Dichromates oxidation

The moderate resistance of DMSO to oxidation permits it to be used as a solvent for oxidations with lead tetraacetate or the 2-nitropropane anion (33,34). Dichromate oxidation and permanganate oxidation have been used for quantitative deterrnination of DMSO (35,36). 

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). 

Oxidation. Benzene can be oxidized to a number of different products. Strong oxidizing agents such as permanganate or dichromate oxidize benzene to carbon dioxide and water under rigorous conditions. Benzene can be selectively oxidized in the vapor phase to maleic anhydride. The reaction occurs in the presence of air with a promoted vanadium pentoxide catalyst (11). Prior to 1986, this process provided most of the world s maleic anhydride [108-31 -6] C4H2O2. Currendy maleic anhydride is manufactured from the air oxidation of / -butane also employing a vanadium pentoxide catalyst. 

The parent compound, cyclic diazomethane , was first obtained from formaldehyde, ammonia and chloramine by dichromate oxidation of the initially formed higher molecular diaziridine-formaldehyde condensation product (61TL612). Further syntheses of (44) started from Schiff bases of formaldehyde, which were treated with either difluoramine or dichloramine to give (44) in a one-pot procedure. Dealkylation of nitrogen in the transient diaziridine was involved (65JOC2108). 

Dichromate oxidation of secondary alcohols produces ketones in good yield, with little additional oxidation. For example, CH,CH2CH(OH)CH3 can be oxidized to CH CH2COCH3. The difference between the ease of oxidation of aldehydes and that of ketones is used to distinguish them. Aldehydes can reduce silver ions to form a silver mirror—a coating of silver on test-tube walls—with Tollens reagent, a solution of Ag1" ions in aqueous ammonia (Fig. 19.3) ... 

Molecular diffusion ( ) has been used in various ways in micro analysis. In Figure 27, is seen the Conway diffusion dish, in which the substance to be tested is placed on the outside, and the reagent is placed in the central cup. The cup is covered, and after a time, the substance being analyzed diffuses into the central cup where it produces an effect which can then be interpreted in various ways. In the Figure, carbon monoxide is being determined. This same method is very useful for alcohol determination, where dichromate oxidizes the alcohol after it diffuses into the dichromate from the blood. 

Dichromate oxidation does tend to give a harsher handle and a less hydrophilic fibre, tending to cause handling problems in subsequent processes such as weaving, and is therefore less suitable for yarn dyeings. The technical merits of dichromate are overshadowed by ecological considerations, however, since chromium compounds in surface waters pose a direct threat to health and are increasingly restricted by water treatment... 

During preparation of acetic acid by acid dichromate oxidation of ethanol according to a published procedure, minor explosions occurred on two occasions after refluxing had been discontinued. This possibly may have involved formation of acetaldehyde (which has an AIT of 140°C) and ingress of air into the reaction vessel as it cooled [1]. Runaway reactions during small scale oxidation of ethanol have apparently been experienced by many teachers, poor initial mixing or starting too cool may be the cause [2],... 

Mixture of 1.35 g Na methoxide (Na in methanol), 3.48 g tropinone (which can be obtained by K dichromate oxidation of tropine), 4 ml dimethylcarbonate and 10 ml toluene. Reflux /2 hour, cool to 0° and add 15 ml water containing 2.5 g NH4CI. Extract with 4X50 ml CHCI3, dry and evaporate in vacuum and dissolve the oil in 100 ml ether. Wash two times with a mixture of 6 ml saturated aqueous K carbonate and 3 ml 3N KOH (dry and evaporate in vacuum the ether to recover unreacted tropinone). Take up the oil which separates in saturated aqueous NH4CI and extract it with CHCI3. Dry and evaporate in vacuum to get an oil which is dissolved in hot acetone. Cool, add a little water and rub to start precipitation of 1.5 g 2-carbomethoxytropinone. This is identical with (IV) of method 1, and can be recrystallized and converted to cocaine as already described. 

Other methods for determining the amount of soil organic matter are available [4], However, they are not as commonly used as is chromate oxidation, which is commonly called the Watley-Black method. Usually, these other methods are both more time-consuming and less accurate than is the dichromate oxidation method. The dichromate oxidation of organic matter is the standard by which all other methods of determining soil organic matter must be compared [4,5],... 

Suggest areas in soil where there might be organic matter that is not determined by dichromate oxidation (refer to earlier chapters). 

