A method for synthesizing 2,4-dichlorobenzoyl chloride and purifying by-products

Abstract

The present invention provides a kind of 2,4-dichlorobenzoyl chloride synthesis and by-product purification method, comprise the following steps, S1, put into reactor 2,4-dichlorotoluene, heat up and drip catalyst solution, chlorine is passed into reactor, obtain chlorination reaction liquid;S2, chlorination reaction liquid is put into hydrolysis kettle, heat up and drip the aqueous solution of ferric chloride, obtain 2,4-dichlorobenzoyl chloride crude product;S3, 2,4-dichlorobenzoyl chloride crude product is put into rectifying kettle, open vacuum pump, heat up and carry out vacuum distillation, collect front fraction and main fraction respectively, main fraction is 2,4-dichlorobenzoyl chloride finished product;S4, front fraction is put into rectifying kettle, open vacuum pump, heat up and carry out vacuum distillation, obtain 1,2,4-trichlorobenzene finished product.The present invention solves the technical problem that the by-product produced in the preparation process of 2,4-dichlorobenzoyl chloride cannot be effectively recovered, produces and effectively recovers by-product 1,2,4-trichlorobenzene technical effect, increases economic benefit.

Description

Technical Field

[0001] The present invention relates to the technical field of fine chemical organic synthesis, in particular to a method for synthesizing 2,4-dichlorobenzoyl chloride and purifying its by-product. Background Art

[0002] 2,4-Dichlorobenzoyl chloride is an organic compound with the chemical formula C7H3Cl3O. It is a colorless liquid that is miscible with ethanol, ether, and carbon disulfide, but insoluble in water. It is mainly used as an intermediate for dyes and medicines.

[0003] Currently, 2,4-dichlorobenzoyl chloride is mainly synthesized using the following two routes: the first is to react 2,4-dichlorobenzoic acid with sulfite chloride. The preparation method is to chlorinate 2,4-dichlorobenzoic acid with an acyl chlorination agent such as thionyl chloride, phosphorus trichloride, etc., and then heat and reflux 2,4-dichlorobenzoic acid and thionyl chloride for 3-4 hours, then evaporate the excess thionyl chloride, and then distill under reduced pressure to obtain the product; the second is to chlorinate 2,4-dichlorotoluene with a side chain to obtain 2,4-dichlorobenzyl trichloride, and then hydrolyze it to obtain the product.

[0004] The existing preparation method of 2,4-dichlorobenzoyl chloride has many side reactions during the reaction process, and produces by-products such as 1,2,4-trichlorobenzene. Since the by-products are mixed with the product, raw materials, catalysts, etc., the by-products produced during the preparation process cannot be effectively recovered, resulting in waste. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method for synthesizing 2,4-dichlorobenzoyl chloride and purifying its by-products, which solves the problem in the prior art that by-products generated during the preparation of 2,4-dichlorobenzoyl chloride cannot be effectively recovered and thus wastes.

[0006] According to an embodiment of the present invention, a method for synthesizing 2,4-dichlorobenzoyl chloride and purifying its by-products comprises the following steps:

[0007] S1. Add 2,4-dichlorotoluene to a reactor, raise the temperature to 90.0-135.0° C., add the catalyst solution dropwise, and introduce chlorine gas into the reactor until the content of 2,4-dichlorobenzyl chloride is ≤0.1%. After stopping the introduction of chlorine gas, introduce nitrogen gas into the reactor to obtain a chlorination reaction solution;

[0008] S2. The chlorination reaction solution obtained in step S1 is placed in a hydrolysis kettle, the temperature is raised to 125.0-135.0° C., and an aqueous solution of ferric chloride is added dropwise until the content of 2,4-dichlorobenzyl chloride is ≤0.1%. The addition of the aqueous solution of ferric chloride is stopped to obtain a crude product of 2,4-dichlorobenzoyl chloride;

[0009] S3, the crude 2,4-dichlorobenzoyl chloride obtained in step S2 is put into a distillation kettle, the vacuum pump is turned on to maintain the negative pressure in the distillation kettle above -0.095 MPa, the temperature is raised to 150.0-180.0 ° C for vacuum distillation, and the front fraction and the main fraction are collected respectively. The main fraction is the finished 2,4-dichlorobenzoyl chloride;

[0010] S4. Put the fore fraction obtained in step S3 into a distillation kettle, turn on the vacuum pump to maintain the negative pressure in the distillation kettle above -0.095 MPa, raise the temperature to 120.0-150.0° C. and perform vacuum distillation to obtain 1,2,4-trichlorobenzene finished product.

