The Experts below are selected from a list of 33 Experts worldwide ranked by ideXlab platform

Graham R Cooks - One of the best experts on this subject based on the ideXlab platform.

  • Reaction acceleration at air solution interfaces anisotropic rate constants for Katritzky transamination
    Journal of Mass Spectrometry, 2020
    Co-Authors: Tsdale F Mehari, Zhenwei Wei, Yong Liu, Graham R Cooks
    Abstract:

    To disentangle the factors controlling the rates of accelerated Reactions in droplets, we used mass spectrometry to study the Katritzky transamination in levitated Leidenfrost droplets of different yet constant volumes over a range of concentrations while holding concentration constant by adding back the evaporated solvent. The set of concentration and droplet volume data indicates that the Reaction rate in the surface region is much higher than that in the interior. These same effects of concentration and volume were also seen in bulk solutions. Three pyrylium reagents with different surface activity showed differences in transamination reactivity. The conclusion is drawn that Reactions with surface-active reactants are subject to greater acceleration, as seen particularly at lower concentrations in systems of higher surface-to-volume ratios. These results highlight the key role that air-solution interfaces play in Katritzky Reaction acceleration. They are also consistent with the view that Reaction-increased rate constant is at least in part due to limited solvation of reagents at the interface.

  • accelerated chemical synthesis three ways of performing the Katritzky transamination Reaction
    Journal of Chemical Education, 2019
    Co-Authors: Robert L Schrader, Patrick W Fedick, Tsdale F Mehari, Graham R Cooks
    Abstract:

    Typical laboratory exercises for undergraduate organic chemistry students involve bulk phase Reactions with work up of product. In this study, students performed accelerated versions of the Katritzky Reaction of para-substituted anilines with pyrylium salts in three ways: (i) by dropcasting reagents onto a paper surface and allowing solvent to evaporate, (ii) by evaporation of solvent from the reagent mixture in a rotary evaporator, and (iii) at an organic/water interface (“on water”). Students determined the Reaction yield for all three accelerated Reactions as well as in the conventional bulk phase by mass spectrometry. Acceleration factors (the ratio of the product to reagent ion signals in the accelerated vs conventional Reaction) were used to compare the paper spray and rotary evaporator method as well as the “on water” method. Substituent effects were explored by using substituted anilines. Students’ understanding of acceleration of organic Reactions was increased as seen in both laboratory reports and exit interviews.

  • chemical reactivity assessment using reactive paper spray ionization mass spectrometry the Katritzky Reaction
    ChemPlusChem, 2013
    Co-Authors: Xin Yan, Rodinei Augusti, Graham R Cooks
    Abstract:

    Paper spray ionization can be used to study organic Reactions in solution under ambient conditions by utilizing the rate acceleration that occurs in Reactions in small volumes of solution. In this novel approach to performing Reactions, reagents are transferred onto a triangular paper surface by drop-casting and charged droplets of the Reaction product mixture are released by field evaporation and examined online by mass spectrometry. The increase in the rate of product formation is attributed to solvent evaporation, which increases reagent concentrations, changes the pH, and enhances intermolecular interactions. As a proof of principle, the Katritzky Reaction between a pyrylium salt and mono- or diamines, including substituted anilines, was investigated. The influence of electronic and steric effects was evaluated straightforwardly. The carbon chain length of α,ω-diamines was found to control the formation of mono- versus disubstituted products, thus reflecting the strong destabilizing coulombic effects in the shorter carbon-chain systems. Information on the mechanism was provided by the observation of 2H-pyran intermediates and mixed pyridinium-2H-pyran ions. The rates of product formation in the base-assisted Katritzky Reaction increase linearly from 0.1 to 10 equivalents of triethylamine. The reactive paper spray technique, owing to its speed and information content, has potential pedagogical value and provides a tool to explore organic Reactions and correlate experimental results with current mechanistic understanding.

Licia Viggiani - One of the best experts on this subject based on the ideXlab platform.

