JPH046177B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides one guiding substituent (guide substituent) for inducing chloro groups at the ortho and para positions when producing an aromatic compound chlorinated at the para position.
This invention relates to a method for chlorinating aromatic compounds with substituent). Aromatic compounds chlorinated at the para position such as parachlorotoluene are used as pesticides,
It is known as a chemical intermediate in the production of dyes or pharmaceuticals. Said compounds can be used as such, for example paradichlorobenzene can be used as a deodorizing agent. The chlorination of aromatic compounds having ortho- or para-derivatizing substituents is usually carried out in the liquid phase in the presence of ferric chloride as the chlorinating agent. This technique is described in J.Gen.Chem.USSR 8 1780 (1938), CA 33
4037 (1939) or JACS, (1954), 5, 5491-94
discloses the chlorination of toluene or monochlorobenzene, but the technique suffers from the disadvantage that reaction products with relatively low para/ortho isomer ratios are obtained. To increase this para/ortho ratio, it has been proposed to combine ferric chloride with other metal chlorides such as TiCl ₄ or AlCl ₃ (J.Org.
Chem. (1961), 26 , 214-7). Finally, according to DE 2230369, aromatic compounds chlorinated in the para position, in particular parachlorotoluene, can be prepared by chlorinating toluene with FeCl ₃ promoted with AlCl ₃ using trichlorobenzene as the reaction solvent. Manufactured by The ferrous chloride must then be separated by filtration and carefully washed with carbon tetrachloride to ensure that not even traces of trichlorobenzene remain which could interfere with subsequent regeneration steps. .
This is because trichlorobenzene produces heavy products. Ferrous chloride is regenerated by suspending it in carbon tetrachloride and then chlorinating it. The ferric chloride formed then has to be passed again and then carefully washed with trichlorobenzene to remove carbon tetrachloride, which is susceptible to react with toluene in a Friedel-Crafts reaction promoted with _FeCl3 . . This conventional method has the disadvantage of having a complex working cycle caused by the necessity of using two solvents which must be removed and recovered in each case. According to the present invention, this drawback is solved in the chlorination process of aromatic compounds having one derivatizing substituent to induce chloro groups in ortho and para positions and in the regeneration process of ferrous chloride produced by chlorination. The aromatic compound is rescued by chlorination in the liquid phase with ferric chloride in the presence of a single solvent. Such processes are particularly useful for chlorinating toluene and monochlorobenzene for the purpose of producing parachlorotoluene and paradichlorobenzene. The solvent used must, of course, be totally inert to the reaction and is preferably a halogenated, i.e. chlorinated or fluorinated, solvent with a melting point below 50°C and a boiling point above 200°C. preferable. As a guide, mention may be made of solvents such as fluorinated oils, hexachlorobutadiene and hexachlorocyclopentadiene, which meet the above conditions. Solvents of this type are particularly useful in the chlorination of toluene and monochlorobenzene. This is because, apart from the simplification of the two reaction steps, the fact that the solvent has a higher boiling point than monochlorotoluene and dichlorobenzene allows the reaction product to be removed without first having to distill off the solvent. This is because they can be separated. In this case, the products of the synthesis are first recovered by distillation, and the residual solvent can be directly recycled many times without purification after regenerating the ferric chloride in situ. By way of example, this type of synthesis is known per se and described in numerous publications, such as French Patent No. 2,144,709;
In step (2), an aromatic compound having one derivatizing substituent for deriving a chloro group in the ortho and para positions is reacted with ferric chloride in the presence of a solvent according to the invention. The produced chloroaryl compounds are recovered by fractional distillation, and unreacted aromatic compounds are recycled. In the second step, the ferrous chloride formed and dispersed in the solvent of the distillation residue is regenerated in situ by chlorination to form ferric chloride, and finally the solvent and ferric chloride are combined. and recirculate. The accompanying drawing is a flow sheet illustrating a complete reaction cycle when chlorinating toluene or monochlorobenzene. In the figure, 1 is FeCl ₃ in hexachlorobutadiene.
and toluene or monochlorobenzene, 2 is a fractional distillation process, 3 is a _FeCl2 regeneration process, 4 is a toluene or monochlorobenzene supply pipe, and 5 is a chlorine supply pipe. , 6 is a take-off pipe for monochlorotoluene or dichlorobenzene, 7 is a discharge pipe for excess chlorine, 8 is a recirculation pipe for unreacted toluene or monochlorobenzene, and 9 is a recirculation pipe for regenerated _FeCl3. It is. Ferric chloride can react with AlCl ₃ , TaCl ₅ , without any disadvantage and without affecting the reaction working cycle.
It can be used in conjunction with known catalysts selected from metal chlorides such as TiCl ₄ , MoCl ₄ , HfCl ₄ , WCl ₆ and GaCl ₃ . The invention is illustrated by the following examples, in which yields are given in weight percent. Example 1 700 g of hexachlorobutadiene heated to 80° C. are contacted with 2 moles of anhydrous ferric chloride and 30 g of TiCl ₄ in a reactor. At this temperature 1.3 mol of toluene is introduced in 30 minutes. The mixture is then diluted with approx.
Hold at 90-110°C for an hour or until the release of hydrochloric acid has ended. The mixture is degassed for 30 minutes with a stream of nitrogen at a flow rate of 30/hour. Then the device is 30mm
Unreacted toluene and produced monochlorotoluene are separated by distillation under Hg vacuum.
The TiCl ₄ is collected along with the toluene fraction and recycled to the next reaction. After the distillation is finished, break the vacuum of the apparatus,
1.25 mol of chlorine is introduced in 1 hour and 15 minutes at a temperature of 110-125°C. A second working cycle is started by introducing recycled toluene and then bringing up to 1.3 moles with fresh toluene. After 7 working cycles,
The results obtained are as follows;

