Acyl Transfer Reagents and Catalysts

Amine Base promoted reactions

Esterifications

Pyridine, triisopropylamine, DMAP, N-methylimidazole, and TEA are commonly used to promote reactions of alcohols and thiols. These reactions typically involve a reactive acylating agent, an alcohol or thiol nucleophile, and an NH-free organic amine base. These amine bases have conjugate acid pKa values ranging from 6 to 11.

Importantly, these amine bases are not strong enough to fully deprotonate alcohols or thiols, in contrast to strong bases that produce nucleophilic conjugate bases. However, the organic amine bases are strong nucleophiles themselves—often even more so than the alcohols and thiols, which are the intended nucleophiles for the acylation reactions. This nucleophilic property is a key feature in the mechanisms of acylation reactions, such as the DMAP-catalyzed process.

pKa Values of Common Amine Bases:

• Pyridine: 5.23
• Imidazole: 6.95
• N-Methylimidazole: 7.4
• DMAP: 9.6
• TEA: 10.75

Most of these reagnets behave as catalysts.  

Some typical reactions of these catalysts

Imidazole and Imidazolium

reactivity of 

Amidations

DCC/EDC (carbodiimide) Coupling Agents

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