DD253810A1 - PROCESS FOR PREPARING IMIDAZOL-CONTAINING COMPLEXES - Google Patents

Abstract

The invention relates to imidazole-containing complexes which decompose thermally and / or chemically with elimination of imidazoles and complex cyanometallates. The complexes are formed by reaction of complex cyanides with an imidazole and can serve for the polymerization of epoxide compounds or for the enriching separation of imidazoles from waste products.

Description

R ₄ -C - c - R ₂ - (II)

η '

and in which in formula (I) M denotes a hydrogen or metal ion, M 'a transition metal ion with several possible valence states, X organic or inorganic ions, radicals or molecules, the indices r and t integer values in the range r>t> 0 and the indices a, b, c are integer values determined by valence and coordination number of M and M ', and in formula (II) Ri and R ₂ each represents an alkyl or phenyl radical or hydrogen and R ₃ and R ₄ each hydrogen or a methyl radical and the sum of R ₃ and R ₄ denotes a divalent, optionally substituted benzene radical.

2. The method according to claim 1, characterized in that the acids of the general formula (I) are used as complex cyanides.

3. The method according to claim 1, characterized in that the salts of complex cyanides are reacted with imidazolium salts.

4. The method according to claim 1, characterized in that the common solution of the salts of complex cyanides and imidazoles mixed with mineral acids and the reaction product is worked up.

5. The method according to claim 1, characterized in that the imidazole-containing complexes are treated with 1 to 10 wt .-% of an acidic or basic compound.

6. The method according to claim 5, characterized in that the acidic compounds are alcoholic solutions of metal salts in the form of their alkoxo acids.

7. The method according to claim 5, characterized in that as basic compounds are used which are capable of reacting with the acids of the cyanometalates.

Field of application of the invention

The invention relates to the preparation of imidazole-containing complexes which can disintegrate with time-dependent and temperature-dependent cleavage of imidazole and are suitable both for the separation and purification of imidazoles and for the polymerization of epoxide-containing compounds.

Characteristic of the known state of the art

It is known that imidazoles have both basic and pseudo acidic properties and therefore are able to form salts both with acids and with metals. The basic properties are by eiektronenlieferde substituents, eg. B. by a methyl group, reinforced and by electron-attracting substituents, eg. As a phenyl group, reduced. The acidic properties require an unsubstituted imino group and are enhanced by electronegative substituents (see, e.g., K. Hofmann, The Chemistry of Heterocyclic Compounds, Imidazoles and Derivatives, Part 1,1953). Metal salts or coordination compounds of the type mentioned have been described (eg GPBrown and S.Aftergut, J. Polm. Sei., Part A, Vol. 2 [1964] 1839) and are intended for temperature-dependent masking of the polymerizing effect of imidazoles on epoxy resins ( US 3678007). Same uses are known for complexes of imidazoles with isocyanuric acid (DE-OS 2811764) or diaminotriazines (EP 138209). In addition, it is stated in DE-OS 2811 764,

that complexes of imidazole or imidazole derivatives with isocyanuric acid can be used for the separation and purification of the imidazoles. In terms of their polymers obtainable with epoxy resins, their physical characteristics are highly dependent on the chemical habit of the respective complexes, while the decomposition temperatures are dictated by both the substituents, their arrangement in the molecule and the particular complex.

Object of the invention

It results from the state of the art that the composition of the complexes on the one hand and the accessibility of the components capable of complexing or adsorbing and of their thermally activatable polymer-inducing properties exert a decisive influence on their choice for the respective intended use. It is therefore the object of the invention to propose a process for the preparation of thermally and / or chemically decomposable imidazole-containing complexes, suitable for the curing of epoxy resins and for the purification of imidazoles, the preparation of which, both for raw material as well as manufacturing economic reasons in conjunction with resource requirements optimal expectations should correspond.

