Sulfites selectivity

Nonetheless, much excellent use has been made of this system. Receptor 5, for example, extracts p-nitrobenzoate quantitatively from water into chloroform (43), and the chirality of the receptor allows the possibility of chiral anion recognition (44). Guanidinium has also been incorporated into devices, such as a hydrogen sulfite selective electrode (45). Recently, Mendoza and co-workers (46) reported a chiral double helical array of polyguanidinium strands assembled around sulfate templating anions, the first anion centered helical structure. 

Sulfur Dioxide. Hensina Based on Sulfite Selective Membrane Electrode. The Hg(DCC)2 based sulfite selective electrode described above can be used as a transducer to devise new SO2 selective gas sensing systems according to the detection schemes depicted in Figure 1. The addition of the outer gas permeable membrane enables measurements to be made in the presence of ions which would normally be... 

This approach greatly enhances the selectivity for measuring sulfites as SO2 relative to sensing systems that detect SO2 via pH changes in a recipient electrolyte solution. Indeed, as illustrated in Figure 8, sulfite can be detected to levels below 10 HM even in the presence of 0.IM acetic acid. While the acetic acid does permeate the gas membrane into the recipient stream, acetate ions formed in the recipient stream go undetected by the Hg(DCC)2-based sulfite selective sensor. This type of enhanced selectivity would be extremely valuable when determining sulfites in wine-vinegar or other samples that contain volatile acidic species. 

As described above, significant progress in the design of anion and gas selective membrane electrodes has been made. While further work is needed to understand fully the response mechanisms and to improve the performance of the new thiocyanate, salicylate, and sulfite selective membrane electrodes, each of these sensors appears to offer adequate selectivity for use in real sample measurements. In addition, by carefully... 

Figure 3. Structure of the guanidinium-based ionophore on which hydrogen sulfite-selective electrodes are based.

In an alternative industrial process, resorcinol [108-46-3] is autoclaved with ammonia for 2—6 h at 200—230°C under a pressurized nitrogen atmosphere, 2.2—3.5 MPa (22—35 atm). Diammonium phosphate, ammonium molybdate, ammonium sulfite, or arsenic pentoxide maybe used as a catalyst to give yields of 60—94% with 85—90% selectivity for 3-aminophenol (67,68). A vapor-phase system operating at 320°C using a siUcon dioxide catalyst impregnated with gallium sesquioxide gives a 26—31% conversion of resorcinol with a 96—99% selectivity for 3-aminophenol (69). 

Sulfite pulps have properties that are desirable for tissues and top quaHty, fine papers. Because sulfite pulping is not as versatile as kraft pulping, various options have been developed, and the choice of a specific process is dependent on individual mill situations. The unbleached pulp has high (60+) brightness compared to kraft pulp and is easily bleached. However, it is limited to select wood species. The heartwood of pine, Douglas fir, and cedars are not easily pulped. Additionally, pulps produced from hardwood have limited economic value because of low strength. 

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... 

Miscellaneous. In ore flotation, sodium sulfite functions as a selective depressant. In textile processing, sodium sulfite is used as a bleach for wood (qv) and polyamide fibers and as an antichlor after the use of chlorine bleach. Synthetic appHcations of sodium sulfite include production of sodium thiosulfite by addition of sulfur and the introduction of sulfonate groups into dyestuffs and other organic products. Sodium sulfite is useful as a scavenger for formaldehyde in aminoplast—wood compositions, and as a buffer in chrome tanning of leather. 

Boiler scales and corrosion product deposits also may form from the thermal breakdown of treatment chemicals. Breakdown products of chemicals such as sulfite, amines, hydrazine, and chelants often are steam-volatile, and subsequent reactions may produce corrosion debris that forms deposits and causes blockages. This problem typically occurs when chemical treatments selected for use are applied under unsuitable operating conditions (as when the boilers are highly rated or raise steam at particularly high operating pressure or temperature). 

CuCl, especially in a single crystal form, is extensively used as an optical material for its special optical properties. Orel et al. [2] first proposed a new method to obtain CuCl particles by the reduction of Cu with ascorbic acid. Several dispersants were used in the reduction and monodispersed CuCl particles can be obtained by selecting the proper dispersant and reduction conditions. In this work, the above method was used to modify the traditional process of CuCl preparation, namely, by reducing the Cu " with sodium sulfite to obtain the highly active CuCl catalyst to be used in the direct process of methylchlorosilane synthesis. 

Highly active CuCl catalysts for the direct process of methylchlorosilane synthesis were prepared by reducing Cu with a sodium sulfite solution in the presence of dispersing agents. Several well-known dispersants, e.g. SDBS, were used in this study. When SDBS was used, a catalyst in the form of small flakes was obtained that gave the best performance in reactivity, product selectivity and silicon conversion. This provides a convenient way to prepare the CuCl catalyst for use in industrial production. 

Selective staining of polysaccharide in the cell is said to depend upon the oxidizing action of periodate on such chemical configurations as a, p glycols and a-hydroxyketones. Polyaldehydes generated by this selective oxidation react with sulfite-decolorized fuchsin. Polysaccharide areas in the cell are colored red by the stain. 

Use of sodium sulfite allows selective replacement of iodine by hydrogen at C4 without affecting the ortho-position in 4-iodo-3-(2-iodophenyl)sydnone <2005SC639>. Acrylate groups attached at the C4 position of 4-arylsydnones reacted with guanidine hydrochloride but the result was replacement of the G4 substituent by hydrogen instead of formation of the planned pyrimidinone products <2003T4103>. 

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