A solution of sodium 2-ethyl hexanoate (475.0 g, 2.850 mol) in ethanol (2.00 L) was added to a solution of tetrabutylammonium [(2S,5R)-2-carbamoyl-7-oxo-1,6-diazabicyclo[3.2.1]octan-6-yl] sulfate 13 (723.0 g) in ethanol (2.50 l) and water (50 mL) over approximately 1 h, and the temperature was maintained at rt. The reaction mixture was held for 2 h. The product was filtered, washed with ethanol (2 × 2.0 L), and dried to yield a white crystalline solid 1 (395.0 g, 96.2%), mp 259.1–262.4 °C (decomposition); [α]D20 = ?46.40 (c = 0.79, MeOH/H2O = 1/1); 1H NMR (500 MHz, D2O) δ 4.15 (dd, J = 5.8, 2.8 Hz, 1H), 4.01 (d, J = 7.5 Hz, 1H), 3.28 (d, J = 12.2 Hz, 1H), 3.06 (d, J = 12.2 Hz, 1H), 2.23–2.09 (m, 1H), 2.06–1.96 (m, 1H), 1.94–1.82 (m, 1H), 1.81–1.69 (m, 1H). 13C NMR (126 MHz, D2O) δ 174.72 (s), 169.53 (s), 60.43 (s), 59.93 (s), 47.33 (s), 20.03 (s), 18.31 (s). IR (cm–1): 3459, 1749, 1675, 1361, 1270, 1013, 857, 768. MS (ESI) m/z: 279.0 [M + H]+.