Oxidation reactions of amines

Figure 34 Oxidative reactions of amines. Formation of N-oxides from oxidation of tertiary amines and formation of hydroxylamines from oxidation of primary and secondary amines.

This chapter highlights the ruthenium-catalyzed dehydrogenative oxidation and oxygenation reactions. Dehydrogenative oxidation is especially useful for the oxidation of alcohols, and a variety of products such as ketones, aldehydes, and esters can be obtained. Oxygenation with oxo-ruthenium species derived from ruthenium and peroxides or molecular oxygen has resulted in the discovery of new types of biomi-metic catalytic oxidation reactions of amines, amides, y3-lactams, alcohols, phenols, and even nonactivated hydrocarbons tmder extremely mild conditions. These catalytic oxidations are both practical and useful, and ruthenium-catalyzed oxidations will clearly provide a variety of futrue processes. 

Although there are flavin-dependent as well as copper-dependent amine oxidases, this section will only deal with the copper enzymes. Amine oxidase (EC 1.4.3.6) catalyzes the oxidative reaction of amines to aldehydes and ammonia. The two-step process generates two electrons which are utilized to reduce oxygen to hydrogen peroxide (H202) [28,113] ... 

Typical nucleophiles known to react with coordinated alkenes are water, alcohols, carboxylic acids, ammonia, amines, enamines, and active methylene compounds 11.12]. The intramolecular version is particularly useful for syntheses of various heterocyclic compounds[l 3,14]. CO and aromatics also react with alkenes. The oxidation reactions of alkenes can be classified further based on these attacking species. Under certain conditions, especially in the presence of bases, the rr-alkene complex 4 is converted into the 7r-allylic complex 5. Various stoichiometric reactions of alkenes via 7r-allylic complex 5 are treated in Section 4. 

Carbamates are produced by the oxidative carbonylation of amines in alcohol, and active research on the commercial production of carbamates as a precursor of isoyanates based on this reaction has been carried out. As an example, ethyl phenylcarbamate (582) is produced in a high yield (95%) with... 

Many of the reactions of amines are familiar from past chapters. Thus, amines react with alkyl halides in S 2 reactions and with acid chlorides in nucleophilic acyl substitution reactions. Amines also undergo E2 elimination to yield alkenes if they are first qualernized by treatment with iodomethane and then heated with silver oxide, a process called the Hofmann elimination. 

Type I MCRs are usually reactions of amines, carbonyl compounds, and weak acids. Since all steps of the reaction are in equilibrium, the products are generally obtained in low purity and low yields. However, if one of the substrates is a bi-funchonal compound the primarily formed products can subsequently be transformed into, for example, heterocycles in an irreversible manner (type II MCRs). Because of this final irreversible step, the equilibrium is forced towards the product side. Such MCRs often give pure products in almost quantitative yields. Similarly, in MCRs employing isocyanides there is also an irreversible step, as the carbon of the isocyanide moiety is formally oxidized to CIV. In the case of type III MCRs, only a few examples are known in preparative organic chemistry, whereas in Nature the majority of biochemical compounds are formed by such transformations [3]. 

Me and coworkers reported a novel oxidation reaction of Af-Boc-phenethyl amines 21a and 21b to the corresponding cyclic carbamate 22 and aldehydes 23a and 23b (equation 21). ... 

The first example of catalysis by a polymer-metal complex was presented by Lautsch et al. u3 Metalloporphyrin was linked to a poly(phenylalanine) chain by a peptide bond. The catalytic properties of this polymer-Fe(III)porphyrin complex were compared with Fe(III)porphyrin in the oxidative reaction of phenylenedi-amine. The catalytic activity of the polymer complex was twice as large as that for the corresponding analog. 

N2)Os-(NH3)4(CO)]4+ has also been prepared by the oxidative coupling of amine ligands (58). Other coupling reactions have been used to prepare trans,trans-[ (CH3CN)(NH3)4Os(N2)Os(NH3)4(NCCH3) ]5+ from [Osvi(NH3)4(N)] under UV/Vis irradiation in acetonitrile (269). 

According to reaction (559) these reactions can occur by an oxidation reaction of platinum(II). With one-electron oxidants, the intermediate formation of platinum(III) complexes occurs. The best early example of this type of reaction is in the oxidation of PtCi - and Pt(en)2+ by IrIVCl - in the presence of free chloride ion. The presence of platinum(III) intermediates has been inferred from the rate law.2036 For the oxidation of platinum(II) by gold(III) the kinetic data are consistent with a mechanism requiring a complementary two-electron transfer,2037 with a rate independent of chloride ion. For the substituted pyridine derivatives PtCkLj (L = substituted pyridine) however, the third-order rate law is found with first-order dependencies on PtCl I, Aum and Cl-.2038 Comparisons have been made with the amine complexes PtC L (L = NH2R).2039... 

There has been a review of die effects of high pressure on the substitution reactions of amines witii haloaromatic compounds, including polyhalobenzenes.17 Nucleophilic substiditions by amines often proceed readily hi dimethyl sulfoxide (DMSO). The pKa values, hi DMSO, have been reported for some ammonium ions derived from amines widely used as nucleophiles in 5nAt reactions.18 Correlations have been established19 between die oxidation potentials and the basicities of some arylamhie and diarylamine anions and die rate constants for dieir reactions with aiyl halides in DMSO. 

A few of these imply the carbonylation of nitroaromahc substrates [41], or the oxidative carbonylation of amines [42], or the reaction of amines with carbonic acid diesters [11] that are currently available, even on an industrial scale, through phosgene-free routes [43]. 

Combined, these studies demonstrate the importance of evaluating sorption of VOCs under the appropriate conditions, that is, with typical indoor levels of C02, NH3, humidity, temperature, and so forth. Since most polar organic compounds are Lewis bases, or are amphoteric, they may also be influenced by changes in surface acid sites or the presence of competitive gas-phase species. Destaillats et al. (2006a) note that only the free-base form of nicotine is susceptible to oxidation. This may mean that interactions with acid sites on the surface could also suppress the oxidation reaction of this and other amines. 

The fact that products of type Nu-CR2-N02 can be unstable, in particular if the group Nu has an unshared electron pair, and that nitroalkanes are efficient one-electron oxidants with a pronounced tendency to undergo radical reactions, add further uncertainty to the outcome of these reactions. Thus, the reaction of amines with bromonitromethane, for instance, is assumed to yield nitromethylamines initially these, however, decompose to N-nitrosoamines [148] (Scheme 4.36). 

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