of calcium carbonate calcium carbonate was again added over 15 minutes and sampled for analysis as shown below in table ii table ii______________________________________sample carbonate analysis ph min by chittick method observed______________________________________10 0 043 3 3130 0 027 3 3767 0 017 3 2792 0 000 3 28______________________________________ this example shows that even at higher levels of calcium carbonate carbonate removal as carbon dioxide is complete no fumarate was observed by nmr in the product thereby indicating that the maleic acid was not isomerized under the conditions of this reaction use of calcium carbonate filter cake in the preparation of calcium maleate and the synthesis of hoptc doohc mixtures calcium carbonate recycle filter cake 38 2 g obtained in accordance with the above described process and having the analysis shown in table iii below was slurried with 40 g of water table iii______________________________________component weight______________________________________calcium carbonate 24 80 gdisodium d l tartrate 0 31 gdisodium fumarate 0 38 gdisodium maleate 0 30 gdisodium malate 0 08 ghoptc 4 81 gdoohc 0 23 gwater 7 29 g______________________________________ over a 40 min period this slurry was added to a mixture of maleic anhydride 39 2 g 0 4 mole and water 80 g that had been heated to 60 u00b0 c to convert all the anhydride to maleic acid while the mixture was held at 65 u00b0 c all the carbon dioxide was removed and calcium maleate was formed an additional 0 5 g 0 005 mole of calcium carbonate was added to make up the total amount of calcium needed in the synthesis reaction calcium hydroxide 1 11 g 0 015 mole d l tartaric acid 45 4 g 0 303 mole.