An efficient, soluble, and recyclable multiwalled carbon nanotubes-supported TEMPO for oxidation of alcohols

Abstract

The immobilization of homogeneous catalysts is a continuing goal for combining the advantages of both homogeneous and heterogeneous catalysis. However, a significant loss in catalytic activity is often found in the immobilization of a homogeneous catalyst. Herein, we report a novel strategy consisting of multiwalled carbon nanotubes (MWNTs) functionalized with homogeneous catalysts that are developed to combine the positive aspects of solid and soluble supports. Using the oxidation of alcohols as a model reaction, the supported catalysts (MWNTs-TEMPO) can be homogeneously dispersed in the reaction medium to conquer the mass transfer limitation, which leads to their catalytic activity being far superior to their heterogeneous counterpart and similar to their parent catalysts. In addition, they exhibit the additional advantages of characterization with solution-based techniques, easy separation and reutilization.

Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

“…This indicates that the 2D translational symmetry of MWCNTs subsequently decreased after the alkylation process. An increase in the I D /I G , observed due to the influence of the grafted organic moieties on the electronic properties of the MWCNT-COOH, has been reported by other researchers [24][25][26]. The results also reveal that the I D /I G values of the alkylated MWCNTs were increased with the molecular weight of the Jeffamine Ò polyetheramine used.…”

Nanopatterning of Stable Radical Containing Block Copolymers for Highly Ordered Functional Nanomeshes

“…degree of polymerization and molecular weight as expected from the amount and ratio of reagents ‡ degree of polymerization and molecular weight as calculated from GPC in THF with a UV-detector Weight ratios range from 3:2 to 1:3, suggesting morphologies in the lamellar and cylindrical regime. While the degree of polymerization of the PS block, as obtained from GPC PTMA polymers at this wavelength are equal since the intensity is normalized to this peak) with the intensities of carbonyl (C=O) or nitroxide (N-O•) peaks (at 1725 cm -1 and 1367 cm -1 , respectively) confirms the order of PS-to-PTMA block ratios (smallest PS-to-PTMA block ratio in PS 15 -b-PTMA 45 , followed by PS 45 -b-PTMA 45 and PS 69 -b-PTMA 45 ≈ PS 35 -b-PTMA 22 ) 29,30,32. NMR spectroscopy and CV data (Figures SI-2and SI-3 in the Supporting Information, respectively) also confirm the existence of stable radical groups in the final polymers (NMR data: aromatic CH and OCH(CH 2 ) 2 peaks at approx.…”

“…The dispersity and degree of polymerization are expected to support ordered structure formation, and the highly asymmetric composition makes the spherical or cylindrical morphology the most probable structure.Additionally to the GPC measurements, we analyzed the resulting PtBMA-b-PTMA polymers by IR and NMR spectroscopy and cyclic voltammetry. IR spectroscopy (Figure SI-1in theSupporting Information) clearly shows the existence of nitroxide groups in the final polymers (N-O• peak at 1367 cm -1 ) 29,30. Because of similar block ratios, spectra (both concerning peak occurrence and intensities) are almost identical.…”

Hydrodynamic Rocking Disc Electrode Study of the TEMPO‐mediated Catalytic Oxidation of Primary Alcohols

“…TEMPO derivatives alone or combinations of TEMPO with metals [22,23] or with enzymes [24] provide versatile tools in bio-mass conversion [25,26,27] and in electrosynthetic processing [28]. TEMPO usually is employed in aqueous media as a homogeneous catalyst [29], but recently new methods for "heterogenisation" of TEMPO have also been suggested via covalent attachment [30,31,32] or via embedding into a polymer of intrinsic microporosity [33,34]. Mechanistic aspects of electrochemical TEMPO mediated alcohol oxidations have been investigated with the following key conclusions: (i) catalytic currents were affected by the pH [35], (ii) catalytic currents increase non-linearly with the concentration of alcohol to reach a plateau as expected for EC'-type processes, (iii) the rate limiting process at sufficiently high applied potentials is a chemical step (as opposed to electrochemical), (iv) the driving force and rate for the primary alcohol oxidation are linked to the reversible potential for TEMPO derivatives [36], and (v) at high pH (> 11) some TEMPO catalysts are irreversibly degraded by hydroxide ions [28].…”