Summary                                

The kinetic studies for copper-catalyzed homocoupling reaction of phenylboronic acids have been successfully carried out in an aqueous micellar medium under environmentally benign conditions (water as a solvent, micelle to help solubilize hydrophobic adducts). In this study cetyl trimethyl ammonium bromide (CTAB) is used as a surfactant to produce micelle. Different copper salts and copper complexes were used as catalysts to perform the reaction under mild conditions at a temperature range (40-65˚C, under air) without the addition of any additives (base, oxidant, and ligands). The reactions were followed using UV-Vis spectrophotometer and the absorbances were measured at maximum wavelengths for the biphenyl production of each four selected phenylboronic acids. The observed rate constants (k_obs) were calculated using (pseudo) first-order equation and unsubstituted phenylboronic acid was selected for optimization processes. The experimental results showed a good to excellent fit (R²=0.9908-0.9998) to the (pseudo) first-order equation and origin software was used for this purpose. Among all copper catalysts, the observed rate constant (k_obs) for cupric acetate (Cu(OAc)₂) is much higher than other copper catalysts, (k_obs=0.1605 min^-1), while CuCl_2.2H₂O has a minimum observed rate constant, k_obs=0.0216min^-1. The two copper complexes [Cu(4-mba)₂(tmeda)], and [Cu(3-mba)₂(H₂O)₂(tmeda)] (4-mbaH = 4-methylbenzoic acid, 3-mbaH = 3-methylbenzoic acid, tmeda = N,N,N’,N’ -tetramethylethyleneamine) require a higher temperature condition (85˚C) compared to other copper catalysts for the reaction of unsubstituted phenylboronic acid, the value of k_obs is (0.0176, 0.0343 min^-1) ,respectively. The reaction p-tolylboronic acid, the value of k_obs is (0.0173, 0.0147 min^-1) ,respectively In addition, the reaction was carried out using commercially purchased copper nanoparticles CuO NPs.

The stability of the CuO NPs in stock solution and as a function of temperature (40-85˚C) was studied before using it as a a catalyst for the homocoupling reaction of phenylboronic acids the results showed that the spectrum does not change as a function of time and CuO NPs stay stable over at least two weeks. The homocoupling reaction of phenylboronic acids was performed at optimum conditions using CuO NPs as catalysts and the result showed that the k_{obs ­­}for the homocoupling reaction of unsubstituted phenylboronic acid at 60˚C was (0.0173 min^-1), and _­­for homocoupling reaction of p-tolylboronic acid, 4-Acetylphenylboronic acid, and 4-Formylphenylboronic acid at 85˚C k_obs were (0.0115, 0.0294, and 0.0375 min^-1) ,respectively. Finally, based on literature and our kinetic data a plausible mechanism was suggested for the reaction.