[0011] Compared with the prior art, the present invention has the following beneficial effects: by utilizing the difference between the boiling points of 2,4-dichlorobenzoyl chloride and 1,2,4-trichlorobenzene, a front fraction is collected during the distillation process of 2,4-dichlorobenzoyl chloride, the front fraction includes 1,2,4-trichlorobenzene, and the collected front fraction is distilled and purified to obtain 1,2,4-trichlorobenzene, thereby avoiding the waste caused by treating the front fraction containing 1,2,4-trichlorobenzene as hazardous waste. The present invention solves the technical problem of waste caused by inability to effectively recover by-products generated in the preparation process of 2,4-dichlorobenzoyl chloride, achieves the technical effect of effectively recovering the by-product 1,2,4-trichlorobenzene generated in the preparation process of 2,4-dichlorobenzoyl chloride, avoiding environmental pollution while increasing economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a step diagram of the method for synthesizing 2,4-dichlorobenzoyl chloride and purifying the by-product according to Example 1 of the present invention;

[0013] Figure 2 This is a partial step diagram of step S1 in the method for synthesizing 2,4-dichlorobenzoyl chloride and purifying by-products according to Example 1 of the present invention. DETAILED DESCRIPTION

[0014] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0015] Example 1

[0016] like Figure 1 and Figure 2 As shown, Example 1 of the present invention provides a method for synthesizing 2,4-dichlorobenzoyl chloride and purifying by-products, comprising the following steps:

[0017] S1. Add 2,4-dichlorotoluene into the reactor, raise the temperature to 90.0-120.0°C and dropwise add the prepared catalyst solution. Then, introduce chlorine gas into the reactor to start the chlorination reaction. The chlorination reaction includes the following three stages:

[0018] S101, the temperature in the reactor is controlled at 90.0°C, the chlorine flow rate is controlled at 100.0 L / h, the time for passing chlorine into the reactor is 2.0 h, and the dropwise addition rate of the catalyst solution is 0.2 ml / min;

[0019] S102, the temperature in the reactor was controlled at 110.0°C, the chlorine flow rate was controlled at 200 L.0 / h, the time for passing chlorine into the reactor was 7.0 h, and the dropwise addition rate of the catalyst solution was 0.3 ml / min;

[0020] S103, the temperature in the reactor was controlled at 120.0°C, the chlorine flow rate was controlled at 50.0 L / h, the time for passing chlorine into the reactor was 1.0 h, and the dropwise addition rate of the catalyst solution was 0.5 ml / min;

[0021] Chlorine gas was introduced into the reaction kettle for monitoring by a chromatographic analyzer until the content of 2,4-dichlorobenzyl chloride was ≤0.1%. After the introduction of chlorine gas was stopped, nitrogen gas was introduced into the reaction kettle to drive out the chlorine gas and hydrogen chloride dissolved in the reaction liquid by the nitrogen gas to obtain a chlorination reaction liquid, wherein the main component of the chlorination reaction liquid was 2,4-dichlorobenzyl trichloride.

[0022] S2. The chlorination reaction solution obtained in step S1 is added to a hydrolysis kettle, the temperature is raised to 125.0° C., and an aqueous solution of ferric chloride is added dropwise. The mixture is monitored by a chromatograph until the content of 2,4-dichlorobenzyl chloride is ≤0.1%. The addition of the aqueous solution of ferric chloride is stopped to obtain a crude product of 2,4-dichlorobenzoyl chloride.

[0023] S3, the crude 2,4-dichlorobenzoyl chloride obtained in step S2 is put into a distillation kettle, the vacuum pump is turned on to maintain the negative pressure in the distillation kettle above -0.095 MPa, the temperature is raised to 165.0 ° C for vacuum distillation, and the front fraction and the main fraction are collected respectively. The main fraction is the finished 2,4-dichlorobenzoyl chloride;

[0024] S4. Put the fore fraction obtained in step S3 into a distillation kettle, turn on the vacuum pump to maintain the negative pressure in the distillation kettle above -0.095 MPa, raise the temperature to 150.0° C. and perform vacuum distillation to obtain 1,2,4-trichlorobenzene finished product.

