External oxidant method

For many decades, the standard technique for measuring carotenoids has been high-pressure liquid chromatography (HPLC). This time consuming and expensive chemical method works well for the measurement of carotenoids in serum, but it is difficult to perform in human tissue since it requires biopsies of relatively large tissue volumes. Additionally, serum antioxidant measurements are more indicative of short-term dietary intakes of antioxidants rather than steady-state accumulations in body tissues exposed to external oxidative stress factors such as smoking and UV-light exposure. 

Aluminum borate whiskers are produced commercially by an external flux method. Chlorides, sulfates, or carbonates of alkali metals are added to alumina and boric oxide (or boric acid) and the mixture is heated to 800°C-1000°C to produce aluminum borate whisker (length 10-30 pm and diameter 0.5-1.0 pm). It has a melting point of 1440°C, a very low coefficient of thermal expansion, and an excellent chemical resistance toward acids. The aluminum borate whisker was reported to be effective in improving not only the thermal degradation but also the glass transition temperature of epoxy76... 

Other methods, involving neither external oxidation nor reduction, may be classified according to the starting materials employed. 

The total gas flow from the reactor oudet is monitored on-hne by an FTIR analyzer (MKS Multigas 2030) and an EI-MS (V F, H-sense). The FTIR is operated at a cell temperature of 463 K. A sample gas cooler is installed between FTIR and EI-MS to protect the EI-MS from excessive amounts of water in the gas composition. The sample gas cooler is set to 278 K to remove water and other species, e.g., unconverted hydrocarbons, which condense at these conditions. Additionally, an IMR-MS (V F, Air-sense) and a GC-MS (6890 N, Agilent) can be used. The total gas flow is fully oxidized in the flame of a bunsen burner after it leaves the analytics. To quantify the total gas flow that reaches the FTIR, an adapted external standard method is used (Hartmann, 2009 Hartmann et al., 2009 Kaltschmitt, 2012). 

A method to calculate the critical aluminium content for breakaway oxidation has been proposed which is based on Wagner s ideas on selective oxidation in ternary alloys. It focusses on the transition between internal and external oxidation, because after spallation of the oxide the bare metal is exposed again to the atmosphere. The calculation shows that the critical aluminium content is temperature dependent and varies from 0 wt.% at about 1000°C to 3 wt.% at 1300°C. This corresponds to the scatter range reported in the literature for the critical aluminium content. 

Various convenient methods for the synthesis of protected indoles have been reported by several groups [7a-e]. Interesting C-H oxidative coupling reactions of various arenes with alkynes are shown in Eqs. (5.5)-(5.9). These methods allow quick access to a number of functional molecules in good yields via an N-N bond oxidative cleavage or use of an external oxidant. Excellent regioselectivity was achieved by using asymmetrically substituted alkynes. 

Lavis and Ellman reported an efficient method for the preparation of Af-aryl-2//-indazoles 18 by Rh(III)-catalyzed C-H bond addition of azobenzenes to aldehydes without external oxidant (Eq. (5.18)) [13]. In this reaction, the regioselective activation of azobenzenes can be controlled either by electronic or by steric effects, and the azo moiety serves as a nucleophile to trap the initial aldehyde addition product. A wide range of aldehydes and azobenzenes participate in the reaction to afford differently substituted indazoles. An interesting feature of this reaction... 

In 2010, Fagnou and coworkers reported a cascade method for the synthesis of isoquinolones 58 by Rh-catalyzed annulation of Af-methoxybenzamides with internal alkynes [32]. Both symmetrical and unsymmetrical alkynes were examined as the coupling partners (Eq. (5.56)). This external oxidant-free process used a N-O bond to unlock the C-N bond formation and catalyst release. 

A/ -oxidant as an external oxidant. The reaction proceeds efficiently with extremely good substrate scope and significant opportunities for structural diversification. This method provides a diazo compound-free access to this type of products [29]. 

Transition metal-catalyzed C-H activation has proven to be a reliable method for the construction of complex products. However, the requirement of stoichiometric quantities of external oxidants has limited the sustainability of this method. In 2014, Rueping and coworkers [56] developed an oxidative Heck reaction that included recycling of the metal catalyst through a photoredox process. As a continuation of their work on photoredox catalysis, they recently disclosed a new combined photoredox- and palladium-catalyzed system useful for indole... 

Method for the external generation of oxidizing and reducing agents in coulometric titrations. 

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