NL8003564A - Herbicidal bipyridylium salts - the products being herbicides - Google Patents

Abstract

-4,4'-bipyridylium salts (I) in which each of the substituents contains up to 10 carbon atoms are prepared by the reaction of a N-substd. pyridinium salt (II) with a cyanide (III) in a basic medium followed by oxidation of the intermediate obtained.

Description

* /.

Process for preparing a 1,1'-disubstituted H, U'-bipyridylium salt.

The invention relates to a process for the preparation of a 1,1'-disubstituted 4, k'-bipyridylium salt by reaction of a 1-substituted pyridinium salt with cyanide ions and oxidation of the intermediate formed therein.

Such a method is known from the article in Tetrahedron Letters 2k, (1967), 2313-2315.

According to this article, 1-dodecylpyridinium bromide is reacted at room temperature with a solution of sodium cyanide in water, after which the intermediate didodecylviologene cation radical formed is oxidized with a solution of iodine in alcohol to 1,1'-didodecyl-H, H'- bipyridylium salt. When starting from 1-ethylpyridinium bromide, the formation of the violog cation radical could only be detected after prolonged heating at 100 ° C. The authors suspect that the remarkable difference in reactivity between the two starting products must be attributed to micelle formation when starting from 1-dodecylpyridinium bromide.

It has now been found that starting from a 1-methylpyridinium salt, the corresponding bipyridylium salt is obtained in reasonable yield when the reaction with cyanide ions is carried out in a reaction medium containing one or more polar aprotic solvents.

The rights applied for exclude the use of aqueous acetone as a reaction medium, since this has already been described in the earlier unpublished Netherlands patent application 69.05892.

The products prepared according to the invention have become known primarily as herbicides (see U.S. Pat. No. 2,972,528.)

The temperature at which the reaction is carried out is not critical, although in some cases it is very advantageous to heat the reaction mixture. Generally, the reaction is carried out at a temperature of from 25 to 120 ° C, and preferably from 100 to 90 ° C. Temperatures above 150 ° C should generally be avoided. Usually the reaction is carried out in an inert atmosphere.

The amount of cyanide is not critical although an excess of this reagent is preferably used. Preferably more than Π mole of cyanide per mole of pyridinium salt is used. The concentration of the pyridinium salt depends on the solvent used. The optimum concentration can be determined by simple tests. Generally, however, concentrations of 0.1-2.0 mol per liter and in particular about 0.5 mol per liter are suitable.

As the oxidizing agent in the last step of the process of the invention, air or an electron acceptor with a redox potential in water that is more than -0.50 volts relative to the saturated calomel electrode can be used. Examples of suitable oxidizing agents are cerisulfate (in dilute sulfuric acid), metal salts, especially the halides; inorganic oxyanhydrides, in particular sulfur dioxide, chlorine, air, preferably in conjunction with water and / or carbon dioxide and / or an acid such as acetic acid or sulfuric acid; and organic oxidizing agents such as quinones, for example benzoquinone, chloroanil and anthraquinone. The oxidation is preferably carried out under acidic conditions, the pH of the reaction mixture 30 being preferably less than 7 and between H and 6.

The temperature at which the reaction is carried out is not critical, although in some cases it is very advantageous to heat the reaction mixture. Generally, the reaction is conducted at a temperature of from 25 to 120 ° C, and preferably from 35 ° C to 0 to 90 ° C. Temperatures above 150 ° C should generally be avoided in 8 0 0 3 5 64 r 3. Usually the reaction is carried out in an inert atmosphere.

The amount of cyanide is not critical although "preferably an excess of this reagent is used. Preferably 1-4 mol is used. The concentration of the pyridinium salt depends on the solvent used. The optimum concentration can be determined by simple tests. Generally, however, concentrations of 0.1-2.0 mol per liter and in particular about 0.5 mol per liter are suitable.

As the oxidizing agent in the last step of the method according to the invention, air or an electron acceptor with a redox potential in water which is more than -0.50 volts relative to the saturated calomel electrode can be used. Examples of suitable oxidizing agents are cerisulfate (in dilute sulfuric acid), metal salts, especially the halides; inorganic oxyanhydrides, in particular sulfur dioxide, chlorine, air, preferably in conjunction with water and / or carbon dioxide and / or an acid such as acetic acid or sulfuric acid; and organic oxidizing agents such as quinones, for example benzoquinone, chloroanil and anthraquinone. The oxidation is preferably carried out under acidic conditions, the pH of the reaction mixture preferably being less than 7 and between 4 and 6.

