Nanoflowers of Cu1.8S: Free and Decorated on Graphene Oxide (GO–Cu1.8S) as Efficient and Recyclable Catalysts for C–O Coupling
journal contributionposted on 27.04.2018, 00:00 by Ved Vati Singh, Ajai Kumar Singh
The nanoparticles of phase, Cu1.8S in flower shape, have been synthesized for the first time by reacting 3-(phenylthio)propylamine (H2N–(CH2)3–SPh) dissolved in 1-octadecene as a sulfur source with CuCl2 in a 1:1 mixture of 1-octadecene and oleylamine at 250–280 °C. The nanoflowers were anchored on GO (graphene oxide) at 25 °C resulting in a nanocomposite (GO–Cu1.8S). The Cu1.8S nanoflowers and their nanocomposite (GO–Cu1.8S), were authenticated with X-ray diffraction (powder), HR-TEM, FT-IR, and XPS (X-ray photoelectron spectroscopy). The oxidation state of large fraction of Cu in the nanoflowers is +I and a small one +II, as revealed by XPS. IR spectral analyses indicate that some oxygen containing functional groups of GO coordinate with copper of Cu1.8S, resulting in anchoring of the nanoflowers onto GO surface. The size of Cu1.8S nanoflowers was found between 14 and 21 nm. The catalytic activities of air insensitive nanoflowers of Cu1.8S and its composite GO–Cu1.8S were explored for C–O coupling between phenols and ArX (X = Cl/Br). For good conversions in DMSO, optimum loading of Cu (in mol %) was 1.25 in the presence of K2CO3 and TBAB, added as an additive. Both the catalysts were efficient and reusable (up to three times) for O-arylation of phenols, resulting diaryl ethers in good yield. They are cheap, easy to prepare and recover. The % conversion was 53–92 and 33–70 for aryl bromides and chlorides respectively and better for GO-Cu1.8S compared to that of free Cu1.8S nanoflowers. The XPS of the nanocomposite suggests that its high activity is due to enhanced surface area as well as synergistic effects of Cu1.8S nanoflowers with the supporting GO. In comparison to most of the other copper based nanophases, reported earlier the present Cu1.8S nanoflowers and GO-Cu1.8S nanocomposite are better activators for O-arylation of phenols, and they function predominantly as a heterogeneous catalyst.