7th International Electronic Conference on Synthetic Organic Chemistry (ECSOC-7), http://www.mdpi.net/ecsoc-7, 1-30 November 2003

[E008]

THE COMPARATIVE STUDY OF THE KINETICS OF KNOEVENAGEL CONDENSATION UNDER MICROWAVE AND CONVENTIONAL CONDITIONS. Part III.

Szczepan Bednarz, Dariusz Bogdal*

*e-mail: [email protected]

Department of Polymer Science and Technology Politechnika Krakowska ul. Warszawska 24, 31-155 Krakow, Poland


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Abstract
The reaction of the Knoevenagel condensation of salicylaldehyde, diethylmalonate in the presence of 4-piperydinopiperidyne as a catalyst in toluene as a solvent has been studied. The research were focused on the influence of microwave radiation on the reaction kinetics.

Keyworts
microwave irradiation, microwave effect, chemical kinetics, knoevenagel reaction

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In the recent articles [1][2] we presented comparative study of the Knoevenagel condensation under microwave radiation and conventional heating where rate enhancement of investigated reaction was observed. We studied kinetic of reaction between salicylaldehyde and diethylmalonate in the presence of piperidyne as a catalyst in toluene as a solvent. To settle the matter existence of non-thermal microwave effect in Knoevenagel condensation a similar reaction has been studied (fig. 1).
 

Figure 1. Knoevenagel condensation: salicylaldehyde (A), diethylmalonate (M), 4-piperidinopiperidine (PP), 3-ethoxycarbonylcoumarine (C). Experiments conditions: [A]0=0.35 mol/l, [M]0=0.36 mol/l, [PP]=0.092 mol/l, solvent - toluene.

To improve consistency of experiments other catalyst was applied. The 4-piperidinopiperidine is soluble in non-polar solvents (e.g. toluene), non hygroscopic, air resist and crystalline solid in room temperature (mp 64-66°C).

The rate of disappearance of diethylmalonate is expressed by equation:

The reaction rate constant (kobs) is dependent on the temperature and can be described by the Arrhenius-like equation:

where C1, C2 are kinetic parameters, R is a gas constant and T is a temperature. The conversion of diethylmalonate was calculated from the measured temperature profiles and kinetic parameters obtained under conventional heating (C1=29.9 l/mol·s, C2=36.9 kJ/mol).

Figure 2. Experimental (circles) and calculated conversions of diethylmalonate in conventional conditions.

Figure 3. Experimental (circles) and calculated conversions of diethylmalonate in microwave conditions.

The agreement between the calculated and experimental concentrations shows that is no specific microwave effect on the investigated reaction (fig. 2 and 3).

Presented results does not confirm existence of non-thermal microwave effect in Knoevenagel condensation. Observed in previous [2] experiments reaction rate enhancement could be explain as influence of catalyst (piperidine) activity probably depended on trace amount of water.


[1]  THE COMPARATIVE STUDY OF THE KINETICS OF KNOEVENAGEL CONDENSATION UNDER MICROWAVE AND CONVENTIONAL CONDITIONS, Szczepan Bednarz, Dariusz Bogdal, Fifth International Electronic Conference on Synthetic Organic Chemistry (ECSOC-5)

[2]  THE COMPARATIVE STUDY OF THE KINETICS OF KNOEVENAGEL CONDENSATION UNDER MICROWAVE AND CONVENTIONAL CONDITIONS. Part II, Szczepan Bednarz, Dariusz Bogdal, Sixth International Electronic Conference on Synthetic Organic Chemistry (ECSOC-6)