RU2496571C1 - Anion-exchange sorbent for simultaneous ion chromatographic determination of polarisable and non-polarisable inorganic anions and method for production thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: disclosed is an anion-exchange sorbet based on a styrene and divinyl benzene copolymer with a quaternary ammonium functional group that is chemically grafted to the copolymer through an alkyl or acyl radical (R₁). R₁ is selected from: CH-CH₃, C(O)(CH₂)_n, (CH₂)n, (n= 1-6). The quaternary ammonium functional group contains one methyl radical and two 2-hydroxypropyl radicals. The sorbent has the general formula

.

R₂ is selected from: H, OH, Hal (halogen), Alkyl (alkyl radical).

EFFECT: invention reduces the effect of the matrix on retention of polarisable anions.

10 cl, 2 tbl, 1 dwg

Description

The invention relates to a new polymer anion-exchange material, which can be used in ion chromatography as a sorbent for the simultaneous determination of polarizable and non-polarizable inorganic anions with increased efficiency, allowing selective separation of the mixture of more than seven anions, in particular, for analysis of water for the content of inorganic anions.

In recent years, there has been significant interest in the search for new sorbents for ion chromatography. As a matrix for such sorbents, it is most promising to use styrene-divinylbenzene copolymers with a high degree of crosslinking, which is determined by the high content of divinylbenzene in the copolymer, since they are characterized by greater mechanical stability, withstand high pressures in the system, making it possible to reduce particle size and increase separation efficiency.

However, when using ion-exchange resins based on styrene-divinylbenzene copolymers, the retention of anions can be determined not only by ion-exchange, but also by non-ion-exchange interactions. Adsorption types of interactions are observed, as a rule, with all polarizable inorganic and organic ions, which are characterized by low hydration energy, hydrophobicity, and strong π-π interactions (interactions of the π-electron shells of polarizable anions with the π-electron shells of aromatic rings that make up the matrix structure) . As a result of these interactions, the so-called π-π complexes are formed with the aromatic base of the ion exchanger. In some cases, even the separation of simple inorganic anions, such as nitrate and bromide, is largely determined by the adsorption properties of the sorbent. The negative influence of π-π interactions with the matrix is manifested in large retention times of polarizable anions and a decrease in the efficiency of their separation.

In this regard, the search for new approaches to the synthesis of anion exchangers based on matrices with a high degree of crosslinking, as well as ways to reduce the influence of the matrix on anion retention, is an urgent scientific problem.

Known (Xu N., Hu X. // Reactive and Functional Polymers. 1999. V.42. P.235-242) sorbent based on macroporous copolymer of styrene and divinylbenzene (degree of crosslinking 8%, particle size 0.3-1.0 mm), in which the chemically grafted functional group is a trimethylammonium group remote from the benzene ring of the matrix with a tertiary carbon atom with a methyl side group.

However, the low degree of crosslinking of the polymer matrix and the large particle diameter make this sorbent unsuitable for highly efficient determination of inorganic anions.

A method of obtaining this sorbent is to carry out the following steps:

1) acylation of the matrix with acetic anhydride in the ratio of 1 g of reagent per 1 g of the matrix, the synthesis is carried out at a temperature of 50 ° C for 4 hours;

2) reductive amination with dimethylamine hydrochloride and sodium cyanoborohydride;

3) methyl iodide alkylation.

This synthesis method is simple to implement and does not require the use of highly toxic reagents.

However, the trimethylammonium functional group with this synthesis method does not provide a reduction in the contribution of nonion exchange interactions of polarizable anions, such as nitrate and bromide, with the aromatic base of the sorbent. This affects the determination efficiency and relative retention of such anions.

Known (RF patent No. 2429070, IPC B01J 20/26 (2006.01), publ. 09/20/2011) adopted as a prototype sorbent for simultaneous ion chromatographic determination of polarizable and non-polarizable inorganic anions based on a copolymer of styrene and divinylbenzene with a chemically grafted functional group remote from benzene matrix rings with a tertiary carbon atom with a methyl side group, in which the functional group is a 2-hydroxypropyl-N, N-dimethylammonium group of the general formula

,

,

where R is selected from the series: H, OH, Hal (halogen), Alkyl (alkyl radical).

A method for producing such a sorbent involves sequentially carrying out in an organic solvent acylation of the matrix with acetic anhydride, reductive amination and alkylation with a reagent from the group of oxiranes.

However, in order to meet the requirements of modern sorbents for ion chromatography, anion exchangers must provide an increasingly efficient and rapid determination of inorganic anions.

