RU2693385C1 - Method for producing biodegradable branched oligomeric esters of lactic acid and glycerine - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing biodegradable branched oligomeric esters of lactic acid and glycerol of formula

,

where n = 2–10, with number-average molecular weight from 620 to 2,500, as a starting substance, an aqueous solution of glycerol is used, at the first stage is converted to aqueous mixture of lactic acid and glycerine in controlled molar ratio lactic acid: glycerol = 6:1; 10:1; 20:1; 30:1 in the presence of a highly selective heterogeneous copper-containing oxide catalyst in amount of 1.5–3.0 wt % of weight of glycerol while heating to 220–240 °C for 6–8 hours, with further reaction of obtained mixtures while heating to 140–180 °C and residual pressure of 4,000–400 Pa to form branched oligoester.

EFFECT: technical result consists in obtaining oligomeric esters of lactic acid and glycerine from an aqueous solution of glycerol in a controlled molar ratio while heating in the presence of a catalyst followed by condensation in a vacuum.

1 cl, 1 tbl, 8 ex

Description

The invention relates to the chemical industry, namely, to obtain lactic acid and new derivatives based on it - branched oligomeric esters of lactic acid and glycerin, which can be used as food additives, plasticizers, as well as in biodegradable materials for biomedical use.

Currently, lactic acid is industrially produced by enzymatic methods from various plant materials [WO 2006124633 A1, publ. 11/23/2006; CA 2748354 A1, publ. 06/01/2010] These processes have a number of significant drawbacks, such as low productivity of the process, the obligatory presence of complex and costly stages of isolation and purification of the target product, causing a high final cost of purified lactic acid.

Known methods for the catalytic synthesis of lactic acid, in particular, from bioavailable glycerol, formed as a by-product in the production of biodiesel. So, in the patent [US 20090088589 A1, publ. 04/02/2009] described hydrothermal synthesis of lactic acid at 300 ° C and 100 MPa, carried out in an autoclave. Its disadvantage is the need to conduct the process in harsh conditions, which leads to high material and energy costs. In addition, the reaction mixture after the completion of the process contains a complex of difficult to separate by-products, which makes it impractical for the industrial implementation of the proposed process.

Known methods for the synthesis of lactic acid in the presence of heterogeneous catalytic systems. Thus, the described liquid-phase method of producing lactic acid using Pt-containing catalysts deposited on various substrates, such as Pt / Al ₂ O ₃ , Pt / ZrO ₂ , Pt / C [patent EP 2606968 A2, publ. 06.26.2013] The disadvantage of the process is the low selectivity of the formation of lactic acid (40-70%), as well as the need for complex separation of the target product from by-products, namely other carboxylic acids (glyceric, glycolic, pyruvic and acetic).

Closest to the proposed in the first stage of this invention, the method of producing lactic acid is hydrothermal synthesis of lactic acid in the presence of various copper-containing catalysts in an alkaline medium [US patent 20120253067 A1, publ. 10/04/2012]. Its disadvantage is also an insufficiently high value of selectivity for the target product (40-78%). However, the patent does not reflect the dependence of the influence of the properties of catalytic particles on the selectivity of the formation of lactic acid.

Known products based on lactic acid, which are:

- glycerolactate or glyceroacetate esters used as an energy source for muscles and tissues (US 6743821 B2, publ. 06/01/2004);

- esters of polyglycerol and lactic acid, used as emulsifiers in the food and tobacco industry (CN 103145552 A, publ. 12.06.13);

- esters of lactic acid, used as a ferroelectric liquid-crystalline material (US 7005535, publ. February 28, 2006);

The objective of the invention is to develop a method for the synthesis of new branched oligomeric esters of lactic acid and glycerin formula I, consisting of the stages of selective production of lactic acid and glycerol from an aqueous solution of glycerin in a different controlled ratio, followed by their condensation with the formation of the target oligomeric products.

where n = 2-10.

