JPH05170706A - Nitration of toluene - Google Patents

Abstract

(57) [Summary] [Structure] In the nitration reaction carried out by dropwise addition of a mixed acid of sulfuric acid and nitric acid into toluene, the molar ratio of nitric acid to toluene is 1.02 to 1.15, 2. A method for nitration of toluene, characterized in that the weight ratio of sulfuric acid to water is 2.5 to 4.0, the mixed acid dropping time to the total reaction time is 80% or less, and the reaction temperature is 0 to 50 ° C. [Effect] The production of m-nitrotoluene can be suppressed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for nitrating toluene to produce nitrotoluene.

[0002]

BACKGROUND OF THE INVENTION Dinitrotoluene (hereinafter abbreviated as DNT) is an intermediate in the synthesis of tolylene diisocyanate (hereinafter abbreviated as TDI) which is a raw material for synthesizing polyurethane. TDI is the starting material of toluene-sulfuric acid-
DNT produced by nitration with nitric acid-based mixed acid is aminated by hydrogenation to tolylenediamine, and this amine is phosgenated to synthesize. In this reaction process, in the present process, a by-product ortho-tolylenediamine (hereinafter referred to as O
A few percent of TD is generated. This OTD is separated after the amination process in order to reduce the purity of TDI during TDI synthesis.

The problems that occur when this OTD is generated are: Since OTD is separated by a distillation method, waste energy is required for separation. 2. The conversion rate of toluene, which is a raw material, into TDI also decreases. The amount of sulfuric acid and nitric acid generated by OTD is wasted, and there is a point that the capacity of the reactor and the like cannot be fully utilized.

The cause of OTD formation is 2, in nitration.
In the production of 3- and 3.4-DNT. As a method of reducing OTD, it can be considered to reduce the production of 2,3- and 3,4-DNT.
For a reduction in the production of 3- and 3.4-DNT, m-
It is necessary to reduce the production of nitrotoluene (hereinafter abbreviated as m-NT). That is, by reducing the production of m-NT in the primary nitrification, it is possible to reduce OTD, further reduce the amount of toluene used as a raw material, and effectively utilize the existing nitrification facility.

Here, as a conventionally known method for nitration of toluene, some examples of some nitration reactions of toluene which have been reported in the past will be given. A nitration method using 94% nitric acid alone (1) and There is a nitration method (2) in which the difference in composition ratio and composition of mixed acid is observed.

As for the method (1), toluene was added to 5.5.
Method of nitration by dropping an equivalent amount of 94% nitric acid [Journal of the Chemical Society (J. Ch.
em. Soc. , 1922, 121,270. )], And the production ratio of m-NT at 0 ° C. is 2.5%, but there is no description of conversion rate, yield, and reaction time. However, in the same nitration method, although the production ratio of m-NT is not described, it is reported that the conversion is poor [Industrial Engineering Chemistry (Ind. Enng. Chem., 48, (195
6), 1278. )] Is also done.

For the method (2), the DVS value (DVS
Value = g number of sulfuric acid in mixed acid / g number of water in waste acid) = 3.1
3. Nitration method with mixed acid using about 2 equivalents of nitric acid and nitrous acid [J. Chem. Soc., 1947, 921.]
The production ratio of m-NT at 0 ° C. is 3.3%, but the reaction time is long.

[0008] As described above, for those producing a small amount of m-NT, the reaction time is long and it is necessary to use a large excess amount of nitric acid. Compared with the above, it was unsuitable in terms of volumetric efficiency, reaction time, and effective use of resources.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for suppressing the formation of m-NT in the process of nitration of toluene.

[0010]

Means for Solving the Problems The inventors of the present invention have made extensive studies to solve the above problems. As a result, as shown in FIG. 1, by lowering the reaction temperature during primary nitrification,
The yield of m-NT in the obtained mononitrotoluene was 3
It can be reduced by a relatively strong amount, and in the reaction, the composition ratio of the nitric acid-sulfuric acid-based mixed acid, which is a reagent for nitration, and the mixed acid dropping time can be set to appropriate values to reduce the reaction temperature. It was found that the increase in the amount of recovered toluene was suppressed, the reaction proceeded almost quantitatively, and the total reaction time was very short, and the reaction was completed within 1 hour. By further secondary nitrification of the m-NT reduced reaction mass under the current secondary nitrification conditions,
It was confirmed that the yields of 2,3- and 3,4-DNT could be reduced by more than 30%.

That is, according to the present invention, in a nitration reaction carried out by dropping a mixed acid of sulfuric acid and nitric acid into toluene, the molar ratio of nitric acid to toluene is 1.02 to 1.1.
5. Weight ratio of sulfuric acid to water in waste acid after completion of reaction 2.
5 to 4.0, mixed acid dropping time to the total reaction time 80%
Hereinafter, the method for nitrating toluene is characterized in that the reaction temperature is set to 0 to 50 ° C. to suppress the production of m-nitrotoluene.

