Sodium dichromate oxidant

Thiophenes are common pyrolysis products of the Murchison macromolecular material and thiophene, methylthiophene, dimethylthiophene, and benzothiophene have been detected in this way (Biemann, 1974 Holtzer and Oro, 1977 Sephton et al, 1998). Sodium dichromate oxidation has revealed the presence of substituted benzothiophene and dibenzothiophene moieties... 

Pyrolysis has also led to the tentative identifications of the nitrogen heterocychcs, cyanuric acid (Studier et al, 1972), and alkylpyiidines (Hayatsu et al, 1977) in the Murchison macromolecular material. Similar types of analyses have revealed acetonitrile and benzonitrile (Levy et al, 1973 Holtzer and Oro, 1977). Substituted pyridine, quinoline, and carbazole were observed in sodium dichromate oxidation of the macromolecular material (Hayatsu et al, 1977). 

In spite of disputed claims that the sodium dichromate oxidation of coal is not indicative of the aromatic species indigenous to coal, the method has been used to compare the structures of lignite, bituminous coal, and anthracite. As a result, the data indicated that the ring systems increased in size from the lower-rank lignite coal through bituminous coal to anthracite (Figure 10.4) (Hayatsu et al., 1978). 

In neutral aqueous solution at elevated temperatures, sodium dichromate oxidizes benzyl alcohol to benzaldehyde. The mechanism involves formation of a chromate ester and the unfavourable entropy of activation may be due to formation of a cyclic transition state (3) in which the carbonyl group is developed, while a substantial isotope effect (Ath/Atd = 9.4 0.9) indicates transfer of a proton. The oxidation of benzaldehyde to benzoic acid is substantially slower and involves a preequilibrium step in which the carbonyl is hydrated. A similar cyclic transition state is proposed, however. 

Sodium dichromate Oxidative elimination of N-p-aminophenyl groups... 

To prepare acetic acid, aqueous ethanol is added gradually to a hot mixture of aqueous sodium dichromate and sulphuric acid. The oxidising mixture is now always in excess, and therefore the oxidation proceeds as far as possible moreover, the reaction is carried out under reflux, so that any acetaldehyde which volatilises is returned to the oxidising mixture. Hence the final product contains only a small amount of acetaldehyde. 

By the controlled oxidation of primary alcohols with a solution of potassium or sodium dichromate in dilute sulphuric acid. To avoid the further oxidation to the corresponding acid, the aldehyde is removed as rapidly as possible by distillation through a fractionating column, for example ... 

Oxidation of side chains. Aromatic nitro compounds that contain a side chain (e.g., nitro derivatives of alkyl benzenes) may be oxidised to the corresponding acids either by alkahne potassium permanganate (Section IV,9, 6) or, preferably, with a sodium dichromate - sulphuric acid mixture in which medium the nitro compound is more soluble. 

A compound is a cyclic ether of molecular formula C9H10O Its NMR spectrum is shown in Figure 16 10 Oxidation of the compound with sodium dichromate and sulfunc acid gave 1 2 benzenedicarboxylic acid What is the compound d... 

Removal of the ketal protecting groups, followed by oxidation with sodium dichromate ia acetic acid gave... 

The standard potential for the anodic reaction is 1.19 V, close to that of 1.228 V for water oxidation. In order to minimize the oxygen production from water oxidation, the cell is operated at a high potential that requires either platinum-coated or lead dioxide anodes. Various mechanisms have been proposed for the formation of perchlorates at the anode, including the discharge of chlorate ion to chlorate radical (87—89), the formation of active oxygen and subsequent formation of perchlorate (90), and the mass-transfer-controUed reaction of chlorate with adsorbed oxygen at the anode (91—93). Sodium dichromate is added to the electrolyte ia platinum anode cells to inhibit the reduction of perchlorates at the cathode. Sodium fluoride is used in the lead dioxide anode cells to improve current efficiency. 

The starting materials of the aldehyde method may be sulfonated. For example. Cl Acid Blue 9 [2650-18-2] Cl Food Blue 2 (Cl 42090), is manufactured by condensing a-(A/-ethylanilino)-y -toluenesulfonic acid with o-sulfobenzaldehyde. The leuco base is oxidized with sodium dichromate to the dye, which is usually isolated as the ammonium salt. In this case, the removal of the excess amine is not necessary. However, this color caimot be used in the food sector because separation of the chromium compounds from the dye is difficult. An alternative method which gives food-grade Cl Acid Blue 9 (14) and dispenses with the use of sodium dichromate employs oxidative electrolysis of the leuco base (49). 

