## 3 Applications of Magnetically Recyclable Nanocatalysis (MRNCs) in Water
[PERSON] and co-workers reported mesoporous silica supported iron oxide nanoparticles for the oxidation of alkenes using hydrogen peroxide in aqueous medium [39]. Supported iron oxides nanocatalysts have been the focus in various important catalytic applications because of their low cost and toxicity, ready availability, and environmentally benign nature [6,40]. Styrenes and their substituted derivatives are converted to respective aldehydes in excellent yield (Scheme 6). It is important to note that no other side products or oxidations of aldehydes were observed during the reaction. The optimized protocol was suitable to a range of electron-withdrawing and electron-donating substituents localized in all positions of the aromatic ring. **Scheme 6. ** Mesoporous silica supported iron oxide nanoparticles for the oxidation of alkenes using hydrogen peroxide in aqueous medium. Magnetite-supported biguanide/Pd(OAc)\({}_{2}\) ligand has been employed as a recyclable catalyst for the heterogeneous Suzuki reaction in aqueous media [41]. The palladium-catalyzed Suzuki reaction is a most attractive and useful methodology for carbon-carbon bond formation [42]. In general, Suzuki reactions are usually catalyzed by homogeneous palladium catalysts or palladium salts and also by using Pd colloids and supported Pd catalysts [43]. However, these types of homogeneous catalysts could not be reused and are expensive as well. Immobilization of Pd(II) ions on magnetite support has been achieved via surface modification of Fe\({}_{3}\)O\({}_{4}\) nanoparticles with a biguanide (Scheme 7). This magnetite-supported biguanide/Pd(OAc)\({}_{2}\) nano-catalyst (40-45 nm by TEM) exhibits excellent catalytic activity for heterogeneous Suzuki reaction in aqueous media, and could be easily separated by an external magnet and recycled for several runs (Scheme 8). **Scheme 8. ** Magnetic-supported biguanide/Pd(OAc)\({}_{2}\) catalyzed Suzuki reaction in aqueous medium. Importantly, the coupling reaction of deactivated boronic acids; 3-nitrophenyl and 3,4,5,-trifluorobenzeneenboronic acid with bromobenzene and 4-bromobenzaldehyde gave the corresponding products in 95%, 88%, 94% and 95% yields, respectively. [PERSON] _et al_. reported one-pot, three-component synthesis of a spiroxindole-pyrimidines and its derivatives using magnetic nanoparticle supported dodecyl benzenesulfonic acid (DDBSA) in aqueous medium [44]; spiroxindoles-pyrimidines are important heterocyclic moieties, part of natural products and have wide range of applications in medicinal chemistry. The \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)(@SiO\({}_{2}\)-DDBSA nanocatalyst was prepared by a reported procedure [44] wherein \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) was first prepared, then coated by silica using tetraethyl orthosilicate (TEOS), followed by addition of DDBSA (Scheme 9). **Scheme 9. ** Synthesis of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)(@SiO\({}_{2}\)-DBSA. The synthesis of spiroxindole-pyrimidines derivatives was achieved by a one-pot three-component reaction of barbituric acids, is statins, and cyclohexane-1,3-diones in aqueous medium catalyzed by \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)(@SiO\({}_{2}\)-DDBSA. The desired products were obtained in good to excellent yields with the characteristic ease of isolation procedure; \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)(@SiO\({}_{2}\)-DDBSA nano-catalysts could be reused up to 6 times (Scheme 10). **Scheme 10. ** Synthesis of Spirooxindole-Pyrimidines derivatives. The selective oxidation of primary and secondary alcohols is an important and challenging reaction in the organic synthesis [45]. Various oxidizing reagents such as stoichiometric Cr\({}^{\text{IV}}\) salts [46], hypervalent iodine [47] and DMSO-coupled reagents are often employed for these reactions. However, they show poor atom efficiency and are often toxic; their frequent use causes a significant environmental damage. Therefore, it is imperative to design new benign reagents for the selective oxidation of alcohols.