The objective of the invention is to provide a more efficient sorbent for the simultaneous rapid determination of polarizable and non-polarizable inorganic anions with increased efficiency.

The technical effect in this case is to further reduce the influence of the matrix on the retention of polarizable anions.

The problem is solved by creating an anion-exchange sorbent for simultaneous ion chromatographic determination of polarizable and non-polarizable inorganic anions based on a copolymer of styrene and divinylbenzene with a quaternary ammonium functional group chemically grafted to the copolymer via an alkyl or acyl radical (R ₁ ), while this contains a quaternary ammonium group and two 2-hydroxypropyl radicals and the general formula of the sorbent corresponds to the formula (1).

where R _{1 is} selected from the series: CH — CH ₃ , C (O) (CH ₂ ) _n , (CH ₂ ) _n , and n = 1-6

and R _{2 is} selected from the series: H, OH, Hal (halogen), Alkyl (alkyl radical).

One of the specific compounds of this formula may be:

a compound of the general formula (1.1).

Or a compound of the general formula (1.2).

Or a compound of general formula (1.3).

Or a compound of general formula (1.4).

Another aspect of the invention is a method for producing an anion-exchange sorbent for simultaneous ion chromatographic determination of polarizable and non-polarizable inorganic anions of formula 1, comprising sequentially carrying out three stages in an organic solvent:

- modifying the matrix based on a copolymer of styrene and divinylbenzene by its acylation, alkylation or chloromethylation;

- amination of the resulting product with methylamine;

- alkylation of the amino group with a reagent from the group of oxiranes in the presence of a base.

Acylation is preferably carried out with acetic anhydride or ω-chloroacyl chloride.

Alkylation in the first step is preferably carried out with n-bromoalkene.

Chloromethylation is preferably carried out using thionyl chloride.

As a reagent from the group of oxiranes in the third stage, it is preferable to use epichlorohydrin.

Figure 1 shows the chromatograms obtained on anion exchangers of the formula 1.1, having different capacities, using different eluents, where A is a sorbent with a larger capacity, isocratic mode, B - with a smaller, gradient.

Wherein:

Isocratic regime. Eluent: 24 mM NaHCO ₃ . F = 1.0 ml / min.

Gradient mode. Eluent: 5-40 mM NaOH. F = 0.7 ml / min.

Table 1 shows the efficiency (tm / m) of the column with the sorbent according to the invention for polarizable and non-polarizable inorganic anions.

Table 2 shows the asymmetry coefficients of the peaks (A _S ) of some anions on the sorbent prototype and on the sorbent according to the invention (figa), obtained in isocratic elution mode.

The scheme for obtaining the proposed sorbent can be represented as follows

Modification of polystyrene-divinylbenzene (PS-DVB) is carried out by acylation (reagent - acetic anhydride or co-chloroacyl chloride), alkylation (reagent - bromalkenes with different chain lengths) or chloromethylation (reagent - thionyl chloride).

Amination is carried out with methylamine.

If acetic anhydride is used at the stage of PS-DVB modification, reductive amination is carried out with methylamine in the form of an acid salt in the presence of a reducing agent, sodium cyanoborohydride. One example of the resulting compound is a compound of formula 1.1.

If at the stage of modifying PS-DVB, ω-chloroacyl chloride is used, then simple amination with a solution of methylamine is carried out. One example of the resulting compound is a compound of formula 1.2.

Both bromoalkylation and chloromethylation in the first stage, in combination with conventional amination, ultimately give a sorbent, a typical representative of which is a compound of formula 1.3.

Alkylation with oxirane in the presence of a base is the same for all types of sorbents.

The above examples confirm, but do not limit the invention.

Example 1 A method for producing an anion-exchange sorbent based on a copolymer of styrene and divinylbenzene with chemically grafted di (3-chloro-2-hydroxypropyl) -N-methylammonium functional group, remote from the benzene ring of the matrix with a tertiary carbon atom with a methyl side group, of the formula 1.1.

1) Acylation

A suspension of 1 g of a styrene-divinylbenzene copolymer is prepared with a divinylbenzene content of 25% and a grain diameter of 3.3 ± 0.2 μm in 20 ml of carbon disulfide and allowed to swell for 2 hours. Then 3 g of anhydrous aluminum chloride powder was added and 0.04 mol of acetic anhydride was added dropwise with rapid stirring. The reaction mixture is stirred at a speed of 250 rpm for 6 hours at a temperature of 50 ° C. The resulting product is filtered on a glass filter and washed successively with 10% hydrochloric acid, 10% sodium hydroxide, water and ethanol, and then left on the filter until completely dried in a desiccator over CaCl ₂ .

