• Archives of Pharmacal Research
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• v.8 no.4
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• pp.229-236
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• 1985

Oxidation of presenegenin dimethyl ester triacetate with chromium trioxide in acetic acid yielded two compounds, 11-ketone (IV) and 12-ketone (IV) derivatives. The latter was a main product. On mild alkaline hydrolysis, IV afforded 11-keto-presenegenin dimethyl ester (V), mp 232-$234^{\circ}$, $C_{32}H_{48}O_{8}$, whereas VI did 12-keto-presenegenin dimethyl ester 12, 27-hemiketal (VIII), mp 240-$242^{\circ}$, $C_{32}H_{50}O_{8}$.

• Bulletin of the Korean Chemical Society
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• v.25 no.8
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• pp.1277-1279
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• 2004

• Journal of the Korean institute of surface engineering
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• v.52 no.3
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• pp.111-116
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• 2019

Chromium was coated on a steel substrate by the Cr(III) electroplating method, and corroded at $500-900^{\circ}C$ for 5 h in $N_2/0.1%H_2S-mixed$ gas to study the high-temperature corrosion behavior of the Cr(III) coating in the highly corrosive $H_2S-environment$. The coating consisted of (C, O)-supersaturated, nodular chromium grains with microcracks. Corrosion was dominated by oxidation owing to thermodynamic stability of oxides compared to sulfides and nitrides. Corrosion initially led to formation of the thin $Cr_2O_3$ layer, below which (S, O)-dissolved, thin, porous region developed. As corrosion progressed, a $Fe_2Cr_2O_4$ layer formed below the $Cr_2O_3$ layer. The coating displayed relatively good corrosion resistance due to formation of the $Cr_2O_3$ scale and progressive sealing of microcracks.

• Applied Biological Chemistry
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• v.41 no.4
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• pp.241-245
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• 1998

Two oxidation states of chromium commonly occur in natural soil/water systems, Cr(III) and Cr(VI). The oxidized form, Cr(VI), exists as the chromate ion and is more mobile and toxic than Cr(III). Therefore oxidation of Cr(III) by various Mn-oxides in natural systems is a very important environmental concern. Organic substances can inhibit the Cr(III) oxidation by binding, Cr(III) strongly and also by dissolving Mn-oxides. Most of Cr(III) oxidation studies were carried out using in vitro systems without organic substances which exist in natural soil/water systems. In this study effect of organic acids - oxalate and pyruvate - on Cr(III) oxidation by $birnessite({\delta}-MnO_2)$ was examined. The two organic acids significantly inhibited Cr(III) oxidation by birnessite. Oxalate showed more significant inhibition than pyruvate. As solution pH was lowered in the range of 3.0 to 5.0, the Cr(III) oxidation was more strongly depressed. Addition of more organic acids reduced the Cr(III) oxidation mare extensively. Different inhibition effects by the organic acids could be due to their ability of reductive dissolution of Mn-oxides and/or Cr(III) binding. Organic acids dissolved Mn-oxide during the Cr(III) oxidation by the oxide, Dissolution by oxalic acid was much greater than that by pyruvate, and the dissolution was more extensive at lower pH. Inhibition of Cr(III) oxidation was parallel to the dissolution of Mn-oxide by organic acids. Although the effect of Cr(III) binding by organic acids on Cr(III) oxidation is not known yet, Mn-oxide dissolution by organic acids could be a main reason for the inhibition of Cr(III) oxidation by Mn-oxide in presence of organic acids. Thus oxidation of Cr(III) to Cr(VI) by various Mn-oxides in natural systems could be much less than the oxidation estimated by in vitro studies with only Cr(III) and Mn-oxides.

• Bulletin of the Korean Chemical Society
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• v.23 no.3
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• pp.369-373
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• 2002

The liquid phase oxidation of p-xylene has been carried out with oxygen-enriched gas, and the manganese component was precipitated probably via over-oxidation to $Mn^{4+}$. The precipitation increased with rising oxygen concentration in the reaction gas and occurred mainly in the later part of the oxidation. The activity of the reaction decreased, and the blackening of the product and side reactions to carbon dioxide increased with the degree of precipitation. Precipitation can be decreased with the addition of metal ions, such as cerium, chromium and iron.

