Oxygen transfer agents

The mechanism of this reaction involves an activation of the ammonia and hydrogen peroxide because these compounds do not themselves react (118—121). It appears that acetamide functions as an oxygen transfer agent, possibly as the iminoperacetic acid (41) which then oxidizes the transient Schiff base formed between MEK and ammonia (40) to give the oxaziridine (42), with regeneration of acetamide ... 

The carbonyl complex [Ru(EDTAH)(CO)] has been reported to be a very good catalyst for reactions like hydroformylation of alkenes, carbonylation of ammonia and ammines as well as a very active catalyst for the water gas shift reaction. The nitrosyl [Ru(EDTA)(NO)] is an oxygen-transfer agent for the oxidation of hex-l-ene to hexan-2-one, and cyclohexane to the corresponding epoxide. 

Oxidation of thiazoles 137 with HOF MeCN provides easy access to the family of thiazole A-oxides 138 <06CC2262>. The readily made HOF MeCN complex, considered to be one of the best oxygen transfer agents in chemistry, transfers an oxygen atom directly to thiazole-containing compounds without affecting the double bonds of the thiazole moiety. A small amount of /V,SVS -trioxide 139 is also formed in this oxidation. 

The reactions of aldehydes at 313 K [69] or 323 K [70] in CoAlPO-5 in the presence of oxygen results in formation of an oxidant capable of converting olefins to epoxides and ketones to lactones (Fig. 23). This reaction is a zeolite-catalyzed variant of metal [71-73] and non-metal-catalyzed oxidations [73,74], which utilize a sacrificial aldehyde. Jarboe and Beak [75] have suggested that these reactions proceed via the intermediacy of an acyl radical that is converted either to an acyl peroxy radical or peroxy acid which acts as the oxygen-transfer agent. Although the detailed intrazeolite mechanism has not been elucidated a similar type IIaRH reaction is likely to be operative in the interior of the redox catalysts. The catalytically active sites have been demonstrated to be framework-substituted Co° or Mn ions [70]. In addition, a sufficient pore size to allow access to these centers by the aldehyde is required for oxidation [70]. 

In contrast to the processes 1-4 where organohypervalent iodine compounds behave as the electrophilic species, other approaches deal with reactions where these reagents either act as oxygen transfer agents (nucleophilic or radical) or undergo radical processes. 

Chromium complexes in general are poor catalysts for the epoxidation of alkenes with TBHP due to the decomposition of the oxygen donor with formation of molecnlar oxygen . Epoxidation reactions with this metal are known with other oxygen transfer agents than peroxides (e.g. iodosylbenzene) and will not be discnssed here. 

Several different organonitrogen compounds readily undergo metal-catalyzed oxidation using alkyl hydroperoxide or hydrogen peroxide as oxygen transfer agents. In 1961,... 

Nitrones act as oxygen transfer agents to a-lactams, giving l,3-oxazetidin-2-ones in high yields although only two cases are known (Scheme 118) (80DOK(253)886>. 

In this section we will discuss the use of elemental fluorine for the promotion of organic transformations that do not result in the introduction of fluorine into the substrate. As we described above (Sect. 3), fluorine may be used to prepare many extremely useful reagents which may be employed as, for example, oxidising and oxygen transfer agents. The use of O-F compounds, such as acetyl hypofluorite and the HOF.MeCN complex, in functionalisation processes has been indicated above (Sect. 3.2), and this area has been discussed in detail in an excellent account by Rozen [19]. 

Roundhill has recently reported the catalytic oxidation of CO to C02 by 02 using noble metal complexes, but no mechanistic details are given (91). Another direct transfer of oxygen to CO may take place in certain homogeneous catalytic systems for the reduction of nitric oxide by carbon monoxide according to (28) when no water is present to serve as the oxygen transfer agent (92,98). The catalyzed reductions of NO by CO are examined in the nitric oxide section of the review. 

While water acts as the oxygen transfer agent in this catalysis, the electrons are transferred via the rhodium center. 

The reaction mechanism for A-oxidation by performic acid has been studied by AMI calculation methods.174 The iminium salt A-mcthyl-3,4-dihydroisoquinolinium p-toluenesulfonate has been used to catalyse the oxidation of the azo dye calmagite by peracetic acid. The mechanism at pH 10 involves peracid oxidation of the quinolinium ion to form an oxaziridinium salt, which then acts as an oxygen transfer agent for oxidation of cahnagite.175 The presence of lithium salts affects the course of the reaction determining the formation of benzoyl peroxide and benzoic acid as final products in the oxidation of benzaldehyde by perbenzoic acid.176,177... 

Because of growing interest in bcnzisosclena/ol-3(2//)-ones as bioactive species and oxygen-transfer agents, several papers have dealt with an electrophilic attack at... 

---