Grafting of alumina by diphenylphosphinate coupling agents
- PDF / 259,318 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 4 Downloads / 191 Views
.6.1 Downloaded from https://www.cambridge.org/core. Access paid by the UCSB Libraries, on 25 Feb 2018 at 20:47:16, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-628-CC6.6
modification of the surface of alumina particles, under mild and more severe conditions, was investigated by IR and solid-state 31P MAS NMR spectroscopy, using the model crystalline phase Al(O2PPh2)3 synthesized in a parallel work as a reference. EXPERIMENTAL Al2O3 C (90 m2/g), purchased from Degussa, was dried before use. Ph2PO2H (99%, Avocado), Al(NO3)3.9 H2O (Aldrich) were used without further purification. Dichloromethane was distilled over P2O5. Ph2P(O)OSiMe3 was prepared from Ph2P(O)Cl (98%, Avocado) by reaction with anhydrous ethanol in presence of triethylamine, leading to Ph2P(O)OEt, followed by reaction with Me3SiBr (1.5 eq.) in dichloromethane. The manipulations with Ph2P(O)OSiMe3 were carried out under an inert atmosphere. Aluminum diphenylphosphinate Aluminum nitrate dissolved in water was added to a suspension of diphenylphosphinic acid in water in a tube in the molar ratio P:Al:H2O 1:0.166:150. The tube was sealed and held for five days at 180 °C in an oven. The powder obtained was filtered, washed with water, pyridine, ethanol and acetone, and dried for 12 hours at room temperature (yield 90%). Grafting Diphenylphosphinic acid (6.64 mmol) was dissolved in 1000 mL of 3/1 methanol/water. The pH was adjusted to 4 or 6 by addition of NaOH 1N to avoid the aggregation of alumina particles (far from pH 8, the value of chargeless state for Al2O3). A suspension of 2 g (14.6 mmol) of aluminum oxide in 200 mL of permuted water was added slowly to the solution. The resulting suspension was stirred at room temperature for 3 days. The solid was filtered off, washed with 5 aliquots of methanol to remove any physisorbed diphenylphosphinic acid and dried under vacuum at 120 °C. The final Al/P ratio was 20. Grafting with ethyl diphenylphosphinate and trimethylsilyl diphenylphosphinate was performed similarly, except that the solvent was CH2Cl2 (80 ml), and that the temperature was as high as 40 °C in the case of ethyl diphenylphosphinate. The final Al/P ratios were 37 for the former and 11 for the latter. Characterization methods 31 P solid state NMR spectra were obtained with a Bruker ASX400 or a Bruker Advance DPX300 spectrometer, using magic angle spinning (MAS) (spinning rate 10 kHz) and high-power proton decoupling; the flip angle was 45° and the recycling delay 10s. The chemical shifts were referenced to H3PO4 (85% in water). 27Al solid state NMR spectra were obtained with a Bruker ASX400 spectrometer, using magic angle spinning (MAS) (spinning rate 12 kHz), a flip angle of 15° and a 2 s recycling delay. The chemical shifts were referenced to AlCl3 (40% in water). FTIR spectra were obtained on a Perkin-Elmer 2000 spectrophotometer using KBr pellets for aluminum phosphinate and diffuse reflectance (DRIFT) for grafted alumina. X-Ray powder diffraction (XRD) was perfor
Data Loading...
