Charcoal, oxidation

Very H-nch algae phyto- plankton micro- organisms amorphous H-nch Spores pollen cuticle amorphous H-Poor wood humic tissues coal amorphous NoH "Charcoal" oxidized tissues... 

The study of equilibria between Cr and ligands in aqueous solution is complicated by the robustness of Cr complexes. Equilibria can be established quickly in Co systems if charcoal is added because this reduces a little Co to Co, but in Cr systems Cr° must be added as well as charcoal. Oxidation by the medium could remove all the Cr before equilibrium is reached among the Cr" species, but it has been found that a constant concentration of Cr can be maintained by electrolytic reduction until equilibrium is reached. Then the remaining Cr can be allowed to oxidize and the equiUbrium concentrations of the different Cr species determined. In this way log jSg for complexation with ammonia has been found to be 13 (24 C, 4.5 M NH4CI) and logjSs (en) = 19.5 (24 C, IMNaCl). The method works also with pn and edta, but fails with glycine and non-amine ligands like ox and SCN where a steady state concentration of Cr cannot be built up. 

C]2Hi50]2. Colourless needles m.pr. 286-288°C. When heated it decomposes into pyro mellitic anhydride, water and CO2. Occurs as the aluminium salt (honeystone) in some lignite beds. Prepared by oxidation of charcoal with concentrated nitric acid. 

This is formed when arsenic burns in air (cf. phosphorus which gives P4O10). It can exist in two crystalline modifications the stable one at room temperature, which also occurs naturally as arsenolite, has an octahedral form. Solid arsenic(III) oxide is easily reduced, for example by heating with charcoal, when arsenic deposits as a black shiny solid on the cooler parts of the tube. 

For this reaction, charcoal is a catalyst if this is omitted and hydrogen peroxide is used as the oxidant, a red aquopentammino-cobalt(lll) chloride, [Co(NH3)jH20]Cl3, is formed and treatment of this with concentrated hydrochloric acid gives the red chloro-p0itatnmino-coba. t(lll) chloride, [Co(NH3)5Cl]Cl2. In these latter two compounds, one ammonia ligand is replaced by one water molecule or one chloride ion it is a peculiarity of cobalt that these replacements are so easy and the pure products so readily isolated. In the examples quoted, the complex cobalt(III) state is easily obtained by oxidation of cobalt(II) in presence of ammonia, since... 

Prepare a mixture of 30 ml, of aniline, 8 g. of o-chloro-benzoic acid, 8 g. of anhydrous potassium carbonate and 0 4 g. of copper oxide in a 500 ml. round-bottomed flask fitted with an air-condenser, and then boil the mixture under reflux for 1 5 hours the mixture tends to foam during the earlier part of the heating owing to the evolution of carbon dioxide, and hence the large flask is used. When the heating has been completed, fit the flask with a steam-distillation head, and stcam-distil the crude product until all the excess of aniline has been removed. The residual solution now contains the potassium. V-phenylanthrani-late add ca. 2 g. of animal charcoal to this solution, boil for about 5 minutes, and filter hot. Add dilute hydrochloric acid (1 1 by volume) to the filtrate until no further precipitation occurs, and then cool in ice-water with stirring. Filter otT the. V-phcnylanthranilic acid at the pump, wash with water, drain and dry. Yield, 9-9 5 g. I he acid may be recrystallised from aqueous ethanol, or methylated spirit, with addition of charcoal if necessary, and is obtained as colourless crystals, m.p. 185-186°. 

Oxidizing Properties. Nitric acid is a powerful oxidizing agent (electron acceptor) that reacts violentiy with many organic materials (eg, turpentine, charcoal, and charred sawdust) (19,20). The concentrated acid may react explosively with ethanol (qv). Such oxidizing properties have had military appHcation nitric acid is used with certain organics, eg, furfuryl alcohol and aniline, as rocket propellant (see Explosives AND PROPELLANTS). 

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). 

