JPH0437064B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for obtaining a highly purified agricultural soil fungicide raw material pentachloronitrobenzene (hereinafter abbreviated as PCNB).

More specifically, we will discuss hexachlorobenzene (hereinafter referred to as impurity) contained in industrially obtained PCNB.
The present invention relates to a method for obtaining high-purity PCNB with a reduced amount of HCB (abbreviated as HCB).

[Conventional technology]

In recent years, soil environmental pollution caused by pesticides and contaminants in pesticides has become a problem worldwide, and PCNB, which is used as a soil disinfectant, is no exception. There is a high demand for reduction and high purity.

For example, in the United States, the US Environmental Protection Agency
The revised PCNB registration standards stipulated that new technology should be implemented to reduce the HCB content in PCNB to 0.5% by weight or less since March 1983, and 0.1% by weight or less since April 1988.
It was established in April 1982.

Traditionally, the main method for industrially obtaining PCNB is Khim.
Prom.), 1968, 44(5), 334, etc., by chlorinating nitrobenzene or chloronitrobenzenes.
Method of obtaining PCNB and U.S. Patent Specification No.
No. 4026955, No. 4057590, No. 4147732, etc. describe methods for obtaining PCNB by nitration of pentachlorobenzene.

However, in the former method, the by-product of HCB due to the perchlorination reaction is unavoidable, and in the latter method, HCB is produced as a by-product during the nitration of pentachlorobenzene, and the raw material pentachlorobenzene is not always commercially available. There was a crucial problem.

Also, recently, in Japanese Patent Application Laid-open No. 174748/1983,
HCB is reacted with sodium bisulfide to form sodium pentachlorothiophenolate, which is then reacted with mixed acid to produce high purity with low HCB content.
A method for obtaining PCNB is disclosed.

However, this method requires the use of highly toxic specific chemical substances as raw materials, and depending on the reaction conditions.
There were problems such as the possibility that HCB remained.

As described above, there is currently no good method for directly producing PCNB with a low HCB content.

On the other hand, there are two main methods for purifying PCNB containing HCB as an impurity and obtaining highly pure PCNB.

One method is to recrystallize crude PCNB in a benzene-methanol system and then perform column chromatography using an activated carbon column to obtain a pure product [as described in "Agricultural Official Inspection Methods Commentary (Nankodo)".
This is a method for preparing PCNB samples.

The other method is to perform silica gel column chromatography on crude PCNB using carbon tetrachloride alone or a mixed solvent consisting of carbon tetrachloride and a liquid saturated hydrocarbon (Japanese Unexamined Patent Publication No. 53-95926). .

However, although both purification methods are suitable for obtaining high-purity PCNB in the laboratory, they require large amounts of solvents and carriers, which greatly reduces their industrial utility.

Past knowledge regarding the boiling point and vapor pressure of PCNB and HCB is that the melting point of HCB is 226°C [JACS, 62 , 950 (1940)], and the boiling point is 326°C [Annares Dehimy (Ann. .
Chim), (4)15287 (1868)], 322.2℃ [Ann, 150 ,
309 (1809)] Vapor pressure is 283.5℃/400mm
Hg, 235.5℃/100mmHg [Handbook of
The melting point of PCNB is 146°C, and the decomposition point is 328°C [both from Jahresberichteber Dei Holtschülichte der Chemie (J), 1868 ,
353] and its boiling point is unknown.

Furthermore, no literature has been found regarding the technique for purifying PCNB by distillation.

[Problem that the invention seeks to solve]

An object of the present invention is to provide an industrial method for obtaining high-purity PCNB that does not have the drawbacks of these conventional techniques, requires simple operations, and is advantageous for large-scale implementation.

[Means and actions for solving problems]

The present inventors have conducted intensive studies on distillation methods in order to solve the above problems.

