Silica supported urea-hydrogen peroxide as a source of oxygen

Silica...Damandeep Kaur and B.R.Chabra.(determined iodometrically) in UHP adsorbed on silica gel (cf 36.2% in UHP adduct 8 without silica gel).Considering this fact the potential use of UHP- SiO 2 containing system for the allylic oxidation andepoxidation of some monoterpenes and sesquiterpenes containing different functionalities wasinvestigated. In this report, we examined the effect of UHP adsorbed on silica gel on the activity andselectivity in the oxidation reactions using tetrahydrofuran as a solvent and it has been found that it is aninvaluable oxidising reagent.EXPERIMENTALMelting points reported are uncorrected. The IR spectra were recorded in CHCl 3 solution on a PerkinElmer model RX-1 FT-IR spectrophotometer and 1 H NMR spectra in CDCl 3 on Bruker AC 300 F (300MHz) NMR spectrometer (chemical shifts in δ, ppm) with TMS as internal standard. All thechromatographic separations were performed on silica gel.Extraction of starting compounds- Alantolides were obtained from the powdered roots of Inula racemosaby Soxhlet extraction method in hexane followed by refrigeration. The column chromatography of thesolidified material afforded pure alantolactone and isoalantolactone which were identified by comparisonof their melting point and IR and 1 H NMR spectra with that of an authentic sample 10 . Dehydrocostuslactone was obtained from the powdered roots of costus (Saussurea lappa) by similar extractionprocedure.Preparation of UHP on silica gel: A solution of urea in 30% H 2 O 2 , in the molecular ratio 2:3 (12 g ureain 40 mL H 2 O 2 ) was heated in a pyrex dish for a few minutes at temperature of about 60°C. This solutionwas then added to 50 g silica gel (60-120 mesh size). The mixture was stirred for 30 min and dried underreduced pressure. The resulting free flowing powder was then stored at room temperature.REACTION PROCEDUREAllylic oxidation: In a typical allylic oxidation reaction, isoalantolactone (3, 4.31 mmol, 1.0 g) wasdissolved in 20 ml tetrahydrofuran (THF) containing selenium dioxide (0.09 mmol, 10 mg). To this wasadded 30 g of UHP-SiO 2 and the reaction mixture was stirred at room temperature slowly. The reactionwas completed after 5 hrs stirring. The mixture was filtered over a small bed of silica gel followed bywashing with THF. The organic layer was removed on rotary evaporator and extracted withdichloromethane (2 X 50 ml). The solvent was evaporated in vacuo to furnish a crude product, which wasrecrystallised to give a pure compound (4, 0.7 g). It showed mp 157° lit 9 mp 159-160°C. Similarly,geraniol (1) and dehydrocostus lactone (5) on allylic oxidation under similar conditions gave purecompounds (2) and (6, mp 140°C) respectively. The products obtained (Table 1) in this reaction weresimilar to those reported earlier. 6Epoxidation of olefins: Isoalantolactone (3, 4.31 mmol, 1.0 g) was dissolved in 20 ml THF. To this wasadded 30 g of UHP-SiO 2 and catalytic quantity of dodeca-phosphotungstic acid (H 3 [PW 12 O 40 ]xH 2 O). Thereaction mixture was stirred at room temperature for 6 hrs. The mixture was filtered over a small bed ofsilica gel followed by washing with THF. The organic layer was removed on rotary evaporator andextracted with dichloromethane (2 X 50 ml). The solvent was evaporated in vacuo to furnish a crudeproduct, which was recrystallised to give a pure compound (7, 0.68 g). It showed mp 127° lit 10 mp126°C. Similarly, carvone (13) on treatment with UHP-SiO 2 and dodeca-phosphotungstic acid after usualwork up gave compound (14). It showed IR bands at 1660 and 1680 cm -1 confirming the presence of α,βunsaturatedsystem in 6- membered ring.Epoxidation of α,β- unsaturated ketones: To carvone (13, 0.5 ml) in THF (20 ml) was added UHP-SiO 2 (5 g) followed by NaOH solution (10%, 5 ml). The reaction mixture was kept at 4°C for 72 hrs. The981 J. Chem. Bio. Phy. Sci. Sec. A, 2013, Vol.3, No.2, 980-987.