Oxidation of 2,2,2-trifluoro-1-(4-methoxyphenyl)ethanol; 2,2,2-trifluoro-1-(4-methoxyphenyl)ethanone
Submitted Dec 21, 2012, published Dec 28, 2012
(Prepared in House, see SyntheticPage 5504-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate
(Prepared In-House, See Comment 1) 2,6 Lutidine
(Synquest Laboratories (98.0%, Synquest Laboratories)Dichloromethane
(≥99.5%, ACS Reagent Grade, Sigma-Aldrich)Diethyl Ether
(≥99.0%, ACS reagent, anhydrous, contains BHT as inhibitor, Sigma-Aldrich)
Hexanes, Mixture of Isomers (≥99% ,anhydrous, Sigma-Aldrich)Ethyl Acetate
(99.8%, anhydrous, Sigma-Aldrich)
Silica Gel (Dynamic Adsorbants Inc. Flash Silica Gel, 60Å porosity, 32-63 µm).
To a one-neck 50 mL round bottom flask equipped with stir bar was added 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate1 (3.01 g, 10 mmol, 2.5 equiv.), 2,2,2-trifluoro-1-(4-methoxyphenyl)ethanol2 (0.825 g, 4 mmol, 1 equiv.) in dichloromethane (10 mL, 0.4M in the CF3 carbinol) and stirred for about 2 minutes. After this time, 2,6-lutidine (0.964 g, 9 mmol, 2.25 equiv) was added to the flask.3 The flask was sealed with a rubber septum and stirred at room temperature. When the reaction judged complete4 (≈ 4 h), the solvent was removed in vacuo by rotary evaporation to afford a thick red residue. Anhydrous diethyl ether (≈ 30 mL) was added to the flask and allowed to stir for 10 min. This causes immediate precipitation of the spent oxidant (4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl). Note: It is imperative that the sides of the flask be scraped with a spatula to ensure all the oxyl precipitates out and can release the product into solution.
After stirring, the solution was filtered through a coarse-porosity fritted funnel to remove the spent oxidant. The filtrate was then adhered to silica gel by mixing it with 1.5 weight equivalents silica gel (relative to the theoretical yield, in this case 1.23 g) and removing the solvent in vacuo by rotary evaporation. A plug of silica was then assembled (A diagram of this apperatus is in the Data Files). This was done by adding 3-4 weight equivalents of silica (again relative to the theoretical yield) to a 60 mL coarse-porosity fritted glass funnel. An appropriately sized piece of filter paper relative to the size of the funnel was used to the top of the dry silica gel layer and this layer was pre-wet with hexanes. The dry packed material was gentle added evenly atop the filter paper. Another piece of appropriately sized filter paper was added atop this layer. The plug was eluted with a 95:5 by volume mixture of Hex:EtOAc (3-4 column volumes). The solvent was removed in vacuo by rotary evaporation in a room temperature water bath affording the pure trifluoromethylketone (0.737 g, 90%) as a clear yellow oil.
1H NMR (CDCl3, 400 MHz) δ ppm 3.90 (s, 3 H) 6.99 (apparent doublet, J = 9.05 Hz, 2 H) 8.04 (apparent doublet, J = 8.07 Hz, 2 H)
13C NMR (CDCl3, 101 MHz) δ ppm 55.9 (CH3) 112.9 – 121.6 (q, JC-F = 294.2 Hz, CF3) 114.7 (CH) 123.1 (C) 133.0 (q, JC-C-C-C-F =2.2 Hz, CH ) 165.7 (C) 179.2 (q, JC-C-F = 34.5 Hz, C)
19F NMR (CDCl3, 377 MHz, Internal Reference Fluorobenzene(–115.3 ppm) ) δ ppm -71.06
GC-MS (EI) 204 (21%), 135 (100%), 107 (12%), 92 (24%), 77 (26%), 69 (4%), 64 (10%), 63 (10%).
HRMS (ESI+), calcd for C9H7F3O2 [M + H]+ 205.0476, found: 205.0475
Kelly, C. B; Mercadante, M. A.; Hamlin, T. A.; Fletcher, M. H.; Leadbeater, N. E. J. Org. Chem., 2012, 77, 8131
Apperatus (Plug Apperatus.jpg)
1H NMR (1H NMR.jpg)
13C NMR (13C NMR.jpg)
19F NMR (19F NMR.jpg)
e.g. Actual NMR spectra (as images or jdx files for interactive spectra), photographs of apparatus, TLC’s or crystals or videos. Please contact the ChemSpider team (ChemSpider-at-rsc.org) for help with this.
Keywords: alcohols, aromatics/arenes, Green Chemistry, ketones, Organic Oxidants, Organofluorine, oxidation, Oxoammonium Salts