Bisulfite concentration

The dissolved SO2 concentration decreases by a factor of about two for a pH increase of 0.5. This results from a strong decrease in bisulfite concentration with increasing pH the sulfite species increase slightly as pH rises. 

An example of the resulting readout is illustrated in Figure 7. A linear relationship between the AT and sulfite (bisulfite) concentration is predicted by Equation 9. Indeed, substituting... 

SO2 is called sulfite. Rearranging this expression and substituting the bisulfite concentration from above, we get... 

Since these bisulfite addition compounds are ionic water-soluble compounds and can be formed in up to 90% yield, they serve as a useful means of separating aldehydes and methyl ketones from mixtures of organic compounds. At high sodium bisulfite concentrations these adducts crystallize and can be isolated by filtration. The aldehyde or ketone can be regenerated by adding either a strong acid or base ... 

The rate of reaction between HSOj and O2 is shown to be much slower than the mass transfer rate and therefore is kinetically controlled. This rate, on analysis, is found to be 3/2 order in bisulfite concentration during a single experiment (Figure 3). 

As the bisulfite concentration approaches zero, the polythionate concentration levels off and sulfur precipitation begins. Then as the polythionate reacts with hydrogen sulfide, its concentration begins to decrease while the thiosulfate and sulfur concentrations continue to increase. Under the mild conditions used, there was no apparent reaction of thiosulfate or of the trithionate portion of the polythionates to form sulfur. 

Sundman s direct determinations of kz were made by time-controlled analyses of reacting solutions (pH 4.65 and 19° C.) of 0.1 molar sugar starting 60 seconds after mixing. It was found that kz is dependent on bisulfite concentration and time of reaction for five of the seven sugars examined, but glucose and rhamnose kz values showed independence... 

Three experiments were performed, the conditions for which are given in Table VI. All three had the same monomer, persulfate and bisulfite concentrations. Only the amounts of iron(II) ion and SDS were varied. 

The term first order in [HSOJ] is usually dominant, while the [HSO3] component only becomes important at pH values greater than 6.5 and bisulfite concentrations greater than 0.1 moldm . The latter pathway is suggested to involve direct attack of nitrite on metabisulfite. 

Although thiosulfate is one of the few reducing titrants not readily oxidized by contact with air, it is subject to a slow decomposition to bisulfite and elemental sulfur. When used over a period of several weeks, a solution of thiosulfate should be restandardized periodically. Several forms of bacteria are able to metabolize thiosulfate, which also can lead to a change in its concentration. This problem can be minimized by adding a preservative such as Hgl2 to the solution. 

In a typical adiabatic polymerization, approximately 20 wt % aqueous acrylamide is charged into a stainless steel reactor equipped with agitation, condenser, and cooling jacket or coils. To initiate the polymerization, an aqueous solution of sodium bisulfite [7631-90-5] is added, followed by the addition of a solution of ammonium persulfate [7727-54-0] N2HgS20g. As the polymerization proceeds, the temperature rises to about 90°C, and then begins to fall at the end of the polymerization. The molecular weight obtained depends primarily on the initiator concentration employed. 

Sulfur Dioxide and Sulfites. Sulfur dioxide [7446-09-5], SO2, sodium bisulfite [15181-46-1], NaHSO, and sodium metabisulfite [23134-05-6] ate effective against molds, bacteria, and certain strains of yeast. The wine industry represents the largest user of sulfites, because the compounds do not affect the yeast needed for fermentation. Other appHcations include dehydrated fmits and vegetables, fmit juices, symps and concentrates, and fresh shrimp (79). Sulfites ate destmctive to thiamin, and cannot be used in foods, such as certain baked goods, that ate important sources of this vitamin. 

The fermentation-derived food-grade product is sold in 50, 80, and 88% concentrations the other grades are available in 50 and 88% concentrations. The food-grade product meets the Vood Chemicals Codex III and the pharmaceutical grade meets the FCC and the United States Pharmacopoeia XK specifications (7). Other lactic acid derivatives such as salts and esters are also available in weU-estabhshed product specifications. Standard analytical methods such as titration and Hquid chromatography can be used to determine lactic acid, and other gravimetric and specific tests are used to detect impurities for the product specifications. A standard titration method neutralizes the acid with sodium hydroxide and then back-titrates the acid. An older standard quantitative method for determination of lactic acid was based on oxidation by potassium permanganate to acetaldehyde, which is absorbed in sodium bisulfite and titrated iodometricaHy. 

Combined SO2 represents the SO2 present as monosulfite plus, for the same reason, one-half of the SO2 present as bisulfite. All are expressed as percent concentration of SO2 in the Hquor, ie, g of SO2/100 mL of Hquor, in which the specific gravity of the Hquor is taken to be 1.0. 

An evaporator—crystallizer is used to reverse the sodium bisulfite formation reaction and release the sulfur dioxide as a vapor. The regenerated sodium sulfite, which crystallizes out of solution, is redissolved and returned to the absorber. The absorber overhead gas can be vented to the atmosphere. A concentrated sulfur dioxide stream is produced as a by-product of this process. 

Cationic surface-active agents promote wetting of the sulfur and thereby increase the reaction rate (36). The quahty of the product is improved by using photographic-grade sodium sulfite or bisulfite. Excess sulfur is filtered before evaporation (qv) and crystallization (qv). Evaporation is energy-intensive thus it is important to produce the thiosulfate solution at the highest possible concentration. The purity of the product is typically >99% sulfite and sulfate ate the main impurities. 

Both batch and continuous processes employ excess sulfur and operate at 85—110°C. Trace amounts of polysulftdes produce a yellow color which iadicates that all the ammonium sulfite has been consumed. Ammonium bisulfite is added to convert the last polysulfide to thiosulfate and the excess ammonia to ammonium sulfite. Concentrations of at least 70% (NH 2S2 3 obtained without evaporation. Excess sulfur is removed by filtration and color is improved with activated carbon treatment or sodium siUcate (66). Upon cooling the aqueous concentrated solution, ammonium thiosulfate crystallines. 

The enol lactone (12.7 g) is added to 157 ml of 0.5 M perbenzoic acid in benzene and allowed to stand at 25° for 140 hr. The solution is cooled to 15° and 15% sodium bisulfite solution is added to neutralize the excess peracid. The organic layer is separated and washed with saturated sodium bicarbonate solution and water. The benzene solution is dried over anhydrous sodium sulfate, filtered and concentrated to 30 ml. The product is crystallized by adding 80 ml of petroleum ether, filtered and washed with petroleum ether to yield 12.8 g (98%) of 3a,20,23-trihydroxy-16a-methyl-17(20)-oxido-ll-oxo-21-norchol-22-enoic acid-24(20)-lactone 3,23-diacetate mp 225-227°. 

A mixture of a-naphthol 41 (15.0 g, 0.1 mol), phenylhydrazine 42 (11.0 g, 0.1 mol) and sodium bisulfite solution (36 %, 250 g) was heated at reflux for 15 h. A further 4 g of phenylhydrazine was added and heating continued for 15 h, after which time the majority of the a-naphthol was consumed. After cooling, the mixture was extracted with ether. The oily, ether and aqueous insoluble residue was warmed with cone. HCl until a dark crystalline mass developed. After cooling, the mixture was extracted with ether. The organic extract was dried and concentrated to afford a crystalline residue which was purified by recrystallisation from ethanol to afford the product 43 as a white crystalline solid, mp 225 °C. A reaction yield is not given. 

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