Determination of small amounts of ethylene chloride in benzene using a substitution reaction with methanolic potassium hydroxide

Abstract

For the purpose of studying behaviours of trace components during rectification of liquids, a process to determine minor quantities of ethylene dichloride in benzene solution was developed, in which chlorine, linked to carbon in ethylene dichloride molecules, underwent a replacing reaction with potassium hydroxide in methanolic solution at elevated temperature, and resulting free chloride ion was extracted with water to be quantified by a titration procedure or a spectrophotometric method.
1 ml of trial benzene solution, containing the weighed quantity of ethylene dichloride, was packed and sealed. in a glass ampoule together with 10 ml of 30% methanolic potassium hydroxide, and was heated at a constant temperature of boiling water for 2.5 hours, for the replacing reaction to be carried out completely. The reactants mixture was then extracted with chlorine free water and, after the separating of benzene phase, diluted precisely up to 100 ml, and the concentration of chloride ion in this aqueous solution was ascertained by one of different two ways. When the aqueous solution contained enough quantity of chloride ion for the titration measurement because of rich containment of ethylene dichloride in benzene, the determination was performed by a volumetric analysis according to Volhard's method:
Remaining quantities of excess silver ion employed to precipitate chloride ion completely as silver chloride, was titrated with standard solution of ammonium thiocyanate using iron-alum as indicator under presence of nitrobenzene. In the case where the concentration of chlorine was not rich, determination was performed by spectrophotometric measurement of absorption with ferric thiocyanate complex which were formed by ferric ion and thiocyanate ion, equivalently produced from mercuric thiocyanate by replacement reaction of chloride ion.
Above mentioned processes were operated for analysing ethylene dichloride of 0.6, 6 and 60 mg/ml of concentration in benzene, and recoveries of chloride ion vs. ethylene dichloride were estimated. The optimum conditions of the procedures were searched for the 100% recover, and they were; 30% of concentration of potassium hydroxide in methanolic solution as a replacing reagent, 10 : 1 of ratio of mixing volume of methanclic potassium hydroxide to volume of the benzene solution, and 2.5 hours of reaction time of replacement of chlorine.
Average recoveries of ethylene dichloride and mean errors of them obtained as results of six times of analysis under optimum condition were 99.86± 0.12%, 99.95± 0.33% and 99.48± 0.33% for the concentrations of 60 mg/ml, 6 mg/ml and 0.6 mg/ml, respectively.