Real-time Raman monitoring during coumarins synthesis via Pechmann condensation: A tool for controlling the preparation of pharmaceuticals

Casilda, Vanesa Calvino; Bañares, Miguel Á.; Lozano-Diz, Enrique

doi:10.1016/j.cattod.2010.01.068

Cited by 21 publications

(7 citation statements)

References 5 publications

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“…As already observed by means of NMR measurements, comparison of the C4_PEG spectrum with reference compounds shows that the synthesis route was successful and the C4 is anchored to the polymeric support. In particular, there are few vibrational signatures characteristic of aromatic alcohols (1154, 1213, 1334, 1520, and the doublet at 1569 and 1584 cm –1 ) and of conjugated alkenes (the doublet at 1368 and 1387 cm –1 ) recorded in the C4 powders − and retrieved in the C4_PEG samples: at 1154, 1200, 1347, 1560, and 1614 cm –1 (unresolved doublet) for the aromatic vibrations and at 1368 and 1387 cm –1 for the alkenes ones. As a general observation, the vibration frequency is shifted to higher values because of the larger efficient reduced mass in the C4_PEG compound.…”

Section: Resultsmentioning

confidence: 99%

Optical Characterization of PEG-Supported 7-Hydroxy-4-methyl-coumarin in Distilled Water Solution

Carbonaro¹,

Ricci²,

Casula³

et al. 2012

J. Phys. Chem. A

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The optical properties of 7-hydroxy-4-methyl coumarin immobilized on polyethylene glycol support and dissolved in distilled water solution are compared with the optical properties of the dye dissolved in ethanol and discussed on the basis of the formation of different chemical species of the dye molecule. The presence of the polymeric support affects both the absorption and emission features of the coumarin by changing the chemical equilibrium among the different species typically observed at the ground and excited states. The optical properties of synthesized PEG-supported coumarins are able to warrant biomedical applications in water-based environment and enable us to gain insight into the photophysical activity of coumarins; in particular, the steric hindrance of the polymeric support inhibits, as expected, the formation of the tautomeric form of the compound in the excited state, a further proof of the single-step neutral to tautomer reaction in coumarins.

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Section: Resultsmentioning

confidence: 99%

Optical Characterization of PEG-Supported 7-Hydroxy-4-methyl-coumarin in Distilled Water Solution

Carbonaro¹,

Ricci²,

Casula³

et al. 2012

J. Phys. Chem. A

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“…Our results are consistent with previous experimental literature. 7,6 The theoretical study done with ethyl acetoacetate by Daru and Stirling 3 shows that in the Gibbs free energy profile the intermediates are not very stable and not separated from the next step by a large energy barrier and , therefore, less likely to be observable.…”

Section: Scheme 1 Possible Mechanisms For the Pechmann Condensation R...mentioning

confidence: 99%

“…However, they did not report detecting any intermediates, only byproducts that were formed at higher reaction time and temperature. In 2010, Calvino-Casilda et al 7 used Raman spectroscopy to monitor the reaction of resorcinol and ethyl acetoacetate in real time. They were unable to observe any intermediates.…”

mentioning

confidence: 99%

Insight into the Mechanism of the Pechmann Condensation Reaction Using NMR

2015

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The mechanism of the Pechmann condensation is still controversial despite the technological and biochemical importance of coumarins. Here, we present NMR evidence for a mechanism featuring the sequence of initial electrophilic aromatic substitution followed by transesterification and a final dehydration. This mechanism has been convincingly defined and supported by the temporal evolution of two key intermediates which could be purified and identified.

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“…More commonly, real-time reaction monitoring of chemical reactions using Raman spectroscopy has been used for organic reactions occurring under neat conditions or in organic solvents, which may have distinct signals in the Raman spectra that can obscure the signal of interest. − The more common in situ method typically involves immersing a costly Raman probe into a reaction vessel. − There are limited reports that describe using Raman spectroscopy in an ex situ manner to monitor a reaction . An additional benefit of the ex situ noninvasive method is the ability to obtain reaction kinetics data with minimum effort, , which can provide new information about reduction reactions. , …”

Section: Introductionmentioning

confidence: 99%

Real-Time Monitoring of Aqueous Organic Reduction Reactions Using Ex Situ Fiber Optic Raman Spectroscopy

Amberchan

Allen

Golden

et al. 2021

ACS Sustainable Chem. Eng.

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Here, we demonstrate the use of Raman spectroscopy for real-time monitoring and analysis of the reduction of nitroarenes and ketones in an aqueous medium using an external fiber optic probe. In one case, the catalytic reduction of nitroarenes using hydrazine hydrate and a nickel boron composite catalyst was studied by monitoring the disappearance of the distinct nitro stretching frequency at 1350 cm–1. Quantitative Raman spectroscopic techniques showed that the aqueous reduction reaction proceeds with pseudo-first-order kinetics. The biphasic reduction of cyclic ketones by aqueous dimethylamine borane (DMAB) was also examined. A nonpolar carbonyl compound and aqueous DMAB were mixed and an external Raman probe monitored the loss of the starting material via the carbonyl stretch at 1713 cm–1 in the top organic phase. We also found that saturated aliphatic carbonyl compounds were reduced much faster than α,β-unsaturated and aromatic carbonyl compounds. Additionally, DMAB was found to be unreactive toward epoxides and esters, allowing for selective reduction of aliphatic ketones. Density functional theory analysis suggests that carbonyl reduction occurred through a dissociation mechanism followed by a concerted hydride transfer pathway.

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Real-time Raman monitoring during coumarins synthesis via Pechmann condensation: A tool for controlling the preparation of pharmaceuticals

Cited by 21 publications

References 5 publications

Optical Characterization of PEG-Supported 7-Hydroxy-4-methyl-coumarin in Distilled Water Solution

Optical Characterization of PEG-Supported 7-Hydroxy-4-methyl-coumarin in Distilled Water Solution

Insight into the Mechanism of the Pechmann Condensation Reaction Using NMR

Real-Time Monitoring of Aqueous Organic Reduction Reactions Using Ex Situ Fiber Optic Raman Spectroscopy

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