JPS6154182B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to titrants containing amine sulfur dioxide and iodine.

As is well known, the titrimetric determination of liquid and fixed water content was developed by Karl Fischer. The method is based on the oxidation of sulfur dioxide with iodine in the presence of water according to the formula 2H ₂ O + SO ₂ + I ₂ H ₂ SO ₄ + 2HI. This reaction is usually carried out in anhydrous methanol. This reagent (KF reagent) consists of a solution of 790 g of pyridine, 192 g of liquid sulfite and 254 g of iodine in 55 g of absolute methanol (Angew.
(See Chemie Vol. 48 (1935), p. 394). Since this solution is not storage stable, in practice two-component reagents are generally used, one consisting of a solution of sulfur dioxide and pyridine in methanol and the other consisting of a solution of iodine in methanol.

Also, as is already known, pyridine can be replaced by other nitrogenous bases such as quinoline, aniline,
Dimethylaniline, tri-n-butylamine and triethanolamine have also been used, but without satisfactory results (J. Amer. Chem. Soc.,
1939, p. 2407). Other amines that have been attempted in place of pyridine include ethanolamine and hexamethylene-tetramine. However, these amines are said to have the disadvantage of not showing stable titration points or causing troublesome precipitation (Analytic. Chem. Vol. 28 (1956), 1166
(see page). These modified KF reagents contain oxidizing agents,
It was used to measure the water content of reducing agents and amines.

It is an object of the present invention to provide a storage-stable reagent which contains a virtually non-toxic amine instead of pyridine and which is suitable for determining small amounts of water.

The present invention provides a titrant containing an amine, sulfur dioxide and iodine, in which the amine is an aliphatic amine (excluding tributylamine) or one
The above titrant is characterized in that it is an alkanolamine containing 2 or 3 oxygen atoms and that the molar ratio of amine to sulfur dioxide is from 0.5:1 to 1.3:1.

The titrant according to the invention contains a chain aliphatic amine as the amine base. The amines are aliphatic amines or alkanolamines containing 1, 2 or 3 oxygen atoms in the form of hydroxyl groups. Particularly suitable are aliphatic amines or alkanolamines with 2 to 6 carbon atoms. Suitable amines include, for example: n-propylamine, isopropylamine, diethylamine, triethylamine, dimethylamino-propylamine, ethanolamine, diethanolamine, triethanolamine, tris(hydroxymethyl)aminomethane and guanidine. The molar ratio of amine to sulfur dioxide is 0.8:
A range of 1 to 1.2:1 is particularly preferred.

Suitable solvents for the reaction components of the titrants according to the invention are anhydrous low molecular weight alcohols, in particular methanol or ethylene glycol monomethyl ether (for 1 mol of amine) from 2 mol to 50 mol, in particular from 5 mol to 20 mol. used in amounts of

Sulfur dioxide can also be used in mixtures with acids, especially carboxylic acids. In that case, the molar ratio of sulfur dioxide to acid is from 20:1 to 1:5, in particular from 2:1 to 1:2. Suitable acids are, for example, formic acid, oxalic acid, sulfuric acid, hydroiodic acid and especially acetic acid.

The titrant according to the invention combines amines, sulfur dioxide and iodine with alcohol, optionally from 15°C to 50°C.
It is prepared by melting with cooling, especially at temperatures of from 20°C to 40°C. The amount of amine (in each case based on solution 1) is from 0.1 mol to 10 mol, in particular from 0.5 mol to 5 mol, the amount of sulfur dioxide is from 0.1 mol to 10 mol, in particular from 0.5 mol to 3 mol, the amount of sulfur dioxide is from 0.1 mol to 10 mol, in particular from 0.5 mol to 3 mol, and the amount of sulfur dioxide is from 0.1 mol to 10 mol, in particular from 0.5 mol to 3 mol. The amounts range from 0.01 mol to 3 mol, in particular from 0.1 mol to 1 mol. The solution is
It is produced in the usual way, excluding atmospheric moisture and using purified starting materials.

The titrant of the present invention is very suitable for determining small amounts of water by the Karl Fischer method.

The titrants of the invention are used to determine the content of solids or liquids, such as the water content of inorganic acids, organic solvents, fats, oils, foodstuffs and preparations.