2) reductive amination

Dimethylamine hydrochloride was taken as methylamine in the form of an acid salt, and sodium cyanoborohydride was used as a reducing agent.

1 g of the product obtained in the first stage is placed in a 100 ml flask, 5 g of dimethylamine hydrochloride, 0.35 g of sodium cyanoborohydride and 20 ml of methanol are added. The reaction mixture is stirred for 22 hours at a temperature of 67 ° C at a speed of 250 rpm, then acidified with concentrated hydrochloric acid to pH≤2. The obtained aminopolymer with a dimethylamine functional group is filtered off, washed with 10% hydrochloric acid, 10% sodium hydroxide solution, water until neutral and ethanol, then dried on a filter in a desiccator over CaCl ₂ .

3) Alkylation with epichlorohydrin

A suspension of 1 g of the amino copolymer obtained in the second stage is prepared in alcohol, 3 g of sodium carbonate in 10 ml of water and 0.16 mol of epichlorohydrin are added as a base. The reaction mixture was stirred at 70 ° C for 20 hours. After the specified time, the reaction product is filtered off, washed with water and ethanol.

The resulting sorbent is a copolymer of styrene and divinylbenzene with chemically grafted di (3-chloro-2-hydroxypropyl) -N-methylammonium functional group, remote from the benzene ring of the matrix with a tertiary carbon atom with a methyl side group. The anion exchange capacity is 0.098 ± 0.009 mmol / g (n = 3, P = 0.95).

When carrying out the stage of alkylation at a temperature of 60 ° C for 10 hours, the capacity of the obtained sorbent is 0.038 ± 0.004 mmol / g (n = 3, P = 0.95).

Example 2 A method for producing an anion-exchange sorbent based on a copolymer of styrene and divinylbenzene with chemically grafted di (3-chloro-2-hydroxypropyl) -N-methylammonium functional group removed from the matrix benzene ring with an n-valery radical of the formula 1.2.

1) Acylation

A 1 g matrix sample was placed in a 100 ml three-necked flask, 12.5 ml of dichloromethane was added and left to swell for 2 hours. After that, 0.01 mol of 5-chlorovaleroyl chloride is added and the reaction mixture is stirred at room temperature and at 200 rpm for 15 minutes. The acylation reaction is initiated by adding 0.2 g of anhydrous aluminum chloride, while the color of the reaction mixture becomes brown. After 10 minutes, the reaction is stopped by adding 50 ml of tetrahydrofuran. The resulting product is filtered and washed with the following solutions: water-tetrahydrofuran (1: 1), 2 M hydrochloric acid, water and ethanol, then left to dry completely on a filter in a desiccator over CaCl ₂ .

2) Amination

A suspension is prepared from 1 g of the acylated polystyrene-divinylbenzene obtained in the first step in 15 ml of acetonitrile and allowed to swell for 2 hours. Then 0.25 mol of methylamine is added and stirred for 14 hours at a temperature of 70 ° C. After the specified time to stop, the reaction product is filtered off, washed with distilled water and ethanol. After that, the resulting anion exchanger was left on the filter until completely dried in a desiccator over CaCl ₃ .

3) Alkylation with epichlorohydrin

A suspension of 1 g of the amino copolymer obtained in the second stage is prepared in alcohol, 3 g of sodium carbonate in 10 ml of water and 0.16 mol of epichlorohydrin are added as a base. The reaction mixture was stirred at 70 ° C for 20 hours. After the specified time, the reaction product is filtered off, washed with water and ethanol.

The resulting sorbent is a copolymer of styrene and divinylbenzene with chemically grafted di (3-chloro-2-hydroxypropyl) -N-methylammonium functional group, removed from the benzene ring of the matrix by an n-valery radical. The anion exchange capacity is 0.042 ± 0.004 mmol / g (n = 3, P = 0.95).

Example 3 A method for producing an anion-exchange sorbent based on a copolymer of styrene and divinylbenzene with chemically grafted di (3-chloro-2-hydroxypropyl) -N-methylammonium functional group removed from the benzene ring of the matrix by a metal radical of the formula 1.3

1) Chloromethylation

A 1 g sample of the matrix is placed in a 100 ml three-necked flask. 3-5 ml of concentrated acetic acid are added to wet the copolymer. The mixture is left for 1 hour, after which 20 ml of formalin solution are added with stirring. Then the reaction flask was placed in ice water and cooled to 3 ° C, and 10.8 ml of thionyl chloride were slowly added dropwise to it with continuous stirring (the temperature of the mixture should not exceed 3-7 ° C), and then 9.3 ml of concentrated chlorosulfonic acid and stirred for 15 minutes at a temperature of 3 ° C. Then the temperature of the mixture was raised to 35 ° C and stirred at this temperature for 16 hours. After the indicated time, the contents of the flask were cooled to 3 ° C and 25 ml of distilled water was added dropwise to stop the reaction. The resulting product is filtered off on a glass filter, washed in vacuo with a 10% sodium hydroxide solution, then with distilled water until neutral and 2-3 portions of 10 ml of ethanol are left on the filter until completely dried in a desiccator over CaCl ₂ .

