The Research Of The Regulation Of The Hydroxylation Position In The Aromatic C-H Bond Oxidation Of Naphthalene And Its Derivatives Catalyzed By Metalloporphyrin

The selective hydroxylation reaction of the aromatic C-H bond of naphthaleneand its derivatives is of enormous importance for organic synthesis, chemicaldegradation, drug metabolism in organism and other fields. The hydroxylation of thearomatic C-H bond of naphthalene and its derivatives has attracted vast attention, andsome achievements have been obtained in recent years. However, it still needs to befurther studied in searching the catalytic oxidation system with highly selectivity ofthe hydroxylation of the aromatic C-H bond of naphthalene and its derivatives andinvestigating the regulation mechanism of the hydroxylation position in the oxidationof the aromatic C-H bond.In order to get insight into the factors that had effects on the selectivity of thearomatic C-H bond hydroxylation and the regulation mechanism of the hydroxylationposition in the oxidation of the aromatic C-H bond of naphthalene and its derivatives,regioselective hydroxylation of the aromatic C-H bond on a series of naphthaleneswith different β-substituent R (R=H, Me, Et, i-Pr, OMe, COOH, Br, etc.) was studiedand the substituent effect on the selectivity of the aromatic C-H bond hydroxylationwas investigated. The results of the studies showed that the aromatic C-H bondhydroxylation preferred at1α position with more than80%selectivity when thesubstituent was electron-donating group while the aromatic C-H bond hydroxylationpreferred at4α position with more than60%selectivity when the substituent waselectron-withdrawing group of β-substituted naphthalene hydroxylated withmetachloroperbenzoic acid (m-CPBA) catalyzed by tetrakis(pentafluorophenyl)-porphyrin manganese(III)chloride (F20TPPMnCl). Further, the studies of the QSARrelationship between the substituent and the reaction rate, and the results of quantumchemical calculation showed that steric and electronic effects of the substituentplayed a significant role in determining the selectivity of the hydroxylation ofaromatic C-H bond. The mechanism of the hydroxylation position regulated by thesubstituent in the oxidation of the aromatic C-H bond of naphthalene was as follows:the preference of the aromatic C-H bond hydroxylation of naphthalene at thesubstituted aromatic ring or the no-substituted one was controlled by the stericinteraction of the substituent with phenyl groups on metalloporphyrin, and thepreference of the aromatic C-H bond hydroxylation of naphthalene at1α or4α position at the substituted aromatic ring was controlled by the thermodynamicregulation of reaction intermediate by the substituent.This study has some contributions to the investigation of the mechanism ofaromatic C-H bond hydroxylation, and it provides additional proofs for the stepwisemechanism through a cationic intermediate of the hydroxylation of the aromatic C-Hbond of naphthalene and its derivatives.