Method for synthesizing 2, 4-dichlorobenzaldehyde by using 4-chloro-2-nitrotoluene

Abstract

The invention provides a method for synthesizing 2, 4-dichlorobenzaldehyde by using 4-chloro-2-nitrotoluene, which comprises the following steps: by using a byproduct 2-nitro-4-chlorotoluene as a raw material, reacting 4-chloro-2-nitrotoluene with chlorine under the action of ultraviolet light and a catalyst to obtain 2, 4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 2, 4-dichlorobenzyl chloride and 2, 4-dichlorobenzyl chloride; the method comprises the following steps: adding a mixture I of 2, 4-dichlorotrichlorobenzyl into a reaction kettle, carrying out reduced pressure rectification, and carrying out hydrolytic hydroformylation, elutriation alkali washing and distillation on 2, 4-dichlorobenzyl chloride obtained by rectification to obtain a 2, 4-dichlorobenzaldehyde finished product. The process route provided by the invention has the advantages of low raw material cost, simple process, low post-treatment energy consumption and the like, solves the problem of recycling of the by-product 2-nitro-4-chlorotoluene, and meets the development requirements of green fine chemical engineering.

Description

Technical Field

[0001] The present invention belongs to the field of fine chemical industry, and relates to the synthesis and purification technologies of fine pharmaceutical intermediates. In particular, it relates to a method for synthesizing 2,4-dichlorobenzaldehyde by using the by-product 4-chloro-2-nitrotoluene as a raw material, which has low raw material cost, simple process and low energy consumption in post-treatment. Background Art

[0002] Currently, in the context of the era of advocating green environmental protection and safe production, ensuring the safe production of chemical enterprises, energy conservation and emission reduction, and achieving effective control of waste water, waste gas and waste residue are major challenges faced by the chemical industry, and also external pressures for chemical enterprises to accelerate the upgrading of process technologies, strengthen chemical ecological cycles and clean production. In such a general environment, it has had a huge impact on the traditional chemical industry. Many chemical enterprises have problems such as large emissions, high energy consumption and low efficiency, and there is an urgent need for industrial upgrading and technological innovation to reduce the production risk coefficient and solve the problems of the three wastes.

[0003] For example, 2,4-dichlorobenzaldehyde, which is in short supply in the current market, is obtained by using toluene as a raw material according to the existing traditional process route. Through chlorination, rectification, adsorption separation and recrystallization, 2,4-dichlorotoluene is obtained, and then through side-chain photochlorination, rectification and purification, hydrolysis and aldehyde formation and rectification, the finished product of 2,4-dichlorobenzaldehyde is obtained.

[0004] However, due to the disadvantages of the traditional production process such as long route, many post-treatment processes and high energy consumption, the product quality is also difficult to guarantee. At the same time, there are many by-products of hydrochloric acid in the process, serious three-waste pollution and low product yield. Under the pressure of comprehensive environmental governance, due to the serious environmental pollution caused by the production of these raw materials, the previous bulk raw materials have become difficult to obtain, the production cost has increased greatly, and even production has stopped.

[0005] 2-Nitro-4-chlorotoluene is produced as a by-product during the chlorination of o-nitrotoluene to produce 2-chloro-6-nitrotoluene. When o-nitrotoluene is chlorinated to produce 2-chloro-6-nitrotoluene, due to the high para regioselectivity, in actual production, the content of 2-chloro-6-nitrotoluene accounts for about 60%, while the content of 2-nitro-4-chlorotoluene accounts for about 30%.

[0006] 2-Chloro-6-nitrotoluene has a broad industrial application market, and many downstream products have been developed, such as 2-chloro-6-fluorotoluene, 2-chloro-6-fluorobenzaldehyde, dichlorquinic acid, and mesotrione, etc. However, 2-nitro-4-chlorotoluene has rarely been studied and developed. Usually, it is only used as a raw material for ice dye red base KB and naphthol AS-KB, with little demand and lack of more extensive industrial application value. Therefore, it is often discarded as waste by most production enterprises.

[0007] Therefore, it has become particularly urgent and highly valuable and meaningful to solve the development problems of downstream products of 2-nitro-4-chlorotoluene. Summary of the Invention

[0008] To solve the above problems, the present invention provides a method for synthesizing 2,4-dichlorobenzaldehyde from 4-chloro-2-nitrotoluene. The inventors of the present invention have developed a method for synthesizing 2,4-dichlorobenzaldehyde using 2-nitro-4-chlorotoluene, a by-product produced during the chlorination of o-nitrotoluene to produce 2-chloro-6-nitrotoluene, as a raw material. Using the by-product 2-nitro-4-chlorotoluene as a raw material, under the action of ultraviolet light and a catalyst, 4-chloro-2-nitrotoluene reacts with chlorine gas to obtain a mixture I of 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride, 2,4-dichlorobenzylidene chloride, and 2,4-dichlorotrichlorobenzyl. Then, vacuum distillation is carried out, and the obtained 2,4-dichlorobenzylidene chloride is further subjected to hydrolysis, aldehyde formation, water separation, alkali washing, and distillation to obtain the finished product of 2,4-dichlorobenzaldehyde. The process route of the present invention has the advantages of low raw material cost, simple process, and low energy consumption in post-treatment, and solves the problem of resource utilization of the by-product 2-nitro-4-chlorotoluene, meeting the development requirements of green fine chemistry.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for synthesizing 2,4-dichlorobenzaldehyde from 4-chloro-2-nitrotoluene, the method comprising using 4-chloro-2-nitrotoluene as a raw material, and under the action of ultraviolet light, an initiator, and a dehydrating agent, reacting 4-chloro-2-nitrotoluene with chlorine gas to obtain a mixture I of 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride, 2,4-dichlorobenzylidene chloride, and 2,4-dichlorotrichlorobenzyl; subjecting the mixture I to vacuum distillation, and further subjecting the obtained 2,4-dichlorobenzylidene chloride to hydrolysis, aldehyde formation, alkali washing, and distillation to obtain the finished product of 2,4-dichlorobenzaldehyde.