[0025] like Figure 1 As shown, the chlorination reaction in step S1 is that 2,4-dichlorotoluene reacts with chlorine gas under the action of a catalyst to generate 2,4-dichlorobenzyltrichloride, and the reaction equation is:

[0026]

[0027] Since chlorine gas is continuously introduced into the reaction solution during the chlorination reaction, part of the chlorine gas dissolves in the reaction solution. As 2,4-dichlorobenzyl trichloride is generated, 2,4-dichlorobenzyl trichloride inevitably reacts with chlorine gas to form a by-product, 1,2,4-trichlorobenzene. The reaction equation is:

[0028]

[0029] Specifically, the catalyst solution added dropwise in steps S101 and S102 is a solution of azobisisobutyronitrile (AIBN) in 2,4-dichlorotoluene, the content of AIBN in the catalyst solution is 5.0%, and the amount of the catalyst solution added dropwise in steps S101 and S102 is 1.125% of the amount of 2,4-dichlorotoluene charged in step S1. The catalyst solution added dropwise in step S103 is a solution of dibenzoyl peroxide (BPO) in 2,4-dichlorotoluene, the content of BPO in the catalyst solution is 5.0%, and the amount of the catalyst solution added dropwise in step S103 is 0.25% of the amount of 2,4-dichlorotoluene charged in step S1. That is, the method for synthesizing 2,4-dichlorobenzoyl chloride and purifying by-products provided in this embodiment uses a composite catalyst of azobisisobutyronitrile and dibenzoyl peroxide during the chlorination reaction. Both azobisisobutyronitrile and dibenzoyl peroxide are free radical initiators. The decomposition products of azobisisobutyronitrile are mainly gases, while the decomposition products of dibenzoyl peroxide contain organic impurities such as benzoic acid, benzene, and phenyl benzoate, which have a certain impact on the quality of the product. Therefore, azobisisobutyronitrile is preferably used as the catalyst in step S1. However, azobisisobutyronitrile has a lower decomposition temperature than dibenzoyl peroxide, requires a large amount of catalyst, and is relatively expensive. Taking all factors into consideration, azobisisobutyronitrile is used at relatively low temperatures and dibenzoyl peroxide is used at high temperatures to minimize impurities and reduce costs.

[0030] In detail, because azobisisobutyronitrile and dibenzoyl peroxide are unstable when exposed to heat, friction, etc., they are prone to combustion or explosion, resulting in safety accidents. The safety risk of adding solid azobisisobutyronitrile or dibenzoyl peroxide to the reactor intermittently is relatively high. The method for synthesizing 2,4-dichlorobenzoyl chloride and purifying the by-product provided in this embodiment is to dissolve the above-mentioned catalyst in 2,4-dichlorotoluene respectively and adopt a dropwise addition method, which not only reduces the safety risk, but also is easy to operate, while reducing the introduction of other impurities, which is beneficial to improving the quality of the product. The addition of the catalyst solution by dropwise addition also allows the catalyst solution to be added at different reaction stages. The rate of addition is adjusted to facilitate the reaction.

[0031] Please refer to Figure 2Since the chlorination reaction of the benzene ring side chain in step S1 increases with the progress of the reaction, the energy required for the reaction increases, and the chlorination reaction is an exothermic reaction, the method for synthesizing 2,4-dichlorobenzoyl chloride and purifying the by-product provided in this embodiment adopts a gradual temperature increase method, and utilizes the energy released by the reaction to replenish the energy required for the reaction, so that the reaction temperature can be more stably controlled, while also saving energy consumption.

