Aqueous chromic acid

Thus 2-phenyl-4(hydroxymethyl) thiazole upon oxidation with aqueous chromic acid yields 2-phenyl-4-thiazolecarboxylic acid (25,26). 

Note 3. Although in principle the chromate ester can be formed directly from the 18-iodo-l 8,20-ether with silver chromate, hydrolysis and oxidation with aqueous chromic acid sulfurc acid is equally efficient. 

The oxidation of iodide ion by aqueous chromic acid at low acidity is very slow but is subject to marked enhancement in rate on addition of ferrous ion. ... 

The presence of the denominator term in the rate equation (17) suggests that the equilibrium (18) precedes the oxidation step. Two sequences of reactions are proposed (see below), depending on whether the sulphite radical ion dimerises (20) or attacks further acid chromate ion (21). It should be noted that of the species prevalent in dilute aqueous chromic acid, namely CrOj , Cr207, HCrO and H2Cr04, only the last is regarded as possessing oxidising powers. This fact, noted by Westheimer , is tacitly assumed in all recent discussion of... 

Aqueous chromic acid acting on a solution of the alcohol in an inert water insoluble solvent [14] is a well known oxidation procedure giving the carbonyl compound. A stoichiometric amount of reagent is required. The aqueous solution of chromiura(lii) residues can be electrochemically oxidised to the chromium(vr) state [15], however few studies have been made on coupling this process with the excell the oxidation of alcohols. 

Aside from their extensive use in metaUacarborane chemistry, the dicarbollide anions are important intermediates in the synthesis of other carborane compounds. For example, aqueous ferric chloride oxidation of the [7,8-C2B9H1 L] anion results in the 10-vertex cage nido-5,6-C2BgH12 (118) and the aqueous chromic acid oxidation of [7,9-C2B9H1J yields rcz //0-l,3-C2B7H13 [17653-38-2] (29). 

A -(2-Fluoro-2,2-dinitroethyl)hydroxylamine (1) is oxidized by 3-chloroperoxybenzoic acid or bromine to afford oxime 2.218 This compound is unstable and over the course of several weeks at ambient temperature it rearranges quantitatively to amide 3.218 Further oxidation of the oxime 2 with nitric acid or aqueous chromic acid gives a product mixture, from which bis(fluorodinitromethyl)furoxane 4 is isolated.218... 

Mauthner and Suida 2 isolated, as one of three neutral products resulting from the oxidation of cholesterol with aqueous chromic acid in acetic acid solution, the substance later identified as A4-cholesten-3,6-dione. The present procedure is based upon results of a reinvestigation of the oxidation by a low-temperature, non-aqueous procedure.3... 

So far, the most common experimental conditions used for the oxidation of alcohols with chromic acid are the so-called Jones oxidation first described in 1946, in which acetone is used as co-solvent. In fact, the use of chromic acid in the oxidation of alcohols has a long tradition in organic synthesis. As soon as in the 19th century, Beckmann described335 an oxidation of alcohol with aqueous chromic acid, in which no mixing of phases was... 

In 1961, Brown348 described the oxidation of alcohols, using a two-phase system with aqueous chromic acid and diethyl ether. Brown s oxidation349 has a work-up, facilitated by the reluctance of ether to form emulsions with materials containing chromium, and although not as popular as Jones oxidation, it is used quite often. 

Phase-transfer conditions can be used in a two-phase system, consisting of aqueous chromic acid and dichloromethane with tetrabutylammo-nium bisulfate355 or benzyltriethylammonium chloride356 as phase-transfer catalysts. 

Investigation of a cellulose sample that had been oxidized by aqueous chromic acid in the presence of sulfuric acid showed that most... 

Aqueous chromic acid has been used to oxidize alkylboranes derived from cyclic alkenes to ketones. For example, hydroboration and oxidation of 1-methylcyclohexene converts it into 2-methylcyclohexanone (Equation B2.10). 

Aqueous chromic acid solution (the Jones reagent) was prepared according... 

Two-phase oxidation (1. 143 2, 71). Brown ei a . have published the definitive paper on the two-phase oxidation of secondary alcohols in diethyl ether with aqueous chromic acid. A number of water-immiscible solvents were examined, but diethyl ether... 

Thallous Chromate, Tl2Gr04, is precipitated when a solution of a thallous salt is mixed with potassium chromate. It is also produced by adding thallous hydroxide or carbonate to aqueous chromic acid, or by the action of ammonia on the dichromate. Thallous chromate is a yeUow crystalline powder, very sparingly soluble in water, 100 grams of which dissolve 0-03 gram of the salt at 60° C., and 0-2 gram at 100° C. ... 