[0011] As a preferred embodiment of the present invention, the method comprises the following steps:

[0012] 1) Put the by-product 4-chloro-2-nitrotoluene into a reactor and seal it;

[0013] 2) Put the combined catalyst into the reactor of step 1) and place it in an oil bath;

[0014] 3) Stir and heat to raise the temperature of the material to 155 ± 5 °C. Turn on the ultraviolet lamp and conduct light-induced chlorination for denitration and side-chain photochlorination reaction. Monitor the reaction progress by gas chromatography until the conversion rate of the raw material 4-chloro-2-nitrotoluene reaches over 99%. Then stop the reaction to obtain a mixture Ⅰ of 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride, 2,4-dichlorobenzylidene chloride, and 2,4-dichlorotrichlorobenzyl;

[0015] 4) Subject the mixture Ⅰ obtained in step 3) to vacuum distillation, collect the fore-fraction and the middle-fraction to obtain the bottom high-boiling substances;

[0016] 5) Charge sulfuric acid into the aldehyde formation reaction kettle, stir evenly, raise the temperature, and dropwise add the middle-fraction obtained in step 4). Keep the temperature constant, and control the end point of the reaction with the residual raw material ≤ 0.3% as the standard to obtain the aldehyde formation and hydrolysis material Ⅱ;

[0017] 6) Add water to the aldehyde formation and hydrolysis material Ⅱ obtained in step 5), pass chilled brine through the jacket to cool down, let it stand for stratification, and drain off the lower-layer dilute sulfuric acid to obtain the upper-layer organic phase;

[0018] 7) Add liquid alkali to neutralize the upper-layer organic phase obtained in step 6), pass chilled brine through the jacket to cool down, let it stand for stratification to obtain the crude 2,4-dichlorobenzaldehyde;

[0019] 8) Transfer the crude 2,4-dichlorobenzaldehyde obtained by alkali washing and stratification in step 7) into the aldehyde re-distillation kettle, add the impurity removal agent and stir to react, raise the temperature for distillation to obtain the finished product of 2,4-dichlorobenzaldehyde.

[0020] As a preferred embodiment of the present invention, the fore-fraction and the bottom high-boiling substances obtained in step 4) are returned to step 1) as raw materials for recycling.

[0021] As a preferred embodiment of the present invention, in step 4), when collecting the fore-fraction, the vacuum degree is -0.098 MPa, the kettle temperature is 155 - 165 °C, and the top temperature is 125 - 135 °C.

[0022] As a preferred embodiment of the present invention, in step 4), when collecting the middle-fraction, the vacuum degree is -0.098 MPa, the kettle temperature is 175 - 185 °C, and the top temperature is 135 - 145 °C.

[0023] As a preferred embodiment of the present invention, in step 5), the concentration of sulfuric acid is 80 - 85%, raise the temperature to 85 - 95 °C and dropwise add the middle-fraction obtained in step 4), and the reaction temperature is 85 - 95 °C.

[0024] As a preferred embodiment of the present invention, in step 6), after adding water, dilute the sulfuric acid to a concentration of 30 - 40%; cool down to 10 - 20 °C.

[0025] As a preferred embodiment of the present invention, in step 7), the final pH is 9.5 - 10.5.

[0026] As a preferred embodiment of the present invention, in step 2), the combined catalyst is a mixture of azobisisobutyronitrile and phosphorus trichloride. The addition amount of azobisisobutyronitrile is 0.3% of the raw material amount, and the addition amount of phosphorus trichloride is 0.5% of the raw material.

[0027] As a preferred embodiment of the present invention, in step 8), the impurity remover is hexamethylenetetramine, and the addition amount is 0.5% of the weight ratio of the crude 2,4 - dichlorobenzaldehyde.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1) The present invention uses 2 - nitro - 4 - chlorotoluene, a by - product in the production of 2 - chloro - 6 - nitrotoluene by chlorination of o - nitrotoluene, as a raw material to synthesize 2,4 - dichlorobenzaldehyde. The method is as follows: Using 2 - nitro - 4 - chlorotoluene as the raw material, under the action of ultraviolet light and a catalyst, 4 - chloro - 2 - nitrotoluene reacts with chlorine to obtain a mixture I of 2,4 - dichlorobenzyl chloride, 4 - chloro - 2 - nitrobenzyl chloride, 4 - chloro - 2 - nitrocinnamyl chloride, 2,4 - dichlorocinnamyl chloride, and 2,4 - dichlorotrichlorobenzyl. Then, vacuum distillation is carried out. The 2,4 - dichlorocinnamyl chloride obtained by distillation is further subjected to hydrolysis, aldehyde formation, water separation, alkali washing, and distillation to obtain the finished product of 2,4 - dichlorobenzaldehyde.