The intermediate is obtained in the form of a usually brown-colored solution. It can be directly oxidized without being isolated from the mixture in which it was formed. However, if this product is directly oxidized, the final bipyridylium salt is impure and must be purified. The bipyridylium salt thus obtained in particular contains free cyanide ions and these anions can react with the bipyridylium cation, thereby reducing the yield of the desired salt.

It is usually easier to isolate the intermediate before it is oxidized, so that upon oxidation a fairly pure bipyridylium salt is obtained which contains substantially no free cyanide ions. In the case where the 800 35 64 u intermediate is a suspension, the solid can be isolated by filtration or preferably solvent extraction. Suitable solvents for the extraction are hydrocarbons, especially aromatic hydrocarbons and especially toluene. After the solid has been removed, part of the intermediate remains in the liquid phase; this can be recovered by oxidizing it to the bipyridylium salt and isolating this salt in the manner indicated below, or by reducing it to form a dihydrobipyridyl which can be isolated in the manner already indicated before being oxidized. The reduction can be carried out by any ordinary reduction method, such as with an alkali metal amalgam or a dithionite.

A useful isolation method is also to add water, an organic acid, for example acetic acid, or a base (anhydrous or an aqueous solution of the base). A suspension is then obtained. The temperature in this treatment can be between 0 and 120 ° C and preferably between 20 and 50 ° C. The solid and liquid phases can be treated in the above manner to recover the intermediate therefrom.

In addition to obtaining substantially pure bipyridylium salts, this method has the additional advantage that higher yields are obtained than when the solution, again containing intermediate product, is directly oxidized. Moreover, the product obtained as a result of the treatment can easily be oxidized with a greater number of different oxidizing agents than the solution for the treatment. It is believed that the solid obtained by adding water or a base to the intermediate solution is a 1,1'-disubstituted-1,1'-dihydro-1-bipyridyl is.

It may be necessary to separate the final bipyridylium salt from free cyanide ions, for example, if the intermediate has been oxidized without first isolating it from the reaction medium. It has been found that this can be done by treating the reaction mixture with 1 +, M-diamino-stilbene-2,2'-35 disulfonic acid, which is commonly known as "amsonic acid". As a result, the bipyridylium salt in the form of the amsonate salt is precipitated from the mixture, while the cyanide ions remain in the mixture. The precipitate can then be filtered off, washed and dried in the usual manner, and the amsonic acid can be regenerated again by acidifying the amsonate salt, preferably using an aqueous solution of an acid. The acid used to recover the amsonic acid can be selected to provide the desired anion for the final bipyridylium salt. For example, it can consist of hydrochloric, phosphoric or acetic acid.

Amsonic acid is only sparingly soluble in water and therefore it is usually used in the form of an aqueous solution of one of its water-soluble salts, advantageously an alkali metal salt or the ammonium salt. The treatment of the reaction mixture with amsonic acid can advantageously be carried out at a pH of 7-12 and a temperature of 0 to 100 ° C.

The final product can also be separated from the cyanide ions in the reaction mixture by contacting it with a suitable cation exchange resin. Then the cyanide ions pass through the resin and the product remains therein. It can then be released from the resin by treating the resin with an acid. In this way a bipyridylium salt is obtained, in which the anion of the acid originates.

Examples of anions that can be introduced into the mixture in this way are chloride, sulfate and acetate ions.

The cyanide ions can also be separated from the bipyridylium cations with an anion-exchange resin.

The temperature at which the mixture is contacted with the ion exchange resin is not critical, but may suitably be between 0 and 100 ° C. Examples of suitable cation exchange resins are Zeocarb resins such as Zeocarb 225 (SRC-8). Amberlite resins, such as Amberlite Cé-120, and the Deacidite resins. An example of an anion exchange resin that can be used is Amberlite IRA ^ 00.

