Reaction with sodium hydrogen sulfite

All these compounds are made by - esterifleation of the corresponding alcohols or ethoxylates with maleic acid anhydride (monoesters are obtained at 70-100 °C, tgdiile diester formation needs higher temperatures and an azeotropic elimination of water) and subsequent reaction with sodium hydrogen sulfite. All s. have one property in common they are sensitive to - hydrolysis and can be used only in neutral media (pH 6-8). 

Urea-formaldehyde resins are generally prepared by condensation in aqueous basic medium. Depending on the intended application, a 50-100% excess of formaldehyde is used. All bases are suitable as catalysts provided they are partially soluble in water. The most commonly used catalysts are the alkali hydroxides. The pH value of the alkaline solution should not exceed 8-9, on account of the possible Cannizzaro reaction of formaldehyde. Since the alkalinity of the solution drops in the course of the reaction, it is necessary either to use a buffer solution or to keep the pH constant by repeated additions of aqueous alkali hydroxide. Under these conditions the reaction time is about 10-20 min at 50-60 C. The course of the condensation can be monitored by titration of the unused formaldehyde with sodium hydrogen sulfite or hydroxylamine hydrochloride. These determinations must, however, be carried out quickly and at as low temperature as possible (10-15 °C), otherwise elimination of formaldehyde from the hydroxymethyl compounds already formed can falsify the analysis. The isolation of the soluble condensation products is not possible without special precautions, on account of the facile back-reaction it can be done by pumping off the water in vacuum below 60 °C imder weakly alkaline conditions, or better by careful freeze-drying. However, the further condensation to crosslinked products is nearly always performed with the original aqueous solution. 

The practical preparation of melamine-formaldehyde resins is done under the same conditions as for urea-formaldehyde resins. Melamine is at first insoluble in the aqueous reaction mixture but dissolves completely as the condensation proceeds. Because of the greater stability of the N-hydroxymethylmel-amines compared with the corresponding urea compounds the reaction can easily be followed by titration of the unconverted formaldehyde with sodium hydrogen sulfite (see Sect. 4.1.4.1). 

An exception to the generalization that C—O bonds to aromatic systems are difficult both to make and to break is provided by reversible conversion of benzenediols and 1- or 2-naphthalenols to the corresponding amines, usually at elevated temperatures with sodium hydrogen sulfite or an acidic catalyst. The sodium hydrogen sulfite-induced reaction is called the Bucherer reaction ... 

The element was obtained by the reduction of an acidic solution of the iodate ion with sodium hydrogen sulfite, (a) Write the chemical equation for the reaction, assuming the oxidized product to be HS04. (b) Calculate the mass of sodium hydrogen sulfite needed to produce 50.0 g of iodine. 

The effect of surfactant charge on the reaction rate was investigated for a related reaction, ring opening of 1,2-epoxyoctane with sodium hydrogen sulfite (Scheme 2 of Fig. 2). The reaction, which was performed in a Winsor III microemulsion, was fast when a nonionic surfactant was used as the sole surfactant and considerably more sluggish when a small amount of SDS was added to the formulation [9]. 

Aromatic aldehydes react with sodium hydrogen sulfite to yield bisulfite compounds. Further reaction with sodium cyanide forms the hydroxynitrile (cyanohydrin), which can sometimes be formed directly from the aldehyde by reaction with hydrogen cyanide (Scheme 6.11). 

Quinazoline 3-oxide reacts with sodium hydrogen sulfite smoothly in an exothermic reaction to give sodium quinazoline-4-sulfonate (cf. p 105). 

Diaminopyrimidin-4(3/7)-one reacts with aqueous 2-oxopropanal at 100°C to yield, even in the presence of sodium hydrogen sulfite, 7-methylpteridin-4(3T/)-one (6, 60%). However, if the 2-oxopropanal is initially complexed with sodium hydrogen sulfite, a similar reaction carried out at 30 C gives 6-methylpteridin-4(3/f)-one (5, 56%) with only a trace of the 7-iso-mer 6.5 3... 

