MXPA97006066A - Procedure for the obtaining of ammonic salts from 2,2-dioxide of 3-isopropil-2, 1,3-benzotiadiazin-4- - Google Patents

Abstract

The present invention relates to a process for obtaining salts of 3-isopropyl-2,1,3-benzothiadiazin-4-one 2,2-dioxide of the general formula I: wherein [R 1 -R 4 = lower alkyl, hydroxyalkyl lower) by reaction of bentazone (IIa), in an organic solvent, with an amine IIIa, where bentazone (IIa) is reacted, in an organic solvent practically immiscible with water, with an amine IIa or an ammonium salt IIIb, and the salt I is absorbed in water, or where the bentazone (IIa) is reacted in water with an ammonium salt IIIb or sodium bentazone (IIb) in water with an ammonium salt II

Description

Procedure for obtaining ammonium salts of 2,2-dioxide of 3-isopropyl-2, 1,3-benzothiadiazin-4-one Description The present invention relates to a process for the preparation of salts of 3-isopropyl-2,3-benzo-thiadiazin-4-one 2,2-dioxide salts of the general formula I wherein the radicals R1, R2, R3 and R4 mean, each independently of the other, hydrogen, lower alkyl or lower hydroxyalkyl. 2,2-dioxides of benzothiadiazin-4-one herbicides are known from DE-A 15 42 836, DE-A 21 64 459 and DE-A 22 17 722. In these patents the use of ammonium salts is also mentioned, all, ammonium, methylammonium, trimethylammonium, ethylammonium, diethanolammonium and ethanolammonium salts.

Furthermore, it is generally known that the sodium, calcium and potassium salt of 3-isopropyl-2, 1,3-benzothiadia-zin-4-one 2,2-dioxide (name INN: bentazone) are very hydgroscopic. Phenomenon that in case of solid formulations of these salts results in the product begins to caking or even to be dissolved already under the action of humidity of the air, so that it can not be dosed without problems.

When these salts are incorporated in bags of hydrosoluble sheets, then the latter are also dehydrated by the interaction of the hygroscopic active substances with the sheets. All of which results in the sheets becoming brittle, that is, they are no longer stable to storage.

In the synthesis of bentazone, the active substance is normally obtained in a neutral form and usually dissolved in an organic solvent (cf. DE-A 27 10 382).

In most cases, the active substance is transformed, then, into one of its salts, since these improve the biodisposibility of bentazone.

For example, it is known from US Pat. No. 5,266,553 to formulate the ammonium salts of bentazone as water-soluble fluidizable solids. For which is prepared, first, according to the general teaching of the patent, an aqueous mixture of the ammonium salt. The solid formulation of the active substance is obtained from this mixture by evaporation of all the solvent and subsequent treatment of the product with a neutralizing base. However, the evaporation stage requires a lot of energy when water has been used as a solvent, so that the active substance is subject for a long period to the high evaporation temperature.

Therefore, the object of the present invention is a process for the preparation of ammonium salts of bentazone, in which the disadvantages of the above-described preparation process are partially or totally avoided.

Therefore, a process for obtaining 2,2-dioxide salts of 3-isopropyl-2,3,8-benzothiadiazin-4-one of the general formula I was found wherein the radicals R1, R2 and R3 mean, each independently of the other, hydrogen, lower alkyl, hydroxy-lower alkyl, which process is characterized in that the 2,2-dioxide of 3-isopropyl-2, 1 is reacted 3-benzo-thiadiazin-4-one (lia) in an organic solvent, with an amine of the general formula Illa R2 Ri N R3 (Illa) In addition, a process for obtaining salts of 3-isopropyl-2, 1,3-benzothiadiazin-4-one 2,2-dioxide of the general formula I where the radicals Reste R1, R2, R3 and R4 mean , each independently of the other, hydrogen, lower alkyl, lower hydroxyalkyl, which process is characterized in that it is reacted a) 2,2-dioxide 3-isopropyl-2, 1,3-benzothiadiazin-4-one (Ha) in an organic solvent practically immiscible with water, if desired, in the presence of water, with an amine of the general formula Illa R2 Rl N R3 (Illa) or an ammonium salt of the general formula Hlb where X is the anion of an acid with a pKs value above 4, or the hydroxyl ion, and n means the number of negative charges of the X anion, and b) salt I is absorbed in water.

