DE2045885A1 - 3,5-dialkylpyridine prdon - from formaldehyde pre condesnates higher aldehydes - Google Patents

Abstract

Title cpds. of formula: (in which R1 and R2 are 1-6 C opt. branched alkyl) are prepd. by reacting precondensates of 1 mole of HCHO with 0.3 - 1.2 moles of aldehydes having a free alpha-methylene gp. of formula R1-CH2CHO, and amines of formula NRRR (in which R is H or up to 2 R gps. may be CH3) or mixts. of these amines, in the liquid phase in water and/or a lower alcohol at 180 - 350 degrees C under raised pressure. They are solvents, (co)catalysts, and also inters. for plant protection agents, dyes and polymers.

Description

Process for the production of 3,5-dialkylpyridines from precondens of formaldehyde with higher aldehydes having a free L-methylene green.

A number of syntheses are used to produce 3,5-dimethylpyridine known, but all of which lead to mixtures of pyridine derivatives.

In the Belgian patent 738 034 there is a method of manufacture of 3,5-dimethylpyridine from 1.1.1-trimethylolethane described, which good yields results and after two distillation gives a preparation of 98 points of purity.

However, the disadvantage is the need for high temperatures and acidic Catalysts that sizeable. Raise corrosion problems. So are to achieve optimal yields temperatures of over 2700C, strong mineral acids as catalysts and methanol is necessary as a solvent. Stainless steel and titanium autoclaves are under severely attacked these conditions.

It is also known to use 3,5-dialkylpyridines in a gas phase reaction from formaldehyde, ammonia and an aliphatic aldehyde of the formula R-CH2-CHO (French patent 1,332,908). Formaldehyde became n-butyraldehyde and Ammonia at 4000C on an aluminum silicate catalyst impregnated with fluoride 3, 5-diethylpyridine obtained. The yield corresponds to a conversion of 50%. Analogue 3,5-dimethylpyridine was obtained from formaldehyde, n-propionaldehyde and ammonia. The process has so far not achieved any technical importance. Is disadvantageous before especially the need to keep the catalyst in the oxygen or air stream having to regenerate. Tarry forms at the required high temperatures Material and its decomposition products that lead to coking of the apparatus and the The catalyst gives rise to the separation of the desired 3,5-dialkylpyridine make more difficult.

A new process for the preparation of 3,5-dialkylpyridines has now been found which, by reacting precondensates of formaldehyde with higher aldehydes containing a free α-methylene group, with compounds of the formula where R is hydrogen and a maximum of 2 of the radicals R is methyl, or mixtures of such compounds in the presence of water or lower alcohols in the liquid phase at 180-3500C under increased pressure.

The increased pressure naturally results from the choice of implementation components required or involved in the implementation. Generally has it has proven to be expedient, preferably in the pressure range from 10 to 300 atmospheres 30 to 200 and in particular 50 to 150 atmospheres to work.

The process already leads to excellent yields at 2400C of 3,5-dialkylpyridines.

The present invention thus provides a process for the preparation of 3,5-dialkylpyridines of the general formula where R1 and R2 stand for a straight-chain or branched alkyl radical with 1 - 6 carbon atoms, which is characterized in that precondensates of formaldehyde with a free & -Methylene group having higher aldehydes of the general formula R1 -CH2-CHO in which R1 is the has the meaning given above, with compounds of the formula where R is hydrogen and a maximum of 2 of the radicals R is methyl, or mixtures of such compounds are reacted in the presence of water and / or lower alcohols in the liquid phase at 180-3500C at elevated pressure.

The condensates of formaldehyde with a free α-methylene group containing aldehydes which are used for the process of the invention are known or can be obtained by known processes (Organic Reactions, Vol. 16, S94-96, John Wiley & Sons, Inc. New York-London -Sydney), The majority of the precondensates used for the process corresponds to the general formula where R1 has the meaning given above.

As aldehydes of these precondensates z. B. called: acetaldehyde , Propionaldehyde, butyraldehyde, isobutyraldehyde, valeraldehyde, hexanal, heptanal. In addition, tSAlkylacroleins can also be used.

