the liquid phase. Pure oxygen is sparged into the vessel. A pseudo-steady-state results. There is no gas outlet, and the inlet flow rate is adjusted so that the vessel pressure remains constant. Under these circumstances, the inlet flow rate equals the mass transfer rate. Equations (11.5) and (11.12) are combined to give a particularly simple result ... 

The most commonly employed routes for the preparation of the / -sulfatoethylsulfone group, which is the essential structural feature of vinylsulfone reactive dyes, are illustrated in Scheme 8.5. One method of synthesis involves, initially, the reduction of an aromatic sulfonyl chloride, for example with sodium sulfite, to the corresponding sulfinic acid. Subsequent condensation with either 2-chloroethanol or ethylene oxide gives the / -hydroxyethylsulfone, which is converted into its sulfate ester by treatment with concentrated sulfuric acid at 20 30 °C. An alternative route involves treatment of an aromatic thiol with 2-chloroethanol or ethylene oxide to give the /Miydroxyethylsulfonyl compound which may then be converted by oxidation into the /Miydroxyethylsulfone. 

Synthetically useful routes to dibenzo[c,e J[l,2]dithiins are normally based on cyclizations of biphenyI-2,2 -disulfonyl chlorides. A method applied successfully to the parent compound reduces the precursor with zinc in acetic acid to generate the bis thiol, which is then gently oxidized to the dithiin using iron(II) chloride (66HC(21-2)952). An alternative one-step reductive cyclization, which has been applied to the preparation of the 2,9- and 3,8-dinitro derivatives, involves reduction of the appropriate bis sulfonyl chlorides with hydriodic acid in acetic acid (68MI22600). Yet another reductive cyclization uses sodium sulfite followed by acidification, and these conditions lead to dibenzo[c,e][1,2]dithiin 5,5-dioxide. The first step of the reaction is reduction to the disodium salt of biphenyl-2,2 -disulfinic acid which, on acidification, forms the anhydride, i.e. dibenzo[c,e][l,2]dithiin 5,5,6-trioxide. This is not isolated, but is reduced by the medium to the 5,5-dioxide (77JOC3265). Derivatives of dibenzo[c,e] [1,2]dithiin in oxidation states other than those mentioned here are obtainable by appropriate oxidation or reduction reactions (see Section 2.26.3.1.4). 

Among alkyl-substituted ethylene oxides known to umletrn cleavage on treatment with sodium sulfite are propylene oxide, isobutylene oxide, 1,2-epoxybutane, 1,2-epoxyoctane, and 2,3-cpow-butane.1 75 These reactions with sodium sulfite constitute the bani-, ffrail analytical method developed by Swan1875 for the estimation <[Pg.179]

Dinitrocresols present in water samples, especially when present at low concentrations, can be lost via oxidation by hypochlorite (Di Corcia and Marchetti 1992). This can be eliminated through the addition of sodium sulfite prior to extraction. In the multiresidue method of Chen et al. (1991), Mn + dissolved in the sample would be oxidized to manganese(lll,IV) oxides during base extraction, which in turn would oxidize the phenols during acid extraction. The oxidation of phenols can be eliminated by adding sodium thiosulfate to the sample prior to extraction or extraction at acidic pH as the first step, providing that manganese(lll,IV) oxides are not present in the sample before extraction. 

A definite method for the determination of D-fructose in the presence of aldoses was worked out by Kruisheer 98.3% of theory was found. The aldoses were oxidized with sodium hypoiodite, after which the excess iodine was titrated with sodium sulfite. Thiosulfate could not be used here, since the subsequent determination of D-fructose was carried out with an alkaline copper solution by the Luff-Schoorl method. 

The presence of a methyl group may be detected by the method of Denig6s. This method depends on the oxidation of the methyl group to formaldehyde and detection of this aldehyde by rosaniline-sodium sulfite solution. Methyl ester and ether linkages may be distinguished... 

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