[0032] like Figure 1 As shown, the hydrolysis reaction in step S2 is that 2,4-dichlorobenzyl trichloride reacts with water in the presence of a catalyst to generate 2,4-dichlorobenzoyl chloride, and the reaction equation is:

[0033]

[0034] Specifically, the ferric chloride content in the aqueous solution of ferric chloride added dropwise in step S2 is 0.8%, and the amount of the aqueous solution of ferric chloride added dropwise in step S2 is 6.8% of the amount of the chlorination reaction solution charged in step S2. The method for synthesizing 2,4-dichlorobenzoyl chloride and purifying by-products provided in this embodiment uses ferric chloride as a catalyst. Ferric chloride has moderate activity, which not only allows the reaction to proceed thoroughly but also is less likely to produce side reactions.

[0035] Please refer to Figure 1 In step S3, since the boiling point of the product 2,4-dichlorobenzoyl chloride is relatively high, at 251.8°C, negative pressure distillation is adopted to lower the distillation temperature, and a reboiler is used to circulate and heat the material to reduce the residence time of the material in the distillation kettle. The reflux ratio is controlled by an automatic reflux ratio regulator to ensure the quality and yield of the product.

[0036] Specifically, in step S4, the boiling point of the by-product 1,2,4-trichlorobenzene is 214.0° C., so in the distillation process of step S3, 1,2,4-trichlorobenzene is mixed in the fore-fraction, and the fore-fraction is collected and then distilled and purified to obtain the by-product 1,2,4-trichlorobenzene. This avoids the disposal of the fore-fraction containing 1,2,4-trichlorobenzene as hazardous waste, reduces waste, and increases economic benefits while protecting the environment.

[0037] like Figure 1 As shown, in step S1, in order to smoothly input chlorine into the reactor, liquid chlorine is put into a vaporizer, and water at 75°C or above is input into the vaporizer to heat the liquid chlorine so that the liquid chlorine is vaporized to produce chlorine gas. The chlorine gas is first passed from the vaporizer into a buffer tank and then into the reactor from the buffer tank to ensure that the chlorine gas can be stably input into the reactor and to facilitate adjustment of the rate at which the chlorine gas is input into the reactor.

[0038] Specifically, before step S101, the process further includes step S100, connecting the reactor to the tail gas absorption device, and adjusting the air pressure in the reactor and the tail gas absorption device so that the reactor and the tail gas absorption device are in a slightly negative pressure state. Step S2 also includes step S201, connecting the hydrolysis reactor to the tail gas absorption device, and adjusting the air pressure in the hydrolysis reactor and the tail gas absorption device so that the hydrolysis reactor and the tail gas absorption device are in a slightly negative pressure state. The tail gas absorption device is provided to absorb waste gas generated by the chlorination reaction and the hydrolysis reaction, thereby preventing the waste gas from being directly discharged into the external environment and causing environmental pollution.

[0039] Example 2

[0040] Embodiment 2 of the present invention provides a method for synthesizing 2,4-dichlorobenzoyl chloride and purifying the by-product, comprising the following steps:

[0041] S1. Add 2,4-dichlorotoluene into the reactor, raise the temperature to 95.0-130.0°C and dropwise add the prepared catalyst solution. Then, introduce chlorine gas into the reactor to start the chlorination reaction. The chlorination reaction includes the following three stages:

[0042] S101, the temperature in the reactor is controlled at 95.0°C, the chlorine flow rate is controlled at 100.0 L / h, the time for passing chlorine into the reactor is 2.0 h, and the catalyst solution is added at a rate of 0.2 ml / min;

[0043] S102, the temperature in the reactor was controlled at 105.0°C, the chlorine flow rate was controlled at 200 L.0 / h, the time for introducing chlorine into the reactor was 7.0 h, and the dropwise addition rate of the catalyst solution was 0.3 ml / min;

[0044] S103, the temperature in the reactor was controlled at 130.0°C, the chlorine flow rate was controlled at 50.0 L / h, the time for passing chlorine into the reactor was 1.0 h, and the catalyst solution was added at a rate of 0.5 ml / min;

[0045] Chlorine gas was introduced into the reaction kettle for monitoring by a chromatographic analyzer until the content of 2,4-dichlorobenzyl chloride was ≤0.1%. After the introduction of chlorine gas was stopped, nitrogen gas was introduced into the reaction kettle to drive out the chlorine gas and hydrogen chloride dissolved in the reaction liquid by the nitrogen gas to obtain a chlorination reaction liquid, wherein the main component of the chlorination reaction liquid was 2,4-dichlorobenzyl trichloride.