In addition, a process for obtaining salts of 3-isopropyl-2, 1,3-benzothiadiazin-4-one 2,2-dioxide salts of the general formula I was found. wherein the radicals R1, R2, R3 and R4 mean, each independently of the other, hydrogen, lower alkyl or lower hydroxyalkyl, which process is characterized in that it is reacted 2,2-dioxide 3-isopropyl-2, l, 3-benzothiadiazin-4-one (Ha) in water, with an ammonium salt of the general formula IHb where X is the acid anion with a value pKs above 4 or the idroxyl ion and n is equal to the number of negative charges of the X anion, or b) the sodium salt of bentazone (Hb) in water, with an ammonium salt of the general formula IHe where Y is the anion of an acid and n is equal to the number of negative charges of the anion Y.

By "lower alkyl" or "lower hydroxyalkyl" we mean alkyl or hydroxyl groups with up to 8, preferably up to 6 carbon atoms, such as, for example, methyl, hydroxymethyl, ethyl, 2-hydroxyethyl, propyl, 3-hydroxypropyl and butyl.

The methods of the invention will be referred to hereinafter as procedure A, B or C.

Procedure A In process A the bentazone (Ha) is reacted with an amine Illa in an organic solvent (see scheme 1).

Illa amines are generally known.

In general, amine Illa is used in an equimolar amount with respect to bentazone (Ha). To complete the reaction it may be convenient to use the amine Illa in an excess. But this excess does not have to be more than 10% in mole, with respect to Ha, to achieve a total conversion.

Suitable organic solvents are: aromatic hydrocarbons, preferably monobenzene, up to trimethyls, especially toluene, and xylene; ketones, preferably with 3 to 9 carbon atoms, especially acetone; esters, preferably monocarboxylic acids having 1 to 5 carbon atoms with monoalcohols of 1 to 4 carbon atoms, especially ethyl acetate; ethers, preferably with 4 to 8 carbon atoms, especially tetrahydrofuran; haloalkanes, preferably mono- or dichloroalkanes with 2 to 4 carbon atoms, in particular 1,2-dichloroethane, and furthermore alkanols, preferably C 4 -C alkanols, especially methanol or ethanol, as well as mixtures of two or more of the -solvents mentioned above.

Very advantageously, 1,2-dichloroethane is used by itself as a solvent. ro Scheme 1 R1-R3 each independently of the other, H, lower alkyl or lower hydroxyalkyl 00 With respect to one mole of bentazone (Ha), 0.2 to 25 and, especially, 1 to 10 kg of solvent are used. The bentazone (Ha) can contain up to 2% by weight of water, without this harming the process.

The procedure can be carried out at a temperature of 10 to 80 ° C. The temperature during the reaction mainly influences the solubility of bentazone (Ha), which increases the higher the temperature.

Especially in those cases in which gaseous or low-boiling amines participate, the temperature should not exceed a value of 60 ° C. Preferably, the reaction will be carried out at temperatures of from 20 to 60, and especially from 25 to 50 ° C.

Generally, the reaction is carried out at a pressure of 0.5 to 10, preferably 1 to 3 bar and especially at normal pressure (atmospheric pressure).

As reactors, the devices usually used for these reactions can be used.

The salt I is precipitated at the reaction temperature and / or during the cooling of the mixture and can be separated in a manner known per se, especially by filtration, from the liquid phase.

The yield in salt I amounts to 95 to 100%.

Process A is especially suitable for obtaining the NH4 * - salt of bentazone (I; Rr-R4 = H).

Here, advantageously, it proceeds in such a way that the ammonia gas is introduced directly into the bentazone solution (Ha) in the organic solvent, or the bentazone solution (Ha) in the organic solvent is mixed with aqueous ammonia.

Procedure B In this process the bentazone (Ha) is reacted in an organic solvent practically immiscible with water with an amine Illa or an ammonium salt Hlb, if desired, in the presence of water, and the salt I is absorbed in water (see scheme 2). ro ro Scheme 2 (I) Ri-R4 = each independently of the other, H, lower alkyl or lower hydroxyalkyl; X = the anion of an acid with a value pKs > 4 or the hydroxyl ion; n = the number of negative charges of the X anion Illa amines are generally known. The same goes for the Hlb ammonium salts (see Houben-Weyl, Methoden der Orga-nischen Chemie, 4th edition, Thieme Verlag, Stuttgart, Vol. 11/2, pp. 591 ff.).

