Dichromate oxidation with

For the preparation of the parent substance, cyclic diazomethane (67), formaldehyde, chloramine, and ammonia were reacted. Diaziri-dine formation was successful in about 20% yield the diaziridine condensed with further formaldehyde to high molecular weight products the diaziridine detected by its oxidizing power was nonvolatile. Oxidation with dichromate in dilute sulfuric acid led to gaseous diazirine (67) [Eq. (56)]. It was only investigated in solution. 

The naphthalimide ring system has the drawback of low effectiveness, which is mainly attributable to the low molar extinction coefficient. The industrial synthesis of alkoxynaphthalimides begins with acenaphthene. Chlorination and subsequent oxidation with dichromate give the corresponding naphthalic acids [116], which are converted to the anhydrides on drying. Mild reaction with methyla-mine, followed by reaction with sodium methoxide or sodium ethoxide, gives, e.g., 64 or 65. 

Knicker, H., Hilscher, A., and Muller, P. (2007). How useful is chemical oxidation with dichromate for the determination of black carbon in fire-affected soils Geoderma 142, 178-196. 

The oxidation number of Cr changes from +6 to +3. The solution becomes light green, the colour originating from Cr3+ ions. Some important oxidations with dichromate are as follows ... 

In a run twice this size the checkers observed that at this stage some of the semi-solid material on the top of the stirred solution burned. The burning ceased after a few minutes. The yield of final product was slightly lower. It must be emphasized that careful control of the temperature is necessary during the oxidation with dichromate in order to prevent the reaction from becoming too vigorous. 

Figure 2 shows the results of a second photochemical study. Hand-sheets made from bleached sulfate pulp were first oxidized with dichromate solution and then with chlorous acid following dichromate oxida-... 

Chromate and dichromate are capable of displacing halide from benzylic and allylic halides. Oxidation with dichromate has been performed under traditional conditions (equation 37) with the aqueous sodium salt, or with a quaternary ammonium salt in an aptotic solvent (equation 38). Of the two procedures the first would seem to be preferable from the point of view of simplicity and safety. 

To examine the idea of a long-range transmittance of electronic effects to the iron atom, several ortho-, meta-, and para-substituted phenyl-ferrocenes were prepared and their oxidation potentials studied potentio-metricly by oxidation with dichromate 44). Little and associates concluded from the o-phenylferrocenes that steric effects are relatively unimportant and do not much influence the potential. Likewise, Mason and Rosenblum 47) observed good correlation between potentials for a series of -phenyl-ferrocenes and Op constants. 

Surface oxide formation undoubtedly is involved in the Fe(II)-dichromate titration curves, which Smith and Brandt found to be different when the direction of titration was reversed (Figure 15-2, right). Kolthoff and Tanaka found that the rate of oxidation with dichromate was slow, whereas the rate of reduction with Fe(II) was fast. Ross and Shain found the same sort of behavior and noted also that the rates of oxidation and reduction decreased in more dilute solutions. The oxidized surface in a dichromate solution may be largely covered with adsorbed dichromate, as chromium surfaces have been shown to be in some experiments with radio-chromium, so that it is relatively ineffective as an electron-transfer surface for the Fe(III)-Fe(II) system. 

Benzoin can be oxidized to the a-diketone, benzii, very efficiently by nitric acid or by copper(II) sulfate in pyridine. On oxidation with sodium dichromate in acetic acid the yield is lower because some material is converted into benzaldehyde by cleavage of the bond between two oxidized carbon atoms and activated by both phenyl groups (a). Similarly, hydrobenzoin on oxidation with dichromate or permanganate yields chiefly benzaldehyde and only a trace of benzii (b). 

Oxidations with dichromates can be accomplished in nonaqueous media or in a two-phase system by using phase-transfer reagents. The addition of 1-phenylethanol to a slurry of potassium dichromate and Adogen 464 (methyltrialkylammonium chloride) in benzene heated at 55 °C for 15 h results in an 80% yield of acetophenone. However, 2-octanol gives only a 33% yield of the ketone after being heated at 55 °C for 24 h [651]. Other solvents suitable for the reaction are dichloromethane, chloroform, and carbon tetrachloride, but not hexane [651], Better results are obtained when the alcohol is shaken for 1 min at room temperature with a mixture of a catalytic amount (10%) of tetrabutylammonium bisulfate and sodium dichromate in dichloromethane and aqueous 3 M sulfuric acid [630. ... 

The glycerol content may be determined, if required, by acetylation, or by oxidation with dichromate. 

