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On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes
Published on: August 5, 2016
Nucleophilicities and carbon basicities of pyridines
Frank Brotzel1, Bernhard Kempf, Thomas Singer
1Department Chemie und Biochemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13 (Haus F), 81377 München, Germany.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|September 30, 2006
Summary
This study quantifies pyridine reactivity with benzhydrylium ions, revealing comparable nucleophilicities between 4-(dimethylamino)pyridine (DMAP) and phosphanes. These findings offer guidelines for designing new organocatalysts based on reactivity parameters.
Area of Science:
- Organic Chemistry
- Physical Chemistry
- Catalysis
Background:
- Understanding nucleophilic reactivity is crucial for organocatalyst development.
- Benzhydrylium ions serve as useful electrophilic probes.
- Pyridines and phosphanes are important classes of nucleophiles.
Purpose of the Study:
- To determine the rate and equilibrium constants for reactions between pyridines and donor-substituted benzhydrylium ions.
- To establish nucleophilicity parameters for various pyridines in different solvents.
- To compare the nucleophilicities of pyridines, 4-(dimethylamino)pyridine (DMAP), and tertiary phosphanes.
Main Methods:
- Spectrophotometric determination of reaction kinetics and equilibria.
- Application of the correlation equation log k(20 degrees C)=s(N+E) to quantify nucleophile (N) and electrophile (E) parameters.
- Utilizing the Marcus equation to calculate intrinsic reaction barriers.
Main Results:
- Nucleophilicity parameters for pyridines were determined in dichloromethane and aqueous solutions.
- 4-(dimethylamino)pyridine (DMAP) and tertiary phosphanes exhibit similar nucleophilicities and carbon basicities.
- Significant differences in Brønsted basicity do not correlate with observed nucleophilicities.
Conclusions:
- Reactivity parameters, specifically nucleophilicity and carbon basicity, are valuable for predicting and comparing the behavior of organocatalysts.
- The comparable nucleophilicities of DMAP and phosphanes, despite differing Brønsted basicities, highlight the importance of considering multiple reactivity facets.
- The findings provide a basis for the rational design of novel organocatalysts with tailored reactivity profiles.
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