Flow Reactors for Preparative Chemistry in Supercritical Fluid Solution: "Solvent-Free" Synthesis and Isolation of Cr(CO)5(C2H4) and (.eta.5-C5H5)Mn(CO)2(.eta.2-H2)

1995 ◽  
Vol 14 (8) ◽  
pp. 3876-3885 ◽  
Author(s):  
James A. Banister ◽  
Peter D. Lee ◽  
Martyn Poliakoff
Keyword(s):  
Supercritical Fluid ◽  
Solvent Free ◽  
Fluid Solution ◽  
Flow Reactors ◽  
Solvent Free Synthesis

“Solvent-Free” Photochemical Activation of CH4, C2H4, and C2H6by (C5Me5)Ir(CO)2in Supercritical Fluid Solution

1996 ◽  
Vol 15 (7) ◽  
pp. 1804-1812 ◽  
Author(s):  
James A. Banister ◽  
Andrew I. Cooper ◽  
Steven M. Howdle ◽  
Margaret Jobling ◽  
Martyn Poliakoff
Keyword(s):  
Supercritical Fluid ◽  
Solvent Free ◽  
Fluid Solution ◽  
Photochemical Activation

Temperature Dependent Green Synthesis of 3-Carboxycoumarins and 3,4-unsubstituted Coumarins

2019 ◽  
Vol 16 (1) ◽  
pp. 130-135 ◽  
Author(s):  
Jack van Schijndel ◽  
Dennis Molendijk ◽  
Luiz Alberto Canalle ◽  
Erik Theodorus Rump ◽  
Jan Meuldijk
Keyword(s):  
Knoevenagel Condensation ◽  
Ammonium Bicarbonate ◽  
Solvent Free ◽  
Temperature Dependent ◽  
Step Procedure ◽  
Synthetic Routes ◽  
High Yields ◽  
Temperature Optima ◽  
Solvent Free Synthesis ◽  
Full Conversion

Aim and Objective: Because of the low abundance of 3,4-unsubstituted coumarins in plants combined with the complex purification process required, synthetic routes towards 3,4-unsubstituted coumarins are especially valuable. In the present work, we explore the possibilities of a solvent-free Green Knoevenagel condensation on various 2-hydroxybenzaldehyde derivatives and malonic acid without the use of toxic organocatalysts like pyridine and piperidine but only use ammonium bicarbonate as the catalyst. Materials and Methods: To investigate the scope of the Green Knoevenagel condensation for the synthesis of 3,4-unsubstituted coumarins, various 2-hydroxybenzaldehyde derivatives were screened as starting material in the optimized two-step procedure developed for 2-hydroxybenzaldehyde. </P><P> Results: This study shows that the intramolecular esterification and the decarboxylation are in competition, but show different temperature optima. In order to suppress premature decarboxylation and maximize the yield of coumarin, a two-step procedure was adopted. The reaction mixture containing ammonium bicarbonate is initially kept at 90ºC for 1 hour. After completion of the cyclization, the temperature of the reaction mixture is increased to 140ºC for 2 hours. Following this protocol, coumarin could be isolated with a yield of 95%. Conclusion: A two-step procedure for the solvent-free synthesis of several 3,4-unsubstituted coumarins was developed using ammonium bicarbonate, resulting in high yields of the desired products. Moreover, this procedure has a low E-factor and is, therefore an environmental friendly reaction in line with the principles of Green Chemistry. It was shown that by initially capping the temperature at 90ºC, premature decarboxylation can be suppressed. After full conversion to the intermediate 3-carboxycoumarin, the temperature can be increased to 140ºC finalizing the reaction. Ammonium bicarbonate was shown to catalyze both the Green Knoevenagel condensation and the decarboxylation step.

Niobic Acid as a Recyclable Heterogeneous Catalyst for the Solvent-Free Synthesis of Substituted Benzimidazoles

2013 ◽  
Vol 1 (2) ◽  
pp. 136-144 ◽  
Author(s):  
Beatriz Vieira ◽  
Angelita Barcellos ◽  
Ricardo Schumacher ◽  
Eder Lenardao ◽  
Diego Alves
Keyword(s):  
Heterogeneous Catalyst ◽  
Solvent Free ◽  
Niobic Acid ◽  
Recyclable Heterogeneous Catalyst ◽  
Solvent Free Synthesis
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