Bg. Cox et al., Synthesis, characterisation and metal ion binding properties of crown ethers incorporating 4,5-dioxyxanthones, J CHEM S P2, (2), 1999, pp. 289-296
Citations number
40
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
An efficient preparation of 4,5-dihydroxyxanthone, 5, is described, and its
incorporation into crown ethers with 18-, 21- and 24-membered macrocyclic
arrays, 3 (n = 3, 4 and 5), and a model compound, 4,5-diethoxyxanthone, 10.
Metal ion complexation of the crowns causes a strong quenching of the high
ly fluorescent 4,5-diethoxyxanthone chromophore. Binding constants for comp
lex formation with sodium, potassium, and caesium ions in methanolic soluti
on have been measured by spectrofluorimetric and conductimetric methods and
range from <10(2) for 3 (n = 5) binding sodium ion to 4.1 x 10(3) for 3 (p
r = 4) binding potassium ion. The behaviour of the 4,5-dioxyxanthones in aq
ueous sulfuric acid mixtures has been examined by UV spectroscopy and treat
ment of the data by the excess acidity method yields -2.6 < pK(a) < -2.3 fo
r the conjugate acids with 0.33 < m* < 0.40. The behaviour of the crowns co
ntaining 4,5-dioxyxanthones is compared with that of analogues containing 1
,8-dioxyxanthones.