Chromium Removal System. Chlorate manufacturers must remove chromium from the chlorate solution as a result of environmental regulations. During crystallization of sodium chlorate, essentially all of the sodium dichromate is recycled back to the electrolyzer. Alternatively, hexavalent chromium, Cr, can be reduced and coprecipitated in an agitated reactor using a choice of reducing agents, eg, sodium sulfide, sulfite, thiosulfate, hydrosulfite, hydrazine, etc. The product is chromium(III) oxide [1333-82-0] (98—106). Ion exchange and solvent extraction techniques have also... 

The primary Cr—O bonded species is cbromium (VT) oxide, CrO, which is better known as chromic acid [1115-74-5], the commercial and common name. This compound also has the aliases chromic trioxide and chromic acid anhydride and shows some similarity to SO. The crystals consist of infinite chains of vertex-shared CrO tetrahedra and are obtained as an orange-red precipitate from the addition of sulfuric acid to the potassium or sodium dichromate(VI). Completely dry CrO is very dark red to red purple, but the compound is deflquescent and even traces of water give the normal mby red color. Cbromium (VT) oxide is a very powerful oxidi2er and contact with oxidi2able organic compounds may cause fires or explosions. 

When a potential is appHed across the ceU, the sodum and other cations are transported across the membrane to the catholyte compartment. Sodium hydroxide is formed in the catholyte compartment, because of the rise in pH caused by the reduction of water. Any polyvalent cations are precipitated and removed. The purified NaOH may be combined with the sodium bicarbonate from the sodium dichromate process to produce soda ash for the roasting operation. In the anolyte compartment, the pH falls because of the oxidation of water. The increase in acidity results in the formation of chromic acid. When an appropriate concentration of the acid is obtained, the Hquid from the anolyte is sent to the crystallizer, the crystals are removed, and the mother Hquor is recycled to the anolyte compartment of the ceU. The electrolysis is not allowed to completely convert sodium dichromate to chromic acid (76). Patents have been granted for more electrolytic membrane processes for chromic acid and dichromates manufacture (86). 

A number of manufacturers around the world are using the decomposition of ammonium dichromate to produce chrome oxide (eq. 5) (78). Generally, an excess of finely ground ammonium sulfate is mixed with sodium dichromate, and the dry mixture is heated to form chrome oxide and sodium sulfate, evolving nitrogen and steam. 

Sodium dichromate and various chromic salts are employed in the textile industry (195,196). The former is used as an oxidant and as a source of chromium, for example, to dye wool and synthetics with mordant acid dyes, oxidi2e vat dyes and indigosol dyes on wool, aftertreat direct dyes and sulfur dyes on cotton to improve washfastness, and oxidi2e dyed wool. Premera11i2ed dyes are also employed. These are hydroxya2o or a2omethine dyes in which chromium or other metals are combined in the dye (see Azine dyes DYES Azo dyes). 

It is prepared by pasting potassium or sodium dichromate with three times its weight of boric acid, roasting the mixture at 500°C in a muffle furnace in an oxidizing atmosphere, then hydrolyzing the melt with water and superheated steam. The product is then dried and ground. 

Ferric ammonium ferrocyanide—The blue pigment obtained by oxidising under acidic conditions with sodium dichromate the acid-digested precipitate resulting from mixing solutions of ferrous sulfate and sodium ferrocyanide ia the presence of ammonium sulfate. The oxidized product is filtered, washed, and dried. The pigment consists principally of ferric ammonium ferrocyanide with small amounts of ferric ferrocyanide and ferric sodium ferrocyanide. 

Terephthalic acid has been obtained from a great many /)-disubstituted derivatives of benzene or cyclohexane by oxidation with permanganate, chromic acid, or nitric acid. The following routes appear to have preparative value from />-toluic acid, />-methylacetophenone,2 or dihydro-/)-tolualdehyde by oxidation with permanganate from f>-cymene by oxidation with sodium dichromate and sulfuric acid from />-dibromobenzene or from /i-chloro- or -bromobenzoic acid by heating at 250° with potassium and cuprous cyanides and from />-dibromo-benzene, butyllithium, and carbon dioxide. ... 

Chromium trioxide (chromic anhydride) [1333-82-0] M 100.0, m 197°, dec at 250° to Cr203, d 2.70 (pK 0.74, pK 6.49, for H2Cr04, chromic acid). Red crystals from water (0.5mL/g) between 100° and -5°, or from water/conc HNO3 (1 5). It separates when potassium or sodium dichromate are dissolved in cone H2SO4. Dried in a vacuum desiccator over NaOH pellets hygroscopic, powerful oxidant, can ignite with organic compounds. It is a skin and pulmonary IRRITANT. 

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