二溴代萘酰亚胺的高效合成

Efficient synthesis of dibromonaphthalimides

[目的]母核卤代的萘二酰亚胺(NDI)是制备各种NDI衍生物的重要前体,通过萘核C—X(X=Br,I)的定向转化,不仅可以有效调控分子能级,还有利于实现分子间的可控组装,是高效创制新型萘酰亚胺材料的有效手段,但传统合成卤代NDI的方法往往存在着合成效率低、选择性差等问题.为提高溴代NDI的合成效率,对其合成条件进行优化.[方法]通过提高溴化反应中溴源的回流程度和改善酰亚胺反应中二溴代萘四甲酸二酐(NDA-2Br)在反应溶剂中的溶解度,以2-乙基己基胺为研究对象,优化了酰亚胺反应的溶剂体系及时间,并将优化的溶剂体系应用于其他类型的胺.[结果]将溴化反应改用耐压瓶为反应容器后,在80℃下反应12 h合成的NDA-2Br产率达92%;优化后的酰亚胺反应溶剂体系为V(二甲亚砜)∶V(乙酸)=1∶2,在优化的反应条件下可高效合成二溴代NDI.[结论]与传统方法相比,该方法缩短了反应时间,避免了亲核取代副产物的生成,高效合成了二溴代NDI,具有操作简单、产物单一、可大量制备等优点.

[Objective]Naphthalene diimide(NDI)is an important precursor for the preparation of various naphthalimide derivatives.The C—X(X=Br,I)directional conversion of naphthalene nuclei not only effectively regulates molecular energy level,but also facilitates controlled assembly between molecules.This method proves to be an effective means for efficiently creating new naphthalimide materials.However,conventional methods for the synthesis of halogenated naphthalimides often suffer from low synthetic efficiency and poor selectivity.Here,the synthesis conditions of dibromonaphthalenetetracarboxylic dianhydride(NDA-2Br)were optimized to improve the synthesis yield.[Methods]The synthesis conditions of brominated NDI were divided into two steps for optimization.Firstly,the bromination reaction was optimized.The reaction vessel was replaced by a pressure bottle suitable for pressurized reaction instead of a round-bottom flask used under traditional conditions to ensure the full reflux of bromine vapor to the greatest extent.The bromine vapor was reacted at 80℃for 12 h.After allowing the reaction solution to cool to room temperature,it was poured into ice water and filtered to obtain an orange solid.Secondly,the solubility of NDA-2Br in acetic acid in the imide reaction was improved by adding the co-solvent dimethyl sulfoxide(DMSO).The products were characterized by nuclear magnetic resonance(NMR)and high resolution mass spectrum(HRMS).[Results]By using pressure resistant bottles as reaction vessels for bromination reactions,the degree of reflux of bromine vapor can be improved.The NDA-2Br obtained is not only of high purity,but also of large amount of synthesis,obtaining about 30 g(yield 92%)at a time.When the volume ratio of DMSO/AcOH is 1∶2,it reacts with 2-ethylhexylamine in an oil bath at 114℃for 1 h,washes with ethanol to remove a few red by-products,and filters to obtain the yellow imide product dibrominated NDI-C_2C_4.The yield increases significantly.At the same time,the products in the reaction process are also tracked by ^(1)H-NMR spectrum.The results show that dibrominated NDI-C_2C_(4)is the main product,and no nucleophilic byproducts are observed,which is also the reason leading to the significant increase in yield in this step.The optimized synthesis conditions of dibrominated NDI are also applicable to other types of amines.In this experiment,it is found that the imidization results varied with different amine configurations.Compared to the straight chain amine,the branched chain amine has a certain steric hindrance,and therefore the yield of dibrominated NDI-C_8C_(10)is low.In contrast,2,6-diisopropylaniline has a high yield of dibrominated NDI-iPr due to its good solubility.[Conclusion]In this study,a large amount of purer NDA-2Br was synthesized at one time by first enhancing the reflux degree of bromine source in the bromination reaction,and then the solubility of dibrominated NDA in acetic acid was improved in the imide reaction to improve the reaction efficiency and obtain dibromo-NDI products with high yield.Dibromo-NDI is an important precursor of naphthalene ring functionalized naphthalene diimide derivatives,and its efficient synthesis lays an important foundation for subsequent research.