Process for the continuous synthesis of mercaptoacetic acid isooctyl ester

Abstract

This invention relates to the field of fine chemical synthesis technology, and more particularly to a method for the continuous synthesis of isooctyl mercaptoacetate. The invention utilizes a positive displacement pump to pump a mixture of mercaptoacetic acid and an acid catalyst, along with isooctanol, into a mixer for mixing. This mixture then enters a coil reactor for esterification. The resulting reaction product is further fed into a collector via a microfluidic pipe, yielding a reaction solution containing isooctyl mercaptoacetate. The synthesis method provided by this invention features a high degree of automation, short reaction time, high product yield, low risk of equipment corrosion and leakage, and is operator-friendly.

Description

Technical Field

[0001] This invention relates to the field of fine chemical synthesis technology, and in particular to a method for the continuous synthesis of isooctyl mercaptoacetate. Background Technology

[0002] Isooctyl mercaptoacetate (also known as isooctyl thioglycolate), with the molecular formula C2... 10 H 20 O2S is a colorless and transparent liquid with a molecular weight of 204.34 g / mol, a boiling point of 125 ℃, and a relative density of approximately 0.970. Isooctyl mercaptoacetate, as an important fine chemical product, is mainly used industrially as a key intermediate in the production of non-toxic heat stabilizers for polyvinyl chloride (PVC) (such as tin thiolate, tin ester, and antimony thiolate). It also serves as a chain transfer agent, initiator, and catalyst in the synthesis of bisphenol A.

[0003] The synthesis methods of isooctyl mercaptoacetate can be divided into two main categories according to the technical route: one is direct esterification using mercaptoacetic acid and isooctyl alcohol as raw materials, and the other is the isooctyl chloroacetate route (i.e., esterification followed by thiolation). Currently, the mainstream batch reactor process still faces a series of insurmountable technical bottlenecks in the esterification reaction stage. (1) Traditional catalysts are highly corrosive. Concentrated sulfuric acid is currently the most commonly used catalyst in esterification reactions. Although it is inexpensive and has high catalytic activity, it is highly corrosive and has strict requirements on the materials of reaction equipment. Long-term operation can easily cause equipment corrosion and leakage.

[0004] (2) Limitations of reversible equilibrium in esterification. Esterification is a thermodynamically controlled reversible equilibrium reaction. The forward reaction rate gradually decreases as the acid concentration in the system decreases, while the reverse hydrolysis reaction intensifies with the accumulation of water in the product. The reaction equilibrium naturally limits the conversion rate. In a batch reactor system, the water generated in the reaction is difficult to remove in time, resulting in a limited equilibrium conversion rate.

[0005] (3) Long reaction time. The ratio of heat transfer area to volume of batch reactor is small and the mass transfer efficiency is low. The reaction needs to be stirred continuously and the reaction time needs to be more than 5 hours.

[0006] (4) Insufficient production safety and low degree of automation. Traditional batch processes have many steps and insufficient continuity. Every time the reactor is opened and closed, there is a probability of hazardous materials escaping or operators being exposed to hot acid and alkali environments, especially when sulfuric acid is used as a catalyst. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a method for the continuous synthesis of isooctyl mercaptoacetate. The synthesis method provided by this invention has a high degree of automation, short reaction time, high product yield, low risk of equipment corrosion and leakage, and is operator-friendly.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for the continuous synthesis of isooctyl mercaptoacetate, which employs a microfluidic reactor, the microfluidic reactor comprising: Positive displacement pump; A mixer connected to the positive displacement pump via a microfluidic conduit; A coil reactor connected to the mixer via a microfluidic conduit; The collector is connected to the coil reactor via a microfluidic pipe; Heating equipment for heating coil reactors; The method for continuous synthesis of isooctyl mercaptoacetate includes the following steps: using a volumetric pump, a mixture of mercaptoacetic acid-acid catalyst and isooctyl alcohol is pumped into a mixer and mixed, and then fed into a coil reactor for esterification reaction. The resulting reaction product is fed into a collector through a microfluidic pipe to obtain a reaction solution containing isooctyl mercaptoacetate. The esterification reaction is carried out at a temperature of 110~130℃, a pressure of 0.2~0.8 MPa, and a time of 15~30 min.

