Ring forming method of complex monomer

Abstract

The invention relates to a cyclization method of a complex monomer. The invention belongs to the field of compound synthesis methods. The invention solves the problems of complex steps, harsh conditions and need of adding a catalyst in the cyclization reaction of a complex monomer. The cyclic monomer is prepared by directly reacting carboxyl in molecules with amino, hydroxyl and sulfydryl. The preparation method comprises the following steps: mixing a complex monomer raw material containing carboxyl and amino, carboxyl and hydroxyl or carboxyl and sulfydryl in molecules with a solvent, and dehydrating at a certain temperature to form a ring to generate a cyclic monomer; the cyclization method does not need to protect functional groups in a complex monomer, does not need to prepare carboxylic ester, does not need to use a catalyst, is simple in process, high in product yield, low in production cost, environment-friendly and suitable for industrial production, and the used solvent is a large amount of common solvent, low in price and easy to obtain, and can be recycled and reused.

Description

Technical Field

[0001] The invention belongs to the field of compound synthesis methods, and specifically relates to a ring-forming method for a complex monomer. Background Art

[0002] Using complex monomers with multiple functional groups (such as amino acids, hydroxy acids, etc.) as raw materials and developing new synthetic methods to prepare polymers can not only significantly reduce the dependence of the synthetic polymer industry on petroleum, but also obtain polymer materials with unique properties and rich functional side groups. It has become the forefront and hot area of ​​polymer synthetic chemistry in the world today. Ring-opening polymerization has the characteristics of few side reactions and easy to obtain high molecular weight polymers. It is an effective means of polymerizing complex monomers. How to develop effective and atom-economical cyclization reactions of complex monomers has always been a challenge faced in polymer synthetic chemistry research.

[0003] Direct cyclization through the reaction of carboxyl groups with amino groups, hydroxyl groups and thiol groups in the molecule is one of the effective ways to form a ring of complex monomers. The prior art discloses: a method for preparing aminocaprolactam by using lysine with a protective group in the α-amino group as the starting material, first closing the ring and then deprotecting, which method requires first protecting the α-amino group of lysine; a method for preparing cyclic lactam by using amino acid ester as the raw material through intramolecular aminoester exchange reaction, which method requires first preparing the carboxyl group into carboxylic acid ester; a method for preparing aminocaprolactam by using lysine as the raw material, first performing methyl esterification, and then performing aminoester exchange reaction, which method requires advanced methyl esterification reaction, and a large amount of acid and base need to be used in the synthesis process; a method for preparing caprolactone by using 6-hydroxycaproic acid ester as the raw material under certain temperature, pressure and catalyst, which method also requires first preparing the carboxyl group into carboxylic acid ester, and a catalyst needs to be used in the cyclization process; using amino acid and hydroxy acid as the starting material, first synthesizing N (hydroxy acyl) amino acid ester, and then using intramolecular carboxylic acid A method for preparing cyclic lactone amide by reacting ester with hydroxyl group, which method requires the use of a catalyst and also requires the synthesis of carboxylic acid ester first; a method for preparing caprolactam at 250°C using lysine as a raw material and iridium-loaded HB-124 molecular sieve as a catalyst, which method requires the use of a specific catalyst and has a maximum yield of only 23.9%; a method for directly utilizing the intramolecular carboxyl group to react with hydroxyl or amino group to prepare cyclic lactone and cyclic lactam, but requires the use of organic tin oxide as a catalyst and xylene or trimethylbenzene as a solvent for reflux water reaction; a method for synthesizing aminocaprolactam using lysine as a raw material, but requires the use of high temperature and high pressure (330°C, 30MPa) conditions and has a low yield (the maximum yield is only 35%); a method for directly preparing caprolactone using 6-hydroxycaproic acid as a raw material, but requires the use of a loaded metal oxide as a catalyst and the reaction at 200-350°C.

