[ap51ntus86]

hello,

I`m a newbie..

i wanna ask something about orange II`s synthesis...
1. Why do we use salt when recrystalline???
2. are there any detail for diazo-coupling reaction in this synthesis???
3. when we dye cotton precisely what reaction does it happen???

Thanx before and after..

[DrCMS]

By Orange II do you mean:
Acid Orange 7; C.I. 15510; p-(2-Hydroxy-1-naphthylazo)benzenesulfonic acid, sodium salt; CASNo.  633-96-5  

1) Salt is usually used to precipitate water soluble dyes by saturating the water and "pushing" the dye out of solution.
2) I don't know the synthetic details but i guess it's sulphanilic acid diazotised and reacted with 2 naphthol.
3) Unless you're using a reactive dye it's not a chemical reaction that bonds the dye to the cotton.  

Cotton would not normally be dyed with an acid dye. You'd use a direct or reactive dye.