Formation mechanism of p-methylacetophenone from citral via a tert-alkoxy radical intermediate.
Formation mechanism of p-methylacetophenone from citral via a tert-alkoxy radical intermediate.
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柠檬醛通过叔烷氧基自由基中间体形成对甲基苯乙酮的机理。
DOI：
10.1021/jf035517j
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发表时间：
2004
影响因子：
6.1
通讯作者：
Chi
中科院分区：
文献类型：
--
作者：
Toshio. Ueno;H. Masuda;Chi
本研究的目的是阐明柠檬醛在酸性水条件下生成高效无臭剂对甲基苯乙酮的机理。将含有10 mg/L柠檬醛的酸性水溶液(pH 3.0)在40℃下保存2周。在储存的柠檬醛溶液中检测到的化合物中，4-(2-羟基-2-丙基)苯甲醛首次被鉴定为柠檬醛的降解产物。柠檬醛溶液中加入抗氧化剂后，对甲基苯乙酮和4-(2-羟基-2-丙基)苯甲醛的生成行为相同。此外，这两个化合物都是通过Fe(2+)诱导8-羟基过氧基对伞花烃的分解而形成的，8-羟基过氧基对伞花烃是在储存的柠檬醛溶液中发现的另一种化合物。这些结果表明，对甲基苯乙酮和4-(2-羟基-2-丙基)苯甲醛都可以通过相同的自由基中间体[p-CH3C6H4C(CH3)2O*]生成，该中间体可以由8-羟基过氧基对伞花烃的O-O键均解而得。在酸性条件下，不含Fe2+的8-羟基对伞花烃的降解不生成对甲基苯乙酮和4-(2-羟基-2-丙基)苯甲醛，而不含Fe2+的柠檬醛的降解生成对甲基苯乙酮和4-(2-羟基-2-丙基)苯甲醛。因此，在柠檬醛溶液中生成对甲基苯乙酮和4-(2-羟基-2-丙基)苯甲醛，除了8-羟基-对伞花烃的分解外，还提出了生成叔烷氧基中间体的机理。
The aim of this study was to clarify the formation mechanism of a potent off-odorant, p-methylacetophenone, from citral under acidic aqueous conditions. An acidic aqueous solution (pH 3.0) containing 10 mg/L of citral was stored at 40 degrees C for 2 weeks. Among the compounds detected in the stored citral solution, 4-(2-hydroxy-2-propyl)benzaldehyde was identified for the first time as a degradation product from citral. The formation of p-methylacetophenone and 4-(2-hydroxy-2-propyl)benzaldehyde behaved the same when antioxidants were added to the citral solution. In addition, both compounds were formed by the Fe(2+)-induced decomposition of 8-hydroperoxy-p-cymene, another compound identified in the stored citral solution. These results suggested that both p-methylacetophenone and 4-(2-hydroxy-2-propyl)benzaldehyde can be formed via the same radical intermediate [p-CH3C6H4C(CH3)2O*] that can be derived from the O-O bond homolysis of 8-hydroperoxy-p-cymene. On the other hand, the degradation of 8-hydroperoxy-p-cymene without Fe2+ under acidic aqueous conditions did not yield p-methylacetophenone and 4-(2-hydroxy-2-propyl)benzaldehyde, but the degradation of citral without Fe2+ did. Therefore, other than the decomposition of 8-hydroperoxy-p-cymene, a mechanism to generate the tert-alkoxy radical intermediate was proposed for the formation of p-methylacetophenone and 4-(2-hydroxy-2-propyl)benzaldehyde in the citral solution.