Non-oxidative conversion

Non-oxidative conversion of a tetrahydro-)8-carboline into a 3,4-dihydro derivative has also been described. Dehydration of 1-hydroxymethyl-1,2,3,4-tetrahydro-j8-carboline (146) yielded 1-methyl-3,4-dihydro-j8-carboline (135). Harmaline and l-methyl-3,4-dihydro-j8-carboline-3-carboxylic acid were obtained in an analogous manner. ... 

The carbon conversion efficiency is emphasized here because (for non-oxidative conversion processes) nc provides an excellent measure of how well the energy and chemical content of the solid fuel feedstock is converted to gaseous fuels and chemicals. 

A most important clue to the nature of the steps between pentose phosphate and hexosemonophosphate, and thus to the role of the pentose phosphate pathway in photosynthesis, came from our discovery in 1953 of sedoheptulose 7-phosphate as the first product formed from pentose phosphate. The enzyme transketolase had been purified from rat liver and spinach in my laboratory and crystallized from yeast by Racker and his coworkers and the two laboratories simultaneously discovered that this enzyme contained thiamine pyrophosphate as its functional group, f Isotope studies in my laboratory showed that sedoheptulose was formed by the transfer of a C2 group ( active glycolaldehyde ) from one molecule of pentose phosphate to another, and that the reaction was fully reversible thus sedoheptulose 7-phosphate was also a Ca-donor. In addition, Racker s laboratory made the important finding that fructose 6-phosphate would also yield active glycolaldehyde, and Arturo Bonslgnore and his coworkers discovered that rat liver extracts catalyzed the rapid non-oxidative conversion of hexose phosphate to sedoheptulose phosphate. ... 

Secondary alicyclic amines, such as pyrrolidine and piperidine, have many properties typical of the corresponding aliphatic amines. Metabolic oxidation at secondary alicyclic nitrogens results in the formation of hydroxylamines, which may then undergo enzymic or non-enzymic conversion to nitrones, and in some cases to nitroxide radicals. For example, the 2-substituted piperidino derivative (- )-anabasine (1), a tobacco alkaloid, is metabolized initially to a hydroxylamine (2) and then to the nitrone (3), when incubated with liver and... 

TPP-dependent enzymes catalyze either simple decarboxylation of a-keto acids to yield aldehydes (i.e. replacement of C02 with H+), or oxidative decarboxylation to yield acids or thioesters. The latter type of reaction requires a redox coenzyme as well (see below). The best known example of the former non-oxidative type of decarboxylation is the pyruvate decarboxylase-mediated conversion of pyruvate to acetaldehyde and C02. The accepted pathway for this reaction is shown in Scheme 10 (69MI11002, B-70MI11003, B-77MI11001>. 

These compounds have been obtained by cyclization of the appropriate reduced bilin but the resulting conversions operate non-oxidatively and are acid catalyzed. 

In the following sections some examples are given of the ways in which these principles have been utilized. The first example is the use of these techniques for the low temperature preparation of oxide ceramics such as silica. This process can also be used to produce alumina, titanium oxide, or other metal oxides. The second example describes the conversion of organic polymers to carbon fiber, a process that was probably the inspiration for the later development of routes to a range of non-oxide ceramics. Following this are brief reviews of processes that lead to the formation of silicon carbide, silicon nitride, boron nitride, and aluminum nitride, plus an introduction to the synthesis of other ceramics such as phosphorus nitride, nitrogen-phosphorus-boron materials, and an example of a transition metal-containing ceramic material. 

Compared with the common high-temperature conversion of natural gas and further carbon oxide conversion on a catalyst [131], the current process promotes process simplification the reaction is implemented at relatively low temperature (860-900 °C instead of 1400-1600 °C for existing non-catalytic processes of methane conversion) and an additional unit for catalytic conversion of carbon oxide is excluded (in NH3 production). 

Test reaction. Non-oxidative dehydrogenation experiments were carried out in an automated apparatus as described by Stohbe et al [5]. Calculations of conversion, selectivity to product i and yield of product i were carried out in the same manner as was done earlier [5]. 

Difficulties are encountered in determining NO2 using the ozone-chemiluminescence technique due to the non-specific conversion of several nitrogen oxides/oxyacids on the Mo catalyst. Use of FeS04 f°r N02-to-N0 conversion has been described, but humidity-dependent sorption/desorption effects have been reported, e.g., PAN (11). Alternatively, a commercial NO2 analyzer based on surface chemiluminescence of NO2 in the presence of a luminol solution, has been introduced which exhibits the requisite sensitively and selectivity. 

The main drawbacks of the non-oxidative dehydrogenation reaction can be summarized as, the thermodynamic limitation, the low conversion rate, the need for recovery of unreacted ethylbenzene, the high energy consumption, and deactivation of the catalyst. Thus in recent years several alternatives to overcome those problems have been investigated. 

Capsaicin and capsaicinoids undergo Phase I metabolic bioconversion to catechol metabolites via hydroxylation of the vanillyl ring moiety (Lee and Kumar, 1980 Miller et al, 1983). Metabohsm involves oxidative, in addition to non-oxidative, mechanisms. An example of oxidative conversion involves the liver mixed-function oxidase system to convert capsaicin to an electrophilic epoxide, a reactive metabolite (Olajos, 2004). Surh and Lee (1995) have also demonstrated the formation of a phenoxy radical and quinine product the quinine pathway leads to formation of a highly reactive methyl radical (Reilly et al, 2003). The alkyl side chain of capsaicin also undergoes rapid oxidative deamination (Wehmeyer et al, 1990) or hydroxylation (Surh et al, 1995 Reilly et al, 2003) to hydroxycapsaicin as a detoxification pathway. An example of nonoxidative metabolism of capsaicin is hydrolysis of the acid-amide bond to yield vanillylamide and fatty acyl groups (Kawada et al, 1984 Oi et al, 1992). 

It is also possible to synthesize amines in a sequence of reactions where the non-isohypsic conversion (reduction) occurs at the nitrogen atom and the oxidation state of the carbon attached to it is not affected ... 

The good activity and the almost 100% selectivity to aromatics (mainly is benzene and toluene) have been obtained for the conversion of CH4 to aromatics over Mo(Vl) /HZSM-5 catalysts as reported previously [2-3]. CH4 activation under non-oxidizing conditions over bifunctional Mo(Vl)/HZSM-5 is initiated by CH3+ carbonium ion formation and the CH3+ further forms CH2 carbene active transients as proposed in [2, 3], The reaction mechanism suggested is as follows ... 

The initial photochemical step, (211) to (212), can be most simply viewed as a perturbed 6e electrocy-clic process, suggesting a trans configuration via conrotation for die dihydrophenanthrene intermediate (212). In support of this hypothesis, the stabilization of (216) by tautomerism to (217) in the photolysis of diethylstilbestrol (214), followed by ozonolysis, aiffor d only the racemic form of 1,2,3,4-buta-netetracarboxylic acid (218).The majority of dihydrophenanthrenes, however, are thermally unstable and undergo conversion to phenanthrenes (under oxidative or non-oxidative conditions) or l -H shifts to isomeric 9,10-dihydrophenanthrenes. ... 

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