Preparation of 1-amino-4-hydroxyanthraquinones
View Patent ↗The present invention relates to a process for preparing 1-amino-4-hydroxyanthraquinones of the formula (I) wherein R is an aliphatic or aromatic radical, by reacting 1,4-dihydroxyanthraquinone, optionally as a mixture with 2,3-dihydro-1,4-dihydroxyanthraquinone, with aliphatic or aromatic amines in the presence of N-methyl-2-pyrrolidone.
1. A process for preparing 1-amino-4-hydroxyanthraquinones of the formula (I)
wherein R is an aliphatic or aromatic radical,
comprising reacting 1,4-dihydroxyanthraquinone, optionally as a mixture with 2,3-dihydro-1,4-dihydroxyanthraquinone, with an aliphatic or aromatic amine in the presence of N-methyl-2-pyrrolidone.
2. A process according to claim 1 wherein the amine is an aromatic amine.
3. A process according to claim 1 wherein the amine is an aromatic amine having the formula (II)
wherein
R 1 , R 3 , R 4 and R 6 are indepently H, C 1 -C 12 -alkyl, halogen, C 1 -C 4 -alkoxy, or C 6 -C 10 -aryloxy, and
R 2 is H, C 1 -C 12 -alkyl, halogen, C 1 -C 4 -alkoxy, C 8 -C 10 -aryloxy, or —SO 2 —NH—R 8 , where
R 8 is optionally substituted aryl or alkyl.
4. A process according to claim 3 wherein R 6 is C 8 -C 10 -aryl substituted with C 1 -C 4 -alkyl, OH, halogen, C 1 -C 4 -alkoxy, or C 9 -C 10 -aryloxy or is C 1 -C 4 -alkyl.
5. A process according to claim 1 wherein the aromatic amine is aniline, o-toluidine, 3,5-dimethylaniline, 2,4-dimethylaniline, p-toluidine, or p-aminoacetanilide.
6. A process according to claim 1 wherein the reaction is carried out in the presence of boric acid.
7. A process according to claim 1 wherein the reaction is carried out in the presence of an auxiliary acid.
8. A process according to claim 7 wherein the auxiliary acid is a hydroxycarboxylic acid.