[0030] 2) The process route of the present invention has the advantages of low raw material cost, simple process, and low energy consumption in post - treatment, solves the problem of the resource utilization of the by - product 2 - nitro - 4 - chlorotoluene, and meets the development requirements of green fine chemistry.

[0031] 3) The present invention seeks a more economical synthetic route for the industrial production of 2,4 - dichlorobenzaldehyde. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 is the process flow chart of the present invention.

[0034] Figure 2 is the spectrum of the finished product of 2,4 - dichlorobenzaldehyde obtained in step 8) of Example 1.

[0035] Figure 3 It is the finished product spectrum of 2,4-dichlorobenzaldehyde obtained in step 8) of Example 2.

[0036] Figure 4 It is the finished product spectrum of 2,4-dichlorobenzaldehyde obtained in step 8) of Comparative Example 1. Specific embodiments

[0037] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0038] See Figure 1 , the present invention provides a method for synthesizing 2,4-dichlorobenzaldehyde using 4-chloro-2-nitrotoluene, and the reaction equation is as follows:

[0039]

[0040] The present invention uses 4-chloro-2-nitrotoluene (1) as a raw material. Under the action of ultraviolet light, an initiator and a dehydrating agent, 4-chloro-2-nitrotoluene (1) reacts with chlorine gas to obtain a mixture I of 2,4-dichlorobenzyl chloride (3), 4-chloro-2-nitrobenzyl chloride (4), 4-chloro-2-nitrobenzylidene chloride (5), 2,4-dichlorobenzylidene chloride (6) and 2,4-dichlorotrichlorobenzyl (8); the mixture I is subjected to vacuum distillation, and the 2,4-dichlorobenzylidene chloride obtained by distillation is further subjected to hydrolysis and aldehyde formation, water precipitation and alkali washing, and distillation to obtain the finished product of 2,4-dichlorobenzaldehyde.

[0041] Furthermore, the method includes the following steps:

[0042] 1) Put the by-product 4-chloro-2-nitrotoluene into a reactor and seal it.

[0043] 2) Put the combined catalyst into the reactor in step 1) and place it in an oil bath.

[0044] Furthermore, the combined catalyst is a mixture of azobisisobutyronitrile and phosphorus trichloride. The addition amount of azobisisobutyronitrile is 0.3% of the raw material amount, and the addition amount of phosphorus trichloride is 0.5% of the raw material amount.

[0045] 3) Stir and heat to raise the material temperature to 155 ± 5 °C. Turn on the ultraviolet lamp and carry out light-induced chlorination for nitro group removal and side-chain photochlorination reaction. Monitor the reaction progress by gas chromatography until the conversion rate of raw material 4-chloro-2-nitrotoluene reaches over 99%, then stop the reaction to obtain mixture I containing 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride, 2,4-dichlorobenzylidene chloride and 2,4-dichlorotrichlorobenzyl.

[0046] 4) Carry out vacuum distillation on the mixture I obtained in step 3), collect the fore-fraction and middle-fraction to obtain the bottom high-boiling substances.

[0047] Among them:

[0048] The collected fore-fraction mainly contains 2,4-dichlorobenzyl chloride, 2,4-dichlorobenzylidene chloride and other low-boiling substances, which are used to return to step 1) to replace the raw material 4-chloro-2-nitrotoluene;

[0049] The middle-fraction collected by distillation mainly consists of 2,4-dichlorobenzylidene chloride, in which the content of 2,4-dichlorobenzylidene chloride ≥ 95.0%, 2,4-dichlorobenzyl chloride ≤ 0.5%, 2,4-dichlorotrichlorobenzyl ≤ 5%, and it is used for hydrolysis to produce 2,4-dichlorobenzaldehyde;

[0050] The main components of the bottom high-boiling substances are 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride and 2,4-dichlorotrichlorobenzyl, which are returned to step 1) as raw materials for recycling.

[0051] 5) Put sulfuric acid into the aldehyde-forming reaction kettle, stir evenly, raise the temperature, dropwise add the middle-fraction obtained in step 4), keep the temperature, and control the reaction end point with the residual raw material ≤ 0.3% as the standard to obtain aldehyde-forming hydrolysis material II.

[0052] 6) Add water to the aldehyde-forming hydrolysis material II obtained in step 5), pass chilled brine into the jacket for cooling, let it stand for stratification, and drain the lower-layer dilute sulfuric acid to obtain the upper-layer organic phase.

[0053] 7) Add liquid alkali to neutralize the upper-layer organic phase obtained in step 6), pass cooling water into the jacket for cooling, let it stand for stratification to obtain the crude product of 2,4-dichlorobenzaldehyde.

