Chromium reagents sulfuric acid

Preparation. The reagent has been prepared by oxidation of the corresponding carbinol with chromium trioxide (sulfuric acid).1... 

Jacobsen reaction 19, 611 Japp-Klingemann cleavage 7,406 19,28,185 Jones reagent (chromium trioxide-sulfuric acid-acetone) 2, 289 12, 335... 

Again, as with pyridopyrimidines, the main reaction is oxidation of di- or poly-hydro derivatives to fully aromatic structures, often merely by air or oxygen. In some cases the reagent of choice is mercury(II) oxide, whilst other reagents used include sulfur, bromine, chloranil, chromium trioxide-acetic acid, hydrogen peroxide, and potassium ferricyanide, which also caused oxidative removal of a benzyl group in the transformation (306) (307)... 

When a solution of chromic and sulfuric acids in water is added at 0-20° to an alcohol or formate dissolved in acetone, a rapid oxidation takes place with the separation of the green chromium III reduction product as a separate layer. This system is commonly known as Jones reagent. The rate of oxidation is so fast that it is often possible to run the reaction as a titration to an... 

A 8 A solution of chromic acid is prepared by dissolving 26.72 g of chromium trioxide in a mixture of 23 ml of concentrated sulfuric acid and enough water to make the total volume of the solution 100 ml. Rapid dropwise addition of a slight excess of this reagent to an acetone solution (2 % or less) of the hydroxy steroid at room temperature or below with stirring usually results in complete conversion to ketone in less than 10 min. The product is isolated by dilution with water followed by filtration or extraction. 

Snatzke has found that a solution prepared from chromium trioxide and dimethylformamide with a small amount of sulfuric acid has similar chemical properties as the Sarett reagent. It is useful with acid sensitive compounds and oxidation occurs at such a moderate rate that selective oxidations are often possible. Although the position allylic to a A -double bond is not attacked, the 3-hydroxy-A -system cannot be oxidized satisfactorily to the cor-... 

The immediate outcome of the Hantzsch synthesis is the dihydropyridine which requires a subsequent oxidation step to generate the pyridine core. Classically, this has been accomplished with nitric acid. Alternative reagents include oxygen, sodium nitrite, ferric nitrate/cupric nitrate, bromine/sodium acetate, chromium trioxide, sulfur, potassium permanganate, chloranil, DDQ, Pd/C and DBU. More recently, ceric ammonium nitrate (CAN) has been found to be an efficient reagent to carry out this transformation. When 100 was treated with 2 equivalents of CAN in aqueous acetone, the reaction to 101 was complete in 10 minutes at room temperature and in excellent yield. 

The chromic acid oxidizing reagent is prepared by dissolving 13.4 g of chromium trioxide in 25 ml of water. To this solution is added 12 ml of concentrated sulfuric acid. An additional minimum quantity of water is added if necessary to dissolve any precipitated salts. 

Jones reagent is prepared by dissolving chromium oxide (C1O3) (23.5 g) in coned sulfuric acid (21 mL) with cooling and then diluting with distilled water to give a total volume of 175 mL.4... 

Jones reagent was prepared by the method in Fieser and Fieser Dissolve 13.36 g of chromium trioxide in 11.5 nt of coned sulfuric acid, and carefully dilute this cooled solution (0 C) with water to 50 ml. 

A selection of cases in which 2 has been found to be particularly efficacious is given in the Table. Additional examples are cited in references 1 and 5. Particularly noteworthy examples include the oxidation of acid- and base-sensitive systems, systems containing sulfur and selenium, and 1,3-diols to 1,3-dicarbonyl compounds. Use of chromium reagents in these latter cases often leads to fragmentation products. 

The chromic acid reagent is prepared by dissolving sodium dichromate (Na2Cr207) in a mixture of sulfuric acid and water. The active species in the mixture is probably chromic acid, H2Cr04, or the acid chromate ion, HC1O4. Adding chromium trioxide (C1O3) to dilute sulfuric acid achieves the same result. 

Sodium dichromate in sulfuric acid ( chromic acid, H2Cr04) is the traditional laboratory reagent for oxidizing secondary alcohols to ketones. Bleach (NaOCl) is an inexpensive, chromium-free alternative that also oxidizes secondary alcohols to ketones. Primary alcohols are usually over-oxidized to carboxylic acids under these conditions. 