2) Amination (analogous to example 2)

A suspension of 1 g of the chloromethylated polystyrene-divinylbenzene obtained in the first stage is prepared in 15 ml of acetonitrile and allowed to swell for 2 hours. Then 0.25 mol of methylamine is added and stirred for 14 hours at a temperature of 70 ° C. After the specified time to stop, the reaction product is filtered off, washed with distilled water and ethanol. After that, the obtained anion exchanger was left on the filter until completely dried in a desiccator over CaCl ₂ .

3) Alkylation with epichlorohydrin in the same way as in example 2.

A suspension of 1 g of the amino copolymer obtained in the second stage is prepared in alcohol, 3 g of sodium carbonate in 10 ml of water and 0.16 mol of epichlorohydrin are added as a base. The reaction mixture was stirred at 70 ° C for 20 hours. After the specified time, the reaction product is filtered off, washed with water and ethanol.

The resulting sorbent is a copolymer of styrene and divinylbenzene with chemically grafted di (3-chloro-2-hydroxypropyl) -N-methylammonium functional group, remote from the benzene ring of the matrix by the methyl radical. The anion exchange capacity is 0.061 ± 0.006 mmol / g (n = 3, P = 0.95).

Example 4 A method for producing an anion-exchange sorbent based on a copolymer of styrene and divinylbenzene with chemically grafted di (3-chloro-2-hydroxypropyl) -N-methylammonium functional group removed from the matrix benzene ring with an n-pentyl radical of the formula 1.4.

1) Alkylation

1 g of the matrix is suspended in 5.3 ml of 1,2-dichloropropane at room temperature in a 100 ml flask. After stirring for 10 minutes, 0.63 g of trifluoromethanesulfonic acid is added, and the reaction mixture is colored cherry red. Then a mixture of 1.66 ml of 5-bromo-1-pentene and 1.66 ml of 1,2-dichloropropane was slowly added dropwise. After that, the reaction mixture was stirred for 48 hours at 50 ° C. After a lapse of time, the mixture was cooled to 10 ° C to stop the reaction, filtered and washed successively with tetrahydrofuran, hydrochloric acid, distilled water, 2-propanol, methanol and acetone.

2) Amination (completely analogous to example 2)

3) Alkylation (completely analogous to example 2)

The anion exchange capacity is 0.033 ± 0.003 mmol / g (n = 3, P = 0.95).

Example 5. Ion-chromatographic determination of polarizable and non-polarizable inorganic anions using an anion-exchange sorbent based on a copolymer of styrene and divinylbenzene with chemically grafted di (3-chloro-2-hydroxypropyl) -N-methylammonium functional group, remote from the matrix benzene ring with a tertiary carbon atom with a side carbon atom methyl group, formula 1.1

Obtained in example 1, anion-exchange sorbents based on a copolymer of styrene and divinylbenzene with chemically grafted di (3-chloro-2-hydroxypropyl) -N-methylammonium functional group, remote from the benzene ring of the matrix with a tertiary carbon atom with a lateral methyl group, are packed into chromatographic columns of size 4 × 50 mm under a pressure of 250 bar and carry out ion chromatographic separation of a mixture of polarizable and non-polarizable anions in the variant of ion chromatography with suppression of the background conductivity. As mobile phases, when working in the isocratic elution mode, solutions of carbonate, bicarbonate and sodium hydroxide are used; in the gradient mode, sodium hydroxide.

