JP2808174B2 - Method for producing 2,6-dichlorotoluene - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention The present invention relates to 2,6
The present invention relates to a method for producing dichlorotoluene (hereinafter abbreviated as 2,6-DCT). More specifically, 3,5-di-t-butyl-toluene (hereinafter abbreviated as DBT) is used.
The present invention relates to an improved method for producing 2,6-DCT via 2,6-dichlorotoluene (hereinafter abbreviated as DBDCT).

Prior art To produce 2,6-DCT, simply chlorinating toluene, o-chlorotoluene, etc., produces various isomers, such as 2,4-dichlorotoluene, and converts 2,6-DCT. I can't get it selectively. Therefore, conventionally, in order to suppress the generation of isomers and improve the yield of 2,6-DCT, after chlorinating alkyltoluene into 2,6-dichloroalkyltoluene, the alkyl group is eliminated. A method for producing 2,6-DCT has been proposed (JP-B-47-26495, JP-A-62-5930).
issue).

The method described in JP-B-47-26495 uses toluene and t-
After chlorinating DBT obtained from butyl chloride or isobutene into DBDCT, a catalytic dealkylation reaction is performed at 100 to 500 ° C. in the presence of a catalyst to remove the butyl group of the protecting group as isobutene, and 2,6 -A method of obtaining DCT.
This method has the disadvantage that the life of the dealkylation catalyst is short, and the productivity of 2,6-DCT is poor. In addition, since the t-butyl group is eliminated as isobutene, a recovery step is required. For this reason, there is a point to be improved in industrial production of 2,6-DCT.

As a method for improving the above-mentioned JP-B-47-26495, JP-A-62-5
Issue 930 has been proposed. This method includes (1) a step of obtaining DBT and toluene from t-butyltoluene (hereinafter abbreviated as BT), (2) a step of chlorinating DBT to obtain DBDCT, and (3) a step of obtaining toluene and t-butylating agent in DBDCT. And add 2,6-
This is a method consisting of the steps of obtaining DCT and BT. However, this method also has some problems in industrial practice. For example, 2,6-DCT and BT are separated by removing the catalyst from the reaction solution obtained by transalkylation of DBDCT and alkylation of toluene (t-butylation), and the boiling points of both are similar. And 2,6-DCT of the reaction solution used for distillation.
The ratio of BT is approximately 1: 3, and the large amount of BT requires large-scale distillation equipment and enormous energy. In addition, DBT is produced by the disproportionation reaction of the separated BT. However, if the disproportionation reaction rate is not increased, the amount of BT recycled increases, and the disproportionation reactor and the DBT distillation column become large. Further, the catalyst requires two operations of separating the catalyst, that is, the decatalysis after the transalkylation and alkylation reactions and the decatalysis after the disproportionation reaction, which complicates the process.

Problems to be Solved by the Invention In a method for producing 2,6-DCT via DBT and DBDCT, operations such as distillation operation, disproportionation reaction, decatalysis, and the like, which are problems described above, are essentially required. However, simplification of these operations is required. An object of the present invention is to meet such a demand.

In view of the above situation, the present inventors have proposed that DBDCT
As a result of diligent research on a method for producing 2,6-DCT via 2,2,6-DCT obtained by transalkylation reaction of DBDCT
By subjecting DCT to a disproportionation reaction and an alkylation reaction without separation, the production process was simplified and the present invention was achieved.

Means for Solving the ProblemsThe constitution of the present invention is a transalkylation step in which DBDCT and toluene are transalkylated in the presence of a catalyst to obtain 2,6-DCT and BT, and BT is a transalkylation catalyst. In a method for producing 2,6-DCT comprising a disproportionation step for obtaining DBT by disproportionation in the presence of the same catalyst and an alkylation step, 2,6-DCT is obtained after the disproportionation reaction and alkylation reaction of BT.
In the method for producing 2,6-DCT, which separates the above, and the method for producing 2,6-DCT comprising the above steps, the reaction rate of the disproportionation step of obtaining DBT from BT is limited to 10 to 60%,
A method for producing 2,6-DCT which separates 2,6-DCT after the disproportionation reaction and the alkylation reaction.

 Hereinafter, the present invention will be described in detail.

i) Chlorination Step and Transalkylation Step Known methods can be applied to the chlorination reaction to obtain DBDCT by chlorinating DBT and the transalkylation reaction of DBDCT.

That is, in the chlorination of DBT, a Lewis acid and elemental sulfur are used as catalysts, and a chlorine gas is blown into the DBT at a molar ratio of 2.0 to 2.2 times to cause a reaction. If the amount of chlorine gas is less than 2.0 mol, the formation of the dichloro form is not sufficient, and if it is more than 2.2 mol, the production amount of the trichlor form is undesirably increased. After removing the catalyst, the chlorination reaction solution is subjected to distillation and crystallization operations to achieve a purity of 99%.
% DBDCT can be obtained.

