TY - JOUR
T1 - Kinetic study on the esterification of hexanoic acid with N,N-dialkylamino alcohols
T2 - Evidence for an activation by hydrogen bonding
AU - Breitenlechner, Stefan
AU - Bach, Thorsten
N1 - Funding Information:
This work has been generously supported by the BASF AG (Ludwigshafen). We thank Drs. M. Gerst, K. Michl, and B. Reck for valuable discussions and their continuing interest in this research.
PY - 2006/5
Y1 - 2006/5
N2 - The pseudo-first order rate constant for the esterification of hexanoic acid (1) and five different N,N-dialkylamino alcohols (2) was determined in comparison to 1-hexanol (k = 0.67 · 10-5 s-1). The values range from 0.60 · 10-5 s-1 to 9.3 · 10-5 s-1. The data suggest a differing reactivity for structurally related compounds, which is directly correlated to the ability of the corresponding amino alcohol to activate the carboxylic acid by hydrogen bonding. A seven-membered transition state C≠ is postulated for reactions of 2-amino alcohols. The fastest reaction was observed for trans-2-(N,N- dimethylamino)cyclohexanol (2e), in which the amino and the hydroxyl groups are in an almost perfect synperiplanar 1,2-position. Attempts to further enhance the rate of the esterification by the addition of potential catalysts failed. Only Cu(OTf)2 (2.5 mol-%) allowed for a moderate rate increase from 7.5 · 10-5 s-1 (uncatalyzed) to 14.8 · 10 -5 s-1 (catalyzed) in the esterification of hexanoic acid (1) with 2-(N,N-dimethylamino)ethanol (2a).
AB - The pseudo-first order rate constant for the esterification of hexanoic acid (1) and five different N,N-dialkylamino alcohols (2) was determined in comparison to 1-hexanol (k = 0.67 · 10-5 s-1). The values range from 0.60 · 10-5 s-1 to 9.3 · 10-5 s-1. The data suggest a differing reactivity for structurally related compounds, which is directly correlated to the ability of the corresponding amino alcohol to activate the carboxylic acid by hydrogen bonding. A seven-membered transition state C≠ is postulated for reactions of 2-amino alcohols. The fastest reaction was observed for trans-2-(N,N- dimethylamino)cyclohexanol (2e), in which the amino and the hydroxyl groups are in an almost perfect synperiplanar 1,2-position. Attempts to further enhance the rate of the esterification by the addition of potential catalysts failed. Only Cu(OTf)2 (2.5 mol-%) allowed for a moderate rate increase from 7.5 · 10-5 s-1 (uncatalyzed) to 14.8 · 10 -5 s-1 (catalyzed) in the esterification of hexanoic acid (1) with 2-(N,N-dimethylamino)ethanol (2a).
KW - Acylation
KW - Amino Alcohols
KW - Hydrogen Bonds
KW - Kinetics
KW - Transition States
UR - http://www.scopus.com/inward/record.url?scp=33744966639&partnerID=8YFLogxK
U2 - 10.1515/znb-2006-0513
DO - 10.1515/znb-2006-0513
M3 - Article
AN - SCOPUS:33744966639
SN - 0932-0776
VL - 61
SP - 583
EP - 588
JO - Zeitschrift fur Naturforschung - Section B Journal of Chemical Sciences
JF - Zeitschrift fur Naturforschung - Section B Journal of Chemical Sciences
IS - 5
ER -