Recovery and comprehensive utilization of dipropyl malonic acid monoester

Abstract

The invention relates to a method for recovering dipropyl malonic acid monoester as shown in a chemical structural formula I. The method comprises the following steps: carrying out dipropylation on 1-chloropropane and malonic acid diester in DMF (Dimethyl Formamide) under the action of potassium carbonate or sodium carbonate and quaternary ammonium salt to obtain dipropyl malonic acid diester; in the process of preparing dipropyl malonate, an alcohol solvent is added into a filter cake inorganic salt [residual dipropyl malonate monoester (III)], and dipropyl malonate monoester # imgabs0 # shown in a formula I is obtained through pulping, acidification, crystallization, filtration and low-temperature vacuum drying, wherein M is selected from K or Na; r1 is selected from straight chain alkyl with 1 to 5 carbon atoms or branched chain alkyl with 3 to 5 carbon atoms; the alcohol solvent is selected from methanol, ethanol, C3-C6 straight chain or C3-C6 branched chain monohydric alcohol, ethylene glycol, C3-C5 straight chain dihydric alcohol or C4-C5 branched chain dihydric alcohol; h < + > is selected from hydrochloric acid, phosphoric acid or sulfuric acid.

Description

Technical Field

[0001] The invention relates to a method for recovering dipropyl malonate monoester in a dipropyl malonate diester preparation process and application thereof in preparing valproic acid by a malonate diester process. Background Art

[0002] Sichuan Koride Pharmaceutical Co., Ltd. [A method for detecting dipropylmalonic acid-related impurities, ZL201911229436.7, authorized on October 28, 2022] used high performance liquid chromatography to detect dipropylmalonic acid in the reaction solution, and arranged it in the order of HPLC peaks and calculated it by peak area normalization method. Its structural formula and content are listed in Table 1.

[0003] Table 1 HPLC test results of dipropylmalonic acid reaction solution

[0004]

[0005] The HPLC test results of the reaction liquid for preparing dipropylmalonic acid showed that it contained dipropylmalonic acid monomethyl ester (sodium valproate impurity 20) and dipropylmalonic acid monoethyl ester.

[0006] Peng Xiangyun and Xu Chengzhi [Study on solid-liquid phase alkylation reaction I. Alkylation reaction of diethyl malonate and ethyl cyanoacetate using potassium carbonate as base, Acta Chimica Sinica, 1983, 41(6):514-518] selected diethyl malonate and 1-bromopropane for reaction for 12 hours to obtain 2-propyl diethyl malonate with a yield of 66.8% and dipropyl diethyl malonate (II2) with a yield of 0.2%.

[0007]

[0008] Steffen et al. [Process for C-alkylation of unsubstituted and monosubstituted malonic acid esters. DE3737377, 1989.05.18] described the reaction of diethyl dipropyl malonate (II2) as solvent, sodium ethoxide as base, diethyl malonate and 1-chloropropane in a high pressure reactor (3 bar to 4 bar) for 6 hours to obtain diethyl dipropyl malonate II2 with a yield of 81%:

[0009]

[0010] Beijing Yuekang Kechuang Pharmaceutical Technology Co., Ltd. [A method for preparing diethyl dipropyl malonate, CN115433081B, 2024.04.26] selects diethyl malonate and 1-bromopropane as starting materials, and reacts in ethanol under the action of sodium ethoxide to produce diethyl dipropyl malonate. During the reaction, an additional step is added to remove the sodium bromide in the reaction solution by filtration to make the reaction more complete.

