Copper benzoate

With ligand 170 (R = Bn), Fahmi reports the formation of an equal amount of byproduct, formulated as the allylic imide 171, Eq. 103. Indeed, Fahmi suggests that this is the correct structure of the same byproduct observed by Katsuki et al. (116) (cf. Section III.A.4, Structure 161). Fahmi suggests that this product may be formed by insertion of solvent in copper benzoate intermediate 172, as illustrated in Scheme 12. The generated copper imidate 174 then reacts with the allylic radical and combines to provide the allylic amination product 175 that rearranges to the observed imide 171. 

Both the Sandmeyer and Meerwein reactions have been interpreted by heterolytic and homolytic mechanisms. Both reactions resemble halide replacements by involving solutions of complexes of Cu(I) with the reacting species, a diazonium compound. Cohen and Lewin have reported that a mixture of p-tolyldiazonium tetrafluoroborate and copper benzoate in aprotic solvents rapidly evolves nitrogen and forms toluene, bi(/)-tolyl), />-tolyl benzoate, and p,p-dimethylazobenzene (54). As was earlier suggested by Kochi 177), the azobenzene derivative is believed to arise from a reaction between an arylcopper species and the diazonium compound. A similar mechanism was suggested for the analogous reac-... 

The crucial step of the new phenol synthesis is oxidizing the obtained benzoic acid to phenol. Early literature data indicated that heating copper benzoate or benzoic acid in the presence of copper salts gave various phenol precursors—e.g., phenyl benzoate and salicylic acid, as well as phenol itself (3, 10, 13, 24, 26, 36). In one of the initial approaches, by Dow Chemical Co., mixtures of benzoic acid vapors, air, and steam were passed over a CuO catalyst promoted with metal salts, giving phenol and phenyl benzoate (5). However, much tar was produced, probably because of the high reaction temperature, which led to excessive decomposition. Because of this, the vapor-phase method was abandoned in favor of the liquid-phase process. Next, benzoic acid was oxidized in aqueous solution with inorganic copper salts, as shown below (18) ... 

The chlorobenzene processes for the production of phenol have lost then-importance since the 1970 s. Occasionally, the toluene oxidation process, also developed by Dow is still used. In the first stage of this process, toluene is oxidized to benzoic acid with air in the liquid phase at 150 to 170 °C and 5 to 10 bar, in the presence of cobalt salts, with 90% selectivity. By-products are methylbiphenyls, benzyl alcohol, benzaldehyde and esters. Following the purification of the crude product by distillation or crystallization, the benzoic acid is transformed into phenol in the presence of copper (II) salts with air and steam at 230 to 250 °C, and 2 to 10 bar, by way of the intermediate compounds copper benzoate, benzoyl-salicylic add and phenyl benzoate. The recovered crude phenol is refined by distillation. The molar yield of phenol is around 85 to 90%. 

The reverse ATRP using AIBN as the initiator has been performed successfully for copper-based heterogeneous (Xia and Matyjaszewski, 1999) and homogeneous (Xia and Matyjaszewski, 1997) systems in solution and in emulsion as well as for iron complexes (Matyjaszewski and Xia, 2001). A general outline of reverse ATRP is shown in Scheme PI 1.9.1. As shown in this Scheme, the starting materials in reverse ATRP are a thermal free radical initiator (I-I), transition metal halide in the oxidized state (XMt ), and monomer (M), while the propagation step resembles a normal ATRP. It may be noted, however, that the reverse ATRP initiated by peroxides sometimes behaves quite differently than that initiated by azo compounds like AIBN. The differences between the benzoyl peroxide (BPO) and AIBN systems possibly arise due to an electron transfer and the formation of a copper benzoate species in the BPO system (Xia and Matyjaszewski, 1999). 

Within a few days, we found a reliable reaction protocol in which a combination of the benzoic acid and aryl bromide in NMP is stirred for several hours at 120°C in the presence of stoichiometric amounts of basic copper carbonate and potassium fluoride, molecular sieves, and 2 mol% of a Pd(acac)2/P( -Pr)Ph2 catalyst [36, 37]. The addition of molecular sieves, which effectively trapped the reaction water, allowed to deprotonate the benzoic acid in situ with carbonate bases. It was thus no longer necessary to use preformed and carefully dried copper benzoates. Beside copper, silver carbonate was also found to be effective, but due to the higher cost of this metal, we initially did not follow up on this. 

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