The carbonate ion, the hydrogencarbonate ion and the hydroxyl ion are preferred as the X anion in the general formula IIIb.

As a rule, the amine Illa or the ammonium salt IHb is used in an equimolar amount with respect to the bentazone (Ha.) However, to complete the reaction it may be convenient to use the amine Illa or the ammonium salt Hlb in a slight excess But in order to achieve a total conversion, an excess of 10% in mol is generally sufficient.

As organic solvents practically immiscible with water are appropriate; alkanes, preferably having 5 to 8 carbon atoms, especially n-alkanes, such as, for example, n-pentane and n-hexane and halogenated hydrocarbons, preferably haloalkanes, such as, for example, mono and dichloroalkanes with 2 to 4 carbon atoms such as, for example, 1,1-dichloroethane, 1,3-dichloropropane, 1,2-dichloropropane and especially 1,2-di-chloroethane.

In addition, mixtures of two or more of these mousible organic solvents are also suitable.

As the organic solvent which is practically immiscible with water, the 1,2-dichloroethane used alone is preferred.

With respect to bentazone mole (Ha), usually 1 to 4 and above all 1.5 to 3 kg of solvent are used.

The procedure can be carried out at temperatures of 20 to 80 ° C. The temperature in the reaction influences above all in the solubility of bentazone (Ha), since it increases with one with a higher temperature.

Especially in those cases in which a gaseous or low-boiling amine is involved, the temperature should not exceed 60 ° C. Preferably, the reaction of bentazone Ha with amines Illa or ammonium salts IHb will be carried out at temperatures of 20 to 60, and especially of 25 to 50 ° C.

Generally, the reaction will take place at a pressure of 0.5 to 10, preferably 1 to 3 bar and especially to normal pressure (atmospheric pressure).

Reactors are suitable devices that are usually used for these reactions.

The salt I formed is absorbed in water, this water can be added already during the reaction or just at the end of it. When in this action small amounts of the organic solvent are separated together with the aqueous phase, then these can be removed in a known manner prior to the isolation of the salt I, for example by extraction or, optionally, by azeotropic distillation - such as, for example. in the case of 1,2-dichloroethane / water as a reaction medium - at normal pressure or reduced pressure.

In order to absorb the salt completely, it is generally used with respect to 1 kg of the salt I, 1 to 5, preferably 2 to 4 and especially 2.5 to 3.5 kg of water. Generally, salt I is already precipitated at the reaction temperature. To complete the precipitation, the solution is usually cooled. The crystallization is preferably carried out at 5 to 40 and especially at 15 to 25 ° C.

A special advantage of method B of the invention is that the organic solvent after being separated from the aqueous phase can be used directly for the following reactions, without it being necessary to evaporate it totally or partially to be able to isolate or product and / or purify it. by distillation.

Process B allows, when the mother liquor is recycled, to generate salt I, generally, in a yield of 98 to 100% with a purity of at least 98%.

Process B is particularly suitable for obtaining the NH 4 + salt of bentazone (I; Ri-R 4 = H).

Procedure C In process C the bentazone (Ha) is reacted in water with an ammonium salt IHb, or the sodium salt of bentazone (Hb) in water with an ammonium salt Ule (see scheme 3).

Process C is especially well suited for obtaining the NH 4 + salt of bentazone (I; R! -R 4 = hydrogen).

Ill ammonium salts are generally known (see Hou-ben-Weyl, Methoden der Organischen Chemie, 4th edition, Thieme Verlag, Stuttgart, Band 11/2, pp. 591 ff.).

Suitable anions Y of the general formula Ule are: sulfate, hydrogen sulfate, phosphate, hydrogen phosphate or dihydrogen phosphate, preferably halide or acetate and especially chloride, nitrate, formate, carbonate and hydrocarbonate.

As an acid anion Y in the general formula Ule or as an anion X of an acid of the pKs > 4 are suitable carbonate ion and hydrogencarbonate ion and for Y especially the hydroxyl ion.

