Process for the production of 2,6-dichloro-3,5-di(secondary...

Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing

Reexamination Certificate

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Reexamination Certificate

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06271426

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for producing 2,6-dichloro-3,5-di(secondary or tertiary alkyl)toluene which is a useful compound as an intermediate for production of medicines and agricultural chemicals.
BACKGROUND ART
2,6-Dichloro-3,5-di(secondary or tertiary alkyl)toluene which can be produced according to the present invention is known as a useful compound capable of deriving into 2,6-dichlorotoluene which is an intermediate for production of insecticidal 2,6-dichlorobenzamide derivatives or herbicidal 2,6-dichlorobenzonitrile.
Japanese Patent Application Laid-Open No. 53743/1990 discloses that 2,6-dichloro-3,5-di(1,1-dimethylethyl)toluene is obtained in high yield by chlorinating 3,5-di(1,1-dimethylethyl)toluene in the presence of aluminium chloride or ferric chloride together with sulfur, as compared with the case of chlorinating in the presence of sulfur monochloride, zinc sulfide, ferric sulfide or cupric sulfide.
Further, Japanese Patent Application Laid-Open No. 202148/1992 discloses that the yield is improved by choosing the ratio of sulfur and Lewis acid to be used.
However, since there is a demand for higher yield and the process described in the Japanese Patent Application Laid-Open No. 202148/1992 has a problem on operation because of the sulfur being poor soluble in the reaction mixture, more improvement is desired.
On the other hand, William David Watson has proposed chlorination of phenols by reacting with a chlorinating agent in the presence of a Lewis acid together with a sulfur compound (including phenyl sulfide or phenyl disulfide), by which chlorination of high para-selectivity can be conducted (Japanese Patent Application Laid-Open No. 122031/1976).
William David Watson has promptly reported the effect of phenyl sulfide described in the above proposal in Tetrahedron Lett., 1976, 2591-2594., and reported the detail including consideration in J. Org. Chem., 50, 2145-2148 (1985).
The Watson's report discloses chlorination of mono-substituted benzenes other than phenols, but the description of it is only “when chlorobenzene, toluene or ethylbenzene and isopropylbenzene are chlorinated in the presence of aluminium chloride and phenyl sulfide, both of sulfuryl chloride and chlorine produce the same ortho/para ratio” (J. Org. Chem., 50, 2147, right column, paragraph 3). Consequently, it is not found a concrete report concerning effect of coexistence of the Lewis acid and phenyl sulfide or phenyl disulfide upon chlorination of 3,5-di(secondary or tertiary alkyl)toluene.
DISCLOSURE OF THE INVENTION
The present inventors aimed at finding a novel promoter capable of obtaining the target compound in a high yield upon production of 2,6-dichloro-3,5-di(secondary and tertiary alkyl)toluene.
As the result of many studies concerning compounds having a property of dissolving in the reaction mixture, for the purpose of attaining the above mentioned object, the present inventors have found that the 2,6-dichloro-3,5-di(secondary and tertiary alkyl)toluene is obtained in a high yield by using an aromatic sulfur compound represented by the following formula as a cocatalyst of Lewis acid, leading to the present invention.
Ar
1
—(S)
n
—Ar
2
  (III)
The present invention has the following constitutional characteristics.
The present invention relates to a process for producing 2,6-dichloro-3,5-di(secondary and tertiary alkyl)toluene represented by the formula (I) which comprises chlorinating 3,5-di(secondary and tertiary alkyl)toluene represented by the formula (II) according the following reaction formula by reacting with a chlorinating agent in the presence of a Lewis acid together with an aromatic sulfur compound represented by the formula (III) as a promoter.
wherein R
1
and R
2
are independently a secondary alkyl or tertiary alkyl group, Ar
1
and Ar
2
are independently an unsubstituted or substituted aromatic ring, and n is 1 or 2.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be illustrated in detail in the following.
In the description hereafter, abbreviations shown in [ ] will be used.
2,6-Dichloro-3,5-di(secondary and tertiary alkyl)toluene represented by the formula (I): [referred to as Product (I), hereinafter], 3,5-di(secondary and tertiary alkyl)toluene represented by the formula (II): [referred to as Base material (or substrate) (II), hereinafter], and aromatic sulfur compound represented by (III) [referred to as Promoter (III), hereinafter].
Examples of the base material (II), the chlorinating agent, the Lewis acid and the promoter (III) to be used in the present invention include the following.
As the base material (II), 3,5-di(secondary or tertiary C3-C4 alkyl)toluenes are preferably used. Examples of them include 3,5-di(1-methylethyl)toluene and 3,5-di(1,1-dimethylethyl)toluene.
As the chlorinating agent, chlorine and sulfuryl chloride are used. Chlorine is more preferable to use.
Examples of Lewis acid include aluminium chloride, ferric chloride, antimony trichloride, antimony pentachloride and stannic chloride. Of these, aluminium chloride or ferric chloride is more preferably used.
In the promoter (III), the aromatic ring is preferred to be benzene ring. The benzene ring may be unsubstituted or substituted by 1-5 substituents selected from halogen and C1-C4 alkyl. Examples of them include phenyl sulfide and phenyl disulfide.
In case of using the disulfide, it is possible to produce it by oxidizing the corresponding thiol compound by means of a chlorinating agent in the reaction system.
In the present invention, the solvent is not necessary, but solvents such as carbon tetrachloride, chloroform, nitromethane, nitoroethane, nitoropropane and nitorobenzene, etc. may be used if the solvent is desired to use.
In the present invention, the chlorination of the base material (II) can be carried out as follows.
A mixture is prepared, which contains a base material (II), 0.0001-2% by weight, and preferably 0.005-0.5% by weight, of a Lewis acid, 0.0006-35% by weight, and preferably 0.06-20% by weight of a promoter (III), based on the base material (II), and if necessary solvents.
The mixture is kept at a reaction temperature of from −10° C. to 70° C., and preferably from 30° C. to 60° C. with sufficiently stirring, and a chlorinating agent is introduced to the mixture to chlorinate so as to be a chlorination degree of 1.4-2.4 and preferably 1.8-2.1.
The chlorination degree means a value obtained by examining composition of the reaction mixture on the basis of the following criteria; that is, chlorination degree of the base material (II) is 0, that of the monochloride is 1, that of the dichloride is 2 and that of the trichloride is 3.
Main side reactions which causes reduction of the yield of the product (I) include dealkylation reaction of the base material (II), isomerization chlorination reaction of the base material (II) and over chlorination reaction (=reaction of forming trichloride).
According to the invention, however, such side reaction can be prevented by chlorinating the base material (II) in the presence of 10-150 times by mol, preferably 20-70 times by mol of the promoter (III) based on 1 mol of Lewis acid, whereby the product (I) of the chlorination degree of about 2 can be obtained in the yield of 90% or more.
There is another characteristic of the present invention. Namely, in the present invention, since the amount of insoluble materials is very small during the reaction and after the reaction, it is easily cooled a part of the reaction solution by the exterior heat exchanger.
Consequently, it is not necessary to control the heat of reaction by adjusting the chlorination rate. Because of using the promoter (III), this process is hardly subjected to restriction by the scale of reaction.


REFERENCES:
patent: 4010214 (1977-03-01), Gelfand
patent: 0257866 (1988-03-01), None
patent: 0 424 847 B1 (1996-01-01), None
patent: 1110029 (1968-04-01), None
patent: 62-153234 (1987-07-01), None
patent: 2-53743 (1990-02-01), None
patent: 4-1143 (19

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