L-charcoals

Amino-6-methylpteridin-4(3//)-one (1 100 g, 0.565 mol) was added to a vigorously stirred solution of Br2 (310 g, 1.94 mol) in 48% HBr (3 L). The mixture was stirred on a water bath until the reaction was complete (approx 2.5 h), and then it was concentrated under reduced pressure to 1 L. Charcoal was added, the solution was then boiled and filtered, and the solution was reduced in volume further (to 600 mL). After cooling the solution overnight, the product crystallized. It was collected, washed with HOAc, then Et20, and dried. A second crop was obtained from the filtrate after further concentration total yield 109 g (58%). The free base could be obtained by adding the salt to cold H20 or to EtOH. 

The Kestner-Johnson dissolver is widely used for the preparation of silver nitrate (11). In this process, silver bars are dissolved in 45% nitric acid in a pure oxygen atmosphere. Any nitric oxide, NO, produced is oxidized to nitrogen dioxide, NO2, which in turn reacts with water to form more nitric acid and nitric oxide. The nitric acid is then passed over a bed of granulated silver in the presence of oxygen. Most of the acid reacts. The resulting solution contains silver at ca 840 g/L (12). This solution can be further purified using charcoal (13), alumina (14), and ultraviolet radiation (15). 

Chemical Properties. The most significant chemical property of L-ascorbic acid is its reversible oxidation to dehydro-L-ascorbic acid. Dehydro-L-ascorbic acid has been prepared by uv irradiation and by oxidation with air and charcoal, halogens, ferric chloride, hydrogen peroxide, 2,6-dichlorophenolindophenol, neutral potassium permanganate, selenium oxide, and many other compounds. Dehydro-L-ascorbic acid has been reduced to L-ascorbic acid by hydrogen iodide, hydrogen sulfide, 1,4-dithiothreitol (l,4-dimercapto-2,3-butanediol), and the like (33). 

Because of the time and expense involved, biological assays are used primarily for research purposes. The first chemical method for assaying L-ascorbic acid was the titration with 2,6-dichlorophenolindophenol solution (76). This method is not appHcable in the presence of a variety of interfering substances, eg, reduced metal ions, sulfites, tannins, or colored dyes. This 2,6-dichlorophenolindophenol method and other chemical and physiochemical methods are based on the reducing character of L-ascorbic acid (77). Colorimetric reactions with metal ions as weU as other redox systems, eg, potassium hexacyanoferrate(III), methylene blue, chloramine, etc, have been used for the assay, but they are unspecific because of interferences from a large number of reducing substances contained in foods and natural products (78). These methods have been used extensively in fish research (79). A specific photometric method for the assay of vitamin C in biological samples is based on the oxidation of ascorbic acid to dehydroascorbic acid with 2,4-dinitrophenylhydrazine (80). In the microfluorometric method, ascorbic acid is oxidized to dehydroascorbic acid in the presence of charcoal. The oxidized form is reacted with o-phenylenediamine to produce a fluorescent compound that is detected with an excitation maximum of ca 350 nm and an emission maximum of ca 430 nm (81). 

Anthraquinone-l,5-disulfonic acid [117-14-6] (44), and anthraquinone-1, 8-disulfonic acid [82-48-4] (45) are produced from anthraquinone by disulfonation in oleum a higher concentration of SO than that used for 1-sulfonic acid is employed in the presence of mercury catalyst (64,65). After completion of sulfonation, 1,5-disulfonic acid is precipitated by addition of dilute sulfuric acid and separated. After clarification with charcoal, 1,5-disulfonic acid is precipitated as the sodium salt by addition of sodium chloride. The 1,8-disulfonic acid is isolated as the potassium salt from the sulfuric acid mother hquor by addition of potassium chloride solution. 

The synthesis of indazoles from their 4,5,6,7-tetrahydroderivatives (439) by means of sulfur or, better, by catalytic dehydrogenation over palladium on charcoal (67HC(22)l) can also be included here. 

Amino-l,2,4-triazole [61-82-5] M 84.1, m 159 , pKj 4.04, pK 11.08. Crystd from EtOH (charcoal), then three times from dioxane [Williams, McEwan and Henry J Phys Chem 61 261 1957]. 