[0054] 8) Transfer the crude product of 2,4-dichlorobenzaldehyde obtained by alkali washing and stratification in step 7) into the aldehyde re-distillation kettle, add a decontaminant and stir for reaction, raise the temperature for distillation to obtain the finished product of 2,4-dichlorobenzaldehyde.

[0055] Furthermore, the decontaminant is hexamethylenetetramine, and the addition amount is 0.5% of the weight ratio of the crude product of 2,4-dichlorobenzaldehyde.

[0056] The raw materials used in the present invention: 4-chloro-2-nitrotoluene, which is a by-product in the production of 6-chloro-2-nitrotoluene, is obtained by rectification and recrystallization, and the content of 4-chloro-2-nitrotoluene is ≥98%. Liquid chlorine, industrial grade, commercially available. 2,2'-Azobis(2-methylpropionitrile), industrial grade, commercially available. Phosphorus trichloride, industrial grade, commercially available. Sulfuric acid, 98%, industrial grade, commercially available. Sodium hydroxide, 30%, industrial grade, commercially available. Hexamethylenetetramine, industrial grade, commercially available.

[0057] Example 1

[0058] See Figure 1 , the present invention provides a method for synthesizing 2,4-dichlorobenzaldehyde using 4-chloro-2-nitrotoluene, comprising the following steps:

[0059] 1) Put 175 g of the by-product 4-chloro-2-nitrotoluene (content 98%) into a three-necked round-bottomed closed photoreaction flask. After assembling and sealing the reaction flask, a thermometer, a pressure gauge and an LED ultraviolet lamp (power 15 W, wavelength 365 nm) are provided on the reaction device.

[0060] 2) Put 0.525 g of the catalyst 2,2'-azobis(2-methylpropionitrile) and 0.875 g of the catalyst phosphorus trichloride into the photoreaction flask in step 1), and then place the reaction device in an oil bath.

[0061] 3) Turn on the stirrer of the reaction device and the heating device of the oil bath, heat the material temperature to 155 ± 5 °C, then turn on the ultraviolet lamp, and carry out photo-chlorination and side-chain photo-chlorination reactions for de-nitration by passing chlorine. Monitor the reaction process by gas chromatography until the conversion rate of the raw material 4-chloro-2-nitrotoluene reaches 99%, then stop the reaction. The reaction time is 42 h, and a mixture I of 229 g of 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride, 2,4-dichlorobenzylidene chloride and 2,4-dichlorotrichlorobenzyl is obtained.

[0062] In the mixture I, the content of 2,4-dichlorobenzyl chloride is 2.0%, the content of 4-chloro-2-nitrobenzyl chloride is 10.2%, the content of 4-chloro-2-nitrobenzylidene chloride is 13.3%, the content of 2,4-dichlorobenzylidene chloride is 70.0%, the content of 2,4-dichlorotrichlorobenzyl is 4.2%, and other impurities are 1.7%.

[0063] 4) Carry out vacuum rectification on the reaction mixture obtained in step 3). When collecting the fore-fraction, the vacuum degree is -0.098 MPa, the kettle temperature is 160 ± 5 °C, and the top temperature is 130 ± 5 °C; when collecting the middle-fraction, the vacuum degree is -0.098 MPa, the kettle temperature is 180 ± 5 °C, and the top temperature is 140 ± 5 °C; the rest are the bottom high-boiling substances.

[0064] Among them:

[0065] 16.3 g of the fore fraction was collected, mainly containing 27.55% of 2,4-dichlorobenzyl chloride, 48.12% of 2,4-dichlorobenzal chloride, and 24.33% of other low-boiling substances, which was used to return to step 1) to replace the raw material 4-chloro-2-nitrotoluene.

[0066] 144.2 g of the middle fraction collected by rectification, mainly consisting of 2,4-dichlorobenzal chloride, with a content of 98.02% of 2,4-dichlorobenzal chloride and 1.98% of 2,4-trichlorobenzal chloride, was used for hydrolysis to produce 2,4-dichlorobenzaldehyde.

[0067] 68.3 g of the high-boiling residue at the bottom of the kettle, containing 34.07% of 4-chloro-2-nitrobenzyl chloride, 44.69% of 4-chloro-2-nitrobenzal chloride, 11.49% of 2,4-dichlorobenzal chloride, and 9.75% of 2,4-trichlorobenzal chloride, was returned to step 1) as a raw material for recycling.

[0068] 5) 140 g of sulfuric acid (sulfuric acid concentration is about 80%) was added to the aldehyde-forming reaction kettle. After stirring evenly, the temperature was raised to 90 ± 5 °C, and then the middle fraction obtained by rectification in step 4) was added dropwise. The reaction was carried out while maintaining the temperature at 90 ± 5 °C. The end point of the reaction was controlled by the residual raw material ≤ 0.3%. The total reaction time was 8 h to obtain the aldehyde-forming hydrolysis material II.

