JPS5922904B2 - Solvent for moisture measurement by Karl Fischer method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to analytical reagents, and particularly to a solvent used for measuring water content in organic acid and ketone reagents by the Karl Fischer method.

In the Karl Fischer moisture measurement method (hereinafter abbreviated as the KF method), a small amount of 12 and 502 dissolved in a mixture of pyridine and methanol is used as the sample solvent. When measuring the water content in an organic acid or ketone sample, the organic acid or ketone reacts with the alcohol in the solvent to produce water, so the water content in the solvent gradually increases. RCOOH+W
'OH→RCOOW-IH2O・・・・・・(1)R
,,R\10BiC20+2WOH→C +H2O...
・(2) R/R”NOW, that is, the moisture measured at this time is the sum of the moisture originally contained in the sample and the moisture generated by the reaction in equation (1) or (2) above. becomes.

Therefore, since the moisture originally contained in the sample cannot be accurately measured, the interfering reactions of equations (1) and (2) above must be reduced as much as possible. but,
Since alcohol in the solvent used in this measurement is an essential substance for the KF reaction to proceed quantitatively, it cannot be excluded. For this purpose, conventionally, a solvent containing pyridine as the main component mixed with a small amount of an alcohol having a low reaction rate as shown in equations (1) and (2) has been used.A typical solvent is a mixture of 5 pairs of pyridine and ethylene glycol. Capacity ratio of 1,
Alternatively, the solvent was a mixture of pyridine and propylene glycol at a volume ratio of 1:1. [Kaname Muroi, Kunihiko Ogawa, Yaeko Ishii, Analytical Chemistry, 12, 963 (1963)]
During actual measurements, the solvent was cooled to below 15°C in order to delay the reaction in equation (2) above.The conventional KF method was applied to coulometric titration to Table 1 shows an example of measuring water content in acid or ketone reagents.

In this case, the anode electrolyte used was a conventional solvent made by dissolving a small amount of 12,502 in a 5:1 mixture of pyridine and methanol to make a total volume of 77 ml, and the cathode electrolyte was a KI solution. This method uses a methanol solution. Samples were prepared by adding approximately 1 g of commercially available acetone reagent one after another.
These are the results measured at 5°C. In Table 1, the measured value is the sum of the water in the sample and the water produced by the reaction of equation (2) above.

The background value is a value obtained by measuring the amount of moisture generated in the solvent within a certain period of time after each moisture measurement, and corresponds to the rate of moisture generation according to equation (2). Moisture % indicates the moisture % in the sample acetone calculated from the above value, and this value is reproducible until the same sample acetone is measured 5 times, but increases rapidly after the 6th measurement.
Therefore, it is shown that the amount of sample that can be accurately measured in this case is up to about 5 g. One of the characteristics of coulometric titration using the KF method is that the same solvent can be used many times as mentioned above, and the measurement efficiency is excellent. It cannot be said that the measurement efficiency is good because it requires analysis.

Furthermore, since the above-mentioned solvent consumes a large amount of fairly expensive reagents, it is necessary to increase the number of measurements from an economic standpoint. In order to increase the number of measurements using a certain amount of solvent, it is sufficient to suppress the reaction in equation (2), and for this purpose, it is necessary to reduce the alcohol content in the solvent, but if the alcohol content is reduced, the solvent That is, the electrical resistance of the electrolytic solution increases, generating heat and raising the temperature of the solvent. As a result, the reaction of formula (2) is accelerated, resulting in an increase in the rate of water production. For the above reasons, in conventional solvents using pyridine, it was appropriate to set the mixing ratio of alcohol to s volume of pyridine. Can the present invention be repeated more times with a fixed amount of solvent? The purpose of this product is to provide a solvent for measuring the water content of organic acids or ketones using the KF method, which can be used to measure the water content of organic acids or ketones. The reason is that ethylene glycol or propylene glycol, which is a small lower dihydric alcohol, is used. Acetonitrile was once tried as a solvent when preparing the KF reagent by Smith et al. [Smith, . D
．． M. et al. J. Arn. Chem. SOc.

6l, 2407 (1939)] has never been used as a solvent for moisture determination.

As a result of experimental studies on mixed solvents of acetonitrile and several types of alcohols and their mixing ratios, the present inventors have confirmed that a mixed solvent mainly consisting of 60 ml of acetonitrile and 2 ml of ethylene glycol or propylene glycol is optimal. Ta. This will be explained below using examples.

