Method for preparing alkoxy amine by Schiff base reduction one-pot method

Abstract

The invention provides a method for preparing alkoxy amine through a Schiff base reduction one-pot method, and belongs to the technical field of reversible inactivation free radical polymerization. Comprising the steps of Schiff base reaction, reduction reaction, oxidation reaction and the like, raw materials are easy to obtain, a purification method is easy, and industrialization is easy. The alkoxy amine has good polymerization regulation performance on methacrylate, and can be used for controllable synthesis of functional polymers.

Description

Technical Field

[0001] The invention relates to a method for preparing alkoxyamine by a one-pot Schiff base reduction method, and belongs to the technical field of reversible deactivated free radical polymerization technology. Background Art

[0002] In 2016, Steven van Es et al. reported a new type of alkoxyamine (ACS Macro Letters 5(9):1019-1022), whose structure is as follows Figure 1 As shown, it was named Dispolreg 007. This type of alkoxyamine can regulate methacrylates and styrene, solving the long-standing problem that NMP is difficult to regulate the polymerization of methyl methacrylate monomers.

[0003] In the synthesis method of Dispolreg007, Steven van Es et al. firstly react cyclohexylamine with benzyl bromide, then oxidize with monopersulfate, and then react with azobisisobutyronitrile through coupling reaction to obtain the product. In the first step, since theoretically one cyclohexane can react with two benzyl bromides, in order to avoid the generation of by-products, the molar ratio of cyclohexylamine to benzyl bromide is 3:1, and cyclohexylamine is greatly excessive; at the same time, benzyl bromide is highly toxic and expensive, and is not suitable for industrial production.

[0004] Therefore, there is an urgent need in the art for a one-pot method for preparing alkoxyamines by Schiff base reduction. Summary of the invention

[0005] The invention aims to solve the problems of high toxicity and excessive cyclohexylamine in the preparation reaction process of alkoxyamine in the prior art.

[0006] In order to achieve the purpose of solving the above problems, the technical solution adopted by the present invention is to provide a method for preparing alkoxyamines by a one-pot Schiff base reduction method, comprising the following steps:

[0007] Step 1: Add cyclohexylamine and benzaldehyde into an organic solvent and stir to react.

[0008] Step 2, adding a reducing agent and an organic solvent, then washing with saturated brine, taking the organic phase, adding a desiccant to dry, filtering, and removing the solvent to obtain benzylcyclohexylamine.

[0009] Step 3, dissolving the benzylcyclohexylamine obtained in step 2 in an organic solvent, then adding an oxidant for oxidation, washing with saturated brine, taking the organic phase, adding a desiccant for drying, filtering, removing the solvent, and recrystallizing to obtain N-benzylcyclohexylamine oxide.

[0010] Step 4: dissolving the N-benzylcyclohexylamine oxide obtained in step 3 in an organic solvent, adding a free radical source, heating, removing the solvent after the reaction is completed, and recrystallizing to obtain Figure 1 The alkoxyamine shown is Dispolreg007.

[0011] The reaction route is as follows:

[0012]

[0013] Preferably, in step 1, the organic solvent is one or more of methanol, ethanol, dichloromethane and tetrahydrofuran.

[0014] Preferably, in step 1, 0.1% to 5% of acetic acid based on the molar number of benzaldehyde is added to catalyze the reaction to proceed rapidly; and 1% to 5% of molecular sieve based on the molar number of benzaldehyde is added during the process to absorb water.

[0015] Preferably, in step 2, the reducing agent is one or more of sodium borohydride, potassium borohydride, sodium cyanoborohydride, sodium triacetoxyborohydride or lithium aluminum hydride, more preferably sodium triacetoxyborohydride; the molar ratio of the reducing agent to the cyclohexylamine in step 1 is (1-2):1, preferably (1.1-1.5):1.

[0016] Preferably, in step 3, the oxidant is a monopersulfate compound, the molar ratio of the oxidant to the benzaldehyde in step 1 is (1-2):1, and the pH value in the reaction is controlled to be 8-10.

[0017] Preferably, in the step 4, the heating temperature is 85-90° C., and the molar ratio of the free radical source to the N-benzylcyclohexylamine oxide obtained in step 3 is (1-1.8):1; the free radical source is azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptanenitrile, azobisisobutylimidazoline hydrochloride, 4,4'-azobis(4-cyanovaleric acid), 4,4'-azobis(4-cyanopentanol), 4,4'-azobis(4-cyanovaleric acid) or 4,4'-azobis(4-cyanopentanol).