[0009] Preferably, the molar ratio of the thioglycolic acid and isooctyl alcohol is 1:(1~3).

[0010] Preferably, the acid catalyst comprises concentrated sulfuric acid; the mass fraction of the concentrated sulfuric acid is 98%; and the molar ratio of the acid catalyst to mercaptoacetic acid is (3~10):100.

[0011] Preferably, the mixer is further cooled; the cooling temperature is 0°C.

[0012] Preferably, the process also includes cooling the microfluidic pipe downstream of the coil reactor and upstream of the back pressure valve, so that the temperature of the cooled reaction products is 18~25°C.

[0013] Preferably, the positive displacement pump is a plunger pump.

[0014] Preferably, the microfluidic channel has an inner diameter of 1.6 mm and an outer diameter of 3 mm.

[0015] Preferably, the mixer is a T-type mixer or a microchannel plate mixer.

[0016] Preferably, after obtaining the reaction solution containing isooctyl mercaptoacetate, the reaction further includes allowing the mixture to stand and separate into layers, collecting the upper organic phase, and obtaining isooctyl mercaptoacetate.

[0017] Preferably, the coil reactor has a tube length of 8 m, an inner diameter of 1.6 mm, and an outer diameter of 3 mm.

[0018] Compared with the prior art, the present invention has the following advantages: Traditional batch reactors require continuous stirring during the reaction of raw materials, and the reaction time is more than 5 hours. This invention, through a continuous flow synthesis method, can shorten the reaction time to 15-30 minutes.

[0019] In traditional batch reactors, the yield of isooctyl mercaptoacetate (MGA) produced by the reaction of mercaptoacetic acid and isooctanol is generally no more than 95%, and a dehydrating agent or water separator is required to separate water in time to promote the esterification reaction. The process is cumbersome and costly. This invention uses a microfluidic reactor to continuously synthesize isooctyl mercaptoacetate. The product flows out continuously and stably. The organic phase and the generated water can achieve rapid stratification in the pipeline (with some of the effect of a water separator), promoting the forward esterification reaction. The yield of isooctyl mercaptoacetate is high, reaching over 98%. At the same time, it eliminates the need for a dehydrating agent and water separator, making the process simple and low-cost.

[0020] Concentrated sulfuric acid is currently the most commonly used catalyst in esterification reactions. It is highly corrosive. Traditional batch reactors have stringent requirements for the materials of the reaction equipment, and long-term operation can easily lead to equipment corrosion and leakage. This invention uses a microchannel reaction device and a continuous flow reactor, which can reduce the risk of equipment corrosion and leakage.

[0021] The raw material, mercaptoacetic acid, has an odor. Continuous flow operation can isolate the odor and is operator-friendly. Attached Figure Description

[0022] Figure 1 A photograph of the apparatus used to synthesize mercaptoacetic acid; Figure 2 This is the carbon NMR spectrum of isooctyl mercaptoacetate. Detailed Implementation

[0023] This invention provides a method for the continuous synthesis of isooctyl mercaptoacetate, which employs a microfluidic reactor, the microfluidic reactor comprising: Positive displacement pump; A mixer connected to the positive displacement pump via a microfluidic conduit; A coil reactor connected to the mixer via a microfluidic conduit; The collector is connected to the coil reactor via a microfluidic pipe; Heating equipment for heating coil reactors; The method for continuous synthesis of isooctyl mercaptoacetate includes the following steps: using a volumetric pump, a mixture of mercaptoacetic acid-acid catalyst and isooctyl alcohol is pumped into a mixer and mixed, and then fed into a coil reactor for esterification reaction. The resulting reaction product is fed into a collector through a microfluidic pipe to obtain a reaction solution containing isooctyl mercaptoacetate. The esterification reaction is carried out at a temperature of 110~130℃, a pressure of 0.2~0.8 MPa, and a time of 15~30 min.

