Sodium sulfite, oxidation

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... 

The sodium sulfite oxidation technique has its limitation in the fact that the solution cannot approximate the physical and chemical properties of a fermentation broth. An additional problem is that this technique requires high ionic concentrations (1 to 2 mol/L), the presence of which can affect the interfacial area and, in a lesser degree, the mass-transfer coefficient (Van t Riet, 1979). However, this technique is helpful in comparing the performance of fermenters and studying the effect of scale-up and operating conditions. 

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. 

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. 

Interaction of sodium sulfite and atmospheric oxygen occurs in the diffusion zone, i.e., the process rate is completely defined by the stage of oxygen transfer from the gas phase to the liquid phase. Due to the poor solubility of oxygen in water, the mass transfer coefficient is defined by the mass delivery coefficient in a liquid phase (the stage of oxygen diffusion from the phase boundary to the liquid volume). Therefore, the change in the rate of sodium sulfite oxidation is related to the intensification of the mass delivery in the liquid phase. 

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. 

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

The reaction with sodium sulfite or bisulfite (5,11) to yield sodium-P-sulfopropionamide [19298-89-6] (C3H7N04S-Na) is very useful since it can be used as a scavenger for acrylamide monomer. The reaction proceeds very rapidly even at room temperature, and the product has low toxicity. Reactions with phosphines and phosphine oxides have been studied (12), and the products are potentially useful because of thek fire retardant properties. Reactions with sulfide and dithiocarbamates proceed readily but have no appHcations (5). However, the reaction with mercaptide ions has been used for analytical purposes (13)). Water reacts with the amide group (5) to form hydrolysis products, and other hydroxy compounds, such as alcohols and phenols, react readily to form ether compounds. Primary aUphatic alcohols are the most reactive and the reactions are compHcated by partial hydrolysis of the amide groups by any water present. 

The aromatic rings of kraft lignins can be sulfonated to varying degrees with sodium sulfite at high temperatures (150—200°C) or sulfomethylated with formaldehyde and sulfite at low temperatures (<100° C). Oxidative sulfonation with oxygen and sulfite is also possible. 

The names adopted for salts consisted of a generic part derived from the acid and a specific part from the metallic base r oxide de plomb + I acide sulfurique le sulfate de plomb. The names for salts of acids containing an element in different degrees of oxidation were given different terminations sufte de soude and sulfate de soude for sodium sulfite and sulfate, and nitrite de baryte and nitrate de baryte for barium nitrite and nitrate. 

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. 

Oxidation of N -substituted pyrazoles to 2-substituted pyrazole-l-oxides using various peracids (30) facilitates the introduction of halogen at C, followed by selective nitration at C. The halogen atom at or is easily removed by sodium sulfite and acts as a protecting group. Formaldehyde was... 

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). 

Aqueous solutions of sodium sulfite are alkaline and have a pH of ca 9.8 at 1 wt %. The solutions are oxidized readily by air. The redox potential is a function of pH, as would be expected from the foUowing equation ... 

Shipment and Storage. Anhydrous sodium sulfite is suppHed in 22.7- and 45.4-kg moistureproof paper bags or 45.4- and 159-kg fiber dmms. Most sodium sulfite is shipped by rail in hopper cars. Sodium sulfite should be protected from moisture during storage. When dry it is quite stable, but when wet it is oxidized by air. 

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). 

Physical Properties. Sodium metabisulfite (sodium pyrosulfite, sodium bisulfite (a misnomer)), Na2S20, is a white granular or powdered salt (specific gravity 1.48) and is storable when kept dry and protected from air. In the presence of traces of water it develops an odor of sulfur dioxide and in moist air it decomposes with loss of part of its SO2 content and by oxidation to sodium sulfate. Dry sodium metabisulfite is more stable to oxidation than dry sodium sulfite. At low temperatures, sodium metabisulfite forms hydrates with 6 and 7 moles of water. The solubiHty of sodium metabisulfite in water is 39.5 wt % at 20°C, 41.6 wt % at 40°C, and 44.6 wt % at 60°C (340). Sodium metabisulfite is fairly soluble in glycerol and slightly soluble in alcohol. 

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. 

Aqueous sodium thiosulfate solutions ate neutral. Under neutral or slightly acidic conditions, decomposition produces sulfite and sulfur. In the presence of air, alkaline solutions decompose to sulfate and sulfide. Dilute solutions can be stabilized by small amounts of sodium sulfite, sodium carbonate, or caustic, and by storage at low temperatures away from air and light. Oxidation is inhibited by Hgl2 (10 Ppm) amyl alcohol (1%), chloroform (0.1%), borax (0.05%), or sodium benzoate (0.1%). 

Many enzymes need a certain ionic strength to maintain an optimum stabiHty and solubiHty, eg, bacterial a-amylases show optimal stabiHty in the presence of 1—2% NaCl. Some enzymes may need certain cations in low amounts for stabilization, eg, Ca " is known to stabilize subtiHsins and many bacterial a-amylases. Antioxidants (qv) such as sodium sulfite can stabilize cysteine-containing enzymes which, like papain, are often easily oxidized. 

Sodium carbonate reacts with sulfur oxides in a dry scrubber to form sodium sulfite and CO2. Sodium sulfite is then removed with a baghouse. 

---