Preparation method of trichlorotoluene

Abstract

The invention relates to the technical field of organic synthesis, and particularly discloses a preparation method of trichlorotoluene. The preparation method of the trichlorotoluene comprises the following steps: under the action of an initiator and a screening agent, introducing chlorine into toluene serving as a raw material, and carrying out a chlorination reaction to obtain the trichlorotoluene, the shielding agent comprises at least one of sulfur, red phosphorus or phosphorus trichloride. Under the action of the shielding agent, in cooperation with the initiator, trace metal ions in a reaction system can be shielded, the possibility that iron ions and chloride ions react to form ferric trichloride is eliminated, ring chlorination catalysis is avoided, impurities are reduced, the conjugation effect of alpha-site free radicals and benzene rings is enhanced, smooth side chain chlorination reaction is guaranteed, and the reaction efficiency is improved. Therefore, the yield and the purity of trichlorotoluene are improved, the difficulty of subsequent rectification and purification and the treatment capacity of solid waste are reduced, the efficiency of vacuum rectification is obviously improved, the cost of the product is effectively reduced, the economic benefit is increased, and the method has better market application value.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, in particular to a method for preparing trichlorotoluene. Background Art

[0002] Trichlorotoluene, also known as phenylchloroform and benzyl trichloride, is an organic compound with the chemical formula C7H5Cl3. It is a colorless to light yellow transparent liquid, insoluble in water, soluble in ethanol, benzene, ether, etc. It is mainly used as a solvent and can also be used to prepare pesticides, dyes, medicines, fragrances, ultraviolet absorbers, transformer oils, electrolytes, lubricating oils and heat transfer media.

[0003] The synthesis process of trichlorotoluene is the chlorination of the aromatic ring side chain, which belongs to the free radical substitution reaction. In the production process, it is necessary to use light, heat or initiator to initiate catalysis. Adding initiator is the most commonly used method at present, and the initiator can be selected from organic peroxides or azo compounds. However, no matter which initiator is selected in actual production, there is an unavoidable problem: while the side chain is chlorinated, the benzene ring is also chlorinated to varying degrees. At present, in the production process of trichlorotoluene, while the side chain chlorination generates trichlorotoluene, it will also generate about 3% of p-chlorotoluene trichloride and about 2% of m-chlorotoluene trichloride and a trace of ortho-chlorotoluene trichloride, forming high-boiling impurities, which not only reduces the mass content of the target product, but also reduces the yield of the product, and also increases the difficulty of subsequent distillation and purification and the amount of solid waste to be processed, so that the cost of the product increases and the economic benefit decreases. Therefore, it is currently urgent to seek a preparation method that can improve the yield and purity of trichlorotoluene. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for preparing trichlorotoluene. By adding a shielding agent, the adverse effect of metal ions on the chlorination of the side chain of the benzene ring is reduced, and the chlorination reaction on the benzene ring is inhibited, thereby increasing the yield and purity of trichlorotoluene, reducing costs and increasing economic benefits.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: The present invention provides a method for preparing trichlorotoluene, comprising the following steps: Under the action of an initiator and a shielding agent, toluene is used as a raw material, chlorine gas is introduced to carry out a chlorination reaction, and trichlorotoluene is obtained; the shielding agent comprises at least one of sulfur, red phosphorus or phosphorus trichloride.

[0006] In the preparation process of trichlorotoluene, it is inevitable to contact with steel equipment (such as liquid chlorine storage tanks, vaporizers, and transportation pipelines, which are directly in contact with metal materials), so that trace iron ions are mixed into the chlorination reaction system. These iron ions will form ferric chloride when they meet chloride ions. Ferric chloride has a very strong ring chlorination catalytic effect, and then produce impurities such as para-chlorotrichlorotoluene, meta-chlorotrichlorotoluene and ortho-chlorotrichlorotoluene, forming high-boiling point impurities.

