Sodium Triacetoxyborohydride. A 100” Schlenk flask equipped
with a Schlenk filter was charged with 186 mg (4.93 mmol) of sodium
borohydride and 50 mL of anhydrous benzene. The slurry was cooled
to 10 OC and 860 pL (15.0 mmol, 3.04 equiv) of anhydrous acetic acid was added dropwise so as to maintain an internal temperature no higher
than 20 OC. Hydrogen evolution was measured with a gas buret. After
addition of acetic acid was complete the mixture was allowed to warm
to ambient temperature and stirred at that temperature for 8 h. Hy-
drogen evolution had ceased at 330 mL (theoretical for 3.00 equiv is 331
mL) after 5 h. The colorless slurry was filtered and the resultant white
powder washed with three 20-mL portions of freshly distilled, anhydrous
ether. The combined ether filtrates did not liberate hydrogen when
treated with 1 N aqueous hydrochloric acid. The powder was held under vacuum over night to afford 961 mg (92%) of analytically pure sodium
triacetoxyborohydride as a white, hygroscopic solid: IR (Nujol) 2500,
1682, 1375, 1316, 1149, 1023, 962, 845 cm-I; ‘H NMR (250 MHz
CD3CN) 6 1.88 (s, 9 H, CH,CO,B); "C NMR (75.5 MHz, CDJCN)
6 175.25, 23.36; "B NMR (96.3 MHz, CD3CN) 6 -1.47 (d, JBH 122
Hz).
Anal. Calcd for C6HloO6BNa: C, 34.00; H, 4.76. Found: C, 33.87;
H, 4.79. |