Preparation Of 2,5-Xylenol By Catalytic Hydroxylation Of Xylene

2,5-Xylenol is a very important intermediate in organic synthesis.It is widely used in the synthesis of Gemfibrozil,resin,dye,medicine,spices,disinfectants and other products.The traditional synthesis methods use a large amount of acid and alkali,which corrode equipment and pollute the environment seriously.This research is about the direct hydroxylation of p-xylene into 2,5-xylenol under the conditions of suitable catalyst and H2O2 as oxidant.Research findings are as follows:1.When copper phthalocyanine(CuPc)was used as catalyst,the better conditions of the direct hydroxylation were studied.The better conditions are: 1.2g CuPc,6mL pxylene and 15 mL H2O2 solution are added to 40 mL acetonitrile;reaction temperature 65?;reaction time 2h.The conversion rate of p-xylene is 57.39%,the selectivity and yield of 2,5-xylenol phenol is 44.20% and 25.37% respectively.The operation of this reaction is simple.CuPc is a kind of industrial pigments,so it's cheap.And it can be easily separated from the system and reused.This reaction is carried out in accordance with the free radical mechanism.2.When TS-1,a kind of titanium-silicon molecular sieves was used as catalyst,the better conditions of the direct hydroxylation were studied.The better conditions are: 5.0g TS-1,10 mL p-xylene and 4mL H2O2 solution are added to 40 mL acetonitrile;reaction temperature 75?;reaction time 6h.The conversion rate of p-xylene is 57.39%,the yield of 2,5-xylenol is 43.66% and the selectivity is 61.68%.Adding 0.5mL acetic acid is good for the reaction and yield of 2,5-xylenol is up to 47.15%.The operation of this reaction is also simple.TS-1 is heterogeneous catalyst.So it can be easily separated from the system and reused.This reaction is carried out in accordance with the electrophilic reaction mechanism.3.The modification of TS-1 was studied.(1)The sulfuric acid modification enhances the catalytic activity.The conversion rate reaches 73.61%,the yield is 57.34% and the selectivity is up to 77.89%.But phosphoric acid and acetic acid modification reduce the catalytic activity.Morphology character of acid modified TS–1 doesn't change obviously.But acid modification change the content of titanium in skeleton and the Ti-OH content.(2)Ammonia and TPAOH modification can etching the molecular sieve hole,which increases the number of mesoporous and contact area.That can enhance the catalytic activity.TS-1 modified with ammonia is the best,with the conversion rate of 76.99%,yield of 57.07% and the selectivity of 74.13%.Morphology character of alkali modified TS-1 doesn't change obviously.But the modification can collapse some skeleton structure and produce anatase TiO2 crystal phase.(3)Nitrate modification doesn't change morphology character of TS-1 obviously.But the introduction of metal oxide can change the electron cloud density and eletrophilicity of activated Ti,which will affect the catalytic activity.Aluminum nitrate,cobalt nitrate,magnesium nitrate and zinc nitrate modification enhance the catalytic activity of TS-1.Zinc nitrate modification makes the yield reach to 54.36%.