Chromium trioxide chromic acid preparation

Chromium Trioxide, Chromic Anhydride, CrOg, was first obtained by Unverdorben by the interaction of ehromyl fluoride and water. It is usually prepared by the action of concentrated sulphuric acid on solutions of a chromate, usually of potassium diehromate. Zettnow... 

It is doubtful if hydrated chromium trioxide has been prepared in the solid state. H. Moissan 2 said that if an almost sat. aq. soln. of chromium trioxide be kept for several hrs. at about 90°, and then cooled below 0°, small red crystals of chromic acid, H2Cr04, collect on the walls of the containing vessel. This does not agree with J. J. Berzelius s observations, while F. Mylius and R. Funk, T. Costa, and E. Field were unable to confirm H. Moissan s observation. H. C. Jones showed that the f.p. of aq. soln. of chromium trioxide agreed with the assumption that the solvation for soln. with m mols of Cr03 per litre, can be represented by the mols of water in combination with a mol of CrOs ... 

Usually, organoboranes are sensitive to oxygen. Simple trialkylboranes are spontaneously flammable in contact with air. Nevertheless, under carefully controlled conditions the reaction of organoboranes with oxygen can be used for the preparation of alcohols or alkyl hydroperoxides (228,229). Aldehydes are produced by oxidation of primary alkylboranes with pyridinium chi orochrom ate (188). Chromic acid at pH < 3 transforms secondary alkyl and cycloalkylboranes into ketones pyridinium chi orochrom ate can also be used (230,231). A convenient procedure for the direct conversion of terminal alkenes into carboxyUc acids employs hydroboration with dibromoborane—dimethyl sulfide and oxidation of the intermediate alkyldibromoborane with chromium trioxide in 90% aqueous acetic acid (232,233). 

A similar procedure may be used for the preparation of /)-cyanobenzaldiacetate from -tolunitrile. Information submitted by Rorig and Nicholson, of G. D. Searle and Company, indicates that the critical step in this preparation is to maintain the reaction temperature below 10° throughout the process. Exposure of -cyanobenzaldiacetate to excess chromic, acetic, and sulfuric acids causes a reduction in yield. During the oxidation care should be taken to prevent chromium trioxide from adhering to the walls of the flask above the reaction mixture and then dropping in large amounts into the solution. 

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. 

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. 

T. Urbanski, Szyc-Lewanska et al. [18] have recently found that dinitrobenzene-diazo-oxide can be prepared by oxidation of picramic acid with chromium trioxide in the presence of sulphuric acid at 55-60°C. One part of picramic acid is fully oxidized by chromic acid to yield gaseous products CO, C02, N02, NH3 and H20. Nitrogen dioxide acts further as a diazotizing agent on undecomposed picramic acid to yield the diazo compound. The yield of this reaction does not exceed 31% of theoretical calculated on the picramic acid used. 

It is also possible to prepare a chromic acid solution by treating sodium dichromate (Na2Cr207) or potassium dichromate (K C Ot) with sulfuric acid. Consequently, sodium14 and potassium15 dichromate can be used, instead of chromium trioxide, in Jones oxidations. 

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. 

The 8i 7 chromic acid solution is prepared by dissolving 534 g. of chromium trioxide in ice water, adding 444 ml. of cone, sulfuric acid carefully, and diluting to 2 1. with water. 

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]. 

J. Thomsen, and J. Krutwig similarly treated silver chromate with hydrochloric acid. A. Mailfert found that chromium trioxide is formed when soln. of chromic salts or chromic oxide are treated with ozone. M. Prud homme and F. Binder observed that if barium chloride is added to a soln. of barium dichromate, normal barium chromate is precipitated, and potassium chloride and chromic acid remain in soln. In preparing chromic acid, V. V. Polyansky first obtained calcium chromate by addition of calcium hydroxide paste, followed by calcium chloride soln., to... 

F. A. H. Scbreinemakers could not prepare lithium tetrachromate, Li2Cr40is but be showed that sodium tetrachromate, Na2Cr40i3.H20, can exist under the conditions indicated in Fig. 34. F. Mylius and R. Funk prepared this salt by evaporating a soln. of sodium chromate in an excess of chromic acid. Tbe garnet-red, deliquescent plates melt at 40°-50° with tbe separation of chromium trioxide. Tbe salt dissolves in water without decomposition. A sat. soln. at 18° has 74-60 per cent, of Na2Cr40i3, and has a sp. gr. of 1-926 and at 0°, 16°, and 22°, tbe respective percentage solubilities are 72-19, 74-19, and 76-01. 

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