Neutral Sulfite Method

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

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

Chemical recovery ia sodium-based sulfite pulpiag is more complicated, and a large number of processes have been proposed. The most common process iavolves liquor iaciaeration under reduciag conditions to give a smelt, which is dissolved to produce a kraft-type green liquor. Sulfide is stripped from the liquor as H2S after the pH is lowered by CO2. The H2S is oxidized to sulfur ia a separate stream by reaction with SO2, and the sulfur is subsequendy burned to reform SO2. Alternatively, ia a pyrolysis process such as SCA-Bidemd, the H2S gas is burned direcdy to SO2. A rather novel approach is the Sonoco process, ia which alumina is added to the spent liquors which are then burned ia a kiln to form sodium aluminate. In anther method, used particulady ia neutral sulfite semichemical processes, fluidized-bed combustion is employed to give a mixture of sodium carbonate and sodium sulfate, which can be sold to kraft mills as makeup chemical. 

Similar development has occurred in Germany.In 1943 it was reported that 250,000 hectoliters of alcohol were produced from sulfite waste liquor. The preferred method of fermentation was a continuous method in which the yeast was grown on chips or twigs and the neutralized sulfite waste liquor flowed through these chips. ... 

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. 

It is. significant in that it gives not only amines but also o- and p-amino sulfonic acids, all in one reaction. It is generally carried out with excess sodium bisulfite (4.5-6.0 moles per mole of nitro compound), usually with the addition of enough caustic soda to form the required amount of neutral sulfite. A solvent, such as ethyl alcohol or pyridine, often helps to speed up the reaction, particularly for nitro compounds that are either difficultly soluble or wettable. It is interesting to note that sulfamic acids have also been isolated from this reaction in certain cases. Examples of nitro compounds that may be reduced by the Piria method are p-nitrotoluene, which forms p-toluidine in about 70 per cent yield p-nitrobenzoic acid, which forms 4-amino-3-sulfobenzoic acid and 4-nitronaphthalic anhydride, which forms 4-amino-3-sulfonaphthalic anhydride. 

Although acidic pulping methods have largely been displaced over the past 50 years by neutral and alkaline processes, there is still a significant amount carried out. Acid sulfite pulping uses combinations of sulfur dioxide and water at high temperatures and pressures. An appropriate base is used to control the pH and, although usually acidic, it is possible to perform these reactions at neutral or even alkaline pH. The most active nucleophile present is the bisulfite ion,... 

There are two noncolumn cleanup methods, one of which uses acid partition (EPA SW-846 3650) to separate the base/neutral and acid components by adjusting pH. This method is often used before alumina column cleanup to remove acid components. The other method (EPA SW-846 3660) is used for sulfur removal and uses copper, mercury, and tetrabutylammonium sulfite as desulfurization compounds. Sulfur is a common interfering compound for petroleum hydrocarbon analysis, particularly for sediments. Sulfur-containing compounds are very common in crude oil and heavy fuel oil. Elemental sulfur is often present in anaerobically biodegraded fuels. Thus, abnormally high levels of sulfur may be... 

Method II. Pipette 25 ml sample in 400 ml beaker. Add 50 ml distd w and 4-5 drops of methyl red indicator. If the soln is alkaline, neutralize it with N/10.HNOS. Titrate with std Na sulfite soln (prepd by dissolving l8g of CP anhyd NaaS04 in a mixt of 900 ml distd w and 100 mi methanol or ethanol and stored in the dark) to faint, but definite yel... 

In the future, it seems likely that most processes that currently entail the discharge of SO2 will have to be adapted with the introduction of scrubbers . Two main methods can be employed for this either the reduction of SO2 to snllur using the Claus process or, alternatively, neutralization nsing milk of lime (equation 18) to give either calcium sulfite or, with complete oxidation, calcium sulfate (gypsum). 

The recent studies of the Finnish group further emphasize the complexity of the xylan in wood cellulose. These workers have shown that the properties of the xylan in wood pulps depend not only on the method of pulping but also on the type of raw material. It was observed that, when pulps are prepared by the (acidic) sulfite process from the softwoods, pine and spruce, a substantial part of the xylan is of the acidic type (see Fig. 2, p. 303). Even when these sulfite pulps are refined further with hot alkali, some acidic xylan remains. However, when pulps are prepared from pine and spruce by the (alkaline) sulfate process, the acidic xylan is removed and only neutral xylan remains. 

The thereby formed sulfuric acid is neutralized by adding magnesium hydroxide. Independently of the production method, the precipitated uranium concentrate is washed to remove adhering salt solution and then dried. The precipitates produced with ammonia are subsequently calcined in a multiple hearth kiln at 750°C, ammonia, sulfite and chloride being driven off and U3O8 being formed ... 

The method of Fan and Dasgupta (1994) relics on tlie reaction of formaldehyde with 1,3-cyclohexane-dione in acidified ammonium acetate to form the fluorescent dihydropyridine derivative in a flow injection analysis system. Formaldehyde trapped in water can be reacted with pararosaniline and sodium sulfite under mild conditions (neutral pH, room temperature equilibration) to produce a colored product that is measured at 570 nm (Petreas et al. 1986). The presence of bisulfite is an interference in this reaction so the method cannot be used to sample atmospheres that contain sulfur dioxide. In addition, the method is reported to suffer from interferences resulting from the presence of other aldehydes and phenol (Hoogenboom et al. 1987). The indirect method of Hoogenboom et al. (1987) relies on the reaction of excess bisulfite in an aqueous solution of formaldehyde with 5,5 -dithiobis(2-nitrobenzoic acid) to form a colored product, the absorbance of which is measured at 412 nm. The method reported by Naruse et al. (1995) relies on the formation of a colored product obtained by reacting the aqueous formaldehyde with acetylacetone and ammonium acetate in acetic acid. Absorbance is measured at 414 nm. 

The reaction of 2-oxopropanal with 2,5,6-triaminopteridin-4(37/)-one has been extensively studied.54 59 In neutral, or mildly acidic solution, a mixture of 2-amino-7-methylpteridin-4(3//)-one (7) and its 6-methyl isomer 8 are formed, but the 7-isomer is greatly preponderant. Separation may be achieved by recrystallization methods. Separation has also been achieved by utilizing the different propensity to form adducts with hydrogen sulfite.272... 

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