In the present invention, nitric acid is used in a small excess over the equivalent amount to toluene. However, if the equivalent ratio is less than 1.02, the reaction cannot be completed in a short time and the reaction amount becomes 1.15 or more. Then, a side reaction occurs, the conversion rate of toluene decreases,
The yield of mononitrotoluene (hereinafter, abbreviated as MNT) decreases, which is not economical.

Further, since the production of DNT is increased, when the primary nitrated mass is subjected to secondary nitration, the DNT in the primary nitrated mass is further nitrated to produce trinitrotoluene. However, since the risk increases, the equivalent ratio is preferably about 1.02 to 1.15. Even more preferably, it is about 1.04 to 1.10.

As for the reaction temperature, when the temperature is lower than 0 ° C., the reaction rate becomes slow and a long reaction time is required.
Further, cooling becomes very difficult, and when the temperature exceeds 50 ° C., the production of DNT increases and the conversion rate of toluene decreases, so 0 to 50 ° C. is preferable. Lower reaction temperature is m-
Although the yield of NT is remarkably reduced, it is more preferably 0 to 30 ° C. in consideration of a decrease in reaction rate, difficulty in cooling, and the like.

Regarding the DVS value, the larger the value, the more the production of DNT in the primary nitrification process, the higher the consumption of nitric acid, the lower the conversion of toluene, and the smaller the value, the slower the reaction rate. Since the conversion rate of toluene will decrease,
2.5 to 4.0 is preferable, and even more preferably,
It is 2.7 to 3.3 at 20 ° C and about 3.0 to 3.7 at 10 ° C.

When the mixed acid is added dropwise for more than 80% of the total reaction time, the reaction is not completed within the total reaction time and unreacted toluene remains, so that the total reaction It is preferably 80% or less of the time. Also,
If the mixed acid is added dropwise in less than 50% of the total reaction time, the reaction will be completed in a shorter time, so less than 50% is even more preferable.

[0017]

EXAMPLES Hereinafter, the method of the present invention will be described more specifically with reference to examples.

Example 1 27.6 g of toluene was placed in a 200 ml four-necked flask equipped with a stirrer, a dropping funnel, a thermometer, and a Dimroth condenser, and 98% of the dropping funnel was maintained while keeping the temperature at 0 ° C. Nitric acid 21.2g, 95% sulfuric acid 68.1g,
And 6.8 g of water were added over 25 minutes. 50 minutes after the start of the addition of the mixed acid, the content was added to 100 ml of ice water and extracted with ethyl acetate to obtain an oil layer of 38.9 g. As a result of analyzing this by gas chromatography, toluene was 1.
0 g, o-NT 18.2 g, m-NT 0.8 g (m
-NT / MNT = 2.3%), p-NT 14.9 g,
3.4 g of 2,4-DNT and 0.7 g of 2,6-DNT
It turned out to include.

Example 2 27.6 g of toluene was placed in a 200 ml four-necked flask equipped with a stirrer, a dropping funnel, a thermometer, and a Dimroth condenser, and 98% from the dropping funnel was maintained while keeping the temperature at 10 ° C. Nitric acid 21.2g, 95% sulfuric acid 68.1
g and 10.4 g of water were added over 25 minutes. 50 minutes after the start of the addition of the mixed acid, the content was taken in a separating funnel, the waste acid was separated, and a part of the obtained oil layer was analyzed by gas chromatography to find that toluene was 0.02% and o-
NT is 55.0%, m-NT is 2.3% (m-NT / M
NT = 2.4%), p-NT 38.9%, 2,4-D
It was found to contain 3.0% of NT and 0.7% of 2,6-DNT.

Example 3 46.0 g of toluene was placed in a 200 ml four-necked flask equipped with a stirrer, a dropping funnel, a thermometer, and a Dimroth condenser, and 98% was taken from the dropping funnel while keeping the temperature at 20 ° C. Nitric acid 35.4 g, 95% sulfuric acid 113.5
g and 20.5 g of water were added over 25 minutes. 50 minutes after the start of the addition of the mixed acid, the content was put in a separating funnel and the waste acid was separated to obtain 68.0 g of an oil layer. As a result of analyzing this by gas chromatography, o-NT was 39.6.
g, m-NT 1.8 g (m-NT / MNT = 2.7)
%), 26.0 g of p-NT, and 0.6 g of DNT.

