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Diazotization reaction is an important reaction in organic chemistry. Aryl diazonium salts are a class of active inter-mediates, also, their reaction can form many compounds and have high application value in the synthesis. Many reactions which aryl diazonium salts have been participated in, have been received widely application, but the mechanism has not yet conclusive, and in most time, it was preferred to deduced as free radical mechanism at the presence of copper ions. Over a long period of time, people have little study on diazonium salt, although in recent years, researchers have focused their attention intensely on it, yet, the reaction mechanism of diazonium salt has few reports. In this paper, we changed the form of diazotization, in anhydrous conditions, using nitrite as the diazotization reagent, synthesized substituted biphenyl and substituted benzoxazole compounds to investigate the reaction mechanism, when the aryl diazonium acid was participated. At the same time, two series of the compounds of substituted biphenyl and benzoxazole compounds were synthesized by using this method, the synthesis methods and spectral properties were also investigated. Specific contents are as follows:1. The properties and application of diazonium salts were described in detail, also, variety reactions that diazonium salts were token part in, and the research progresses of diazotization, as well as the importance of diazotization in organic synthesis were detailedly introduced. While, the properties, application and synthesis methods of biphenyl compounds were also exhibited at length.2. In this paper, the formation of aryl diazonium acid, the reaction mechanism and some applications of diazonium salts were discussed. In order to investigate the mechanism of the reactions that aryl diazonium salts were participated in, substituted aniline were used as a radical probe molecule, through the aromatic amine and butyl nitrite diazotization in anhydrous conditions, we designed and synthesized a series of biphenyl compounds. From the fact that biphenyl compounds were generated by diazotization, it can be initially confirmed: Firstly, aryl diazonium acid intermediates were formed after aryl diazonium, then, aryl radicals which were formed by heating aryl diazonium acid intermediates, executed free radical reactions between molecules.This kinds of reactions of aryl diazonium are significantly different from traditional diazonium salt radical reactions which mainly produced azo compounds, and can be applied to biphenyl compounds. 3. The synthesis of heterocyclic benzoxazole compounds was studied, the experimental results show that aromatic amines was diazotized by using nitrite, then the diazotized product got rid of N2 to form into aryl radicals under the conditions of being heated, and then generated into phenol after hydroxyl radicals were successfully captured. The carbon cation of amide carbonyl were attacked by oxygen anion of phenolic hydroxyl, then the structure of benzoxazole was formed by getting rid of a molecule of water. This reaction can be occurred at the condition of using 1,2-dichloroethane as the solvent, molecular sieve as catalyst and water absorbent. And concrete methods are described as follows:Firstly, 2-amino-phenyl-substituted amides was diazotized by using n-butyl nitrite under the conditions, then free radical reactions and intra-molecular cyclization were occurred with slowly warming. By using this method, a series of 18 compounds were synthesized, and their structures were analysed and confirmed by IR,1H-NMR,13C-NMR, ESI-MS.
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