DE1270022B - Process for the preparation of alpha-bromoalkylaryl ketones - Google Patents

Description

Process for the preparation of a-bromoalkylaryl ketones It is known z-bromoalkylaryl ketones by bromination of alkylaryl ketones in the presence of solvents, such as carbon tetrachloride, ether, carbon disulfide or glacial acetic acid. As can be seen from "Chemischeberichte", 86 (1953), p. 1558, it is necessary to achieve this high yields of alkylaryl ketones brominated in the side chain alone are necessary, that the alkylaryl ketone to be brominated is in high dilution. To side reactions To avoid this, it is also necessary in this process to reduce the bromine very slowly and to be introduced into the reaction mixture with cooling. Nevertheless it is necessary Briefly heat the reaction mixture at the beginning of the addition of bromine to the induction time abbreviate the response. In some cases this goal can also be achieved thereby that a small amount of hydrogen bromide is added to the reaction mixture.

The use of solvents in the bromination of alkyl aryl ketones however, has at least the disadvantage that the solvent after the end of the bromination must be separated from the o; -Bromoalkylarylketonen again. The α-bromoalkylaryl ketones are in the vast majority of cases liquid and have lacrimogenic effects.

Because of this effect and the strong odor of the os-bromoalkylaryl ketones the solvents separated from these by distillation can at most again used for the bromination of the same alkylaryl ketone but not for any other purpose will. In addition, in order to protect the personnel working with it, it is desirable lacrimogenic substances in as few operations as possible and as few as possible Generate reaction volumes.

According to the procedure of the German Auslegeschrift 1 164 381, as Diluent used in the end product of the bromination. For this purpose the bromine fed to the mixture of diluent and alkylaryl ketones, whereupon the bromination is carried out with forced circulation of the diluent. In this procedure a slight bromine deficit must always be maintained compared to the theoretical amount. In addition, this process can only be carried out continuously, whereby a complicated device that can only be used for this process can, is necessary.

Such continuous circulation devices are prone to failure and require extremely precise dosing of the individual reactants. In the case of the discontinuous Working method is with by-products by overhalogenation and condensation too calculate.

It has therefore been looking for ways to avoid the hitherto in the Production of oc-bromoalkylaryl ketones sought disadvantages occurring.

It became a process for the preparation of oc-bromoalkylaryl ketones in addition to gaseous hydrogen bromide through the reaction of alkylaryl ketones with bromine found at temperatures from -20 to + 80 ° C, which is characterized in that in the absence of solvents or diluents, alkylaryl ketones and bromine with one another are reacted in a molar ratio of 0.9: 1 to 1: 1 and that during the reaction resulting hydrogen bromide is collected, while the oc-bromoalkylaryl ketone after is distilled off from the reaction mixture when the reaction has ended.

The process according to the invention can be used to produce alkylaryl ketones brominate, the at least one substitutable in the a-position of the side chain Own hydrogen atom. The alkylaryl ketones can contain halogen atoms, hydroxy, Carry amino or alkyl groups as substituents. Such alkyl aryl ketones are, for example Acetophenone, propiophenone, 1-chloroacetophenone, 1,3,5-tribromopropiophenone or 4-methylpropiophenone.

To carry out the method according to the invention, the relevant Submitted alkylaryl ketone and slowly fed bromine to him with stirring.

The amount of bromine to be fed per mole of alkylaryl ketone is 0.9 to 1 mol. During the bromination, a temperature of -20 in the reaction mixture Maintained up to + 80 ° C. During the addition of the first half of the amount of bromine is this requires cooling. During the bromination, it escapes from the reaction mixture pure gaseous hydrogen bromide that is collected.

After the addition of bromine is complete, nitrogen is passed through for some time the reaction mixture passed to remove all of the hydrogen bromide to remove the reaction mixture. After the escaping gas is no or only still contains traces of hydrogen bromide, the introduction of nitrogen is stopped. The reaction mixture is then distilled, advantageously under reduced pressure.

