Chromic acid, oxidation with

Oxidation with chromic acid gives 4-benzoquinone. 

An optically active, secondary terpene alcohol. ( —)-Piperilol is found in various eucalyptus oils and (-l-) piperitol in the oil from a species of Andropogon. A somewhat viscous oil of pleasant smell. It yields piperitone on oxidation with chromic acid. 

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. 

At low temperatures, oxidation with chromic acid gives propynal [624-67-9] C2H2O (14), or propynoic acid [471-25-0] C2H2O2 (15), which can also be prepared in high yields by anodic oxidation (16). 

Constitution. On oxidation with chromic acid, conhydrine yields Z-piperidyl-2-earboxylic acid. It is converted into Z-coniine either by reduction of the iodo-derivative (iodoconiine), C,HijNI, formed by the action of hydriodic acid and phosphorus at 180° or by hydrogenation of the mixture of coniceines produced, when it is dehydrated by phosphorus pentoxide in toluene. These and other observations indicate that the p- ygen atom must occur as a hydroxyl group, in the w-propyl side-chain in either the a- (XV) or (XVI) position, since the y-position would involve... 

Constitution. The alkaloid yields a crystalline semicarbazone, m.p. 169°, a liquid hydrazone, b.p. 154-5°/29 mm., and a liquid oxime, b.p. 160°/12 mm., from which a crystalline picrate, m.p. 106°, can be prepared. The methiodide crystallises in cubes, m.p. 156°. On oxidation with chromic acid in sulphuric acid solution the base yields A -methylpiperdine-... 

Cinchoninone, CigHaaONj, produced by the oxidation of either cinchonine or cinchonidine by chromic acid in presence of sulphuric acid forms pale yellow prisms, m.p. 126-7°, [a]j) -(-71° to -(-76°, is sparingly soluble in light petroleum, easily in ether or chloroform and insoluble in water. The hydrochloride forms minute colourless needles, m.p. 245-7°, [a]r) -(-175-9°. By further oxidation with chromic acid, cinchoninone yields cinchoninic acid and meroquinenine (meroquinene). 

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... 

On reduction with sodium amalgam the acid adds on two atoms of hydrogen the resulting amorphous aeid yields a crystalline dimethyl ester, C2iH2gOgN2, colourless prisms, m.p. 143-7° dec.). On hydrogenation in presenee of platinic oxide as catalyst 2 mols, of hydrogen are absorbed to form the acid, CjgHjgOgNj, colourless prisms, [ajo - -17-7° (HjO). On oxidation with chromic acid the Cjg acid is converted into Wieland s Ci7 acid and Hanssen s Cjg acid. ... 

Oxidation of Vpmicine. On oxidation with chromic acid, vomicine yields three acids (Parts I, IX, XII and XXIII) —... 

On oxidation with chromic acid in dilute sulphuric acid, cevine produces an acid fraction, which on heating at 180° gives a good yield of decevinic acid, C14H14O, m.p. 273-8° (dec.), [a] f° 47-6° (pyridine). 

The mechanism of oxidation with chromic acid has been the object of much study. The pioneering efforts of Westheimer and his group have resulted in the postulation of the mechanism shown in the reaction sequence below... 

By oxidation with chromic acid, this is converted into cyclohexanone-3-carboxylic acid, in which the —CH. OH— group is converted into the —CO— group. This is converted into its ethyl ester and treated with magnesium methyl iodide, and the product, on hydrolysis, yields l-methyl-cyclohexane-l-ol-3-carboxylic acid, which is converted byhydro-bromic acid into 1-bromo-l - methyl - cyclohexane - 3 - carboxylic acid. When this is digested with pyridine, hydrobromic acid is eliminated and yields l-methyl-A -cyclohexane-3-carboxylic acid of the formula—... 

It can be identified by oxidation with chromic acid, when its ketone, thujone, results. This can then be characterised by its oxime, melting at 54 ... 

It forms a phenylurethane which appears to consist of two isomers melting at 82° to 84° and at 94° to 95° respectively. The formation of these two phenylurethanes makes it probable that pinocarveol is itself a mixture of two isomeric compounds. On oxidation with chromic acid pinocarveol yields a compound CjqHj40 which forms two semi-carbazones,. melting at 210° and 320° respectively. 

On oxidation with chromic acid in acetic acid solution, dihydrocarveol yields dihydrocarvone, which has a specific gravity 0 928 at 19°, and refractive index 1-47174. The dihydrocarvone from Zae o-dihydro-carveol is dextro-rotatory, and -vice versa. Its oxime melts at 88° to 89° for the optically active variety, and at 115° to 116° for the optically inactive form. 

On oxidation with chromic acid in acetic acid solution, myrtenol yields a corresponding aldehyde, which has been termed myrtenal. This body has the following characters —... 

By heating carvacrol with alkalis, it is converted into isocuminic-acid, C(jH3(C3Hy)(OH)(COOH), melting at 93°. By oxidation with chromic acid mixture, thymoquinone results. This compound forms-crystalline tables melting at 45° to 46°. 

Vincristine may also be prepared in a semisynthetic process starting from vinblastine. Vinblastine or a salt thereof, preferably the sulfate, is oxidized with chromic acid or with one of its salts at a low temperature, the reaction mixture is neutralized or rendered alkaline and the product is separated therefrom by extraction, the extract is evaporated to dryness, the dry residue is optionally formylated, vincristine, and optionally N-demethylvinblastine also, are Isolated from the product, and the product(s) are optionally converted into their salts preferably into the sulfates, according to U.S. Patent 3,899,493. 

Acenaphthenequinone has been prepared from acenaplithene by oxidation with chromic acid, 1 2 3 with calcium permanganate,4 with air in the presence of catalysts in various solvents,6 6 7 and by the formation of an oxime with amyl nitrite followed by hydrolysis.8... 

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