摘要
2,4-二氟苯甲酸是一种重要的药物、农药中间体,同时也可以用于液晶材料,具有价值高、市场前景好的优点。但目前国内对2,4-二氟苯甲酸的传统合成工艺,通常采用重铬酸盐为氧化剂,需要经氧化,氟化两步进行合成,且该工艺体系中重铬酸盐毒性巨大,对环境污染严重,收率偏低。因此,本课题的目的,就是针对其缺点对2,4-二氟苯甲酸的合成工艺进行改进,优化,寻找生产工艺简单,对环境友好,收率高,成本低的工艺路线。
本课题主要进行了如下三方面内容研究工作:(1)改进传统的以2,4-二硝基甲苯为原料经氧化、氟化两步合成2,4-二氟苯甲酸的工艺,采用高锰酸钾代替重铬酸盐作为氧化剂,氟化钾作为氟化剂,以相转移催化法进行合成,探讨了相转移催化机理,并利用正交实验优化其合成工艺;(2)本课题提出以2,4-二氯苯甲酸为原料,经氟化一步合成2,4-二氟苯甲酸的新方法,催化剂采用聚乙二醇代替季铵盐,探讨了卤素交换氟化的反应机理,通过正交实验得出了最佳合成工艺。(3)应用现代分析仪器气相色谱、傅立叶变换红外光谱、质谱,对目标产物2,4-二氟苯甲酸的含量与结构进行分析。
经以上研究得出:(1)以2,4-二硝基甲苯为原料的传统工艺,经优化后,避免了毒性巨大的重铬酸盐,对环境友好,总收率为65.6%,高于文献所报导的60.6%的收率。(2)以2,4-二氯苯甲酸为原料,经氟化一步合成2,4-二氟苯甲酸的新工艺,缩短了反应工艺,以大众化的聚乙二醇代替价格昂贵的季铵盐,降低了生产成本,收率为69.9%,进一步提高了反应收率。
本课题所研究的以2,4-二氯苯甲酸为原料的2,4-二氟苯甲酸的合成路线,工艺简单,较以2,4-二硝基甲苯为原料的合成路线短,收率高,成本低,是比较理想的合成路线;通过实验确定的工艺条件对工业化生产有重要的指导意义。
2,4-difluorobenzoic acid is a very important intermedia of medication and pesticide.It also can be applied to the liquid crystals.It has high prize and good foreground in marketing.But it always be used the dichromate as the oxidizer in the traditional synthesis method of the 2,4-DFBA.It needs oxygenation and fluorination to synthesize the 2,4-DFBA.The dichromate is virulent,it's very harmful to the surroundings.And the yield on the low side.So the purpose we research at the present time is that we should optimize the method and find a new method which is simple,high yield and low cost.
Research in three aspects is studied in this paper:(1) The traditional method which be used 2,4-DNT as raw material was optimized and synthesized by oxygenation and fluorination.The dichromate as the oxidizer was instead by KMnO_4 in the synthesis,KF as fluridizer. Synthesized 2,4-DFBA by phase transfer catalysis(PTC).The reaction mechanism of PTC was discussed.The best method through Orthogonal Experiments was obtained.(2) A new method of the synthesis of 2,4-DFBA which used 2,4-DCBA as raw material,PEG-6000 as catalyzer instead the quaternary ammonium salt,just synthesized by fluorination was researched.Reaction mechanism of the halogen exchange fluorination was discussed.The best method through Orthogonal Experiments was obtained.(3)The content and structure of 2,4-DFBA by GC,IR and MS were analysed.
According to the research:(1)The optimized method reduces the pollution and avoids using the virulent dichromate.The total yield of this method was 65.6%,tower over the literature search 60.6%.(2)The new method which used 2,4-DCBA as raw material shortens the process and cuts the cost effectively.The yield was 69.9%higher than the literature search.
The new method of this paper is better than the traditional method.The process is shorter than the traditional one,lower cost and higher yield.This new method is significant to industrial production.
引文
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