Oxybromination Of Activated Aromatic Compounds Catalyzed By Nonmetal Compounds With Oxygen As Oxidant

Bromination as the basic reaction unit is very important in organic synthesis, brominated aromatic compounds are not only key precursors to other functional compounds, also as flame-retards and antifungal, antiviral Pharmaceuticals. for classical bromination, It is toxic, harmful and poor atom economy, and also high regioselectivity and conversion are not observed. It is significant for the conventional industry to develop a novel process of bromination. In this paper, the brominations of activated arenes are investigated in the solvent of acetic acid and water with 2,2,6,6-tetramethyl-piperidyl-1-oxy (TEMPO) and NO as catalysts and oxygen as oxidant.Initial investigation is the synthesis of methyl aryl ethers as substrates with dimethyl sulfate, and also with the environmentally benign dimethyl carbonate. The effect of diverse solvent on the conversion of bromination is carried out using anisole as substrate in vessel. Ascertaining acetic acid and water as solvent, then the effect of different volume ratio of acetic acid to water on conversion is investigated. Reaction time, temperature and quantum of sodium are examined with p-methyl anisole as substrate. The optimal reactive conditions are obtained as follow: The molar ratio of substrate:sodium bromide:TEMPO is 1: (1.2-2.0) :0.003, The volume ratio of acetic acid and water is 10:3, The pressure of NO is 0.05MPa and that of oxygen is up to 0.4-0.5MPa. After reaction, the system is converted into two phases, the unreacted substrate and products are in the same phase, and can be obtained through liquid-liquid separation. A plausible overall mechanism of this catalytic bromination circle is described.After systematic optimization of reaction temperature, time and quantum of sodium, highly selectivity and conversion was achieved for different substituted aromatic compounds. It is found that the reactions abide with the orientation effect of substituted group. Alkanoxy substituted arenes exhibit high regioselectivity and high conversion, moderate conversion is for alkyl substituted arenes.