Those pectic substances that are essentially void of methoxyl groups and have carboxyl groups only. They have varying degrees of neutralization. The divalent salts are slightly soluble in water and must be converted to the sodium or potassium forms for dissolution. It gels in the presence of calcium or other divalent cations.
Citrus pectic acid (500g) is refluxed for 18hours with 1.5L of 70% EtOH, and the suspension is filtered hot. The residue is washed with hot 70% EtOH and finally with ether. It is dried in a current of air, ground and dried for 18hours at 80o under vacuum. [Morell & Link J Biol Chem 100 385 1933.] It can be further purified by dispersing it in water and adding just enough dilute NaOH to dissolve the pectic acid, then passing the solution through columns of cation-and anion-exchange resins [Williams & Johnson Ind Eng Chem (Anal Ed) 16 23 1944], and precipitating with two volumes of 95% EtOH containing 0.01% HCl. The precipitate is worked with 95% EtOH, then Et2O, dried and ground. [Rees & Walsh Angew Chem Int Edn 16 214 1977, Rees Adv Carbohydr Chem 24 267 1969.]