[0011] Sichuan Kred Pharmaceutical Co., Ltd. [A method for preparing diethyl dipropyl malonate, an intermediate of valproic acid, CN202111473302.7, 2023.6.6] discloses that diethyl malonate and 1-bromopropane react in an amide solvent under the action of a base and a phase transfer catalyst to prepare diethyl dipropyl malonate; the impurity content of diethyl propyl malonate is controlled to be ≤0.17% (GC); the purity of diethyl dipropyl malonate is ≥98.16% (GC), and the yield is ≥85%:

[0012]

[0013] Peking University Founder Group Co., Ltd. and others [Tao Jing, Lin Songwen, Zhong Xuechao, Deng Xiaobing. Crystallization method of 2,2-dipropylmalonic acid, ZL201110457073.X, 2015.8.12] described a crystallization method of 2,2-dipropylmalonic acid: the crude 2,2-dipropylmalonic acid was crystallized in two mixed organic solvents (ethyl acetate, dichloromethane, tetrahydrofuran, acetonitrile, dioxane and n-hexane, cyclohexane or petroleum ether, respectively) to obtain 2,2-dipropylmalonic acid with a recovery rate of 65.0% to 74.5% and a purity of 99.50% to 99.78%.

[0014] Hunan University [A method and application of preparing dipropylmalonic acid using chloropropane as an alkylating agent, CN116768697B, authorized on March 29, 2024; Preparation of dipropylmalonic acid dimethyl ester and its hydrolysis and application, CN118373737A, July 23, 2024] discloses that a diester of malonic acid and 1-chloropropane are reacted in an aprotic solvent such as DMF to prepare a diester of dipropylmalonic acid (II), and II is hydrolyzed and decarboxylated to prepare valproic acid:

[0015]

[0016] II R = methyl or ethyl

[0017] When R is methyl, the reaction for preparing dimethyl dipropylmalonate (II1) is as follows:

[0018]

[0019] Hunan University [Preparation of dipropyl malonate, its hydrolysis and application, CN118373737A, 2024.07.23] In the process of preparing dipropyl malonate II1, the inorganic salt solid obtained by filtration may contain dipropyl potassium malonate monomethyl ester (III1):

[0020]

[0021] When R is ethyl, the reaction for preparing diethyl dipropylmalonate (II2) is as follows:

[0022]

[0023] Hunan University [A method and application of preparing dipropylmalonic acid using chloropropane as an alkylating agent, CN116768697B, authorized on March 29, 2024] In the process of preparing diethyl dipropylmalonate Ⅱ2, the inorganic salt solid obtained by filtration may contain dipropyl potassium monoethyl malonate (Ⅲ2):

[0024] Summary of the invention

[0025] The object of the present invention is to provide a method for recovering dipropyl malonate represented by chemical formula I:

[0026] 1-Chloropropane and malonate diester are dipropylated in DMF under the action of potassium carbonate or sodium carbonate and quaternary ammonium salt to obtain dipropyl malonate diester shown in formula II;

[0027]

[0028] M is selected from K or Na; R 1 Selected from: C1-C5 straight chain alkyl or C3-C5 branched chain alkyl; R 2 Selected from: C1-C5 straight chain alkyl or C3-C5 branched chain alkyl; R 1 With R 2 Same or different; H + Selected from hydrochloric acid, phosphoric acid or sulfuric acid.

[0029] The dipropyl malonate diester is selected from the group consisting of dipropyl malonate dimethyl, dipropyl malonate diethyl, dipropyl malonate, dipropyl methyl ethyl, dipropyl ethyl malonate, and dipropyl methyl propyl malonate.

[0030] In the process for preparing dipropyl malonate diester (II), dipropyl malonate monoester (III) remains in the inorganic salt solid obtained by filtration; an alcohol solvent is added to the inorganic salt containing dipropyl malonate monoester III, and the dipropyl malonate monoester shown in formula I is obtained through pulping, acidification, crystallization, filtration and low-temperature vacuum drying; I is hydrolyzed to obtain dipropyl malonate, and the latter is decarboxylated to obtain valproic acid:

[0031]

[0032] M is selected from K or Na; H + Selected from hydrochloric acid, phosphoric acid or sulfuric acid; R 1 Selected from: C1~C5 straight chain alkyl or C3~C5 branched chain alkyl; the pulping temperature is selected from 40℃~90℃.