Formaldehyde and higher aldehyde are used to produce the precondensates combined with one another in a molar ratio of 1: 0.6 to 1: 1.2, preferably in the presence of water and / or methanol and preferably in the presence of a basic or acidic condensation catalyst. The precondensates are produced in a known manner Way. In general, weakly acidic catalysts such as formic acid, Acetic acid, ammonium chloride or weakly basic catalysts such as aluminum oxide, Magnesium oxide, sodium carbonate, sodium hydrogen carbonate, potassium carbonate are used. But also amines such as butylamine, diethylamine, dimethylamine, methylamine or ammonia can be used. Secondary or primary amines can also be used in opposite the higher aldehyde equivalent amounts are used, so that Mannich bases form as condensates. The condensates formed are non-volatile and more hydrophilic as the starting aldehydes of the general formula R1-CH2-CHO For the process of Invention particularly suitable starting products are obtained, for example, when a mixture of 30-40% strength by weight aqueous formaldehyde and the higher aldehyde in Presence of 0.5-3% by weight of potassium carbonate or ammonium chloride for 1-3 hours at 80 ° C be stirred.

In general, for the preparation of the precondensate per mole of aldehyde 0.12 to 1 mole of catalyst was added. Appropriately becomes this not removed prior to the inventive conversion to pyridine.

Particularly suitable amines for the process of the invention are methylamine and dimethylamine. However, the reaction is preferably carried out with ammonia. The amount of amine or ammonia used is generally from 0.5 to 10 (preferably 0.8 to 5) moles per mole of precondensate. Of course you can too any mixtures of the above amines can be used. Because of the volatility of the amines used, the reaction is carried out under pressure.

The reaction time depends on the other reaction conditions between about 1 and 20 (preferably 3 to 12) hours. Naturally, they are all the more shorter reaction times to be expected, the higher the chosen reaction temperature. The order in which the reaction components are combined is arbitrary.

The mixture of the reaction components prepared at room temperature can be used - Pre-condensate plus NH3 or amine - heat to the desired temperature or Submit the basic component and add the precondensate at a higher temperature.

In the case of a discontinuous procedure, the precondensate is preferably used Submitted together with water and / or methanol, ammonia or amine pressed on and heated up.

It is particularly preferred to carry out the process continuously under pressure in a tubular reactor. For this purpose, the components are fed via metering pumps fed into a pressure pipe, in which the conversion to pyridine at 180 - 350 ° C, preferably 220-300 whether takes place in the liquid phase.

Depending on the volume of the pipe and the dosing speed the desired residence time of about 10 minutes to 10 hours can be achieved without difficulty to adjust. The reaction product is drained off via an expansion valve. Excess ammonia or amine can be recycled, as can unreacted starting material or water-soluble intermediates.

The process can be carried out without a catalyst. Advantageous read However, acidic catalysts with a pKa value of less than 6 (preferably less than 3.0) applied. If necessary, these can already be used in the precondensate be included in its manufacture. Is the production of the pre-condensate in In the presence of a basic catalyst, it is expedient to use the for Acid catalyst used was added before the further reaction.

A wide variety of acidic catalysts can be used, such as sulfuric acid, selenic acid, hydrochloric acid, hydrobromic acid, hydriodic acid, Perchloric acid, arsenic acid, pyrophosphoric acid, ammonium chloride, benzenesulfonic acid, o-aminobenzenesulfonic acid, picric acid, naphthalenesulfonic acid, o-nitrobenzoic acid, Dichloroacetic acid, trichloroacetic acid, formic acid, lactic acid, acetic acid, trichlorophenol, Oxalic acid, succinic acid, phosphoric acid, phosphorous acid, methanesulfonic acid, Ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, p-toluenesulfonic acid. These Catalysts are preferably used in the form of their ammonium or amine salts ((R) 3N). In general, they are used in a concentration of 0.05 to 0.8 (preferably 0.1 to 0.5) moles per mole of the compound (R) 3N.

The catalysts are advantageously preferably homogeneous in the reaction mixture solved; However, insoluble solid catalysts such as acidic Aluminum oxide, silica, acidic carbon blacks are used in suspension.