[0024] The microfluidic reactor will be described below.

[0025] The microfluidic reaction device provided by the present invention includes a volumetric pump; the volumetric pump is used to pump a mixture of thioglycolic acid and concentrated sulfuric acid and isooctanol. In an embodiment of the present invention, the volumetric pump is a plunger pump; the plunger pump includes plunger pump 1 and plunger pump 2, which are used to pump the mixture of thioglycolic acid and concentrated sulfuric acid and isooctanol to the mixer, respectively.

[0026] The microfluidic reaction device provided by this invention includes a mixer connected to the volumetric pump via a microfluidic conduit; the mixer is used to mix a mercaptoacetic acid-acid catalyst mixture and isooctanol. In embodiments of this invention, the mixer is a T-type mixer or a microchannel plate mixer. In this invention, the microfluidic conduit is a Teflon tube with an inner diameter of 1.6 mm, an outer diameter of 3 mm, and a wall thickness of 0.5 mm.

[0027] The microfluidic reactor provided by this invention includes a coil reactor connected to the mixer via a microfluidic channel; the coil reactor provides a site for the esterification reaction. In an embodiment of this invention, the coil reactor has a length of 8 m, a liquid holding capacity of 60 mL, an inner diameter of 1.6 mm, an outer diameter of 3 mm, and is made of PFA (fusible polytetrafluoroethylene). Those skilled in the art can adjust the specifications of the coil reactor as needed; for example, the tube length can be appropriately extended when the reaction time needs to be extended.

[0028] The microfluidic reactor provided by this invention includes a collector connected to the coil reactor via a microfluidic channel; the collector is used to collect reaction products. This invention does not have special requirements for the collector; a conventional container with a collection function is sufficient, and in the embodiments of this invention, a separating funnel is specifically used.

[0029] The microfluidic reactor provided by this invention includes a heating device; the heating device is used to heat the coil reactor to provide the temperature required for the esterification reaction. In an embodiment of this invention, the heating device is a water bath. When used to synthesize isooctyl mercaptoacetate, this invention places the coil reactor in a water bath.

[0030] The microfluidic reactor provided by this invention includes a back pressure valve disposed on a microfluidic channel between a coil reactor and a collector. In this invention, the back pressure valve is used to control the pressure in the microfluidic channel, provide a stable working load, and prevent fluid from flowing out due to gravity or inertia.

[0031] As an embodiment of the present invention, the microfluidic reactor provided by the present invention further includes a cooling device; the cooling device is used to cool the reaction products and / or mixer of the coil reactor. In the present invention, the cooling device can be one unit or two units; for example, two units can be set up, one for cooling the reaction products of the coil reactor and the other for cooling the mixer, or one unit can be set up to simultaneously cool the reaction products of the coil reactor and the other for cooling the mixer. In an embodiment of the present invention, the cooling device is a circulating cooling tank.

[0032] The synthesis steps are described below.

[0033] The method for the continuous synthesis of isooctyl mercaptoacetate includes the following steps: A volumetric pump is used to pump the mercaptoacetic acid-acid catalyst mixture and isooctanol into a mixer for mixing, and then into a coil reactor for esterification. The resulting reaction product is then fed into a collector via a microfluidic pipe to obtain a reaction solution containing isooctyl mercaptoacetate.

