JPS6317849A - Production of high-purity pentachloronitrobenzene - Google Patents

Abstract

PURPOSE:To obtain the titled compound useful as a soil germicide in high purity and industrially advantageously, by dissolving the titled compound containing hexachlorobenzene as an impurity in an inert organic solvent, feeding the solution to a distillation column and continuously distilling under reduced pressure at a specific temperature. CONSTITUTION:Pentachloronitrobenzene containing hexachlorobenzene as an impurity is purified. In the operation, the pentachloronitrobenzene is dissolved in a solvent (e.g. chlorobenzene, nitrobenzene, etc.), fed to a distillation column, continuously distilled under reduced pressure at 70-250 deg.C to give high-purity pentachloronitrobenzene. Operation can be carried out at low temperature, stable and improved operation condition is obtained with reduced energy by simple operation, the method can be industrially done at low cost and has extremely high industrial value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for obtaining a high-purity product of pentachloronitrobenzene (hereinafter abbreviated as PCNB), a raw material for an agricultural fungicide.

More specifically, hexachlorobenzene (hereinafter abbreviated as HCB) is an impurity contained in industrially obtained PCNB.
The present invention relates to a method for obtaining high purity P CN B with a reduced amount of P CN B.

[Conventional technology]

In recent years, pollution of the civil and building environment due to pesticides and their contaminants has become a problem worldwide, and PCNB, which is used as a souvenir disinfectant, is no exception to this, and is an undesirable H
There is a high demand for reducing the content of inclusions such as CB and increasing the purity.

For example, in the United States, the US Environmental Protection Agency announced that new technology should be implemented to reduce the HCB content in PCNB to 0.5% by weight or less since March 1983, and to 1% by weight or less since April 1988. Registration revision standards were established in April 1982.

Conventionally, the following methods are known as main methods for industrially obtaining PCNB.

■ A method of chlorinating nitrobenzene or chloronitrobenzenes.

[Himiches Rikiya Promshrennostii, 196
8゜1Ago5), 334) ■, Method for nitrating pentachlorobenzene.

(U.S. Patent No. 4,026,955, etc.) (2) A method in which HCB and sodium hydrogen sulfide are reacted to form sodium pentachlorothioferlate, and the mixture is then reacted with a mixed acid.

(Japanese Unexamined Patent Publication No. 174748/1983) However, these methods reduce HC due to the perchlorination reaction.
Problems include the inability to suppress B by-products, the difficulty in obtaining raw materials on an industrial scale even though HCB production is relatively low, or the legal restrictions on earth odor and the qualitative impossibility of use. It existed.

On the other hand, there are two main methods for purifying P CN B containing HCB as an impurity to obtain highly pure PCNB.

(2) A method of recrystallizing crude PCNB with a benzene-methanoyl system and then performing column chromatography using an activated carbon column to obtain a pure product [PCNB standard preparation method described in "Commentary on Official Pesticide Testing Methods (Nankodo)"] ■, Crude PCNB is carbon tetrachloride alone or carbon tetrachloride-
A method of performing silica gel column chromatography using a mixed solvent consisting of a liquid saturated hydrocarbon (Japanese Unexamined Patent Publication No. 53
-95926).

However, both purification methods required large amounts of high-purity agents and carriers in the laboratory, and had very little industrial utility.

Past knowledge regarding the boiling point and vapor pressure of P CN B and HCB is that the melting point of HCB is 226'CC Journal of the American Chemical Society (JAC3), 62 950 (1940)], and the boiling point is 326°C [Anna Dehymi (Ann, C
hin, ), (4) 15287 (1868)], 332
2.2°CAnn, Lshi, 309 (1809)), vapor pressure is 283.5°G/400rrmHg,
235.5℃7100mxHg (Handbook of Chemistry and Physics)
OK of CHEMISTR/ and Physi
cs) :), etc., but the melting point of PCNH is 146°C, and the decomposition point is 328°C [both in Jahresberichteber die Holtschlichte der Hemi (J) February J 353]. Boiling point is unknown. Furthermore, no literature has been found regarding a technique for purifying PCNB by distillation.

As mentioned above, there is no method for industrially obtaining PCNB with a low HCB content, including a purification method.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for industrially obtaining high-purity PCNB, which does not have the drawbacks of these conventional techniques, requires simple operations, and is advantageous for large-scale implementation, especially a continuous distillation purification method. .

