Oxygen acceptor

The selectivity for (/ ,/ )( ,S)-10 has been rationalized by invoking a synperiplanar enolate species whose conformation is enforced by a donor(enolate oxygen)- acceptor) peril uo-rophenyl) interaction depicted in structure N47. Infrared and variable temperature NMR spectroscopic studies of the neutral precursor complex 8 support the existence of such a donor-acceptor interaction. 

In a recent series of experiments, Suksangpanya et al. [67] have investigated the interactions between pyrimidine bases and [Cu(Lkl)]2+ cations. Amidino-O-alky-lureas contain an A-D-D sequence, similar to that of guanine. The only difference lies in the oxygen acceptor, which is part of an ether linkage in the amidino-0-alkylurea but part of a carbonyl functionality in guanine. Despite this difference, the formation of a triple complementary interaction between amidino-O-alky-lurea and cytosine, which has a D-A-A sequence was thought to be feasible. 

Iu search for efficieut aud greeuer processes over the past few years various heterogeneous catalysts such as titanium incorporated mesoporous molecular sieves [45,46], Schiff-base complexes supported on zeolite [47] and Zn(II)-Al(III) layered double hydroxide (LDH) [48], oxomolybdenum(VI) complexes supported on MCM-41 and MCM-48 [49], polyoxometallate supported materials [50], Co and Mn-AlPO s [51] etc. have been developed and studied for the catalytic epoxidatiou of a-pinene. Many of these processes suffer from drawbacks and limited applicability due to the poor conversion and also the selectivities. Sacrificial aldehydes are often used as an oxygen acceptor in such processes to achieve reasonable yield and selectivities but, this procedure leads to an increase in the E-factors and decrease in the atom economy [51]. 

Oxo species (M = O) are almost unknown in Rh and Ir chemistry with the exception of the unique terminal iridium oxo complex, [Ir = 0(mes)3] (mes = 2,4,6-trimethylphenyl) [91]. This compound surprisingly displays httle reactivity towards organic substrates, despite its high formal oxidation state. It only oxidizes the most reactive oxygen acceptors such as phosphanes or arsanes [92]. 

Figure 1 gives examples of the substrates mentioned above. They are divided into two groups (1) substrates which have been found to give rise to the same addition products, A02, in direct and indirect photooxygenation reactions, and (2) substrates which have been studied so far only as oxygen acceptors in type II indirect photooxygenation reactions. 

Recently, sulfides, 421, have been investigated as oxygen acceptors.277 When subjected to the same conditions as were applied to sulfoxides, a much faster oxygen consumption occurs which results in the formation of sulfoxides (422) in approximately quantitative yields after consumption of one-half mole of 02 per mole sulfide according to the overall reaction... 

In sulfite we have, apparently, a reducing agent which can function both as an oxygen acceptor and an electron acceptor and can serve as its own trap for these active Cr(IV) and Cr(V) intermediates. We have carried out the kinetics of this reaction at pH 5 in an acetate buffer, where, according to the literature, the species present in solution are HCrOf for the chromate and HSO3- for the bisulfite. The kinetics follow the stoichiometry... 

Diphenylbenzo[c]furan is one of the fastest singlet oxygen acceptors known and has become a standard compound in preparative and kinetic studies in the O2 ( Ag) field its disappearance can easily be followed either by measuring the absorbance in the 415 nm region or by fluorescence emission (e.g., at 458 nm) Table VIII summarizes work where 138 has been used either for preparative purposes or for mechanistic investigations. 1 7.342-349,3 52,354-3 59,362-394... 

Hydrogen (or electron) donors, coenzymes and electron carriers involved in the monooxygenase reactions are listed in Table 1. In some monooxygenase reactions, the substrate itself serves as an electron donor as well as an oxygen acceptor [Eq.(6)],... 

Dioxygenases are defined as a group of enzymes that catalyze the incorporation of two atoms of molecular oxygen into the substrate. In most cases, one substrate acts as an oxygen acceptor and a single molecule of the substrate receives 2 atoms of oxygen as shown in Eq. (8),... 

Finally, catalytic hydrogen production from manganese porphyrin complexes using triphenylphosphine as an oxygen acceptor has been demonstrated.98... 

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