Gif systems

This was also accomplished with BaRu(0)2(OH)3. The same type of conversion, with lower yields (20-30%), has been achieved with the Gif system There are several variations. One consists of pyridine-acetic acid, with H2O2 as oxidizing agent and tris(picolinato)iron(III) as catalyst. Other Gif systems use O2 as oxidizing agent and zinc as a reductant. The selectivity of the Gif systems toward alkyl carbons is CH2 > CH > CH3, which is unusual, and shows that a simple free-radical mechanism (see p. 899) is not involved. ° Another reagent that can oxidize the CH2 of an alkane is methyl(trifluoromethyl)dioxirane, but this produces CH—OH more often than C=0 (see 14-4). ... 

There is a variety of systems used to quantify colour and to assist in the comparison of colours, two important ones being the CIE-Lab system and the Munsell colour classification. Details of these systems are given in Wyszecki Styles (1982) and Heine Volz (1993). Very briefly, the GIF systems are based on the principle of tri-... 

The GIF systems and diffuse reflectance spectra (DRS) (see Chap. 7) have also been used for soils. By applying the CIE-Yxy system to 309 soils with varying Fe oxide... 

Information of the Gif system has been summarized,1055 1123 and new results, including new oxidants such as bis(trimethylsilyl) peroxide,1124 the synergistic oxidation of saturated hydrocarbons and H2S,1125 studies with the Fe3+-picolinate complex encapsulated within zeolites,1126 and the use of Udenfriend s system under Gif conditions1127 were disclosed. Gif-type oxidations were found to be moderately stereoselective.1128 Iron/zinc-containing species involved in Gif-type chemistry were synthesized, and their reactivity and catalytic behavior were studied.1129... 

Subsequently, the original Gif systems (described above, Gif1 and Gif11, respectively) [3] were subjected to various alterations named after the places of their discovery (Table 3.1). 

Much effort has been devoted to the elucidation of the oxygenation mechanism (see reviews [8,9]). Extensive studies by Barton and coworkers led to the assumption that Gif chemistry was not a radical process. This assumption was based on two observations. First, in radical chemistry, the order of reactivity is C -H > Csec-H 3> Cprim-H, whereas in Gif systems, a significant preference for oxidation in the secondary position of the hydrocarbon was observed [10, 11] (Csec-H > C -H 3> Cprim-H). A second hint was the low kinetic isotope effect (about 2 for the ketone). Both findings were combined to the mechanism depicted in Scheme 3.2. 

The pathway followed during these reactions appears different from that of the Gif system, because use of the same complexes under strict Gif conditions (pyridine-acetic acid-Zn powder) gives a different product ratio the same reactivity and selectivity is obtained for all monomeric and dimeric complexes (15-18). The reactivity observed with 2 is reminiscent of the chemistry of the dinuclear ferrous active site found in MMO, although their mechanistic similarities must still be demonstrated (19, 20). 

Although the [ Fe(HBpz3)(hfacac) 20] system is quite intriguing, it is unclear whether ferrous decomposition products are responsible for the observed chemistry, particularly in light of the reported reactivity properties of several less well characterized mononuclear nonheme iron systems that are capable of hydroxylating aromatic compounds (22-26). The relationship between the chemistry of these iron-based systems, such as 4 and the Gif (and modified Gif) systems (15-18) is currently unclear. 

The addition of (PhSe)2 to the Gif system, mentioned above, leads to trapping of the radical intermediates with the formation of products with C—Se bonds, for example, 12% of 2-adamantyl phenyl selenide is formed from adamantane. 

Related to the above is the Gif system discovered by Barton [18]. In essence, it involves Fe -1- O2 -1- reducing agent or Fe -1- H2O2. The mechanism is unsettled although a high-valent Fe=0 species has been implicated in the C-H cleavage step. The reactivity profile appears to be inconsistent with the generation of... 

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