Clean synthesis of benzylidenemalononitrile by Knoevenagel condensation of benzaldehyde and malononitrile: effect of combustion fuel on activity and selectivity of Ti-hydrotalcite and Zn-hydrotalcite catalysts

  • Amarsinh L Jadhav
  • Ganapati D YadavEmail author
Regular Article


Benzylidene malononitrile find applications in pharmaceutical industries, pharmacology, biotech, specialty chemicals, perfumery, and for fluorescence-based assay to determine methane and is produced by polluting routes. Hydrotalcites (HT) have been very effective as solid bases in different reactions and their properties can be changed by using different synthetic methods. In this work, the effect of additional metal in the synthesis of Al-Mg hydrotalcite was systematically studied to prepare Ti-Al-Mg (Ti modified hydrotalcite) and Zn-Al-Mg HT (Zn modified hydrotalcite) using combustion method with glycine as well as glycerol as a fuel. All synthesized catalysts were evaluated in Knoevenagel condensation of benzaldehyde with malononitrile to give benzylidene malononitrile. The catalysts were completely characterized by SEM, EDXS, \(\text {N}_{2}\) Adsorption, \(\text {CO}_{2}\)-TPD and \(\text {NH}_{3}\)-TPD and XRD techniques. Ti-Al-Mg hydrotalcite using glycine as a fuel was found to be the most active, selective and reusable catalyst. Langmuir-Hinshelwood-Hougen-Watson (LHHW) model was used to establish the reaction mechanism and kinetics. All species were weakly adsorbed leading to the second order power law model. Using mole ratio of 1:3 of benzaldehyde to malononitrile with ethyl acetate as a solvent and \(2.5 \times 10^{-4}\) g/\(\text {cm}^{3}\) catalyst loading, 67.1% conversion of benzaldehyde and 97.6% selectivity to benzylidene malononitrile were achieved in 4 h at 60 \({^{\circ }}\)C. The apparent activation energy was 10.01 kcal/mol. The process is green.

Graphic abstract

Ti-Al-Mg and Zn-Al-Mg hydrotalcites were prepared using combustion method with glycine and glycerol as fuel and used in the Knoevenagel condensation of benzaldehyde with malononitrile to give benzylidene malononitrile. Ti-Al-Mg hydrotalcite (glycine) was the most active, selective and reusable catalyst.


Combustion synthesis hydrotalcite Ti-Al-Mg hydrotalcite Knoevenagel condensation benzelidine malonontrile (or 2-benzylidenepropanedinitrile) 



reactant species A, benzaldehyde


reactant species B, malononitrile

\(\text {C}_{\mathrm{A}}\)

concentration of A, benzaldehyde (mol/cm\(^3\))

\(\text {C}_{\mathrm{A0}}\)

initial concentration of A in bulk liquid phase \((\hbox {mol/cm}^{3})\)

\(\text {C}_{\mathrm{AS1}}\)

adsorption concentration of A on active site \(\text {S}_{1}\)

\(\text {C}_{\mathrm{B}}\)

concentration of B \((\hbox {mol/cm}^{3})\)

\(\text {C}_{\mathrm{B0}}\)

initial concentration of B in bulk liquid phase \((\hbox {mol/cm}^{3})\)

\(\text {C}_{\mathrm{BS1}}\)

concentration of B on active sites of type \(\mathrm{S}_1 \) (mol/g)

\(\text {C}_{\mathrm{E}}\)

concentration of E, product species \((\hbox {mol/cm}^{3})\)

\(\text {C}_{\mathrm{ES1}}\)

concentration of E on active sites of type \(\text {S}_{1}\) (mol/g)

\(\text {C}_{\mathrm{S1}}\)

concentration of vacant sites of type \(\text {S}_{1}\) (mol/g)

\(\text {C}_{\mathrm{S2}}\)

concentration of vacant sites of type \(\text {S}_{2}\) (mol/g)

\(\text {C}_{\mathrm{T1}}\)

total concentration of vacant sites of type \(\text {S}_{1}\) (mol/g)

\(\text {C}_{\mathrm{T2}}\)

total concentration of vacant sites of type \(\text {S}_{2}\) (mol/g)

\(\text {C}_{\mathrm{W}}\)

concentration of W, product species (\(\text {mol}/\text {cm}^3\))

\(\text {C}_{\mathrm{WS2}}\)

concentration of W on active sites of type \(\text {S}_{2}\) (mol/g)


product species E, benzylidene malononitrile

\(\text {K}_{\mathrm{A}}\)

adsorption equilibrium constant for A (\(\hbox {cm}^{3}\)/mol)

\(\text {K}_{\mathrm{B}}\)

adsorption equilibrium constant for B (\(\hbox {cm}^{3}\)/mol)

\(\text {K}_{\mathrm{E}}\)

adsorption equilibrium constant for E (\(\hbox {cm}^{3}\)/mol)

\(\text {K}_{\mathrm{W}}\)

adsorption equilibrium constant for W (\(\hbox {cm}^{3}\)/mol)


mole ratio of \(\text {C}_{B0}\)/\(\text {C}_{A0}\)

\(-\text {r}_{\mathrm{A}}\)

rate of reaction (mol \(\hbox {cm}^{-3}\hbox { min}^{-1})\)


product species W, water


catalyst loading \((\hbox {g/cm}^{3})\)

\(\text {X}_{A}\)

fractional conversion of A


time (min)



ALJ thanks the management of D.Y. Patil College of Engineering and Technology, Kolhapur for permitting him to do this doctoral work. Thanks are also due to Dr. Godfree Fernandes for his help. GDY acknowledges support from R.T. Mody Distinguished Professor Endowment, Tata Chemicals Darbari Seth Distinguished Professor of Leadership and Innovation, and J. C. Bose National Fellowship of Department of Science and Technology, GoI.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary material

12039_2019_1641_MOESM1_ESM.pdf (325 kb)
Supplementary material 1 (pdf 325 KB)


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Copyright information

© Indian Academy of Sciences 2019

Authors and Affiliations

  1. 1.Departmental of Chemical EngineeringInstitute of Chemical TechnologyMumbaiIndia

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