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The synthetic route for synthesizing alkoxyamine provided by the present invention uses benzaldehyde and cyclohexylamine as raw materials, which are easily available, cheap and low in toxicity. The Schiff base reduction method prepares benzylcyclohexylamine in one pot, and is an equimolar ratio reaction, atom-economical, high in yield, suitable for industrial production, and has good industrial prospects.

[0020] The alkoxyamine provided by the present invention has good telomerization performance for methacrylate monomers and has good application prospects in functional polymers. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the structural formula of the alkoxyamine prepared by the present invention;

[0022] Figure 2 is the hydrogen nuclear magnetic resonance spectrum of the alkoxyamine prepared by the present invention;

[0023] Figure 3 This is the GPC chart of the telomerization of methyl methacrylate by the alkoxyamine prepared in the present invention. DETAILED DESCRIPTION

[0024] In order to make the present invention more clearly understood, a preferred embodiment is described in detail with reference to the accompanying drawings as follows:

[0025] like Figure 1-3 As shown, the present invention provides a method for preparing alkoxyamines by a one-pot Schiff base reduction process.

[0026] Example 1

[0027] (1) Cyclohexylamine (5 g, 0.05 mol) and benzaldehyde (5.3 g, 0.05 mol) were placed in a 250 ml three-necked flask, and a magnetic bar and 50 ml of anhydrous methanol were added. After stirring evenly, nitrogen was introduced at 60°C and the reaction was continued for 2 h.

[0028] (2) Sodium borohydride (2.84 g, 0.075 mol) was added to the flask described in (1) in several portions and slowly added. After the addition was completed, the mixture was stirred for 2 h and the reaction was monitored by a plate. 30 ml of ethyl acetate was added and then washed twice with 40 ml of saturated brine. The organic phase was taken and dried with 5 g of anhydrous magnesium sulfate, filtered, and the solvent was removed to obtain 9.37 g of benzylcyclohexylamine with a yield of 99.1%.

[0029] (3) 9.37 g of benzylcyclohexylamine was added to a three-necked flask with mechanical stirring, and 24 g of acetone and 24 g of water were added, followed by 12 g of sodium bicarbonate. Under stirring, 22.83 g of monopersulfate oXone was slowly added in several portions. After the addition, the reaction was continued for 1 h, and then 30 ml of acetone was added to dissolve the mixture. The mixture was washed twice with 40 ml of saturated brine. The organic phase was taken, dried with anhydrous magnesium sulfate, and filtered to obtain 9.5 g of a crude product. After recrystallization, 8.9 g of a white solid was obtained with a yield of 88%.

[0030] (4) 8 g of N-benzylcyclohexylamine oxide was dissolved in 100 ml of toluene, 9.7 g of azobisisobutyronitrile was added, the temperature was raised to 92°C, the reaction was carried out for 6 h, the solvent was removed, and recrystallization was performed to obtain 10.7 g of a white solid with a yield of 80%. Its NMR spectrum is shown as follows: Figure 2 As shown, it is consistent with the literature reports.

[0031] Example 2

[0032] (1) Cyclohexylamine (5 g, 0.05 mol) and benzaldehyde (5.3 g, 0.05 mol) were placed in a 250 ml three-necked flask, and a magnetic bar and 60 ml of anhydrous ethanol were added. After stirring evenly, nitrogen was introduced at 70°C and the reaction was continued for 2 h.

[0033] (2) Sodium triacetoxyborohydride (13.77 g, 0.065 mol) was added to the flask described in (1) in several portions and slowly added. After the addition was completed, the mixture was stirred for 4 hours and the reaction was monitored by a plate. 30 ml of ethyl acetate was added, and then the mixture was washed twice with 40 ml of saturated brine. The organic phase was taken, dried with 5 g of anhydrous magnesium sulfate, filtered, and the solvent was removed to obtain 9.17 g of benzylcyclohexylamine with a yield of 97.5%.

[0034] (3) 9 g of benzylcyclohexylamine was added to a three-necked flask with mechanical stirring, and 24 g of acetone and 24 g of water were added, followed by 12 g of sodium bicarbonate. Under stirring, 20.1 g of monopersulfate oXone was slowly added in several portions. After the addition was complete, the reaction was continued for 2 h, and then 30 ml of acetone was added to dissolve the mixture. The mixture was washed twice with 40 ml of saturated brine. The organic phase was taken, dried with anhydrous magnesium sulfate, and filtered to obtain 9.1 g of a crude product. After recrystallization, 8.2 g of a white solid was obtained with a yield of 84.9%.