800 35 64 6

Another method of removing cyanide ions from the reaction mixture containing the 1,1-disubstituted-H'-bipyridylium salt consists in that the reaction mixture is acidified and then degassed. In this way the 5 cyanide ions in the form of hydrogen cyanide are removed from the mixture. This process is particularly effective because the hydrogen cyanide thus released can be directly converted into a cyanide with a base, for example, sodium hydroxide, which can be used to prepare a further amount of bipyridylium cations. Any mineral or organic acid can be used if it can form hydrogen cyanide. Examples of suitable acids are hydrochloric acid, sulfuric acid, phosphoric acid and acetic acid. The solution can also be acidified with sulfur dioxide. The acid may be selected in accordance with the anion desired in the final 1,1'-dimethyl, U 'bipyridylium salt.

The reaction mixture can be acidified at any temperature at which the bipyridylium cation is stable, such as at 0 to 100 ° C. The mixture can be degassed in the usual manner, such as, for example, by bubbling air or an inert gas under reduced pressure or by boiling the mixture. It will be understood that this method of acidifying the mixture and then degassing it is easy to carry out and can be used to remove from the mixture any anion which forms with the proton a volatile product which is degassed can be removed from the mixture. In addition to cyanide ions, halide ions, in particular fluoride and chloride ions, can also be removed with this technique.

Cyanide ions can be removed from mixtures containing the 1,1'-dimethyl-U, 4'-bipyridylium cations by adding a reagent at a temperature between 0 and 100 ° C, which contains a complex salt with the cyanide ions.

The addition of ferric or ferrous ions in the form of a salt, such as a sulfate or halide, for example, results in the formation of a ferrocyanide. In this case, the cyanide ions are not actually removed from the reaction mixture, but they are effectively prevented from reacting with the bipyridylium salt due to the fact that they have formed a complex salt with the added cations.

Example I

2.9 grams (0.02 mole) of 1-methylpyridine chloride was dissolved in 30 ml of dry dimethyl sulfoxide and the solution was stirred quickly with a solution of k, 9 grams (0.1 mole) of sodium cyanide in 20 ml of dry dimethyl sulfoxide at 75 ° C and added under a nitrogen atmosphere. The mixture was refluxed for 30 minutes.

The resulting deep brown mixture was oxidized in excess sulfuric acid in dilute sulfuric acid to give 1,11-dimethyl-β-bipyridylium chloride. Yield; 73% compared to 1-methylpyridinium chloride.

Example II

The procedure of Example I was repeated except that the sodium cyanide was dissolved in 30 ml of dimethyl sulfoxide containing 10 grams of sodium carbonate and the reaction temperature was 70 ° C. 20 Yield: 88%.

Example III

A mixture of Tan 3.1 grams of 1-methylpyridinium chloride, U, 9 grams of sodium cyanide and 10 grams of sodium bicarbonate in 80 ml of dimethyl sulfoxide was heated at 70 ° C for 20 minutes under stirring and under a nitrogen atmosphere. The resulting brown mixture was treated with a solution of cerisulfate in dilute sulfuric acid to give 1.1 l-dimethyl-V-bipyridylium chloride in 89% yield with respect to H-methylpyridinium chloride.

The above procedure was repeated, except that the sodium bicarbonate was omitted from the reaction mixture. Yield: 85 #.

Example IV

3.1 grams of 1-methylpyridinium chloride in 50 ml of dimethyl sulfoxide was added with stirring and under a nitrogen atmosphere at 70 ° C in a suspension of 0.9 grams of sodium cyanide in 30 ml of dimethyl sulfoxide under a nitrogen atmosphere. After 30 minutes, a cooled solution of sulfur dioxide in dimethyl sulfoxide was added to the brown reaction mixture. The mixture turned blue immediately and browned after 1.5 hours.

Then excess sulfur dioxide was removed from the mixture by bubbling nitrogen gas through it. Upon analysis, the mixture was found to contain 1,1'-dimethyl-, -1'-bipyridylium chloride. Yield: 95% over 1-methylpyridinium-10 chloride.

