Enhanced solvent-free selective oxidation of cyclohexene to 1,2-cyclohexanediol by polyaniline@halloysite nanotubes

Abstract

Enhanced solvent-free selective oxidation of cyclohexene to 1,2-cyclohexanediol was achieved by polyaniline@halloysite nanotubes with H2O2 as oxidant at 70 °C.

Effective solvent-free oxidation of cyclohexene to allylic products with oxygen by mesoporous etched halloysite nanotube supported Co2+

“…6 Based on the above results, the etching time and Co(NO 3 ) 2 $6H 2 O/eHA weight ratio in the preparation will exert a signicant impact on the cyclohexene oxidation efficiency of HA/HCl-T/Co 2+ -R. Thereinto, HA/HCl-18 h/Co 2+ -2 : 1 performs the highest catalytic efficiency, corresponding to a 1209.98 TON and 1140.69 mmol g À1 h À1 mass-normalized activity. This activity is signicantly higher than that of halloysite nanotubes supported PANI (PANI@HA/1 M/2.04-HCl, 148.66 TON and 67.33 mmol g À1 h À1 ) 27 and Co(II)-containing metal-organic frameworks (MOFs) (Co-MOF, 80.22 TON and 68.07 mmol g À1 h À1 ). 6 So HA/HCl-18 h/Co 2+ -2 : 1 is an effective catalyst for allylic oxidation of cyclohexene and chosen for further studies.…”

“…It consist of 17.5% Si, 17.6% Al and 64.9% O and with 31.7 m 2 g À1 BET surface area. 19,20,[22][23][24][25][26][27] To demonstrate the Al 2 O 3 in halloysite nanotubes can be controlled etched by HCl, the TEM of etched halloysite nanotubes (eHA) at different etching time is given in Fig. 1.…”

“…Considering the facilitation of later purication and allylic products as the main oxidation with O 2 as oxidant, O 2 is selected as oxidant in the current catalytic reaction system. 27 In the following, the effect of solvent (CH 3 CN, CH 2 Cl 2 , THF, DMF, n-heptane and acetic anhydride) on the selective oxidation of cyclohexene is investigated and compared with the solvent-free reaction system. Noting: the volume of solvent is six times (4.8 mL) the volume of cyclohexene (0.8 mL) to avoid the evaporation of cyclohexene in the oxidation process.…”

“…It could be under the high polar solvent, the epoxy cyclohexene and 1,2-cyclohexanediol can easily desorb from the catalyst, thus facilitating the formation of epoxy cyclohexene and 1,2-cyclohexanediol. 27,32 Other reaction condition, for example, the effect of reaction temperature (20-80 C) and reaction time (0-24 h) is further investigated. It shows that the cyclohexene conversion increases signicantly with the increase of reaction temperature when the reaction temperature is in the range of 20-75 C and the conversion achieves 58.30% with 94.03% allylic products selectivity when the reaction temperature is 75 C (Fig.…”

“…17 Compared to other supports, halloysite nanotube has the advantage of abundant reserves, high porosity and excellent chemical stability, which is usually utilized as an attractive support for catalyst. [18][19][20][21][22][23][24][25][26][27] In our previous studies, 24 it has been demonstrated that mesoporous SiO 2 and SiO 2 /Al 2 O 3 can been controlled synthesized in large scale by selective etching of the interior Al 2 O 3 from hydrophobically modied halloysite nanotube or halloysite nanotubes by HCl. As the selective etching by HCl is the positive charged Al 2 O 3 , the surface of the etched halloysite nanotubes should be negative charged and can induce the adsorption of metal cation to achieve mesoporous etched halloysite nanotubes supported metal ions.…”