Another large appHcation is as an ingredient in the production of charcoal briquettes. The amount of sodium nitrate used in charcoal briquette manufacture depends on the type and amount of wood and coal used. Typically charcoal briquettes contain up to almost 3% sodium nitrate. Sodium nitrate is also used in the manufacture of enamels and porcelain as an oxidizing and fluxing agent. In porcelain—enamel frits used for metal coating, the amount of sodium nitrate in a batch varies with the various metal bases to be coated, typically from about 3.8 to 7.8 wt %. 

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). 

Later, a completely different and more convenient synthesis of riboflavin and analogues was developed (34). It consists of the nitrosative cyclization of 6-(A/-D-ribityl-3,4-xyhdino)uracil (18), obtained from the condensation of A/-D-ribityl-3,4-xyhdine (11) and 6-chlorouracil (19), with excess sodium nitrite in acetic acid, or the cyclization of (18) with potassium nitrate in acetic in the presence of sulfuric acid, to give riboflavin-5-oxide (20) in high yield. Reduction with sodium dithionite gives (1). In another synthesis, 5-nitro-6-(A/-D-ribityl-3,4-xyhdino) uracil (21), prepared in situ from the condensation of 6-chloro-5-nitrouracil (22) with A/-D-ribityl-3,4-xyhdine (11), was hydrogenated over palladium on charcoal in acetic acid. The filtrate included 5-amino-6-(A/-D-ribityl-3,4-xyhdino)uracil (23) and was maintained at room temperature to precipitate (1) by autoxidation (35). These two pathways are suitable for the preparation of riboflavin analogues possessing several substituents (Fig. 4). 

Metafile arsenic can be obtained by the direct smelting of the minerals arsenopyrite or loeUingite. The arsenic vapor is sublimed when these minerals are heated to about 650—700°C in the absence of air. The metal can also be prepared commercially by the reduction of arsenic trioxide with charcoal. The oxide and charcoal are mixed and placed into a horizontal steel retort jacketed with fire-brick which is then gas-fired. The reduced arsenic vapor is collected in a water-cooled condenser (5). In a process used by Bofiden Aktiebolag (6), the steel retort, heated to 700—800°C in an electric furnace, is equipped with a demountable air-cooled condenser. The off-gases are cleaned in a sembber system. The yield of metallic arsenic from the reduction of arsenic trioxide with carbon and carbon monoxide has been studied (7) and a process has been patented describing the gaseous reduction of arsenic trioxide to metal (8). 

Extensive research has been conducted on catalysts that promote the methane—sulfur reaction to carbon disulfide. Data are pubhshed for sihca gel (49), alurnina-based materials (50—59), magnesia (60,61), charcoal (62), various metal compounds (63,64), and metal salts, oxides, or sulfides (65—71). Eor a sihca gel catalyst the rate constant for temperatures of 500—700°C and various space velocities is (72)... 

Carbon monoxide was discovered in 1776 by heating a mixture of charcoal and 2inc oxide. It provided a source of heat to industry and homes as a component of town gas and was used as a primary raw material in German synthetic fuel manufacture during World War II its compounds with transition metals have been studied extensively (see Carbonyls). Most recently, carbon monoxide emission from vehicle exhausts has been recognized as a primary source of air pollution (qv). 

Heating a mixture of tetrachloroethane vapors and chlorine over active charcoal at 400°C gives carbon tetrachloride and hydrogen chloride (125). Miscellaneous. Air oxidation of 1,1,2,2-tetrachloroethane under ionizing radiation gives dichloroacetyl chloride (117). Contact of... 

Macerals. Coal parts derived from different plant parts, are referred to as macerals (13). The maceral names end in "-inite" as do the mineral forms of rocks. The most abundant (about 85%) maceral in U.S. coal is vitrinite, derived from the woody tissues of plants. Another maceral, called liptinite, is derived from the waxy parts of spores and poUen, or algal remains. The liptinite macerals fluoresce under blue light permitting a subdivision based on fluorescence. A third maceral, inertinite, is thought to be derived from oxidized material or fossilized charcoal remnants of early forest fires. 

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