Aerobic oxidation salts

An air dried sample of the lead salt of trinitrosophoroglucinol exploded when disturbed, possibly owing to aerobic oxidation to the trinitro compound. 

Available information on the thermal instability of halogenated anilines during vacuum distillation is presented and analysed, and the roles of dehyrohalogenation, polymerisation, salt formastion and dissociation, aerobic oxidation, corrosion and metal-catalysed decomposition are discussed. Experimental work on these topics is presented, and preventive measures proposed. 

The aerobic oxidation of alcohol under neutral or acidic conditions to produce the corresponding adds, which can avoid the neutralization of the carboxylate salts, is also an important R D issue. In Au-catalyzed alcohol oxidation in methanol, the corresponding methyl esters are obtained with high seledivity instead of carboxylic acids by using metal oxide supported Au NPs [157, 160], In this case, base is not necessary, or only a catalytic amount of base is required to promote the readion. However, in water, it was demonstrated that alcohols were not oxidized under acidic conditions [161] and only aldehydes were oxidized to carboxylic adds [162]. Even under solvent-free conditions or in organic solvents, alcohols were converted into aldehydes without base however, the alcohols were not fully oxidized to carboxylic acid under acidic conditions [163-166]. 

Recently, N-hydroxyphthalimide (NHPI) catalysis has been applied to a variety of aerobic oxidations of organic compounds [12], We have reported how NHPI, in the presence of Co(II) salts, is able to generate the phthalimido N-oxyl (PINO) radical, which rapidly abstracts hydrogen from aromatic and aliphatic aldehydes, in a free-radical chain mechanism under aerobic conditions (Scheme 14.2) [13]. The role of oxygen is to oxidize Co(II) to Co(III), which is also involved in the oxidation of the intermediate (Equation 14.8). 

Such a simple mechanistic proposal accomodated the observation that highly activated, benzylic alcohols were good substrates due to the enhanced lability of their a-hydrogen atoms. In contrast, aliphatic alcohols are far less reactive towards H-radical abstraction and, accordingly, poor conversions should ensue. However, it was rather disturbing to note that allylic alcohols, such as geraniol and nerol, displayed poor reactivity in this system. Furthermore, it was observed that the aerobic oxidation of aliphatic alcohols invariably resulted in the rapid formation of a green copper(II) salt, with concomitant deactivation of the catalyst. 

Nearly all indigo is produced from N-phenylglycine (see Fig. 8.18) via fusion with potassium and sodium hydroxide, followed by treatment with sodamide [103]. The melt containing the dialkalimetal salt of indoxyl is subsequently dissolved in water, and indigo is formed by aerobic oxidation. Filtration and wash-... 

A number of systems consist of a palladium salt, typically PdCb or Pd(OAc)2, with abase. For example, PdCb-NaOAc catalyzes the aerobic oxidation of secondary alcohols in ethylene carbonate under nuld conditions. Sheldon has carried out mechanistic investigations on a number of related Pd systems and shown that water-soluble complexes of Pd(II) with phenanthrohnes are stable, recyclable catalysts for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic liquid liquid system. The active catalyst is a dihydroxy-bridged palladium dimer. 

Recently, we found that a copper catalyst - as well as ruthenium - is effective for the oxidation of alkanes with molecular oxygen in the presence of acetaldehyde [157]. The catalytic system CUCI2 and 18-crown-6 has proved to be efficient [157cj. Furthermore, we found that specific copper complexes derived from copper salts and acetonitrile are convenient and highly useful catalysts for the aerobic oxidation of unactivated hydrocarbons [158], For example, oxidation of cyclohexane with molecular oxygen (1 atm of O2 diluted with 8 atm of N2) in the presence of acetaldehyde and Cu(OAc)2 catalyst (0.0025 mol%) in CH3CN/CH2CI2 (3 2) at 70°C in an... 

In a recent compilation of the wetland CH4 oxidation literature, Segers (1998) concluded that pH is not an important factor governing aerobic CH4 oxidation, salt concentrations of —40 mM inhibit the process, and aerobic CH4 oxidation responds to temperature with Qiq = —2. The Qiq for CH4 oxidation can be <2 when there is a phase-transfer limitation on CH4 diffusion (e.g., King and Adamsen, 1992). 

Oxidation of alcohols. The pernithenate salt is an excellent catalyst for aerobic oxidation of alcohols to aldehydes and ketones in the presence of 4A molecular sieves. The use of a polymer-supported ammonium perruthenat is perhaps an improvement, with good discrimination in the oxidation in favor of primary alcohols. Another versioif specifies a system containing CuCl and 2-aminopyridine also. 

F. Minisci, F. Recupero, G. F. Pedulli, M. Lucarini, Transition metal salts catalysis in the aerobic oxidation of organic compounds Thermochemical and kinetic aspects and new synthetic development in the presence of N-hydroxy-derivative catalysts, /. Mol. Catal. A. 63 (2003) 204-205. 

F. Minisci, F. Recupero, A. Cecchetto, C. Gambarotti, C. Punta, R. Faletti, R. Paganelli, G. F. Pedulli, Mechanism of the aerobic oxidation of alcohols to aldehydes and ketones, catalysed under mild conditions by persistent and non-persistent nitroxyl radicals and transition metal salts-polar, enthalpic and captodative effects, Eur. J. Org. Chem. (2004) 109. 

Miao and his coworkers developed an efficient and reusable catalytic system containing TEMPO functionalized imidazolium salt ([Imim-TEMPO]" X", Cat-la or Cat-lb), a carboxylic acid substituted imidazolium-based ionic liquid ([Imim-COOH]" X , Cat-2a or Cat-2b), and NaNO for the aerobic oxidation of alcohols with oxygen in water as solvent (Scheme 14.34) [31]. 

A novel methodology, including the aerobic oxidation of alcohols to their corresponding carbonyl compounds in the presence of several ruthenium catalysts in various ammonium salts, as ionic liquids, was proposed by Wolfson et al. (Scheme 14.39) [41]. 

Scheme 14.39 Ruthenium and ammonium salts used in the aerobic oxidation of alcohols...

Miao CX, He LN, Wang JQ, Wang JL (2009) TEMPO and carboxyhc acid functionalized imidazohum salts/sodium nitrite an efficient, reusable, transition metal-free catalytic system for aerobic oxidation of alcohols. Adv Synth Catal 351 2209-2216... 

Newmann R, Levin M (1991) Selective aerobic oxidative dehydrogenation of alcohols and amines catalyzed by a supported molybdenum-vanadium heteiopolyanion salt. J Oig Chem 56 5707-5710... 

TEMPO, polystyrene-supported TEMPO, sol-gel TEMPO, PEG-TEMPO, supported oxammoium salts, etc.). These catalysts have shown good activity and selectivity, and were also readily recyclable. The aerobic oxidation of alcohols with supported TEMPO employing oxygen as co-oxidant has been explored [19k, 191, 20], either in the presence of Co(N03)2 and Mn(N03)2 (Minisci s conditions) or in the presence of Cu(II), giving interesting results. 

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