[Means and effects for solving the problems] In order to solve the above problems, the present inventors have made intensive studies on distillation methods.

The present inventors have discovered that P CN B thermally decomposes at a wide range of temperatures below the decomposition point, and HCB is produced as a by-product. Under these circumstances and past knowledge, distillation purification of PCNB was thought to be extremely difficult, but as a result of intensive study on a method to remove HCB by vacuum distillation and obtain high-purity PCNB, we found that HC due to thermal decomposition of PCNB
It was found that the by-product of B almost disappears below 250°C, and if distillation is carried out in the temperature range of both the melting point of PCNB, 146°C, and the temperature at which PCNB thermally decomposes, 250°C,
We discovered that it was possible to fractionally distill HCB and PCN B, and filed an application earlier (Japanese Patent Application No. 71202/1982).

Although this method can be carried out using either a batch-type apparatus or a continuous-type apparatus, it is considered more advantageous to use a continuous-type apparatus for industrial implementation. When using a continuous distillation apparatus, PCN B containing impurities such as HCB is fed into the middle stage of the distillation column, and impurities such as HCB, which have a lower boiling point than PCNB, are distilled out from the upper part of the column. PCNB with low HCB content is obtained as a product from the bottom. however,
Since the melting point of PCNB is 146°C, the distillation column and all the distillation equipment must be kept at a higher temperature, which is not energy-saving. Furthermore, PCNB and HCB have a high sublimation property. There was a problem in that the above-mentioned parts adhered to the vicinity of the distillate part, especially the condenser, and there was a risk of clogging in some cases.

As a result of further intensive studies to solve the problems of the above-mentioned continuous distillation method, the present inventors found that PC containing HCB
NB with high solubility, and even crude PCNB.
If the solution is dissolved in a solvent with a relatively lower boiling point than PC and fed to the distillation column, the temperature at the top of the distillation column will be lower than
Compared to the case where only NB is supplied, it is possible to reduce the amount of heat required for heat retention, and it is also possible to suppress sublimation, thereby avoiding clogging in the system due to PCNB solidification and achieving stability. The present invention was completed based on the discovery that it is possible to carry out the operation.

That is, when purifying pentachloronitrobenzene containing hexachlorobenzene as an impurity, the present invention involves dissolving the pentachloronitrobenzene in a solvent, supplying the liquid to a distillation column, and continuously distilling it under reduced pressure at a temperature of 70 to 250°C. This is a method for obtaining high purity pentachloronitrobenzene, which is characterized by:

The present invention will be explained in detail below.

In the present invention, the crude PCNB that is subjected to vacuum distillation is obtained by chlorinating nitrobenzene or chloronitrobenzene and contains tetrachloronitrobenzene, HCB, etc. as impurities, and it is obtained by nitration of pentachlorobenzene, which contains unreacted impurities. This applies to substances containing pentachlorobenzene, HCB, etc.
Of course, it is not limited to these.

In addition, the solvent used in the method of the present invention is liquid at room temperature, has high solubility in PCNB, and has a boiling point of HC.
B and P CN Relatively lower than B lobenzenes, diethylene glycol dibutyl ether, diethylene glycol diethyl ether, dimethyl sulfoxide, N,
N-dimethylformamide, ethylene glycol, N-
Examples include methylpyrrolidone and ethylbenshade. Among them, nitrobenzene and chloronitrobenzene have particularly high distillation efficiency due to the temperature and vapor pressure during vacuum distillation operation, and furthermore, these substances can be converted to PCNB by chlorination, so it is preferable to use them as a solvent. is most preferred.

The feed concentration of P CN B containing HCB can be arbitrarily selected within the range allowed by the solubility in the solvent or mixed solvent thereof at the temperature of the feed point, but is preferably 10 to 80% by weight. If the amount of solvent used exceeds this range, the advantages obtained by the present invention cannot be expected, and if it falls below this range, the size of the distillation equipment will increase, and at temperatures suitable for industrial implementation, thermal decomposition will occur. In order to cause
Performed at pressures in the range ~17 ChzHg.

Further, the pressure at the bottom of the column is necessarily determined from the degree of pressure loss specific to the distillation column used and the set pressure at the top of the column.

As mentioned above, the temperature in the system during distillation is above the temperature corresponding to the set pressure in the column, and below the decomposition point of PCNB.
It is carried out in a temperature range of 0°C.

