Oxidizing agent Palladium

Direct hydroxylation of benzene to phenol could be achieved using zeolite catalysts containing rhodium, platinum, palladium, or irridium. The oxidizing agent is nitrous oxide, which is unavoidable a byproduct from the oxidation of KA oil (see KA oil, this chapter) to adipic acid using nitric acid as the oxidant. 

Alkenes can also be oxidized with metallic acetates such as lead tetraacetate or thallium(III) acetate " to give bis-acetates of glycols. Oxidizing agents such as benzoquinone, Mn02, or 02, along with palladium acetate, have been used to convert conjugated dienes to l,4-diacetoxy-2-alkenes (1,4 addition). ... 

Again we see that an alkene isomerisation reaction has taken place. Another important, useful reagent applied in this field is also pictured in Figure 15.7, viz. the use of benzoquinone as the re-oxidant for palladium. Quinone takes the role of dioxygen as oxidising agent. It is very efficient and both quinone and hydroquinone are inert towards many substrates. Furthermore, no water is formed, as is the case when dioxygen is used. 

The electrochemical Wacker-type oxidation of terminal olefins (111) by using palladium chloride or palladium acetate in the presence of a suitable oxidant leading to 2-alkanones (112) has been intensively studied. As recyclable double-mediatory systems (Scheme 43), quinone, ferric chloride, copper acetate, and triphenylamine have been used as co-oxidizing agents for regeneration of the Pd(II) catalyst [151]. The palladium-catalyzed anodic oxidation of... 

Palladium is not combustible except as fine powder or dust. Several of palladiums compounds are oxidizing agents, and some react violently with organic substances. 

Beccalli et al. reported a new synthesis of staurosporinone (293) from 3-cyano-3-(lH-indol-3-yl)-2-oxo propionic acid ethyl ester (1464) (790). The reaction of 1464 with ethyl chlorocarbonate and triethylamine afforded the compound 1465, which, on treatment with dimethylamine, led to the corresponding hydroxy derivative 1466. The triflate 1467 was prepared from 1466 by reaction with trifluoromethanesulfonic anhydride (Tf20) in the presence of ethyldiisopropylamine. The palladium(O)-catalyzed cross-coupling of the triflate 1467 with the 3-(tributylstannyl)indole 1468 afforded the vinylindole 1469 in 89% yield. Deprotection of both nitrogen atoms with sodium ethoxide in ethanol to 1470, followed by photocyclization in the presence of iodine as the oxidizing agent provided the indolocarbazole 1471. Finally, reductive cyclization of 1471 with sodium borohydride-cobaltous chloride led to staurosporinone (293) in 40% yield (790) (Scheme 5.248). 

The oxidative coupling of CO in the presence of an alcohol to yield oxalate esters is under study by Ube Industries and Union Carbide. As oxidizing agent, oxygen or nitric oxide (Equation 8 and 9) can be used in the presence of a palladium catalyst (7 ). 

Benzoquinone has been used as an alternative oxidizing agent to oxygen in the oxidation of olefins catalyzed by palladium acetate (1). Presumably it has the same role as a regenerating agent in oxidizing some... 

The direct palladation procedure is limited to substitution with aryl and heterocyclic groups. The met-allation is an electrophilic process and therefore does not work well with deactivated aromatics. When possible, mixtures of isomers may be obtained. Since the palladium salts employed for the metallation are moderately strong oxidizing agents, the reaction cannot be used with easily oxidizable alkenes or aromatics. The only effective method for making this procedure catalytic is to reoxidize the palladium in situ with oxygen under pressure an inconvenient and potentially dangerous procedure. 

Other bidentate N-heterocyclic carbenes were used to form stable chelate complexes. A fine example is the use of palladium NHC complex 24 in the catalytic conversion of methane to methanol (Fig. 10) [111]. In this case the stability of the complexes is a requirement, since the reaction takes place in an acidic medium (trifluoroacetic acid) at elevated temperatures (80 °C) mediated by strong oxidizing agents (potassium peroxodisulfate). 

The reduction of operation temperature and pressure is possible by using a suitable catalyst. Especially in combination with N2/02 as oxidizing agent an effective catalysis is of great interest. As metal-catalysts platinum, palladium and iron oxide (poroton) were investigated. 

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