Selective Oxychlorination Of The Phenolic Ring C-H Bond

2,4-Dichlorophenol is an important fine chemical,but also a key raw material for the synthesis of pesticides,herbicides and dyes.In the traditional process,2,4-dichlorophenol is usually prepared by the direct reaction of phenol and chlorine,only less than 50% of the chlorine atoms enter the product and the rest of the chlorine atoms form hydrogen chloride by-product.The atomic utilization of chlorine is low and it is heavily polluted.Therefore,to carry out theoretical research on C-H bond selective activation of phenol ring has important theoretical significance and potential market value for understanding the activation rules of C-H bonds in phenol rings and developing a green and efficient phenol-catalyzed chlorination technology.In this paper,phenol as raw materials,hydrochloric acid as a chlorination agent,hydrogen peroxide as an oxidant,water as a solvent.Firstly,systematically investigated the activation effect of common metal salt catalysts on the phenolic ring C-H bond,and screened the catalyst Mn2+ which is suitable for the conversion of the phenol ring adjacent to the para-C-H bond to the C-Cl bond.Furthermore,Mn SO4 was used as a catalyst to systematically study the influence of the amount of catalyst,reaction temperature,amount of hydrochloric acid,amount of hydrogen peroxide,and number of times the catalyst was used on the conversion and selectivity,and the synthesis of phenol to 2,4-dichlorophenol under mild conditions was realized.However,Mn SO4 is a heavy metal salt and it is difficult to recover.Loss can cause environmental pollution.In order to solve the problems of heavy metal catalysts,a phase transfer catalyst is used.In a two-step process,phenol is first monochlorinated and then further chlorinated to 2,4-dichlorophenol.Then a series of common phase transfer catalysts were investigated to screen out biodegradable PEG 1000.Then systematically study the influence of the amount of catalyst,the amount of hydrochloric acid and the amount of hydrogen peroxide on the reaction,and select the optimal reaction conditions.In the catalyst of PEG 1000,the possible reaction process of oxidative chlorination of phenol was proposed.Finally,the two-step system was applied to the2,4-dichlorinates of some other aromatics,and the corresponding target product was obtained with higher selectivity.This system was further promoted.In summary,this paper uses hydrochloric acid as chlorinated reagent,hydrogen peroxide as oxidant,water as solvent,oxidative chlorination,biodegradable materials as catalysts to achieve the chlorination reaction of phenol,not only overcoming the traditional reaction to produce acid exhaust and other pollution problems,but also greatly improved the utilization of the reaction materials,the entire process atom economy and green.