Examples V to VIII

A suspension of 3.1 grams of 1-methylpyridinium chloride in 50 ml of dimethylacetamide was added with stirring at 75 ° C under a nitrogen atmosphere to a suspension of 0.9 grams of sodium cyanide in 50 ml of dimethyl acetamide. A yellow color was immediately formed and after 1 hour the color had turned dark orange. The mixture was then poured into a solution of cerisulfate in dilute sulfuric acid to form 1,1'-dimethyl-2'-bipyridylium ion. The yield of the reaction 20 was 66% relative to 1-methylpyridinium chloride.

The above procedure was repeated three times (examples V, VI, VII and VIII), except that the solvents listed below were used instead of dimethylacetamide.

Yields are listed below: Example Number Solvent Yield,% V dimethylacetamide 66 VI dimethylformamide 36 VII acetone 23 VIII hexamethylenephosphoric triamide b5

Example IX

3.0 grams of 1-methylpyridinium chloride and 0.9 grams of sodium cyanide were reacted with each other for 30 minutes at 80 ° C in 80 ml of dimethyl sulfoxide. The mixture was then cooled to room temperature and poured into a solution of the oxidizing agent (see Table F) in 80 ml of dimethyl sulfoxide. After 800 minutes, 2 N sulfuric acid was added to adjust the pH to 1 and the solution was analyzed for bipyridylium cations.

In some cases (see table), 80 ml of water, or pearls of solid sodium hydroxide or 10 ml of acetic acid were added to the reaction mixture 5 minutes before the oxidation was carried out.

Table

Oxidizing agent equivalents further% yield * oxidizing agent reagent IQ maleic anhydride 2 none 23 maleic anhydride 2 water 69 maleic anhydride 2 sodium hydroxide 61 maleic anhydride 2 acetic acid 55 maleic anhydride 6 none 65 JU chloroanil (tetrachloroquinone) 2 none 0 chloroanil 2 water 53 alluoroanil 2 water 50 2 none 3 20 alloxan monohydrate 2 water 78 alloxan monohydrate U, 5 none 63 indane trion monohydrate 2 no 65 m dinitrobenzene 2 no 5 m dinitrobenzene 2 water 0 25 m dinitrobenzene 2 sodium hydroxide 59 followed by acetic acid m dinitrobenzene 2 acetic acid 14 based on 1 methyl pyridinium chloride.

30 Example X

3.0 grams of 1-methylpyridinium chloride and 9 grams of sodium cyanide were reacted together in 80 ml of dimethyl sulfoxide at 80 ° C for 30 minutes. The mixture was then cooled and 200 ml of toluene was added, followed by 50 ml of water. The mixture was separated and the toluene layer was oxidized in a two-phase system consisting of 10 grams of m-dinitróbenzene in 100 ml of toluene and 10 ml of acetic acid in 100 ml of water to form a water phase containing bipyridylium cations without free cyanide ions. and an organic phase containing unchanged m-dinitrobenzene 5 was obtained, Yield: 77%

Example XI

A reaction mixture consisting of 3.0 grams of methyl pyridinium chloride and 1.9 grams of sodium cyanide in 80 ml of dimethyl sulfoxide was kept at 80 ° C for 30 minutes. The reaction mixture was then cooled and treated by one of methods A or B.

A. Dilute the reaction mixture to 500 ml with deoxygenated water. The resulting suspension suspension is filtered and the filtered solid is oxidized with m-di-nitrobenzene. This gave the bipyridylium salt with a yield of 30 µt. The filtrate was oxidized with sulfur dioxide and yielded 62% bipyridylium salt.

B. The reaction mixture is mixed with 250 ml of toluene and 80 ml more mixed. The oxidation layer with oxidation with sulfur oxide with a yield of 15 # yielded the bipyridylium salt and the toluene layer yielded the oxidation with sulfur oxide with a yield of 77%.

800 35 64

Claims (1)

. Process for the preparation of a 1,1'-disubstituted bipyridylium salt by reaction of a 1-substituted pyridinium salt with cyanide ions and oxidation of the intermediate product formed therein, characterized in that to prepare a 1,1'-dimethyl-, 4'-bipyridylium salt starts from a 1-methyl-pyridinium salt, which is reacted with cyanide ions in a reaction medium containing one or more polar aprotic solvents, it being understood that the use of 10 aqueous acetone is excluded from the requested duties 800 35 64