Regeneration of Chromic Acid

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... 

Regeneration of chromic-sulfuric acid mixtures from wax bleaching processes... 

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 —... 

Maintenance of chromium plating baths causes ecological problems that can be solved by electrochemical methods, especially by using membrane electrolysers (i.e. electrodialysis) [39-41]. In these processes, chromium(III) is oxidized at the anode, usually made of lead, to chromium(VI), whereby chromic acid is regenerated. The chromic acid consumed in the plating process is then replaced by adding CrO in the solid form. 

These etchants for solder- and tin-plated boards were preferred for many years. More recently, their use has been completely eliminated due to Cr(VI) listing as a critical environmental hazard. Other problems with chromic-sulfuric etchants are difficulty in regeneration, inconsistent etch rate, the low limit of dissolved copper (4 to 6 oz/gal), and dangerous degradation of PVC and polypropylene equipment. Chromic add etchant is suitable for use with solder, tin/nickel, gold, screened vinyl lacquer, and dry or liquid film photoresists. Chromic-sulfuric mixtures etch copper slowly, and additives are needed to increase the etch rate. For example, sodium sulfate and iodine have been used for rate increase. Alkaline etchants have become so well controlled that there is no justification for the risks and costs of chromic acid formulations. 

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 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). 

---