[plain]

 I know how to make 4-bromoresorcinol using 2,4-dihydroxybenzoic acid, but now want to make it using resorcin, please help me.

[Custos]

The direct bromination of resorcinol can be carried out using bromine in methanol (for example) but you will end up with a mixture of monobromoresorcinol (both 2 and 4) and di-bromoresorcinols... all difficult to separate. The Organic Synthesis prep of 4-bromoresorcinol (http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0100)  goes through the benzoic acid. Or of course you could just buy 4-bromoresourcinol from Aldrich.

[tbuihuu]

 resorcinol reacts with Br₂/Fe --->4-bromresorciol (major)

[maurice]

NBS or Br2/H2O2

[plain]

I want to synthesize 1 kg 4-bromoresorcinol and what mean is the best choise for me to do it. Of course, the cost is as lower as possible and the process is simple. Thanks.

[Custos]

For large scale work I would stick to the Organic Synthesis prep. They are usually very robust as they have been tested, usually at reasonable scale. Make the dihydroxybenzoic acid from resorcinol using this prep: http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0557 then brominate and decarboxylate using this prep: http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0100

I seriously think that if you try a direct bromination you will end up with a mess of positional isomers and overbrominated products that will be difficult to purify.