[0034] In this invention, the thioglycolic acid-acid catalyst mixture is preferably obtained by mixing thioglycolic acid and an acid catalyst; the acid catalyst preferably comprises concentrated sulfuric acid; the mass fraction of the concentrated sulfuric acid is preferably 98%. In this invention, the molar ratio of the acid catalyst to thioglycolic acid is preferably (3~10):100, and in specific embodiments it can be 3:100, 5:100, 7:100, 8:100, or 10:100. In this invention, the molar ratio of thioglycolic acid to isooctanol in the mixer is preferably 1:(1~3), and in specific embodiments it can be 1:1, 1:1.5, 1:2, 1:2.5, or 1:3. In this invention, the flow rate ratio of the thioglycolic acid-acid catalyst mixture to isooctanol is preferably 1:(1.5~3), and in specific embodiments it can be 1:1.5, 1:2, 1:2.5, or 1:3.

[0035] In the synthesis of isooctyl mercaptoacetate, the present invention preferably employs a cooling device to cool the mixer; the cooling temperature is preferably 0°C. The present invention prevents premature aging and failure of the mixer by cooling it. In an embodiment of the present invention, the mixer is specifically placed in a circulating cooling chamber, the temperature of which is set to 0°C.

[0036] In this invention, the temperature of the esterification reaction is 110~130℃, and in specific embodiments it can be 110, 115, 120, 125 or 130℃; the pressure is 0.2~0.8 MPa, and in specific embodiments it can be 0.2, 0.4, 0.6 or 0.8 MPa; the time of the esterification reaction is 15~30 min, and in specific embodiments it can be 15, 20, 25 or 30 min. In an embodiment of this invention, the coil reactor is placed in a water bath, and the water bath temperature is set to 110~130℃. In this invention, after the esterification reaction, isooctyl mercaptoacetate is generated, and the product flows out continuously into a collector. Unlike traditional batch reactors (materials are added in batches and removed in batches after the reaction), in this invention, the reactants are continuously pumped in at a stable flow rate in a microchannel reactor, and the product flows out continuously. The water produced in the esterification reaction has already been separated in the pipeline, promoting the esterification reaction and thus improving the yield of isooctyl mercaptoacetate.

[0037] As a preferred embodiment, the present invention preferably cools the microfluidic pipe between the coil reactor and the back pressure valve, so that the temperature of the cooled reaction product is 18~25℃. The present invention reduces the risk of high-temperature aging of the back pressure valve by cooling. In an embodiment of the present invention, specifically, the microfluidic pipe between the coil reactor and the back pressure valve is placed in a circulating cooling box, the temperature of which is set to 0℃. After cooling, the temperature of the reaction product is 18~25℃.

[0038] After obtaining the reaction solution containing isooctyl mercaptoacetate, the present invention preferably allows it to stand and separate into layers, and collects the upper organic phase to obtain isooctyl mercaptoacetate.

[0039] The following detailed description of the method for continuous synthesis of isooctyl thioglycolate provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0040] The following examples show photographs of the apparatus used to synthesize thioglycolic acid. Figure 1 As shown, the system includes plunger pump 1, plunger pump 2, T-type mixer, coil reactor, separatory funnel, water bath, circulating cooling tank, back pressure valve, and microfluidic pipe. The microfluidic pipe is a Teflon tube with an inner diameter of 1.6 mm, an outer diameter of 3 mm, and a wall thickness of 0.5 mm. The coil reactor has a length of 8 m, a liquid holding capacity of 60 mL, an inner diameter of 1.6 mm, an outer diameter of 3 mm, and is made of PFA.

[0041] The raw materials used in the following examples and comparative examples are as follows: Mercaptoacetic acid, purchased from Anaiji Chemical, 99% purity; isooctyl alcohol, purchased from Jingrui Technology, 99% purity; concentrated sulfuric acid, purchased from Jingrui Technology, 98% concentration.

