Oxidation with potassium dichromate

In acidic solution, orange dichromate ion is a powerful oxidant that is reduced to chromic ion  

In 1 M HC1, the formal potential is just 1.00 V and, in 2 M H2S04. it is 1.11 V so dichromate is a less powerful oxidizing agent than Mn04 or Ce4+. In basic solution, Cr20 is converted into yellow chromate ion (CrO -), whose oxidizing power is nil  

Potassium dichromate, K2Cr207, is a primary standard. Its solutions are stable, and it is cheap. Because Cr20 is orange and complexes of Cr3+ range from green to violet, indicators with distinctive color changes, such as diphenylamine sulfonic acid or diphenylbenzi-dine sulfonic acid, are used to find a dichromate end point. Alternatively, reactions can be monitored with Pt and calomel electrodes. 

K2Cr207 is not as strong an oxidant as KMn04 or Ce4+. It is employed chiefly for the determination of Fe2+ and, indirectly, for species that will oxidize Fe2+ to Fe3+. For indirect analyses, the unknown is treated with a measured excess of Fe2+. Then unreacted Fe2+ is titrated with K2Cr207. For example. CIO7, NOj, Mn04, and organic peroxides can be analyzed this way. Box 16-1 describes the use of dichromate in water pollution analysis. 

Cr(VI) waste is toxic and should not be poured down the drain. See Box 2-1. 

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First the amino group was converted to a hydroxy group via a diazonium ion (Section 17.10). The benzene ring was reduced with hydrogen and a catalyst to produce cyclohexanol. Oxidation with potassium dichromate (Section 10.14) gave cyclohexanone. The bonds between the carbonyl carbon and both a-carbons were then cleaved by a series of reactions not covered in this book. The carbon of the carbonyl group was converted to carbon dioxide in this process. One-half of the original radioactivity was found in the carbon dioxide, and the other one-half was found in the other product, 1,5-pentanediamine. Additional experiments showed that the 14C in the diamine product was located at C-l or C-5. 

The 3-amino-l,2-benzisothiazolium salt 147 can be oxidized with potassium dichromate to salt 280a,b in moderate yields (70CB3166, Scheme 93). 

In contrast to 23, 2,3,5-triarylpyrroles (35) were oxidized with potassium dichromate in acetic acid to give a mixture of products resulting from coupling of two pyrrole nuclei, one of which (4-6%) was the 3JF/-pyrrole derivative (36).40 Mechanisms involving migration of the 5-aryl group are suggested for the formation of the various products. 

New spectroscopic data on the 1 2 adduct (18) of pyridine and dimethyl acetylenedicarboxylate have been reported together with the products derived from it by oxidation and by thermolysis. Oxidation with potassium dichromate yields a mixture of the indolizine (19) and the quinolizinone (20).38... 

Degradable organic matter determined by oxidation with potassium dichromate Total nitrogen... 

Oxidation with potassium dichromate/sulfuric acid achieved more than 99% destruction of all the PAH tested, and nonmutagenic residues were obtained. Despite the good reproducibility obtained during the collaborative study, the method was discarded for the reasons outlined in Section 3.1. 

For the determination of ethanol in blood, the alcohol is oxidized with potassium dichromate in nitric acid. The excess of dichromate is measured polarographically. The method is claimed to determine 2-3 per cent ethanol with an accuracy of 0-05-0-3 per cent in the presence of less than 0-6 per cent acetone, provided that the excess of dichromate is not too large. 

S. M. Sultan, Spectrophotometric determination of paracetamol in drug formulations by oxidation with potassium dichromate, Talanta, vol. 34, no. 7, pp. 605-608, 1987. 

By the oxidation of secondary alcohols with potassium dichromate and dilute sulphuric acid, for example ... 

In 1885, from a detailed study of juglone (52) it was proposed that its stmcture was 5-hydroxy-l,4-naphthoquinone (9). This stmcture was confirmed by oxidizing 1,5-dihydroxynaphthalene with potassium dichromate in sulfuric acid (53). Juglone occurs in walnuts as a glycoside of its reduced form, 1,4,5-trihydroxynaphthalene (54). Later it was deterrnined that the sugar is in the 4-position (10) (55). 

