DE1206434B - Process for the production of bipyridyls - Google Patents

Description

Process for the preparation of bipyridyls It is known that bipyridyls by oxidation of reaction products of sodium and pyridine can. There are already processes for the production of bipyridyls by oxidation of reaction products of magnesium and pyridine and aluminum and pyridine have been proposed been.

It has now been found that on the usual oxidation level, which for used the conversion of the reaction products of metal and pyridine into bipyridyls waived, and this can be replaced by a treatment with water, practically in the absence of an oxidizing agent such as air or oxygen. This process produces bipyridyls with practically no reduction in yield Comparison with the known working methods achieved, and the long air oxidation process and the use of conventional oxidizing agents is not required.

The invention relates to a process for the production of bipyridyls, which is characterized in that a metal-pyridine reaction product which is on at least 70 ° C has been heated in the presence of a free pyridine, with at least 1 mole of water per equivalent of metal is treated.

From the work of E m e r t in Ber., 50 (1917), p.31, it is known treat a reaction product of sodium and pyridine with moist ether. That so treated product was made by reacting sodium with an excess of pyridine prepared, whereupon the excess pyridine was removed; both treatments were practically carried out at room temperature. The residue of the sodium-pyridine reaction was heated under reduced pressure and thus converted into a second sodium-pyridine reaction product convicted. In this process the product obtained is not a bipyridyl, but a tetrahydrobipyridyl.

The upper temperature limit is usually determined by the boiling point of the Mix set; but this can be done by heating under pressure or by addition higher boiling diluents are increased. If with a very responsive Metal, like sodium, is worked, which works with pyridine below this temperature can convert, if necessary, heat is added to keep the temperature the mixture increases accordingly. This warming can occur during or after Implementation take place. In the case of less reactive metals such as aluminum and magnesium, the required elevated temperature is usually during the Metal-pyridine conversion stage reached.

The free pyridine can be present in excess of the amount required for Formation of the metal-pyridine reaction product is used.

The pyridine is preferably composed of pyridine itself, but can Other pyridine compounds can also be used, insofar as they are compatible with the selected Metal react, e.g. B. alkyl pyridines. In general, however, are alkyl pyridines less reactive than pyridine itself in the present process.

The metal-pyridine reaction product can be a sodium-pyridine, magnesium-pyridine or aluminum-pyridine reaction product; but are also conversion products of other metals, as long as they react with the pyridine, for example those which are derived from the other alkali metals. These conversion products can by reacting the metal and the pyridine with heating and optionally be prepared in the presence of a diluent from an excess of pyridine or z. B. trimethylbenzene may exist. The metals can be pure or be alloyed metals. The reaction of magnesium with pyridine can start up the reaction be too slow and then by adding a small amount of an initiator be encouraged, especially a substance that causes the formation of free radicals promotes in the mix, such as sodium, potassium, or bromine Iodine. In The reaction of aluminum and pyridine through a compound can also be carried out in a similar manner are introduced, which destroys the surface oxide film of the metal, for example by a mercury compound such as mercury chloride, optionally together with an initiator, whereby free radicals are formed in the mixture.

The process is advantageously carried out using a metal-pyridine reaction product carried out in which the excess pyridine used for its preparation has not been removed prior to treatment with water. Be that way Problems avoided by the isolation of the metal-pyridine reaction product can arise. In the case of sodium-pyridine reaction products, when touched are highly explosive with air, this is particularly important for safety reasons.

The treatment of the metal-pyridine reaction product with water is preferably carried out at an elevated temperature, which is at least 40 ° C and especially between 80 and 120 ° C. The upper temperature limit here becomes common determined by the boiling point of the reaction mixture; this can rise to over 120 ° C be increased, e.g. B. by adding higher-boiling diluents such as dimethylaniline, or by applying positive pressure. Thus, the present method can also be used for Temperatures above 120 ° C can be carried out. When using temperatures below 40 ° C, the reaction mixture tends to become too thick and lumpy. In this In this case, the implementation is difficult to complete.

The treatment of the metal-pyridine reaction product with water can carried out in a simple manner by mixing at the desired elevated temperature will. The metal-pyridine reaction product and the water can initially be mixed at a lower temperature and then or simultaneously to the desired increased temperature. This warming can be used in a subsequent treatment, for example in a distillation treatment, and does not necessarily have to be during of the treatment stage, although that which occurs during the water treatment violent reaction is a convenient source of heat. Preferably the method carried out so that cold water slowly stirring the metal-pyridine reaction product is added at such a rate that the mixture is at the desired rate Temperature is maintained without overheating. This can be used for cooling.

The metal-pyridine reaction product or the still an excess of pyridine-containing mixture can before treatment with water with an inert Liquid to be diluted. Inert liquids suitable for this purpose are Hydrocarbons such as trimethylbenzenes.

