Oxidation with potassium chromate

Cathylates are stable to oxidation with potassium chromate in acetic acid and with A-bromoacetamide, acetylation and formylation with 85 % formic acid at room temperature. They are cleaved by bases to give the parent alcohol, carbon dioxide and ethanol. 

Codeine-N-oxide sulphonic acid on heating with potassium chromate is converted to norcodeine sulphonic acid, which yields norcodeine on heating with superheated steam [352] (the nature of this change was not at first appreciated [339, 350]). Codeine-N-oxide likewise yields norcodeine and formaldehyde when oxidized with potassium chromate [352]. 

Bentley and Murray (201) reported another method for synthesis of protopine alkaloids allocryptopine (392) and cryptopalmatine (395) from tetrahydroprotoberberine /V-oxides (35a and 400) through oxidative rearrangement with potassium chromate (Scheme 73). 

Selenious acid readily decomposes potassium permanganate, but analytical results are untrustworthy in the presence of more than a limited quantity of sulphuric acid.1 The oxidation should be carried out at 50° C., a known quantity of 0-lN potassium permanganate being used and the excess determined either by means of standard oxalic acid solution or by electrometric titration with ferrous sulphate. In the presence of tellurium, the latter is also oxidised and should be determined in a separate sample by oxidation with potassium di-chromate, which does not oxidise the selenium, and the necessary deduction can then be made.2... 

The amount of absorption of chromium(VI) and chromium(III) was measured in four male and two female volunteers (ages ranging from 25 to 39 years) treated orally with potassium chromate (chromium(VI)) or chromic oxide (chromium(III)) in capsules at doses of 0.005 mg/kg/day and 1.0 mg/kg/day, respectively (Finley et al. 1996b). Subjects were exposed to each compound for 3 days. Based on urinary excretion data, mean absorption of potassium chromate was 3.4% (range 0.69-11.9%). No statistically significant increase in urinary chromium was observed during chromic oxide dosing,... 

Oxo-steroids, which are not usually very accessible, may be prepared by the allylic oxidation of 8(14)-enes with potassium chromate. Yields, which vary between 20—60%, are highest when a 12-oxo-group is present." ... 

Hydroxy-a- and 16-hydroxy-/ -colubrines have been isolated43 from Strychnos nux vomica and partially synthesised from the corresponding colubrines by the standard procedure of N(4) oxidation and then reaction with potassium chromate. 

Another degradation of laudanosine involves the use of its A-oxide (LXXXVI). On treatment with potassium chromate it affords A-nor-laudanosine (LXXVI) [B-HCl, mp 216°-216.5°] 145) while on pyrolysis an unstable stilbene is obtained which was isolated as the methiodide of the methine (LXXX) 146). 

Sihcon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between sihcon carbide and a variety of compounds at relatively high temperatures. Sodium sihcate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal sihcide. Sihcon carbide decomposes in fused alkahes such as potassium chromate or sodium chromate and in fused borax or cryohte, and reacts with carbon dioxide, hydrogen, ak, and steam. Sihcon carbide, resistant to chlorine below 700°C, reacts to form carbon and sihcon tetrachloride at high temperature. SiC dissociates in molten kon and the sihcon reacts with oxides present in the melt, a reaction of use in the metallurgy of kon and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new sihcon nitride-bonded type exhibits improved resistance to cryohte. 

Zinc yellow is made by a variety of processes, all based on the reaction of 2inc compounds, chromates, and potassium salts in aqueous solution. If products free of chloride and especially sulfate are desired, they are excluded from the system. In one process, for example, 2inc oxide is swollen with potassium hydroxide and the chromates are added as a solution of potassium tetrachromate [12422-53-6] (194). 

Zirconium reduces almost all oxygen-containing salts. This is the case for alkali hydroxides (accidents with the lithium, sodium and potassium compounds) and zirconium hydroxide, lithium, sodium and potassium carbonates, alkaline sulphates sodium tetraborate and copper (II) oxide. This is true especially for oxidising salts such as alkaline chromates and dichromates, chlorates (accident with potassium salt) and nitrates (accident with potassium salt). 

The effects of various metal oxides and salts which promote ignition of amine-red fuming nitric acid systems were examined. Among soluble catalysts, copperQ oxide, ammonium metavanadate, sodium metavanadate, iron(III) chloride (and potassium hexacyanoferrate(II) with o-toluidine) are most effective. Of the insoluble materials, copper(II) oxide, iron(III) oxide, vanadium(V) oxide, potassium chromate, potassium dichromate, potassium hexacyanoferrate(III) and sodium pentacyanonitrosylferrate(II) were effective. 

The finely divided metal may ignite in contact with a range of oxidants, usually on heating [1], Mixtures of the metal powder with barium chromate and potassium chlorate are used as a pyrotechnic fuse [2],... 

DeNOx (1) A Denox process for removing nitrogen oxides from the gaseous effluents from nitric acid plants. The oxides are reduced with ammonia, over a catalyst containing potassium chromate and ferric oxide. Developed by Didier Werke in the 1980s. 

A technique of developing Aniline Black directly on the fiber was found by Lightfoot in the period between 1860 and 1863. In accordance with this process, the fiber is soaked with aniline, aniline hydrochloride, and sodium chlorate in the presence of an oxidation catalyst (e.g., ammonium vanadate, potassium hexa-cyanoferrate(II)). The compound is developed at 60 to 100°C and then oxidized further with sodium chromate. It should be noted, however, that Perkin had already synthesized a black compound which he called Aniline Black as early as 1856. He oxidized aniline (containing toluidine) with potassium dichromate and separated Aniline Violet from the resulting black mixture (Aniline Black). 

W. Ostwald considers that the presence of the highly oxidized salts—iodates and perchlorates—shows that the deposits were formed in an atm. highly charged with ozone. H. Guyard says the yellow coloration of some samples is due to the presence of potassium chromate and the violet to manganese nitrate. The... 

Preparation of Potassium Chromate. (Perform one experiment on each table.) Melt a mixture of 1 g of potassium carbonate, 1 gof potassium hydroxide, and 2 g of potassium nitrate in an iron crucible by heating with the flame of a burner. While stirring the melt with an iron wire, introduce 1 g of finely comminuted chromite or -0.8 g of chromium oxide into the crucible. Roast the mixture for 5-10 minutes on a blowpipe. Treat the cooled melt with water. Filter the solution and evaporate it until a crystalline film appears. What is the composition of the formed crystals Why was potassium carbonate introduced into the reaction Write the equation of the reaction. 

Methyl 3-Carbethoxyoxy-7-keto-12a-hydroxycholanate.79 A solution of 4 g (8.6 mmoles) of crude methyl 3-carbethoxyoxycholate in 50 ml of acetic acid containing 10 g of sodium acetate trihydrate is treated gradually with a solution of 3 g (0.015 mole) of potassium chromate in 8 ml of water with shaking. After 10 hr at 25° the solution is diluted with water and the product collected by filtration to afford 3.9 g (97%) of methyl 3-carbethoxyoxy-7-keto-12a-hy-droxycholanate, mp 150-158°. Crystallization from methanol gives hard, compact needles or rods mp 157-158° [a]D25 41°. The same substance is also obtained (93 % yield) by conducting the above oxidation in the absence of sodium acetate but stopping the reaction after 6-7 hr. 

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