[0004] The main problems of the complex monomer cyclization method in the prior art are that the synthesis reaction is complicated, the functional group needs to be protected first or the carboxylation reaction needs to be carried out first, the production efficiency is low, and it is not conducive to atom economy; catalysts are required or the preparation conditions are harsh, the energy consumption is large, the production cost is increased, and it is not conducive to industrial scale-up production. Therefore, it is of great significance to develop a simple, efficient and low-cost complex monomer cyclization method. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of complicated steps, harsh conditions and the need to add a catalyst in the cyclization reaction. The present invention provides a cyclization method for a complex monomer.

[0006] The technical solution of the present invention is as follows:

[0007] One of the purposes of the present invention is to provide a method for cyclization of a complex monomer, wherein:

[0008] The complex monomer raw material is added to a solvent to prepare a mixed solution, dehydrated to form a ring at a certain temperature, and purified to obtain a cyclic monomer, wherein the complex monomer structure is generally represented by Formula I or Formula II:

[0009] wherein n is an integer of 0 to 8, X1 and X3 are one of NH2, OH and SH, X2 is one of NH, O and S, and R1, R2 and R3 are one of hydrogen, amino or substituted amino, linear or branched alkyl, cycloalkyl, hydroxyl or hydroxyl with a protecting group, carboxyl or carboxyl with a protecting group, heterocyclic group, alkenyl, alkynyl, allyl, alkoxy, aryl, heteroaryl, benzyl or substituted benzyl, and halogen.

[0010] It is further defined that the complex monomer is one of an amino acid, a hydroxy acid, a mercapto acid, an amino acid salt, a hydroxy acid salt, a mercapto acid salt, an amino acid aqueous solution, a hydroxy acid aqueous solution or a mercapto acid aqueous solution.

[0011] It is further defined that when the complex monomer is one of an amino acid salt, a hydroxy acid salt or a mercapto acid salt, an equimolar amount of acid or base should be added for neutralization before the reaction.

[0012] It is further defined that the solvent is one or more of an m-hydroxy alcohol having z carbon atoms, toluene, xylene, mesitylene, tetrahydrofuran, dioxane, dichloromethane, chloroform, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

[0013] In further limitation, z is an integer of 1-30, and m is an integer of 1-10.

[0014] It is further defined that the molar concentration of the complex monomer in the mixed solution is 0.05 to 10 mol / L.

[0015] It is further defined that the certain temperature is 80 to 300°C.

[0016] It is further defined that the reaction time is 0.15 to 10 hours.

[0017] Further defined, the purification process is:

[0018] S1: Evaporating to dryness to recover the reaction solvent or filtering and then evaporating to dryness to recover the reaction solvent;

[0019] S2: Purify by one or more of the following methods: washing, solvent extraction, recrystallization, vacuum distillation, vacuum sublimation or column chromatography to obtain the target cyclic monomer.

[0020] The second object of the present invention is to provide a cyclic monomer prepared by the above method, wherein the general structural formula of the cyclic monomer is shown in Formula III or Formula IV:

[0021] Wherein X4 and X5 are one of NH, O, and S, and R1, R2, and R3 are one of hydrogen, amino or substituted amino, straight-chain or branched alkyl, cycloalkyl, hydroxyl or hydroxyl with a protecting group, carboxyl or carboxyl with a protecting group, heterocyclic group, alkenyl, alkynyl, allyl, alkoxy, aryl, heteroaryl, benzyl or substituted benzyl, and halogen.

[0022] Compared with the prior art, the specific advantages of the present invention are as follows:

[0023] (1) Compared with the existing method of preparing cyclic monomers by reacting carboxyl groups with amino, hydroxyl and thiol groups in complex monomer molecules, the preparation method provided in the present invention does not require protection of functional groups, does not require prior carboxyl esterification reaction, and does not require the use of catalysts, which can effectively improve atom economy and reduce the complexity of the preparation process and production costs.

[0024] (2) The preparation method of the present invention has the advantages of simple process, high product yield, and the solvent used is a common solvent, which is cheap, easily available, and recyclable, and is suitable for industrial production. DETAILED DESCRIPTION

[0025] 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.