As a rule, the ammonium salt Illb, with respect to the bentazone (lia), and the ammonium salt lile, with respect to the sodium salt of the bentazone (Ilb), are used in an equimolar amount. However, to obtain a complete conversion it may be advantageous to use the ammonium salts in an excess, but to achieve a total conversion, this excess, generally, does not have to exceed 10 mol%, with respect to lia or. II.

With respect to one mole of bentazone (Ha) or its sodium salt Hb, 0.2 to 4 and especially 0.2 to 2 kg of water are usually used.

The sodium salt NanY is normally more soluble in water than the salt I. If the latter remains partially undissolved, then it can be separated by crystallization (fractionated). This method is known to the expert, so it is not necessary to detail it in the present.

In order to obtain a good yield in the crystallization, a molar ratio between water and salt I of 50 to 1 up to 30 to 1 has been proved.

The procedure can be performed at temperatures of 10 to 80CC. The temperature in the reaction influences above all in the solubility of bentazone (lia) and its sodium salt Ilb, since these are more soluble at a high temperature. Preferably, the reaction will be carried out at a temperature of from 20 to 70, and especially from 40 to 60 ° C.

Generally, it is worked at a pressure of 0.5 to 10, preferably 1 to 3 bar, especially at normal pressure (atmospheric pressure).

Reactors are suitable devices that are usually used for this type of reactions.

With process C, salts I can be obtained, generally in a yield of more than 80% and in a purity of at least 98%. By recirculation of the er liquor a yield of more than 98% can be achieved.

Salt I obtained according to one of the processes A to C can be isolated in a known manner. In cases where it has already crystallized from the reaction mixture, it will be isolated by filtration. Provided that the salt is obtained in dissolved form, all the solvent can be removed from the solution, using a generally known method, for example, by evaporation, especially under reduced pressure.

Salt I obtained according to process B or C which has been crystallized from an aqueous phase, generally contains less than 10% by weight of water.

The wet salt I (due to organic solvent or water) is dried, generally at a temperature of 20 to 80, preferably 40 to 60 ° C. The drying can be carried out in conventional drying devices. Preferably, work will be carried out under reduced pressure or the product I will be heated in the air stream.

The er liquors that remain after the separation of the crystallized salt I contain in some cases even up to 20% of the salt I in the disulfide form. If desired, this dissolved active substance can be isolated in a manner known per se, for example by concentration of the solution followed by a second crystallization or by total concentration of the er liquor. Frequently, the er liquor can also be recycled to the process.

Granules of solutions of the salts I are obtained, starting from the obtained solutions in the obtaining, or of the mother liquors coming from the crystallization, using a fluidized bed process, or by agglomeration with a powder of I, which in turn it has been obtained by spray drying or vacuum drying.

The granules thus obtained generally comprise from 20 to 100% by weight of the salt I. The particle size of these granules varies, generally, from 200 μm to 3000 μm. The proportion of powder in the granules is reduced. The dust content of a 30 g sample amounts to less than 20 mg (CIPAC MT 171: "Dustiness of Granular Formulation"), thus achieving high safety for the user.The apparent specific gravity of such granulates amounts, as a rule, at 400 - 800 g / 1.

Salts I exhibit excellent storage behavior in film bags. These film bags are known per se (EP-A 449 773, EP-A 493 553), so that it is not necessary to detail them.

The filled film bags generally contain 0.1 to 10 kg, preferably 0.5 to 5 kg, of active substance I. The thickness of the films is 20 to 100 μm, preferably 30 to 60 μm. The water content in the polymeric films can be up to 20% by weight.

The granules obtained in the above-described form or the filled film bags may contain, in addition to the salts I, conventional additives, eg surfactants, fillers or other phytosanitary active substances.

It has been found that the salts I, especially the NH.sub.f salt of bentazone, are very poorly soluble in the respective reaction media, compared to the starting substances either lía or Hb. This effect is used in the foregoing of the invention to isolate the product I in a simple manner in solid form.

On the other hand, the ammonium salts, especially the NH4 + salts, dissolve much more rapidly in water than the sodium salts generally used, thus reducing the preparation time of the aqueous broths of the active substances.

Examples Example 1 In a solution of 24 g of bentazone (Ha) in 2376 g of 1,2-dichloroethane, 1.7-3 g of gaseous ammonia are introduced under stirring at a temperature of 20-50 ° C, forming a suspension. The solid is separated at 20 ° C by filtration and reduced pressure of the solvent residues. 25.4 g of ammonium bentazone are obtained (mp 180 ° C).