It has been demonstrated recently that the dichromate oxidation of wool cystine proceeds as shown in Scheme 5.18. The cystine crosslinks (5.73) are cleaved to give dehydroalanine (5.74) and perthiocysteine (5.75) residues, the latter being readily oxidised by the dichromate ions to yield cysteine-S-sulphonate (Bunte salt) residues (5.76). 

The reaction sequence Is based on the readiness with which a-pinene undergoes oxidation predominantly to the tertiary acetate with Pb(OAc)4.3 4 Dichromate oxidation of the derived alcohol proceeds by way of a second allylic rearrangement to give verbenone without affecting the neighboring stereogenic centers. 

Steric effects dominate in the oxidation of dialkyl, alkyl phenyl and benzal methyl phenyl sulfides to their sulfoxides by quinolinium fluorochromate (QFC) in aqueous acetic acid. QFC oxidation of phenoxyacetic acids has been smdied. Imidazolium dichromate oxidations of a-hydroxy acids have been smdied. ... 

The Collins/Sarett oxidation (chromium trioxide-pyridine complex), and Corey s PCC (pyridinium chlorochromate) and PDC (pyridinium dichromate) oxidations follow a similar pathway as the Jones oxidation. All these oxidants have a chromium (VI), normally yellow, which is reduced to Cr(IV), often green. 

Nitrogen (i) by Kjeldahl digest (ii) elemental analyser, or (iii) dichromate oxidation. 

Fluoro-oct-1-en-3-one (82) has been synthesized by allylic hydroxylation of vinyl fluoride (Scheme 31) [77,78], Oxidation of vinyl fluoride (83) using 0.5 equiv. of Se02 and 2 equiv. of ferf-butyl hydroperoxide with a catalytic amount of acetic acid followed by elimination formed to 2-fluoroalk-1-en-3-ols (84) in 32% overall yield for three steps. Subsequent pyridinium dichromate-oxidation of 84 yielded 2-fluoro-oct-1-en-3-one (83) in 81% (Scheme 31). 

When cyclohexane-1,4-dione reacted with 3-aminocarbazole, the presumed initial double condensation product was dehydrogenated and 212 was actually isolated. Dichromate oxidation of this diamine gave the quinone... 

H2O addn, isooctane extn, SPE cleanup, pyridinium dichromate oxidation, liq-liq partns, SPE cleanup... 

It is used for detg the DEtPh content by saponifiqation with KOH soln the alcohol liberated in the reaction is separated by azeotropic distillation and measured by means of iodometric analysis afte dichromate oxidation... 

Other related work in surface area was the phosporic acid-dichromate oxidation of coke by Riley. In an early paper (2), on the basis of reaction rates on different particles sizes, Riley suggested that coke smaller than 60 mesh had no available internal area. Later (1) Riley reversed himself and suggested that different cokes had different amounts of available internal area. In this paper both vapor absorptions and reactivity measurements were made on different cokes. However, no correlation was found between these two items. 

Recently, Honda and Hirose (13), on the basis of Riley s experiments on coke, suggested that the available internal area of coal in a phosphoric acid-dichromate oxidation should be proportional to the internal area of the coal as determined by a vapor absorption. 

For large-scale operations dichromate oxidation procedures provide precision. Microdistillation and careful temperature and acidity control make dichromate oxidation procedures rapid, accurate, time saving, and well-adapted to a multi-scale operation and automation (27, 28). 

The present method is the result of a study by Cason, Harman, Goodwin, and Allen.6 7 The sequence of electrolytic reduction followed by oxidation has been used for the preparation of 5-bromotoluquinone,8 5-chlorotoluquinone,9 and 3-chlorotolu-quinone.10 The preparation of an intermediate />-aminophenol from the corresponding aromatic nitro compound by electrolytic reduction is a useful general method.11-18 Chloro-/>-quinone has been prepared by acid dichromate oxidation of chlorohydro-quinone 19-22 or 2-chloro-4-aminophenol.23 24 It has been shown that pure chloro-/>-quinone is obtained only with some difficulty when chlorohydroquinone is used.7... 

The submitters report that 2 may be recovered from the mother liquors enriched in the unwanted diastereomer. The mother liquors were saponified to 3/4 as described in section D, followed by dichromate oxidation to 2 In 77-81 yield according to a procedure given for menthone.5 However, this recovery was not checked. 

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