| 摘要 |
<p>Selective bromination of alkylarenes to the alpha monobrominated derivative is desirable as a precursor for the selective production of, for example, the corresponding alcohols. The product can be obtained by a photolytic reaction between the substrate, hydrogen peroxide and hydrogen bromide in approximately equimolar ratios in an organic solvent, but improvement in the yield of the product coupled with similar or improved selectivity in its production was either not achieved or was actually impaired by a range of variations in the ratios and by omitting the solvent. The invention employs mole ratios of H2O2:substrate of 0.1:1 to 0.4:1, preferably 0.2:1 to 0.33:1 and of H2O2:bromide of 1:1.2 to 1:2, preferably about 1:1.3 to 1:1.8 and progressive introduction of the H2O2, either in the presence or absence of the solvent, whilst irradiating with light preferably having principal emmisions in the range of 250 to 600 nm, and the process thereby achieves either or both of improved yield and improved selectivity of the alpha monobrominated product. The reaction mixture is preferably maintained at 50 to 70 DEG C. The process is especially suitable for deactivated alkylarenes, such as o-nitrotoluene.</p> |
