EFFECT OF ALKALI CATIONS ON THE METHOXIDE ION ADDITION TO CORANDS INCORPORATING A THIOPYRYLIUM SUBUNIT

The incorporation of a thiopyrylium ring in a corand structure forms a system with a weak binding ability in methanol towards the alkali cat ions K+, Rb+ and Cs+. The binding substantially increases in basic sol ution because of the reversible addition of methoxide ion to the heter oaromatic ring to form a neutral 4H adduct. The effect of the length o f the polyoxyethylene chain and of the presence of a bulky group (tert -butyl) in the gamma position of the heteroaromatic ring has been quan titatively investigated. Results obtained from molecular mechanics cal culations were used to rationalise the depressing effect of the gamma tert-butyl group on the ligand ability of thiopyrans.