[0033] The alcohol solvent is selected from methanol, ethanol, C3-C6 straight chain or C3-C6 branched monohydric alcohol, ethylene glycol, C3-C5 straight chain dihydric alcohol or C4-C5 branched chain dihydric alcohol.

[0034] C3-C6 straight chain monohydric alcohol is selected from propanol, butanol, pentanol or hexanol;

[0035] C3-C6 branched monohydric alcohol is selected from isopropanol, tert-butyl alcohol, neopentyl alcohol or cyclohexanol;

[0036] C3-C5 straight-chain diol is selected from 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol or 1,4-butylene glycol;

[0037] The C4-C5 branched diol is selected from 2-methyl-1,3-propanediol or 2,2-dimethyl-1,3-propanediol.

[0038] The dipropyl malonate is selected from dipropyl malonate monomethyl ester, dipropyl malonate monoethyl ester, dipropyl malonate mono-n-propyl ester, dipropyl malonate mono-isopropyl ester, dipropyl malonate mono-n-butyl ester or dipropyl malonate mono-tert-butyl ester.

[0039] In the recovery of dipropyl malonate, hydrochloric acid or sulfuric acid is used for acidification, and the pH value of acidification is controlled at 1.0 to 3.5.

[0040] The object of the present invention is to also provide a method for recovering dipropyl malonate represented by the chemical structural formula Ⅰ1:

[0041] 1-Chloropropane and dimethyl malonate are dipropylated in DMF under the action of potassium carbonate and quaternary ammonium salt (PTC) to obtain dipropyl dimethyl malonate shown in formula II1; the preparation reaction is as follows:

[0042]

[0043] The dipropylated quaternary ammonium salt (PTC) is selected from the group consisting of tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, tetrapropylammonium chloride, tetrapropylammonium bromide, tetrapropylammonium iodide, tetraethylammonium chloride, tetraethylammonium bromide, tetraethylammonium iodide, tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide, tetradecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium iodide, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, benzyltriethylammonium chloride, benzyltriethylammonium bromide, benzyltriethylammonium iodide, benzyltrimethylammonium chloride, benzyltrimethylammonium bromide or benzyltrimethylammonium iodide.

[0044] In the process for preparing dipropyl malonate (II1), potassium dipropyl malonate monomethyl ester (III1) remains in the inorganic salt solid obtained by filtration; an alcohol solvent is added to the inorganic salt containing potassium dipropyl malonate monomethyl ester III1, and the dipropyl malonate monomethyl ester shown in formula I1 is obtained through pulping, acidification, crystallization, filtration and low-temperature vacuum drying; I1 is hydrolyzed to obtain dipropyl malonic acid; and dipropyl malonic acid is decarboxylated to obtain valproic acid.

[0045]

[0046] The alcohol solvent is selected from methanol, ethanol, C3-C6 straight chain or C3-C6 branched monohydric alcohol, ethylene glycol, C3-C5 straight chain dihydric alcohol or C4-C5 branched dihydric alcohol; H + The pulping temperature is selected from 40℃ to 90℃.

[0047] In the recovery of dipropylmalonate, hydrochloric acid or sulfuric acid is used for acidification, and the pH value of acidification is controlled at 1.0 to 3.5.

[0048] The object of the present invention is to provide a method for recovering dipropyl ethyl malonate shown in the chemical structural formula I2:

[0049] 1-Chloropropane and diethyl malonate are dipropylated in DMF under the action of potassium carbonate and quaternary ammonium salt to obtain diethyl dipropyl malonate shown in formula II2; the preparation reaction is as follows:

[0050]

[0051] The dipropylated quaternary ammonium salt (PTC) is selected from the group consisting of tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, tetrapropylammonium chloride, tetrapropylammonium bromide, tetrapropylammonium iodide, tetraethylammonium chloride, tetraethylammonium bromide, tetraethylammonium iodide, tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide, tetradecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium iodide, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, benzyltriethylammonium chloride, benzyltriethylammonium bromide, benzyltriethylammonium iodide, benzyltrimethylammonium chloride, benzyltrimethylammonium bromide or benzyltrimethylammonium iodide.