Further, 68.0 g of the obtained primary nitrification mass was placed in the same apparatus as used for the above reaction, and 98% nitric acid 3% was added from the dropping funnel while maintaining the temperature at 70 ° C.
A mixed acid of 4.8 g, 95% sulfuric acid 111.7 g, and water 6.1 g was added over 25 minutes. 40 minutes after the start of the addition of the mixed acid, the contents were transferred to a separating funnel to separate the waste acid, and the oil layer 92.
0 g was obtained. As a result of analyzing this by gas chromatography, 70.6 g of 2,4-DNT, 2,6-DNT
NT 17.5g, 2,3-DNT 1.2g (1.3
%), 1.4 g (1.5%) of 3,4-DNT, and 1.3 g of water and waste acid.

Example 4 To a 200 ml four-necked flask equipped with a stirrer, a dropping funnel, a thermometer, and a Dimroth condenser, 27.6 g of toluene was placed, and the temperature was kept at 50 ° C., and 98% was taken from the dropping funnel. Nitric acid 19.7 g, 95% sulfuric acid 68.1
g and 18.6 g of water were added over 30 minutes. 50 minutes after the start of the addition of the mixed acid, the content was taken in a separating funnel, the waste acid was separated, and a part of the obtained oil layer was analyzed by gas chromatography to find that toluene was 0.02% and o-
NT is 59.0%, m-NT is 3.6% (m-NT / M
NT = 3.6%), p-NT 36.4%, 2,4-D
It was found that it contained 0.7% of NT and 0.2% of 2,6-DNT.

Comparative Example 1 27.6 g of toluene was placed in a 200 ml four-necked flask equipped with a stirrer, a dropping funnel, a thermometer, and a Dimroth condenser, and 98% was added from the dropping funnel while keeping the temperature at 70 ° C. Nitric acid 21.2g, 95% sulfuric acid 68.1
g and 16.6 g of water were added over 45 minutes. 60 minutes after the start of the addition of the mixed acid, the content was put in a separating funnel and the waste acid was separated to obtain 41.4 g of an oil layer. As a result of analyzing this by gas chromatography, o-NT was found to be 23.4.
1.6 g of g and m-NT (m-NT / MNT = 4.1
%), 15.0 g of p-NT, and 1.4 g of DNT.

Further, 41.4 g of the obtained primary nitrification mass was placed in an apparatus similar to the apparatus used for the above reaction, and 98% nitric acid 2% was added from a dropping funnel while maintaining the temperature at 70 ° C.
A mixed acid of 0.7 g, 66.3 g of 95% sulfuric acid, and 3.6 g of water was added over 25 minutes. 40 minutes after the start of the addition of the mixed acid, the content was transferred to a separating funnel to separate the waste acid, and the oil layer 54.5
g was obtained. As a result of analyzing this by gas chromatography, 41.8 g of 2,4-DNT, 2,6-DN
T is 10.5 g and 2,3-DNT is 0.9 g (1.7
%) And 1.3 g (2.4%) of 3,4-DNT.

Comparative Example 2 27.6 g of toluene was placed in a 200 ml four-necked flask equipped with a stirrer, a dropping funnel, a thermometer, and a Dimroth condenser, and 98% of the dropping funnel was maintained while maintaining the temperature at 60 ° C. Nitric acid 19.9 g, 95% sulfuric acid 68.1
g and 18.6 g of water were added over 25 minutes. 50 minutes after the start of the addition of the mixed acid, the content was taken in a separating funnel, waste acid was separated, and a part of the obtained oil layer was analyzed by gas chromatography. As a result, o-NT was 57.6%, m-N
T is 3.9% (m-NT / MNT = 3.9%), p-N
T is 36.4%, 2,4-DNT is 1.8%, 2,6-
It was found to contain 0.5% DNT.

[0026]

INDUSTRIAL APPLICABILITY The present invention is based on TDI which is a raw material of urethane.
In the nitration of toluene with nitric acid-sulfuric acid mixed acid, which is the first step of the production, the production of m-NT, which is a precursor of OTD, is taken out as an unnecessary by-product during the synthesis of TDI by a very easy method. It is a useful invention for controlling waste, effective use of resources, and reduction of waste.

[Brief description of drawings]

FIG. 1 Reaction temperature and m-N in primary nitrification of toluene
It is a figure which shows the relationship with the production ratio of T.

Claims (1)

[Claims] 1. In a nitration reaction carried out by dropwise adding a mixed acid of sulfuric acid and nitric acid into toluene, a molar ratio of nitric acid to toluene of 1.02 to 1.15, and sulfuric acid to water in waste acid after completion of the reaction. Weight ratio of 2.5 to 4.0, mixed acid dropping time to the total reaction time of 80% or less, reaction temperature of 0 to 50
A method for nitration of toluene, characterized in that the production of m-nitrotoluene is suppressed by setting the temperature to ℃.