Selenium 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). 

This ch ter contains reactions which prepare the oxides of nitrogen, sulfur and selenium. Included are W-oxides, nitroso and nitro compounds, nitrile oxides, sulfoxides, selenoxides and sulfones. Oximes are considered to be amines and appear in those sections. Preparation of sulfonic acid derivatives are found in Chapter Two and the preparation of sulfonates in Chapter Ten. 

Reduction is used for carbonyl functionalities [71, 230] such as thioesters [231], amides [232], and carbamates [233], as well as for sulfur [234] and selenium [122] compounds. Recently, the synthesis of a potential carbohydrate vaccine is described via an reduction-oxidation sequence [235]. An efficient solid-phase synthesis of pyrimidine derivatives that involved reduction of the corresponding nitro derivatives was developed by Makara et al. in 2001 (Scheme 3.9) [236]. 

Molecular structure and thermochemistry are interrelated here for species chosen from contributions to the earlier Volume 3 of this book series. Discussion includes halogenated species gaseous nonmetal dioxides X-Y bond-containing species (X,Y = C, N, O) small carbon molecules arenols and substituted arenes steroids aromatic carbocycles difluoramines and nitro compounds selenium- and tellurium-nitrogen compounds. 

Selenium and selenium compounds as catalysts. The use of selenium or its compounds as catalysts in the N-carbonylation of aromatic nitro compounds to carbamates, seems to be limited by the toxicity and volatility of these species. 

We -finally note that selenium, sulphur and their compounds have also been used in combination with platinum group metals in the catalytic carbonyl at i on o-f aromatic nitro compounds to carbamates 309j[. 

The catalytic carbonylation of nitro compounds is a field of great interest, as a number of important industrial products can be produced (Scheme 9.1), [1-4] such as the synthesis of isocyanates, carbamates, ureas, etc., which normally needed toxic phosgene as the reaction reagent and can be replaced by cheap CO in the case of carbonylation of nitro compounds. After decades developments, several transition metals are known to be active for this transformation—for example, palladium, rhodium, ruthenium, and even iron, cobalt and selenium—all of which will be discussed in this chapter. 

Moreover, selenium was also applied in the carbonylation of nitro compounds, even its toxic. Yu, Lu and colleagues found that selenium can catalyze the carbonylation of nitroarenes to symmetrical 1,3-diarylureas under atmospheric pressure of carbon monoxide [66]. In the presence of KOH or NaOAc as base, various... 

As to the interests and importance of heterocycles, selenium catalysts were also applied in the carbonylation of nitro compounds for heterocycle production [68-70]. Indoles, quinazoUnones, and quinazolindiones were produced from the corresponding nitro compounds in good yields (Scheme 9.6). In the presence of catalytic amounts of a selenium catalyst, under pressure of carbon monoxide, nitro compounds were reduced and heterocyclized. 

In order to circumvent the problem of the use of selenium, analogous systems based on the use of sulphur compounds have been developed [85-88]. Aromatic nitro compounds can be reduced by CO in water/methanol media at 120-150 °C and 1-1.5 bar pressure [85, 86]. From nitrobenzene, aniline was obtained with selectivity over 97 % at 100 % PhN02 conversion. The reaction proceeds in the presence of a multicomponent catalyst consisting of a base (preferably a strong base such as sodium hydroxide or methoxide) and sulphur compounds. The ratio of catalytic effectiveness of sulphur compounds is as follows S CS2 H2S COS = 1 1.3 10 10. Vanadium(V) compounds can be added to improve selectivity in aniline formation. Aromatic dinitro derivatives undergo this reaction and selectivity to one of the two main products (phenylenediamine and nitroaniline) can be switched by the choice of reaction conditions. The main byproduct of the reaction of nitrobenzene is PhNHCOOMe [85, 86]. It has been shown that, under the catalytic conditions, methyl phenylcarbamate can be hydrolysed to afford aniline. More forcing conditions (up to 300 bar CO) have also been employed in order to increase the activity [87]. The same catalytic system has been used to reduce nitrophenols to the corresponding aminophenols [88]. 

Heterocyclcs have also been obtained by carbonylation of o/V/70-substituted nitro compounds, by using selenium in water as catalyst. This route seems to be limited by the toxicity and volatility of compounds such as H2SC and COSe. Besides 2-benzoxazolones (37) (cq. 17) [70] ... 

Nitrogen-, Sulfur- and Selenium-containing Compounds.- 2,3.4-Tri-O-acetyl-P-D-arabinopyranosyl azide, 5 the azido orthoester 15, the diazirine 16, episulfide 17, selenourea 18, a-D-ribopyranosylamine l,3-(cyclic carbonate), lactams 19a/b and 20, the 6-nitro-7-methylthioheptitol 21,2-acetamido-2-deoxy-P-D-glycopyranosyl nitromethane (3-... 

Furalazine, Acetylfuratrizine, Panfuran-S. Heating nitrovin in butanol or dimethylformamide at 100—130°C affords furalazine, 6-[2-(5-nitro-2-furanyl)ethenyl]-l,2,4-triazine-3-amine (34). An improved synthesis originates with 5-nitro-2-furancarboxaldehyde and acetone, proceeds through 4-(5-nitro-2-furanyl)-3-buten-2-one followed by a selenium dioxide oxidation to the pymvaldehyde hydrate, and subsequent reaction with aininoguariidine (35). Furalazine, acetylfuratrizine (36), and the A[-A/-bis(hydroxymethyl) derivative, Panfuran-S, formed from the parent compound and formaldehyde (37), are systemic antibacterial agents. 

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