[0069] 6) 200 g of water was added to the aldehyde-forming hydrolysis material II obtained in step 5) to dilute the sulfuric acid to a concentration of about 30 - 40%. Then, cooling water was passed through the jacket to cool down until the material temperature dropped to 15 °C. After standing and separating, the lower-layer dilute sulfuric acid was drained to obtain 116.7 g of the upper-layer organic phase.

[0070] 7) 5% liquid alkali was added to the upper-layer organic phase obtained by separation in step 6) for neutralization. The end point pH was controlled at 10.0. After standing and separating, 109.4 g of the crude product of 2,4-dichlorobenzaldehyde was obtained.

[0071] 8) The crude product of 2,4-dichlorobenzaldehyde obtained by alkali washing and separation in step 7) was transferred to the aldehyde re-distillation kettle. After adding 0.55 g of the impurity-removing agent hexamethylenetetramine and stirring for 30 min, the temperature was raised for distillation to obtain 105 g of the finished product of 2,4-dichlorobenzaldehyde.

[0072] The obtained finished product of 2,4-dichlorobenzaldehyde was tested. The analysis results are shown in Figure 2 Table 1.

[0073] Table 1. Analysis Results

[0074]

[0075] As Figure 2As shown, the finished product of 2,4-dichlorobenzaldehyde has a 2,4-dichlorobenzaldehyde content of 99.77%, 2,4-dichlorobenzyl chloride of 0.06%, and 2,4-dichlorobenzal chloride of 0.16%, meeting the quality requirements specified for 2,4-dichlorobenzaldehyde.

[0076] Example 2

[0077] In this example, 16.3 g of the fore fraction and 68.3 g of the bottom high-boiling substances obtained by rectification in step 4) of Example 1 were used to replace part of the by-product 4-chloro-2-nitrotoluene in step 1) of Example 1 for recycling, and the others were the same as in Example 1.

[0078] See Figure 1 , the present invention provides a method for synthesizing 2,4-dichlorobenzaldehyde using 4-chloro-2-nitrotoluene, comprising the following steps:

[0079] 1) 16.3 g of the fore fraction obtained by rectification in step 4) of Example 1, 68.3 g of the bottom high-boiling substances obtained by rectification in step 4) of Example 1, and 90.4 g of the by-product 4-chloro-2-nitrotoluene (content 98%) were put into a three-necked round-bottom closed photoreaction flask. After the reaction flask was assembled and sealed, a thermometer, a pressure gauge, and an LED ultraviolet lamp (power 15 W, wavelength 365 nm) were installed on the reaction device.

[0080] 2) 0.525 g of the catalyst azobisisobutyronitrile and 0.875 g of the catalyst phosphorus trichloride were put into the photoreaction flask in step 1), and then the reaction device was placed in an oil bath.

[0081] 3) The stirrer of the reaction device and the heating device of the oil bath were turned on. The temperature of the material was heated to 155 ± 5 °C, and then the ultraviolet lamp was turned on for photo-chlorination and side-chain photo-chlorination reactions with chlorine to remove the nitro group. The reaction process was monitored by gas chromatography until the conversion rate of the raw material 4-chloro-2-nitrotoluene reached 99%, and the reaction was stopped. The reaction time was 36 h, and a mixture I of 190 g of 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzal chloride, 2,4-dichlorobenzal chloride, and 2,4-dichlorotrichlorobenzene was obtained.

[0082] The content of 2,4-dichlorobenzyl chloride in mixture I was 1.22%, the content of 4-chloro-2-nitrobenzyl chloride was 6.33%, the content of 4-chloro-2-nitrobenzal chloride was 8.31%, the content of 2,4-dichlorobenzal chloride was 75.33%, the content of 2,4-dichlorotrichlorobenzene was 6.72%, and other impurities were 2.09%.

[0083] 4) The reaction mixture obtained in step 3) is subjected to vacuum distillation. When collecting the fore-fraction, the vacuum degree is -0.098 MPa, the kettle temperature is 160 ± 5 °C, and the top temperature is 130 ± 5 °C; when collecting the middle-fraction, the vacuum degree is -0.098 MPa, the kettle temperature is 180 ± 5 °C, and the top temperature is 140 ± 5 °C; the rest are high-boiling residues at the bottom of the kettle.

[0084] Among them:

[0085] 13.4 g of fore-fraction is collected, mainly containing 17.27% of 2,4-dichlorobenzyl chloride, 53.20% of 2,4-dichlorobenzal chloride, and 29.52% of other low-boiling substances, which is used to return to step 1) to replace the raw material 4-chloro-2-nitrotoluene.

[0086] 133 g of the middle-fraction collected by distillation, the main component is 2,4-dichlorobenzal chloride, among which the content of 2,4-dichlorobenzal chloride is 97.11% and the content of 2,4-trichlorobenzal chloride is 2.89%, which is used for hydrolysis to produce 2,4-dichlorobenzaldehyde.

[0087] 43.9 g of high-boiling residues at the bottom of the kettle, among which the content of 4-chloro-2-nitrobenzyl chloride is 27.40%, the content of 4-chloro-2-nitrobenzal chloride is 35.94%, the content of 2,4-dichlorobenzal chloride is 16.30%, and the content of 2,4-trichlorobenzal chloride is 20.36%, which is returned to step 1) as raw materials for recycling.

