Potassium dichromate , oxidation

Pyridine carboxamide [98-92-0] (nicotinamide) (1) and 3-pyridine carboxylic acid [59-67-6] (nicotinic acid) (2) have a rich history and their early significance stems not from their importance as a vitamin but rather as products derived from the oxidation of nicotine. In 1867, Huber prepared nicotinic acid from the potassium dichromate oxidation of nicotine. Many years later, Engler prepared nicotinamide. Workers at the turn of the twentieth century isolated nicotinic acid from several natural sources. In 1894, Su2uki isolated nicotinic acid from rice bran, and in 1912 Funk isolated the same substance from yeast (1). 

A synthetic protocol involving condensation of 302 and oximes 345 or 348 followed by potassium dichromate oxidation was applied to l-(pyrid-2 -yl)propane-i,2-dione-l-oxime 346 and 2,3/4-pentanetrione-3-oxime 349 to provide the ligands phenanthrolin-2-yl-pyrid-2-yl-methanone 347 and di-(phenathrolin-2-yl)-methanone 350, respectively (Scheme 74). 

Under hot, acidic conditions, potassium dichromate oxidizes practically all organic substances as well as a number of inorganic components and ions. The level of oxidation depends on the type and concentration of the organic materials, the concentration of the potassium dichromate and sulphuric... 

Potassium dichromate oxidation of ethanol to acetic acid is the basis for the original breath alcohol screening test used by law enforcement agencies to determine a person s blood alcohol content. The test is based on the difference in color between the dichromate ion (reddish orange) in the reagent and the chromium(lll) ion (green) in the product. Thus, color change can be used as a measure of the quantity of ethanol present in a breath sample ... 

Following the published procedure,oxidation of 5-hydrox)onethyl-2-furfural (HMF) with the DMSO-potassium dichromate oxidative complex was performed without sonica-tion. The desired dialdehyde was obtained in 58% yield after 5 h at lOO C. Using Acharya s... 

Of little use commercially except as a route to anthraquinone. For this purpose it is oxidized with acid potassium dichromate solution, or better, by a catalytic air oxidation at 180-280 C, using vanadates or other metal oxide catalysts. 

Oxidation, (i) Dissolve 5 g. of potassium dichromate in 20 ml. of dil. H2SO4 in a 100 ml. bolt-head flask. Cool and add 1 ml. of methanol. Fit the flask with a reflux water-condenser and warm gently a vigorous reaction soon occurs and the solution turns green. The characteristic pungent odour of formaldehyde is usually detected at this stage. Continue to heat for 3 minutes and then fit the flask with a knee-tube (Fig. 59, p. 100) and distil off a few ml. Test the distillate with blue litmus-paper to show that it is definitely acid. Then apply Test 3 p. 350) for formic acid. (The reflux-distillation apparatus (Fig. 38, p. 63) can conveniently be used for this test.)... 

By the oxidation of secondary alcohols with potassium dichromate and dilute sulphuric acid, for example ... 

The methyl group of -nitrotoluene is activated by the para nitro group. -Nitrotoluene is oxidized to -nitrobenzoic acid [62-23-7] by potassium hexacyanoferrate(III) in alkaline solution, potassium permanganate, or potassium dichromate. -Nitrotoluene is converted to -nitrobenzaldehyde... 

The estimation of alkoxy groups is not such a simple task. One method (26,68) involves hydrolysis and oxidation of the Hberated alcohol with excess standard potassium dichromate solution. The excess may then be estimated iodometrically. This method is suitable only for methoxides, ethoxides, and isopropoxides quantitative conversion to carbon dioxide, acetic acid, and acetone, respectively, takes place. An alternative method for ethoxides is oxidation followed by distillation, and titration of the Hberated acetic acid. 

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. 

Chlorate Analysis. Chlorate ion concentration is determined by reaction with a reducing agent. Ferrous sulfate is preferred for quaHty control (111), but other reagents, such as arsenious acid, stannous chloride, and potassium iodide, have also been used (112). When ferrous sulfate is used, a measured excess of the reagent is added to a strong hydrochloric acid solution of the chlorate for reduction, after which the excess ferrous sulfate is titrated with an oxidant, usually potassium permanganate or potassium dichromate. 

The primary routes of entry for animal exposure to chromium compounds are inhalation, ingestion, and, for hexavalent compounds, skin penetration. This last route is more important in industrial exposures. Most hexavalent chromium compounds are readily absorbed, are more soluble than trivalent chromium in the pH range 5 to 7, and react with cell membranes. Although hexavalent compounds are more toxic than those of Cr(III), an overexposure to compounds of either oxidation state may lead to inflammation and irritation of the eyes, skin, and the mucous membranes associated with the respiratory and gastrointestinal tracts. Skin ulcers and perforations of nasal septa have been observed in some industrial workers after prolonged exposure to certain hexavalent chromium compounds (108—110), ie, to chromic acid mist or sodium and potassium dichromate. 

In 1885, from a detailed study of juglone (52) it was proposed that its stmcture was 5-hydroxy-l,4-naphthoquinone (9). This stmcture was confirmed by oxidizing 1,5-dihydroxynaphthalene with potassium dichromate in sulfuric acid (53). Juglone occurs in walnuts as a glycoside of its reduced form, 1,4,5-trihydroxynaphthalene (54). Later it was deterrnined that the sugar is in the 4-position (10) (55). 

Appropriate pyrido[2,3-d]pyrimidin-5-ones with formyl groups in the 6-position have been oxiized to piromidic (68) and pipemidic (69) acids, or to intermediates for these, using moist silver oxide, chromium trioxide (potassium dichromate), potassium permanganate or, alternatively, sodium chlorite/hydroxylamine-O-sulfonic acid. 6-Acetyl groups have been similarly oxidized using sodium hypobromite in aqueous dioxane, whilst 2-acetyl groups give dimethylaminomethylene derivatives en route to 2-pyrazolylpyrido[2,3-d]pyrimidines. 

Thymoquinone has been prepared directly from thymol by sulfonating and oxidizing the sulfonation mixture with manganese dioxide or potassium dichromate the same process has been successfully applied to carvacrol. The oxidation of sa ts of aminothymol with dichromate, ferric chloride, or nascent bromine also leads to satisfactory yields of thymoquinone. The above procedure is based on the observation that the diazonium salt obtained from aminothymol is almost quantitatively con-... 

By the oxidation of furfural with potassium dichromate and sulfuric acid in 75 per cent yield. Hurd, Garrett, and Osborne, J. Am. Chem. Soc. 55, 1084 (1933). 

Strychnine, brucine Oxidation is performed with potassium dichromate solution This oxidizes brucine to the o-qumone which can then be separated chromatographically [17]... 

Atropine causes dilation of the pupil of the eye. A drop or two of an aqueous solution, containing 1 part in 130,000 parts of water, introduced into the eye of a cat is sufficient to produce this effect. When warmed with sulphuric acid and a small crystal of potassium dichromate, atropine develops a bitter almond odour. Evaporated to dryness on a water-bath with concentrated nitric acid, it gives a residue which becomes violet on adding a drop of sodium hydroxide solution in alcohol (Vitali s test). With a solution of mercuric chloride atropine gives a yellow to red precipitate of mercuric oxide. 

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