[0026] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0027] The terms "comprising," "including," "having," "containing," or any other variations thereof, as used in the following examples, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus comprising the listed elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0028] When equivalent, concentration or other value or parameter is represented by the range limited by range, preferred range or a series of upper preferred value and lower preferred value, this should be understood as specifically disclosing all ranges formed by any pairing of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether the scope is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the scope is intended to include its end value and all integers and fractions within the scope. In the present application specification and claims, range limitation can be combined and / or interchanged, if these ranges are not otherwise stated, include all sub-ranges contained therein.

[0029] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0030] The "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure or characteristic that can be included in at least one implementation of the present invention. The "in one embodiment" that appears in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0031] The endpoints and any values ​​of the ranges disclosed in the invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

[0032] Embodiment 1:

[0033] Aminobutyric acid (in formula I, n=1, X1=NH2, R1=H) is used to prepare α-pyrrolidone (in formula III, n=1, X4=NH, R1=H).

[0034] In a 5L reactor, add 0.35mol of aminobutyric acid and 3.5L of methanol, stir and react at 150°C for 3h, cool to room temperature, evaporate to dryness and recover methanol, and obtain α-pyrrolidone after recrystallization from ethyl acetate with a yield of 98%.

[0035] The H NMR spectrum is: 1 H NMR (300MHz, D2O) δ2.42(t,2H),2.35(t,2H),2.02-2.22(m,2H).

[0036] The purity was 99% according to H NMR analysis.

[0037] Embodiment 2:

[0038] Glutamic acid (in formula I, n=1, X1=NH2, R1=COOH located on the carbon adjacent to X1) is used to prepare pyroglutamic acid (in formula III, n=1, X4=NH, R1=COOH located on the carbon adjacent to X4).

[0039] In a 5L reactor, add 3.5mol of glutamic acid and 3.5L of n-butanol, stir and react at 160°C for 4h. Cool to room temperature, evaporate to dryness and recover n-butanol, wash with water to obtain pyroglutamic acid, with a yield of 90% and a purity of 98% according to H-NMR analysis.

[0040] The H NMR spectrum is: 1 H NMR (300MHz, DMSO-d6) δ12.74(brs,1H),7.89(s,1H),4.06(dd,1H),2.25-2.38(m,1H),2.04-2.21(m,2H),1.91-2.01(m,1H).

[0041] The purity was 99% according to H NMR analysis.

[0042] Embodiment 3:

[0043] Ornithine (in formula I, n = 2, X1 = NH2, R1 = NH2 is located on the carbon adjacent to the carbonyl group) is used to prepare 3-amino-2-piperidone (in formula III, n = 2, X4 = NH, R1 = NH2 is located on the carbon adjacent to the carbonyl group).

[0044] In a 5L reactor, 1.75 mol of ornithine and 3.5L of toluene were added and stirred at 130°C for 4 hours. The mixture was cooled to room temperature, evaporated to dryness, toluene was recovered, and 3-amino-2-piperidone was obtained after washing with a mixed solvent of dichloromethane / methanol (v / v=90 / 10) with a yield of 93%.

[0045] The H NMR spectrum is: 1H NMR (300MHz, DMSO-d6) δ7.34(brs,1H),3.03-3.10(m,3H),1.90-1.98(m,1H),1.71-1.79(m,1H),1.57-1.68(m,1H),1.36-1.47(m,1H).

[0046] The purity was 99% according to H NMR analysis.

[0047] Embodiment 4:

[0048] Lysine (in formula I, n=3, X1=NH2, R1=NH2 is located on the carbon adjacent to the carbonyl) is used to prepare α-amino-ε-caprolactam (in formula III, n=3, X4=NH, R1=NH2 is located on the carbon adjacent to the carbonyl).

[0049] In a 5L reactor, 0.35mol of lysine and 3.5L of methanol were added and stirred at 150°C for 6h. The mixture was cooled to room temperature, evaporated to dryness and methanol was recovered, and α-amino-ε-caprolactam was obtained after extraction with ethyl acetate, with a yield of 96%.

