Sample preparation oxidation reactions

CO2 reference standard. A special interface, employing the necessary oxidation and reduction reaction chambers and a water separator, was used employed. For standards of 5-nonanone, menthol and (/ )-"y-decalactone, they were able to determine the correct ratios, with relatively little sample preparation. The technical... 

Like other 2,2-diaryltrichloroethanes, DFDT undergoes dehydrohalogenation in the presence of a base to yield l,l-dichloro-2,2-bis(p-fluorophenyl)-ethylene. The rate of this reaction has been found to be directly proportional to the temperature, and the rate constant for DFDT is approximately one seventh that for DDT at ordinary temperatures (18, 110). This ethylene derivative has been oxidized by the use of chromic anhydride to p,p -difluorobenzophenone, a sample of which did not depress the melting point of an authentic sample prepared by a different route (10). 

Heat-flow calorimetry may be used also to detect the surface modifications which occur very frequently when a freshly prepared catalyst contacts the reaction mixture. Reduction of titanium oxide at 450°C by carbon monoxide for 15 hr, for instance, enhances the catalytic activity of the solid for the oxidation of carbon monoxide at 450°C (84) and creates very active sites with respect to oxygen. The differential heats of adsorption of oxygen at 450°C on the surface of reduced titanium dioxide (anatase) have been measured with a high-temperature Calvet calorimeter (67). The results of two separate experiments on different samples are presented on Fig. 34 in order to show the reproducibility of the determination of differential heats and of the sample preparation. 

Recently, we reported that an Fe supported zeolite (FeHY-1) shows high activity for acidic reactions such as toluene disproportionation and resid hydrocracking in the presence of H2S [1,2]. Investigations using electron spin resonance (ESR), Fourier transform infrared spectroscopy (FT-IR), MiJssbauer and transmission electron microscopy (TEM) revealed that superfine ferric oxide cluster interacts with the zeolite framework in the super-cage of Y-type zeolites [3,4]. Furthermore, we reported change in physicochemical properties and catalytic activities for toluene disproportionation during the sample preparation period[5]. It was revealed that the activation of the catalyst was closely related with interaction between the iron cluster and the zeolite framework. In this work, we will report the effect of preparation conditions on the physicochemical properties and activity for toluene disproportionation in the presence of 82. ... 

A number of hydrolysis products of chloroaluminafe salfs have been defecfed using FAB MS. The problem here is that under some circumstances FAB MS can provide only a restricted view on the surface of fhe sample that is more likely to be oxidized or hydrolyzed rather than the average sample [13]. Nevertheless, this problem is not directly related to MS itself, but rather to a problem of proper sample preparation. Inert conditions during sample preparation and construction of special sample inlet chambers for MS can help avoid fhese reacfions. The addition of phosgene was suggested to reduce problems encountered with such side reactions [22], but here the problems encountered in working with an extremely toxic chemical have to be taken into account. 

The solution to the problem was discovered when a titrated sample (clear solution) was left on the bench and, after a period, it started changing back to a faint yellow color. We hypothesized that air oxidation may have caused that effect and, consequently, air may have interfered with analysis. Standard samples prepared and purposely delayed during the analysis showed that end-point volumes were larger, indicating that some of the iodide ions turned into free-iodine by air oxidation which, in turn, required more thiosulfate for titration and, therefore, larger end-point volume. The following chemical equations obtained from the literature 8) show what happens before, during, and after titration. The reaction of a chlorinated isocyanuric acid compound with potassium iodide in acidic pH is ... 

A methoxyaldehyde, m.p. 52-53°, of unassigned structure is reported in the patent literature [6] as the product from the reaction of 2-methoxy-5,6,7,8-tetrahydronaphthalene with N-methylformanilide and phosphorus oxychloride. This reaction in our hands gave a 50% yield of methoxyaldehyde (VII), m.p. 51 6-52°, whioh was oxidized with potassium permanganate in acetone solution to 3-methoxy-5,6,7,8-tetrahydro-2-naphthoic acid. The structure of the latter was established by mixture m.p. with an authentic sample prepared [7] by converting 3-hydroxy-5,6,7,8-tetrahydro-2-naphthoic acid to the... 

Finally, Rong and coworkers discuss the roll of surface oxygen on the MCS process75. Rong employed a lab-scale stirred bed reactor and then applied XPS to analyze the silicon samples before and after the reaction. The reactivity of silicon depended on the initial thickness of the native oxide on the silicon. After the reaction the surfaces of all of the samples were mostly covered with Si02. There was no observed correlation between the surface and bulk O content. XPS analysis showed the presence of Al, Ca and Ti impurities in some samples. Titanium on the surface appeared to increase the reactivity, whereas Ca decreased the selectivity of Di formation. Addition of ZnO to the silicon before CuCl improved reactivity and also decreased the induction period of the reaction. XPS studies of samples prepared in this manner exhibited a lower Zn surface concentration compared to the samples where CuCl, Si and ZnO were mixed together. 

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