Sodium ascorbate, reduction

Reduction of diaryltellurium dichlorides with sodium ascorbate (typical procedure). Bis (p-methoxyphenyl)tellurium dichloride (0.20 g, 0.48 mmol) dissolved in acetone (10 mL) was added to a stirred solution of sodium ascorbate (0.20 g, 1.0 mmol) in water/methanol (2+8 mL). After 24 h, water (50 mL) and CH2CI2 (50 mL) were added and the two phases separated. The organic phase was dried (CaCl2) and the solvent evaporated in vacuo. Flash chromatography yielded 0.14 g (84%) of bis(p-methoxyphenyl) telluride. 

D-Glucitol (Sorbitol or Hexanhexol), HOCH2(CHaOH)4CH2OH raw 182.17, ndls (with lA or 1 w), tnp about ll0°(dry), -100° or less (with w), very hygr when dry sol in w hot ale. Found in various fruits prepd by sodium amalgam reduction of d-sorbose or by pressure hydrogenation of dextrose with Ni catalyst. Used far prepn of ascorbic acid (Vitamin C), for synthesis of resins, surface-active agents, varnishes, syrups, cosmetic creams aod for explosive Sorbitol Hexanitrate... 

Ascorbate reduction This method (7) entails the fairly rapid addition of sodium ascorbate to chloroauric acid while stirring. If the reaction is carried out on ice, the gold particle size range is between 6 and 8 nm. Higher temperatures tend to increase the particle size The method is also really of academic interest nowadays, since it is not easy to control the final sphere diameter. 

Figure 3.42 a General reaction scheme for the thermal Huisgen cycloaddition b the copper-catalyzed reaction between phenyl propargyl ether (phenyl 2-propynyl ether) and benzyl azide. The catalytic reaction is performed in the presence of a reductant (sodium ascorbate) and gives just one of the product isomers in high yield. 

JA Schmidt, C Heitner. Light-induced yellowing of mechanical and ultrahigh yield pulps. Part 1. Effect of methylation, sodium borohydride reduction and ascorbic acid on chromophore formation. JWood Chem Technol 11(4) 397 18, 1991. 

Reaction vials contained in a total volume of 0,4 mL, 227 X 10 heterocysts isolated in the presence of sodium ascorbate, 5mM ATP, 8milf MgCk, 13mAf TES pH 72, 5mM sodium ascorbate, 50fiM dichlorophenol indophenol as reductant, and 5mM a-keto-glutarate. 

Cu(I) salts make the reaction between azides and alkynes faster (up to 10 times) and regiospecific [131,132] (only the 1,4-regioisomer is obtained). The reaction usually proceeds at room temperature and is compatible with a plethora of functional groups present in the substrates. Many different sources of Cu(I) species have been used, such as Cu(I) salts [132], Cu(I) complexes soluble in organic media [133], and Cu(I) derivatives [134] stabilized with polytriazolylamines. Finthermore, Cu(I) species can be also be obtained by in-situ reduction of Cu(II) derivatives [131]. A standard procedure involves the use of a mixture of Cu(II) sulfate and sodium ascorbate as a source ofCu(I). 

Fig. 2. Mossbauer spectra of the Fx cluster in the Photosystem I core protein. Left panels Spectra following Fx reduction by illumination under simultaneous freezing of the sample in the presence of 1 mM DCPIP and 10 mM sodium ascorbate. Right panels Spectra with Fx in the oxidized state obtained after subsequent dark adaptation at -8 C for 10 min. Spectra labaeled D are those left after subtraction of 15% of the spectra on the right. Spectra on the bottom panels were obtained in the presence of a 1 kG magnetic field applied perpendicular to the gamma rays.

Though in case of the azide-alkyne 13-dipolar cycloaddition process, exclusively Cu(l) catalysts have been used (in 0.25-2 molcatalysts (Ru, Ni, Pd, and Pt salts) have also been employed. For Cu(l) catalysts, most methods directly use Cu(T) salts, while other methods generate Cu(I) by reduction of Cu(ll) salts with sodium ascorbate or metallic copper. The catalyzed cycloaddition reaction is experimentally simple, perfecdy rehable, quantitative, proceeds well in aqueous solutions under ambient conditions without protection from oxygen, requires only stoichiometric... 

PC vesicles were preparated at an initial concentration of 30 mM by sonication in either 0.5 M K3Fe(CN)0or 0.5 M sodium ascorbate (pH 6.5). The two populations of vesicles were purified by centrifugation and gel filtration on Sepharose 4B (Holloway Katz, 1975). For each experiment shown ferricyanide (FeCN)-loaded vesicles or ascorbate (ASC)-loaded vesicles were added with d-bs to 10 mM Tris acetate/0.1 mM EDTA pH 8.0 in the orders indicated. The final concentration of d-bs in all but experiment 4 was 1 yM and the final concentration of each species of vesicle was 1 mM. The mixtures were incubated at 37° under argon and the rate of FeCN reduction by ASC was monitored at 420 nm. 

The kinetics of reduction [K4Fe(CN)s, SO2", Sa04 , sodium ascorbate, and cytochrome C2] and oxidation [K3Fe(CN)6 and cytochrome Cg] of HIPIP from Chro-matium vinosum have been reported, and it is concluded that HIPIP undergoes rapid outer-sphere electron transfer (there being no indication of complex formation with the various reactants). Moreover, steric restrictions and differences in oxidation-reduction potential are less important than electrostatic attraction and/or repulsion in determining the absolute rate constants (Table 2). Rawlings et al. have deter-... 

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