Chromic acid, regeneration

The oldest process of organic electrochemistry is the indirect oxidation of hydrocarbons with chromic acid. It has been employed industrially for more than 90 years by Hoechst— now Clariant—in Gersthofen, Germany [102]. Other sites are or were located in Great Britain. The oxdiations of naphthalene, anthracene, and camphene are examples. Companies like Emery Industries, L. B. Holliday, and Boots have also used chromic acid regeneration commercially [103]. It has been employed for the bleaching of montan waxes for more than 70 years. 

Since 1927 chromic acid has been used for the oxidative bleaching of Montan waxes. Hoechst has been operating the electrochemical regeneration of chromic acid for more than 90 years. The newly developed electrochemical process (as enlargement and partial replacement for the existing plant) is based on the... 

Side-chain oxidations of alkyl aromatic compounds to aromatic carboxylic acids by electrogenerated and regenerated chromic acid have been studied extensively in the case of saccharin formation from o-toluene sulfonamide This... 

The main inconvenience was the lifetime of the electrode, which was lowered by gradual passivation with compounds present in urine. However, the use of an optimised mercury film, high urine dilutions and short accumulation times minimised this effect. Surface fouling was also alleviated by fibre regeneration along lmin in concentrated chromic acid. The same fibre could normally be used for five different urine analysis runs involving approximately 35 measurements before it had to be replaced. This problem had not been noticed when the mercury film was generated in situ. 

The revival of spent chromic acid is closely connected with these oxidations, since it has been the practice, for some time, to regenerate the chromic acid after use by electrolysis6 —... 

The presence of the /3-hydroxypropionic ester unit in deacetylpicraline is established by oxidation with chromic acid in acetone, which yields an aldehyde base, picralinal, C21H22N2O4 the latter is readily deform yla ted by short treatment with methanolic potassium hydroxide, which affords picrinine in quantitative yield. Reduction of picralinal with sodium borohydride regenerates deacetylpicraline. Vigorous treatment of deacetylpicraline with sodium borohydride gives a noncrystalline indoline base, which exhibits the UV-absorption of an anilinium ion in concentrated perchloric acid hence, the Na-carbinol-amine ether function must have suffered reduction. Since acetylation of the noncrystalline base gives a product which exhibits acylaniline UV-absorption, picraline and its derivatives must contain an NaH group (53, 54). 

Among the alkaloids of Hunteria ebumea Pichon (Table I) were four interrelated ones (11). Two of them, eburnamine and isoeburnamine, were diastereoisomeric pentacyclic indoles (XVII) convertible by acids into eburnamenine, an A-vinylindole (XVIII), on the one hand, and by chromic acid into eburnamonine, an V-acylindole (XIX), on the other. Reduction of eburnamonine with lithium aluminum hydride regenerated the alcohols, XVII (7,11). When eburnamonine was heated with selenium... 

The iodine reacts with the chromic acid yielding iodic acid the latter, in the presence of concentrated sulphuric acid and especially on warming, liberates chlorine from chlorides, regenerating iodide. This explains the failure to form chromyl chloride. 

The first regeneration of the strong base anion exchange resin with a near stoichiometric quantity of sodium hydroxide converts the loaded dichromate form of the resin to the chromate form whereafter it is able to efficiently take up chromic acid again. The anion column effiuent of sodium chromate may be cation exchanged across a strong acid resin in the hydrogen form to recover chromic acid ... 

Chromic acid solutions can also be produced from acid chromium(III) solutions anodically (regeneration of chromium(III) solutions obtained from chromic acid solutions employed in oxidation processes). 

H SO CrC (usually around 1 100) and an organic acid is used as catholyte, the small amounts of organic anion which do migrate across the membrane are oxidized by the chromic acid. An additional problem in the regeneration of chrome plating solutions is removal of low concentrations of cations such as Fe3+, Cu2+, Ni2" ". 

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