Organic 2 Review Problem 309

Organic 2 Review Problem 309 - P REPARATIONS 293 tallised...

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PREPARATIONS 293 tallised material in a vacuum desiccator, preferably over fresh paraffin-wax shavings to absorb traces of xylene. The addition product is obtained as colourless crystals, m.p. 256-258°. Yield ca. 2 g. 2,4-Dimethylpyrrole-3,5-dicarboxylic Acid Diethyl Ester. This synthesis of the pyrrole ring system, due to Knorr, consists in the con- densation of an a-aminoketone with a i,3-diketone or the ester of a p-keto-acid. ot-Aminoketones are unstable in the free state, readily undergoing self-condensa- tion: consequently they must be prepared, by the reduction of an oc-nitroso (or oximino) ketone, in the presence of the i,3-diketone or p-ketoester, to ensure rapid interaction. In the present preparation, ethyl acetoacetate is treated with sufficient nitrous acid to convert half into the a-nitroso (or a-oximino) ester, which is reduced by zinc and acetic acid to the a-amino ester (I). The latter then condenses with CH 3 COCHC-NO)-COOC 8 H 6 ^ CH S COC(:NOH)-COOC S H 6 I CH 3 COCH(-NH
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This note was uploaded on 09/19/2011 for the course CHM 2211 taught by Professor Castalleano during the Fall '06 term at University of Florida.

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