Nitro reductive carbonylation

Reductions Epoxide hydroplase Azo and nitro reduction Carbonyl reductase Disulfide reduction Sulfoxide reduction Quinone reduction Reductive dehalogenation Microsomes, cytosol Gut microflora Cytosol Cytosol Cytosol Cytosol, microsomes Microsomes... 

Reductive carbonylation of nitro compounds is catalyzed by various Pd catalysts. Phenyl isocyanate (93) is produced by the PdCl2-catalyzed reductive carbonylation (deoxygenation) of nitrobenzene with CO, probably via nitrene formation. Extensive studies have been carried out to develop the phosgene-free commercial process for phenyl isocyanate production from nitroben-zene[76]. Effects of various additives such as phenanthroline have been stu-died[77-79]. The co-catalysts of montmorillonite-bipyridylpalladium acetate and Ru3(CO) 2 are used for the reductive carbonylation oLnitroarenes[80,81]. Extensive studies on the reaction in alcohol to form the A -phenylurethane 94 have also been carried out[82-87]. Reaction of nitrobenzene with CO in the presence of aniline affords diphenylurea (95)[88]. 

Attempts have been made to develop methods for the production of aromatic isocyanates without the use of phosgene. None of these processes is currently in commercial use. Processes based on the reaction of carbon monoxide with aromatic nitro compounds have been examined extensively (23,27,76). The reductive carbonylation of 2,4-dinitrotoluene [121 -14-2] to toluene 2,4-diaLkylcarbamates is reported to occur in high yield at reaction temperatures of 140—180°C under 6900 kPa (1000 psi) of carbon monoxide. The resultant carbamate product distribution is noted to be a strong function of the alcohol used. Mitsui-Toatsu and Arco have disclosed a two-step reductive carbonylation process based on a cost effective selenium catalyst (22,23). 

Reductive carbonylation of nitro compounds (in particular aromatic dinitro compounds) is an important target in industry for making diisocyanates, one of the starting materials for polycarbamates. At present diisocyanates are made from diamines and phosgene. Direct synthesis of isocyanates from nitro compounds would avoid the reduction of nitro compounds to anilines, the... 

Cenini, S. Ragaini, F. In Reductive Carbonylation of Organic Nitro Compounds, Catalysis by Metal Complexes, Ugo, R. James, B. R., Eds. Kluwer, Dordrecht, The Netherlands, 1997. 

S. Cenini and F. Ragaini Catalytic Reductive Carbonylation of Organic Nitro Compounds. 1997 ISBN 0-7923 1307-7... 

Platinum dioxide, also known as Adams catalyst, is used commercially in many hydrogenation reactions at ordinary temperatures, such as reduction of olefinic and acetylenic unsaturation, aromatics, nitro, and carbonyl groups. 

These results of the analysis of the ESR spectra are consistent with the chemical data depicted in Scheme 3-45 (below). Namely, upon reduction with tin in hydrochloric acid, 4,4 -dinitrobenzophenone forms 4,4 -diaminobenzophenone (only the nitro groups are reduced, Staedel 1883). Under the same conditions, 4,4 -dinitrodibenzoyl gives 4,4 -diamin-odesoxybenzoin (both nitro and carbonyl groups are reduced, Golubeff 1873). 

A number of functional groups, such as nitro, diazo, carbonyl, disulfide sulfoxide, alkene, and pentavalent arsenic, are susceptible to reduction, although in many cases it is difficult to tell whether the reaction proceeds enzymatically or nonenzymatically by the action of such biologic reducing agents as reduced flavins or reduced pyridine nucleotides. In some cases, such as the reduction of the double bound in cinnamic acid (C6H5CH=CHCOOH), the reaction has been attributed to the intestinal microflora. Examples of reduction reactions are shown in Figure 7.12. 

Ruthenium is not an effective catalyst in many catalytic reactions however, it is becoming one of the most novel and promising metals with respect to organic synthesis. The recent discovery of C-H bond activation reactions [38] and alkene metathesis reactions [54] catalyzed by ruthenium complexes has had a significant impact on organic chemistry as well as other chemically related fields, such as natural product synthesis, polymer science, and material sciences. Similarly, carbonylation reactions catalyzed by ruthenium complexes have also been extensively developed. Compared with other transition-metal-catalyzed carbonylation reactions, ruthenium complexes are known to catalyze a few carbonylation reactions, such as hydroformylation or the reductive carbonylation of nitro compounds. In the last 10 years, a number of new carbonylation reactions have been discovered, as described in this chapter. We ex-... 

A number of functional groups, such as nitro, diazo, carbonyls, disulfides, sulfoxides, and alkenes, are susceptible to reduction. In many cases it is difficult to determine whether these reactions proceed nonenzymatically by the action of biological reducing agents such as NADPFI, NADH, and FAD or through the mediation of functional enzyme systems. As noted above, the molybdenum hydroxylases can carry out, in vitro, a number of reduction reactions, including nitro, azo, A-oxidc, and sulfoxide reduction. Although the in vivo consequences of this are not yet clear, much of the distribution of reductases described below may be, in whole or in part, the distribution of molybdenum hydroxylases. 

It is important to note that six different chemical transformations occur in a one-pot process (i) reduction of C-C double bond of (26), (ii) reduction of carbonyl to alcohol [(26)-(27)], (iii) conversion of the nitro into carbonyl (Nef reaction), (iv) emiketalization [(27)-(28)], (v) removal of tetrahydropyranyl, and (vi) ketalization with the formation of (29). 

Quite recently, novel cyclization reactions involving CO to give carbocydic and heterocyclic compounds, which are characteristic for mthenium catalysts, have been developed. Ruthenium complexes provide new avenues for cydization reactions. In addition, CO is often used as a reducing agent, and reductive carbonylations of nitro compounds catalyzed by mthenium complexes are very attractive reactions that provide phosgene-free processes [3]. 

Very recently, phosgene-free methods for producing organic isocyanates have been developed. One method involves reductive carbonylation of a nitro compound in the presence of a monoalcohol to produce a urethane compound, followed by thermal dissociation of the resulting urethane compound, as shown below ... 

Reductive carbonylation of nitro compounds, especially nitroaromatic compounds according to eq. (1), has been the subject of thorough industrial research starting in 1962 and continuing until the beginning of the 1990s due to the demand for a new, phosgene-free method for the production of isocyanates [1] and the discussions on the chlorine cycle in industry. 

The trinuclear Ru3(CO)12 can be used in combination with [NEtJCl to catalyze the selective reductive carbonylation of aromatic nitro compounds to carbamates. Thus, nitro benzene reacts in toluene with CO and methanol (160- 170°C, 82 bar, 5 hr) to give methyl JV-phenylcarbamate in 93% yield, the catalytic turnover being 92 ... 

Nitro and carbonyl groups are prone to reduction by reductases, whilst amides and esters are prone to hydrolysis by esterases. 

The chemoselective reduction of nitro and carbonyl functions with /-PrOH/ KOH over nickel-stabilized zirconia has recently been reported by Upadhya et al. [10]. This catalytic system selectively reduced 4-nitroacetophenone and... 

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