The lower limit of the temperature at the top of the column during distillation is the higher of the boiling point of the solution used at the set vacuum degree at the top of the column or the freezing point (crystallization point) of the composition distilled from the top of the column. Further, the upper limit of the temperature at the bottom of the tower is the temperature at which thermal decomposition of PCNB occurs. That is,
The temperature at the top of the column is 70-230°C, preferably 90-2
The temperature at the bottom of the column is 150-250°C, preferably 170-230°C.

The reflux ratio during distillation is 0.1 to 100, preferably 1 to 5.
Execute with 0.

This is undesirable as it leads to a decrease in productivity.

The number of theoretical plates in the distillation column is 1 to 100, preferably 5 to 60.
It is best to use something with a tiered level. The type and packing of the distillation column are not particularly selected, but the bottom temperature is lowered as much as possible to near the melting point of P CN B to save energy.
Furthermore, in order to prevent temperature rise in order to avoid thermal decomposition of PCNB, it is preferable to use a column type and packing that has a pressure drop as small as possible between the column top and the column bottom (reboiler).

Theoretically, it is possible to feed the nitrobenzene solution of PCNB to the continuous distillation apparatus at the top of the column or at the bottom (part of the reboiler). It is preferable to do so.

Since it has a lower boiling point, it is possible to distill it out by distillation and use the PCNB remaining at the bottom (reboiler) as a product, but if desired, after removing impurities by distillation, distillation should be performed again to make PCNB. Even higher purity PCN can be obtained by distillation.
You can also get B.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples. The following percentages indicate weight percentages.

Example-1 Continuous distillation column equivalent to 15 theoretical plates (150 mil
Rough PCNB at 80℃ in the 6th stage of 3659mm filling part H)
About 50% solution of Trobenzene 48.1%, Tetrachloronitrobenzene 6.3%, HCB 0.3%, PCN
B45.3%) was supplied to 17.1 at a flow rate of 9/Hr,
Purified PCNB (tetrachloronitrobenzene: trace, HCB: 0.1%, PCNB) was purified from the bottom of the column under the following operating conditions: top pressure 20 torr, bottom pressure 32 torr, top temperature 128°C, bottom temperature 197°C, reflux ratio 2. :99
．． 9%) at a color ratio rate of 7.4 kg/Hr, and at the same time, tetrachloronitrobenzene, HCB,
Trobenzene 84.6 in nitrobenzene solution of PCNB
%, Tetrachloronitrobenzene 11.1%, HCBO
03%, P CN B 4.0%) to 9-7 9/Hr
was obtained at a distillation rate of .

〔Effect of the invention〕

There is no industrial production method or purification method for high-purity P CN B, and there is no vapor pressure data.On the basis of the data on the melting point and decomposition point of PCNB, and the melting point, boiling point, and vapor pressure of HCB, it is possible to estimate the separation of PCNB and HCB by distillation. Under conditions where separation is presumed to be difficult, the method of obtaining high purity PCNB by continuous vacuum distillation that supplies crude PCNB as a solution according to the present invention can be operated at low temperatures, saving energy and providing simple operation. This method is industrially very valuable as it can be carried out industrially at low cost and provides good operating conditions.

[Brief explanation of the drawing]

Figure 1 shows the distillation column used in Example-1, which has a theoretical plate number of 15, with the 6th stage serving as the liquid feed port, and the column top pressure being 20 torr.
r, when a crude PCNB 50i mass % nitrobenzene solution was supplied under the conditions of a column top reflux ratio of 2 and crude P CN B
FIG. 2 is a diagram showing the relationship between the number of distillation column plates and the temperature distribution at the top of the distillation column when only the distillation column is supplied. In the figure, the ○ mark represents the case where a 50% by weight crude PCNB nitrobenzene solution was supplied, and the X mark represents the case when only PCNB was supplied.

Claims (2)

[Claims] (1) When purifying pentachloronitrobenzene containing hexachlorobenzene as an impurity, the pentachloronitrobenzene is dissolved in an inert organic solvent, fed to a distillation column, and continuously distilled under reduced pressure at a temperature of 70 to 250°C. A method for obtaining high purity pentachloronitrobenzene, characterized by: (2) The method according to claim 1, wherein the inert organic solvent is nitrobenzene or chloronitrobenzenes.