[0052] In the process of preparing dipropyl malonate (II2), potassium monoethyl dipropyl malonate (III2) remains in the inorganic salt solid obtained by filtration; an alcohol solvent is added to the inorganic salt containing potassium monoethyl dipropyl malonate III2, and the dipropyl malonate shown in formula I2 is obtained through pulping, acidification, crystallization, filtration and low-temperature vacuum drying; the latter is hydrolyzed to obtain dipropyl malonic acid; and dipropyl malonic acid is decarboxylated to obtain valproic acid.

[0053]

[0054] The alcohol solvent is selected from methanol, ethanol, C3-C6 straight chain or C3-C6 branched monohydric alcohol, ethylene glycol, C3-C5 straight chain dihydric alcohol or C4-C5 branched dihydric alcohol; H + Selected from hydrochloric acid, phosphoric acid or sulfuric acid.

[0055] The beating temperature is selected from 40°C to 90°C.

[0056] In the recovery of dipropyl malonate, hydrochloric acid or sulfuric acid is used for acidification, and the acidification pH value is controlled at 1.0 to 3.5.

[0057] Compared with the prior art, the present invention has the following advantages:

[0058] (1) The present invention is the first to recover the dipropyl malonate monoester shown in Formula I from the inorganic salt solids treated after the process of preparing dipropyl malonate diester by pulping in an alcohol solvent, and characterize and confirm its structure.

[0059]

[0060] (2) The recovered dipropylmalonate is hydrolyzed and decarboxylated to obtain valproic acid.

[0061] (3) The recovery and utilization of dipropylmalonate can improve the total yield of valproic acid, reduce the production cost of valproic acid, and also reduce environmental pressure. DETAILED DESCRIPTION

[0062] The present invention is further described in detail below in conjunction with the embodiments.

[0063] Example 1

[0064] Preparation of dimethyl dipropylmalonate (Ⅱ1)

[0065]

[0066] 6.0mmol TBAB and 100mLDF were stirred, and then 0.4mol potassium carbonate (200 mesh), 0.2mol dimethyl malonate and 0.6mol 1-chloropropane were added, and the mixture was stirred at 75℃~130℃ for 12.0h to recover the excess 1-chloropropane; after the reaction was complete, the temperature was lowered to 40℃, and the inorganic salt was filtered off to obtain the inorganic salt (for recovering dipropyl monomethyl malonate); the filtrate was vacuum distilled at 80~90℃ to recover DMF to obtain a light yellow liquid (dipropyl dimethyl malonate Ⅱ1).

[0067] Example 2

[0068] Recovery of dipropylmalonate (Ⅰ1)

[0069]

[0070] Add 60 mL of methanol to the inorganic salt obtained in Example 1, stir and slurry at 50°C, filter and recover the inorganic salt (dry the filter cake to obtain potassium chloride), add concentrated hydrochloric acid to the combined filtrate to acidify to pH 1.5, distill and recover methanol, cool, crystallize, filter and low-temperature vacuum dry to obtain 1.5 g of dipropylmalonate (Ⅰ1), melting point 60-61°C.

[0071] Dipropylmalonate: 1 H NMR (400MHz, DMSO-d6) δ: 0.86 (t, J=7.2Hz, 6H, CH3×2), 1.18–1.02 (m, 4H, CH2×2), 1.72 (t, J=8.4Hz, 4H, 2×CH2), 3.66 (s, 3H, OCH3); 13 C NMR (100 MHz, DMSO-d6) δ: 13.94, 16.65, 33.78, 51.68, 56.47, 171.81 and 172.26.

