: ##STR1##wherein the R groups are hydrogen or hydrocarbyl groups generally containing from 1 to 6 carbon atoms per group or alkoxy-substituted hydrocarbyl groups generally containing from 2 to 6 carbon atoms per group, with the further proviso that compounds offormula I or II contain a maximum of 12 carbon atoms per molecule and wherein M is an alkali metal or quaternary ammonium group of up to a