There is a strong preference for attack at C-3, even when that position carries a substituent, and this is nicely shown by examples in which there is the possibility for nucleophilic trapping of the Wheland intermediate the reaction of indole with sodium hydrogen sulfite is a simple example. 

Sulfur dioxide can be generated by the reaction of sodium hydrogen sulfite with hydrochloric acid, (a) Write the balanced chemical equation for the reaction, given that the other products are sodium chloride and water, (b) If 1.9 g of sodium hydrogen sulfite are reacted with excess HCl, what mass of SO2 is produced (c) If the gas generated is in a 100-mL vessel at 25°C, and 0.05 mol of O2 is introduced, equilibrium between SO2, O2, and SO3 will be established. 

An aqueous solution of fuchsin (/7-rosaniline hydrochloride) decolorized with sodium hydrogen sulfite or with sodium sulfite becomes red-violet to blue if aldehydes are added to it. The reappearance of this color is not caused by simple oxidation to fuchsin, but represents a specific reaction of the aldehydic group —CHO. However, unsaturated aldehydes and certain aromatic aldehydes (vanillin, p-aminobenzaldehyde, p-dimethylaminobenz-aldehyde) and glyoxal do not react. According to more recent views (15), both amino groups of the fuchsinleukosulfonic acid (VI) react with the... 

Many of the modifications of the pyrazolone antiinflammatory agents are intended to increase the limited hydrophilicity of the parent molecules. Reaction of aminopyrine (157) with formaldehyde and sodium hydrogen sulfite affords dipyrone (158). The first step can be rationalized as an Eschweiler-Clark type N-methylation reaction, with bisulfite acting as the reducing agent. The resulting mono N-methyl analogue of 157 then apparently forms the sulfite adduct of the carbinolamine of formaldehyde. 

Reaction of the spirocyclic imidazoline 316 with glyoxal and sodium hydrogen sulfite results in hydrolysis of the aminal and subsequent double condensation to give the tetrazolopyridopyrazine 317 (Equation 109) <1999JHC117>. The pyridopyridazinylhydrazine 318 can be cyclized to the fused triazole 319 by reaction with formic acid (Equation 110) <1998SC2871>. 

The checkers found that the procedure of Helberger and Lan-terman,2 which avoids the use of an ion-exchange resin, is also satisfactory in case it is regarded as inconvenient to set up the resin column. According to this procedure, after completion of the reaction with sodium sulfite, anhydrous hydrogen chloride is passed into the hot solution to liberate sulfur dioxide. After removal of sulfate as in the described procedure, the undiluted aqueous solution is saturated with hydrogen chloride gas at a temperature below 25°. The precipitated sodium chloride is removed by suction filtration, the filter cake is... 

One equiv of the alkylated hydrazone is dissolved in 5 equiv of iodomethane and the solution is heated to 60 cC in a reflux condenser. After 20 -48 h the reaction is complete (monitored by TLC) and excess iodomethane is removed in vacuo. The remaining methoiodide (viscous brown oil) is dissolved in 3 4N hydrochloric acid (50 mL/10 mmol) and stirred for 5 min at 20 C. Pentane (200 mL/10 mmol) is then added and the two-phase system is vigorously stirred for 30 min. The organic layer is separated, washed with a few mL of a sodium hydrogen sulfite soln and a pH 7 buffer soln, and dried over Na2S04. The solvent is removed in vacuo and the remaining crude product is purified by short path or Kugelrohr distillation. 

A 500-ml three-necked flask was charged with 2,7-dibromo-9-fluorenone (6.65 g), 140 ml trifluoroacetic acid/chloroform, 1 1, and sodium perborate monohydrate and then stirred for 20 hours. The reaction liquid was filtrated through Celite and then washed with toluene. The filtrate was washed with water, sodium hydrogen sulfite, and saturated saline and then dried over Na2SC>4. After concentration 6.11 g of residue was obtained. After recrystallization from chloroform 1.19 g of product was isolated. 

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