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Oxide Nanoparticles in Heterogeneous Catalysis
Published in Varun Rawat, Anirban Das, Chandra Mohan Srivastava, Heterogeneous Catalysis in Organic Transformations, 2022
Garima Sachdeva, Jyoti Dhariwal, Monika Vats, Varun Rawat, Manish Srivastava, Anamika Srivastava
Ghomi et al. reported the synthesis of xanthene derivatives via a multicomponent reaction of aldehyde, dimedone, and 2-napthol using ZnO nanoparticles under solvent-free conditions. The methodology is effective as the catalyst can be recovered easily, is eco-friendly, and needs low catalyst loading to obtain corresponding xanthenes in high yield (Figure 2.11) [30]. It was observed that on increasing the catalyst amount from 5 to 10 mol%, a better yield was obtained, but a further increase of the molar amount of catalyst to 15 mol% did not increase the product yield.
Reactions With Disinfectants
Published in Richard A. Larson, Eric J. Weber, Reaction Mechanisms in Environmental Organic Chemistry, 2018
Richard A. Larson, Eric J. Weber
Rook (1976) demonstrated that cyclic 1,3-diketones such as ninhydrin (20), dimedone (21), and 1,3-cyclohexanedione were efficient precursors of chloroform (50–100% yields with 3 mM starting concentrations of chlorine). In a later publication, he (Rook, 1977) found that m-dihydroxybenzenes also gave very high yields of chloroform. Substances such as resorcinol (22), 3,5-dihydroxybenzoic acid, and several flavonoids such as hesperetin (23) contain “masked” β-diketones (cf. Figure 5.6), and Rook suggested that the 2-position of such compounds might be expected to be chlorinated readily and to react rapidly as haloform precursors. This suggestion was confirmed by an elegant experiment using isotopically labeled resorcinol (22) (Boyce and Hornig, 1983). The detailed mechanisms of formation of CHCl3 from this position are not completely understood, but a reasonable pathway invokes a triketocyclohexene (24): ring opening of this intermediate could give rise to the principal observed products, chloroform, CO2, 2-chlorobutenedioic acid, and di- and trichloroacetic acids (Boyce and Hornig, 1983: Lin et al., 1984: De Leer and Erkelens, 1988). Christman et al. (1978) also chlorinated resorcinol, showing that during chloroform formation it underwent ring contraction to produce the unusual cyclopentenedione 25. Larson and Rockwell (1979) confirmed Rook’s and Christman’s observations that resorcinol derivatives were active haloform precursors, and also found that even if the 2-carbon of resorcinol was blocked by a carboxyl group (cf. 26), yields of chloroform were still high. (However, an –OH or –CH3 substituent reduced the yields to < 10%: De Leer and Erkelens, 1988). The reaction of the 2-carboxylated resorcinol derivative is an example of hypochlorite-induced decarboxylation, which is also an important reaction with aliphatic carboxylic acids.
Ultrasound-assisted synthesis of 1, 8-dioxodecahydroacridine derivatives in presence of Ag doped CdS nanocatalyst
Published in Journal of Dispersion Science and Technology, 2020
Divya Verma, Vikash Sharma, Shubha Jain, Gunadhor Singh Okram
On the basis of our investigations and other reported similar results,[11] a plausible mechanism for the synthesis of DODHAs using CdS6 NPs is shown in Figure 16. Initially, the acidic active sites (Ag+ and Cd2+) increase the electrophilicity of carbonyl groups of aldehydes as well as the enolization of dimedone. Then nucleophilic attack of dimedone to activated form of aldehyde afforded Knoevenagel product I. Subsequently, the Knoevenagel product I reacted in Michael fashion with another molecule of dimedone to form intermediate II. Afterwards, the intermediate II was attacked by amine molecule which undergoes intramolecular cyclization by dehydration to give the final product.