Bromination of hydroxyaromatic compounds and further conversion to dihydroxyaromatic compounds
View Patent ↗Brominated hydroxyaromatic compounds such as p-bromophenol are prepared by contacting a hydroxyaromatic compound with oxygen and a bromine source such as hydrogen bromide or an alkali metal or alkaline earth metal bromide in an acidic medium, in the presence of elemental copper or a copper compound as catalyst. The brominated product of this reaction may be converted alternately to a dihydroxyaromatic compound such as hydroquinone by hydrolyses, or a dihydroxybiphenyl compound such as 4,4′-dihydroxybiphenyl by reductive coupling.
1. A method for preparing a brominated hydroxyaromatic compound which comprises contacting a hydroxyaromatic compound with oxygen and a bromine compound selected from the group consisting of hydrogen bromide and ionic bromide salts in an acidic medium, in the presence of elemental copper or a copper compound as catalyst.
2. A method according to claim 1 wherein said medium is anhydrous.
3. A method according to claim 1 wherein the hydroxyaromatic compound has the formula
wherein each R is independently hydrogen or C 1-4 alkyl.
4. A method according to claim 1 wherein the hydroxyaromatic compound is phenol, o-cresol or m-cresol.
5. A method according to claim 4 wherein the hydroxyaromatic compound is phenol.
6. A method according to claim 4 wherein the hydroxyaromatic compound is o-cresol.
7. A method according to claim 1 wherein the bromine compound is hydrogen bromide.
8. A method according to claim 1 wherein the oxygen is provided by air.
9. A method according to claim 1 wherein the copper is provided as cupric bromide, cupric sulfate, cupric chloride, cuprous chloride or cuprous bromide.
10. A method according to claim 9 wherein the copper is provided as cupric bromide.
11. A method according to claim 1 wherein flowing oxygen is employed.
12. A method according to claim 1 wherein oxygen under pressure is employed.
13. A method according to claim 1 wherein a polar organic solvent is also present.
14. A method according to claim 1 wherein the solvent is acetonitrile, dimethyl sulfoxide, chloroform, o-dichlorobenzene, water, phenol, o-cresol, m-cresol, propionic acid or acetic acid.
15. A method according to claim 14 wherein the solvent is acetonitrile or acetic acid.
16. A method according to claim 1 wherein a temperature in the range of about 20–150° C. is employed.
17. A method according to claim 1 wherein a molar ratio of ionic bromide to hydroxyaromatic compound less than 1:1 is employed.
18. A method according to claim 1 wherein the proportion of copper source is in the range of about 0.1–30 mole percent of copper based on hydroxyaromatic compound.
19. A method for preparing 4-bromophenol, 4-bromo-o-cresol or 4-bromo-m-cresol which comprises contacting phenol, o-cresol or m-cresol with air and hydrogen bromide in an acidic medium, in the presence of cupric bromide.