The presence of polar solvents such as water, methanol, methanol, Propanol, isopropanol is required. Water and / or methanol are preferred, in particular But water. Ammonia and amines can be used in the form of aqueous solutions will. However, the amount of the solvent should, if possible, match the amount of the reactants not significantly exceed. In addition, non-polar solvents, e.g. (Chlorine) hydrocarbon fractions can also be used.

The 3,5-dialkylpyridines obtained can be removed from the reaction mixture easily separate in the usual way, e.g. by distillation or extraction with non-polar solvents; e.g. gasoline, methylene chloride or toluene. Particularly beneficial is the work-up by steam distillation at 100-1600C with if necessary superheated steam and optionally salting out the aqueous phase. You get here directly 3,5-dialkylpyridines in a purity of 70-90%, which no longer need to be cleaned for many further conversions. For example the upper phase of the steam distillate can be converted directly to dinicotinic acid oxidize.

Since the steam distillate has no isomers that are difficult to separate Contains dialkylpyridines, a 90 can easily be obtained by a simple distillation - 99% product obtained.

It is easily possible to produce the formaldehyde precondensate and its further conversion to dialkylpyridine continuously in one operation perform.

For this purpose, for example, at one end of the reaction tube, the both aldehydes together with water and optionally the condensation catalyst fed in. After the required residence time, if necessary at temperatures from 200 to max. 3500C, preferably 200 to 1000C and below pressure ammonia is then preferably added in the middle part of the tube and at temperatures between 180-3500C, preferably 220-300 ° C, the pyridine synthesis is carried out.

3,5-Dialkylpyridines are extremely valuable for technology Products. They are used as solvents, catalysts and cocatalysts, optionally in the form of metal complex salts, and as intermediates e.g.

for the synthesis of pesticides, dyes and for production of precursors for temperature-resistant polymers. Are of particular importance 3,5-dimethylpyridine or mixtures of 3-methyl-S-ethylpyridine and 3,5-diethylpyridine as a precursor to the production of pyridine-3,5-dicarboxylic acid and its derivatives. Mixtures of different 3,5-dialkylpyridines can easily be used for this purpose are used, which according to the invention from precondensates of formaldehyde with various higher aldehydes having a free ethylene group, e.g. Mixtures of propionic and butyraldehyde are obtained.

The temperature data in the examples relate to C.

Example 1 A reaction of 72 g of n-butyraldehyde (1 mol), 82.5 g of 40% strength by weight aqueous formaldehyde solution (1.1 mol) and 40 g of ammonium chloride Aqueous precondensate formed by heating at 120 ° C. for one hour is mixed with 51 g (3 Nol) liquid ammonia and in the stainless steel autoclave 10 hours to 2700 heated. After cooling, the two-phase reaction mixture is subjected to steam distillation subject. The upper organic phase is dried over solid KOH. Yield: 32 g. The gas chromatographic analysis shows a content of 80.4 56 3,5-diethylpyridine and 1.4% 3-methyl-5-ethylpyridine. This corresponds to a yield of 39 56 the Theory.

Example 2 The procedure is as in Example 1, but the Precondensation in 2 hours at room temperature and therefore only incomplete. Man receives 18 g of dry upper phase with a content of 62.0 96 and 3,5-diethylpyridine 6.3 56 3-methyl-3-ethylpyridine. This corresponds to a theoretical yield of 18 56.

Example 3 One made from 72 g of n-butyraldehyde, 89.1 g of dimethylamine hydrochloride and 82.5 g of 40% strength by weight aqueous formaldehyde solution obtained at 500 within 6 hours Precondensate is together with 180 g of aqueous dimethylamine solution (50 Gew.56ig) in Stainless steel autoclave heated to 2700 for 10 hours. After steam distillation 24 g of upper phase dried over potassium hydroxide were obtained. The product contains 70 * 1 % 3,5-diethylpyridine and 2,496 3-methyl-5-ethylpyridine. Yield: 26% of theory

Example 4 One of 36 g of n-butyraldehyde, 41 g of 40% by weight formaldehyde, 20 g water and 40 g ammonium chloride by standing at room temperature for 24 hours The pre-condensate produced is stored in a stainless steel autoclave with 51 g of ammonia for 10 hours heated to 2700. After working up according to Example 1, 32 g of a product are obtained which contains 71% 3,5-diethylpyridine and 4.5% 3-methyl-5-ethylpyridine. Yield: 35, d. Th.

