کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5218174 | 1383318 | 2012 | 8 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Bromination of phenols in bromoperoxidase-catalyzed oxidations Bromination of phenols in bromoperoxidase-catalyzed oxidations](/preview/png/5218174.png)
Phenol and ortho-substituted derivatives furnish products of selective para-bromination, if treated with sodium bromide, hydrogen peroxide, and the vanadate(V)-dependent bromoperoxidase I from the brown alga Ascophyllum nodosum. Relative rates of bromination in morpholine-4-ethane sulfonic acid (MES)-buffered aqueous tert-butanol (pH 6.2) increase by a factor 32, as the ortho-substituent in a phenol changes from F via Cl, OCH3, C(CH3)3, and H to CH3. The polar effect in phenol bromination by the enzymatic method, according to a Hammett-correlation (Ï=â3), compares to reactivity of molecular bromine under identical conditions (Ï=â2). Hypobromous acid is not able to electrophilically substitute bromine for hydrogen at pH 6.2 in aqueous tert-butanol. The tribromide anion behaves in MES-buffered aqueous tert-butanol as electrophile (Ïâ¼â3), showing a similar polar effect in phenol bromination as molecular bromine.
Journal: Tetrahedron - Volume 68, Issue 46, 18 November 2012, Pages 9456-9463