Example 2 In a solution of 24 g of bentazone (lía) in 16 g of acetone are introduced at 30-50 ° C, while stirring, 1.7 g of ammonia gaso. The ammonium bentazone is precipitated and filtered at room temperature. The crystallizate obtained is freed under reduced pressure and 50 ° C of the solvent. 19.5 g of ammonium bentazone are obtained. The mother liquors of the filtration are concentrated under reduced pressure and 50 ° C until dry. There remain another 6 g of ammonium bentazone.

Example 3 In a suspension of 24 g of bentazone (Ha) and 300 g of water, 4.8 g of ammonium carbonate are introduced under stirring. The reaction mixture is further stirred for 2 hours at 50 ° C and is freed from the solid particles by filtration. Having concentrated the solution under reduced pressure, 25.5 g of ammonium bentazone remain.

Example 4 Work is carried out as in Example 3, but 7.9 g of ammonium hydrogencarbonate are used instead of ammonium carbonate. 25.5 g of ammonium bentazone are obtained.

Example 5 In a solution of 26.3 g of sodium bentazone in 21.7 g of water, 8 g of ammonium nitrate are introduced at 50 ° C under stirring, and the reaction mixture is stirred for one hour. After the mixture has cooled to 20 ° C, the precipitate is filtered, washed twice with 5 ml of ice water and dried under reduced pressure and 50 ° C. 18.9 g of ammonium ben-tazone are obtained with a purity of 99%.

Example 6 The procedure is as in Example 5, but 6.3 g of ammonium formate are used instead of ammonium nitrate. The yield in ammonium bentazone amounts to 21 g. The product has a purity of 98.4%.

Example 7 A solution of 24 g of bentazone (lia) in 216 g of 1,2-dichloroethane is mixed under stirring at a temperature of 50-60 ° C with 34 g of ammonia water (5% solution of ammonia in water) . When the addition is complete, the aqueous phase is separated at 50-60 ° C. During the cooling of the aqueous phase the ammonium bentazone is precipitated in crystalline form. The solid is separated at 20 ° C by filtration and is freed at reduced pressure and a temperature of 50 ° C from the solvent residues. 11.8 g of ammonium bentazone are obtained (mp 180 ° C). From the wood liquor, a further 13.7 g of ammonium bentazone is obtained by evaporating the water under reduced pressure and 50-60 ° C.

Example 8 A solution of 24 g of bentazone (Ha) in 216 g of 1,2-dichloroethane is mixed under stirring at a temperature of 30-50 ° C with 22.5 g of a 20% aqueous solution of dimethylamine. When the addition is complete, the aqueous phase is separated at 50-60 ° C and under reduced pressure and 50-60 ° C is dried until dry. 28 g of ammonium dimethylbentazone are obtained (mp 145-147 ° C, purity> 99% according to HPLC analysis for bentazone and titration for dimethylammonium).

Example 9 A mixture of 24 g of bentazone (Ha), 4.8 g of ammonium carbonate, 220 g of 1,2-dichloroethane and 300 g of water is stirred for one hour at 50-60 ° C. Then the phases are separated, and the water is removed under reduced pressure and 50-60 ° C. 25.5 g of ammonium bentazone are obtained.

Example 10 As in Example 9 but without using the 7.9 g of ammonium hydrogen carbonate, 25.5 g of ammonium bentazone are obtained.

Example 11 A 20% aqueous solution of ammonium bentazone is dried in a fluidized bed granulator at a drying air temperature of 120 ° C. During which the ammonia solution is concentrated and granulate particles formed by agglomeration and drying are formed. The granulate obtained contains 99.6% by weight of ammonium bentazone and has a residual water content of 0.4% by weight. The average particle size in the granulate is 0.3 mm (maximum diameter). The granulate obtained is free of dust and dissolves quickly in water. In addition, it is hygroscopic, that is, it remains slidable even when exposed to humid air.

Example 12 In a fluidized bed spray granulator, 75 g of ammonium sulfate powder are introduced. Subsequently, 375 g of a 20% by weight aqueous solution of ammonium bentazone at a drying air temperature of 120 ° C are introduced into the granulator thus prepared. Granulate particles are formed by agglomeration and drying. The granulate obtained contains 50% by weight of ammonium bentazone and a residual water content of 0.1-0.5% by weight. The average particle size of the granulde amounts to 1-2 mm (maximum diameter). The granulate obtained is free of dust and dissolves quickly in water. In addition, it is not hygroscopic, that is, it remains fluid even when exposed to humid air.