[0050] The H NMR spectrum is: 1 H NMR (300MHz, D2O) δ3.69-3.72(dd,1H),3.22-3.26(m,2H),1.26-1.99(m,6H).

[0051] The purity was 99% according to H NMR analysis.

[0052] Embodiment 5:

[0053] Lysine hydrochloride (in formula I, n=3, X1=NH2, R1=NH2 is located on the carbon adjacent to the carbonyl) is used to prepare α-amino-ε-caprolactam (in formula III, n=3, X4=NH, R1=NH2 is located on the carbon adjacent to the carbonyl).

[0054] In a 5L reactor, add 3.5mol of lysine hydrochloride, 3.5mol of sodium hydroxide and 3.5L of methanol, stir and react at 175℃ for 2h. Cool to room temperature, filter, remove insoluble matter, evaporate to dryness and recover methanol, extract with ethyl acetate to obtain α-amino-ε-caprolactam, with a yield of 92%.

[0055] The H NMR spectrum is: 1 H NMR (300MHz, D2O) δ3.69-3.72(dd,1H),3.22-3.26(m,2H),1.26-1.99(m,6H).

[0056] The purity was 99% according to H NMR analysis.

[0057] Embodiment 6:

[0058] N,N-dimethyllysine (in formula I, n=3, X1=NH2, R1=N(CH3)2 located on the carbon adjacent to the carbonyl group) is used to prepare α-dimethylamino-ε-caprolactam (in formula III, n=3, X4=NH, R1=N(CH3)2 located on the carbon adjacent to the carbonyl group).

[0059] In a 5L reactor, add 7.0mol N,N-dimethyllysine and 3.5L methanol, stir and react at 150℃ for 4h. Cool to room temperature, evaporate to dryness and recover methanol, and recrystallize from ethyl acetate to obtain α-dimethylamino-ε-caprolactam with a yield of 95%.

[0060] The H NMR spectrum is: 1 H NMR (300MHz, CDCl3) δ6.98(s,1H),3.46-3.53(m,1H),2.83-2.98(m,2H),2.23(s,1H),1.79-1.91(m,1H),1.66-1.69(m,2H),1.42-1.58(m,3H).

[0061] The purity was 99% according to H NMR analysis.

[0062] Embodiment 7:

[0063] 6-Amino-2-hydroxy-hexanoic acid (in formula I, n=3, X1=NH2, R1=OH located on the carbon adjacent to the carbonyl group) is used to prepare α-hydroxy-ε-caprolactam (in formula III, n=3, X4=NH, R1=OH located on the carbon adjacent to the carbonyl group).

[0064] In a 5L reactor, add 0.35mol 6-amino-2-hydroxy-caproic acid and 3.5L ethanol, stir and react at 175°C for 4h. Cool to room temperature, evaporate to dryness and recover ethanol, and obtain α-hydroxy-ε-caprolactam after recrystallization from ethyl acetate, with a yield of 85%.

[0065] The H NMR spectrum is: 1 H NMR (300MHz, CDCl3) δ6.62-6.64(s,1H),4.13-4.25(m,1H),4.05-4.13(d,1H) ,3.08-3.36(m,2H),1.96-2.09(m,2H),1.76-1.89(m,1H),1.29-1.71(m,3H).

[0066] The purity was 97% according to H NMR analysis.

[0067] Embodiment 8:

[0068] 6-aminocaproic acid (in formula I, n=3, X1=NH2, R1=H) is used to prepare caprolactam (in formula III, n=3, X4=NH, R1=H).

[0069] In a 5L reactor, add 3.5mol 6-aminocaproic acid and 3.5L methanol, stir and react at 150°C for 4h, cool to room temperature, evaporate to dryness and recover methanol, extract with ethyl acetate to obtain caprolactam, with a yield of 91%.

[0070] The H NMR spectrum is: 1 H NMR (300MHz, D2O) δ3.23-3.25(m,2H),2.46-2.48(m,2H),1.74-1.79(m,2H),1.59-1.66(m,4H).

[0071] The purity was 99% according to H NMR analysis.