The present inventors attempted fractional distillation of HCB and PCNB at normal pressure, but PCNB was severely thermally decomposed and implementation was difficult. In addition, as shown in Reference Example 1, the HCB content could not be reduced even under vacuum distillation conditions with a pot temperature of around 280°C, and on the contrary, an increase in HCB was observed, and the purpose of obtaining high-purity PCNB was I couldn't achieve it at all. Although the detailed mechanism is unknown, this
This is thought to be caused by thermal decomposition of PCNB.
This is thought to be due to the fact that HCB formation occurs over a wide range of temperatures below the decomposition point described in the literature.
Coupled with the fact that PCNB has a very high melting point of 146°C, the possibility of separating PCNB and HCB by distillation was extremely pessimistic.

However, in view of the industrial large-scale implementation of the distillation method, the present inventors conducted extensive research to see if there was any possibility of fractionating HCB and PCNB by distillation, which was extremely narrow. As shown in Figure 1, we found that heat-induced decomposition of PCNB occurs at temperatures above about 250°C, and almost never occurs at temperatures below 250°C.
They have discovered that fractional distillation is possible if carried out in a temperature range of

That is, the present invention is a method for obtaining high purity pentachloronitrobenzene, which is characterized by distilling pentachloronitrobenzene containing hexachlorobenzene as an impurity under reduced pressure at a temperature of 150 to 250°C. PCNB where it was difficult to reduce the HCB content to 0.3% by weight or less
The purification technology has been developed into a technology that can be easily implemented industrially.

The present invention will be explained in detail below.

Crude PCNB subjected to vacuum distillation in the present invention
is obtained by chlorination of nitrobenzene or chloronitrobenzene and contains tetrachloronitrobenzene, HCB, etc. as impurities, and is obtained by nitration of pentachlorobenzene and contains unreacted pentachlorobenzene, HCB, etc. as impurities. This also applies to, but is not limited to, of course.

Since PCNB thermally decomposes at temperatures above 250°C, the internal pressure during distillation is naturally determined from the vapor pressure at that temperature and the vapor pressure at the melting point of PCNB of 146°C, and is preferably in the range of 3 to 70 mmHg. It is carried out at pressures in the range of 5-50 mmHg.

As mentioned above, the temperature inside the system during distillation is PCNB
The temperature range is 150°C, which is above the melting point of the substance, and 250°C, which is below the decomposition point.

The temperature at the top of the tower is 150-240℃, preferably 160-220℃
The temperature at the bottom of the column is from 160 to 250°C, preferably from 170 to 230°C.

The reflux ratio during distillation is 1 to 100, preferably 5 to 100.
Conducted at 50.

If the reflux ratio is less than 1, impurities in PCNB
The HCB content increases, and if it exceeds 100, productivity will decrease, which is not preferable.

The vacuum distillation apparatus can be either a batch type apparatus or a continuous type apparatus, and it is preferable to use a distillation column having a theoretical number of plates of 1 to 100, preferably about 5 to 30.
The type and packing of the distillation column are not particularly selected, but the bottom temperature should be lowered as much as possible to near the melting point of PCNB to save energy, and in order to prevent temperature rise to avoid thermal decomposition of PCNB, the top and column It is preferable to use column types and packings that have as low a pressure drop across the bottom as possible.

Impurities such as the reaction intermediate tetrachloronitrobenzene and HCB contained in crude PCNB are
Since it has a lower boiling point than PCNB, it can be distilled off and the PCNB remaining at the bottom of the column can be used as purified PCNB, but if desired, after removing impurities by distillation, higher purity PCNB can be obtained by further distillation. You can also.

Examples Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 PCNB obtained by chlorination of nitrobenzene [PCNB 95.0% by weight,
Charge 400 g of HCB (0.5% by weight, 4.5% by weight of tetrachloronitrobenzene (hereinafter abbreviated as TeCNB)), and place the distillation column (inner diameter 25mmφ, height 830mm) on the flask.
Distillation column bottom temperature 216-220℃, column top temperature 150-176℃, column bottom pressure 48-61mmHg, column top pressure 9-12mmHg, reflux ratio.
Batch distillation was carried out at 10 (using a magnetic timer reflux controller).