By the oxidation of furfural with potassium dichromate and sulfuric acid in 75 per cent yield. Hurd, Garrett, and Osborne, J. Am. Chem. Soc. 55, 1084 (1933). 

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. ... 

Strychnine, brucine Oxidation is performed with potassium dichromate solution This oxidizes brucine to the o-qumone which can then be separated chromatographically [17]... 

Trimethylacetic acid may be made by the hydrolysis of tert-butyl cyanide with weak hydrochloric acid at ioo0.1 It is also obtained by oxidation of trimethylpyroracemic acid with silver oxide or potassium dichromate and sulfuric acid,2 by oxidation of tertf-butylethylene with permanganate solution,3 or by oxidation of dimethyl 2,2-propanol with chromic acid.4 Schroeter reports the formation of trimethylacetic acid by rearrangement of the oxime of trimethylacetophenone to give the anilide of trimethylacetic acid, which can be hydrolyzed to give the acid.5... 

Mention should be made of one of the earliest internal indicators. This is a 1 per cent solution of diphenylamine in concentrated sulphuric acid, and was introduced for the titration of iron(II) with potassium dichromate solution. An intense blue-violet coloration is produced at the end point. The addition of phosphoric(V) acid is desirable, for it lowers the formal potential of the Fe(III)-Fe(II) system so that the equivalence point potential coincides more nearly with that of the indicator. The action of diphenylamine (I) as an indicator depends upon its oxidation first into colourless diphenylbenzidine (II), which is the real indicator and is reversibly further oxidised to diphenylbenzidine violet (III). Diphenylbenzidine violet undergoes further oxidation if it is allowed to stand with excess of dichromate solution this further oxidation is irreversible, and red or yellow products of unknown composition are produced. 

Hydroxylamine is a powerful reducant, particularly when anhydrous, and if exposed to air on a fibrous extended surface (filter paper) it rapidly heats by aerobic oxidation. It explodes in contact with air above 70°C [1]. Barium peroxide will ignite aqueous hydroxylamine, while the solid ignites in dry contact with barium oxide, barium peroxide, lead dioxide and potassium permanganate, but with chlorates, bromates and perchlorates only when moistened with sulfuric acid. Contact of the anhydrous base with potassium dichromate or sodium dichromate is violently explosive, but less so with ammonium dichromate or chromium trioxide. Ignition occurs in gaseous chlorine, and vigorous oxidation occurs with hypochlorites. 

The chemical method for the determination of the chemical oxygen demand of non-saline waters involves oxidation of the organic matter with an excess of standard acidic potassium dichromate in the presence of silver sulfate catalyst followed by estimation of unused dichromate by titration with ferrous ammonium sulfate. Unfortunately, in this method, the high concentrations of sodium chloride present in sea water react with potassium dichromate producing chlorine ... 

A technique of developing Aniline Black directly on the fiber was found by Lightfoot in the period between 1860 and 1863. In accordance with this process, the fiber is soaked with aniline, aniline hydrochloride, and sodium chlorate in the presence of an oxidation catalyst (e.g., ammonium vanadate, potassium hexa-cyanoferrate(II)). The compound is developed at 60 to 100°C and then oxidized further with sodium chromate. It should be noted, however, that Perkin had already synthesized a black compound which he called Aniline Black as early as 1856. He oxidized aniline (containing toluidine) with potassium dichromate and separated Aniline Violet from the resulting black mixture (Aniline Black). 

Take the total amount of succinaldehyde (obtained from 4 of the above syntheses combined) and without further treatment or purification (this had better be 15.5 g of succindialdehyde) put into an Erlenmeyer flask of 4-5 liters capacity. Add 21.6 g of methylamine hydrochloride, 46.7 g of acetonedicarboxylic acid, and enough water to make a total volume of 2 liters. Adjust the pH to 8-10 by slowly adding a saturated solution of disodium phosphate. The condensate of this reaction (allow to set for about 6 days) is extracted with ether, the ethereal solution is dried over sodium sulphate and distilled, the product coming over at 113° at 25 mm of pressure is collected. Upon cooling, 14 g of tropinone crystallizes in the pure state. Tropinone can also be obtained by oxidation of tropine with potassium dichromate, hut I could not find the specifics for this operation. 

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