[0042] Example 1 100 mol of mercaptoacetic acid was measured and placed in a bottle, and 3 mol of sulfuric acid was added dropwise. The mixture was stirred with a magnetic rotor and connected to plunger pump 1. 110 mol of isooctyl alcohol was measured and connected to plunger pump 2. The flow rates of plunger pump 1 and 2 were set to 1 mL / min and 1.5 mL / min, respectively, with a flow ratio of 1:1.5. The plunger pumps were started, and the mixture was mixed using a T-mixer and then connected to a coil reactor. The oil bath temperature was set to 130℃, the pressure to 0.4 MPa, and the reaction time to 25 min. The microfluidic pipe after the coil reactor was placed in a circulating cooling box to cool the product to 18-25℃. The product was then transferred to a separatory funnel, allowed to stand, and the upper organic phase was collected to obtain isooctyl mercaptoacetate. NMR analysis was performed to determine whether all mercaptoacetic acid was converted, and the yield of isooctyl mercaptoacetate was found to be 96%. Figure 2 The image shows the carbon NMR spectrum of isooctyl mercaptoacetate, indicating a composition of isooctyl mercaptoacetate and trace amounts of isooctyl alcohol.

[0043] Example 2 100 mol of mercaptoacetic acid was measured and placed in a bottle, and 3 mol of sulfuric acid was added dropwise. The mixture was stirred with a magnetic rotor and connected to plunger pump 1. 110 mol of isooctyl alcohol was measured and connected to plunger pump 2. The flow rates of plunger pump 1 and 2 were set to 1 mL / min and 1.5 mL / min, respectively, with a flow ratio of 1:1.5. The plunger pumps were started, and the mixture was mixed using a T-type mixer and then connected to a coil reactor. The oil bath temperature was set to 120℃, the pressure to 0.4 MPa, and the reaction time to 25 min. The microfluidic pipe after the coil reactor was placed in a circulating cooling box to cool the product to 18-25℃. The product was then transferred to a separatory funnel, allowed to stand, and the upper organic phase was collected to obtain isooctyl mercaptoacetate. NMR analysis was performed to determine whether all mercaptoacetic acid was converted, and the yield of isooctyl mercaptoacetate was found to be 98%.

[0044] Example 3 100 mol of mercaptoacetic acid was measured and placed in a bottle, and 3 mol of sulfuric acid was added dropwise. The mixture was stirred with a magnetic rotor and connected to plunger pump 1. 110 mol of isooctanol was measured and connected to plunger pump 2. The flow rates of plunger pump 1 and 2 were set to 1 mL / min and 1.5 mL / min, respectively, with a flow ratio of 1:1.5. The plunger pumps were started, and the mixture was mixed using a T-type mixer and then connected to a coil reactor. The oil bath temperature was set to 110℃, the pressure to 0.4 MPa, and the reaction time to 25 min. The microfluidic pipe after the coil reactor was placed in a circulating cooling box to cool the product to 18-25℃. The product was then transferred to a separatory funnel, allowed to stand, and the upper organic phase was collected to obtain isooctyl mercaptoacetate. NMR analysis was performed to determine whether all mercaptoacetic acid was converted, and the yield of isooctyl mercaptoacetate was found to be 98%.

[0045] Comparative Example 1 100 mol of mercaptoacetic acid was measured and placed in a bottle, and 3 mol of sulfuric acid was added dropwise. The mixture was stirred with a magnetic rotor and connected to plunger pump 1. 110 mol of isooctanol was measured and connected to plunger pump 2. The flow rates of plunger pump 1 and 2 were set to 1 mL / min and 1.5 mL / min, respectively, with a flow ratio of 1:1.5. The plunger pumps were started, and the mixture was mixed using a T-mixer and then connected to a coil reactor. The oil bath temperature was set to 100℃, the pressure to 0.4 MPa, and the reaction time to 25 min. The microfluidic pipe after the coil reactor was placed in a circulating cooling box to cool the product to 18-25℃. The product was then transferred to a separatory funnel, and after standing, the upper organic phase was collected to obtain crude isooctyl mercaptoacetate. NMR analysis was performed to determine whether all mercaptoacetic acid was converted. The yield of isooctyl mercaptoacetate was found to be 84%. Some mercaptoacetic acid raw material was not completely converted.

[0046] The results of Comparative Example 1 show that when the esterification temperature is below 110°C, the yield of the product isooctyl mercaptoacetate decreases.