Antipyrine [2,3-dihydro-l,5-dimethyl-3-oxo-2-phenylpyrazole] [60-80-0] M 188.2, m 114 , b 319 , pK 1.45. Crystd from EtOH/water mixture, bcnzene, bcnzene/pet ether or hot water (charcoal), and dried under vacuum. 

Chloro-l-nitrobenzene [88-73-3] M 157.6, m 32.8-33.2°. Crystd from EtOH, MeOH or pentane (charcoal). 

Luminol (5-aminophthalazin-l,4-dione) [521-31-3] M 177.2, m 329-332°, pK] 3.37, pK2 6.35. Dissolved in KOH soln, treated with Norit (charcoal), filtered and ppted with cone HCl. [Hardy, Sietz and Hercules Talanta 24 297 1977.] Stored in the dark in an inert atmosphere, because its structure changes during its luminescence. It has been recrystd from O.IM KOH [Merenyi et al. J Am Chem Soc 108 77716 1986]. 

L-Malic acid [97-67-6] M 134.1, m 104.5-106 , [ajp -2.3 (c 8.5, HjO), pK, 3.46, pK 5.10. Crystd (charcoal) from ethyl acetate/pet ether (b 55-56°), keeping the temperature below 65°. Or, dissolved by refluxing in fifteen parts of anhydrous diethyl ether, decanted, concentrated to one-third volume and crystd at 0°, repeatedly to constant melting point. 

Potassium phenol-4-sulfonate (4-hydroxybenzene-l-sulfonic acid K salt) [30145-40-5] M 212.3. Crystd several times from distilled water at 90°, after treatment with charcoal, by cooling to ca 10°. Dried at 90-100°. 

Sodium anthraquinone-l-sulfonate (HjO) [107439-61-2] M 328.3. Crystd from hot water (4mL/g) after treatment with active charcoal, or from water by addition of EtOH. Dried under vacuum over CaCl2, or in an oven at 70°. Stored in the dark. 

Trisodium 8-hydroxy-l,3,6-pyrenetrisulfonate [6358-69-6J M 488.8, m >300(dec). Purified by chromatography with an alumina column, and eluted with -propanol-water (3 1, v/v). Recrystd from aqueous acetone (5 95, v/v) using decolorising charcoal. 

Phospho-L-threonine (L-threonine-O-phosphate) [1114-81-4] M 199.1, m 194 (dec), [a]p -7.37 (c 2.8, H2O) (pK as above). Dissolve in the minimum volume of H2O, add charcoal, stir for a few min, filter and apply onto a Dowex 50W (H" " form) then elute with 2N HCI. Evaporate the eluates under reduced pressure whereby the desired fraction produced crystals of the phosphate which can be recrystd from H2O-MeOH mixtures and the crystals are then dried in vacuo over P2O5 at 80 . [de Verdier Acta Chem Scand 7 196 7955.]... 

Triphenylene has been prepared by self-condensation of cyclohexanone using sulfuric acid or polyphosphoric acid followed by dehydrogenation of the product, palladium-charcoal, or selenium by electrolytic oxidation of cycloliexanone from chlorobenzene and sodium or phenyllilhium from 2-cyclolu xyl-l-phenylcyelohexanol or... 

Turner, L., Improvement of activated charcoal-ammonia adsorption heat pumping/refrigeration cycles. Investigation of porosity and heat/mass transfer characteristics. Ph.D. Thesis, University of Warwick, UK, 1992. 

A solution of 4,4-dimethyl-5a-androst-l-en-3-one (128, 14 mg) in cyclohexane (3 ml) is stirred in a microhydrogenation apparatus in the presence of 10 % palladium-on-charcoal (15 mg) at atmospheric pressure and room temperature. The uptake of one eq of deuterium (1.15 ml) is complete in about 1 min and no more deuterium is consumed. After 5 min the catalyst is removed by filtration, and the solvent evaporated under reduced pressure. The resulting l<, 2< -d2-4,4-dimethyl-5a-androstan-3-one (129, 13 mg, 93%), mp 120-122°, exhibits 87% isotopic purity and 13% d species. ... 

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