The technical result consists in obtaining oligomeric esters of lactic acid and glycerol from an aqueous solution of glycerin in a controlled molar ratio when heated in the presence of a catalyst, followed by condensation in vacuum.

The technical result is achieved in the method of obtaining biodegradable branched oligomeric esters of lactic acid and glycerol by the formula

where n = 2-10, with number average molecular weights from 620 to 2500, an aqueous solution of glycerin is used as the starting material, which in the first stage turns into an aqueous mixture of lactic acid and glycerin in a controlled molar ratio of lactic acid: glycerin = 6: 1; 10: 1; 20: 1; 30: 1 in the presence of highly selective heterogeneous copper-containing oxide catalyst in the amount of 1.5-3.0% of the mass. from the mass of glycerol when heated to 220-240 ° C for 6-8 hours, with the further interaction of the mixtures when heated to 140-180 ° C and a residual pressure of 4000-400 Pa with the formation of branched oligoesters.

Identification of the reaction mixture after the first stage was performed using gas chromatography-mass spectroscopy on a GCMS-QP2010 gas chromatograph (Shimadzu) using a ZB-FFAP column (30 mx 0.32 mm x 0.25 µm). Quantitative analysis of the products was carried out by HPLC on a liquid chromatograph with a refractometric detector on a Rezex ROA-Organic acid column (300 mm x 7.8 mm, Phenomenex). An aqueous 0.01 M solution of sulfuric acid was used as the eluent with a flow rate of 0.5 ml / min. The temperature of the analysis is 60 ° C.

The structures of the synthesized oligomeric esters of lactic acid and glycerol are proved by IR and NMR spectroscopy data.

The molecular weight distribution of the oligomers obtained was determined by GPC.

The invention allows to achieve the following advantages: the lactic acid used in the process is obtained as a result of hydrothermal synthesis in the presence of a highly selective heterogeneous copper-containing oxide catalyst from an aqueous solution of glycerol. Under the proposed conditions, a highly selective formation of lactic acid takes place over a specified time, with partially unreacted glycerin being used as the reactant in the second stage. The required ratio of components, on which the structure and properties of oligomeric esters of lactic acid and glycerin depend, is ensured by controlled variation of the parameters of the hydrothermal process.

To implement the method uses the following substances:

Glycerin qualification h.d.a. (GOST 6259-75);

Sodium hydroxide x.h. (GOST 4328-77);

Copper (I) oxide with a particle size of 30-45 nm [MA Khan, Mahboob Ullah, Tariq Iqbal, Hasan Mahmood, Ayaz A. Khan, Muhammad Shafique, A. Majid, Azhar Ahmed and Nawazish A. Khan. Surfactant Assisted Synthesis of Cuprous Oxide (Cu ₂ O) Nanoparticles via Solvothermal Process. Nanoscience and Nanotechnology Research . 2015; 3 (1): 16-22];

Tin (II) oxide, "Aldrich", CAS No. 21651-19-4;

Methanol h.ch. (GOST 6995-77);

Chloroform (GOST 20015-88);

Distilled water (GOST 6709-72).

The method of obtaining oligomeric esters of lactic acid and glycerin is implemented in two stages:

1. Synthesis of lactic acid from an aqueous solution of glycerin, as a result of which the resulting product is a mixture of lactic acid: glycerin: water (MGW) in various ratios.

Example 1. Synthesis of MHV-1.

15.0 g (0.163 mol) of glycerin, 7.16 g (0.179 mol) of NaOH, 0.45 g (0.0031 mol) of freshly prepared Cu ₂ O, 285.0 are placed in a reactor equipped with a pressure gauge, an overhead stirrer and a thermocouple. ml of water, rinsed with an inert gas, heated with stirring (1000 rpm) to 220 ° C and incubated for 6 hours. Then the reactor is cooled, the oxide catalyst is separated by centrifugation.