[0035] (4) 8 g of N-benzylcyclohexylamine oxide was dissolved in 100 ml of toluene, 8.8 g of azobisisobutyronitrile was added, the temperature was raised to 88°C, the reaction was carried out for 9 h, the solvent was removed, and recrystallization was performed to obtain 10.3 g of a white solid with a yield of 77%. Its NMR spectrum and Figure 2 Consistent.

[0036] Application Example 1

[0037] Telomerization of methyl methacrylate by the alkoxyamine obtained in Example 1:

[0038] Methyl methacrylate (5 g, 0.05 mol) and the alkoxyamine obtained in Example 1 (0.169 g, 0.0005 mol) were placed in a 50 ml eggplant-shaped bottle with a magnet, 10 ml of toluene was added, vacuum was evacuated and nitrogen was filled for 3 cycles under ice bath conditions, the temperature was raised to 95°C, and the reaction was carried out for 5 hours. The conversion rate was 98.5% as measured by weighing method, and the GPC was sampled and tested, and the spectrum was as follows: Figure 3 As shown, Mn=10100, PDI=1.27, and controllability is good.

[0039] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and equivalent changes made by using the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing alkoxyamines by one-pot Schiff base reduction, characterized in that: The following steps are involved: Step 1, adding cyclohexylamine and benzaldehyde into an organic solvent and stirring to react; Step 2, adding a reducing agent and an organic solvent, then washing with saturated brine, taking the organic phase, adding a desiccant to dry, filtering, and removing the solvent to obtain benzylcyclohexylamine; Step 3, dissolving the benzylcyclohexylamine obtained in step 2 in an organic solvent, then adding an oxidant for oxidation, washing with saturated brine, taking the organic phase, adding a desiccant for drying, filtering, removing the solvent, and recrystallizing to obtain N-benzylcyclohexylamine oxide; Step 4: dissolving the N-benzylcyclohexylamine oxide obtained in step 3 in an organic solvent, adding a free radical source, heating, and after the reaction is completed, removing the solvent and recrystallizing to obtain the alkoxyamine shown in FIG. 1 .

2. The method for preparing alkoxyamines by one-pot Schiff base reduction according to claim 1, characterized in that: In the step 1, the organic solvent is one or more of methanol, ethanol, dichloromethane and tetrahydrofuran.

3. The method for preparing alkoxyamines by one-pot Schiff base reduction according to claim 1, characterized in that: In the step 1, acetic acid accounting for 0.1% to 5% of the molar number of benzaldehyde is added to catalyze the reaction to proceed rapidly; during the process, molecular sieves accounting for 1% to 5% of the molar number of benzaldehyde are added to absorb water.

4. The method for preparing alkoxyamines by one-pot Schiff base reduction according to claim 1, characterized in that: In the step 2, the reducing agent is one or more of sodium borohydride, potassium borohydride, sodium cyanoborohydride, sodium triacetoxyborohydride or lithium aluminum hydride, and the molar ratio of the reducing agent to the cyclohexylamine in step 1 is (1-2):

1.

5. The method for preparing alkoxyamines by one-pot Schiff base reduction as claimed in claim 4, characterized in that: The reducing agent is sodium triacetoxyborohydride, and the molar ratio of the reducing agent to the cyclohexylamine in step 1 is (1.1-1.5):

1.

6. The method for preparing alkoxyamines by one-pot Schiff base reduction according to claim 1, characterized in that: In the step 3, the oxidant is a monopersulfate compound, the molar ratio of the oxidant to the benzaldehyde in the step 1 is (1-2):1, and the pH value in the reaction is controlled to be 8-10.

7. The method for preparing alkoxyamines by one-pot Schiff base reduction according to claim 1, characterized in that: In the step 4, the heating temperature is 85-90° C., and the molar ratio of the free radical source to the N-benzylcyclohexylamine oxide obtained in the step 3 is (1-1.8):

1.

8. The method for preparing alkoxyamines by one-pot Schiff base reduction according to claim 1, characterized in that: The free radical source is azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptanenitrile, azobisisobutylimidazoline hydrochloride, 4,4'-azobis(4-cyanovaleric acid), 4,4'-azobis(4-cyanopentanol), 4,4'-azobis(4-cyanovaleric acid) or 4,4'-azobis(4-cyanopentanol).

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