The sex pheromone structure, 10-methyl-2-tridecanone, was synthesized using the carboxyl group as the source of the methyl branch (lA) (Figure 6). Undecylenic acid was a-propylated and resolved via amides. The procedure followed allowed us to obtain the alcohols,(R)- and (S)-2-propyl-10-undecenol (>99.6% ee). The corresponding bromide was reduced with lithium triethylborohydride (15) then the double bond was converted to a methyl ketone by a) oxymercuration, b) reduction of the C-Hg bond with sodium borohy-dride, and c) oxidation with dichromate. The male southern corn rootworm responds only to the (R)-configuration no biological activity was noted for the (S)-enantiomer. Therefore, in this instance the racemic compound would be predicted to monitor this species adequately. 

Zinc metal can be determined in zinc oxide by means of indirect methods. Zinc is oxidized with dichromate (in an H2SO4 or H3PO4 medium), and then the unreacted part of Cr(VI) is determined with 1,5-diphenylcarbazide [106]. In another version, the sample is dissolved in dil. sulphuric acid in the presence of Fe(III) and 1,10-phenanthroline. The red Fe(n)-phen complex is equivalent to the content of Zn in the zinc oxide studied [107]. 

The bright-red formazans of the compounds obtained from cellulose and starch by oxidation with dichromate were also prepared. 

Lindberg and Theander obtained D-allose, along with small amounts of D-mannose, by hydrolyzing cellulose which had been oxidized with dichromate and then reduced with borohydride, indicating that keto groups were mainly present at C-3, as observed in model experiments under similar conditions. 

Figure 10.1 is a material flow sheet for the first cycle of one form of the Redox process [F3]. Rutonium in the feed was converted to hexavalent plutonyl nitrate Pu 02(N0s)j, by oxidation with dichromate ion Cr2 07 ", as this is the plutonium valence with highest distribution coefficient into hexone. In the decontamination contactor, hexavalent uranium and plutonium nitrates were extracted into hexone solvent, and fission-product nitrates were removed from the solvent by a scrub solution containing aluminum nitrate, sodium nitrate, and sodium dichromate. 

For all types of waters (drinking, surface, waste) oxidation with dichromate in a strongly acid environment of H2SO4 is used (2 hours boiling) the dichromate method. The following reaction takes place ... 

The usud form of oxidation with dichromates is in the presence of sulfuric Mid- and with the sodium or potassium salt. Althou the dichromates exert an oxidizing tendency in the absence of acid, the oxidation reaction can be made to occur much more quickly in the presence of acid, and acid solutions are almost invariably used. Such mixtures react to give oxygen as follows ... 

Apart from gas-phase oxidation, liquid-phase oxidation with dichromate is an expedient process if the chromium-(III)-sulfate by-product can be used as a tanning agent. The largest anthraquinone plant Bayer/ Qsi Germany) with a capacity of 11,000 tpa applies this process. Batch oxidation is carried out with pulverized 94-95% anthracene in a stirred tank reactor with the addition of sodium dichromate and sulfuric add at 60 to 105 °C. The reaction takes between 25 and 30 hours. The yield of anthraquinone, which is produced in purities of around 95%, is over 90%. The purity can be increased to over 99% by recrystallization from nitrobenzene or cyclohexanol/cyclohexanone. 

Ferrari (1949) studied the HSppler method for the chemical determination of alcohol. This is based on oxidation with dichromate in the presence of sulfuric acid, adding iodide, and titrating the iodine with thiosulfate. He studied temperature, time of reaction, order of adding the solutions, volume, and concentration of alcohol and the reagent. Results comparable to those of the pycnometer method were obtained. Cordebard (1939) and Jaulmes (1951) reported better results using a nitric acid-dichromate mixture. 

Fractions of neutral hpids can be easily and accurately determined gravimetrically after elution from the adsorbent [37, 103, 112]. A relatively large sample (>50 mg) is admittedly needed. Triglycerides can be determined by IR-spectrophoto-metry [105]. Smaller amounts are better determined colorimetrically after oxidation with dichromate-sulphuric acid [3, 43, 213] a separate calibration curve is however 4 necessary for each lipid class (see... 

Procedure. First oxidize the monoglycols with periodic acid to aldehydes and distil off the resulting aldehydic compounds. Remove the excess of periodic acid by reduction with hydrogen peroxide in alkaline solutions, and destroy the excess hydrogen peroxide by boiling. Acidify the resulting solution, oxidize with dichromate and in alkaline solution measure polarographically the decrease of dichromate. 

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