Quinones hydrogen peroxide synthesis

Quinones in Hydrogen Peroxide Synthesis and Cataiytic Aerobic Oxidation Reactions... 

A hydrogen peroxide and acetic acid mixture is also used in the following reactions carbon-carbon bond break [50], aromatic hydrocarbon and phenol oxidation to n-quinones [51], 2,6-dihaloanilines oxidation to nitroso-compounds and synthesis of N-oxides of pyridine... 

Use of transition metal catalysts opens up previously unavailable mechanistic pathways. With hydrogen peroxide and catalytic amounts of methyl trioxorhe-nium (MTO), 2-methylnaphthalene can be converted to 2-methylnaphtha-l,4-qui-none (vitamin K3 or menadione) in 58 % yield and 86 % selectivity at 81 % conversion (Eq. 10) [43, 44]. Metalloporphyrin-catalyzed oxidation of 2-methylnaphtha-lene with KHSOs can also be used to prepare vitamin K3 [45]. The MTO-catalyzed process can also be applied to the synthesis of quinones from phenols [46, 47]. In particular, several benzoquinones of cardanol derivatives were prepared in this manner [48], The oxidation is thought to proceed through the formation of arene oxide intermediates [47]. 

A model system for the synthesis of lignin-like polymers showed that jols would react with the quinone-methlde intermediates in this system by a 1-6 addition (J ). Utilizing this model system, chloroanilines were copolymerized with coniferyl alcohol in the presence of horseradish peroxidase Type II enzyme, hydrogen peroxide, vanillyl alcohol initiator and pH 7.2 buffer (J57). The mechanism of this copolymerization reaction is shown in Equation 36. The... 

Quinone Mediated Stabilization of a Palladium Catalyst for the Synthesis of Hydrogen Peroxide from Carbon Monoxide, Water and Oxygen... 

An improved method for the synthesis of hydrogen peroxide from carbon monoxide, water and oxygen catalyzed by palladium complexes in presence of a quinone co-catalyst is described. The use of 1,4-naphthoquinone and 1,10-phenanthroline as palladium ligand resulted in a marked catalyst stabilization against deactivation processes such as polynuclear species formation and Pd-black precipitation, which are very fast operating in the absence of quinone. 

The same quinones series was tested in the presence of oxygen (CO/H,0/0,) under the reaction conditions suitable for the synthesis of hydrogen peroxide. 

Table 2 reports the catalytic activities of a series of palladium complexes with the bidentate nitrogen ligands in the synthesis of hydrogen peroxide carried out in presence or in absence of the selected quinone 8 (used in catalytic amount). 

The use of palladium complexes witli 1,10-phenanthroline in the presence of a catalytic amount of a suitable quinone, provides a stable and efficient catalyst for the synthesis of hydrogen peroxide from carbon monoxide, oxygen and water. 

Prior to the discovery of the aryl-Heck reaction (Chapter 72), the direct Pd-promoted oxidative cyclization of diaryl amines to carbazoles was well known. In 1975 Akennark reported this reaction (Scheme 1, eqnation 1) [1], In addition, A -phenylanthranUic acid gave carbazole-l-carboxylic acid (60%). Miller and Moock used Pd(OAc)j to cyclize 6-anilino-5,8-dimethylisoquinoIine to eUipticine in low yield [2]. The second advance in this chemistry was reported independently by Bittner [3] and Furukawa [4], who described the Pd-mediated (stoichiometric) oxidative conversion of 2-anilino-l,4-benzoquinones and 2-anilino-l,4-naphthoquinones to the corresponding carbazole-l,4-diones and benzo[ ]carbazole-l,6-diones (equations 2, 3). Furukawa s studies included syntheses of several carbazolequinone alkaloids. In 1995 Akermark and colleagues developed catalytic versions (i.e., using tert-butyl hydrogen peroxide [TBHP] or oxygen) of this cyclization (equation 3) [5,6], which elevated the importance of this palladium oxidative cyclization, mainly because of the expense of Pd(OAc)2. Somewhat earlier, Knbiker used cupric acetate as a reoxidant in a synthesis of carbazole-l,4-quinones [7]. 

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