Dehydrogenative aromatizations oxide

Besides stmctural variety, chemical diversity has also increased. Pure silicon fonns of zeolite ZSM-5 and ZSM-11, designated silicalite-l [19] and silicahte-2 [20], have been synthesised. A number of other pure silicon analogues of zeolites, called porosils, are known [21]. Various chemical elements other than silicon or aluminium have been incoriDorated into zeolite lattice stmctures [22, 23]. Most important among those from an applications point of view are the incoriDoration of titanium, cobalt, and iron for oxidation catalysts, boron for acid strength variation, and gallium for dehydrogenation/aromatization reactions. In some cases it remains questionable, however, whether incoriDoration into the zeolite lattice stmcture has really occurred. 

Crich and Rumthao reported a new synthesis of carbazomycin B using a benzeneselenol-catalyzed, stannane-mediated addition of an aryl radical to the functionalized iodocarbamate 835, followed by cyclization and dehydrogenative aromatization (622). The iodocarbamate 835 required for the key radical reaction was obtained from the nitrophenol 784 (609) (see Scheme 5.85). lodination of 784, followed by acetylation, afforded 3,4-dimethyl-6-iodo-2-methoxy-5-nitrophenyl acetate 834. Reduction of 834 with iron and ferric chloride in acetic acid, followed by reaction with methyl chloroformate, led to the iodocarbamate 835. Reaction of 835 and diphenyl diselenide in refluxing benzene with tributyltin hydride and azobisisobutyronitrile (AIBN) gave the adduct 836 in 40% yield, along with 8% of the recovered substrate and 12% of the deiodinated carbamate 837. Treatment of 836 with phenylselenenyl bromide in dichloromethane afforded the phenylselenenyltetrahydrocarbazole 838. Oxidative... 

More recently, chemiluminescence detectors based on redox reactions have made possible the detection of many classes of compounds not detected by flame ionization. In the redox chemiluminescence detector (RCD), the effluent from the column is mixed with nitrogen dioxide and passed across a catalyst containing elemental gold at 200-400°C. Responsive compounds reduce the nitrogen dioxide to nitric oxide. The nitric oxide is reacted with ozone to give the chemiluminescent emission. The RCD yields a response from compounds capable of undergoing dehydrogenation or oxidation and produces sensitive emissions from alcohols, aldehydes, ketones, acids, amines, olifins, aromatic compounds, sulfides, and thiols. 

Ethylbenzene (EB) is the precursor molecule for production of styrene monomer. It may be synthesized via alkylation of benzene and is also produced as a component of the C8 aromatics fractions obtained from catalytic crackers and reforming units (4). EB is converted to styrene via dehydrogenative or oxidative routes. As much as... 

This method is well suited to the formation of symmetrical pyrazines, " but if both diketone and diamine are unsymmetrical, two isomeric pyrazines are formed. The dihydro-pyrazines can be dehydrogenated and they will also react with aldehydes and ketones, with introduction of another alkyl group at the same time as achieving the aromatic oxidation level. ... 

In 2013, AstraZeneca researchers reported an application of copper-catalyzed aerobic dehydrogenative aromatization in the 120 g scale synthesis of AZD8926, a drug candidate for the treatment of central nervous system disorders (Scheme 5.6) [29]. This aerobic dehydrogenation process was determined to be superior for large-scale implementation over other oxidation methods, such as a benzoquinone-mediated oxidation and various protocols using peroxide-based... 

Stabilization process which is carried out in air (oxidative stabilization) constitutes the first and very important operation of the conversion of the PAN fiber precursor to carbon as well as activated carbon fiber. During stabilization, the precursor fiber is heated to a temperature in the range of 180-300 °C for over an hour. Because of the chemical reactions involved, cyclization, dehydrogenation, aromatization, and oxidation and cross linking occur and as a result of the conversion of CH N bonds to C=N bonds fully aromatic cyclized ladder type structure forms [36, 49]. 

These oxidations are, in fact, dehydrogenations. Aromatizations of 6-membered rings and the formation of carbonyl groups from alcohols fall into this class of reactions, for which a variety of reagents are known in the literature. 

While numerous hterature deals with oxygenation of sp C—H bonds, reviews that focus, at least partially, on the oxidation of aromatic sp C—H bonds are scarce [11-14], The aim of this chapter is to give the reader an overview on the current state of the art in the field of the selective aromatic oxidation. The scope of this review is hmited to aromatic C—H bond oxygenation and oxidative dehydrogenation, that is, to the formation of C—O and C=0 bonds with retention of ring C—C... 

This oxygenation reaction proceeds under milder conditions as compared to conventional methods. Despite the lower reactivities, VO(OR)3 and VO(acac>2 can be employed as an oxidant, although a stoichiomettic amount is required in each case. Use of a,p-unsaturated ketones leads the different reaction routes. 2-Cyclohexen-l-ones 54 undergo dehydrogenative aromatization to give the aryl alkyl ethers 55 [105]. More than 2 equiv. of VO(OR)Cl2 are required to complete the reaction, since the oxovanadium(V) compound is a one-electron oxidant. Isophorone is also oxidatively aromatized to the aryl ether 56 with the migration of the methyl group (Scheme 2.45). 

Alkyl groups attached to aromatic rings are oxidized more readily than the ring in alkaline media. Complete oxidation to benzoic acids usually occurs with nonspecific oxidants such as KMnO, but activated tertiary carbon atoms can be oxidized to the corresponding alcohols (R. Stewart, 1965 D. Arndt, 1975). With mercury(ll) acetate, allyiic and benzylic oxidations are aJso possible. It is most widely used in the mild dehydrogenation of tertiary amines to give, enamines or heteroarenes (M. Shamma, 1970 H. Arzoumanian. 1971 A. Friedrich, 1975). 

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