[0072] Embodiment 9:

[0073] 11-aminoundecanoic acid (in formula I, n=8, X1=NH2, R1=H) is used to prepare azacyclododecan-2-one (in formula III, n=8, X4=NH, R1=H).

[0074] In a 5L reactor, add 0.35mol 11-aminoundecanoic acid and 3.5L tetrahydrofuran, stir and react at 170°C for 2h. Cool to room temperature, evaporate to dryness and recover tetrahydrofuran, and obtain azacyclododecane-2-one after recrystallization from chloroform, with a yield of 80%.

[0075] The H NMR spectrum is: 1 H NMR (300MHz, CDCl3) δ5.98(s,1H),3.25(t,2H),2.44(t,2H),1.81-1.87(m,4H),1.52-1.58(m,12H).

[0076] The purity was 95% according to H NMR analysis.

[0077] Embodiment 10:

[0078] 4-Hydroxybutyric acid (in Formula I, n=1, X1=OH, R1=H) is used to prepare γ-butyrolactone (in Formula III, n=1, X4=O, R1=H).

[0079] In a 5L reactor, add 7 mol 4-hydroxybutyric acid and 3.5L xylene, stir and react at 200°C for 2h. Cool to room temperature, evaporate to dryness and recover xylene, and distill under reduced pressure to obtain γ-butyrolactone with a yield of 95%.

[0080] The H NMR spectrum is: 1H NMR (300MHz, CDCl3) δ4.29(t,2H),2.43(t,2H),2.21(m,2H).

[0081] The purity was 98% according to H NMR analysis.

[0082] Embodiment 11:

[0083] 5-Hydroxyvaleric acid (in formula I, n=2, X1=OH, R1=H) is used to prepare δ-valerolactone (in formula III, n=2, X4=O, R1=H).

[0084] In a 5L reactor, add 3.5mol 5-hydroxyvaleric acid and 3.5L xylene, stir and react at 180°C for 3h. Cool to room temperature, evaporate to dryness and recover xylene, and distill under reduced pressure to obtain δ-valerolactone with a yield of 90%.

[0085] The H NMR spectrum is: 1 H NMR (300MHz, CDCl3) δ4.20(t,2H),2.40(t,2H),1.74(m,4H).

[0086] The purity was 98% according to H NMR analysis.

[0087] Embodiment 12:

[0088] 9-Hydroxynonanoic acid (in Formula I, n=6, X1=OH, R1=H) is used to prepare oxadecan-2-one (in Formula III, n=6, X4=O, R1=H).

[0089] In a 5L reactor, add 0.35mol 9-hydroxynonanoic acid and 3.5L xylene, stir and react at 180°C for 3h. Cool to room temperature, evaporate to dryness and recover xylene, and distill under reduced pressure to obtain oxacyclodecane-2-one with a yield of 80%.

[0090] The H NMR spectrum is: 1 H NMR (300MHz, CDCl3) δ4.25-4.30(m,1H),4.11(t,1H),2.75-2.80(m,1H),2.65(td,1H),2.32-2.36(m,1H),1 .73-1.83(m,2H),1.59-1.66(m,2H),1.51-1.56(m,2H),1.44-1.50(m,1H),1.34-1.43(m,2H),0.94(t,2H).

[0091] The purity was 98% according to H NMR analysis.

[0092] Embodiment 13:

[0093] 4-Mercaptobutyric acid (in Formula I, n=1, X1=SH, R1=H) is used to prepare γ-thiobutyrolactone (in Formula III, n=1, X4=S, R1=H).

[0094] In a 5L reactor, add 0.35mol 4-mercaptobutyric acid and 3.5L trimethylbenzene, stir and react at 200℃ for 2h. Cool to room temperature, evaporate to dryness and recover trimethylbenzene, and distill under reduced pressure to obtain γ-thiobutyrolactone with a yield of 75%.

[0095] The H NMR spectrum is: 1 H NMR (300MHz, CDCl3) δ3.42(t,2H),2.49(t,2H),2.28(m,2H).

[0096] The purity was 95% according to H NMR analysis.

