| 摘要 |
<p>A regioselective process is provided for preparing 4-bromo-o-xylene in an isomer mixture of 4-bromo-o-xylene and 3-bromo-o-xylene by combining a molar excess of bromine with o-xylene. The produced 3-bromo-o-xylene isomer preferentially reacts with the excess bromine to produce dibromo-o-xylenes. The weight ratio of the 4-bromo-o-xylene to the 3-bromo-o-xylene in the product isomer mixture can be as high as about 97:3. Concurrent production of alpha-bromo-o-xylene is avoided by conducting the admixing in either darkness or in sulfur dioxide solution. The dibromo-o-xylene by-products are easily separated by subsequent vacuum distillation or similar expedients. The use of small amounts of sulfur dioxide also provides for enhanced selectivity for the formation of 4-bromo-o-xylene relative to 3-bromo-o-xylene even when the mole ratio of bromine to o-xylene is 1:1 and lower.</p> |