[0007] Compared with the prior art, the preparation method of trichlorotoluene provided by the present invention can shield trace metal ions in the reaction system under the action of a shielding agent and in combination with an initiator, eliminate the possibility of iron ions reacting with chloride ions to form ferric chloride, avoid ring chlorination catalysis, reduce the generation of impurities, strengthen the conjugation effect of α-position free radicals and benzene rings, ensure the smooth progress of side chain chlorination reaction, thereby improving the yield and purity of trichlorotoluene, reducing the difficulty of subsequent distillation and purification and the amount of solid waste to be treated, significantly improving the efficiency of vacuum distillation, effectively reducing the cost of products, and increasing economic benefits.

[0008] Preferably, the shielding agent includes at least one of sulfur or red phosphorus.

[0009] The present invention has found through a large number of tests that the effect of using sulfur or red phosphorus and a composite thereof as a shielding agent is better than that of phosphorus trichloride and a composite thereof, and can further improve the yield and purity of trichlorotoluene.

[0010] Preferably, the preparation method of trichlorotoluene comprises the following steps: S1, adding an initiator, a shielding agent and a solvent into a mixing device to obtain a mixed solution; S2, adding toluene and the mixed solution into a reaction kettle, introducing chlorine gas to carry out chlorination reaction, and obtaining a crude trichlorotoluene product; S3, sending a part of the crude benzotrichloride product into the mixing device as a solvent for preparing the mixed solution in the next round; sending the remaining part of the crude benzotrichloride product into a distillation kettle for vacuum distillation, adjusting the reflux ratio, and obtaining benzotrichloride.

[0011] In the present invention, the preparation of trichlorotoluene is cyclically carried out. In the first preparation, commercially available trichlorotoluene can be selected as the solvent of the initiator and the shielding agent, or the initiator and the shielding agent can be directly added to the reactor without adding the solvent. In the subsequent preparation of the mixed solution, the crude trichlorotoluene prepared in the previous round is preferably used as the solvent; accordingly, a part of the crude trichlorotoluene prepared in this round needs to be reserved as the solvent for the next round of preparation of the mixed solution.

[0012] The preparation method of trichlorotoluene provided by the present invention, the initiator and the shielding agent of the solid component are added to the crude trichlorotoluene, and the solid is changed into a liquid, the fluidity is increased, the initiator and the shielding agent are more evenly dispersed during the chlorination reaction relative to the solid substance, and the chlorination reaction of the benzene ring side chain is more conducive to the progress. In addition, in the continuous preparation process of trichlorotoluene, the crude trichlorotoluene obtained in the previous round will not bring in extra impurities, will not have an adverse effect on the quality of trichlorotoluene, and the post-processing steps do not need to be adjusted; after the chlorination reaction is completed, the crude trichlorotoluene contains trace amounts of high-boiling impurities such as benzoyl chloride, dichlorotoluene and complexes, and these impurities can be effectively removed by vacuum distillation, and finally a trichlorotoluene finished product with a purity of ≥99% is obtained.

[0013] Preferably, the initiator comprises an organic peroxide.

[0014] More preferably, the organic peroxide is dibenzoyl peroxide.

[0015] Preferably, the mass ratio of the initiator, the shielding agent, the toluene and the chlorine is (2.5-5):(0.6-1.2):1000:(2200-2500).

[0016] Further preferably, in S1, the mass ratio of the shielding agent to the solvent is 1:(13-17).

[0017] The invention is beneficial to promoting the toluene side chain chlorination reaction by controlling the addition amount of each material, thereby further reducing reaction impurities and improving the yield and purity of trichlorotoluene.

[0018] Further preferably, in S2, the chlorination reaction is carried out in a main reactor and a sub-reactor in sequence, and the main reactor and the sub-reactor are connected in series.

