Potassium dichromate, supported

It is also possible to oxidize o-allylphenols to chromenes with potassium dichromate. The oxidant may be supported on an anionic exchange resin, but it is preferable to dissolve the dichromate in benzene using Adogen 464, a mixture of methyltrialkylammonium chlorides (77TL4167). The oxidation is assumed to proceed through the chromate ester (107) which yields the quinoneallide (79CC836). 

Glass slides with the dimensions of 76 x 26 x 1 mm were used as supports for the multilayers. The slides were thoroughly cleaned by a mixture of sulfuric acid and potassium dichromate at 80 °C for about 2 hours in an ultrasonic bath prior to the films deposition. The initial concentration co of polyelectrolytes in the solution was 1 x 10 2 mole of the repeating units per liter. The pH value of the solution was about 6. Adsorption was carried out at room temperature in open glass beakers of 100 mL without stirring for 20 min. After every deposition step, the glass slides were rinsed three times for 1 min with Millipore Milli-Q water. The substrate was not dried between the adsorption steps. 

Potassium dichromate is another inorganic oxidant that can be supported on alumina and used to convert alcohols into carbonyl compounds. Its chief merit is its selectivity for allylic and benzylic alcohols. For instance, l-phenylpropane-l,3-diol is oxidized selectively to the benzylic oxidation product. 

When both the substance titrated and the titrant undergo electrochemical reactions at the voltage selected, the current wiU decrease (linearly) up to the equivalence point, then increase again with addition of excess titrant, resulting in a V-shaped titration curve. An example of this is the titration of Pb with potassium dichromate in a weakly acidic supporting electrolyte. Dichromate ion is reduced to Cr at the DME with 0 V versus SCE. If —1.0 V is applied to the indicator electrode, both Pb " and Cra07 are reducible, and a V-shaped titration curve will result. If, on the other hand, the applied voltage is —0.2 V, only dichromate ion is reducible, and a reverse L-shaped titration curve results. 

In the case of potassium dichromate we did not observe modifications of UV absorption spectra (which means that no direct bond to DNA bases is formed), while the effect on thermal stability differed "in vivo" and "in vitro", in both cases suggesting a break down of the molecule, supported by viscosity variations, too. These data are in agreement with the mutagenic (14) and carcinogenic (15) action of Cr I compounds and strengthen the hypothesis that Cr effect on the cells is mediated by oxidizing molecules produced by its intracellular reduction to Cr (9). 

In dilute aqueous solution the chief constituent is undoubtedly dichromic acid, HjCr O, and a study of the molecular solution volumes and molecular refraetivities of chromic acid, potassium chromate, and potassium diehromate affords further evidence in support of tliis formula for the acid. ... 

Catalyst samples were prepared and provided by Synetix, a division of Johnson-Matthey. A solution of ammonium dichromate or potassium hydroxide and ammonium dichromate was added to the support (Engelhard A1-3992E, S.A. 200 m g ) and the resulting suspension evaporated to dryness. The solid was then calcined in air at 823 K for 3 hours. The catalyst, with 1% Cr203 by weight, is yellow. The catalyst was pressed into pellets. 

As explained earlier, alkali metal oxides are often used as promoters for chromia-alumina, and it is of some interest to determine the manner in which the promoter interacts with the chromia. Voltz and Weller (29) studied the influence of various amounts of potassium on chromia-alumina, and concluded that potassium stabilizes the chromia against reduction to the state, although the effect was less with chromia-alumina than it was with unsupported chromia. It was postulated that the potassium combined with the supported chromia to form chromate or dichromate, and that the stabilization against reduction was due to the higher stability of potassium chromate or dichromate compared to that of the higher chromium oxides. 

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