[0072] Example 3

[0073] Hydrolysis of dipropylmalonate (Ⅰ1)

[0074]

[0075] To 6.0g of dipropylmalonic acid monomethyl ester (Ⅰ1), add potassium hydroxide aqueous solution (3g KOH, 3mL H2O) and 2mL methanol, heat to 95℃ for hydrolysis for 3h, and obtain solid by rotary evaporation. Add 10mL of water to dissolve the solid, adjust pH to 1 with concentrated hydrochloric acid, solid precipitates, filter with suction, and recrystallize the solid in methanol aqueous solution to obtain 5.5g of dipropylmalonic acid, melting point 157-158℃.

[0076] Alternatively, dipropylmalonic acid is prepared by combining dipropylmalonic acid monomethyl ester with dipropylmalonic acid dimethyl ester II1 obtained in Example 1 and hydrolyzing them.

[0077] Dipropylmalonic acid: 1 H NMR (400MHz, DMSO-d6) δ: 0.87 (t, J=7.3Hz, 6H, CH3×2), 1.07~1.19 (m, 4H, CH2×2), 1.65~1.74 (m, 4H, CH2×2), 12.56 (bs, 2H, COOH×2).

[0078] Example 4

[0079] Preparation of diethyl dipropylmalonate (Ⅱ2)

[0080]

[0081] 32.02g (0.2mol) of diethyl malonate, 6.0mmol of tetrabutylammonium bromide, 55.2g (0.4mol) of anhydrous potassium carbonate, 100mL of DMF, and 0.6mol of 1-chloropropane were stirred and reacted at 70-130°C for 12h. The temperature was lowered to below 50°C, and the filter cake (inorganic salt) was used to recover dipropyl malonate (Ⅰ2). The filtrate was vacuum distilled to recover DMF to obtain a light yellow liquid (dipropyl malonate Ⅱ2).

[0082] Diethyl dipropylmalonate Ⅱ2: 1 H NMR (400MHz, CDCl3) δ: 0.81 (t, J=7.2Hz, 6H, 2×CH3), 1.10–1.06 (m, 4H, 2×CH2), 1. 40 (t, J=7.2Hz, 6H, 2×CH3), 1.79–1.68 (m, 4H, 2×CH2), 4.06 (q, J=7.2Hz, 4H, OCH2). 13 C NMR (101 MHz, CDCl3) δ: 13.7, 14.0, 17.0, 34.1, 57.2, 60.5 and 171.5.

[0083] Example 5

[0084] Recovery of dipropylmalonate (Ⅰ2)

[0085]

[0086] Add 60 mL of ethanol to the inorganic salt obtained in Example 4, stir and slurry at 60°C, filter and recover the inorganic salt (dry the filter cake to obtain potassium chloride), add concentrated hydrochloric acid to the combined filtrate to acidify to pH 1.5, distill and recover ethanol, cool, crystallize, filter and low-temperature vacuum dry to obtain 1.0 g of dipropylmalonate (Ⅰ2), melting point 59-60°C.

[0087] Dipropylmalonate: 1 HNMR (400MHz, DMSO-d6) δ: 0.86 (t, J=7.2Hz, 6H, CH3×2), 1.06–1.13 (m, 4H, CH2×2), 1.14 (t, J=7.2Hz, 3H, CH3), 1.69–1.74 (m, 4H, CH2×2), 4.06 (q, J=7.2Hz, 2H, OCH2); 13 C NMR (101 MHz, DMSO-d6) δ 13.8, 14.2, 16.9, 33.5, 56.7, 60.3, 171.4 and 172.6.

