JPH043502B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolytic solution for Karl Fischer coulometric titration. The Karl Fischer coulometric titration method is well known, and the electrolyte used is usually a solution prepared by adding a small amount of water to iodine, sulfur dioxide, pyridine, and methanol to ionize iodine. A solution containing potassium iodide or sodium iodide instead of iodine may also be used. Solutions using various aliphatic amines, heterocyclic compounds, etc. in place of pyridine have also been proposed. Electrolyte solutions for Karl Fischer coulometric titrations have conventionally contained pyridine, which has a peculiar odor, as one of its components, which has caused inconvenience in analytical operations. Therefore, an odorless electrolyte has been desired. In addition, as the electrolyte, an electrolyte with a high reaction rate for the Karl Fischer reaction is desirable because it can shorten the titration time, and an electrolyte with a gradual potential change near the titration end point is desirable from the standpoint of ease of controlling the device. Liquids have been desired for measurement accuracy. Although it is preferable that the electrolytic solution has the above-mentioned advantages, the known electrolytic solutions mentioned above are not necessarily sufficient in this respect. An object of the present invention is to provide an electrolyte having the above-mentioned advantages. The present invention provides an electrolytic solution for Karl Fischer coulometric titration containing iodine or an iodide, sulfur dioxide, alcohol, chloroform, and at least one pyridine compound selected from the group consisting of (a) and (b) below. Regarding. (a) General formula [] (In the formula, R ¹ , R ² , R ³ , R ⁴ and R ⁵ are hydrogen atoms, alkyl groups or alkokyl groups, and at least one of them is an alkyl group or an alkoxyl group.) ) General formula [] (In the formula, R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ , R ¹² and R ¹³ are hydrogen atoms, alkyl groups or alkoxyl groups, and n is an integer of 1 to 5) Represented Compounds To explain the present invention in detail, the electrolytic solution consists of the following components. Suitable iodides include iodic acid, potassium iodide, and sodium iodide. The content of iodine or iodide in the electrolytic solution is 3 to 0.1% by weight, preferably 2 to 0.3% by weight in terms of iodine. Alcohols include methanol, ethanol,
Lower aliphatic alcohols such as isopropanol, n-butanol, isobutanol, and tert-butanol are usually used, but ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and the like can also be used. The concentration of alcohol in the electrolyte is preferably 30 to 70% by weight. The concentration of sulfur dioxide greatly influences the reaction rate as well as the basicity of the base used, and even when a base with low basicity is used, the reaction will be faster if the concentration of sulfur dioxide is increased. Usually the content of sulfur dioxide in the electrolyte is 10-0.3% by weight, preferably 6-0.3% by weight.
It is 1.2% by weight. Chloroform has a large dissolving power for various substances and has the effect of promoting the Karlfischer reaction, so it is used as a component of the electrolyte. Its content is 10-50% by weight in the electrolyte. The pyridine compound as a base used in the present invention is a pyridine compound represented by the above general formula [] or []. Examples of the alkyl group for R ¹ to ^{R 13} include methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl, and the like. Examples of the alkoxyl group include methoxyl group and ethoxyl group. The pyridine derivative represented by the general formula [] is preferably a compound in which one to three of R ¹ to R ⁵ are alkyl groups, and specific examples thereof include picoline, lutidine, collidine, diethylpyridine, and the like. The pyridine compound represented by the general formula [] is a compound in which all of R ⁶ to ^{R 13} are hydrogen atoms, or a compound in which 1 to 4 of R ⁶ to ^{R 13} are an alkyl group, and n is Compounds that are an integer from 2 to 4 are preferred. The bonding position of the -(CH ₂ -) _o group to the pyridine ring is 4-
It may be a 4-position and the other a 2-position.
- position or both positions. Specific examples include 1,3-di(4-pyridyl)propane and 1,3-di(2-pyridyl)propane. However, as mentioned above, the molar ratio of the pyridine compound to sulfur dioxide is important for the concentration of the pyridine compound in the electrolyte.
