Carbonyl compounds nitro compound conversion

A number of studies of the important (non-phosgene) route to aryl isocyanates via carbonylation of nitro compounds have appeared. In a comparative study of Rh(I), Ir(I), Pd(I) and Pd(II) catalysts, Bu,N+[RhX2(CO)2] (X Cl, Br, I) was most effective giving 83-89% PhNCO with 100% PhN02 conversion at 125 C under 80 atm CO pressure . The kinetics of carbonylation by [PdCl2py2l at 170-230 C and 23-94 atm CO pressure are first order in p[CO] and catalyst and zero order in PhNOj . The reductive N-carbonylation of nitroarenes to the carbamates is catalysed by tPtCl2 (PPh3 >2] in ethanol, promoted by Lewis acids (SnCli,... 

The conversion of a primary or secondary nitro alkane 1 to a carbonyl compound 3 via an intermediate nitronate 2 is called the Nef reaction. Since carbonyl compounds are of great importance in organic synthesis, and nitro alkanes can on the other hand be easily prepared, the Nef reaction is an important tool in organic chemistry. 

Conversion of carbonyl to nitro groups fretro Nef Reacdoni is tin importiint method for the preparadon of nitro compounds. Such conversion is generally effected vii oximes using strong oxidiints such as CF-vCOaH. 

When the substrate does not contain a reactive carbon-carbon double bond, the ozonolysis procedure appears to provide a convenient and efficient method for the conversion of primary and secondary nitro compounds into carbonyl compounds fEq. 6.7. ... 

Oxidation of oximes to nitro compounds with m-CPBA has been applied to the synthesis of dialkyl 1-nitroalkanephosphonates (Eq. 2.63),124 which are useful reagents for conversion of carbonyl compounds to nitroalkenes.125... 

Nitro compounds are versatile precursors for diverse functionalities. Their conversion into carbonyl compounds by the Nef reaction and into amines by reduction are the most widely used processes in organic synthesis using nitro compounds. In addition, dehydration of primary nitro compounds leads to nitrile oxides, a class of reactive 1,3-dipolar reagents. Nitro compounds are also good precursors for various nitrogen derivatives such as nitriles, oximes, hydroxylamines, and imines. These transformations of nitro compounds are well established and are used routinely in organic synthesis. 

Selected examples of the oxidative conversion of nitro compounds into carbonyl derivatives... 

Conversion of carbonyl compounds into nitro compounds... 

The conversion of nitro compounds into carbonyls is known as the Nef Reaction. Various methodologies have been developed, but the most important is the standard procedure a preformed nitronate salt is poured into strong aqueous acid (pH < 1). Some oxidative variations have also found wide application, and some reductive methods have even been developed. 

The first experiments which were carried out in the author s laboratory on organometallic phase-transfer catalysis were concerned with the reduction of nitrobenzenes (4) to anilines (5) by triiron dodecacarbonyl. Such a conversion was reported to occur in benzene containing methanol at reflux for 10-17 h, with the hydridoundecacarbonyltriferrate anion as the likely key intermediate (16). It was our expectation that the trinuclear iron hydride should be generated by phase-transfer catalysis and if so, effect reduction of nitro compounds (4) under exceedingly mild conditions. Indeed this was the case, as illustrated by the results shown in Table I (17). Not only is the reaction complete in 2 h or less using sodium hydroxide as the aqueous phase, benzene as the organic phase, and benzyltrieth-ylammonium chloride as the phase-transfer catalyst, but it occurs at room temperature and requires less metal carbonyl than when the reaction was... 

Aromatic nitro compounds can be carbonylated to isocyanates in the presence of palladium catalysts such as PdCh/pyridine (equation 60). Although high conversions can be obtained the reaction conditions are somewhat vigorous (200 C, 150 bar CO). Rhodium catalysts have also been shown to be active for this transformation. From an industrial point of view, however, the simplicity of the reaction offers an attractive route to isocyanates, which are important intermediates for polyurethanes. ... 

Likewise, Oxone is useful for the conversion of nitro groups into carbonyl compounds (Nef reaction) in the presence of aqueous base (eq 62). ... 

An interesting topological effect is the increased terminal chlorination of fatty acids when they are adsorbed and aligned on alumina Silicon disulfide and particularly boron sulfide have been used with advantage instead of phosphorus pentasulfide to replace carbonyl oxygen by sulfur The addition of sulfur monochloride to olefins followed by reduction of the adduct with sodium sulfide provides a convenient inexpensive route to a large number of episulfides A direct conversion of ar. nitro compounds to isothiocyanates has been reported Sec. phosphines add easily to olefins under UV-irradiation Advances in peptide synthesis include the use of acyloxyphospho-nium salts prepared with hexamethylphosphoramide a simple synthesis with triphenyl phosphite , and the use 4-picolyl esters at the... 

Being anionic carbonyl synthons, the nitroalkanes have been explored extensively for their conversion into the corresponding carbonyl compounds. For example, the embedment of a nitroalkane onto an activated basic silica gel or the blockage of the C-protonation of nitronate with a protonated concave pyridine. The reaction under the latter condition is called the soft Nef reaction. In addition, the introduction of a y-trimethylsilyl group is proved to smooth the Nef reaction. Moreover, when a primary nitroalkane is treated with nitrite/acetic acid, a carboxylic acid is resolved. Furthermore, the oxidative Nef reaction has successfully converted the nitro cyclohexadienes into the substituted phenols via a nucleophilic addition. 

Since PdCl2 and RhCl3 are catalysts for the carbonyl ation of azo compounds to isocyanates, while this reaction is inhibited by organic bases like pyridine, and by vanadium and molybdenum compounds, it has been concluded that azo compounds were not intermediates in the conversion of nitro compounds to isocyanates with these catalysts 226,2273. In this latter case the intermediate nitrene should be directly carbonylated to give the isocyanate. 

We have recently discovered a new, very active and selective catalytic system able to catalyze the N-carbonyl at i on o-f aromatic nitro compounds [28<. The catalyst comprises Ru3quaternary ammonium salt as co-catalyst. Under optimal experimental conditions (160"C, 60 atm at room temperature, NEt Cl" as co-catalyst, in toluene with small amounts o-f methanol) 100% conversion was observed, with a selectivity -for PhNHC02Me up to 95%, the other product being aniline. The reaction... 

In general high pressure and temperature are required for these reactions to occur. However there are significant examples of reactions catalysed at atmospheric pressure, in part icular for the synthesis of isocyanates (4.2.5.). In the majority of cases the most important steps of these reactions are supposed to be the deoxygenation of the nitro function by carbon monoxide iving a nitrene residue bound to the metal centre, followed by insertion of carbon monoxide into the metal-nitrene bond. This is a likely hyphotesis since nitrene complexes can be obtained by stoichiometric reactions of nitro compounds with metal carbonyls. Conversion of the imido metal complex to the observed... 

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