[0019] Generally, in a chlorination reaction, in order to ensure that the reaction proceeds more thoroughly, a slightly excessive amount of chlorine is introduced into the main reactor. The secondary reactor can be used to reduce the waste of chlorine so that the chlorine overflowing from the main reactor can continue to react with the unreacted toluene, thereby further improving the yield of trichlorotoluene and reducing the cost of raw materials.

[0020] For example, the number of main reactors is 1, and the number of auxiliary reactors is 1 to 2.

[0021] More preferably, in S2, the temperature of the main reactor is 80°C to 100°C, and the pressure is 20kPa to 30kPa.

[0022] More preferably, in S2, the temperature of the secondary reaction kettle is 65°C to 85°C, and the pressure is -20kPa to -30kPa.

[0023] In the present invention, the main reaction kettle is operated under a slight positive pressure, and the sub-reaction kettle is operated under a slight negative pressure, which is conducive to passing the unreacted materials in the main reaction kettle into the sub-reaction kettle, which is safer; the main reaction kettle and the sub-reaction kettle are controlled to operate at a specific temperature, which is conducive to making the side chain chlorination reaction more thorough, reducing the content of impurities, and thus improving the yield and purity of trichlorotoluene.

[0024] Further preferably, in S2, the flow rate of the chlorine gas is 220kg / h~260kg / h.

[0025] Further preferably, in S2, the chlorination reaction time is 18h~22h.

[0026] It should be noted that the flow rate of chlorine in the present invention refers to the flow rate under a stable state, and the time of chlorination reaction refers to the total time used from the start of the reaction to the end of the final reaction. Generally, in the preparation process of trichlorotoluene, the chlorine flow rate is relatively slow in the early stage and the chlorination reaction later stage, so that the chlorination reaction is carried out more thoroughly. The present invention does not require the reaction time under the stable flow rate of chlorine, and the conventional operation of this area can be used.

[0027] For example, in S2, after the chlorination reaction is completed, hydrogen chloride gas will be formed at the upper end of the main reactor and the auxiliary reactor, which will be absorbed by water to form hydrochloric acid. When the predetermined concentration (such as 30%~32%) is reached, it will be transferred to the hydrochloric acid storage tank for recycling.

[0028] Further preferably, in S3, the pressure of the vacuum distillation is -90 kPa to -98 kPa, and the temperature is 145° C. to 155° C.

[0029] Further preferably, in S3, the reflux ratio is (2~3):1.

[0030] The present invention can further effectively remove impurities in the crude trichlorotoluene by controlling the conditions of vacuum distillation, thereby improving the purity of trichlorotoluene. The results of the embodiment show that the purity of the trichlorotoluene prepared by the present invention can reach more than 99%, the high boiling point impurities generated by ring chlorination are less than 0.5%, the quality is excellent, and it has a high market application value. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] Example 1 The present embodiment provides a method for preparing trichlorotoluene, comprising the following steps: S1, add 8.0 kg of dibenzoyl peroxide, 2.0 kg of sulfur and 30.0 kg of crude benzotrichloride (the crude benzotrichloride of this round is selected from the crude benzotrichloride prepared in the previous round) into a mixing device to obtain a mixed solution.

[0033] S2, when the pressure of the secondary reactor is -25 kPa, start heating, control the temperature of the main reactor to 88°C~92°C, and the temperature of the secondary reactor to 73°C~77°C, put 2000.0 kg (21706 mol) of toluene into the main reactor, add the above mixed solution dropwise, and at the same time, introduce 4640 kg of chlorine into the main reactor for chlorination reaction, the flow rate of chlorine is 240 kg / h (the pressure of the main reactor is 26 kPa after the chlorine is stably introduced), the reaction time is 19.6 h, and a crude trichlorotoluene product is obtained.