[Table] An accurate balance sheet of the operation can be obtained by weighing each fraction and analyzing each by gas chromatography. The average meta content of monochlorotoluene is 2%. Example 2 The same conditions as in Example 1 are used, except that 5 g of aluminum chloride is used instead of TiCl ₄ . The results after three working cycles are as follows;

[Table] Example 3 5g of tantalum chloride (TaCl ₅ ) instead of TiCl ₄
The same conditions as in Example 1 are used except that . The results after four working cycles are as follows.

[Table] Example 4 The same conditions as in Example 1 are used, except that monochlorobenzene is used instead of toluene and the reaction is carried out at 100-125°C. The results obtained after 6 working cycles are as follows.

[Table] The composition of dichlorobenzene produced in each case is approximately ortho/meta/para = 3.65/0.15/96.2. Example 5 50g of hexachlorocyclopentadiene and 0.2
Moles of anhydrous ferric chloride and 10 g of TiCl ₄ are contacted in a reactor and then heated to 120° C. for 3 hours in the presence of 0.2 moles and toluene. After the end of the reaction, monochlorotoluene is recovered by distillation in a para/ortho ratio of 7 with a yield of 75% based on the initial FeCl ₃ . After regeneration of FeCl ₃ a new reaction working cycle is started. Example 6 256 instead of hexachlorocyclopentadiene
Example 5 is repeated except that a fluorinated oil (Volntalef 3S) having a boiling point of 0.degree. C. and a freezing point of -45.degree. C. is used. At the end of the reaction, monochlorotoluene was obtained with a yield of 95% based on FeCl ₃ charged and with a para// of 8.5
Collect in ortho ratio. Start a new reaction working cycle after regeneration of FeCl ₃ .

[Brief explanation of drawings]

The drawing is a flow sheet illustrating the reaction cycle when toluene and monochlorobenzene are chlorinated; in the drawing, 1 is the reaction process between FeCl ₃ and toluene or monochlorobenzene, and 3 is the regeneration process of FeCl ₂ . , 6 is a pipe for taking out monochlorotoluene or dichlorobenzene.

Claims (1)

[Scope of Claims] 1. A method for producing an aromatic compound chlorinated at the para position, in which in the first step, an aromatic compound having one inducing substituent is used to induce chloro groups at the ortho and para positions. In the method for producing a para-chlorinated aromatic compound, in which chlorination is performed in a liquid phase using ferric chloride, and the generated ferrous chloride is regenerated by chlorination in the second step, the above two steps include Process for the production of para-chlorinated aromatic compounds, characterized in that it is carried out in the presence of the same solvent with a melting point lower than 200 °C and a boiling point higher than 200 °C. 2. The method according to claim 1, wherein the solvent is a halogenated compound. 3. The method according to claim 2, wherein the solvent is a fluorinated or chlorinated compound. 4. The method according to claim 3, wherein the solvent is hexachlorobutadiene. 5. A method according to any one of claims 1 to 4, wherein in the second step, ferric chloride is regenerated in situ in the solvent of the first step.