The desired o; -bromoalkylaryl ketone is usually in the form of a distillate a colorless liquid. To avoid decomposition during the distillation Avoid, it may be advantageous to add the reaction mixture before the distillation 100 parts by weight of the alkylaryl ketone used still 1 to 5 parts by weight of a lower, aliphatic epoxides, such as ethylene oxide, propylene oxide, epichlorohydrin, Epibromohydrin, to be added.

In the method according to the invention, the amounts used are Bromine based yields 95 to 98% of theory of pure monoo; -Bromoalkylarylketon, which, according to gas chromatographic analysis, has a purity of 98 to 99% and practically free from dibromoalkylaryl ketones and completely free from core substitution products is. It is surprising that when carrying out the bromination according to the invention obtained such high yields of pure mono-o; -bromoalkylaryl ketones from alkylaryl ketones will. According to the known state of the art, it should rather have been expected that the desired bromination products are strongly influenced by undesired dibromoalkylaryl ketones and are contaminated by nuclear brominated derivatives. So far it has always been assumed that pure products are only available when the reactants are in great dilution react with each other. However, it is possible with the method according to the invention have become both to save the solvents and the conversion vessels smaller to dimension or a larger amount of substance in conversion vessels of the same size to brominate in the unit of time. In addition, according to the method according to the invention also obtained high yields of pure, gaseous hydrogen bromide, which is a technical is a valuable by-product that is easy to utilize. Will the bromination oppose it in organic solvents, such as glacial acetic acid, carried out, so dissolve there are large amounts of hydrogen bromide in it, so that both the solvent as the hydrogen bromide is obtained in a form that can hardly be used technically.

The process according to the invention is illustrated below by means of examples explained in more detail.

Example 1 In a glass-lined reaction vessel fitted with a stirrer is provided, 134 ge parts of propiophenone (1 mole) submitted and him within 162 parts by weight of bromine (1.018 mol) were slowly added with stirring from 1 to 2 hours.

During the entire reaction, the reaction mixture increases a temperature of about 25 "C, including during the addition of the first 80 parts by weight Bromine must be cooled. When the addition of bromine is complete, the reaction is mixed stirred for a short time and then passed nitrogen through the reaction mixture. The pure hydrogen bromide escaping here and already with the addition of bromine becomes collected. After about 1 hour the escaping gas is free of hydrogen bromide, whereupon the introduction of nitrogen is ended.

After adding 5 parts by weight of epibromohydrin, the reaction mixture becomes distilled under reduced pressure.

There are 208 parts by weight = 97.5 01o of theory of ov-bromopropiophenone with a bromine content of 37.8 percent by weight and a boiling point of 80 "C obtained a pressure of 0.3 Torr as a colorless, liquid distillate. According to the gas chromatographic Analysis the purity of the or-bromopropiophenone is 990 / o.

Example 2 Following the procedure given in Example 1 are 268 parts by weight of propiophenone (2 moles) reacted with 324 parts by weight of bromine (2.03 moles). The reaction mixture obtained in this way is immediately after the introduction of nitrogen has ended distilled without adding epoxy.

There are 363 parts by weight = 85% of theory of o; -bromopropiophenone with a boiling point of 78 to 80 ° C at a pressure of 0.3 Torr as colorless, get liquid distillate. According to the gas chromatographic analysis, the Purity of the a-bromopropiophenone 98.3%.

Claims (1)

Claim: Process for the preparation of α-bromoalkylaryl ketones in addition to gaseous hydrogen bromide through the reaction of alkylaryl ketones with bromine at temperatures from -20 to +80 "C, characterized by that in the absence of solvents or diluents, alkylaryl ketones and bromine with one another in a molar ratio from 0.9: 1 to 1: 1 are reacted and the hydrogen bromide formed during the reaction is collected, while the a-Blomalkylarylketon after completion of the reaction from the Reaction mixture is distilled off. Publications considered: German AusIegeschrift No. 1 164388.