DE3737464A1 - Process for the preparation of imidazole-containing complexes - Google Patents

Abstract

The invention relates to imidazole-containing complexes which dissociate thermally and/or chemically with liberation of imidazoles and complex cyanometallates. The complexes are formed by reaction of complex cyanides with an imidazole and can be used for the polymerisation of epoxy compounds or for the removal and concentration of imidazoles from waste products.

Description

Field of application of the invention

The invention relates to the production of imidazole-containing Complexes, which depend on time and temperature with the splitting off of Imidazole can disintegrate and both for the separation and purification of Imidazoles and for the polymerization of compounds containing epoxy groups are suitable.

Characteristic of the known prior art

It is known that imidazoles are both basic and pseudo acid Have properties and therefore with both acids and Metal salts are able to form. The basic properties are by electron-donating substituents, e.g. B. by a methyl group, reinforced and by electron-withdrawing substituents, e.g. Legs Phenyl group. The acidic properties put an unsubstituted Imino group ahead and are replaced by electronegative substituents intensified (see e.g. K. Hofman, The Chemistry of Heterocyclic Compounds, Imidazoles and Derivates, Part I, 1953).

Metal salts or coordination compounds of the type mentioned are described (e.g. G.P. Brown and S. Aftergut, 3. Polm. Sci., Part A, Vol. 2 (1964) 1839) and are said to be temperature-dependent Masking of the polymerizing effect of imidazoles on epoxy resins (US 3,678,007) may be suitable. Same uses are for complexes of imidazole with isocyanuric acid (DE-OS 28 11 764) or Diaminotriazines (EP 138 209) known. In addition, DE-OS 28 11 764 stated that complexes of imidazole or imidazole derivatives with isocyanuric acid can be used to separate and purify the imidazoles. In the sense of their polymers obtainable with epoxy resins, they are physical characteristics strongly depend on the chemical habitus of the respective Complexes, while the decay temperatures depend on both Substituents, their arrangement in the molecule as well as by the respective Complexands are dictated.  

Aim of the invention

From the prior art set out, the composition the complex on the one hand and the accessibility of the complex or adductible components and their thermal activatable polymerizing properties significantly influence exercise on their choice for the respective purpose. It is consequently the aim of the invention, a method for the production of thermally and / or chemically decomposable complexes containing imidazole, suitable for curing epoxy resins and for cleaning imidazoles to propose, their manufacture from both raw material and manufacturing-economic reasons in connection with ressorcale requirements should meet optimal expectations.

State the nature of the invention

The object is a process for the preparation of imidazole-containing To develop complexes that meet this goal. According to the invention, the realization of this task enabled by the hardening agent by implementing 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)

is formed and in which in formula (I) M characterizes a hydrogen or metal ion, M 'a transition metal ion with several possible valence levels, 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 determined by the valency and coordination number of M and M 'and in formula (II) R₁ and R₂ each an alkyl or phenyl radical or hydrogen and R₃ and R₄ each Hydrogen or a methyl radical and the sum R₃ and R₄ characterizes a divalent, optionally substituted benzene radical.

The general formula (I) for the case t = 0 corresponds to the free acids of the known complex cyanides. Such connections can have coordination numbers of essentially 1, 4, 6 and 8, this term being understood to mean the number of coordinatively monovalent groups which are able to accumulate around the coordination center M '.

Such complexes can have different valences of M ' are present and are therefore subject to redox reactions, e.g. B. acts in alkaline Environment hexacyanoferrate- (3) oxidizing under simultaneous Reduction to hexacyanoferrate- (2).

The free acids corresponding to formula (I) are not in everyone Preparatively accessible case, or they are due to their inconsistency of minor practical interest.

Are essential. a. following acids:

H₄ [Fe (CN) ₆] H₃ [Fe (CN) ₆] H₃ [Cr (CN) ₆] H₄ [Mn (CN) ₆] H₄ [Mo (CN) ₈] H₃ [Co (CN) ₆] H₄ [W (CN) ₆]

while H₂ [Pt (CN) ₄] or H₄ [Os (CN) ₆] hardly for obvious reasons Find application.

