Pilon

C ₅ H ₄ O ₂ (96.09). Also called pyranone. There are two types, α-pyrone and γ-pyrone. [ I ] α-pyrone (2-pyrone): Prepared by heating and decarbonating mercuric salt of coumaric acid. Melting point 5°C, boiling point 206-209°C. 1.200. 1.5277. Soluble in water. In the presence of alkali, it easily opens the ring to formylcrotonic acid. [ II ] γ-pyrone (4-pyrone): Prepared by dry distillation of comanic acid (4-pyrone-2-carboxylic acid) or chelidonic acid. Colorless crystals. Melting point 32.5°C, boiling point 215°C. It is hygroscopic, and easily soluble in water, ether, chloroform, and acetic acid, but sparingly soluble in petroleum ether and carbon disulfide. It turns yellow in alkali, and decomposes into formic acid and acetone when heated. Both compounds give pyridones when reacted with ammonia or primary amines. In addition, halogenation, nitration, etc., substitution reactions occur rather than addition reactions. The carbonyl group of γ-pyrone does not react with hydrazine or hydroxylamine.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

C₅H₄O₂(96.09)．ピラノンともいう．α-ピロンとγ-ピロンの2種類が存在する．【Ⅰ】α-ピロン(2-ピロン)：クマリン酸の水銀塩を加熱脱炭酸してつくる．融点5 ℃，沸点206～209 ℃．1.200．1.5277．水に可溶．アルカリ存在下では容易に開環して，ホルミルクロトン酸となる．【Ⅱ】γ-ピロン(4-ピロン)：コマン酸(4-ピロン-2-カルボン酸)またはケリドン酸の乾留により得られる．無色の結晶．融点32.5 ℃，沸点215 ℃．吸湿性で，水，エーテル，クロロホルム，酢酸に易溶，石油エーテル，二硫化炭素に難溶．アルカリで黄色を呈し，加熱するとギ酸とアセトンに分解する．両化合物はアンモニア，第一級アミンの作用でピリドンを与える．また，ハロゲン化，ニトロ化などでは，付加反応よりも置換反応が起こる．γ-ピロンのカルボニル基は，ヒドラジンやヒドロキシルアミンとは反応しない．

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