DE2225695A1 - PROCESS FOR THE MANUFACTURE OF HALOGENATED BENZONITRILE - Google Patents

Description

, ASSOCIATES

DR. I. MAAS DR. F. VOITHENLEJTNER

8 MUNICH 40 SCHLEISSHEIMER STR _. 299: TEL 3592201/205

B-22 226

Jefferson Chemical Company, Inc., Houston, Texas, V.St.A. Process for the preparation of halogenated benzonitriles

The invention relates to the production of halogenated benzonitriles.

In Japanese patent specification / 22 591, the manufacturer is. ment of pentachlorobenzonitrile by reaction of vaporous tolunitriles with chlorine gas at temperatures from 200 to 400 ⁰ C in the presence of a catalyst described. The patent states that pentachlorobenzonitrile is useful as a chemical for agricultural use as well as a raw material for the manufacture of heat-resistant resins.

In the article "Thermal Stability of Some Organic Compounds", Journal of Chemical and Engineering Data, 7, 227 (1962) indicated that benzonitrile decomposed in the gas phase at 570 to 600 ⁰ C.

Our own laboratory tests initially carried out showed that benzonitrile was effective under the most varied of reaction conditions compared to chlorine even in the presence of

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Chlorination catalysts are quite stable when attempting the chlorinations in the liquid phase perform. The process according to the invention carried out at high temperature in the gas phase represents an improvement compared to the prior art in so far as no catalyst is required. This is not necessary expensive purification processes, and in addition, both extremely high yields as well Sales achieved.

The invention relates to a process for the preparation of halogenated benzonitriles by reacting a halogen with benzonitrile or a partially halogenated derivative of benzonitrile in the gas phase, which is characterized in that the reaction of the halogen with the benzonitrile is carried out in an open reaction tube which is heated to a temperature of 650 to 850 ^{° C.}

Benzonitrile or partially halogenated benzonitrile can by the action of a halogen, in particular of Chlorine, can be halogenated smoothly at high temperature in the gas phase in the absence of a catalyst. The = ,, non-catalytic gas phase chlorination of benzonitrile can be carried out so that pentachlorobenzonitrile of high purity is formed. As stated in the literature The decomposition temperature of benzonitrile is 570 to 6OO C, it had to be assumed that in the invention High-temperature processes a decomposition of the starting material take place and as a result of the expected Cleavage of the benzonitrile hexachlorobenzene would be obtained.

The following examples show the conditions that exist in various gas phase reactions between * chlorine and

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Benzonitrile can be used in the presence of nitrogen as a diluent. The implementations are in one

(TU

533x25mm pipe made of Vycor ^v 'carried out _K which is heated in its entire length from the outside by an electric furnace. The maximum temperature given in the examples is that which occurs at about the middle of the reaction tube. In all examples, the chlorine is injected into the reactor and measured using a rotometer. The benzonitrile is pumped into an evaporation vessel with the aid of a Dosierpumjp (Ruska). The gaseous benzonitrile is mixed with nitrogen - which is also introduced into the evaporation vessel. The gaseous mixture of benzonitrile and nitrogen is then passed to the reactor inlet where it comes into contact with the chlorine. Chlorine, benzonitrile and nitrogen then flow through the open reaction tube and the halogenated product formed is collected in a water scrubber. The purity of the product obtained is determined by gas-liquid chromatography. It is found that the portion of the product which does not consist of pentachlorobenzonitrile is a mixture of less strongly chlorinated benzonitrile products.

The invention is explained in more detail with the aid of the following examples. Under the conditions used is the Yield (conversion of benzonitrile to chlorinated benzonitrile) at or near 100%.

example 1

A mixture of 91.2 l / h chlorine, 173.1 l / h nitrogen and 12 ml / h benzonitrile is introduced into a tubular reactor system made of Vycor glass (533x25mm), that with an electric oven for about 4.8 hours

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a maximum reactor ^{temperature of 721 0} C is heated. The material emerging from the reactor is passed through a collection system that leads to a sodium hydroxide scrubber. 159.0 g (yield 99.4%) of colorless pentachlorobenzonitrile, which ^{melts at 212 to 214 °} C., are obtained.

Analysis for C ₇ Cl ₅ N:

calc .: Cl 64.34%;
found: Cl 64.3%

After recrystallizing twice from chlorobenzene, the melting point of the substance is 214 to 214.5 C.

Analysis for C ₇ Cl ₅ N:

Calculated: C 30.53%; Cl 64.34%; N 5.09%; Found: C 30.71%; Cl 63.88%; N 5.03%.

The purity of the pentachlorobenzonitrile is accordingly over 96%. In addition, the gas chromatographic shows Analysis of the crude reaction product that the benzonitrile conversion is complete, d. H. 100%.