Chromium is a white, hard, lustrous, and brittle metal (mp 1903 10°C). It is extremely resistant to ordinary corrosive agents, which accounts for its extensive use as an electroplated protective coating. The metal dissolves fairly readily in nonoxidizing mineral acids, for example, hydrochloric and sulfuric acids, but not in cold aqua regia or nitric acid, either concentrated or dilute. The last two reagents passivate the metal in a manner that is not well understood. The electrode potentials of the metal are... 

Reagent Dissolve/suspend 13.4 g of chromium trioxide in 11.5 mL of concentrated sulfuric acid and add this carefully with stirring to enough water to bring the volume to 50 mL. 

Chromium trioxide [chromium(VI) oxide, chromic add, or chromic anhydride], Cr03 (dark red crystals, mp 195 °C), is one of the most powerful and universal oxidants. It is applied in solutions in acetic acid, dilute sulfuric acid, a mixture of acetic acid and dilute sulfuric acid, dilute sulfuric acid and acetone (Jones reagent), acetic anhydride and acetic acid (Fieser reagent) [535], water, water and ether [536,537,535], dichloromethane [539],... 

The main applications of oxidation with chromium trioxide are transformations of primary alcohols into aldehydes [184, 537, 538, 543, 570, 571, 572, 573] or, rarely, into carboxylic acids [184, 574], and of secondary alcohols into ketones [406, 536, 542, 543, 575, 576, 577, 578, 579, 580, 581, 582, 583, 584]. Jones reagent is especially successful for such oxidations. It is prepared by diluting with water a solution of 267 g of chromium trioxide in a mixture of 230 mL of concentrated sulfuric acid and 400 mL of water to 1 L to form an 8 N CrOj solution [565, 572, 579, 581, 585, 556]. Other oxidations with chromic oxide include the cleavage of carbon-carbon bonds to give carbonyl compounds or carboxylic acids [482, 566, 567, 569, 580, 587, 555], the conversion of sulfides into sulfoxides [541] and sulfones [559], and the transformation of alkyl silyl ethers into ketones or carboxylic acids [590]. 

Chromyl chloride, Cr202Cl2, a dark-red liquid (mp -96.5 °C, bp 117 °C, d 1.911), is prepared from chromium trioxide or sodium dichromate, hydrochloric acid, and sulfuric acid [665]. The reagent is used in solutions in carbon disulfide, dichloromethane, acetone, tert-butyl alcohol, and pyridine. Oxidations with chromyl chloride are often complicated by side reactions and do not always give satisfactory yields. The mechanism of the oxidation with chromyl chloride, the Etard reaction, is probably of free-radical nature [666]. Complexes of chromyl chloride with the compounds to be oxidized have been isolated [666, 667, 668]. 

A solution of chromium trioxide in dilute sulfuric acid used in aqueous acetone is called Jones reagent [572]. Other solvents of chromium trioxide are ether [535] and hexamethylphosphoric triamide (HMPA) [543. Oxidations are also carried out with chromium trioxide adsorbed on Celite (diatomaceous earth) [53S], silica gel [537], or an ion exchanger such as Amberlyst A26 (a macroreticular quaternary ammonium salt anion exchanger) [571, 617]. Such oxidations often take place at room temperature and can be used not only for saturated alcohols but also for unsaturated and aromatic alcohols (equations 208 and 209). 

Oxidations of hydroxy ketones to diketones occur frequently in steroidal alcohols. If the alcoholic group, usually secondary, is remote enough from the keto group, its oxidation takes place independently and is achieved by the same reagents that are used for the oxidation of alcohols. A solution of chromium trioxide in aqueous sulfuric acid oxidizes 5-pregnen-3p-ol-20-one in acetone solution at room temperature within 2-5 min to 5-pregnen-3,20-dione in 90% yield [579]. Similarly, lip-hydroxytestosterone 17-acetate is transformed by chromium trioxide in 80% acetic acid at room temperature in 30 min into 11-ketotestosterone 17-acetate in 92% yield [807]. 

Chromium trioxide (267 g, 2.67 mol) is dissolved in 400 mL of water, and 230 mL of concentrated sulfuric acid is added with cooling. The cold solution is diluted with water up to 1 L to form an 8 N reagent. The reagent is added dropwise to a solution of the compound to be oxidized in acetone (distilled from potassium permanganate) at 20 °C. 

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