In the transalkylation reaction of DBDCT, 2 to 30 moles, preferably 10 to 20 moles, of toluene are reacted with 1 mole of DBDCT in the presence of a Lewis acid catalyst to obtain 2,6-DCT and BT. As the Lewis acid of the catalyst, aluminum chloride, iron chloride, titanium chloride, and the like can be used, and the amount of use is 1 to 2 with respect to DBDCT.
0 mol%, preferably 5 to 15 mol%. The reaction is carried out at a temperature of 0 to 100 ° C, preferably 30 to 70 ° C.

ii) Disproportionation and alkylation reaction of BT The desired 2,6-DC is obtained by transalkylation of DBDCT.
When T is produced, the BT produced at the same time is subjected to a disproportionation reaction to return to the DBT as a chlorination reaction raw material. Conventionally, BT was subjected to a disproportionation reaction after separating the target product 2,6-DCT, that is, in a system free of 2,6-DCT. And a distillation operation was required. Removal of the catalyst from the reaction solution requires acid washing, neutralization, and water washing, and the operation is complicated. Further, it is difficult to separate 2,6-DCT and BT by distillation from the decatalyzed reaction solution as the BT content increases. Usually, 2,6-DCT in the transalkylation solution
The ratio of BT is approximately 1: 2 (weight ratio). According to the study of the present inventors, the disproportionation reaction and alkylation reaction of BT are 2,6.
-The catalyst used for the transalkylation reaction can be used as it is as a catalyst for the disproportionation reaction and the alkylation reaction without being affected by the presence of DCT. Therefore,
In the present invention, the transalkylation reaction solution is directly used under reduced pressure by using a vacuum distillation apparatus at a degree of vacuum of 20 to 200 Torr and a temperature of 4 ° C.
The disproportionation reaction of BT is carried out at a temperature of 0 to 100 ° C, preferably 50 to 70 ° C, and the produced toluene is sequentially taken out of the system. BT
The disproportionation reaction proceeds relatively quickly up to a disproportionation reaction rate of about 50%, but the reaction rate thereafter becomes extremely slow. To further increase the disproportionation reaction rate, higher vacuum Requires a long reaction time. Therefore, in the present invention, the disproportionation reaction rate is limited to 10 to 60%, preferably 15 to 40%, and the remaining BT is reacted with an alkylating agent to form DBT. Here, the disproportionation reaction rate is represented by the following equation.

(However, when the alkylating agent is added during disproportionation, the BT weight after disproportionation is obtained by adding 148 times the number of moles of the alkylating agent added to the BT weight after the reaction.) The reaction yields a reaction solution having a BT content of 40 to 60% by weight. This reaction solution was used as it is, that is, without separating 2,6-DCT and the catalyst, alkylation of BT, that is, DBT
For the production of The alkylation of BT is carried out by adding an alkylating agent such as t-butyl chloride or isobutylene and reacting at a reaction temperature of 10 to 40 ° C for 3 to 6 hours. The amount of the alkylating agent to be used is equimolar to or slightly in excess of the BT to be alkylated. By this reaction, the ratio of BT to 2,6-DCT in the alkylation reaction completed solution was about 1: 0.
2,6-DCT by reducing to 1 to 0.3 (weight ratio)
And the distillation equipment and energy costs are significantly reduced.

Of course, the disproportionation reaction of BT and an alkylation reaction can also be advanced simultaneously by adding an alkylating agent at the time of disproportionation. In this case, a part of the alkylating agent is likely to flow out of the system without being reacted, and the preferable reaction temperature of the disproportionation reaction is not the same as the preferable reaction temperature of the alkylation reaction. It is preferable to carry out the reaction separately after the completion of the leveling reaction.

iii) Separation of 2,6-DCT After the completion of the alkylation reaction, after removing the catalyst from the reaction solution, 2,6-DCT is separated by distillation. Distillation by boiling point B
Each fraction of T, 2,6-DCT and DBT may be fractionated, but as another method, first, a mixed fraction of BT and 2,6-DCT and a DBT fraction, and then BT and 2 , 6-DCT mixed fraction may be rectified and separated. The separated DBT may be used as a raw material for a chlorination reaction, and BT may be subjected to a disproportionation reaction or an alkylation reaction.

 Hereinafter, the present invention will be described specifically with reference to examples.

Example I. Chlorination Step In a five-necked flask equipped with a stirrer, a chlorine blowing tube, a thermometer, and a condenser, 464.4 g of DBT having a purity of 98.8% (2.2
49g), 3.0g of aluminum chloride as catalyst (0.023mo)
l) and 1.5 g (0.047 mol) of elemental sulfur, and a reaction temperature of 50
Chlorination was performed at 2.1 ° C. using 2.1 times mol of chlorine. The obtained chlorinated solution was subjected to distillation and crystallization to obtain 377.5 g of DBDCT (purity 99.5%, D
BDCT 1.375 mol) was obtained.

