1,354,909 research outputs found
Pechmann condensation
No full textA simple preparation of a coumarin product via an Pechmann condensation catalyzed by sulfuric acid. The product can be analyzed by NMR and LC/MS. Fluorescence is examined at various pHs in water using a UV lamp
Volhard's Anleitung zur Qualitativen chemischen Analyse
No full textvon H. v. Pechmann. Rev. durch: K. A. Hofmann ..
Extending the Conjugation of Pechmann Lactone Thienyl Derivatives: A New Class of Small Molecules for Organic Electronics Application
No full textThe preparation and spectroscopic characterization of some symmetrical small molecules containing the disubstituted (E)-3,3′-bifuranylidene-2,2′-dione chromophore (the so-called Pechmann lactone) and featuring an extended conjugation are reported. The synthetic approach of such compounds is based on the Stille-Migita coupling reaction, which is carried out in very mild conditions, suitable to be applied with the very sensitive Pechmann core. The absorption and emission spectra of the new molecules obtained have been recorded in solution and clearly show how their photophysical properties can be modulated by a proper choice of the (hetero)aromatic terminal groups. The compounds prepared in this study (or close analogues thereof) have interesting optical properties and could find application as semiconductors in organic electronics or as near-IR fluorescent dyes
A REVISIT OF PECHMANN REACTION UNDER MICROWAVE RADIATION
No full textABSTRACT
A series of coumarins have been prepared by the Pechmann reaction of different phenols with ethyl
acetoactate as well as malic acid using catalytic amount of sulfuric acid under microwave irradiation for few seconds.
Keywords: Pechmanreaction, Coumarins, Microwave irradiatio
A REVISIT OF PECHMANN REACTION UNDER MICROWAVE RADIATION
No full textABSTRACT
A series of coumarins have been prepared by the Pechmann reaction of different phenols with ethyl
acetoactate as well as malic acid using catalytic amount of sulfuric acid under microwave irradiation for few seconds.
Keywords: Pechmanreaction, Coumarins, Microwave irradiatio
A REVISIT OF PECHMANN REACTION UNDER MICROWAVE RADIATION
No full textA series of coumarins have been prepared by the Pechmann reaction of different phenols with ethyl acetoactate as well as malic acid using catalytic amount of sulfuric acid under microwave irradiation for few seconds.
Keywords: Pechman reaction, Coumarins, Microwave irradiatio
Pechmann Condensation-I Use of Catalytic Amount of Condensing Agents
No full textIt has been found that the Pechmann condensation could be effected using only a catalytic amount of the reagent. Excellent yields are obtained with concentrated sulphuric acid, phosphorus trichloride and phosphorus oxychloride. Basic reagents do effect the condensation, though in poor yields
Appendage patterning in the South American bird spider Acanthoscurria geniculata (Araneae: Mygalomorphae)
No full textPattern formation by the genes dachshund (dac), Distal-less (Dll), extradenticle (exd) and homothorax (hth) in spider appendages has been studied previously only in members of the higher spiders (Araneomorphae). In order to study the diversity and conservation of pattern formation in spiders as a whole, we studied homologs of these genes in embryos of the bird spider Acanthoscurria geniculata, which belongs to the Mygalomorphae, a more primitive spider group. We show that the patterns of dac and Dll are largely conserved in all spiders studied so far. We find a duplication of hth and exd genes as previously identified in the higher spider Cupiennius salei. These data suggest that pattern formation shows little diversity in all spiders, including the duplication of hth and exd that likely occurred before the split of Mygalomorphae and Araneomorphae. We also find that the legs and pedipalps bear endites of which only the pedipalpal endite expresses Dll and is retained in the adult. Similarly, the limb buds of the posterior spinnerets express Dll and become segmented appendages in the adult, whereas the anterior spinnerets lack Dll expression and are absent in postembryonic stages. In both cases, the expression of Dll or the lack of it indicates structures which will be retained as adult traits or rudimentary structures that degenerate, respectively. The presence of embryonic rudiments of leg endites in Acanthoscurria and the leg-like pattern formation in the posterior spinnerets are interpreted as primitive traits that have been lost in the Araneomorphae.German Research Council [PR1109/1-1
A statistical test to show negligible trend: Reply
No full textCamp et al. (2008) extend the ideas discussed in Dixon and Pechmann (2005). Our paper used equivalence regions to test for negligible trends (null hypothesis that trends are not negligible). Their paper suggests also using equivalence regions to test an alternative hypothesis of “ecologically meaningful” trends (null hypothesis that trends are negligible but not zero).This is an article from Ecology 89 (2008): 1473, doi:10.1890/07-1871.1. Posted with permission.</p
Eco-friendly Synthesis of Coumarin Derivatives via Pechmann Condensation Using Heterogeneous Catalysis
No full textA coumarin derivatives has been synthesized via Pechmann condensation naphthol with a β-ketoester using Amberlyst-15 as a green and efficient catalyst.The optimal conditions are: molar ration of reagents (1:1), Amberlyst-15 (10mol.%, 0.2 g) at 110°C for 150min. in solvent-free conditions. The recyclability of amberlyst 15 adds an advantage to the studied reaction.These coumarins derivatives have biological activity and momentousness in the industrial fields Keywords: Coumarins, Phenols, β-Ketoesters, Pechmann Reaction, Amberlyst-1
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