[0088] 5) 133 g of sulfuric acid (sulfuric acid concentration is about 80%) is put into the aldehyde-forming reaction kettle. After stirring evenly, the temperature is raised to 90 ± 5 °C, and then the middle-fraction obtained by distillation in step 4) is dropped. The reaction is always carried out at a temperature of 90 ± 5 °C. The end point of the reaction is controlled by the standard that the residual raw material ≤ 0.3%. The total reaction time is 8 h to obtain aldehyde-forming hydrolysis material II.

[0089] 6) 200 g of water is added to the aldehyde-forming hydrolysis material II obtained in step 5) to dilute the sulfuric acid to a concentration of about 30 - 40%, and then frozen brine is passed into the jacket for cooling until the material temperature drops to 15 °C. After standing and separating, the lower-layer dilute sulfuric acid is drained away to obtain 118.3 g of the upper-layer organic phase.

[0090] 7) 5% liquid alkali is added to the upper-layer organic phase obtained by separation in step 6) for neutralization, and the end point pH is controlled at 10.0. After standing and separating, 108.3 g of crude 2,4-dichlorobenzaldehyde is obtained.

[0091] 8) The crude 2,4-dichlorobenzaldehyde obtained by alkali washing and separation in step 7) is transferred into an aldehyde re-distillation kettle. After adding 0.55 g of the impurity-removing agent hexamethylenetetramine and stirring for 30 min, then heating up for distillation to obtain 104 g of 2,4-dichlorobenzaldehyde finished product.

[0092] The obtained 2,4-dichlorobenzaldehyde finished product was tested, and the analysis results are shown in Figure 3 Table 2.

[0093] Table 2. Analysis Results

[0094]

[0095] As Figure 3 shown, for the 2,4-dichlorobenzaldehyde finished product, the content of 2,4-dichlorobenzaldehyde is 99.77%, 2,4-dichlorobenzyl chloride is 0.05%, 2,4-dichlorobenzal chloride is 0.18%, meeting the specified quality requirements of 2,4-dichlorobenzaldehyde.

[0096] Comparative Example 1

[0097] In this comparative example, the addition of the impurity removing agent hexamine in step 8) of Example 1 was cancelled, and the others were the same as in Example 1.

[0098] Steps 1) to 7) were the same as in Example 1.

[0099] Step 8) Transfer the 109.4 g of 2,4-dichlorobenzaldehyde crude product obtained from the alkali washing and layering in step 7) into an aldehyde re-distillation kettle, and then heat up for distillation to obtain 97.8 g of 2,4-dichlorobenzaldehyde finished product.

[0100] The obtained 2,4-dichlorobenzaldehyde finished product was tested, and the analysis results are shown in Figure 4 Table 3.

[0101] Table 3. Analysis Results

[0102]

[0103]

[0104] As Figure 4 shown, for the 2,4-dichlorobenzaldehyde finished product, the content of 2,4-dichlorobenzaldehyde is 98.92%, 2,4-dichlorobenzyl chloride is 0.47%, 2,4-dichlorobenzal chloride is 0.30%, 2,4-dichlorobenzoic acid is 0.13%, and other unknown impurities are 0.18%, not meeting the specified quality requirements of 2,4-dichlorobenzaldehyde.

[0105] Comparative Example 2

[0106] In this comparative example, the addition of the catalyst in step 2) of Example 1 was cancelled, and the others were the same as in Example 1.

[0107] 1) Put 175 g of the by-product 4-chloro-2-nitrotoluene (content 98%) into a three-necked round-bottom closed photoreaction flask. After assembling and sealing the reaction flask, a thermometer, a pressure gauge, and an LED ultraviolet lamp (power 15 W, wavelength 365 nm) are provided on the reaction device.

[0108] 2) Turn on the stirrer and the oil bath heating device of the reaction device, heat the material temperature to 155 ± 5 °C, then turn on the ultraviolet lamp, and carry out the light-induced dechlorination of nitro and side-chain photochlorination reactions. Monitor the reaction process by gas chromatography. The reaction time is 168 h, and the conversion rate of the raw material 4-chloro-2-nitrotoluene only reaches 82%. Therefore, the reaction can only be stopped to obtain a mixture Ⅰ of 198 g of 4-chloro-2-nitrotoluene, 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride, 2,4-dichlorobenzylidene chloride, and 2,4-dichlorotrichlorobenzene.

[0109] In mixture Ⅰ, 4-chloro-2-nitrotoluene is 18%, 2,4-dichlorobenzyl chloride content is 11.37%, 4-chloro-2-nitrobenzyl chloride content is 13.14%, 4-chloro-2-nitrobenzylidene chloride content is 17.66%, 2,4-dichlorobenzylidene chloride content is 31.22%, and 2,4-dichlorotrichlorobenzene content is 3.37%, and other impurities are 5.24%.

[0110] Therefore, without adding a catalyst, it has a great impact on the reaction rate, and after 168 h of reaction, the target product only accounts for 31.22%, which is far lower than that of Example 1 of the present invention, and other impurities are significantly higher. Therefore, it shows that the effect of the present invention cannot be achieved without adding a catalyst.