The amount of water should be at least 1 mole and preferably between 1.75 and 2.5 moles per equivalent of metal in the metal-pyridine reaction product. If desired, larger amounts can also be used, but such a strong dilution can make the subsequent isolation of the product difficult. If smaller amounts are used, the reaction will be less complete and the reaction mixture will be thicker and less easy to handle. . In the case of the treatment of a sodium-pyridine reaction product, it has been found to be particularly advantageous to use an amount of water which is essentially 2.2 moles per equivalent of sodium used. If such an amount of water is used, the sodium hydroxide which forms during the treatment separates out as a liquid phase, which contains essentially all of the water, so that the liquid organic phase, which contains the bipyridyls and the excess pyridine, remains practically dry. If the amount of water is decreased, the sodium hydroxide will tend to separate out in solid form, and if the amount of water is increased, the organic phase will retain more water. This embodiment of the method is particularly advantageous because it results in a very simple and effective separation of the sodium hydroxide and a chemical treatment and cumbersome filter treatments are avoided; nor is it necessary to include a special dry treatment before the further treatment of the crude bipyridyl-pyridine mixture, for example by distillation, takes place. In this case, the mixture, which is obtained by treating the metal-pyridine reaction product with water, can be kept at a temperature above 80 ° C., but below the boiling point of the mixture and preferably at 100 ° C., whereupon the mixture is in can separate two liquid phases, the aqueous sodium hydroxide solution is separated and removed. As mentioned, the mixture is expediently kept hot, which reduces the possibility of the aqueous sodium hydroxide phase solidifying and the organic phase is obtained with only 0.1 to 0.2 percent by weight of water.

The exclusion of air and oxygen can be up to a satisfactory level Degree done by the fact that the process is carried out in a vessel which has been flushed with nitrogen and also during the addition of water a slow stream of nitrogen is passed through the reaction vessel.

There is no need to take precautions for total exclusion of air or oxygen, because the presence of small traces these gases, dissolved in nitrogen or in water, are not harmful. Of the The process of implementation is not clear, but implementation is very rapid and usually finishes in an hour.

The isolation of the bipyridyls can be carried out in a known manner , for example by fractional distillation and / or crystallization of the product. It is particularly useful to use the crude product containing the bipyridyls first dissolve in dilute acid and separate the insoluble components, then neutralize the resulting dilute acid solution and with a Water immiscible organic solvent, preferably at elevated temperature, to extract. The bipyridyls are in this way in the form of a solution in the organic solvents which are immiscible with water can be obtained through Evaporation of the solvent can be obtained. The 4,4'-bipyridyl can be in the form its hydrate can be obtained, for example by adding water not to a cold solution of the mixed bipyridyls in the one with water mixable organic solvents such as those obtained by the extraction method mentioned above can be obtained.

The method forming the subject of the invention has the advantage that the conversion of pyridine into bipyridyls is simplified. Also many will Disadvantages and dangers of the previously known methods avoided; become special a long period of oxidation, formation of explosive pyridine-oxygen mixtures, Loss of pyridine and volatile products in the oxidant gas stream and the need to pass inert gases through the apparatus and the Avoided formation of by-products.

The crude mixture of bipyridyls produced by the present process obtained in certain cases contains a higher proportion of the 4,4'-isomer, than is the case with the raw bipyridyls, as is the case with the oxidation that has hitherto been customary have been manufactured.

The parts and percentages in the following examples relate focus on the weight. Example 1 46 parts of sodium metal (2 equivalents) were in Disperse in 92 parts of dimethylbenzene over 45 minutes to give 632 Parts of pyridine (8 mol) are added with stirring in a nitrogen atmosphere, so that a Temperature of 90 ° C was maintained. After the whole amount of sodium is added the mixture was kept at 90 ° C. for a further 15 minutes, with stirring, then 80 parts of water (2.2 moles per equivalent of sodium) were added continuously. The initially violent development of heat due to the reaction was dampened by cooling, so that the temperature of the mixture was kept between 85 and 90 ° C. The addition of water took place within 15 minutes, after which the mixture was stirred for a further 15 minutes became. The color of the reaction product changed with the addition of water from black to brown. The product was heated to 100 ° C and at this temperature held without stirring for 1 hour, whereupon the upper organic consisting of 740 parts Layer was separated from the lower aqueous layer consisting of 125 parts. Less than 1 part of the 80 parts sodium hydroxide that formed in the reaction, remained in the upper layer after separation, and less than 1 part of pyridine was withdrawn with the lower aqueous layer.

The organic layer was fractionally distilled; there were 476 Parts of pyridine recovered and a mixture of 0.2 parts of 2,2'-bipyridyl, 5 parts of 2,4'-bipyridyl and 49 parts of 4,4'-bipyridyl were obtained. Example 2 The way of working of Example 1 was repeated with the modification that the reaction between Sodium and pyridine and the subsequent addition of water were carried out at 100 ° C. There were 471 parts of pyridine recovered and a mixture of 0.2 parts of 2,2'-bipyridyl, 4 parts of 2,4'-bipyridyl and 42 parts of 4,4'-bipyridyl were obtained.