Distillation rate of distillate from distillation column is 0.08~0.19
29.7 g of distillate was obtained in 4.8 hours at g/min.

The hold-up amount in the column was 17.6 g, and 350 g of purified PCNB (99.6% by weight of PCNB, 0.2% by weight of HCB, 0.2% by weight of TeCNB) was obtained as a residue at the bottom of the column.

Example 2 PCNB obtained by nitration of pentachlorobenzene was placed in a distillation flask similar to Example 1.
[PCNB 98.97% by weight, HCB 0.50% by weight,
270 g of TeCNB (0.02% by weight, 0.51% by weight of pentachlorobenzene (hereinafter abbreviated as PeCB)) were charged in the same distillation column as in Example 1, and the bottom temperature of the distillation column was set at the reflux ratio.
215℃, top temperature 165-167℃, bottom pressure 46mmHg
Batch distillation was carried out at a column top pressure of 7.5 mmHg.

The distillate rate from the distillation column was 0.08 g/min, and 19.9 g of distillate was obtained in 4 hours.

The hold-up amount in the column was 23.6 g, and 226.4 g of purified PCNB (99.9% by weight of PCNB, 0.07% by weight of HCB, TeCNB trace,
PeCB trace) was obtained.

Example 3 350 g of PCNB obtained by chlorination of nitrobenzene [94.5% by weight of PCNB, 0.7% by weight of HCB, 4.8% by weight of TeCNB] was placed in the same distillation flask as in Example 1.
and place a distillation column (inner diameter 36.5 mmφ,
Distillation column bottom temperature 212-216℃, column top temperature 194-206℃, column bottom pressure 45-48mmHg, column top pressure 29-36mmHg, reflux ratio. Batch distillation was carried out at 10.

The distillate rate from the distillation column was approximately 0.21 g/min, and 49 g of distillate was obtained in 3.75 hours.

The hold-up amount in the column was 63.0 g, and 235.6 g of purified PCNB (99.8% by weight of PCNB, 0.1% by weight of HCB, 0.1% by weight of TeCNB) was obtained as a residue at the bottom of the column.

Reference Example 1 Obtained by chlorination of nitrobenzene using the same distillation flask, distillation column, and reflux ratio as in Example 1.
400 g of PCNB (composition is the same as in Example 1) was distilled at a bottom temperature of 280 to 285°C, a top temperature of 232 to 265°C, and a bottom pressure of
Batch distillation was carried out at a pressure of 130-142 mmHg and an overhead pressure of 50-73 mmHg.

The distillate rate from the distillation column was about 0.21 g/min, and 29.2 g of distillate was obtained in 2.3 hours.

The hold-up amount in the tower was 18.4g, and the bottom of the tower contained 351.4g of PCNB (98.5% by weight of PCNB,
0.9% by weight of HCB, 0.5% by weight of TeCNB).

〔Effect of the invention〕

Industrially high purity PCNB manufacturing method, high purity
There is no industrial refining method for crude PCNB to obtain PCNB, and there is also no data on the vapor pressure of PCNB.
Based on common sense data on the melting point and decomposition point of PCNB, and the melting point, boiling point, and vapor pressure of HCB, the distillation method of the present invention is used in a situation where it is assumed that separation of PCNB and HCB by industrial distillation is difficult. low
The method for obtaining high-purity PCNB of HCB is economically advantageous, can be implemented on an industrial scale, and is extremely valuable industrially.

[Brief explanation of drawings]

Figure 1 shows the heating temperature when heating PCNB.
FIG. 3 is a diagram showing the relationship between the amount of HCB produced.

Claims (1)

[Claims] 1. A method for obtaining high purity pentachloronitrobenzene, which comprises distilling pentachloronitrobenzene containing hexachlorobenzene as an impurity under reduced pressure at a temperature of 150 to 250°C.