Table 2 shows that 15 ml of a solution of 12 and SO2 dissolved in pyridine is added to a mixture of 60 ml of acetonitrile and 2 ml of ethylene glycol, making the total volume 77 ml! , using the solvent as the anolyte and the methanol solution of KI as the catholyte.V)? The water in the acetone reagent is reduced to 11
These are the results of measurements taken over several times.

As is clear from Table 2, the number of accurate measurements was approximately 10 (more than 10 g of sample in total), which is twice as many measurements as with the conventional solvents shown in Table 1.

Further, the best mixing ratio of alcohol to acetonitrile is 60 ml to 2 ml, and even if the mixing ratio is higher than that, at least the number of measurable times will decrease. However, the practical mixing amount of alcohols is in the range of 1 to 4 ml for good measurement efficiency. Figure 1 is a diagram showing the relationship between the amount of sample acetone added and the background value, where the vertical axis shows the background value in μGH2(1), and the horizontal axis shows the amount of sample acetone added in g. ing.

Line 1 is for the conventional solvent shown in Table 1 (mixed volume ratio of pyridine and methanol 5:1), and line 2 is for the solvent of the present invention shown in Table 2 (mixed volume ratio of acetonitrile and propylene glycol 30:1). This is the case of vs. 1). In both lines 1 and 2, the water production rate increases approximately in proportion to the amount of sample acetone reagent added, but since the slope of line 2 is small, the water production rate is slow. Therefore, it is shown that this solvent can be used more times with less harmful reaction. This means that
A similar relationship was observed not only in the measurement of ketones such as acetone, but also in the measurement of water content in organic acid reagents. Furthermore, when comparing the electrical conductivity of the above-mentioned solvents, with the conventional solvent mainly composed of pyridine, the voltage between the electrodes required to flow an electrolytic current of 107 ml was 25 to 35V, but with the solvent mainly composed of acetonitrile in this example, the voltage between the electrodes was 25 to 35 V. In the same electrolytic cell, the voltage was 12-17V.

As described above, the smaller the interelectrode voltage Δ, the smaller the calorific value of the solvent, which indicates that the damage prevention reaction (moisture generation reaction shown by equations (1) and (2)) is small. The solvent of this example has the following effects.

a This solvent can be used for twice as many measurements as conventional solvents, so it eliminates the trouble of replacing the solvent, improves analysis efficiency, and lowers the unit cost of analysis. b Since this solvent has good conductivity, the rate of damage prevention reaction can be reduced, and it is particularly suitable for coulometric titration. c) Since the mixing ratio of alcohols is smaller than that of conventional solvents, the harm prevention reaction can be reduced.

d Since this solvent does not use a large amount of pyridine, it has little odor and viscosity and is easy to handle. e This solvent mainly uses inexpensive chemicals that are easy to purify, so it can be made with high purity and is cheaper than conventional solvents.

The above example describes a solvent that is a mixture of acetonitrile and ethylene glycol or propylene glycol, but as a result of an experiment, a mixture of ethylene 1 glycol and propylene glycol in an arbitrary ratio and acetonitrile in the above ratio were found. The mixed solvents also showed similar effects.

Moreover, although the above-mentioned examples are given as examples of coulometric titration, the solvent can also be used satisfactorily as a solvent for measuring the water content of organic acids and ketones by the general KF method. As described above, the solvent of the present invention can be used for more measurements than conventional solvents as a solvent for measuring the water content of organic acids or ketone reagents by the KF method, and therefore has the effect of improving analysis efficiency.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of sample acetone reagent added and the background value, comparing the conventional method and the example of the present invention.

Claims (1)

[Scope of Claims] 1. A solvent used when measuring the water content in organic acid and ketone reagents by the Karl Fischer method, wherein the solvent contains acetonitrile and at least one of ethylene glycol and propylene glycol. Curls that are mainly composed of a mixture of
Solvent for moisture measurement using the Fisher method. 2 The above solvent contains 60 volumes of the above acetonitrile and the above ethylene glycol or the above propylene glycol 1 to 4
The solvent for measuring water content by the Karl Fischer method according to claim 1, which is a solvent mainly composed of a mixture in a volume ratio. 3. The Karl Fischer method according to claim 1, wherein the solvent is a solvent mainly composed of a mixture of 60 volumes of the acetonitrile and 1 to 4 volumes of the mixture of ethylene glycol and propylene glycol. solvent for moisture determination.