1 to 0.3:1, preferably 5:1 to 0.5:1. The composition of the electrolytic solution according to the present invention is as described above, but in addition to the above-mentioned components, a small amount of other components may be included in order to improve the performance of the electrolytic solution depending on the sample. For example, carbon tetrachloride. Moisture determination using the electrolytic solution according to the present invention is carried out according to a conventional method. That is, an electrolytic solution according to the present invention is placed in the anode chamber, and a suitable catholyte is placed in the cathode chamber and electricity is applied to remove water in the anolyte. Next, a sample is added to the anode chamber and electricity is applied again to titrate the water content in the sample. Note that when iodine is used to prepare the anolyte, water is added until the color of the iodine disappears before use. A suitable catholyte is, for example, a mixed solution of 75% by weight of methanol, 20% by weight of carbon tetrachloride and 5% by weight of sulfur dioxide. The electrolytic solution according to the present invention can be used to measure the moisture content of various substances, such as organic compounds, inorganic compounds, petroleum products, and petrochemical products. Since the electrolytic solution according to the present invention does not have a bad odor and has a high reaction rate, it has the advantage that the measurement time is short and the potential change near the end point of titration is gradual. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Example 1 and Comparative Examples 1 and 2 26.8 g of 2,6-lutidine, 3.8 g of sulfur dioxide,
Dissolve 1.27 g of iodine and 37 g of chloroform in methanol, add water to reduce the iodine, and then bring the volume to 100 ml with methanol. The electrolytic solution prepared as described above is placed in the anode chamber of a commercially available Karl Fischer coulometric titration device (digital trace moisture measuring device CA-02 model, manufactured by Mitsubishi Kasei). A 4:1 mixture of 1M methanol solution of sulfur dioxide and carbon tetrachloride is placed in the cathode chamber. Water was injected and measured according to the operating method of the coulometric titration device described above. The results are shown in Table 1. The measured values are in good agreement with those obtained when similarly measured using pyridine (Comparative Example 1), and the measurement time is shorter. Furthermore, the potential change at the titration end point is gradual, as shown in FIG. 1, and the end point can be easily detected. On the other hand, when similarly measured using imidazole, the potential change at the end point of titration (Comparative Example 2 in Figure 1) was sudden and over-titration was likely to occur. Example 2 2,4,6-collidine 30.3g, sulfur dioxide 3.8
Dissolve 1.27 g of iodine, 37 g of chloroform in methanol, add water to reduce the iodine, and then make up to 100 ml with methanol. Measurements were carried out in the same manner as in Example 1 using this electrolyte. Example 3 9.9 g of 1,3-di-(4-pyridyl)propane,
6.4g sulfur dioxide, 1.27g iodine, chloroform
Dissolve 37g in methanol, add water to reduce the iodine, and then adjust the volume to 100ml with methanol.
Measurements were carried out in the same manner as in Example 1 using this electrolyte. Example 4 A similar measurement was carried out using 19.8 g of 1,3-di-(4-pyridyl)propane instead of 9.9 g of 1,3-di-(4-pyridyl)propane in Example 3. Example 5 20.0 g of 1,3-di-(2-pyridyl)propane,
7.7g sulfur dioxide, 0.64g iodine, chloroform
Dissolve 37g in methanol, add water to reduce the iodine, and make up to 100ml with methanol.
Measurements were carried out in the same manner as in Example 1 using this electrolyte. 【table】

[Brief explanation of drawings]

FIG. 1 is a graph showing the potential change at the titration end point, where the solid line shows the measurement end point using the electrolytic solution of the present invention (Example 1), and the broken line shows the measurement end point using the electrolytic solution using imidazole (Comparative Example 2).

Claims (1)

[Scope of Claims] 1. A Karlfischer coulometer containing iodine or an iodide, sulfur dioxide, alcohol, chloroform, and at least one pyridine compound selected from the group consisting of (a) and (b) below. Electrolyte for titration. (a) General formula (In the formula, R ¹ , R ² , R ³ , R ⁴ and R ⁵ are hydrogen atoms, alkyl groups or alkoxyl groups,
At least one of which is an alkyl group or an alkoxyl group) (b) A compound represented by the general formula (In the formula, R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ , R ¹² and R ¹³ are hydrogen atoms, alkyl groups or alkoxyl groups, and n is an integer of 1 to 5) Compound represented. 2. The electrolytic solution according to claim 1, wherein the molar ratio of the pyridine compound to sulfur dioxide is in the range of 6:1 to 0.3:1.