Zinc Dichromate, ZnCrgO. SHjO, is obtained by evaporation of a solution of zinc carbonate in cold aqueous chromic acid. It yields, when pure, orange-red crystals, but the colour is usually dark red. The crystals are hygroscopic and readily dissolve in water, by which the diehromate is decomposed on boiling. 

Cacodylic acid is reduced to cacodyl when treated -with an excess of sodium hypophosphite in hydrochloric acid solution, Cacodyl may be obtained from dimethylarsine by the action of oxides of nitrogen, aqueous chromic acid, le peroxide, cacodyl chloride, auric chloride, or potassium ferricyanide. It also results w hen cv/cZopentamethyl-penta-arsine is distilled under atmospheric pressure in a carbon dioxide atmosphere, the decomposition commencing at 270° C. ... 

Alkene formation by cycloelimination has also been observed for several aminocyclo-propane derivatives. Thus amino acids 526 (equation 135) and 527 (equation 136) were converted into ethene and 1-butene, respectively by electrochemical oxidation or interaction with other oxidizing reagents, e.g. NaOCP aqueous chromic acid ... 

Electrolytic chromium is deposited from aqueous chromic acid acidified with sulphuric acid. 

Aqueous chromic acid solutions are used, for instance, as pickling and chromium plating baths in metal and plastic processing. They can be produced by dissolving chromium(VI) oxide in water or from sodium dichromate(VI) and sulfuric acid. 

When hydroboration of an olefin is carried out with the intention of oxidizing an initially formed secondary alcohol to a ketone, hydrogen peroxide oxidation can be dispensed with and the alkylborane oxidized directly with chromic acid. Thus Pappo converted a hydroxyl-free A -steroid into a mixture of stereoisomeric alkyl-boranes comparable to (1) and (2), oxidized the mixture with chromic acid, and obtained the 6-keto-5a-steroid in good yield the initially formed 6-keto-5i3-steroid underwent isomerism in the process. H. C. Brown developed an efficient two-phase system for oxidation of either alkylboranes or free alcohols to the ketones using aqueous chromic acid and ether. 

A similar two-phase procedure involves addition over 15 min. of the theoretical quantity of chromic acid (from Na2Cr207-2 HjO, H2SO4, and water) to a solution of the alcohol in ether. After 2 hrs. at 25-30° the ether layer is separated and the product isolated. Oxidation of (-menthol gave (-menthone in 97% yield with only a trace of d-isomenthone, whereas 3-4% of this isomer was present on oxidation with aqueous chromic acid (50-55°), H2Cr04 in 90% acetic acid (25°), or HjCrO,-acetone (5-10°), and the yields in these oxidations were 90, 71, and 86%. This procedure has been used for Ihc selective oxidation of steroidal l6/l,2()o-diols to l6-keto-20 -ols. ... 

Derivation By heating aqueous chromic acid and moist ferric hydroxide. 

The two-phase system has been used for selective oxidation of an alkylborane group in the presence of a double bond.llb Thus the cyclic diene (3) was treated with 1 equiv. of diborane to give the alkylborane (4). which was then oxidized by aqueous chromic acid-diethyl ether to give 8-cyclohexadecene-l-one (5), a musk compound. 

Aqueous chromic acid solution (the Jones reagent) was prepared according to "Reagents in Organic Syntheses", Fieser Fieser J. Wiley, 1967 Vol. 1, p. 142. 

A solution of the sulfide (10 g) in 80% acetic acid (100 ml) is heated to the boiling point and treated with a saturated aqueous chromic acid solution until an orange color indicates presence of an excess of the oxidant. The mixture is boiled for a further 15 min, then treated with an equal volume of water and cooled. The sulfone is recrystallized from 50% acetic acid. 

Direct oxidation of primary trialkylboranes to aldehydes and of secondary tri-alkylboranes to ketones, without isolation of the alcohol, is possible with pyri-dinium chlorochromate (PCC) or aqueous chromic acid (formed from Na2Cr207 and H2S04). For example, 1-octene was converted directly to octanal using disi-amylborane, followed by oxidation with PCC (5.25). 

Oxidations-The use of a two phase ether-aqueous chromic acid system for oxidation of secondary alcohols to ketones has been reported to afford, in a rapid fashion, ketones which are remarkably free of isomerized and side products. Amine oxides can be prepared in 90% yield from the corresponding amines, using m-chloroperbenzoic acid in chloroform, followed by purification of the reaction mixture on an alumina column. ... 

Phosphites are powerful reducing agents. They will, when added to mercuric chloride, give a white precipitate of mercurous chloride which later turns black on further reduction to metallic mercury. Dilute silver nitrate will give a white precipitate of silver phosphite which quickly turns black on precipitation of silver. Aqueous chromic acid is violently reduced to chromic oxide (5.216) and sulphuric acid is reduced to sulphur dioxide (5.217). 

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