GoAgg systems

A new series, the so-called GoAgg systems, has been introduced.158,166,167 The most practical member is GoAgg11 using iron(III) chloride and H202. Alkyl hydroperoxides were found to be the intermediates in these oxidations.168... 

This section deals with Gif and GoAgg systems that were discovered by Barton and coworkers in the 1980s. After the presentation of the various systems, we will focus on the mechanism of the reaction. The last section will focus on the latest applications of Gif and GoAgg type systems to alkane oxidation. 

The Gif oxidation of aralkanes involving /-BuOOH, FefNOi) 9H2O, pyridine, HOAc (the so-called GoAgg system) gives mixed benzylic peroxides. The addition of MX (M=Li, Na, EtjN X=C1, N3, NCS, CN, NO2,...) enables functionalization of hydrocarbons to afford alkyl chlorides, azides, thiocyanates, cyanides, nitroalkanes, etc. ... 

The GoAgg system uses hydrogen peroxide as an active oxidant in the presence of an iron(III) salt, having the advantage of forming a homogeneous mixture of the reactants. In cyclohexane oxidation Barton et al. reported a 0.053 M solution of one + ol after 5 h of reaction time. In open air we obtained a 0.063 M solution of oxidized products after 8... 

Figure 1. Time dependence of efficiency and concentration of one + ol for the GoAgg system (1 mmol of FeCb, 20 mmol of cyclohexane, 10 mmol of H2O2,20 C).

Under Gif conditions copper(II) salts show a similar reactivity in the oxidation of saturated hydrocarbons with hydrogen peroxide. In the oxidation of cyclododecane, Geletii et alP obtained only a 0.019 M solution of oxidized products which shows that the activity of the copper catalyst is smaller than that of the corresponding iron(III) catalyst. On the other hand, the GoChAgg system, without addition of picolinic acid, is nearly as rapid as the GoAgg system and the addition of water does not reduce its efficiency. There are further differences between the two systems which prove that the metal itself participates actively in the activation process. " ... 

Substitution of pyridine by a less toxic and cheaper solvent is certainly a major challenge as pyridine not only maintains the polarity of the reaction medium but also acts as a ligand for the catalyst and as a buffer in combination with acetic acid. Using acetone, acetonitrile or erf-butanol as a substitute for pyridine and not adjusting the pH of the system, the efficiency of the GoAgg system was strongly reduced (Fig. 8) and the one ol ratio was typically about 1. ... 

The GoAgg system shows a good potential for substituting for the classical cyclohexane oxidation process. In the presence of hydrochloric acid it produces a 0.267 M solution of one + ol with 100% selectivity in 60 min of reaction time. In comparison with the classical process (0.3 M solution of one + ol with only 80% selectivity in 40 min) these results are totally compatible but have the advantage of being obtained at room temperature without applying pressure. On the other hand, the turnover numbers are low... 

University). The GoAgg system consists of pyridine-acetic acid,... 

Comparison of the bromination of a series of saturated hydrocarbons (cyloalkanes) with BrCCl added to the GoAgg system and that with BrCCl alone has given additional support for the two intermediates,... 

Schuchardt, U., KrahembOhl, C.E.Z., and Carvalho, W.A. (1991) High Efficiency of the GoAgg system in the Oxidation of Cyclohexane with Hydrogen Peroxide Under an Inert Atmosphere, New. J. Chem. 15, 955-958. 

Several lines of evidence have recently confirmed that the major oxidant in Gif solutions is hydroxyl radicals rather than the originally proposed Fe =0 species. Hydroxyl radicals are generated via Fenton-like interactions between Fe(II) sites and hydrogen peroxide in GoAgg systems. Gif -type chemistry relies on Fe(II)/O2 interactions and reducing equivalents provided by Zn dust to afford hydroxyl radicals. As the substrate-derived alkyl-hydroperoxide builds up, especially under dioxygen-rich conditions, a secondary oxidant becomes apparent by means of its enhanced selectivity for the activation of tertiary C-H bonds. The... 

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