Aim & Scope: The synthesis of highly substituted piperidine from the one-pot reaction
between aromatic aldehydes, anilines and β-ketoesters in the presence of tartaric acid as a catalyst
has been investigated in both methanol and ethanol media at ambient temperature. Different
conditions of temperature and solvent were employed for calculating the thermodynamic parameters
and obtaining an experimental approach to the kinetics and mechanism. Experiments were carried
out under different temperature and solvent conditions.
Material and Methods:
Products were characterized by comparison of physical data with authentic
samples and spectroscopic data (IR and NMR). Rate constants are presented as an average of several
kinetic runs (at least 6-10) and are reproducible within ± 3%. The overall rate of reaction is followed
by monitoring the absorbance changes of the products versus time on a Varian (Model Cary Bio-
300) UV-vis spectrophotometer with a 10 mm light-path cell.
Results:
The best result was achieved in the presence of 0.075 g (0.1 M) of catalyst and 5 mL
methanol at ambient temperature. When the reaction was carried out under solvent-free conditions,
the product was obtained in a moderate yield (25%). Methanol was optimized as a desirable solvent
in the synthesis of piperidine, nevertheless, ethanol in a kinetic investigation had none effect on the
enhancement of the reaction rate than methanol. Based on the spectral data, the overall order of the
reaction followed the second order kinetics. The results showed that the first step of the reaction
mechanism is a rate determining step.
Conclusion:
The use of tartaric acid has many advantages such as mild reaction conditions, simple
and readily available precursors and inexpensive catalyst. The proposed mechanism was confirmed
by experimental results and a steady state approximation.