Di-tert-butyl dicarbonate is inexpensive, so it is usually purchased. Classically, this compound is prepared from tert-butanol, carbon dioxide, and phosgene, using DABCO as a base:
This route is currently employed commercially by manufacturers in China and India. European and Japanese companies use the reaction of sodium tert-butoxide with carbon dioxide, catalysed by p-toluenesulfonic acid or methanesulfonic acid. This process involves a distillation of the crude material yielding a very pure grade.
Boc anhydride is also available as a 70% solution in toluene or THF. As boc anhydride may melt at ambient temperatures, its storage and handling is sometimes simplified by using a solution.