To remove sodium cations and isolate the target product as a mixture of lactic acid: glycerin: water, the solution after centrifugation is subjected to electrodialysis purification by passing through 20 electrodialysis cells limited to bipolar membranes (Fumatech BWT GmbH). Since the lactic acid in the solution is in the form of the sodium salt, it is not necessary to add additional amounts of NaOH to increase the conductivity. The initial value of the current is 7.5 A. The complete transition of a mixture of sodium lactate and glycerin to lactic acid and glycerin occurs within 4.5 hours at 30 ° C, with the required voltage increasing from 9.0 V to 16.0 V. The pH value of the product mixture after electrodialysis is in the range of 2.5-3.0.

The conversion of glycerol is 86.5%. The yield of lactic acid is 82.2%. The carbon balance is 97.7%. The molar ratio of lactic acid: glycerin = 6.1: 1.

Example 2. Synthesis of MHV-2.

The reaction is carried out analogously to example 1 at 230 ° C for 8 hours.

The conversion of glycerol is 91.7%. The yield of lactic acid is 87.1%. The carbon balance is 96.9%. The molar ratio of lactic acid: glycerin = 10.5: 1.

Example 3. Synthesis of MHV-3.

The reaction is carried out analogously to example 1 in the presence of 0.9 g (0.0062 mol) of freshly prepared Cu ₂ O at 235 ° C for 8 hours.

The conversion of glycerol is 95.8%. The yield of lactic acid is 91.0%. The carbon balance is 96.6%. The molar ratio of lactic acid: glycerin = 21.5: 1.

Example 4. Synthesis of MHV-4.

The reaction is carried out analogously to example 1 in the presence of 0.9 g (0.0062 mol) of freshly prepared Cu ₂ O at 240 ° C for 8 hours.

The conversion of glycerol is 96.9%. The yield of lactic acid is 93.0%. The carbon balance is 96.3%. The molar ratio of lactic acid: glycerin = 30.1: 1.

2. Synthesis of oligomeric esters of lactic acid and glycerin from mixtures of lactic acid: glycerin: water.

Synthesis of oligomeric esters of lactic acid and glycerol (oligoMG) is carried out according to scheme II:

Example 5. Synthesis of oligoMG-1.

In a flask equipped with a Claisen nozzle with a refrigerator, 200.0 g of MGW-1, 2.0 g of SnO catalyst are placed and heated for 8 hours to distill water. The temperature is raised from 100 to 180 ° C and the pressure is reduced from 16,000 to 400 Pa. The product obtained is dissolved in 50 ml of chloroform and 120 ml of methanol is replanted, the precipitate is filtered off and dried at 60 ° C in a vacuum oven to constant weight.

The yield of oligoMG-1 is 49.3%.

IR spectrum: symmetric and asymmetric vibrations of ester C – O – C groups at 1300–1059 cm ^–1 ; stretching vibrations of carbonyl groups at 1754 cm ^-1 , stretching vibrations of СH ₂ -groups at 2947 cm ^-1 , vibrations of OH-groups about 3500 cm ^-1 .

NMR ¹ H (δ, ppm): 1.51 (-CH (C H ₃ ) OH in the final lactate units), 1.59 (-CH (C H ₃ ) O- in the lactate units), 2, 72 (-CH (CH ₃₎ N in the final lactate links), 4.27 (-C H (CH ₃₎ OH in the final lactate links), 4.35 (-OC H ₂ CH segment in glycerol) 5.14 (-CH ₂ C H OCH ₂ - in the glycerin segment), 5.17 (-C H (CH ₃ ) O- in lactate units).

Example 6. Synthesis of oligoMG-2.

The reaction is carried out analogously to example 5, placing in the flask MGV-2.

The yield of oligoMG-2 is 56.3%.

IR spectrum: symmetric and asymmetric vibrations of ester С-О-С-groups at 1298-1054 cm ^-1 ; stretching vibrations of carbonyl groups at 1755 cm ^-1 , stretching vibrations of СH ₂ -groups at 2940 cm ^-1 , vibrations of OH-groups about 3500 cm ^-1 .

