Study On The Catalytic Preparation Of Naphthol By Direct Hydroxylation

Aromatic H substituted directly by hydroxyl group in activation aromatic ring is one of challenging issues. It is difficult to get ArOH with high selectivity mainly due to aromatic reaction inert of high stability, and intermediate's high activity. Naphthol as a basic chemical is obtained by sulfonation alkali-fusion or isopropyl naphthalene methods during industrial production. These technologies have many shortcomings, such as a large number of pollution, long processes, low atoms utilization, or complex operation and poor security. In this paper, naphthalene is hydroxylated directly by H2O2 with the participation of iron, copper oxides (or loaded) or their complexes as the catalyst in liquid phase.Copper ferrite, which was calcined at 500℃for 4h, had the highest activity by comparing multiple ferrite catalysts. Iron hydroxide from low-temperature processing was the main center of hydroxylation. On the contrary, octahedral copper in copper ferrite was the main catalytic center from high-temperature processing, and the intermediate transition state might include Cu(+3) during the hydroxylation. Combined with TGA, XRD, FTIR, DRIFT analysis of doped catalyst Cu0.95Mn0.05Fe2O4, the results showed that the carbonate on the surface led to the initial activation stage of hydroxylation reaction; naphthalene conversion of 79.03% and naphthol selectivity of 17.38% was got under the conditions as follows: reaction temperature 65℃, time 10h, hydrogen peroxide/naphthalene 3-5 (molar ratio), acetonitrile(10% water). The study also showed that little water was conducive to naphthol generated from hydroxyl radicals and adsorptive naphthalene by thin surface layer of water. In addition, acetonitrile and hydrogen peroxide directly generated active species which epoxidized naphthalene and naphthalene oxide generated naphthol via decomposition.By comparing a variety of carriers in naphthalene hydroxylation, MCM-41 is the most suitable one. Metal components are highly dispersed on various MCM-41 sieves doped iron, copper, manganese by hydrothermal synthesis. CuFeMn-MCM had the highest activity and the selectivity was similar with these doped-iron, doped-copper and doped-iron-copper MCM-41 sieves. Its best reaction condition was as follows: acetonitrile(20% water) as solvent, the reaction temperature 65℃, the time 13h, then the result of conversion 52.49% and selectivity 32.45% was produced. The results also showed that the conversion of naphthalene was greater than the selectivity and naphthalene was more adsorbed with the increase of water. While adsorbtive naphthalene was close to the metal center, adsorption played a weak activation between C and H of naphthalene. On the other hand, the metal peroxides generated cationic tetrahedral complexes or cage-type hydroxyl radicals under the influence of the surrounding atoms or groups. The pore structure of MCM-41 sieves influenced the large size of the reaction transition state significantly, causing a strong shape-selective effect and increasing the selectivity of naphthol. When activated carbon was selected as the carrier, the conversion was improving through its oxidation and water changes.The results of naphthalene hydroxylation by many copper complexes showed that 1,2-naphthalenedione-1-oxime copper complex had the best activity, mainly due to its two-naphthyl ligand, more distorted structure from six-atom-membered ring including different atomic configurations, easy electron transfer between N and O atom. In anhydrous acetonitrile, the naphthalene conversion occurred so fast that the conversion was 52.05% and the selectivity was 26.56% at 55℃for 4h. With the increase of water, the conversion rate got increased, but selectivity decreased.