Polycarboxylic acids containing acetal functions: calcium sequestering compounds based on oxidized carbohydrates

A number of polycarboxylic acids containing acetal functions have been prepared by a two‐step oxidation of carbohydrates. Their calcium sequestering behavior is compared with that of a series of model polycarboxylic acids. It is found that calcium sequestration by oxidized carbohydrates is less than that by corresponding ether polycarboxylates, since (a) acetal oxygens have a lower coordinating power than ether oxygens, and (b) there is extra steric repulsion upon calcium complexation by both the additional CH2 OH groups and the unfavorable natural configuration of the oxidized carbohydrates investigated. Some of the oxidized carbohydrates show greater calcium sequestering capacities than corresponds to the stability constant. This is probably caused by crystal growth inhibition or precipitation‐inhibition phenomena. Two model compounds illustrate that the acetal moiety is sufficiently stable under washing conditions, whilst it hydrolyses under acidic waste water conditions into small (hydr)oxycarboxylates.