[0097] Embodiment 14:

[0098] 5-Mercaptopentanoic acid (in formula I, n=2, X1=SH, R1=H) is used to prepare δ-thiovalerolactone (in formula III, n=2, X4=S, R1=H).

[0099] In a 5L reactor, add 0.35mol 5-mercaptovaleric acid and 3.5L trimethylbenzene, stir and react at 200°C for 2h, cool to room temperature, evaporate to dryness and recover xylene, and distill under reduced pressure to obtain δ-thiovalerolactone with a yield of 70%.

[0100] The H NMR spectrum is: 1 H NMR (300MHz, CDCl3) δ3.16(t,2H),2.61(t,2H),1.94-2.06(m,4H).

[0101] The purity was 95% according to H NMR analysis.

[0102] Embodiment 15:

[0103] 2-Hydroxypropionic acid-1-carbonylethyl ester (in formula II, X2=O, X3=OH, R2=CH3, R3=CH3) is used to prepare lactide (in formula IV, X2=O, X5=O, R2=CH3, R3=CH3).

[0104] In a 5L reactor, add 0.35mol of 1-carboxyethyl 2-hydroxypropionate and 3.5L of toluene, stir and react at 200°C for 2h. Cool to room temperature, evaporate to dryness and recover xylene, and recrystallize from toluene to obtain lactide, with a yield of 72%.

[0105] The H NMR spectrum is: 1 H NMR (300MHz, CDCl3) δ5.05(q,2H),1.61(d,6H).

[0106] The purity was 95% according to H NMR analysis.

[0107] Embodiment 16:

[0108] 2-Mercapto-acetylthio-acetic acid (in formula II, X2=S, X3=SH, R2=H, R3=H) is used to prepare glycolide thioester (in formula IV, X2=S, X5=S, R2=H, R3=H).

[0109] In a 5L reactor, add 0.35mol 2-mercapto-acetylthio-acetic acid and 3.5L xylene, stir and react at 180°C for 2h, cool to room temperature, evaporate to dryness and recover xylene, and sublimate under reduced pressure to obtain glycolide thioester with a yield of 65%.

[0110] The H NMR spectrum is: 1 H NMR (300MHz, CDCl3) δ3.96 (s, 4H).

[0111] The purity was 95% according to H NMR analysis.

[0112] Embodiment 17:

[0113] 2-(2-Mercaptoacetoxy)propionic acid (in formula II, X2=O, X3=SH, R2=CH3, R3=H) is used to prepare monothiolide (in formula IV, X2=O, X5=S, R2=CH3, R3=H).

[0114] In a 5L reactor, add 0.35mol 2-(2-mercaptoacetoxy)propionic acid and 3.5L trimethylbenzene, stir and react at 220°C for 2h. Cool to room temperature, evaporate to dryness and recover trimethylbenzene, and recrystallize from dichloromethane to obtain monothiolide with a yield of 63%.

[0115] The H NMR spectrum is: 1 H NMR (300MHz, CDCl3) δ4.98(q,1H), 4.13(d,1H), 3.70(d,1H), 1.58(d,3H).

[0116] The purity was 96% according to H NMR analysis.

[0117] Embodiment 18:

[0118] Valyl-valine (in formula II, X2 = NH, X3 = NH3, R2 = isopropyl, R3 = isopropyl) is used to prepare 3,6-diisopropyl-piperazine-2,5-dione (in formula IV, X2 = NH, X5 = NH, R2 = isopropyl, R3 = isopropyl).

[0119] In a 5L reactor, add 3.5mol of valylvaline and 3.5L of methanol, stir and react at 150°C for 4h. Cool to room temperature, evaporate to dryness and recover methanol, extract with ethyl acetate to obtain 3,6-diisopropyl-piperazine-2,5-dione, with a yield of 95%.

[0120] The H NMR spectrum is: 1 H NMR (300MHz, DMSO-d6) δ8.02(s,1H),7.95(s,1H),3.69(d,1H),3.65(d,1H),2.16-2.23(m,2H),0.84-0.97(m,12H).