[0034] S3, 30.0 kg of crude trichlorotoluene was sent to the mixing device as the solvent for the next round of preparation of the mixed solution; the remaining crude trichlorotoluene was pumped into a distillation kettle at -94 kPa and 150 ° C for vacuum distillation, and the reflux ratio was adjusted to 2.5:1 to obtain 3933.1 kg (20121 mol) of trichlorotoluene, with a yield of 92.7% and a purity of 99.36% (the high boiling point impurities produced by ring chlorination were 0.23%).

[0035] Example 2 The present embodiment provides a method for preparing trichlorotoluene, comprising the following steps: S1, add 6.4 kg of dibenzoyl peroxide, 1.6 kg of red phosphorus and 22.4 kg of crude benzotrichloride (the crude benzotrichloride in this round is selected from the crude benzotrichloride prepared in the previous round) into a mixing device to obtain a mixed solution.

[0036] S2, when the pressure of the secondary reactor is -28 kPa, start heating, control the temperature of the main reactor to 92°C~96°C, and the temperature of the secondary reactor to 77°C~81°C, put 2000.0 kg (21706 mol) of toluene into the main reactor, add the above mixed solution dropwise, and at the same time, introduce 4410 kg of chlorine into the main reactor for chlorination reaction, the flow rate of chlorine is 230 kg / h (the pressure of the main reactor is 22 kPa after the chlorine is stably introduced), the reaction time is 19.5 h, and a crude trichlorotoluene product is obtained.

[0037] S3, 22.4 kg of crude trichlorotoluene was sent to the mixing device as the solvent for the next round of preparation of the mixed solution; the remaining crude trichlorotoluene was pumped into a distillation kettle at -96 kPa and 155 ° C for vacuum distillation, and the reflux ratio was adjusted to 2.3:1 to obtain 3920.4 kg (20056 mol) of trichlorotoluene, with a yield of 92.4% and a purity of 99.18% (the high boiling point impurities produced by ring chlorination were 0.29%).

[0038] Example 3 The present embodiment provides a method for preparing trichlorotoluene, comprising the following steps: S1, add 5.0 kg of dibenzoyl peroxide, 1.2 kg of phosphorus trichloride and 19.2 kg of crude benzotrichloride (the crude benzotrichloride in this round is selected from the crude benzotrichloride prepared in the previous round) into a mixing device to obtain a mixed solution.

[0039] S2, when the pressure of the secondary reactor is -23 kPa, start heating, control the temperature of the main reactor to 84°C~88°C, and the temperature of the secondary reactor to 69°C~73°C, put 2000.0 kg (21706 mol) of toluene into the main reactor, add the above mixed solution dropwise, and at the same time, introduce 4900 kg of chlorine into the main reactor for chlorination reaction, the flow rate of chlorine is 250 kg / h (the pressure of the main reactor is 28 kPa after the chlorine is stably introduced), the reaction time is 20 hours, and trichlorotoluene crude product is obtained.

[0040] S3, 19.2 kg of crude trichlorotoluene was sent to the mixing device as the solvent for the next round of preparation of the mixed solution; the remaining crude trichlorotoluene was pumped into a distillation kettle at -92 kPa and 145 ° C for vacuum distillation, and the reflux ratio was adjusted to 2.8:1 to obtain 3873.7 kg (19818 mol) of trichlorotoluene, with a yield of 91.3% and a purity of 98.02% (the high boiling point impurities produced by ring chlorination were 0.48%).

[0041] Example 4 The present embodiment provides a method for preparing trichlorotoluene, comprising the following steps: S1, add 10.0 kg of dibenzoyl peroxide, 1.2 kg of sulfur, 1.2 kg of red phosphorus and 31.2 kg of crude trichlorotoluene (the crude trichlorotoluene in this round is selected from the crude trichlorotoluene prepared in the previous round) into a mixing device to obtain a mixed solution.

