Three Kinds of Calcium Oxalate Hydrates

Abstract

Formation and properties of calcium oxalate monohydrate, dihydrate and trihydrate were studied as compared with the calcium oxalate crystals isolated from plants. Calcium oxalate monohydrate precipitates at temperatures higher than those for the formation of calcium oxalate dihydrate and trihydrate. Calcium oxalate dihydrate and trihydrate were produced in the presence of sodium citrate or malate depending on the concentration of citrate or malate. The solubility at room temperature of calcium oxalate dihydrate or trihydrate was little greater than that of monohydrate as shown in Table 3. The solubility of calcium oxalate monohydrate slightly increased at 100°C. The shapes of single crystals of calcium oxalate monohydrate, dihydrate and trihydrate were hexagonal plates, octahedron, and parallelogram plates respectively. Calcium oxalate dihydrate and trihydrate changed to monohydrate by boiling in water for 10 min. The nucleus of calcium oxalate monohydrate was assumed to be Ca3(C2O4)3.n H2O from the measurement of the induction period of the precipitation. Calcium oxalate monohydrate and dihydrate were found to be present in plant leaves and trunks. Those formed in plants were very stable and they changed into monohydrate after boiling one or for several hours in water. © 1991, The Chemical Society of Japan. All rights reserved.