[0088] Example 6

[0089] Hydrolysis of dipropylmalonate (Ⅰ2)

[0090]

[0091] 13g of dipropylmalonic acid monoethyl ester (Ⅰ2), 10g of 40% potassium hydroxide solution, 3mL of ethanol, stir, reflux for 3h. Distill and recover ethanol to dryness to obtain a white solid. Add 15mL of water to dissolve the solid, cool to below 40℃, add concentrated hydrochloric acid dropwise to adjust the solution pH to 1, precipitate the solid, filter with suction, and wash the filter cake with an appropriate amount of water to obtain 11g of dipropylmalonic acid.

[0092] Alternatively, dipropylmalonate monoethyl ester and dipropylmalonate diethyl ester II2 obtained in Example 4 are combined and hydrolyzed to obtain dipropylmalonic acid.

[0093] Dipropylmalonic acid: 1 H NMR (400MHz, DMSO-d6) δ: 0.87 (t, J=7.2Hz, 6H, CH3×2), 1.01~1.24 (m, 4H, CH2×2), 1.62~1.83 (m, 4H, CH2×2), 12.58 (bm, 2H, COOH).

[0094] Example 7

[0095] Preparation of dipropylmalonate (Ⅱ3)

[0096]

[0097] Select dipropyl malonate and prepare dipropyl malonate (II3) according to the method of Example 1.

[0098] Example 8

[0099] Recovery of dipropylmalonate (Ⅰ3)

[0100]

[0101] The inorganic salt obtained in Example 7 was added with 50 mL of propanol, stirred and slurried at 70°C, and the inorganic salt was recovered by filtration (the filter cake was dried to obtain potassium chloride). Concentrated hydrochloric acid was added to the combined filtrate to acidify to pH 1.5, and the propanol was recovered by distillation. The mixture was cooled, crystallized, filtered and dried under low-temperature vacuum to obtain dipropyl malonate (Ⅰ3).

[0102] Example 9

[0103] Hydrolysis of dipropylmalonate (Ⅰ3)

[0104]

[0105] Dipropylmalonate (I3) was hydrolyzed according to the method of Example 3 to obtain dipropylmalonic acid.

[0106] Example 10

[0107] Preparation of valproic acid

[0108]

[0109] Prepared according to the method of the invention patent [a method and application of preparing dipropylmalonic acid using chloropropane as an alkylating agent, CN116768697B, Example 11 in the authorization on March 29, 2024; a preparation of dimethyl dipropylmalonate and its hydrolysis and application, CN118373737A, Example 3 in July 23, 2024]: dipropylmalonic acid is added to a reaction bottle, decarboxylated at 160-180°C for 2h to obtain yellow liquid valproic acid, and vacuum distilled to obtain colorless transparent valproic acid.

[0110] Valproic acid: 1H NMR (400MHz, DMSO-d6) δ: 0.86 (t, J=7.2Hz, 6H, CH3×2), 1.22~1.32 (m, 4H, CH2×2), 1.34 ~1.39 (m, 2H, CH2), 1.44 ~ 1.53 (m, 2H, CH2), 2.18 ~ 2.24 (m, 1H, CH), 11.99 (bs, 1H, COOH).

[0111] In this specification, the present invention has been described with reference to specific embodiments thereof. However, it is apparent that various modifications and variations may be made without departing from the spirit and scope of the present invention. Therefore, the description should be regarded as illustrative rather than restrictive.

Claims

1. A method for recovering dipropyl malonate represented by chemical formula I: characterized in that 1-Chloropropane and malonate diester are dipropylated in DMF under the action of potassium carbonate or sodium carbonate and quaternary ammonium salt to obtain dipropyl malonate diester; in the process of preparing dipropyl malonate diester, the inorganic salt solid obtained by filtration contains dipropyl malonate monoester shown in formula III; an alcohol solvent is added to the inorganic salt containing dipropyl malonate monoester III, and the dipropyl malonate monoester shown in formula I is obtained through pulping, acidification, crystallization, filtration and low-temperature vacuum drying; Wherein, M is selected from K or Na; R 1 Selected from: C1-C5 straight chain alkyl or C3-C5 branched chain alkyl; the alcohol solvent is selected from methanol, ethanol, C3-C6 straight chain or C3-C6 branched chain monohydric alcohol, ethylene glycol, C3-C5 straight chain dihydric alcohol or C4-C5 branched chain dihydric alcohol; H + Selected from hydrochloric acid, phosphoric acid or sulfuric acid.