A sorbent with di (3-chloro-2-hydroxypropyl) -N-methylammonium functional group, remote from the benzene ring of the matrix with a tertiary carbon atom with a lateral methyl group, having a large capacity (0.098 ± 0.009 mmol / g), exhibits good separation ability in the isocratic elution mode allows for 10 minutes to separate a mixture of 7 polarizable and non-polarizable anions: fluoride, formate, chloride, nitrite, bromide, phosphate and sulfate. A sorbent of a similar formula having a lower capacity (0.038 ± 0.004 mmol / g) is suitable for operation in a gradient elution mode, while in less than 8 minutes it is possible to separate a mixture of polarizable and non-polarizable anions: fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulfate. (While the sorbents obtained by the prototype method carry out the separation of similar mixtures of the mixture in almost 30 minutes) Chromatograms of the mixtures are presented in figure 1, and table 1 presents the efficiency (tt / m) (Theoretical plates per meter.) Of columns with sorbents for polarizable and non-polarizable inorganic anions when using 24 mM NaHCO ₃ solution in isocratic mode or sodium hydroxide solution in the range of 5-40 mM in gradient mode as eluents. As can be seen from the table, the efficiencies in both isocratic and gradient modes are high for both nonpolarizable and polarizable anions. For polarizable nitrate and bromide ions, the maximum efficiencies are 12,000 and 16,000 tt / m, respectively. In addition, there is an improvement in the shape of the peak, especially for polarizable nitrite, bromide and nitrate, in comparison with the less hydrophilic sorbent from the patent prototype, which is confirmed by the data in Table 2, which shows the asymmetry coefficients of the peaks (A _S ) of some anions on the sorbent prototype and on the sorbent according to the invention (figa), obtained in isocratic elution mode.

A _S is the ratio of two segments formed on a horizontal line drawn at an altitude of 10% from the base of the peak, when it intersects with a vertical dropped from the top of the peak. In this case, the ratio of the “back” segment to the “frontal” one is taken. The asymmetry coefficient should be close to 1 and for columns with a good quality sorbent is 0.8-1.3.

Based on the high efficiencies for polarizable anions and a significant improvement in the shape of the peaks compared to the less hydrophilic sorbent (Table 2), it can be concluded that nonion exchange interactions with the matrix no longer make a significant contribution to the retention of these anions.

Similar results were obtained for all of the claimed compounds.

The above examples confirm that the use of a sorbent based on a styrene-divinylbenzene copolymer of the claimed formula further reduces the influence of the matrix on the retention of polarizable anions. The result is a sharp increase in the efficiency of the sorbent for polarizable anions, the erosion of their peaks becomes insignificant, in the retention row they occupy the place traditional for these anions in ion chromatography. The proposed sorbent shows very good selectivity and provides the ability to separate a mixture of seven anions. It is important to note that the peak shape of polarizable anions on this sorbent is significantly better than on the sorbent from the patent prototype, which is confirmed by the data in Table 2 and is associated with a decrease in the influence of the matrix upon the introduction of an additional hydrophilic radical. In addition, the analysis time is reduced three times (from 30 to 10 minutes).

Claims (10)

1. Anion-exchange sorbent for simultaneous ion chromatographic determination of polarizable and non-polarizable inorganic anions based on a copolymer of styrene and divinylbenzene with a quaternary ammonium functional group chemically grafted to the copolymer through an alkyl or acyl radical (R ₁ ), while the quaternary ammonium functional group contains two 2-hydroxypropyl radicals, and the general formula of the sorbent corresponds to the formula (1):

where R ₁ is selected from the series: CH-CH ₃ , C (O) (CH ₂ ) _n , (CH ₃ ) _n , (n = 1-6), and R ₂ is selected from the series: H, OH, Hal (halogen), Alkyl (alkyl radical). 2. Anion-exchange sorbent according to claim 1, characterized in that it is a compound of the general formula (1.1):

3. Anion-exchange sorbent according to claim 1, characterized in that it is a compound of General formula (1.2):

4. Anion-exchange sorbent according to claim 1, characterized in that it is a compound of General formula (1.3):

5. Anion-exchange sorbent according to claim 1, characterized in that it is a compound of General formula (1.4):

6. A method of producing an anion-exchange sorbent for simultaneous ion chromatographic determination of polarizable and non-polarizable inorganic anions, the general formula of which corresponds to formula 1, which includes sequentially carrying out three stages in an organic solvent:
- modifying the matrix from a copolymer of styrene and divinylbenzene by its acylation, alkylation or chloromethylation;
- amination of the resulting product with methylamine;
- alkylation of the amino group with a reagent from the group of oxiranes in the presence of sodium carbonate. 7. The method according to claim 6, characterized in that acetic anhydride or ω-chloroacyl chloride is used for acylation. 8. The method according to claim 6, characterized in that n-bromalkene is used for the alkylation in the first stage. 9. The method according to claim 6, characterized in that the chloromethylation is carried out in the presence of thionyl chloride. 10. The method according to claim 6, characterized in that epichlorohydrin is preferably used as a reagent from the group of oxiranes in the third stage.

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