摘要
氯代烃的氟化是单分子亲核取代反应,其氟化反应的进程决定于中间体R+的稳定性。以两个碳原子的氯代烃 为例,中间体R+的稳定性取决于α位和β位上5个取代基的供电子能力。若各个取代基的供电子能力为σi,则氟化反应的 进程取决于总的供电子能力σ,σ=multiply from i=1 to 5 σi。本文给出一套σi值,据此可计算σ值以判断各种氯代烃氟化反应的选择性。用此 公式对各种例子的分析,可总结出以下规则:两个碳原子的氯代烃跟氟化氢发生卤交换反应时,首先跟氢原子数较少的碳原 子上的氯原子发生交换。若两个碳原子上的氢原子数相等或都没有氢原子,则首先跟氯原子数较多的碳原子上的氯原子发 生交换。这个规则我们暂叫做避氢趋氯规则。
Fluorination of the chlorohydrocarbon is substitution nucleophilic unimolecular. This fluorinated reaction is decided by the stability of intermediate R+. For example as chlorohydrocarbon containing two carbon atoms, the stability of its intermediate R+ is decided by ability supplied electron of its five substitution radical in α place and β place. If ability supplied electron of each substitutuon radical is σi,then total ability supplied electron σ=multiply from i=1 to 5 σi,This works gives a set of σi value. With these values we calculate the σ value. Then we may judge the selectivity of fluorination of various chlorohydrocarbon. With this formula, we may analyze various examples and obtain following regulation: When hydrogen fluoride happen to haloexchange reaction with chlorohydrocarbon of two carbon atoms, first exchange with the chlorine atom in the carbon atom which links fewer hydrogen atom. If the units of hydrogen atom in each carbon atom is equal or don't link hydrogen atom both,then first exchange with chlorine atom in carbon atom which links more chlorine atom. This is known as evade hydrogen and attract chlorine regulation.
出处
《有机氟工业》
CAS
2005年第1期37-41,共5页
Organo-Fluorine Industry