[0042] S2, when the pressure of the secondary reactor is -20kPa, start heating, control the temperature of the main reactor to 96℃~100℃, and the temperature of the secondary reactor to 81℃~85℃, put 2000.0kg (21706mol) of toluene into the main reactor, drop the above mixed solution, and at the same time, introduce 4780kg of chlorine into the main reactor for chlorination reaction, the flow rate of chlorine is 220kg / h (the pressure of the main reactor is 20kPa after the chlorine is introduced stably), the reaction time is 22h, and the crude trichlorotoluene is obtained. ( S3, 31.2 kg of crude trichlorotoluene was sent to the mixing device as the solvent for the next round of preparation of the mixed solution; the remaining crude trichlorotoluene was pumped into a distillation kettle at -90 kPa and 150 ° C for vacuum distillation, and the reflux ratio was adjusted to 3:1 to obtain 3924.7 kg (20078 mol) of trichlorotoluene, with a yield of 92.5% and a purity of 99.52% (the high boiling point impurities produced by ring chlorination were 0.24%).

[0043] Example 5 The present embodiment provides a method for preparing trichlorotoluene, comprising the following steps: S1, add 8.0 kg of dibenzoyl peroxide, 1.2 kg of sulfur, 0.8 kg of phosphorus trichloride and 34.0 kg of crude benzotrichloride (the crude benzotrichloride in this round is selected from the crude benzotrichloride prepared in the previous round) into a mixing device to obtain a mixed solution.

[0044] S2, when the pressure of the secondary reactor is -30 kPa, start heating, control the temperature of the main reactor to 80°C~84°C, and the temperature of the secondary reactor to 65°C~69°C, put 2000.0 kg (21706 mol) of toluene into the main reactor, add the above mixed solution dropwise, and at the same time, introduce 4600 kg of chlorine into the main reactor for chlorination reaction, the flow rate of chlorine is 260 kg / h (the pressure of the main reactor is 30 kPa after the chlorine is stably introduced), the reaction time is 18 hours, and trichlorotoluene crude product is obtained.

[0045] S3, 34.0 kg of crude trichlorotoluene was sent to the mixing device as the solvent for the next round of preparation of the mixed solution; the remaining crude trichlorotoluene was pumped into a distillation kettle at -98 kPa and 150 ° C for vacuum distillation, and the reflux ratio was adjusted to 2:1 to obtain 3886.5 kg (19883 mol) of trichlorotoluene, with a yield of 91.6% and a purity of 99.07% (the high boiling point impurities produced by ring chlorination were 0.40%).

[0046] Example 6 This embodiment provides a method for preparing trichlorotoluene, which is similar to that of embodiment 1, except that solid dibenzoyl peroxide and sulfur are directly added to the main reaction kettle, and the addition of crude trichlorotoluene as a solvent is omitted. Specifically, the method comprises the following steps: S1, when the pressure of the secondary reactor is -25 kPa, start heating, control the temperature of the main reactor to 88 ℃ ~ 92 ℃, and the temperature of the secondary reactor to 73 ℃ ~ 77 ℃, put 8.0 kg of dibenzoyl peroxide, 2.0 kg of sulfur and 2000.0 kg (21706 mol) of toluene into the main reactor, mix them evenly, and introduce 4640 kg of chlorine into the main reactor for chlorination reaction, the flow rate of chlorine is 240 kg / h (the pressure of the main reactor is 26 kPa after the chlorine is stably introduced), the reaction time is 19.6 h, and the crude trichlorotoluene is obtained.

[0047] S2, the crude trichlorotoluene was pumped into a distillation kettle at -94 kPa and 150 ° C for vacuum distillation, and the reflux ratio was adjusted to 2.5:1 to obtain 3882.2 kg (19861 mol) of trichlorotoluene, with a yield of 91.5% and a purity of 98.65% (the high boiling point impurities produced by ring chlorination were 0.44%).

[0048] Comparative Example 1 This comparative example provides a method for preparing trichlorotoluene, which is similar to Example 1, except that the addition of shielding agent sulfur is omitted in S1. Specifically, the method comprises the following steps: S1, adding 8.0 kg of dibenzoyl peroxide and 30.0 kg of crude benzotrichloride (the crude benzotrichloride in this round is selected from the crude benzotrichloride prepared in the previous round) into a mixing device to obtain a mixed solution.