[0121] The purity was 96% according to H NMR analysis.

[0122] Embodiment 19:

[0123] 2-(2-Hydroxypropionamide)-3-methylbutanoic acid (in formula II, X2 = NH, X3 = OH, R2 = isopropyl, R3 = CH3) is used to prepare 3-isopropyl-6-methylmorpholine-2,5-dione (in formula IV, X2 = NH, X5 = O, R2 = isopropyl, R3 = CH3).

[0124] In a 5L reactor, add 1.75mol 2-(2-hydroxypropionamide)-3-methylbutyric acid and 3.5L toluene, stir and react at 200℃ for 4h. Cool to room temperature, evaporate to dryness and recover toluene, and recrystallize from chloroform to obtain 3-isopropyl-6-methylmorpholine-2,5-dione with a yield of 85%.

[0125] The H NMR spectrum is: 1 H NMR (300MHz, DMSO-d6) δ5.40(s,1H), 4.95-4.98(m,1H), 4.57-4.59(d,1H), 2.17-2.25(m,1H), 1.53-1.55(d,3H), 0.97-0.99(d,6H).

[0126] The purity was 96% according to H NMR analysis.

[0127] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for forming a ring of a complex monomer, characterized in that: The method: The complex monomer raw material is added to a solvent to prepare a mixed solution, dehydrated to form a ring at a certain temperature, and purified to obtain a cyclic monomer, wherein the complex monomer structure is generally represented by Formula I or Formula II: wherein n is an integer of 0 to 8, X1 and X3 are one of NH2, OH and SH, X2 is one of NH, O and S, and R1, R2 and R3 are one of hydrogen, amino or substituted amino, linear or branched alkyl, cycloalkyl, hydroxyl or hydroxyl with a protecting group, carboxyl or carboxyl with a protecting group, heterocyclic group, alkenyl, alkynyl, allyl, alkoxy, aryl, heteroaryl, benzyl or substituted benzyl, and halogen.

2. The method according to claim 1, characterized in that The complex monomer is one of an amino acid, a hydroxy acid, a mercapto acid, an amino acid salt, a hydroxy acid salt, a mercapto acid salt, an amino acid aqueous solution, a hydroxy acid aqueous solution or a mercapto acid aqueous solution.

3. The method according to claim 2, characterized in that When the complex monomer is one of amino acid salts, hydroxy acid salts or mercapto acid salts, an equimolar amount of acid or base is added for neutralization before reacting.

4. The method according to claim 1, characterized in that: The solvent is one or more of an m-hydroxy alcohol having z carbon atoms, toluene, xylene, mesitylene, tetrahydrofuran, dioxane, dichloromethane, chloroform, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

5. The method according to claim 4, characterized in that z is an integer of 1-30, and m is an integer of 1-10.

6. The method according to claim 1, characterized in that The molar concentration of the complex monomer in the mixed solution is 0.05-10 mol / L.

7. The method according to claim 1, characterized in that The certain temperature is 80~300℃.

8. The method according to claim 1, characterized in that The reaction time is 0.15 to 10 hours.

9. The method according to claim 1, characterized in that: The purification process is: S1: Evaporating to dryness to recover the reaction solvent or filtering and then evaporating to dryness to recover the reaction solvent; S2: Purify by one or more of the following methods: washing, solvent extraction, recrystallization, vacuum distillation, vacuum sublimation or column chromatography to obtain the target cyclic monomer.

10. The cyclic monomer prepared by the method according to any one of claims 1 to 9, characterized in that: The general structural formula of the cyclic monomer is shown in Formula III or Formula IV: Wherein X4 and X5 are one of NH, O, and S, and R1, R2, and R3 are one of hydrogen, amino or substituted amino, straight-chain or branched alkyl, cycloalkyl, hydroxyl or hydroxyl with a protecting group, carboxyl or carboxyl with a protecting group, heterocyclic group, alkenyl, alkynyl, allyl, alkoxy, aryl, heteroaryl, benzyl or substituted benzyl, and halogen.

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