Efficient, continuous N-Boc deprotection of amines using solid acid catalysts

N-Boc deprotection (deBoc) is a common reaction in pharmaceutical research and development, as well as pharma manufacturing. Use of a catalyst lowers the required reaction temperature, and heterogeneous catalysts allow the reaction to be conducted in a continuous flow reactor with a low-boiling solvent, facilitating product separation and enhancing efficiency and productivity relative to a batch process. In this study, we explore the use of simple solid Bronsted acid catalysts to achieve continuous N-Boc deprotection of amines, without additional workup steps. Using THF as the solvent, H-BEA zeolite affords high yields of a variety of aromatic and aliphatic amines, often in residence times of less than a minute at 140 degrees C. The same catalyst/solvent combination is ineffective in batch conditions, due to the much lower temperature of refluxing THF. Boc-protected p-chloroaniline was deprotected with a throughput of 18 mmol p-chloroaniline per h per g(cat), sustained over 9 h. The active sites of the zeolite do not appear to be directly associated with the Al framework substitution in the micropores, since partially ion-exchanged Na/H-BEA shows activity similar to H-BEA. The strong Bronsted acid sites (framework [Si(OH)Al]), are likely poisoned by the amine product. Moderate Bronsted acid sites associated with silanol defects near Al on or near the external surface (and not susceptible to Na+-exchange) are presumably the active sites, since they are not poisoned even by more basic aliphatic amines.

Automated summary

N-Boc deprotection using solid Bronsted acid catalysts at 140 degrees Celsius without additional workup steps resulted in high yields, with active sites likely associated with moderate Bronsted acid sites near Al on or near the external surface.