Example 2

The reactor and collection system described in Example 1 are also used in the following described halogenation applied:

Benzonitrile (32.0 ml / h), chlorine and nitrogen in a molar ratio of 1: 19.2: 20.3 are introduced into the reaction tube at a maximum reactor temperature ^{of 741 ° C. for 4 hours.} There are 341 g (yield 99.7%)

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Pentachlorobenzonitrile isolated with a purity of 95%. The benzonitrile conversion "is 100%.

Any halogen can be used to carry out the process of the invention. The preferred halogen is chlorine.

A diluent can be introduced into the reaction zone along with the gaseous halogen and the gaseous benzonitrile. The diluent must be behave inertly in the reaction between the halogen and the benzonitrile and at the reaction temperature be gaseous. Suitable diluents are, for example, nitrogen and hydrogen chloride.

The degree of halogenation and the percentage conversion of the benzonitrile to the halogenated benzonitrile is determined by the temperature used during the conversion, the ratio of reactants and the throughput rate are determined. Since the invention Process subjected to several different reactants and thereby several different products can be obtained, there can be no general validity Specify parameters. The reaction conditions to be used in the individual case can, however, be in a simple one Preliminary test can be determined without further ado.

At a minimum temperature above the boiling point of benzonitrile and HaIOgCnS ₇ about 400 ° C., the reactants begin to react with one another in the gas phase, so that a partially halogenated benzonitrile is obtained in low yield. The yield and degree of halogenation increase with increasing temperature. A further increase in temperature leads to a practically 100 percent yield of halogenated benzonitrile. If the temperature is increased even further,

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the degree of halogenation also reaches a value of about 100%. As already mentioned, the temperature at which a yield of about 100% and halogenation of about 100% takes place, namely from 650 to 850 ^° C., is considerably above the decomposition temperature of the aromatic compound and the halogenated aromatic compound reported in the literature, and yet there is no decomposition in the process according to the invention. The preferred maximum temperature at which an approximately 100 percent yield of approximately 100% halogenated benzonitrile is obtained is approximately 850 ^° C. If desired, however, higher temperatures can also be used. In carrying out the chlorination at comparable ratios of chlorine to comparable benzonitrile and contact times of the maximum temperature in the reactor of 702 to 719 ⁰ C is increased Reiriheit of Pentachlorbenzonitrils formed from 84.3% to 98.0% by increasing.

At the same temperature and the same ratio of the reactants The contact time can have effects comparable to the increase in temperature shortly after long to be changed. The same applies to the ratio of halogen to benzonitrile.

By adjusting the chlorine and nitrogen levels of the feed gas appropriately, the ratio of chlorine to benzonitrile can be varied while maintaining the approximate contact time at three seconds. In a series of experiments, the ratio of chlorine to benzonitrile was changed within the range from 10: 1 to 34.6: 1, while the reaction ^{temperature was kept at about 720 + 6 °} C. and the approximate contact time was kept at three seconds. In all experiments of this kind the benzonitrile conversion was quantitative. Under

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$ 222,563

these reaction conditions resulted in an increase in the molar ratio of chlorine to benzonitrile of 10: 1 15: 1 an increase in the purity of the pentachlorobenzonitrile from 62.6 to 73.5%. By increasing the The ratio of chlorine to benzonitrile to 25: 1, the purity of the pentachlorobenzonitrile to 93.6% and by increasing the ratio of chlorine to benzonitrile to 35: 1 the purity of the pentachlorobenzonitrile increased to 96.1%. In order to obtain pentachlorobenzonitrile with high purity, the aim is therefore to the chlorination can be carried out in the presence of a relatively large excess of chlorine, preferably with a ratio of chlorine to benzonitrile of over 15: 1. The use of ratios of over 25: however, it is not necessary for the formation of high-purity pentachlorobenzonitrile. When pentachlorobenzonitrile with a purity of less than 100% can be achieved by increasing the reaction temperature Contact time and the ratio of chlorine to benzonitrile increases the purity of the pentachlorobenzonitrile will.

The purity of the pentachlorobenzonitrile formed • varies with the contact time. With a number of The contact time at a constant molar ratio of chlorine to benzonitrile of 34.5: 1 and a temperature of 710 + 6 ° C. An increase in the contact time from 1.4 to 2.6 seconds resulted in an increase in the purity of the pentachlorobenzonitrile from 75.7% to 94.9%. The Benzonitrile Conversion was quantitative in these experiments.

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Claims (3)

Patent claims A process for the preparation of halogenated benzonitriles by reaction of a halogen with benzonitrile or a partially halogenated benzonitrile in the gas phase _f characterized in that the halogen with the benzonitrile in an open reaction tube bsi a temperature 650-850 ⁰ C is reacted. 2. The method according to claim 2, characterized in that that one reacts chlorine with benzonitrile. 3. The method according to claim 2, characterized in that chlorine with benzonitrile to pentachlorobenzonitrile implements. 309884/141 1