Mechanistic considerations and characterization of ammonia-based catalytic active intermediates of the green Knoevenagel reaction of various benzaldehydes^*

* The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

ABSTRACT

In the green Knoevenagel reaction of benzaldehyde and malonic acid, the carbon–carbon formation reaction is catalyzed by a double Schiff base formed by benzaldehyde and ammonia. A mechanism for this green Knoevenagel has been proposed. A closed catalytic cycle explains why various ammonium salts, including ammonium bicarbonate, have been correctly reported as catalysts in Knoevenagel-like reactions. Various catalytically active intermediates from derivatives of benzaldehyde were isolated and characterized. Furthermore, these in situ formed double Schiff bases play another catalytic role in the consecutive decarboxylation reaction to various cinnamic acids.

GRAPHICAL ABSTRACT

KEYWORDS:

• Green Knoevenagel
• Sustainable Chemistry
• organocatalysis
• double Schiff base
• decarboxylation

Acknowledgement

The authors are grateful for the financial support from Netherlands Organization for Scientific Research (NWO) (grant 023.007.020 awarded to Jack van Schijndel). We further thank Sebastian van Schijndel for his help on the graphical abstract.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Jack van Schijndel studied chemistry at the State University of Utrecht with a major in the field of structural chemistry. He has been teaching Chemistry at the tertiary level for over 28 years and has supervised both undergraduate and postgraduate research projects in this field at the Avans University of Applied Sciences. His latest work focusses on the sustainable use of renewable resources for the polymer industry. The synthetic routes developed are furthermore designed along the lines of the Green Chemistry principles. He supervised as a senior scientist more than 60 projects with SME’s in the field of biopolymers. His main areas interest is green chemistry, polymer synthesis but also teaching and learning innovations.

Dennis Molendijk received the B.Sc. degree in Chemistry at Avans University of Applied Sciences and is working under the supervision of Jack van Schijndel. He is involved in all ongoing projects in the research laboratory and also guides younger students with their research projects. His current research is focused on the green synthesis of biobased blocks of biopolymers and polymerization of these.

Harmen Spakman is a student of the B.Sc. Degree in Chemistry at Avans University of Applied Sciences.

Edward Knaven is currently an academic technician in the Research group Analysis Techniques in Life Science of Avans University of Applied Sciences. His research interests lie in the study of mass spectrometry of organic compounds.

Luiz Alberto Canalle received the M.Sc. degree in chemistry from the Radboud University Nijmegen, The Netherlands, in 2006. He received his PhD. in bio-organic chemistry from the same university in 2010. Since 2012, he has been with Avans University of Applied Sciences, Breda, The Netherlands as a lecturer in organic chemistry and researcher in the field of biopolymers. His main areas interest are polymer synthesis; green chemistry and the research/teaching nexus.

Jan Meuldijk obtained his M.Sc. degree in chemistry at the State University of Utrecht in 1975. His PhD. work was in the field of inorganic and theoretical chemistry at the Free University of Amsterdam, graduation in 1979. After post-doctoral fellowships in solid state physics and chemical engineering at the State University of Groningen, he was appointed assistant professor in the field of Industrial Catalysis at the Eindhoven University of Technology in 1985. In 1988, he became associate professor in chemical reactor engineering. His work in the Chemical Reaction Engineering Group is focused on process development of complex chemical products. In the department of Chemical Engineering and Chemistry there is a close cooperation with the Polymer Chemistry Group and the Macromolecular and Organic Chemistry Group. As of September 1, 2010 he is full professor in Polymer Reaction Engineering and Scientific Director of the Post MSc. Program “Process and Product Design”.

ORCID

Jack van Schijndel http://orcid.org/0000-0002-2806-7536

Notes

* The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Additional information

Funding

The authors are grateful for the financial support from Netherlands Organization for Scientific Research (NWO): [Grant Number 023.007.020 awarded to Jack van Schijndel].