Polarographic studies of the interaction of boric acid with 1-hydroxy- and 1,2-dihydroxy-9,10-anthraquinones and -anthrahydroquinones

The interaction of 1-hydroxy-9,10-anthrahydroquinones (1-HOAHQ) with boric acid in aqueous borate buffer solutions at pH 9.5 causes a decrease in the anodic limiting current of the 1-HOAHQ and the simultaneous appearance of a new diffusion-controlled anodic wave at more positive potentials. This is...

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Bibliographic Details
Published in:Canadian journal of chemistry 1977-08, Vol.55 (16), p.2946-2952
Main Authors: Broadbent, Arthur D, Hewson, W. Donald, McDonald, Heather A, Melanson, Ronald J
Format: Article
Language:English
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Summary:The interaction of 1-hydroxy-9,10-anthrahydroquinones (1-HOAHQ) with boric acid in aqueous borate buffer solutions at pH 9.5 causes a decrease in the anodic limiting current of the 1-HOAHQ and the simultaneous appearance of a new diffusion-controlled anodic wave at more positive potentials. This is attributed to the formation of a cyclic borate ester of the 1-HOAHQ involving the peri-hydroxyl groups. Ester formation is much slower but still complete when the boric acid - borate to 1-HOAHQ molar ratio exceeds 10-15. These esters are most stable at pH 7.5-9.5 and completely unstable above pH 12. 1,2-Dihydroxy-9,10-anthraquinones (1,2-diHOAQ) react with boric acid to give cyclic esters involving the 1- and 2-hydroxyl groups, but of lower stability than those from 1-HOAHQ. On reduction of a 1,2-diHOAQ in the presence of boric acid at pH 9.5, cyclic borate esters involving the peri-hydroxyl groups are rapidly produced in preference to those involving the ortho-hydroxyl groups.
ISSN:0008-4042
1480-3291
DOI:10.1139/v77-408