• Analytical Science and Technology
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• v.12 no.5
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• pp.447-459
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• 1999

A study was conducted to compare three analytical methods for determination of hexavalent chromium in the welding fume. Precision and accuracy arc documented for colorimetric, ion chromatographic, and inductively coupled plasma-optical emission spectroscopic method. Evidence is presented that welding fume can affect the oxidation of trivalent chromium. A simple sonication extraction method, proposed in this study, instead of hot alkaline extraction has the advantage of minimizing the potential for chromium oxidation.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.118-121
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• 2002

The kinetics and stoichiometry of the reduction of hexavalent chromium (Cr(Ⅵ)) with ferrous iron (Fe(II)) were examined in systems with and without aquifer solids. Cr(Ⅵ) reduction was rapid in the absence of solids, but demonstrated slower and more complex kinetics in the presence of aquifer solids. The aquifer solids removed Fe(II) from solution and a portion of the reducing capacity of Fe(II) was transferred to the aquifer solids. The solid phases were then able to continue to remove Cr(Ⅵ). This suggests in-situ treatment of Cr(Ⅵ) by Fe(II) injection would be feasible in the aquifer environment. In general, re-oxidation of reduced chromium by molecular oxygen was not observed in our systems over time periods of nearly one year.

• Journal of Microbiology and Biotechnology
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• v.22 no.4
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• pp.547-554
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• 2012

Chromium is generated from several industrial processes. It occurs in different oxidation states, but Cr(III) and Cr(VI) are the most common ones. Cr(VI) is a toxic, soluble environmental contaminant. Some bacteria are able to reduce hexavalent chromium to the insoluble and less toxic Cr(III), and thus chromate bioremediation is of considerable interest. An indigenous chromium-reducing bacterial strain, Rb-2, isolated from a tannery water sample, was identified as Ochrobactrum intermedium, on the basis of 16S rRNA gene sequencing. The influence of factors like temperature of incubation, initial concentration of Cr, mobility of bacteria, and different carbon sources were studied to test the ability of the bacterium to reduce Cr(VI) under variable environmental conditions. The ability of the bacterial strain to reduce hexavalent chromium in artificial and industrial sewage water was evaluated. It was observed that the mechanism of resistance to metal was not due to the change in the permeability barrier of the cell membrane, and the enzyme activity was found to be inductive. Intracellular reduction of Cr(VI) was proven by reductase assay using cell-free extract. Scanning electron microscopy revealed chromium precipitates on bacterial cell surfaces, and transmission electron microscopy showed the outer as well as inner distribution of Cr(VI). This bacterial strain can be useful for Cr(VI) detoxification under a wide range of environmental conditions.

• Toxicological Research
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• v.21 no.1
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• pp.15-21
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• 2005

There is now a growing concern about the possible toxicity of heavy metals in cosmetics. Heavy metals can be used as cosmetic ingredients or may be present as low level impurities in some of the raw materials. Chromium derivatives are used as pigments in cosmetics. Chromium is essential and toxic trace elements. Chromium may cause skin allergy. However, the regulations related to cosmetic products give no limit values for Chromium. Hexavalent chromium is significantly more toxic than trivalent chromium. Hexavalent chromium may present a carcinogenic risk at high concentrations. Therefore, it is important to consider oxidation state of chromium when analyze chromium. The purpose of this study is to determine the concentrations of water-soluble trivalent and hexavalent chromium in samples of makeup products, and to assess the safety of cosmetics on the basis of animal sensitization tests using guinea pig. The present study of chromium in 48 makeup products of 12 manufacturers provides a basis for assessing safety of makeup products. Water-soluble hexavalent chromium was not detected in any product. Water-soluble trivalent chromium was detected in only 9 eye shadows out of 48 makeup products, and could not be quantified 3 out of 9 eye shadows. The highest level of water-soluble trivalent chromium was about 10 mg/kg in spite of 90,000 mg/kg of total chromium. The results of animal sensitization tests show that 200 mg/kg of trivalent chromium and 5 mg/kg of hexavalent chromium have no harmful effect. No cross-reaction among these metals was found. Accordingly, the concentrations of water-soluble chromium in makeup products seemed to be safe. The overall results indicate that chromium in cosmetics probably have no significant toxicological effects. However, It is necessary to set guidelines on the maximum permissible concentration of water-soluble chromium in cosmetics.

• Applied Biological Chemistry
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• v.37 no.5
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• pp.414-420
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• 1994

Birnessite, pyrolusite and hausmannite were synthesized and tested for the ability to oxidize Cr(III) to Cr(VI). These oxides differed in zero point of charge, surface area, and crystallinity. The kinetic study showed that Cr(III) oxidation on the Mn-oxide surface is a first-order reaction. The reaction rate was various for different oxide at different conditions. Generally the reaction by hausmannite, containing Mn(III), was faster than the others, and oxidation by pyrolusite was much slower. Solution pH and initial Cr(III) concentration had a significant effect on the reaction. Inhibited oxidation at higher pH and initial Cr(III) concentration could be due to the chance of Cr(III) precipitation or complexing on the oxide surface. Oxidations by birnessite and hausmannite were faster at lower pH, but pyrolusite exhibited increased oxidation capacity at higher pH in the range between 3.0 and 5.0. Reactions were also temperature sensitive. Although calculated activation energies for the oxidation reactions at pH 3.0 were higher than the general activation energy for diffusion, there is no experimental evidence to suggest which reaction is the rate limiting step.