Investigation of the discolouration developed in aged chloramphenicol suppositories

The colouring matter developed in aged chloramphenicol (1) suppositories formulated with polyethylene glycol base was separated by extraction with water/n-butanol mixture, n-butanol or abs. alcohol. These extracts were tested for colour stability, the presence of the main degradation products of 1 p-nitrophenylaminopropandiol (2) and p-nitrobenzaldehyde (3), and investigated by TLC and absorption spectrum. Results showed that the extracted matter gave the tests for the main degradation products of 1. TLC of n-butanol layer of the first mixture or n-butanol extract gave 2 spots with different RF values identified as 2 and 3. In the case of abs. alcohol extract 2 spots adhering to each other were obtained. The same spots in the latter case were obtained for an equimolecular condensation product of 2 and 3 (obtained by condensation in acid medium). The absorption spectrum of the extracted matter showed high absorbance in the visible region and maxima appeared only in the UV region. The condensation product of 2 and 3 gave the same absorbance pattern and did not produce Schiff's base. The colour of the aqueous layer of the first mixture faded gradually which assured its not being due to azocompounds. These findings indicated that the discolouration may be due to complex formation. Using model systems of known chemical reactions showed that discolouration is due to complex formation between 2 and 3 between 1 and 2.