Recent Advances in Several Organic Reaction Mechanisms

Sánchez‐Viesca, Francisco; Berros, Martha; Gómez, Reina

doi:10.11648/j.mc.20190701.14

Cited by 5 publications

(6 citation statements)

References 9 publications

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“…Well, in the Baeyer-Drewsen indigo synthesis, after a long series of reactions, leucoindigo is formed by condensation of 1-hydroxyindoxyl and indolenin-3-one. The extra hydroxyl group is lost by dehydration, obviating one step, [30]. This is conclusive evidence that the two proposed reaction mechanisms are correct.…”

Section: Discussionsupporting

confidence: 57%

On the Formation Mechanism of Indigo Blue and Indigo Red from Vegetable Source

Sánchez-Viesca¹,

Gómez²

2021

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In this communication a series of ionic reactions is advanced in order to explain not only indigo blue formation but also the continuous presence of indigo red as companion, and why this compound is always found in minority. Indican is the glycoside found in Indigofera tinctoria from which the mixture of indigo blue and indigo red is obtained by means of air oxidation in alkaline medium. A reaction mechanism for the hydrolysis of indican, which was advanced decades ago, is criticized in this paper. Fifty years ago a radical mechanism was suggested for indigo formation. However, the supposed reactive species, indoxyl radical, was not detected by electron spin resonance. Besides, there is no free radical promoter, and indirubin (indigo red) was not considered. A series of ionic reactions explain the formation of both indigoids, and why indigo red occurs in minor proportion. Indoxyl, 3-hydroxyindole, is the aglycone from indican. Reaction of indoxyl with oxygen is catalyzed by calcium hydroxide, indoxyl hydroperoxide being formed. Internal reaction in this intermediate produces 3-oxoindolenine, which reacts with indoxyl carbanion to give leucoindigo. Further steps lead to indigo blue. Indirubin is formed from indoxyl hydroperoxide by dehydration to isatin, a keto lactam. Condensation of isatin salt with 3-indolinone affords indigo red. This step is retarded due to electric hindrance.

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Section: Discussionsupporting

confidence: 57%

On the Formation Mechanism of Indigo Blue and Indigo Red from Vegetable Source

Sánchez-Viesca¹,

Gómez²

2021

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“…Hole injection instead of electron injection on the CHO moiety may be considered a counterintuitive mechanism to favor a reduction reaction on the carbon atom. An analogous reaction, the Clemmensen reduction, 120,121 leads to carbonyl hydrogenation catalyzed by amalgamated zinc in the presence of concentrated hydrochloric acid. In this case, two possible mechanisms have been proposed: the reaction goes on through direct protonation of the oxygen atom generating the carbanionic compound or through oxygen adsorption on zinc surface via carbenoid mechanism.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Peeking into the Femtosecond Hot-Carrier Dynamics Reveals Unexpected Mechanisms in Plasmonic Photocatalysis

Dall’Osto,

Marsili,

Vanzan

et al. 2024

J. Am. Chem. Soc.

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Plasmonic-driven photocatalysis may lead to reaction selectivity that cannot be otherwise achieved. A fundamental role is played by hot carriers, i.e., electrons and holes generated upon plasmonic decay within the metal nanostructure interacting with molecular species. Understanding the elusive microscopic mechanism behind such selectivity is a key step in the rational design of hot-carrier reactions. To accomplish that, we present state-of-the-art multiscale simulations, going beyond density functional theory, of hot-carrier injections for the rate-determining step of a photocatalytic reaction. We focus on carbon dioxide reduction, for which it was experimentally shown that the presence of a rhodium nanocube under illumination leads to the selective production of methane against carbon monoxide. We show that selectivity is due to a (predominantly) direct hole injection from rhodium to the reaction intermediate CHO. Unexpectedly, such an injection does not promote the selective reaction path by favoring proper bond breaking but rather by promoting bonding of the proper molecular fragment to the surface.

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“…The one-pot Baeyer–Drewson indigo synthesis was used due to its procedural simplicity. 12 Bromo- and methoxy-substituted 2-nitrobenzaldehyde starting materials were commercially available, while phenyl-substituted derivatives were prepared via a Suzuki coupling of PhB(OH) 2 with the respective bromo-derivatives (see ESI, † Section S1.1). The methoxy-, bromo- and phenyl-substituted 2-nitrobenzaldehydes 8a–g were dissolved in acetone, stirred overnight with 1 M NaOH, the precipitate filtered, rinsed with organic solvents and where necessary recrystallised from ethyl benzoate to yield the respective 5,5′- and 6,6′-dibromo-, diphenyl-, and dimethoxy-indigos 1a–g in 22–58% yield ( Table 1 ).…”

Section: Resultsmentioning

confidence: 99%