The titrant of the present invention is distinguished by high storage stability. It is suitable both as a two-component reagent and as a one-component reagent. In the form of a two-component reagent, its storage stability is at least 12 months. In the form of a one-component reagent, it is stable for approximately 3 weeks. A particular advantage of the titrants of the invention is that they enable high reaction rates (see examples of use). Furthermore, this titrant is excellent in that the centimeter end point of the titration can be fully recognized visually by a color change from colorless to brown. When this titrant is used in a commercially available automatic titrant device (either voltammetrically or dead point indicated), a very stable endpoint is obtained;
High accuracy of moisture measurement is guaranteed. This titrant is furthermore suitable as an electrolyte for coulometer moisture determination.

Hereinafter, the present invention will be explained in more detail by giving examples.

Example 1 a 56 g (0.87 mol) of sulfur dioxide are first introduced into 500 ml of methanol while cooling to a temperature of 50°C, and then 61 g (0.50 mol) of tris(hydroxymethyl)-aminomethane are added to this mixture. . The molar ratio of amine to _SO2 is 0.57:1
It is.

b Dissolve 85 g (0.67 mol) of iodine 1 in methanol (solution B).

c Solution A+B is a two-component reagent. Add solution A to the test solution and titrate with base solution B.

Example 2 a 100g of 96g (1.50mol) liquid sulfur dioxide
(Add 1.69 mol of n-propylamine in 600 ml of methanol and keep the temperature of this mixture at 35-40 °C by cooling (solution A). The molar ratio of amine to SO ₂ is 1.12:1
It is.

b Solution B is identical to solution B of example 1.

Example 3 a 157 g (1.49 mol) diethanolamine, 60
g (1.0 mol) of acetic acid and 49 g (0.77 mol) of general sulfur dioxide were added in turn to 800 ml of ethanol, and the temperature of the mixture was adjusted to 30-35°C by cooling.
(Solution A). The molar ratio of amine to the mixture of SO ₂ and acetic acid is 0.84:1.

b Solution B is identical to solution B of example 1.

Example 4 A solution of 85 g (0.67 mol) of iodine dissolved in 1 part of methanol, 157 g (1.49 mol) of diethanolamine, 60 g (1.0 mol) of acetic acid and 49 g
(0.77 mol) of liquid sulfur dioxide dissolved in 800 ml of methanol. The molar ratio of amine to the mixture of SO ₂ and acetic acid is 0.84:1. The resulting one-component reagent can be used for 30 days.

Example 5 157g (1.49mol) diethanolamine, 92g
(1.43 mol) of liquid sulfur dioxide and 85 g
(0.67 mol) of iodine are added one after another to 820 ml of ethylene glycol monomethyl ether; the temperature of this mixture is kept at 30° C. by cooling. Amine _SO2
The molar ratio to is 1.03:1. The resulting one-component reagent can be used for 10 years.

Comparative Example 1 42.3 g (0.17 mol) of iodine is dissolved in 50 ml of methanol and 125 ml (1.61 mol) of pyridine.
Then 25 ml (0.57 mol) of liquid sulfur dioxide was added to -30
Carefully add to the mixture cooled to a temperature of °C. Add methanol to this solution to make it 250 ml. The molar ratio of amine to _SO2 is 2.82:1.

The reagent thus obtained is used to determine the water in a 30 ml sample of methanol using a commercially available device (Metrohm). Titration time is 5 minutes. The water content of methanol is
It is 23.7 mg (0.079% by weight). 50 in methanol
Repeat the titration after adding mg of water. The titration time is
6.5 minutes (see Figure 1).

It was found that the titer of the reagent decreased with the passage of days. The measured values are shown below.

1 day after preparation 5.97 mg H ₂ O/ml 2 days after preparation 5.73 mg H ₂ O/ml 3 days after preparation 5.63 mg H ₂ O/ml 7 days after preparation 5.51 mg H ₂ O/ml 14 days after preparation 5.12 mg H ₂ O/ml 30 days after preparation 4.90 mg H ₂ O/ml Comparative Example 2 42.3 g (0.17 mol) of iodine is dissolved in 50 ml of methanol and 125 ml (0.94 mol) of triethanolamine. Then 25 ml (0.57 mol) of liquid sulfur dioxide are carefully added to the mixture, which has been cooled to a temperature of -30°C. This mixture is made up to 250 ml with methanol. The molar ratio of amine to _SO2 is 1.65:1.

The mixture becomes cloudy and a precipitate forms. Precipitation start 1
The amount of precipitate after days is 81 g.

This mixture is not suitable as a Karl-Fuchscher reagent.