[0047] Comparative Example 2 The reaction was carried out in a bottle using a traditional reaction vessel method. The equivalent ratio of mercaptoacetic acid to isooctyl alcohol was 1:1.1, and 3% sulfuric acid was added as a catalyst. There was no dehydration device. The reaction was carried out at 110°C and atmospheric pressure for 5 hours. The yield of the final product, isooctyl mercaptoacetate, was measured to be 85%.

[0048] The results of Examples 1-3 and Comparative Example 2 show that the continuous flow synthesis method of the present invention can improve the yield of isooctyl mercaptoacetate and shorten the reaction time compared with the traditional reactor method.

[0049] Comparative Example 3 The molar ratio of mercaptoacetic acid to isooctanol was 1:2. 0.2% of the total reaction mass of catalyst was added, and the reaction was carried out at a certain temperature for 5 hours. Water was removed during the reaction using a dehydrating agent or by applying negative pressure. After the reaction, the pH was adjusted to approximately 7 with a 10% sodium carbonate solution, resulting in a pink solution. The organic phase was separated, washed with water, and then purified. The esterification reaction results are shown in Table 1.

[0050] Table 1. Experimental conditions and results of Comparative Example 3

[0051] As shown in Table 1, the yield of isooctyl mercaptoacetate in traditional batch reactors is only 93.1% in the presence of a dehydrating agent or under negative pressure. However, the present invention uses a microchannel reactor, and even without the use of a dehydrating agent, the yield of isooctyl mercaptoacetate is still as high as 96% or more. Moreover, the reaction time of the present application is shorter.

[0052] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for the continuous synthesis of isooctyl mercaptoacetate, characterized in that, The reaction is carried out using a microfluidic reactor, which includes: Positive displacement pump; A mixer connected to the positive displacement pump via a microfluidic conduit; A coil reactor connected to the mixer via a microfluidic conduit; The collector is connected to the coil reactor via a microfluidic pipe; Heating equipment for heating coil reactors; The method for continuous synthesis of isooctyl mercaptoacetate includes the following steps: using a volumetric pump, a mixture of mercaptoacetic acid-acid catalyst and isooctyl alcohol is pumped into a mixer and mixed, and then fed into a coil reactor for esterification reaction. The resulting reaction product is fed into a collector through a microfluidic pipe to obtain a reaction solution containing isooctyl mercaptoacetate. The esterification reaction is carried out at a temperature of 110~130℃, a pressure of 0.2~0.8 MPa, and a time of 15~30 min.

2. The method according to claim 1, characterized in that, The molar ratio of the thioglycolic acid and isooctyl alcohol is 1:(1~3).

3. The method according to claim 1, characterized in that, The acid catalyst includes concentrated sulfuric acid; the mass fraction of the concentrated sulfuric acid is 98%; the molar ratio of the acid catalyst to mercaptoacetic acid is (3~10):

100.

4. The method according to claim 1, characterized in that, It also includes cooling the mixer; the cooling temperature is 0°C.

5. The method according to claim 1, characterized in that, It also includes cooling the microfluidic pipes after the coil reactor and before the back pressure valve, so that the temperature of the cooled reaction products is 18~25℃.

6. The method according to claim 1, characterized in that, The positive displacement pump is a plunger pump.

7. The method according to claim 1, characterized in that, The microfluidic channel has an inner diameter of 1.6 mm and an outer diameter of 3 mm.

8. The method according to claim 1, characterized in that, The mixer is a T-type mixer or a microchannel plate mixer.

9. The method according to claim 1, characterized in that, After obtaining the reaction solution containing isooctyl mercaptoacetate, the reaction process also includes allowing the mixture to stand and separate into layers, collecting the upper organic phase, and obtaining isooctyl mercaptoacetate.

10. The method according to claim 1, characterized in that, The coil reactor has a tube length of 8 m, an inner diameter of 1.6 mm, and an outer diameter of 3 mm.

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