Example 13 Physical behavior of the products a) Test of the hygroscopicity of salts 1 g respectively of the sample is dried for 48 hours at 50 ° C in vacuum. The dried samples are stored at 55% and 65% relative humidity of the air and at a temperature of 20 ° C, and the weight gain of the samples is examined after the state of equilibrium has been reached. The flow properties of the samples and their appearance are also examined. With regard to hygroscopicity, the Christic substances absorb a lot of water from the air until reaching the state of equilibrium, a phenomenon that results in a caking of the substances. The results are summarized in the following table. b) Test of the behavior of the salts in the film bag: Each time 10 g of substance in the form of granules are welded in a film bag. Filled film bags (film: Monosol 8030, manufacturer: Chris Craft Inc., USA) are then stored for 4 weeks at different temperatures in an additional water vapor tight package. The stability of the films is manifested in the elasticity of the films under mechanical stress. When bentazone salt absorbs water from the filmit becomes brittle. For example, the Monosol 8030 film in the presence of sodium bentazone in a closed container lost a large part of the residual moisture contained in the film. At room temperature it decreased from 14% at the beginning to 6% at steady state. This resulted in the film becoming brittle and the bag cracked under mechanical stress as in transport, under blows and loads. The results of the model tests are summarized in the following table.

Claims (7)

Claims

1. Process for obtaining 2,2-dioxide salts of 3-isopropyl-2, 1,3-benzothiadiazin-4-one of the general formula I wherein the radicals Ri, R2 and R3 mean, each independently of the other, hydrogen, lower alkyl, hydroxyalkyl lower, which process is characterized in that 2,2-dioxide of 3-tisopropyl-2 is reacted , 3-benzothiadiazin-4-one (bundle) in an organic solvent with an amine of the general formula Illa R2 Rl - N R3 (Illa)

2. Process according to claim 1, characterized in that an amine Illa is used in which the radicals R1, R2 and R.}. they mean hydrogen.

Process according to claim 1 or 2, characterized in that 1, 2-dichloroethane is used as the organic solvent.

Process for obtaining 2,2-dioxide salts of 3-isopropyl-2, 1,3-benzothiadiazin-4-one of the general formula I wherein the radicals Subtract R1, R2, R3 and R4 mean, each independently of the other, hydrogen) lower alkyl, lower hydroxyalkyl, which process is characterized in that it is reacted a) 2,2-dioxide 3-isopropyl-2, 1,3-benzothiadiazin-4-one (lia) in an organic solvent practically immiscible with water, if desired, in the presence of water, with an amine of the general formula Illa R2 Rl N R3 (Illa) or an ammonium salt of the general formula Illb where X is the anion of an acid with a value pKs above 4, or the hydroxyl ion, and n means the number of the negative charges of the anion X, and b) salt I is absorbed in water.

5. Process according to claim 4, characterized in that 1, 2-dichloroethane is used as the organic solvent.

6. Process according to claim 4 or 5, characterized in that an amine Illa or the ammonium salt Illb is used where the radicals Ri to R4 mean hydrogen.

7. Process for obtaining 2,2-dioxide salts of 3-isopropyl-2, 1,3-benzothiadiazin-4-one of the general formula I wherein the radicals R1, R2, R3 and R4 mean, each independently of the other, hydrogen, lower alkyl or lower hydroxyalkyl, which process is characterized by reacting a) 3-isopropyl 2,2-dioxide -2, 1, 3-benzothiadiazin-4-one (lia) in water, with an ammonium salt of the general formula IIIb where X is the acid anion with a value pKs above 4 or the hydroxyl ion and n is equal to the number of negative charges of the X anion, or b) the sodium salt of bentazone (IIb) in water, with an ammonium salt of the general formula Ule where Y is the anion of an acid and n is equal to the number of negative charges of the anion Y. Process according to claim 7, characterized in that the ammonium salt Illb contains the hydroxyl ion as the X anion. Process according to claim 7, characterized in that the ammonium salt Ule contains as anion Y the carbonate ion or the hygrogencarbonate ion.