  • ru bpy 2cl2 a catalyst able to shift the course of the photorearrangement in the boulton Katritzky Reaction
    Tetrahedron Letters, 2015
    Co-Authors: Maurizio Dauria, Domenico Spinelli, Vincenzo Frenna, Rocco Racioppi, Magda Monari, Antonio Palumbopiccionello, Licia Viggiani
    Abstract:

    Abstract The Boulton–Katritzky Reaction represents one of the most popular and efficient strategies used to realize azole-into-azole conversions. For example, under different experimental conditions, it allows the rearrangement of Z-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazoles (1) into 2-aryl-4-benzoylamino-5-phenyl-2H-1,2,3-triazoles (2) in very high yields. Moreover, we have recently realized this conversion also by UV-photostimulation. Now we have enlarged the scope of the Reaction irradiating with visible or UV light an acetonitrile solution of some Z-arylhydrazones (1a–e) in the presence of catalytic amounts of Ru(bpy)2Cl2. We have observed the unexpected formation of the 1-aryl-5-benzoylamino-3-phenyl-1,2,4-triazoles (3a–e) eventually together with the expected 2a–d in high yields.

Maurizio Dauria - One of the best experts on this subject based on the ideXlab platform.

  • ru bpy 2cl2 a catalyst able to shift the course of the photorearrangement in the boulton Katritzky Reaction
    Tetrahedron Letters, 2015
    Co-Authors: Maurizio Dauria, Domenico Spinelli, Vincenzo Frenna, Rocco Racioppi, Magda Monari, Antonio Palumbopiccionello, Licia Viggiani
    Abstract:

    Abstract The Boulton–Katritzky Reaction represents one of the most popular and efficient strategies used to realize azole-into-azole conversions. For example, under different experimental conditions, it allows the rearrangement of Z-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazoles (1) into 2-aryl-4-benzoylamino-5-phenyl-2H-1,2,3-triazoles (2) in very high yields. Moreover, we have recently realized this conversion also by UV-photostimulation. Now we have enlarged the scope of the Reaction irradiating with visible or UV light an acetonitrile solution of some Z-arylhydrazones (1a–e) in the presence of catalytic amounts of Ru(bpy)2Cl2. We have observed the unexpected formation of the 1-aryl-5-benzoylamino-3-phenyl-1,2,4-triazoles (3a–e) eventually together with the expected 2a–d in high yields.

Antonio Palumbopiccionello - One of the best experts on this subject based on the ideXlab platform.

  • ru bpy 2cl2 a catalyst able to shift the course of the photorearrangement in the boulton Katritzky Reaction
    Tetrahedron Letters, 2015
    Co-Authors: Maurizio Dauria, Domenico Spinelli, Vincenzo Frenna, Rocco Racioppi, Magda Monari, Antonio Palumbopiccionello, Licia Viggiani
    Abstract:

    Abstract The Boulton–Katritzky Reaction represents one of the most popular and efficient strategies used to realize azole-into-azole conversions. For example, under different experimental conditions, it allows the rearrangement of Z-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazoles (1) into 2-aryl-4-benzoylamino-5-phenyl-2H-1,2,3-triazoles (2) in very high yields. Moreover, we have recently realized this conversion also by UV-photostimulation. Now we have enlarged the scope of the Reaction irradiating with visible or UV light an acetonitrile solution of some Z-arylhydrazones (1a–e) in the presence of catalytic amounts of Ru(bpy)2Cl2. We have observed the unexpected formation of the 1-aryl-5-benzoylamino-3-phenyl-1,2,4-triazoles (3a–e) eventually together with the expected 2a–d in high yields.

Magda Monari - One of the best experts on this subject based on the ideXlab platform.

  • ru bpy 2cl2 a catalyst able to shift the course of the photorearrangement in the boulton Katritzky Reaction
    Tetrahedron Letters, 2015
    Co-Authors: Maurizio Dauria, Domenico Spinelli, Vincenzo Frenna, Rocco Racioppi, Magda Monari, Antonio Palumbopiccionello, Licia Viggiani
    Abstract:

    Abstract The Boulton–Katritzky Reaction represents one of the most popular and efficient strategies used to realize azole-into-azole conversions. For example, under different experimental conditions, it allows the rearrangement of Z-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazoles (1) into 2-aryl-4-benzoylamino-5-phenyl-2H-1,2,3-triazoles (2) in very high yields. Moreover, we have recently realized this conversion also by UV-photostimulation. Now we have enlarged the scope of the Reaction irradiating with visible or UV light an acetonitrile solution of some Z-arylhydrazones (1a–e) in the presence of catalytic amounts of Ru(bpy)2Cl2. We have observed the unexpected formation of the 1-aryl-5-benzoylamino-3-phenyl-1,2,4-triazoles (3a–e) eventually together with the expected 2a–d in high yields.