Solubility of potassium and sodium orthophosphates in ethylene glycol

Abstract

Solubility of potassium and sodium orthophosphates in ethylene glycol was determined.Phosphates of metals are used in various industries (textile, cement, glass, and ceramic) and in everyday life, including the use as components of cleaning agents, mineral fertilizers, structural materials, and food and fodder additives. In the most widespread handbooks and separate papers [1][2][3][4][5] there is only information about dibasic sodium phosphate solubility in methanol and ethanol. Data on the solubility of acid and neutral orthophosphates of alkali metals in other alcohols, glycols, cellosolves, and glycerin are absent. It is known [6-13] that the alcoholysis of weak-acid salts (carbonates, orthophosphates, sulfi des, and cyanides), of organometallic compounds, and other derivatives of alkali metals, such as acetylenides, amides, hydrides, nitrides, and azides, can be considered as a mode of preparation of corresponding alcoholates, whereas the alcoholysis of hydroxides is one of industrial methods of producing potassium and sodium alcoholates:Here M is an alkali metal; X = CO 3 , S, CN, OH, PO 4 , C≡C(H), NH 2 , H, N 3 , N, R; R = an alkyl; n = 1-3.Thus, the term "solubility" for the specifi ed reaction systems is incorrect. Earlier distributions of components over phases in methanolysis reactions of potassium hydroxide and carbonate and also in alcoholysis of sodium sulfi de under the action of various alcohols [9-11] were determined. Furthermore it was found that the methanolysis of potassium hydrocarbonate does not occur [9]. It was reported in the patent [6] that glycolates are formed in reactions of orthophosphates, cyanides, and carbonates of alkali metals with ethylene glycol and propylene glycol.In particular, the data on the alcoholysis of 10.8 wt parts of sodium orthophosphate by 93.2 wt parts of ethylene glycol at a temperature of about 100°С are given:НОСН 2 СН 2 ОН + Na 3 PO 4 = NaOCH 2 CH 2 OH + Na 2 НРО 4 .(2)The reaction duration is not specifi ed. As a result the authors have obtained a solution consisting of 2.7 wt parts of sodium monoethylene glycolate, 0.6 wt parts of sodium hydroorthophosphate, 5.5 wt parts of sodium orthophosphates, and 91.2 wt parts of ethylene glycol. In addition the precipitate consisted of 4 wt parts of Na 2 НРО 4 . The above-given data allow us to calculate that the "solubility" of Na 3 PO 4 and Na 2 HPO 4 in ethylene glycol (at joint presence of these salts and sodium ethylene glycolate) at a temperature of about 100°С is 6.93 and 0.66 g of a salt in 100 g, respectively. However the authors of patent [6] did not specify a mode of analysis of solid and liquid phases, moreover, it is doubtful that the precipitate consisted only of Na 2 НРО 4 and did not contain initial Na 3 РО 4 .The purpose of this work was to determine the solubility of potassium and sodium orthophosphates in ethylene glycol at 30 and 197°С, and also to elucidate a possibility of glycolates formation. EXPERIMENTALEthylene glycol (analytical grade) was rectifi ed in vacuum. Sodium and potassium orthoph...