Carbon monoxide aromatic nitro compounds

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). 

Reduction of aromatic nitro compounds with carbon monoxide [119] (Eq. 60). 

Carbon monoxide reduces aromatic nitro compounds when iron pentacarbonyl is used as catalyst." A direct homogeneous catalytic reduction of nitro derivatives with water under moderate carbon monoxide pressure also occurs when rhodium carbonyl derivatives in aqueous organic bases are used as catalysts (equation 21). Presumably hydridorhodium carbonyl species are the active agents whose preferred formation in aqueous organic base may be analogous to that of iron carbonyl hydrides. 

Aromatic urethanes and dialkyl carbonates were simultaneously prepared by the reaction of aromatic nitro compounds with alcohols and carbon monoxide over a catalyst mixture containing DBU (82JAP(K)32251). 

Aromatic nitro compounds can be converted to carbamates by treatment with carbon monoxide and an alcohol, usually methanol, in the presence of palladium, rhodium, or ruthenium catalysts (2.19).50 Wehman et al. have reported the best yields, which can be close to quantitative.51... 

Schi-f-f bases are probably intermediately -formed during the deoxigenation reactions o-f aromatic nitro compounds with carbon monoxide <150 atm), at 165-170"C, in the presence o-f ortho-phtalaldehyde and with Rh final products are N-aryl-isoindolin-l-ones hydrogen atom o-f the -free carbonyl -function ... 

A trinuclear cobalt(I) complex, PhCCo3(CO)9, can also catalyse the reduction of nitro compounds in the presence of hydroxide ion at room temperature under a normal pressure of CO [49]. Satisfactory results were obtained under phase transfer conditions. The catalyst and the aromatic nitro compounds were dissolved in benzene under carbon monoxide and an aqueous solution of sodium hydroxide containing cethyltrimethylammonium bromide was added. At a substrate/cat =10 ratio, ca. 60-80 % of amine was obtained in a 18 h reaction. The reaction also proceeded in a homogeneous phase (methanol-water, methanol, dioxane-water) but with lower conversions (less than 45 %). Cobalt complexes such as MeCCo3(CO)9 and MeCo(CO)4 were also active, but less effective. At the end of the reaction, the catalyst was recovered only in part (ca. 15 %). In the organic phase, an IR absorption at 1891 cm, attributable to [Co(CO)4] anion, was observed. Strangely enough, the preformed [Co(CO)4] anion has not been tested as catalyst. The active species was supposed to be the hydride cluster anion reported in Scheme 6. 

Recently a process has been reported for preparing aromatic isocyanates by the reaction of aromatic nitro compounds with carbon monoxide in alcohol solution to first form the urethanes. Thermal decomposition of the urethane gives the isocyanate. 

Reduction of tertiary amides to tertiary amines can also be carried out under either thermal or photochemical conditions using 1,1,3,3-tetramethyldisiloxane (TMDS) as the reducing agent and pentacarbonyliron or dodecacarbonyltriiron as catalyst. The corresponding photo-assisted reaction promotes the reduction at room temperature. The reduction of aromatic nitro compounds to amines using carbon monoxide and water... 

Photolytic. Major products reported from the photooxidation of 2,3-dimethylbutane with nitrogen oxides are carbon monoxide and acetone. Minor products included formaldehyde, acetaldehyde and peroxyacyl nitrates (Altshuller, 1983). Synthetic air containing gaseous nitrous acid and exposed to artificial sunlight (A. = 300-450 nm) photooxidized 2,3-dimethylbutane into acetone, hexyl nitrate, peroxyacetal nitrate, and a nitro aromatic compound tentatively identified as a propyl nitrate (Cox et al., 1980). 

The reaction of nitro aromatic compounds with carbon monoxide was recently reviewed by Manov-Yuvenskii and Nefedov [221). Particularly interesting is the formation of isocyanates apparently produced in the same way in Japan (222). 

The reduction of nitro aromatic compounds to isocyanates by CO is preferably carried out with Pd, in the presence of a Lewis acid as promoter. . Recent observations that carbon monoxide bonded to Pd2(CO)2Cl4 has a very high Vco (slightly above 2160 cm with a small dependence on the solvent) indicate the degree of ir-back donation from the metal to the carbonyl ligand is small, if any. 

The electrophilic substitution is the most characteristic reaction for these classes of compounds. Compound (21) undergoes standard electrophilic aromatic substitution reactions. Thus it forms the 6-bromo compound (58) with A7-bromosuccinimide and 6,7-dibromo compound (72) with the excess of the same reagent. It also forms the 6-nitro compound (67) with copper(II) nitrate trihydrate and 6,7-dinitro compound (68) with excess of nitronium tetrafluoroborate. The bis(trifluoro-acetoxy)thallium derivative (73) was formed from trithiadiazepine (21) and thallium(III) trifluoro-acetate in refluxing acetonitrile. Without isolation, (73) was directly converted into the pale yellow 6-iodo compound (74) with aqueous potassium iodide, into the 6-cyano compound (75) with copper(I) cyanide, and into methyl trithiadiazepine-6-carboxylate (76) with carbon monoxide and methanol in the presence of palladium chloride, lithium chloride, and magnesium oxide. Compound (21) is acetylated in the presence of trifluoromethanesulfonic acid (Scheme 7) <85CC396,87JCS(P1)217, 91JCS(P1)2945>. 

Diesel exhaust is a complex mixture of thousands of chemicals in solid and gaseous forms. This mixture contains gases such as carbon monoxide, carbon dioxide, the oxides of nitrogen (i.e., nitric oxide and nitrogen dioxide), and sulfur dioxide hundreds of different hydrocarbons and diesel particulate matter (DPM). DPM is a mixture of chemical compounds composed of nonvolatile elemental carbon hundreds of different adsorbed or condensed hydrocarbons such as polycycUc aromatic hydrocarbons (PAHs) and nitro PAHs sulfates and trace quantities of metallic compounds. 

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