3,4-DIHYDROXYBENZOIC ACID 4,5-Dihydroxybenzoic acid 4-10-00-01459 (Beilstein Handbook Reference) 4-Carboxy-1,2-dihydroxybenzene 99-50-3 BRN 1448841 Benzoic acid, 3,4-dihydroxy- Benzoic acid, 3,4-dihydroxy- (9CI) CCRIS 6291 EINECS 202-760-0 NSC 16631 Protocatechuic acid Protocatehuic acid