Explanation of the essence of the invention

The object is to develop a process for the preparation of imidazole-containing complexes which fulfills this objective. According to the realization of this task is made possible by the curing agent by reaction of complex cyanides of the general formula (I)

M _a {M '[(CH) _r (X) _t ] _b } _c (I)

with an imidazole of the general formula (II)

and in which in formula (I) M characterizes a hydrogen or metal ion, M 'a transition metal ion with several possible valence states, X organic or inorganic ions, radicals, molecules, etc., the indices r and t are integer values in the range r>t> 0 and the indices a, b, c are integer values which are defined by the valency and coordination number of M and M 'and in formula (II) R ₁ and R _{2 are} each an alkyl or phenyl radical or hydrogen and R ₃ and R _{4 are} each hydrogen or a methyl radical and the sum R ₃ and R _{4 is} a bivalent, optionally substituted benzene radical. The general formula (I) correspond to the case T = 0, the free acids of the known complex cyanides. Such compounds may have coordination numbers of substantially 1,4, 6 and 8, which term is understood to mean the number of coordinatively monovalent groups which are able to attach to the coordination center M '.

Such complexes can exist in different valences of M 'and are subject to redox reactions, eg. B. acts in the alkaline medium hexacyanoferrate (3) oxidizing with simultaneous reduction to Hexacyanoferrat- (2). The free acids corresponding to the formula (II) are not always preparatively accessible, or because of their instability they are of secondary practical interest

 Of essential importance are u.a. the following acids:

H ₄ [Fe (CN) ₆ ] H ₃ [Fe (CN) ₆ ]

H ₃ [Cr (CN) ₆ ] H ₄ [Mn (CN) ₆ ]

H ₄ [Mo (CN) ₆ ] H ₃ [Co (CN) ₈ ]

H ₄ [W (CN) ₆ ]

while H ₂ [Pt (CN) ₄ ] or H ₄ [Os (CN) ₆ ] are hardly used for obvious reasons.

For the case r> t> O, further complex acids are known, in that in the above acids cyano groups are replaced by radicals or neutral molecules. Among the many possibilities X can be e.g. Halide, hydroxyl, thiocyanate, oxygen or an acid; such cases are i.a. in the Prussi and Prusso compounds or the addition compounds of cyanoiron (II) acid with acids (for the preparation and / or conversion of such complexes is to Williams, Cyanogen Compounds, London 1948, Hein, Chemical Coordination, Stuttgart 1950 and Remy, Textbook of inorganic chemistry, Volume II, Leipzig 1954, referenced). The acids, both in their free form and in the form of their oxonium compound, tend to occlude ions or dipole molecules. These impurities are usually difficult to remove bar and generally do not interfere with the reaction reactions with the imidazoles and - as far as they are taken over in the reaction reactions with the imidazoles - have curing promoter effects. The production of the acids is expediently carried out from their water-soluble salts. From this they can be obtained either by the addition of mineral acids or by using cation exchangers. Due to the relative instability of the acids, it is expedient to stabilize these - if they do not come immediately for processing. Such a measure is also recommended in the deposition operation from its salts. This can be achieved by compounds with coordinatively unsaturated oxygen, e.g. As ethers or ketones happen by these attach themselves to form oxonium-like bonding states of the acids. In this form, they can also be stored for weeks, even in the moist state, with simultaneous exclusion of light and low temperatures (cf., for example, the oxonium compounds of the hexacyanoic (2) acid Duprat, Bull. Inst, de Pin 1933, 20, 36 ).

The applicable for the process imidazoles according to the general formula (II) may, for. B. preferably comprise either the basic compound itself or the 1-methyl, i, 2-dimethyl, 2-ethyl-4-methyl, 2-isopropyl, 1-vinyl or 2-alkyl-benzene derivatives. The selection of the acids to be added has to be made taking into account the imidazole substituents, if the decomposition temperature in the range of 140 to 180 degrees should be, otherwise too strong a bond imidazole acid is recorded.

The adducts are obtained by, for. B. the water-containing or the resulting from drying processes anhydrous acids -advantageously as a solution or suspension in ketones, ethers, alcohols or m- or p-dioxanes

- Be added with equivalent amounts of imidazole.

