Chromic acid production

Benzoquinone ( quinone ) is obtained as the end product of the oxidation of aniline by acid dichromate solution. Industrially, the crude product is reduced with sulphur dioxide to hydroquinone, and the latter is oxidised either with dichromate mixture or in very dilute sulphuric acid solution with sodium chlorate in the presence of a little vanadium pentoxide as catalyst. For the preparation in the laboratory, it is best to oxidise the inexpensive hydroquinone with chromic acid or with sodium chlorate in the presence of vanadium pent-oxide. Naphthalene may be converted into 1 4-naphthoquinone by oxidation with chromic acid. 

The allyiic oxidation with derivatives of chromic acid (K.B. Wiberg, 1965 H.G. Boscbe, 1975), c.g. di-/-butyl chromate (K. Fujita, 1961), CrOj/pyridine (W.O. Dauben, 1969), or KjCrO (C.Y. Cuiileron, 1970), gives similar products in occasionally very high yields. 

On the other hand an alkyl side chain on a benzene nng is oxidized on being heated with chromic acid The product is benzoic acid or a substituted derivative of benzoic acid... 

A compound was obtained from a natural product and had the molecular formula C14H20O3 It contained three methoxy (—OCH3) groups and a —CH2CH=C(CH3)2 substituent Oxidation with either chromic acid or potassium permanganate gave 2 3 5 trimethoxybenzoic acid What is the structure of the compound" ... 

Chromic acid (H2Cr04) is a good oxidizing agent and is formed when solutions containing chromate (Cr04 ) or dichromate (Cr207 ) are acidified Sometimes it is possible to obtain aldehydes m satisfactory yield before they are further oxidized but m most cases carboxylic acids are the major products isolated on treatment of primary alco hols with chromic acid... 

The anhydride can be made by the Hquid-phase oxidation of acenaphthene [83-32-9] with chromic acid in aqueous sulfuric acid or acetic acid (93). A postoxidation of the cmde oxidation product with hydrogen peroxide or an alkaU hypochlorite is advantageous (94). An alternative Hquid-phase oxidation process involves the reaction of acenaphthene, molten or in alkanoic acid solvent, with oxygen or acid at ca 70—200°C in the presence of Mn resinate or stearate or Co or Mn salts and a bromide. Addition of an aHphatic anhydride accelerates the oxidation (95). 

Oxidation of saligenin with chromic acid or silver oxide yields saUcyladehyde as the first product. Further oxidation results in the formation of sahcyhc acid, which is also obtained when saligenin is heated with sodium hydroxide at 200—240°C. Chlorination of an aqueous solution of the alcohol gives 2,4,6-trichlorophenol, and bromination in an alkaline medium yields 2,4,6-tribromophenol and tribromosaligenin. When saligenin is heated with one mole of resorcinol in the presence of anhydrous zinc chloride, 3-hydroxyxanthene forms. 

Chromic Acid Electrolysis. Alternatively, as shown in Figure 1, chromium metal may be produced electrolyticaUy or pyrometaUurgicaUy from chromic acid, CrO, obtained from sodium dichromate by any of several processes. Small amounts of an ionic catalyst, specifically sulfate, chloride, or fluoride, are essential to the electrolytic production of chromium. Fluoride and complex fluoride catalyzed baths have become especially important in recent years. The cell conditions for the chromic acid process are given in Table 7. 

Fig. 2. Flow diagram for the production of sodium chromate, sodium dichromate, and chromic acid flake and crystals.

Molten chromic acid decomposes at its melting point at a significant rate. The lower oxides formed impart darkness and turbidity to the water solution. Accordingly, both temperature and time are important in obtaining a quaHty product. 

A newer technology for the manufacture of chromic acid uses ion-exchange (qv) membranes, similar to those used in the production of chlorine and caustic soda from brine (76) (see Alkali and cm ORiNE products Chemicals frombrine Mep rane technology). Sodium dichromate crystals obtained from the carbon dioxide option of Figure 2 are redissolved and sent to the anolyte compartment of the electrolytic ceU. Water is loaded into the catholyte compartment, and the ion-exchange membrane separates the catholyte from the anolyte (see Electrochemical processing). 

Water-Soluble Trivalent Chromium Compounds. Most water-soluble Cr(III) compounds are produced from the reduction of sodium dichromate or chromic acid solutions. This route is less expensive than dissolving pure chromium metal, it uses high quaHty raw materials that are readily available, and there is more processing fiexibiHty. Finished products from this manufacturing method are marketed as crystals, powders, and Hquid concentrates. 

The prices of some important chromium chemicals are given ia Table 4, and production and shipment data for sodium chromate and dichromate are given ia Table 5. Data for the productioa and shipment of chromic acid have not been available siace 1972. However, traditionally CrO has held at about 30—35% of sodium dichromate production. The estimated capacity for domestic production of sodium dichromate is 150,000 to 200,000 t/yr. 

Lclobanincs, CuHjjOaN (Formula XVIII). These are diketo-bases resulting from the chromic acid oxidation of the corresponding lelobanidines. Those recorded in Table B are Z- and dZ-forms, derived from ZI and ZII, and dl forms of lelobanidine respectively, dZ-lelobanine is the best known of these products. The methiodide, not isolated, on treatment with silver oxide yields dimethylamine and a neutral, deep-yellow oil convertible by hydrogenation into a glycol, b.p. 117-8°/0-03 mm.,... 

The inadequacy of these formulae became evident when the oxidation of tropine was studied. With potassium permanganate, in presence of acid, or with chromic acid, tropine and tropidine give rise to a series of oxidation products, the interrelationships of which are shown in the scheme on p. 75. 

In the following groups of oxidation products it is the benzene ring which is first destroyed. Hanssen showed in 1884 that brucine, on oxidation with chromic acid, furnished an acid, later corrected... 

The oxidation products of pseudaconitine have been investigated by Henry and Sharp. With chromic acid it yields a weakly basic substance, C34H 50] ] N, prisms, m.p. 255° (dec.), + 67-95°, which forms unstable... 

Siddiqui et al have also investigated the nitration and the bromina-tion of conessine, and its oxidation by permanganate and by chromic acid, and have carried out various reactions with the products one outcome of this work is the suggestion that the structure of conessine includes the chain. CH CH. CHj. 

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