A. Di-tert-butyl tricarbonate. A 1-l., three-necked flask, fitted with a mechanical stirrer, a 200-ml. pressure-equalizing dropping funnel, a calcium chloride-filled drying tube, and gas-inlet tube with a minimum internal diameter of 6 mm. (Note 1) extending nearly to the bottom of the flask, is dried either by heating with a free flame while passing anhydrous nitrogen through the apparatus, or by heating to 120° for several hours in an oven. Before use, the dropping funnel should be calibrated to indicate levels corresponding to 85 ml. and 105 ml. of liquid. While an atmosphere of anhydrous nitrogen (Note 2) is maintained inside the apparatus, it is allowed to cool before a mixture of 44.8 g. (0.400 mole) of alcohol-free potassium tert-butoxide (Note 3) and 550 ml. of anhydrous tetrahydrofuran (Note 4) is added to the reaction flask. The mixture is stirred under an atmosphere of anhydrous nitrogen for 5–10 minutes to obtain a solution. (Note 3), (Note 5). The reaction flask is immersed in an ice–salt bath maintained at −5° to −20°, and all subsequent steps, including solvent removal, are performed with this cooling bath in place. A stream of anhydrous carbon dioxide (Note 2) is passed through the cold reaction solution for 30 minutes with vigorous stirring, resulting in the formation of a thick, creamy slurry in the reaction flask. While the reaction mixture is being saturated with carbon dioxide, 85 ml. of anhydrous benzene is added to the dropping funnel. A stream of phosgene is bubbled through the benzene until the total volume of the solution is 105 ml., corresponding to the addition of approximately 24 g. (0.24 mole) of phosgene (Note 6). When the addition of carbon dioxide is complete, the phosgene solution is added to the cold reaction slurry, dropwise and with vigorous stirring, over 1 hour, maintaining the temperature of the cooling bath at −5° to −15°. During this addition the reaction mixture becomes less viscous but remains a white slurry. When the addition of the phosgene solution is complete, the cold reaction mixture is stirred for an additional 45 minutes while a stream of anhydrous nitrogen is passed through the reaction solution to sweep out most of the excess phosgene. The fittings are removed from the reaction flask, two of the three necks are stoppered, and the volume of solvents in the reaction flask is reduced from about 650 ml. to 100 ml. with a rotary evaporator. During evaporation the flask should be continuously cooled in an ice–salt bath maintained at −5° to 0°. This evaporation should be performed with either a very efficient aspirator or with a mechanical vacuum pump fitted with an efficient cold trap. Since some phosgene is still present in the reaction mixture, the exhaust from the aspirator or the vacuum pump should be discharged in the hood and any material collected in a cold trap should be emptied in the hood. The residual slurry of finely divided potassium chloride is filtered with suction in a large-diameter, fritted-glass funnel, precooled with 50 ml. of ice-cold pentane. During filtration the filter funnel may be loosely covered with an inverted large-diameter funnel through which a stream of nitrogen is passed to protect the contents of the funnel from atmospheric moisture. The residue in the reaction flask is washed into the filter funnel with 350 ml. of ice-cold pentane and washed with two additional 100-ml. portions of ice-cold pentane, leaving white potassium chloride as a residue. The combined filtrate and pentane washings are concentrated to dryness at 0° with a rotary evaporator, under reduced pressure supplied by a vacuum pump equipped with an efficient cold trap, yielding 33.7–39.6 g. (64–75%, (Note 7)) of di-tert-butyl tricarbonate as a colorless solid. This crude product is recrystallized by dissolving it in 1250 ml. of pentane at room temperature, and cooling the solution to −15°. The pentane mother liquors are concentrated with a rotary evaporator, giving two additional crops of crystalline product. The total yield is 31.2–32.8 g. (59–62%) of the pure di-tert-butyl tricarbonate as colorless prisms, m.p. 62–63° (dec.) (Note 8).

B. Di-tert-butyl dicarbonate. A solution of 20.0 g. (0.0763 mole) of di-tert-butyl tricarbonate in 75 ml. of carbon tetrachloride is placed in a 600-ml. beaker fitted with a magnetic stirrer, and 0.10 g. (0.89 mmole) of freshly sublimed 1,4-diazabicyclo[2.2.2]octane (Dabco) is added (Note 9), resulting in the rapid evolution of carbon dioxide. The reaction mixture is stirred at 25° for 45 minutes, to complete the loss of carbon dioxide (Note 10), before 35 ml. of water, containing citric acid sufficient to make the aqueous layer slightly acidic, is added. The organic layer is separated, dried over anhydrous magnesium sulfate, and concentrated at 25° with a rotary evaporator. The residual liquid is distilled under reduced pressure, yielding 13.3–15.1 g. (80–91%) of di-tert-butyl dicarbonate as a colorless liquid, b.p. 55–56° (0.15 mm.) or 62–65° (0.4 mm.) n_D25 1.4071–1.4072 (Note 11).