2. The method for recovering dipropyl malonate as claimed in claim 1, wherein the pulping temperature is selected from 40°C to 90°C.

3. The method for recovering dipropyl malonate as claimed in claim 1, wherein the dipropyl malonate represented by formula I is hydrolyzed to obtain dipropyl malonate, which is then decarboxylated to obtain valproic acid: in, M is selected from K or Na; R 1 Selected from: C1-C5 straight chain alkyl or C3-C5 branched chain alkyl; Alternatively, dipropyl malonate monoester and dipropyl malonate diester are combined and hydrolyzed to obtain dipropyl malonate, which is then decarboxylated to obtain valproic acid.

4. The method for recovering dipropyl malonate as claimed in claim 1, wherein hydrochloric acid or sulfuric acid is used for acidification, and the acidification pH value is controlled at 1.0 to 3.

5.

5. The method for recovering dipropyl malonate as claimed in claim 1, characterized in that The alcohol solvent is selected from methanol, ethanol, C3-C6 straight-chain monohydric alcohol or C3-C6 branched-chain monohydric alcohol.

6. The method for recovering dipropyl malonate as claimed in claim 1, characterized in that The alcohol selected is methanol, ethanol or C3-C6 straight chain monohydric alcohol.

7. The method for recovering dipropyl malonate as claimed in claim 1, wherein the dipropyl malonate represented by formula I is selected from dipropyl malonate methyl ester, dipropyl malonate ethyl ester, dipropyl malonate n-propyl ester, dipropyl malonate isopropyl ester, dipropyl malonate n-butyl ester or dipropyl malonate tert-butyl ester.

8. The method for recovering dipropyl malonate as claimed in claim 1, wherein the dipropyl malonate monoester represented by formula III is selected from dipropyl sodium malonate monomethyl ester, dipropyl sodium malonate monoethyl ester, dipropyl sodium malonate mono-n-propyl ester, dipropyl sodium malonate mono-n-butyl ester, dipropyl potassium malonate monomethyl ester, dipropyl potassium malonate monoethyl ester, dipropyl potassium malonate mono-n-propyl ester or dipropyl potassium malonate mono-n-butyl ester.

9. A method for recovering dipropylmalonate represented by chemical formula I1: characterized in that 1-Chloropropane and dimethyl malonate are dipropylated in DMF under the action of potassium carbonate and quaternary ammonium salt to obtain dimethyl dipropyl malonate; in the process of preparing dimethyl dipropyl malonate, the inorganic salt solid obtained by filtration contains dipropyl potassium monomethyl malonate shown in formula III1; an alcohol solvent is added to the inorganic salt containing dipropyl potassium monomethyl malonate III1, and the dipropyl monomethyl malonate shown in formula I1 is obtained through pulping, acidification, crystallization, filtration and low-temperature vacuum drying; Among them, H + and alcohol solvent as defined in claim 1.

10. A method for recovering dipropyl malonate represented by chemical formula I2: characterized in that 1-Chloropropane and diethyl malonate are dipropylated in DMF under the action of potassium carbonate and quaternary ammonium salt to obtain diethyl dipropyl malonate; in the process of preparing diethyl dipropyl malonate, the inorganic salt solid obtained by filtration contains dipropyl potassium monoethyl malonate shown in formula III2; an alcohol solvent is added to the inorganic salt containing dipropyl potassium monoethyl malonate III2, and the dipropyl monoethyl malonate shown in formula I2 is obtained through pulping, acidification, crystallization, filtration and low-temperature vacuum drying: Among them, H + and alcohol solvent as defined in claim 1.

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