[0111] Comparative Example 3

[0112] In this comparative example, the combined catalyst (azobisisobutyronitrile + phosphorus trichloride) in step 2) of Example 1 was changed to only use phosphorus trichloride, and the others were the same as in Example 1.

[0113] 1) Put 175 g of the by-product 4-chloro-2-nitrotoluene (content 98%) into a three-necked round-bottom closed photoreaction flask. After assembling and sealing the reaction flask, a thermometer, a pressure gauge, and an LED ultraviolet lamp (power 15 W, wavelength 365 nm) are provided on the reaction device.

[0114] 2) Put 1.4 g of the catalyst phosphorus trichloride into the photoreaction flask in step 1), and then place the reaction device in an oil bath.

[0115] 3) Turn on the stirrer of the reaction device and the heating device of the oil bath, heat the material temperature to 155 ± 5 °C, then turn on the ultraviolet lamp, and carry out photo-chlorination reaction for de-nitration and side-chain under light irradiation. Monitor the reaction process by gas chromatography. The reaction time is 144 h, and the conversion rate of the raw material 4-chloro-2-nitrotoluene reaches 94%. Therefore, the reaction can only be stopped to obtain 208 g of a mixture Ⅰ of 4-chloro-2-nitrotoluene, 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride, 2,4-dichlorobenzylidene chloride and 2,4-dichlorotrichlorobenzyl.

[0116] In mixture Ⅰ, the content of 4-chloro-2-nitrotoluene is 6.03%, the content of 2,4-dichlorobenzyl chloride is 14.24%, the content of 4-chloro-2-nitrobenzyl chloride is 8.87%, the content of 4-chloro-2-nitrobenzylidene chloride is 11.57%, the content of 2,4-dichlorobenzylidene chloride is 48.16%, the content of 2,4-dichlorotrichlorobenzyl is 3.16%, and other impurities are 7.97%.

[0117] Therefore, without adding the catalyst azobisisobutyronitrile, it has a great impact on the reaction rate. Moreover, after 144 h of reaction, the target product only accounts for 48.16%, which is far lower than that of Example 1 of the present invention, and other impurities are significantly higher. Therefore, it shows that the effect of the present invention cannot be achieved without adding the catalyst azobisisobutyronitrile.

[0118] Comparative Example 4

[0119] In this comparative example, the combined catalyst (azobisisobutyronitrile + phosphorus trichloride) in step 2) of Example 1 was changed to only use azobisisobutyronitrile, and the others were the same as in Example 1.

[0120] 1) Put 175 g of the by-product 4-chloro-2-nitrotoluene (content 98%) into a three-necked round-bottom closed photoreaction flask. After assembling and sealing the reaction flask, a thermometer, a pressure gauge and an LED ultraviolet lamp (power 15 W, wavelength 365 nm) are installed on the reaction device.

[0121] 2) Put 1.4 g of the catalyst azobisisobutyronitrile into the photoreaction flask in step 1), and then place the reaction device in an oil bath.

[0122] 3) Turn on the stirrer of the reaction device and the heating device of the oil bath, heat the material temperature to 155 ± 5 °C, then turn on the ultraviolet lamp, and carry out photo-chlorination reaction for de-nitration and side-chain under light irradiation. Monitor the reaction process by gas chromatography. The reaction time is 168 h, and the conversion rate of the raw material 4-chloro-2-nitrotoluene reaches 78%. Therefore, the reaction can only be stopped to obtain 196 g of a mixture Ⅰ of 4-chloro-2-nitrotoluene, 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride, 2,4-dichlorobenzylidene chloride and 2,4-dichlorotrichlorobenzyl.

[0123] In mixture I, the content of 4-chloro-2-nitrotoluene is 21.98%, the content of 2,4-dichlorobenzyl chloride is 1.87%, the content of 4-chloro-2-nitrobenzyl chloride is 21.33%, the content of 4-chloro-2-nitrobenzal chloride is 29.44%, the content of 2,4-dichlorobenzal chloride is 16.55%, the content of 2,4-dichlorotrichlorobenzene is 0.64%, and other impurities are 8.19%.

[0124] Therefore, without adding the catalyst phosphorus trichloride, it has a great impact on the reaction rate. Moreover, after 168 hours of reaction, the target product only accounts for 16.55%, which is far lower than that of Example 1 of the present invention, and other impurities are significantly higher. Therefore, it shows that the effect of the present invention cannot be achieved without adding the catalyst phosphorus trichloride.

[0125] It can be seen from Comparative Example 3 and Comparative Example 4 that using only a single catalyst results in a low reaction rate, few target products, and high impurities, and the effect of using the combined catalyst of the present invention cannot be achieved.

