2.4.6- Triphenylpyrylium tetrafluoroborate reaction with nitromethane

Triphenylpyrylium tetrafluoroborate is a versatile and useful stable starting material. Its reaction with nitromethane under basic conditions has made 2,4,6-triphenylnitrobenzene easily available. In addition, pyrylium salts are readily converted to a variety of pyridine derivatives i i . 20 including alkyl- and arylpyridinium salts, to thiopyrylium salts," and to substituted azulenes. ... 

In a 1-1. three-necked flask equipped with a mechanical stirrer, a reflux condenser, and a dropping funnel are placed 119 g. (0.30 mole) of 2,4,6-triphenylpyrylium tetrafluoroborate (Note 1), 21 ml. (24 g., 0.39 mole) of nitromethane (Note 2), and 350 ml. of absolute ethanol (Note 3). Triethylamine (70 ml., 51 g.) (Note 4) is added rapidly from the dropping funnel to the well-stirred suspension. The reaction mixture becomes reddish brown immediately, and the solid dissolves. After all the triethylamine has been added, the mixture is heated under reflux for 3 hours, cooled, and allowed to stand overnight in a refrigerator. The crystalline product that separates is collected on a Buchner funnel and washed with two 50-ml. portions of ice-cold methanol. The product (75-80 g. m.p. 142-144°) is recrystallized from 200-250 ml. of glacial acetic acid to yield 70-75 g. (67-71%) of 2,4,6-tri-phenylnitrobenzene as slightly yellow crystals, m.p. 144-145° (Note 5). 

Triphenylnitrobenzene may be prepared by direct nitration of 1,3,5-triphenylbenzene and by the reaction of 2,4,6-triphenylpyrylium tetrafluoroborate with nitromethane. The present procedure is an adaptation of the latter method. 

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See also in sourсe #XX -- [ , , ]

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