Carbon monoxide/water/selenium

Convenient one-pot syntheses of iV-substituted selenoamides from nitriles, metallic selenium, carbon monoxide, water and amines have been developed on the basis of an amino group exchange reaction between the IV-unsubstituted selenoamides formed in situ and the primary or secondary amines. Aromatic or aliphatic, and IV-mono- or IVA -di-substituted selenoamides can be obtained in good yields by this method (Scheme 27). 

The catalytic formation of hydrogen has been exploited as a means to reduce substrates by carbon monoxide/water. For example, selenium is converted into selenium hydride, SeH2, in the sequence of eqs. (7a-d) under high-pressure autoclave conditions [13]. 

Carbon monoxide has no action on selenium oxychloride.2 Water causes decomposition of the liquid into selenium dioxide and hydrogen chloride. Anhydrous ammonia reacts according to the equation. -... 

Carbon monoxide serves as the sole carbon and energy source for the carboxydo bacteria under aerobic conditions. Using water as the oxygen donor, carbon monoxide oxidase catalyzes the hydroxylation of carbon monoxide, giving carbon dioxide or bicarbonate for assimilation. Most work has been carried out on the enzyme from Pseudomonas carboxydovorans.,ftJ7>W38 The activity of carbon monoxide oxidase is considerably stimulated upon anaerobic treatment with sulfide and dithionite, or by aerobic treatment with selenite. The binding of selenite to the oxidase specifically activates the CO — methylene blue reaction.1039 The molybdenum cofactor liberated from selenium-activated carbon monoxide oxidase does not contain selenium. Here, then, the... 

In Older to avoid the handling of poisonous hydrogen selenide, two other useful syntheses have been devised. One method uses the reaction of aromatic nitriles with aluminum selenide in the presence of pyridine, triethylamine and water (Scheme 24), while the other is performed by the reaction of nitriles with selenium, carbon monoxide and water in the presence of triethylamine (Scheme 25). These methods are exceedingly convenient in terms of manipulation without the isolation of hydrogen selenide for the preparation of selenoamides. Using these methods, a variety of aromatic and heterocyclic selenoamides can be obtained from the corresponding nitriles in high yields. 

Elemental selenium is an excellent catalyst for fhe carbonylation of a variety of nucleophiles such as amines, alcohols, water, and carbon nucleophiles in the presence of oxygen under mild conditions [114]. In fhe synfhesis of ureas from primary amines and CO, for example (Scheme 15.42), the turnover number reaches ca. 10", giving ureas in almost quantitative yields. Successful applications of this Se/CO system include not only synfhetic reactions with a variety of carbamates, carbonates, and sulfur- or selenium-containing compounds but also metallurgical refining of selenium and several important processes as exemplified by isocyanate synfhesis, fhe water-gas shift reaction, and separation of carbon monoxide [115]. 

Elemental selenium can be reduced by carbon monoxide and water in the presence of tertiary amine to produce an amine salt of hydrogen selenide ([HSe"j [R3NH ]) [79], which can be trapped by acid halides and alkyl halides to give selenol esters (Scheme 15) [80]. A variety of acyl or aroyl chlorides can be used as the substrates. However, the bulkiness of the alkyl halides influences the yields of the products. 

A seemingly straightforward method to prepare aromatic selenoamides (451) is to react the corresponding nitrile (450) with elemental selenium in aqueous THF containing Et N under 5 atm of carbon monoxide.Presumably the key reagent is hydrogen selenide formed in a water-gas shift reaction the method is unfortunately much less efficient when applied to aliphatic nitriles. 

The discovery that elemental selenium could easily be reduced to hydrogen selenide with carbon monoxide in the presence of water and triethylamine led to the preparation of selenocarboxamidesThe in situ generation of hydrogen selenide was further employed under slightly modified conditions to give ] -substituted and disubstituted selenocarboxamides by reaction of the initially... 

Carbonate formation from an alcohol and carbon monoxide is known to take place in the presence of a number of metal and non-metal redox couples, e.g. palladium, platinum, cobalt, copper, nickel, rhodium, mercury, selenium, and bromine. Most of these are also active in the oxidation of CO to CO2 in water, due to the similarity of the reaction pathways for CO2 and carbonate formation, which involve intermediate hydroxy carbonyl and alkoxy carbonyl species, respectively. Competition between carbon dioxide and carbonate formation is a major factor that has to be considered when catalyst re-oxidation is carried out by oxygen, as in most technical developments, since in this case water is co-produced in the reaction system. 

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