For the case r < t <0, further complex acids are known in that cyano groups in the above acids are replaced by radicals or neutral molecules. Among the numerous possibilities, X can e.g. B. halide, hydroxyl, thiocyanate, oxygen or an acid; Such cases exist, inter alia, in the Prussi and Prusso compounds or the addition compounds of cyano-iron (II) acid with acids (with regard to the production and / or conversion of such complexes, Williams, Cyanogen Compounds, Londen 1948; Hein, Chemical Coordination Theory, Stuttgart 1950 and Remy, Textbook of Inorganic Chemistry, Volume II, Leipzig 1954).

The acids tend both in their free form and in their form Oxonium compound to occlude ions or dipole molecules.  

These contaminants are usually difficult to remove and interfere with generally not the reaction reactions with the imidazoles and can - insofar as they are involved in the reaction with the imidazoles be taken over - have hardening-promoting effects. The acids are expediently prepared from theirs water soluble salts. From this you can either add Mineral acids or obtained using cation exchangers will. Due to the relative instability of the acids it is expedient, as long as they are not immediately processed - to stabilize. Such a measure is also in the deposition operation recommended from their salts. This can be done through connections with coordinatively unsaturated oxygen, e.g. B. ethers or ketones, happen by forming oxonium-like binding states attach to the acids. They are in this form, also in moist condition, with simultaneous light exclusion and low Temperatures can be stored for weeks, if necessary (see e.g. the oxonium compounds of hexacyanoic (2) acid, Duprat. Bull. Inst. De Pin 1933, 20, 36).

The imidazoles applicable to the process according to the general formula (II) z. B. preferred either the basic connection itself or the 1-methyl, 1,2-dimethyl, 2-ethyl-4-methyl, 2-isopropyl, 1-vinyl or which include 2-alkyl benzene derivatives. The selection of those to be adducted Acids must take into account the imidazole substituents, if the decomposition temperature is in the range of 140 to 180 degrees, otherwise the imidazole acid bond is too strong. The adducts are obtained by z. B. the hydrated or the anhydrous acids obtained from it through drying processes - advantageously as a solution or suspension in ketones, ethers, Alcohols or m- or p-dioxanes - with equivalent amounts of the imidazoles be transferred.

The precipitation that occurs in the form of an oil or a Solid can then be treated with a further z. B. Be subjected to alcohols for cleaning and / or activation. Cleaning operations are also possible by this precipitation, suspended, e.g. B. in an alcohol, with acidic or basic compounds are treated, the proportion of these compounds being about 1 to 10% by weight that constitutes precipitation.  

Either alcoholic solutions of are suitable as acidic compounds Metal salts in the form of their alkoxy acids and as basic compounds those which are able to react with the acids of the cyanometals, e.g. B. urea or amino compounds.

Another possibility of adduct formation is given when imidazolium compounds with appropriate salts of the complex acids for the reaction brought, e.g. B. by the sodium salt of nitroprusside with the equivalent amount of imidazolium chloride is added in aqueous solution. It is even cheaper if the ions to be cut off are sparingly soluble Form salts, for example by imidazolium sulfate with calcium salts Complex acids come to implementation. It is procedural possible to separate the imidazolium compounds immediately before use equivalent in the form of aqueous solutions from neutralization Generate reactant amounts or common solutions of imidazole and complex compounds with an imidazole content To transfer the amount of acid.

The resulting complexes containing imidazole are suitable

• - For the thermal hardening of compounds containing epoxy groups or Mixtures for the purpose of obtaining liquid or solid polymers;
• - To adequately separate imidazole or imidazole derivatives from waste products and then shoot for the recovery of the imidazoles, by using the chemical stability of the Imidazole the complexes formed by adding equivalent amounts a metal salt solution, e.g. B. in the form of the above-mentioned alkoxy acids, in the z. B. Heavy metal salts insoluble in organic solvents the cyanometalates with formation of alcohol-soluble metal salts of Imidazoles are transferred and the filtrate with an inorganic Base neutralized, dried and then distilled off the imidazole becomes.

