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Structural Analyses of N ‐Acetylated 4‐(Dimethylamino)pyridine (DMAP) Salts
Author(s) -
Lutz Volker,
Glatthaar Jörg,
Würtele Christian,
Serafin Michael,
Hausmann Heike,
Schreiner Peter R.
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200901379
Subject(s) - chemistry , pyridine , hydrogen bond , counterion , salt (chemistry) , nucleophile , acetylation , catalysis , nuclear magnetic resonance spectroscopy , polymer chemistry , medicinal chemistry , inorganic chemistry , ion , computational chemistry , organic chemistry , molecule , biochemistry , gene
We have studied the formation of several N ‐acetyl‐4‐(dimethylamino)pyridine (DMAP) salts (with Cl − , CH 3 COO − , and CF 3 COO − counterions), which are considered to be the catalytically active species in DMAP‐catalyzed acetylation reactions of alcohols. Combined crystal structure analyses, variable temperature matrix IR and NMR spectroscopy as well as computational techniques at the UAHF‐PCM‐B3LYP/6‐311+G(d,p)//B3LYP/6‐31G(d) level were utilized to examine the structures and dynamics of salt formation. We found clear evidence for the formation of tight ion pairs that are stabilized by dynamic hydrogen‐bonding interactions. In nonpolar solvents, the nucleophilicity of acetate in its N ‐acetyl‐DMAP salt only allows a steady‐state concentration smaller 1 % at room temperature. Thus, we propose additional hydrogen‐bonding interactions with alcohols to be the key stabilization factor in subsequent acetylations.