A highly efficient, green, rapid, and chemoselective oxidation of sulfides using hydrogen peroxide and boric acid as the catalyst under solvent-free conditions
General procedure for the oxidation of sulfides to sulfoxides. The sulfide (1 mmol) was added to a solution of 30% H2O2 (1.2 equiv, 0.5 g) and boric acid (0.1 mmol, 0.006 g), and the mixture was stirred at room temperature for the time specified in Table 2. The progress was monitored by TLC or GC. After completion of the reaction, the product was extracted with CH2Cl2 (3 x 10 mL) and the combined organics was washed with brine (15 mL) and dried over anhydrous Na2SO4. The solvent was removed under reduced pressure to give the corresponding pure sulfoxide in most cases. Further purification was achieved by short-column chromatography on silica gel with EtOAc/n-hexane (1/10) as eluent. All the products are known and were characterized by IR, 1H NMR, and by melting point comparisons with those of authentic samples. 8, 23, 24, 25 and 26
General procedure for the oxidation of sulfides to sulfones. The sulfide (1 mmol) was added to a solution of 30% H2O2 (3.6-4.8 equiv) and boric acid (0.2-0.3 mmol), and the mixture was stirred at room temperature for the time specified in Table 2. The progress was monitored by TLC or GC. After completion of the reaction, the product was extracted with CH2Cl2 (3 x 10 mL) and the combined organics was washed with brine (15 mL) and dried over anhydrous Na2SO4. The solvent was removed under reduced pressure to give the corresponding pure sulfone in most cases. Further purification was achieved by recrystallization from EtOH. All the products are known and were characterized by IR, 1H NMR, and by melting point comparisons with those of authentic samples. 7, 8 and 25
sulfide
added
1 mmol
mmol
H2O2
1.2 equiv
equiv
H2O2
0.5 g
g
boric acid
0.1 mmol
mmol
boric acid
0.006 g
g
solution
H2O2
30%
%
CH2Cl2
3 x 10 mL
mL
brine
15 mL
mL
EtOAc/n-hexane
1/10
sulfide
added
1 mmol
mmol
solution
H2O2
30%
%
H2O2
3.6-4.8 equiv
equiv
boric acid
0.2-0.3 mmol
mmol
CH2Cl2
3 x 10 mL
mL