[0046] S2. The chlorination reaction solution obtained in step S1 is added to a hydrolysis kettle, the temperature is raised to 130.0° C., and an aqueous solution of ferric chloride is added dropwise. The mixture is monitored by a chromatograph until the content of 2,4-dichlorobenzyl chloride is ≤0.1%. The addition of the aqueous solution of ferric chloride is stopped to obtain a crude product of 2,4-dichlorobenzoyl chloride.

[0047] S3, the crude 2,4-dichlorobenzoyl chloride obtained in step S2 is put into a distillation kettle, the vacuum pump is turned on to maintain the negative pressure in the distillation kettle above -0.095 MPa, the temperature is raised to 150.0 ° C for vacuum distillation, and the front fraction and the main fraction are collected respectively. The main fraction is the finished 2,4-dichlorobenzoyl chloride;

[0048] S4. The fore fraction obtained in step S3 is put into a distillation kettle, the vacuum pump is turned on to maintain the negative pressure in the distillation kettle above -0.095 MPa, and the temperature is raised to 135.0° C. for vacuum distillation to obtain a 1,2,4-trichlorobenzene finished product.

[0049] Example 3

[0050] Embodiment 3 of the present invention provides a method for synthesizing 2,4-dichlorobenzoyl chloride and purifying the by-product, comprising the following steps:

[0051] S1. Add 2,4-dichlorotoluene into the reactor, raise the temperature to 105.0-135.0°C and dropwise add the prepared catalyst solution. Then, introduce chlorine gas into the reactor to start the chlorination reaction. The chlorination reaction includes the following three stages:

[0052] S101, the temperature in the reactor was controlled at 105.0°C, the chlorine flow rate was controlled at 100.0 L / h, the time for passing chlorine into the reactor was 2.0 h, and the dropwise addition rate of the catalyst solution was 0.2 ml / min;

[0053] S102, the temperature in the reactor was controlled at 120.0°C, the chlorine flow rate was controlled at 200 L.0 / h, the time for introducing chlorine into the reactor was 7.0 h, and the dropwise addition rate of the catalyst solution was 0.3 ml / min;

[0054] S103, the temperature in the reactor was controlled at 135.0°C, the chlorine flow rate was controlled at 50.0 L / h, the time for passing chlorine into the reactor was 1.0 h, and the dropwise addition rate of the catalyst solution was 0.5 ml / min;

[0055] Chlorine gas was introduced into the reaction kettle for monitoring by a chromatographic analyzer until the content of 2,4-dichlorobenzyl chloride was ≤0.1%. After the introduction of chlorine gas was stopped, nitrogen gas was introduced into the reaction kettle to drive out the chlorine gas and hydrogen chloride dissolved in the reaction liquid by the nitrogen gas to obtain a chlorination reaction liquid, wherein the main component of the chlorination reaction liquid was 2,4-dichlorobenzyl trichloride.

[0056] S2. The chlorination reaction solution obtained in step S1 is added to a hydrolysis kettle, the temperature is raised to 135.0° C., and an aqueous solution of ferric chloride is added dropwise. The mixture is monitored by a chromatograph until the content of 2,4-dichlorobenzyl chloride is ≤0.1%. The addition of the aqueous solution of ferric chloride is stopped to obtain a crude product of 2,4-dichlorobenzoyl chloride.

[0057] S3, the crude 2,4-dichlorobenzoyl chloride obtained in step S2 is put into a distillation kettle, the vacuum pump is turned on to maintain the negative pressure in the distillation kettle above -0.095 MPa, the temperature is raised to 180.0 ° C for vacuum distillation, and the front fraction and the main fraction are collected respectively. The main fraction is the finished 2,4-dichlorobenzoyl chloride;

[0058] S4. Put the fore fraction obtained in step S3 into a distillation kettle, turn on the vacuum pump to maintain the negative pressure in the distillation kettle above -0.095 MPa, raise the temperature to 120.0° C. and perform vacuum distillation to obtain 1,2,4-trichlorobenzene finished product.