[0049] S2-S3 are the same as those in Example 1 and will not be described again. Finally, 3678.6 kg (18819 mol) of trichlorotoluene was obtained with a yield of 86.7% and a purity of 96.52% (the high boiling point impurities produced by ring chlorination accounted for 2.72%).

[0050] Comparative Example 2 This comparative example provides a method for preparing trichlorotoluene, which is similar to Example 1, except that in S1, sulfur is replaced by dibenzoyl peroxide of the same mass. Specifically, the method comprises the following steps: S1, adding 10.0 kg of dibenzoyl peroxide and 30.0 kg of crude benzotrichloride (the crude benzotrichloride in this round is selected from the crude benzotrichloride prepared in the previous round) into a mixing device to obtain a mixed solution.

[0051] S2-S3 are the same as in Example 1 and will not be described again. Finally, 3699.8 kg (18928 mol) of trichlorotoluene was obtained with a yield of 87.2% and a purity of 97.05% (the high boiling point impurities produced by ring chlorination accounted for 2.13%).

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing trichlorotoluene, characterized in that: The following steps are involved: Under the action of an initiator and a shielding agent, toluene is used as a raw material, chlorine gas is introduced to carry out a chlorination reaction, and trichlorotoluene is obtained; the shielding agent comprises at least one of sulfur, red phosphorus or phosphorus trichloride.

2. The method for preparing trichlorotoluene as claimed in claim 1, wherein The shielding agent includes at least one of sulfur or red phosphorus.

3. The method for preparing trichlorotoluene as claimed in claim 1, wherein The initiator comprises an organic peroxide; and / or The mass ratio of the initiator, the shielding agent, the toluene and the chlorine is (2.5-5):(0.6-1.2):1000:(2200-2500).

4. The method for preparing trichlorotoluene as claimed in claim 3, characterized in that: The organic peroxide is dibenzoyl peroxide.

5. The method for preparing trichlorotoluene as claimed in claim 1, characterized in that: The following steps are involved: S1, adding an initiator, a shielding agent and a solvent into a mixing device to obtain a mixed solution; S2, adding toluene and the mixed solution into a reaction kettle, introducing chlorine gas to carry out chlorination reaction, and obtaining a crude trichlorotoluene product; S3, sending a portion of the crude benzotrichloride product into the mixing device as a solvent for preparing the mixed solution in the next round; sending the remaining portion of the crude benzotrichloride product into a distillation kettle for vacuum distillation, adjusting the reflux ratio, and obtaining benzotrichloride.

6. The method for preparing trichlorotoluene as claimed in claim 5, characterized in that: In S1, the mass ratio of the shielding agent to the solvent is 1:(13-17).

7. The method for preparing trichlorotoluene as claimed in claim 5, characterized in that: In S2, the chlorination reaction is carried out in a main reactor and a sub-reactor in sequence, and the main reactor and the sub-reactor are connected in series.

8. The method for preparing trichlorotoluene as claimed in claim 6, characterized in that: In S2, the temperature of the main reactor is 80°C~100°C, and the pressure is 20kPa~30kPa; the temperature of the secondary reactor is 65°C~85°C, and the pressure is -20kPa~-30kPa.

9. The method for preparing trichlorotoluene as claimed in claim 5, 7 or 8, characterized in that: In S2, the flow rate of the chlorine gas is 220kg / h~260kg / h; and / or In S2, the chlorination reaction time is 18h~22h.

10. The method for preparing trichlorotoluene as claimed in claim 5, characterized in that: In S3, the pressure of the vacuum distillation is -90 kPa to -98 kPa, and the temperature is 145° C. to 155° C.; and / or In S3, the reflux ratio is (2~3):1.