Example 5 360 g (5 mol) of n-butyraldehyde, 450 g (6 mol) of 40% by weight Aqueous formaldehyde solution and 100 g of ammonium chloride are in the autoclave for 1 hour The precondensate is then cooled to 600 and after addition of 255 g (15 mol) of liquid ammonia heated to 1800 for 5 hours. After work-up according to Example 1, 90 g of a product which contains 3,5-diethylpyridine are obtained. Both the organic and the aqueous phase contain intermediates give 3,5-diethylpyridine when heated with ammonia. Under the chosen conditions at 1800 it is therefore advisable to carry out the process continuously Return of the aqueous phase to the reaction.

Example o 360 g of n-butyraldehyde (5 mol), 450 g of 40% formalin and 20 50 g of aqueous dimethylamine solution are heated to 1300 in the autoclave for 3 hours. The precondensate is then cooled to 600 and after adding 255 g of liquid Ammonia heated to 2800 for 8 hours. After working up as in Example 1, one obtains 139g of a product, which 48.5 96 3.5-diethylpyridine and 2.0% 3-methyl-5-ethylpyridine contains. Yield: 21% of theory.

Example 7 116 g propionaldehyde (2 moles), 165 g 40 96 formalin and 40 g of ammonium chloride are heated to 1000 for 1 hour in a stainless steel autoclave. To Cooling to 600, 136 g of liquid ammonia are printed and 8 hours to 2800 heated. After working up according to Example 1, 24 g of a product are obtained which Contains 60% 3,5-dimethylpyridine. Yield: 11% of theory.

Example 8 The procedure is as in Example 7, but using 228 g heptanal (92 fig) worked. The 3,5-diamylpyridine formed is by adding extracted from 100 g of cyclohexane and obtained pure therefrom by distillation. Yield: 25 g, corresponding to 12.5% of theory.

Claims (10)

Claims Process for the preparation of 3,5-dialkylpyridines of the general formula where R1 and R2 stand for a straight-chain or branched alkyl radical with 1 - 6 carbon atoms from precondensates of formaldehyde and ammonia, characterized in that precondensates of formaldehyde with a free t-methylene group having higher aldehydes of the general formula R1- CH2-CHO in which R1 has the meaning given above, with compounds of the formula where R is hydrogen and a maximum of 2 of the radicals are methyl, or mixtures of such compounds are reacted in the presence of water and / or lower alcohols in the liquid phase at 180-3500C under elevated pressure. 2. The method according to claim 1, characterized in that the liquid phase condensation carried out in the presence of the catalysts used in the preparation of the precondensate will. 3. The method according to claim 1, characterized in that the liquid phase condensation is carried out in the presence of acidic catalysts. 4. Process according to Claims 1-3, characterized in that one for the production of 3,5-dimethylpyridine from a formaldehyde-propionaldehyde precondensate and ammonia and / or methylamine in the presence of water and / or methanol a pressure of 10 - 300 atm. 5. Process according to Claims 1-4, characterized in that one for the preparation of a mixture of 50 - 99% 3,5-diethylpyridine and 1 - 50 46 3-methyl-5-ethylpyridine from a formaldehyde-n-butyraldehyde precondensate and ammonia and / or methylamine works in the presence of water and / or methanol at a pressure of 10-300 atm. 6. The method according to claims 1-5, characterized in that at 50 - 150 atmospheres are worked. 7. The method according to claims 1-6, characterized in that at 220 - 3000C is worked. 8. The method according to claims 1-7, characterized in that the Reaction components are fed into a tubular reactor together with water, those formed during the liquid phase condensation are insoluble in the aqueous phase Removed reaction products and the aqueous phase in the reactor is returned. 9. The method according to claim 8, characterized in that the reaction is carried out in the presence of a water-insoluble non-polar solvent. 10. The method according to claim 8, characterized in that the reaction components fed in continuously, the 3,5-dialkylpyridines as a non-aqueous phase continuously be withdrawn while the aqueous phase is recycled.