[0059] The chlorination reaction solution obtained in step S1, the crude 2,4-dichlorobenzoyl chloride obtained in step S2, the finished 2,4-dichlorobenzoyl chloride obtained in step S3, and the finished 1,2,4-trichlorobenzene obtained in step S4 in Example 1, Example 2, and Example 3 were subjected to chromatographic analysis using a chromatographic analyzer. The analysis results are shown in Table 1:

[0060]

[0061]

[0062] From the GC analysis results in Table 1, it can be seen that the methods for synthesizing 2,4-dichlorobenzoyl chloride and purifying by-products provided in Examples 1, 2 and 3 have good yields in preparing the product 2,4-dichlorobenzoyl chloride, and the by-product 1,2,4-trichlorobenzene is effectively recovered in the fore-fraction obtained in step S3.

[0063] Comparative Example 1

[0064] The 2,4-dichlorobenzoyl chloride synthesis and by-product purification method of Comparative Example 1 has the same operating steps as the 2,4-dichlorobenzoyl chloride synthesis and by-product purification method of Example 1, except that the catalysts used in step S101, step S102, and step S103 of the 2,4-dichlorobenzoyl chloride synthesis and by-product purification method of Comparative Example 1 are all 2,4-dichlorotoluene solutions of azobisisobutyronitrile, and the azobisisobutyronitrile content is 5%.

[0065] Comparative Example 2

[0066] The method for synthesizing 2,4-dichlorobenzoyl chloride and purifying the by-product of Comparative Example 2 has the same operating steps as the method for synthesizing 2,4-dichlorobenzoyl chloride and purifying the by-product of Example 1, except that the catalysts used in step S101, step S102, and step S103 of the method for synthesizing 2,4-dichlorobenzoyl chloride and purifying the by-product of Comparative Example 2 are all 2,4-dichlorotoluene solutions of dibenzoyl peroxide, and the content of dibenzoyl peroxide is 5%.

[0067] The chlorination reaction liquid obtained in step S1 of Example 1, Comparative Example 1 and Comparative Example 2 was subjected to chromatographic analysis using a chromatographic analyzer. The analysis results are shown in Table 2:

[0068]

[0069] As can be seen from the GC analysis results in Table 2, the content of 2,4-dichlorobenzyltrichloride in the chlorination reaction liquid obtained in step S1 of the method for synthesizing 2,4-dichlorobenzoyl chloride and purifying by-products provided in Example 1 is superior to that in Comparative Examples 1 and 2. The method of dropwise adding azobisisobutyronitrile in 2,4-dichlorotoluene and dibenzoyl peroxide in 2,4-dichlorotoluene as catalysts in stepwise steps during the chlorination reaction in Example 1 can better facilitate the chlorination reaction.

[0070] Comparative Example 3

[0071] The 2,4-dichlorobenzoyl chloride synthesis and by-product purification method of Comparative Example 3 has the same operating steps as the 2,4-dichlorobenzoyl chloride synthesis and by-product purification method of Example 1, except that the catalyst used in step S2 of the 2,4-dichlorobenzoyl chloride synthesis and by-product purification method of Comparative Example 3 is an aqueous solution of aluminum chloride, and the content of aluminum chloride is 0.8%.

[0072] The crude 2,4-dichlorobenzoyl chloride obtained in step S2 of Example 1 and Comparative Example 3 was subjected to chromatographic analysis using a chromatographic analyzer. The analysis results are shown in Table 3:

[0073] From the GC analysis results in Table 3, it can be seen that the content of 2,4-dichlorobenzoyl chloride in the crude 2,4-dichlorobenzoyl chloride obtained in step S2 of the method for synthesizing 2,4-dichlorobenzoyl chloride and purifying by-products provided in Example 1 is better than that in Comparative Example 3. The operation method of dropwise adding an aqueous solution of ferric chloride as a catalyst during the hydrolysis reaction in Example 1 can better proceed with the hydrolysis reaction.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for synthesizing 2,4-dichlorobenzoyl chloride and purifying by-products, characterized in that: The following steps are included: S1. Add 2,4-dichlorotoluene to a reactor, raise the temperature to 90.0-135.0° C., add the catalyst solution dropwise, and introduce chlorine gas into the reactor until the content of 2,4-dichlorobenzyl chloride is ≤0.1%. After stopping the introduction of chlorine gas, introduce nitrogen gas into the reactor to obtain a chlorination reaction solution; S2. The chlorination reaction solution obtained in step S1 is placed in a hydrolysis kettle, the temperature is raised to 125.0-135.0° C., and an aqueous solution of ferric chloride is added dropwise until the content of 2,4-dichlorobenzyl chloride is ≤0.1%. The addition of the aqueous solution of ferric chloride is stopped to obtain a crude product of 2,4-dichlorobenzoyl chloride; S3, the crude 2,4-dichlorobenzoyl chloride obtained in step S2 is put into a distillation kettle, the vacuum pump is turned on to maintain the negative pressure in the distillation kettle above -0.095 MPa, the temperature is raised to 150.0-180.0 ° C for vacuum distillation, and the front fraction and the main fraction are collected respectively. The main fraction is the finished 2,4-dichlorobenzoyl chloride; S4, the fore fraction obtained in step S3 is put into a distillation kettle, the vacuum pump is turned on to maintain the negative pressure in the distillation kettle above -0.095 MPa, the temperature is raised to 120.0-150.0 ° C and vacuum distillation is performed to obtain 1,2,4-trichlorobenzene finished product; Step S1 includes the following steps, Step S101: The temperature in the reactor is controlled at 90.0-105.0°C, the chlorine gas flow rate is controlled at 100.0 L / h, the time for introducing chlorine gas into the reactor is 2.0 h, and the catalyst solution is added at a rate of 0.2 ml / min; Step S102: the temperature in the reactor is controlled at 105.0-120.0°C, the chlorine flow rate is controlled at 200 L.0 / h, the time for introducing chlorine into the reactor is 7.0 h, and the catalyst solution is added at a rate of 0.3 ml / min; Step S103: the temperature in the reactor is controlled at 120.0-135.0°C, the chlorine gas flow rate is controlled at 50.0 L / h, the time for introducing chlorine gas into the reactor is 1.0 h, and the catalyst solution is added at a rate of 0.5 ml / min; The catalyst solution added dropwise in step S101 and step S102 is a 2,4-dichlorotoluene solution of azobisisobutyronitrile, and the content of azobisisobutyronitrile in the catalyst solution is 5.0%; The catalyst solution added dropwise in step S103 is a solution of dibenzoyl peroxide in 2,4-dichlorotoluene, and the content of dibenzoyl peroxide in the catalyst solution is 5.0%.

2. a kind of 2,4-dichlorobenzoyl chloride synthesis and by-product purification method as claimed in claim 1, it is characterized in that: The amount of the catalyst solution added dropwise in step S101 and step S102 is 1.125% of the amount of 2,4-dichlorotoluene added in step S1.

3. A method for synthesizing and purifying 2,4-dichlorobenzoyl chloride according to claim 1, characterized in that: The amount of the catalyst solution added dropwise in step S103 is 0.25% of the amount of 2,4-dichlorotoluene added in step S1.

4. A method for synthesizing and purifying 2,4-dichlorobenzoyl chloride according to claim 1, characterized in that: The content of ferric chloride in the aqueous solution of ferric chloride added dropwise in step S2 is 0.8%.

5. A method for synthesizing and purifying 2,4-dichlorobenzoyl chloride as claimed in claim 1, characterized in that: The amount of the aqueous solution of ferric chloride added dropwise in step S2 is 6.8% of the amount of the chlorination reaction liquid charged in step S2.

6. A method for synthesizing and purifying 2,4-dichlorobenzoyl chloride as claimed in claim 1, characterized in that: In step S1, liquid chlorine is put into a vaporizer, and water at 75°C or above is input into the vaporizer to heat the liquid chlorine so that the liquid chlorine is vaporized to produce chlorine gas. The chlorine gas is first passed from the vaporizer into a buffer tank and then from the buffer tank into the reactor.

7. A method for synthesizing and purifying 2,4-dichlorobenzoyl chloride as claimed in claim 1, characterized in that: Step S2 also includes step S201, connecting the hydrolysis kettle with the tail gas absorption device, and adjusting the air pressure in the hydrolysis kettle and the tail gas absorption device so that the hydrolysis kettle and the tail gas absorption device are in a slightly negative pressure state.

Images