Acta Pharm. 54 (2004) 177-191

FT-IR and NMR spectroscopic studies of salicylic acid derivatives. II. Comparison of 2-hydroxy- and 2,4- and 2,5-dihydroxy derivatives

MILENA JADRIJEVIC-MLADAR TAKAC^1* and  DRAZEN VIKIC TOPIC² 

mladar@pharma.hr

¹Faculty of Pharmacy and Biochemistry, University of Zagreb, 10000 Zagreb, Croatia
²NMR Center, Rudjer Boskovic Institute, POB 180, 10002 Zagreb, Croatia

The 2,4- and 2,5-dihydroxybenzamides (8, 9) were synthesized from their corresponding methyl esters. The structures and the spectral properties of investigated salicylic acid (1), 2,4- and 2,5-dihydroxy benzoic acids (2, 3), their methyl esters (4-6) and amides (7-9) were analyzed by means of FT-IR and one- and two-dimensional homo- and heteronuclear ¹H and ¹³C NMR spectroscopies. Comparison of FT-IR and NMR spectral data of investigated compounds showed that the spectral characteristics of 2,4-dihydroxy benzoic acid derivatives are more similar to those of 2-hydroxy benzoic acid (salicylic acid) derivatives than to those of 2,5-dihydroxy benzoic acid derivatives. The results suggest that the spatial orientation of amide protons in 2,4-dihydroxy benzamide resembles more that in salicylamide than that in 2,5-dihydroxy benzamide.

Keywords: salicylic acid, 2,4- and 2,5-dihydroxy benzoic acids, methyl esters, amide derivatives, FT-IR, 1D and 2D homo- and heteronuclear ¹H and ¹³C NMR