[0126] As mentioned above, the above are only the preferred embodiments of the present invention, and there is no limitation in any form and essence to the present invention. It should be pointed out that for those of ordinary skill in the art in this technical field, without departing from the method of the present invention, several improvements and supplements can still be made, and these improvements and supplements should also be regarded as the protection scope of the present invention. For those skilled in the art, without departing from the spirit and scope of the present invention, any equivalent changes made by using the technical content disclosed above, such as slight modifications, decorations, and evolutions, are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for synthesizing 2,4-dichlorobenzaldehyde from 4-chloro-2-nitrotoluene, characterized in that, The method includes using 4-chloro-2-nitrotoluene as a raw material, reacting 4-chloro-2-nitrotoluene with chlorine under the action of ultraviolet light, an initiator and a dehydrating agent to obtain a mixture I of 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride, 2,4-dichlorobenzylidene chloride and 2,4-dichlorotrichlorobenzene; subjecting the mixture I to vacuum distillation, and further subjecting the obtained 2,4-dichlorobenzylidene chloride to hydrolysis aldehyde formation, water precipitation alkali washing and distillation to obtain the finished product of 2,4-dichlorobenzaldehyde.

2. The method for synthesizing 2,4-dichlorobenzaldehyde from 4-chloro-2-nitrotoluene according to claim 1, wherein, The method includes the following steps: 1) Put the by-product 4-chloro-2-nitrotoluene into a reactor and seal it. 2) Put the combined catalyst into the reactor in step 1) and place it in an oil bath. 3) Stir and heat to heat the material temperature to 155±5°C, turn on the ultraviolet lamp, carry out light-induced chlorine introduction for nitro group removal and side-chain photochlorination reaction, monitor the reaction process by gas chromatography, and stop the reaction until the conversion rate of the raw material 4-chloro-2-nitrotoluene reaches more than 99% to obtain a mixture I of 2,4-dichlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride, 4-chloro-2-nitrobenzylidene chloride, 2,4-dichlorobenzylidene chloride and 2,4-dichlorotrichlorobenzene. 4) Subject the mixture I obtained in step 3) to vacuum distillation, collect the fore-fraction and the middle-fraction to obtain the bottom high-boiling substances. 5) Put sulfuric acid into the aldehyde formation reaction kettle, stir evenly, raise the temperature, dropwise add the middle-fraction obtained in step 4), keep the temperature, and control the end point of the reaction with the residual raw material ≤0.3% as the standard to obtain the aldehyde formation hydrolysis material II. 6) Add water to the aldehyde formation hydrolysis material II obtained in step 5), cool down by passing cooling water through the jacket, let it stand for separation, and drain the lower-layer dilute sulfuric acid to obtain the upper-layer organic phase. 7) Add liquid alkali to neutralize the upper-layer organic phase obtained in step 6), cool down by passing freezing brine through the jacket, let it stand for separation to obtain the crude product of 2,4-dichlorobenzaldehyde. 8) Transfer the crude product of 2,4-dichlorobenzaldehyde obtained by alkali washing and separation in step 7) into an aldehyde re-distillation kettle, add a decontaminant and stir to react, raise the temperature for distillation to obtain the finished product of 2,4-dichlorobenzaldehyde.

3. A method for synthesizing 2,4-dichlorobenzaldehyde using 4-chloro-2-nitrotoluene according to claim 2, characterized in that, The fore-fraction and the bottom high-boiling substances obtained in step 4) are returned to step 1) as raw materials for recycling.

4. A method for synthesizing 2,4-dichlorobenzaldehyde using 4-chloro-2-nitrotoluene according to claim 2, characterized in that, In step 4), when collecting the fore-fraction, the vacuum degree is -0.098 MPa, the kettle temperature is 155-165°C, and the top temperature is 125-135°C.

5. A method for synthesizing 2,4-dichlorobenzaldehyde from 4-chloro-2-nitrotoluene according to claim 2, characterized in that, In step 4), when collecting the middle-fraction, the vacuum degree is -0.098 MPa, the kettle temperature is 175-185°C, and the top temperature is 135-145°C.

6. A method for synthesizing 2,4-dichlorobenzaldehyde using 4-chloro-2-nitrotoluene according to claim 2, characterized in that, In step 5), the concentration of sulfuric acid is 80-85%, raise the temperature to 85-95°C and dropwise add the middle-fraction obtained in step 4), and the reaction temperature is 85-95°C.

7. A method for synthesizing 2,4-dichlorobenzaldehyde using 4-chloro-2-nitrotoluene according to claim 2, characterized in that, In step 6), after adding water, dilute the sulfuric acid to a concentration of 30-40%; cool down to 10-20°C.

8. A method for synthesizing 2,4-dichlorobenzaldehyde using 4-chloro-2-nitrotoluene according to claim 2, characterized in that, In step 7), the end point pH is 9.5-10.

5.

9. A method for synthesizing 2,4-dichlorobenzaldehyde using 4-chloro-2-nitrotoluene according to any one of claims 2-8, characterized in that, In step 2), the combined catalyst is a mixture of azobisisobutyronitrile and phosphorus trichloride. The addition amount of azobisisobutyronitrile is 0.3% of the raw material amount, and the addition amount of phosphorus trichloride is 0.5% of the raw material amount.

10. A method for synthesizing 2,4-dichlorobenzaldehyde using 4-chloro-2-nitrotoluene according to any one of claims 2-8, characterized in that, In step 8), the impurity remover is hexamethylenetetramine, and the addition amount is 0.5% of the weight ratio of the crude 2,4-dichlorobenzaldehyde.

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