The thereby precipitated precipitates in the form of an oil or a solid can then be further treatment with z. For example, alcohols may be subjected to purification and / or activation. Cleaning operations are also possible by suspending these precipitates, e.g. In an alcohol, with acidic or basic compounds, the proportion of these compounds being about 1 to 10% by weight of the precipitates. Suitable acidic compounds are either alcoholic solutions of metal salts in the form of their alkoxoic acids and as basic compounds those which are able to react with the acids of Cyanometallate, z. As urea or amino compounds. Another possibility of adduct formation is given when imidazolium compounds are reacted with appropriate salts of the complex acids, for. B. by adding the sodium salt of nitroprusside with the equivalent amount of imidazolium chloride in aqueous solution. It is even better if the ions to be deposited form sparingly soluble salts, for example by imidazolium sulfate being reacted with calcium salts of the complex acids. It is procedurally possible to produce the Imidazoliumverbindungen immediately before use separately in the form of aqueous solutions of the neutralization of equivalent amounts of reactants or to enable common solutions of imidazole and complex compounds with an acidity based on the imidazole content. The resulting imidazole-containing complexes are suitable

For the thermal curing of epoxide group-containing compounds or mixtures for the purpose of preserving liquid or solid polymers,

To adequately separate imidazole or imidazole derivatives from by-products and then to disassemble for the purpose of recovering the imidazoles, by taking into account the chemical stability of the imidazoles, the complexes formed by addition of equivalent amounts of a metal salt solution, eg. B. in the form of the above-mentioned alkoxoic acids in the z. B. in organic solvents insoluble heavy metal salts of Cyanometallate be converted to form alcoholic metal salts of imidazole and neutralized the filtrate with an inorganic base, dried and then the imidazole is distilled off.

embodiments

, Example 1

Preparation of Hexacyanoic (II) Acid

108 g of K-hexacyanoferrate (II), K ₄ [Fe (CN) ₆ ], 3H ₂ O are dissolved in 400 ml of water and 200 ml of ether are added with shaking. With vigorous turbining and cooling with ice-water, 240 ml of concentrated hydrochloric acid are then added in portions, with a clear exotherm being observed from about 70 ml of HCl and, depending on the purity of the starting materials

- The white to bluish ferric acid precipitates. After completion of the HCl addition is allowed to stand for about 10 minutes and filtered off. This gives a contaminated by inorganic salts water and ether-moist material with a solids content of about 11%, which can serve as a starting material for further reactions and can be stored at temperatures around 5 ⁰ C for weeks.

This moist material can be dried by drying up to max. 40 ⁰ C are transferred with elimination of the ether in a loose, irritating to sneezing powder, which is also excluded weeks of sunlight and moisture storage. For purification, it can be dissolved in methanol and precipitated again by ether addition.

Example 2

80 g of moist acid according to Ex. 1 are suspended in 200 ml of acetone and 26 g of acetone dissolved imidazole added in portions with turbining, while the suspension gradually clears, the acetone takes on a yellow color, and it separates from a white to yellowish oily precipitate. This is poured after decanting the acetone with 100 ml of ethanol, whereby it decays to a white-yellow powder.

Example 3

43 g of the dried and powdered acid of Example 1 (0.2 mol) are mixed loosely with 55 g of imidazole (0.8 mol) and then poured over with 400 ml of ethanol. It forms under mild exothermicity and depending on the age and habit of complex acid immediately or gradually from a white precipitate, which is filtered off after about 60 min and washed on the filter twice with 150 ml of ethanol. This gives 78 to 82 g (80 to 84% of the theoretical yield) of a white, gradually yellowing in the air material.

Example 4

45 g of benzimidazole are dissolved in 600 ml of acetone and this solution poured into a suspension of 80 g of the moist acid according to Ex. 1 in 400 ml of acetone with vigorous turbining. In this case, the formation of a pink hue, which changes with increasing amount of benzimidazole after orange color with the simultaneous formation of a whitish precipitate in the first quantities. After decanting the acetone is poured over with 300 ml of methanol, filtered off and washed three times with a little methanol.

Example 5

15 g (0.05 mol) of nitroprusside sodium are dissolved in 100 ml of water and poured into a slurry of 10 g of imidazolium chloride in 120 ml of acetone. The imidazole is exothermic in solution with evolution of gas. The dried solution gives biaxial crusts which, when triturated with 100 ml of methanol, dissolve with the separation of sodium chloride. The filtered solution gives after evaporation a pale brownish residue.

Claims (1)

claims: 1. A process for the preparation of thermally and / or chemically decomposable imidazole-containing complexes, characterized in that these complexes by reaction of complex cyanides of the general formula (I) M _a {M '[(CN) _r (X) _t ] _b } _c (I) with an imidazole of the general formula (II)