Comparative Example 3 42.3 g (0.17 mol) of iodine is dissolved in 50 ml of methanol and 125 ml (0.52 mol) of tri-n-butylamine. Then 25 ml (0.57 mol) of liquid sulfur dioxide are carefully added to the mixture, which has been cooled to a temperature of -30°C. Add 250ml of this mixture to methanol.
Make it. The molar ratio of amine to _SO2 is 0.92:1.

The reagent thus obtained is used to determine the water in a sample of 30 ml of methanol using a commercially available titrator (Metrohm E547). Titration time is approximately 20 minutes. The water content of methanol is 20.1 mg (=0.067% by weight). Repeat the titration after adding 50 mg of water. The titration time is approximately 20 minutes (see Figure 2).

It was found that the titer of the reagent decreased rapidly.
The measured values are shown below: 1 day after adjustment 6.54 mg H ₂ O/ml 2 days after adjustment 6.31 mg H ₂ O/ml 3 days after adjustment 6.11 mg H ₂ O/ml 7 days after adjustment 5.59 mg H ₂ O/ml After 14 days 4.92 mg H ₂ O/ml After 30 days of adjustment 3.94 mg H ₂ O/ml Comparative example 4 250 g (3.16 mol) of pyridine and 90 g of sulfur dioxide per 1 ethylene glycol monomethyl ether
20 ml of methanol containing 40 mg of water are titrated using the known KF reagent containing (1.40 mol) and 140 g (1.10 mol) of iodine. Since this titration does not show a satisfactory color change at the equivalence point, it can only be carried out using commercially available automatic titrators. The titration time was 545 seconds (see Figure 3). The end point does not remain constant.

Comparative Example 5 700 g (8.85 mol) of pyridine, 81 g (1.27 mol) of sulfur dioxide and 130 g of pyridine per 1 part of methanol
g (1.02 mol) of iodine and amine SO ₂
Similar reagents to Comparative Example 4 are repeated using the known KF reagent in a molar ratio of 7:1. Titration time is 350 seconds.

Usage Example 1 20 ml of methanol containing 40 mg of water was added to Example 2.
Titrate with the titrant obtained using a commercially available automatic titrator. The titration ended after 140 seconds.

Use example 2 82 g (0.67 mol) of iodine is dissolved in 80 mml of methanol and 157 g (1.49 mol) of diethanolamine. Then 92 g (1.43 mol) of liquid sulfur dioxide are carefully added to the mixture, which has been cooled to a temperature of -30°C. This mixture is made up to 1 with methanol. The molar ratio of amine to _SO2 is 1.03:1.

The thus obtained reagent was measured using a commercially available titration device [Metrom E5477].
Used for measurements using Titration time is approximately 2 minutes. The water content of methanol is 21.0 mg (=
0.070% by weight). Repeat the titration after adding 50 mg of water to the methanol. The titration time is less than about 3 minutes (see Figure 4). It was found that the titer of the reagent decreased slowly. The following values are measured: 1 day after adjustment 4.78 mg H ₂ O/ml 2 days after adjustment 4.73 mg H ₂ O/ml 3 days after adjustment 4.71 mg H ₂ O/ml 7 days after adjustment 4.64 mg H ₂ O/ml 14 After 4.53mg H ₂ O/ml After 30 days of adjustment 4.33mg H ₂ O/ml Usage example 3 20ml of methanol containing 40mg of water using the titrant of Example 1
is titrated using a commercially available titrator. The titration is
Ends after 200 seconds.

[Brief explanation of the drawing]

1 to 3 show the progress of titration in Comparative Examples 1, 3, and 4 recorded by an automatic titrator, and FIG. 4 shows the progress of titration in Use Example 2.

Claims (1)

[Claims] 1. In a titrant containing an amine, sulfur dioxide and iodine, the amine is an aliphatic amine (provided that
tributylamine) or alkanolamines containing 1, 2 or 3 oxygen atoms and the molar ratio of amine to sulfur dioxide is
The above titrant, characterized in that the ratio is from 0.5:1 to 1.3:1. 2. The titrant according to claim 1, wherein the alkanolamine is ethanolamine, diethanolamine, triethanolamine or tris(hydroxymethyl)-aminomethane. 3. The titrant according to claim 1, wherein sulfur dioxide is present in a mixture with the acid, the molar ratio of sulfur dioxide to acid being from 20:1 to 1:5. 4. The titrant according to claim 3, wherein the acid is a carboxylic acid.