Study of dissociation of α-alkyl-substituted dicarboxylic acids

Abstract

Dissociation of α-alkyl-substituted dicarboxylic acids low-soluble in water was studied by the method of рН-potentiometry titration. Equilibrium constants of the dissociation at 25°С were determined.It was shown earlier that alkyl-substituted dicarboxylic acids (DA) are promising collectors for fl otation of some non-sulfi de ores [1,2]. It is necessary to note in this connection that the assortment of reagents used for the fl otation in acid medium and a possibility of their application are rather limited. So, the activity of a fatty-acid collector, such as oleic acid or tall oils, decreases at рН < 5 in view of a low dissociation degree. The presence of the second carboxyl group in a collector molecule appreciably infl uences its acid properties and, hence also its activity in the acid-medium fl otation. For this reason the study of dissociation of α-alkyl-substituted dicarboxylic acids is an important stage in studying their fl oatation operation.Acid-base properties of carboxylic collectors are poorly studied, and available published data are rather confl icting. So, values of the dissociation constants for oleic acid determined by various authors differ by several orders: рK 4.95 [3] and рK 9.80 [4]. There are data on the dissociation of some α-alkyl-1,1-1,3-dicarboxylic acids with rather small hydrocarbon radicals from -С 9 Н 19 up to -С 12 Н 25 . The procedure used for their determination [5] is based on the graphical determination of the constants from the data of the potentiometric titration of an acid aqueous solution by an alkali solution. In view of a low solubility of the acids under consideration in water such procedure can lead to erroneous results.The aim of this work was to study acid-base properties of some α-alkyl-dicarboxylic acids low-soluble in water with hydrocarbon radicals from -С 10 Н 21 up to -С 16 Н 33 and with 1,1-1,7-arrangement of carboxyl groups.Diffi culty of studying physicochemical properties of carboxylic collectors is caused by their low water solubility. Therefore we used the procedure of dissociation constants determination by potentiometric titration of a series of water-alcohol solutions of dicarboxylic acids with various water-alcohol ratios (70 : 30, 50 : 50, 30 : 70, 20 : 80) by alkali followed by extrapolation of the resulting linear dependences to a zero alcohol content. The preliminary test of the procedure by the example of α,ω-dicarboxylic acids has shown a good agreement between calculated dissociation constants and published data.We have studied dissociation of a series of α-alkyldicarboxylic with the common formula HOOC _ (CH 2 ) m-1 _ CH _ COOH, RHere R is an alkyl radical from С 10 Н 21 up to С 16 Н 33 , m = 1-7.All the compounds were preliminary purified by recrystallization from benzene or ethanol and dried up under a reduced pressure.Measuring рН of the systems under study was carried out with a glass electrode and an I-120.1 ionometer accurate to 0.02 at 25°С and an ionic strength of 0.1 provided by potassium chloride. For the titration we used KОН water-a...