Dendritic macromolecules supported Ag nanoparticles as efficient catalyst for the reduction of 4-nitrophenol Javad Safari * , Zohre Zarnegar, Masoud Sadeghi, Azadeh Enayati-Najafabadi Laboratory of Organic Compound Research, Department of Organic Chemistry, College of Chemistry and Biochemistry, University of Kashan, P.O. Box: 87317-51167, Kashan, Iran article info Article history: Received 6 April 2016 Received in revised form 8 May 2016 Accepted 14 July 2016 Available online 20 July 2016 Keywords: Silver nanoparticles Polymer supported catalyst Poly(2-ethyl-2-oxazoline) Macromolecules Nitrobenzene reduction abstract Polymer supported Ag nanoparticles, generated in situ by silver nitrate (AgNO 3 ) reduction under reaction conditions, catalyzed the hydrogenation of 4-nitrophenol with high efficiency in water at room tem- perature in the presence of an excess amount of NaBH 4 . Amphiphilic linear-dendritic copolymers con- taining a poly(ethylene glycol) (PEG) core and poly(2-ethyl-2-oxazoline)-poly(ε-caprolactone) arms were able to load the Ag nanoparticles. The Ag nanoparticles with a diameter of 8e10 nm were found to show a comparable catalytic activity towards formation of the aromatic amine as single product with short reaction time. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Aromatic amines are valuable chemical compounds widely used in the manufacture of pharmaceuticals, fibers, pesticides, explo- sives, polymers, dyes and cosmetics [1]. Recently, numerous pro- tocols have been reported in the literature for the reduction of nitroarenes. They include: i) hydrogenation under H 2 at various pressures promoted by various catalysts [2e5]; ii) catalytic reduc- tion process in the presence of CO and H 2 O [6], iii) photocatalytic hydrogenation [7]; iv) catalytic transfer hydrogenation promoted, for example, by Cu [8], Au [9], Pd [10], Ru [11], Ag [12] and Fe 3 O 4 -Ni [13a,b] nanoparticles with reducing agents other than molecular hydrogen [13a,b], including silanes [14], hydrazine [15], and sodium borohydride [1]. Each of the above protocols has its own merits, while some of the methods are plagued by limitations of poor yields, acidic con- dition, formation of harmful byproducts, excessive amounts of catalysts and generation of large amounts of toxic wastes in scaling up for industrial applications leading to environmental issues. However, this major problems remains unsolved and the devel- opment of more efficient, less toxic, and handle convenient catalysts for this chemical process is still highly desirable [1]. With the aim to develop innovative catalytic processes that enable chemical transformations to be performed under mild and sus- tainable conditions with high efficiency, we decided to evaluate the catalytic activity of a dendritic polymer supported Ag nanocatalyst for the hydrogenation of aromatic nitro compounds in water. Ag nanoparticles have been a subject of much intensive research because of their unique chemical and physical characteristics that are different from their bulk counterparts, leading to a wide range of application in various fields of industry biomedicine, antibacte- rial activity, imaging and nanophotonics, surface-enhanced Raman scattering (SERS) detection [16] and catalytic processes [17e19]. Stability of the nanoparticles is an important issue and sup- ported metal nanoparticles as catalytic systems have potential to show greater efficiency and prevent aggregation during the reac- tion to be catalyzed so that catalytic nanoparticles are usually immobilized on solid supports, such as carbon, metal oxides, polymer and zeolites [20]. Alternative synthetic strategies based on using polymers as support for the generation of stable metal have been developed. The resulting nanoparticle-polymer nano- composites have been shown to be useful in catalytic systems. The major advantage of using a polymeric matrix as a stabilizing agent is that it can be used to tailor the nanocomposite properties and also to provide long term stability of the particles by preventing nanoparticle agglomeration [21]. Although many polymers and * Corresponding author. E-mail addresses: safari_jav@yahoo.com, safari@kashanu.ac.ir (J. Safari). Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc http://dx.doi.org/10.1016/j.molstruc.2016.07.056 0022-2860/© 2016 Elsevier B.V. All rights reserved. Journal of Molecular Structure 1125 (2016) 772e776