Example 3 A mixture of 12 parts of magnesium turnings and 395 Portions of pyridine was heated to reflux, the reaction going through Addition of 2 parts of a 33% dispersion of sodium metal in trimethylbenzene was initiated. The reaction was continued for 2 hours with a nitrogen flow was passed through the reaction vessel. Then 35 parts of water (2 mol per Equivalent of magnesium) was added with stirring over the course of 15 minutes resulting mixture stirred for an additional 15 minutes and then fractionally distilled. There were thus 288 parts of pyridine recovered and a mixture of 1 part of 2,2'-bipyridyl, 3 parts of 2,4'-bipyridyl and 41 parts of 4,4'-bipyridyl were obtained. This yield at 4,4'-bipyridyl corresponds to 38% of theory, based on the pyridine consumed. Example 4 A mixture of 36.4 parts of magnesium turnings and 1264 parts of pyridine was heated to reflux, the reaction by adding 3 parts of a 33% dispersion of sodium metal in trimethylbenzene was initiated. the Reaction was then carried out for 6 hours at a temperature of 105 to 110 ° C with initiation carried out by nitrogen. Then were stirred for 30 minutes 120 parts of water (2.2 moles per equivalent of magnesium metal) are added, the temperature the mixture was kept at 105 to 110 ° C. Part of the reaction product (a Half, d. H. 710 parts) was fractionally distilled. The Products consisted of 419 parts of pyridine and a mixture of 4 parts of 2,2'-bipyridyl, 12 parts of 2,4'-bipyridyl and 63 parts of 4,4'-bipyridyl. The yield of 4,4'-bipyridyl corresponds to 30% of theory, based on the pyridine consumed. Example s one Mixture of 132g dry pyridine (water content estimated 0.010 /, according to the Karl Fischer method) and 4 g of magnesium turnings were stirred and refluxed in a nitrogen atmosphere heated, with 2 cc of a 25 0 / jgen dispersion of sodium in trimethylbenzene added became. The reflux treatment was continued for 1 hour and 25 minutes; then the reaction mixture was cooled to 90 ° C, and over 10 minutes were 25 cc of water were added. Analysis of the product indicated that it was 14.3 g of 4,4'-bipyridyl contained. 100 g of unreacted pyridine was recovered. Example 6 The The procedure of Example 5 was repeated with the modification that the 200 ccm dry oxygen-free trimethylbenzene (a commercially available mixture of isomers) der hot reaction mixture were added, which was then cooled to about 20 ° C. with stirring and was stirred with 25 cc of water. 14.6 g of 4,4'-bipyridyl were obtained and Recovered 100 g of unreacted pyridine.

Example ? The procedure of Example 5 was followed to completion the reflux treatment repeated. Then the reaction mixture became for disposal of unchanged pyridine under reduced pressure up to a temperature of 80 ° C distilled and with 200 cc of dry, oxygen-free trimethylbenzene offset. The resulting mixture was cooled to room temperature with stirring and mixed with 25 cem of water at this temperature. There were 14.6 g of 4,4'-bipyridyl obtained and recovered 98 g of unreacted pyridine.

Example 8 The reaction of a mixture of 10 g of aluminum powder and 399 g of dry pyridine was initiated by adding 3 g of mercuric chloride and carried out at 116 ° C. for 33/4 hours. 25 grams of water was then added to the mixture. The amount of 4,4'-bipyridyl formed was 14.3 g, corresponding to a theoretical yield of 16%, based on aluminum, or 17%, based on pyridine consumed. Example 9 The reaction of a mixture of 10 g of aluminum powder and 150 g of dry pyridine was initiated by adding 3 g of mereurichloride, whereupon 150 g of N, N-dimethylaniline were added and the reflux treatment was carried out at 116 ° C. for 33/4 hours. The mixture was treated with 25 g of water. 1.7 g of 4,4'-bipyridyl were thus formed, which corresponds to a yield of 2 ° / a, based on aluminum, and 70 / " based on pyridine consumed. Example 10 The conversion of a mixture of 10 g of aluminum powder, 150 g of pyridine and 250 g of N, N-dimethylaniline were introduced by adding 3 g of mercuric chloride and the mixture was refluxed for 33/4 hours at 116 ° C. The resulting mixture was treated with 25 g of water. 9 g of 4,4'-bipyridyl obtained, which corresponds to a yield of 3%, based on aluminum, or 5 based on pyridine consumed.

Example 11 The reaction of a mixture of 10 g of aluminum powder and 528 g of dry pyridine was initiated by adding 3 g of meric chloride and 2 g of sodium. The mixture was refluxed for 21/2 hours and then 15 g of water were added. 14.3 g of 4,4'-bipyridyl were obtained, which corresponds to a yield of 16% of theory, based on aluminum, or 18% of theory, based on pyridine consumed.

Claims (1)

Claim: Process for the production of bipyridyls, thereby characterized in that a metal-pyridine reaction product heated to at least 70 ° C has been heated in the presence of a free pyridine with at least 1 mole of water per equivalent of metal is treated.