II. Transalkylation Step The above DBDCT 377.5 g (1.375 mol), aluminum chloride 18.4 g (0.138 mol), and toluene 1898.0 g were placed in a 6-necked flask equipped with a stirrer, a dropper, a fractionator, and a thermometer.
(20.632 mol) and reacted at 50 ° C. for 5 hours to obtain a reaction product. As a result of composition analysis by gas chromatography, 2,3.5-DCT 203.5 g (1.264 mol), BT38
It contained 6.5 g (2.611 mol).

III.Disproportionation step The above reaction solution is mixed with a BT recovered fraction 37.5 obtained in a later step.
(BT88.27% by weight, DCT11.73% by weight) and the reaction temperature was 60
This state was maintained for 6 hours while distilling off toluene at a temperature of 200 ° C. under reduced pressure (200 to 20 Torr). At this time, the amount of distilled toluene was 1677.6 g. By this operation, 622.9 g of reaction product was obtained.
I got As a result of composition analysis by gas chromatography, this product was found to be 5.8 g (2.269 mol) of BT, 2,6-DCT20
It contained 7.9 g (1.291 mol) and 53.3 g (0.261 mol) of DBT.

 The disproportionation rate at this time was 20.0%.

IV. Alkylation Step Next, the inside of the system was returned to normal pressure, and 214.0 g (2.314 mol) of t-butyl chloride was added to the above reaction solution at 30 ° C. under stirring.
It was dropped over time. After the dropwise addition, stirring was further continued for 3 hours, and 50 ml / min of nitrogen gas was blown for 1 hour to remove residual unreacted t-butyl chloride.

After 1000 ml of water was added to the reaction mixture and stirring was continued at 30 ° C. for 0.5 hour, the liquid was allowed to stand and separated into an aqueous layer and an organic layer. The organic layer was dried using anhydrous sodium sulfate to obtain 744.5 g of a reaction product. As a result of composition analysis by gas chromatography, this product was found to be BT43.1 g (0.291 mol),
2.6-DCT 207.9 g (1.291 mol), DBT 467.6 g (2.292 mol)
Was included.

Next, a mixture containing these BT, 2,6-DCT, and DBT was led to a distillation column and rectified. 83 ° C / 20Torr as each fraction:
47.7g (BT: 88.27%, 0.284mol, DCT: 11.73%, 0.034mo
l), 86 ° C / 20 Torr: 197.7 g (2,6-DCT: 99.49%, 1.222mo
l), 121 ° C / 20 Torr: 464.4 g (DBT: 98.80%, 2.249 mol)
Obtained.

The distillation yield of 2,6-DCT and DBT was 94.6 each.
%, 98.1%. The obtained DBT was returned to the chlorination step I. Further, the fraction containing BT and DCT is used in the disproportionation reaction step I.
Used for preparation of BT in II.

The present invention provides a 2,6-DCT comprising a chlorination step, a transalkylation step, a disproportionation step and an alkylation step from DBT.
In the production method of 2, the disproportionation reaction and the alkylation reaction are performed in the presence of 2,6-DCT, thereby having the following advantages.

The catalyst used for the transalkylation can be used for the disproportionation reaction and the alkylation reaction without being separated from the reaction solution. In addition, by suppressing the disproportionation reaction rate in the disproportionation step to 60% or less, the reaction time can be shortened, and the loss of t-butyl groups and the amount of high-boiling products reduced. Furthermore, by performing alkylation of BT in the presence of 2,6-DCT, BT coexisting with 2,6-DCT
, The separation of 2,6-DCT becomes easy.

As a result, operations such as a distillation operation, a disproportionation reaction, and removal of a catalyst are simplified, and the distillation apparatus is reduced in size and energy cost is reduced.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C07C 15/107 C07C 15/107

Claims (2)

(57) [Claims] 1. A transalkylation of 3,5-di-t-butyl-2,6-dichlorotoluene and toluene in the presence of a catalyst to obtain 2,6-dichlorotoluene and t-butyltoluene. A transalkylation step, a disproportionation step in which t-butyltoluene is disproportionated in the presence of the same catalyst as the transalkylation catalyst to obtain 3,5-di-t-butyltoluene, and an alkylation step 2, A method for producing 2,6-dichlorotoluene, which comprises separating 2,6-dichlorotoluene after a disproportionation reaction and an alkylation reaction of t-butyltoluene. 2. The disproportionation reaction rate for obtaining 3,5-di-t-butyltoluene from t-butyltoluene in the disproportionation step is 10 to 60%. 2. The method for producing 2,6-dichlorotoluene as described.