NMR ¹ H (δ, ppm): 1.51 (-CH (C H ₃ ) OH in the final lactate units), 1.59 (-CH (C H ₃ ) O- in the lactate units), 2, 72 (-CH (CH ₃₎ N in the final lactate links), 4.27 (-C H (CH ₃₎ OH in the final lactate links), 4.35 (-OC H ₂ CH segment in glycerol) 5.13 (-CH ₂ C H OCH ₂ - in the glycerol segment), 5.17 (-C H (CH ₃ ) O - in lactate units).

Example 7. Synthesis of oligoMG-3.

The reaction is carried out analogously to example 5, placing in the flask MGV-3.

The yield of oligoMG-3 is 62.1%.

IR spectrum: symmetric and asymmetric vibrations of ester C – O – C groups at 1300–1050 cm ^–1 ; stretching vibrations of carbonyl groups at 1756 cm ^-1 , stretching vibrations of СH ₂ -groups at 2944 cm ^-1 , vibrations of OH-groups about 3500 cm ^-1 .

NMR ¹ H (δ, ppm): 1.51 (-CH (C H ₃ ) OH in the final lactate units), 1.59 (-CH (C H ₃ ) O- in the lactate units), 2, 72 (-CH (CH ₃₎ N in the final lactate links), 4.26 (-C H (CH ₃₎ OH in the final lactate links), 4.35 (-OC H ₂ CH segment in glycerol) 5.13 (-CH ₂ C H OCH ₂ - in the glycerol segment), 5.17 (-C H (CH ₃ ) O - in lactate units).

Example 8. Synthesis of oligoMG-4.

The reaction is carried out analogously to example 5, placing in the flask MGV-4.

The yield of oligoMG-4 is 65.4%.

IR spectrum: symmetric and asymmetric vibrations of ester С-О-С-groups at 1298-1060 cm ^-1 ; stretching vibrations of carbonyl groups at 1755 cm ^-1 , stretching vibrations of СH ₂ -groups at 2945 cm ^-1 , fluctuations of OH-groups about 3500 cm ^-1 .

NMR ¹ H (δ, ppm): 1.50 (—CH (C H ₃ ) OH in the final lactate units), 1.59 (—CH (C H ₃ ) O— in the lactate units), 2, 71 (-CH (CH ₃₎ N in the final lactate links), 4.26 (-C H (CH ₃₎ OH in the final lactate links), 4.35 (-OC H ₂ CH segment in glycerol) 5.13 (-CH ₂ C H OCH ₂ - in the glycerol segment), 5.17 (-C H (CH ₃ ) O - in lactate units).

Table

The effect of molar ratios of lactic acid and glycerin on the properties of the synthesized oligomers

Example nМК / nГЛ,
mol / mol Appearance of the product The product yield,% of the mass. M _N , Yes M _W , Yes M _w / M _N five 6: 1 Viscous yellowish liquid 49.3 620 980 1.58 6 10: 1 Viscous yellowish liquid 56.3 860 1340 1.56 7 20: 1 High viscosity yellowish liquid 62.1 1710 2280 1.33 eight 30: 1 Highly viscous liquid slightly yellowish 65.4 2500 3150 1.26

Claims (3)

The method of obtaining biodegradable branched oligomeric esters of lactic acid and glycerin by the formula

, where n = 2-10, with number average molecular weights from 620 to 2500, characterized in that an aqueous solution of glycerol is used as the starting material, which in the first stage turns into an aqueous mixture of lactic acid and glycerol in a controlled molar ratio of lactic acid: glycerin = 6 :one; 10: 1; 20: 1; 30: 1 in the presence of highly selective heterogeneous copper-containing oxide catalyst in the amount of 1.5-3.0 wt.% From the mass of glycerol when heated to 220-240 ° C for 6-8 hours, with further interaction of the mixtures when heated to 140- 180 ° C and a residual pressure of 4000-400 Pa with the formation of branched oligoesters.