Embodiments Example 1 Production of hexacyanoic (II) acid

108 g of K-Hexacyanoferrat- (II), K₄ [Fe (CN) ₆] × 3 H₂O in 400 ml Dissolved water and added 200 ml of ether while shaking.  

Subsequently, with sharp turbination and cooling with ice water 240 ml of concentrated hydrochloric acid are added in portions, starting from approx. 70 ml HCl a clear exotherm is observed and - depending on the purity of the starting materials - white to bluish iron (II) acid fails. After the HCl addition has ended, the mixture is left to stand for about 10 minutes and filtered off. In this way, one is contaminated by inorganic salts water and ether damp material with a dry content of approx. 11%, which can serve as starting material for further implementations and at Temperatures around 5 ° C can be stored for weeks.

This damp material can be dried by drying up to max. 40 ° C with elimination of ether into a loose powder that is irritating to sneeze be, which also in the absence of sunlight and moisture can be stored for weeks. For cleaning it can be dissolved in methanol and can be precipitated from it again by adding ether.

Example 2

80 g of moist acid according to Example 1 are suspended in 200 ml of acetone and 26 g of imidazole dissolved in acetone are added in portions with turbination, the suspension gradually clears, the acetone takes one yellow color and a white to yellow oil-like color separates Precipitation. After decanting the acetone with 100 ml Poured on ethanol, causing it to crumble into a white-yellow powder.

Example 3

43 g of the dried and powdered acid according to Example 1 (0.2 mol) are loosely mixed with 55 g imidazole (0.8 mol) and then with Pour 400 ml of ethanol over it. It forms under weak exothermic conditions and depending on the age and habit of the complex acid immediately or gradually a white precipitate, which filters off after about 60 min and washed twice on the filter with 150 ml of ethanol. Man receives 78 to 82 g (80 to 84% of the theoretical yield) of one white material that gradually turns yellow in the air.

Example 4

45 g of benzimidazole are dissolved in 600 ml of acetone and this solution in a suspension of 80 g of the moist acid according to Example 1 in 400 ml of acetone Poured in with strong turbinating.  

With the first quantities, a pink color is formed, which increases with increasing amount of benzimidazole according to orange colors simultaneous formation of a whitish precipitation. After decanting the acetone, pour 300 ml of methanol over it, 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 in a slurry of 10 g imidazolium chloride in 120 ml acetone poured. The imidazole goes exothermic with gas evolution Solution. The dried solution produces pale red crusts, which, triturated with 100 ml of methanol, with separation of sodium chloride in Solution go. The filtered solution gives one after evaporation pale brown residue.

Claims (7)

1. A process for the preparation of thermally and / or chemically decomposable imidazole-containing complexes, characterized in that these complexes by reacting 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) are formed and in which in formula (I) M characterizes a hydrogen or metal ion, M 'a transition metal ion with several possible valence levels, X organic or inorganic ions, radicals or molecules, the indices r and t are integer values in the range r < t 0 include and the indices a, b, c are integer values which are determined by the valency and coordination number of M and M ', and in formula (II) R₁ and R₂ each an alkyl or phenyl radical or hydrogen and R₃ and R₄ are each hydrogen or a methyl radical and the sum of R₃ and R₄ characterizes a divalent, optionally substituted benzene radical. 2. The method according to claim 1, characterized in that as complex Cyanides the acids of the general formula (I) can be used. 3. The method according to claim 1, characterized in that the salts are more complex Cyanides can be 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 with mineral acids added and the reaction product is worked up. 5. The method according to claim 1, characterized in that the imidazole-containing Complexes with 1 to 10 wt .-% of an acidic or basic Connection to be treated.   6. The method according to claim 5, characterized in that the acidic compounds alcoholic solutions of metal salts are in the form of their alkoxy acids. 7. The method according to claim 5, characterized in that as basic compounds used are those that are compatible with the Acids of the cyanometalates are able to react.