SU1746283A1 - Method for quantitative determination of sulfoxides by potentiometric titration with perchloric acid in acetic anhydride - Google Patents

Abstract

The invention relates to analytical chemistry and can be used in the petroleum and petroleum refining industry in the determination of sulfoxides in petroleum and gas condensates. SUMMARY OF THE INVENTION: The method is carried out by potentiometric titration of a sample previously dissolved in chloroform at 20-50 ° C followed by by adding acetic anhydride at a volume ratio of ingredients 1 1

Description

This invention relates to analytical chemistry and can be used in research practice, as well as in the petroleum and petrochemical industries, in determining the group composition of organic sulfur compounds.

A known method for the determination of sulfoxides, which consists in the potentiometric titration of sulfoxides with perchloric acid in dioxane (titrant) in acetic anhydride (background). Calomel and glass electrodes are used.

The sulfur content of sulfoxide is determined by the formula

NHCIO4 3.2 VHCIO4

9 where N is the normality of the titrant,

cheo in efshogo

okat-ov) in that

re (1)

V is the volume of titrant consumed for titration,

g - sample weight

3.2 is a conversion factor for wt.% Sulfur.

The known method is applicable for the quantitative determination of individual sulfoxides and sulfoxides concentrates obtained by the oxidation of sulphides isolated from petroleum fractions with sulfuric acid.

Closest to the present invention is a method consisting in the preliminary separation of sulfoxides from petroleum fractions by liquid chromatography on cation exchangers. The sulfoxides concentrated in the alcoholic fraction are then titrated with 0.01 N perchloric acid in dioxane. A mixture is used as a background.

v4 En O GO 00

s

benzene and acetic anhydride in the ratio of 1: 2.

A disadvantage of the known method is the need to concentrate sulfoxides by using liquid adsorption chromatography.

The aim of the invention is to simplify the analysis and expand the number of objects to be analyzed, by allowing the direct determination of sulfoxides in petroleum and gas condensates.

The goal is achieved by the fact that the sample to be analyzed is pre-dissolved in chloroform at 20-50 ° C, followed by the addition of acetic anhydride and titration using known techniques.

The completeness of the dissolution is determined visually - the solution is clear. The volume of chloroform as well as acetic anhydride is 15 ml. Titration is carried out with perchloric acid in dioxane. The volume of titrant to be added is 0.1 ml.

Typically, the magnitude of the potential jump varies between 50-80 mV. According to the data obtained, a curve is constructed in millivolts – milliliters coordinates and an equivalence point is determined. The equivalence point is determined by the middle of the titration jump curve. The amount of sulfoxides is calculated by the formula (1).

The use of pre-dissolving the sample to be analyzed in chloroform is due to the fact that petroleum and petroleum products (especially high boilers) are poorly soluble in acetic anhydride, which precludes analysis in a known manner.

A distinctive feature of the proposed method is the preliminary dissolution of the sample in chloroform, followed by the addition of acetic anhydride.

Petroleum and petroleum products do not dissolve in acetic anhydride. Curd mass is formed and it is not possible to carry out an analysis in a known manner.

Example. A weighed weight of 0.128 g of oil, weighed on an analytical balance, is placed in a 75.0 ml tube and dissolved in 15 ml of chloroform at 50 ° C and stirred on a magnetic stirrer. Then 15 ml of acetic anhydride are added to the tube. The temperature of the solution decreases to 3530 ° C. Then, glass and calomel electrodes are inserted into the tube, which are connected to a pH-meter-voltmeter (pH 34.0, pH 121). The temperature of the solution in the bottle is reduced to 25-20 ° C by this time. A burette with a solution of perchloric acid in dioxane (titrant) is supplied to the bale. The normality of the solution is 0.0547. Include agitator and pH meter / millivoltmeter. The initial potential of the solution is recorded and 0.1 ml of the titrant is added. Record new potential, etc. Thus, it is titrated until a potential jump occurs. Typically, the potential jump for sulfoxides ranges from 400-800 mV. After a potential jump occurs, several more portions of the solution are added and, with a clearly repeated decrease in the potential gain from addition of equal amounts of solution, the titration is stopped. According to the data obtained, the curve is plotted in the millivolt – milliliter coordinates and the equivalent point and volume of the solution that was titrated are determined.

The proposed method allows the determination of sulfoxides in the presence of nitrogen compounds. If basic nitrogen is present in the analyzed sample, then two potential jumps are observed on the titration curves, corresponding to the end of the titration of basic nitrogen and sulfoxides. Artificial mixtures have shown that basic nitrogen does not interfere with the quantitative determination of sulfoxides.

Claims (1)

Claims The method of quantitative determination of sulfoxides by potentiometric titration with perchloric acid in acetic anhydride, characterized in that, in order to simplify the method and expand the number of objects analyzed by allowing the direct determination of sulfoxides in oils and hydroelectric condensates. before the potentiometric titration, the analyzed sample is dissolved in chloroform at 20–50 ° C, followed by the addition of acetic anhydride with a 1: 1 volume ratio of ingredients.