ORGN 708 |
| Traditional modes of synthetic reactions usually involve a solvent medium. It may be noted that solvents mask the intrinsic energy aspects of reactions. Therefore, only solvent-free reactions will be considered here. Some solvent-free organic reactions are endothermic, others are exothermic. Most exothermic reactions appear to need a short burst of external energy for initiation; some exothermic reactions, however, are spontaneous and proceed to completion on just mixing the reagents in the absence of a solvent. The variation in the exothermicity of a particular type of reaction depends on the components. The Knoevenagel condensation of benzaldehyde with malonic acid or malonic ester in the presence of a base for coumarin formation requires energy input. But when 4-nitrobenzaldehyde is mixed with malononitrile on a 2-3-gm scale, there is a spontaneous reaction and the temperature of the mixture reaches about 170 °C in about 1 min. A very different type of spontaneous reaction is self-assembly in high yield of a mixture of 6 moles of benzyl amine and 3 moles of glyoxal (catalyze by a few drops of formic acid). This cage compound is key intermediate for a high energy molecule.
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Heterocycles and Aromatics
8:00 AM-12:00 PM, Thursday, 1 September 2005 Washington DC Convention Center -- Ballroom B, Oral
Division of Organic Chemistry |