Synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material

Abstract

The present invention discloses a synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material, wherein the method comprising: (I) synthesis of catalyst; (II) synthesis of lactide by confinement effect catalysis; and (III) purification of lactide. In the present invention, a yield of L-lactide by catalysis of L-lactic acid by crystalline polymers is as high as 85.6%, which is 10% higher than the yield of lactide by H-? molecular sieve reported in documents currently available; it is easy to prepare the crystalline porous polymer material catalyst, which is environmental friendly, has a high yield and is recyclable, for consecutive 7 times the catalysis yield is maintained to be higher than 70%, and catalysis yield conservation rate is far higher than catalysis effects of catalysts reported in documents currently available.

Claims

1. A synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material, comprising following steps: step (I) synthesis of catalysts comprising: a) placing a compound A, a compound B, mesitylene and 1,4-dioxane into a reaction vessel; b) mixing the contents of the reaction vessel evenly; c) adding acetic acid to the reaction vessel; d) de-aerating the contents of the reaction vessel; e) vacuum sealing the reaction vessel; f) placing the reaction vessel in an oven for heating; g) filtering precipitates from the reaction vessel; h) washing the precipitates with a Soxhlet extractor; i) vacuum drying the precipitates; and j) obtaining solid catalysts; wherein a structural formula of the compound A is: ##STR00011## wherein R.sub.1 ?OH, CH.sub.3, OCH.sub.3, C.sub.2H.sub.5, F, Cl, Br or I; wherein compound B is: ##STR00012## step (II) synthesis of lactide by confinement effect catalysis comprising: a) adding the catalysts obtained in step (I), solvents, and lactic acid to a reaction vessel for reaction; b) cooling down the reaction vessel slowly after the reaction; c) filtering the contents of the reaction vessel after the reaction; d) washing the contents of the reaction vessel after the reaction; e) removing the solvents from the contents of the reaction vessel after the reaction at low pressure; and f) obtaining crude lactide; step (III) lactide purification comprising: a) conducting liquid-liquid extraction on the crude lactide obtained in step (II) with methylbenzene and water, b) combining organic phases of the liquid-liquid extraction, c) removing the solvents of the combined organic phases at low pressure, and d) obtaining lactide, wherein in step (I) a mole ratio between the compound A and the compound B is 4:7; a volume ratio among the mesitylene, the 1,4-dioxane, and the acetic acid is 15:5:1; and a mole ratio between the compound A and the mesitylene is 1:25; wherein in step (I) the method for de-aerating comprises freeze-pump-thaw cycling; wherein in step (I) the conditions for heating in the oven comprise 80? C. for 3 days; wherein in step (I) the conditions for washing with the Soxhlet extractor comprise specifically: washing four hours with THF and acetone; and conditions for vacuum drying comprise: 80? C. for 12 hours; wherein lactic acid in step (II) comprises L-lactic acid of 90 percent purity; wherein the solvents in step (II) comprise methylbenzene or ortho-xylene; wherein a mass ratio between the catalysts and the lactic acid is 1:10, and a weight/volume ratio of the catalysts and the solvents is 1:1 g/cm.sup.3; wherein reaction conditions in step (II) comprise: reaction time of 5 hr and reaction temperature 120? C.; wherein in step (II) washing is done by washing with acetonitrile.

2. The synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material according to claim 1, wherein the structural formula of the compound A is ##STR00013##

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows .sup.1H NMR data after catalysis reaction of the catalyst in embodiment 1 of the present invention;

(2) FIG. 2 is an XRD data diagram showing the catalyst going through repeated tests in the present invention (A is before the first catalysis reaction, and B is after the seventh catalysis reaction experiment);

(3) FIG. 3 shows .sup.1H NMR data of the catalyst after the first catalysis experiment among the repeated tests in the present invention;

(4) FIG. 4 shows .sup.1H NMR data of the catalyst after the second catalysis experiment among the repeated tests in the present invention;

(5) FIG. 5 shows .sup.1H NMR data of the catalyst after the third catalysis experiment among the repeated tests in the present invention;

(6) FIG. 6 shows .sup.1H NMR data of the catalyst after the fourth catalysis experiment among the repeated tests in the present invention;

(7) FIG. 7 shows .sup.1H NMR data of the catalyst after the fifth catalysis experiment among the repeated tests in the present invention;

(8) FIG. 8 shows .sup.1H NMR data of the catalyst after the sixth catalysis experiment among the repeated tests in the present invention; and

(9) FIG. 9 shows .sup.1H NMR data of the catalyst after the seventh catalysis experiment among the repeated tests in the present invention.

EMBODIMENTS

(10) To enable those of ordinary skill in the art to understand the technical solutions in the present invention more clearly, hereinafter the technical solutions of the present invention will be further described in conjunction with the accompanying drawings and the embodiments.

Embodiment 1

(11) A synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material, comprising the following steps:

(12) (I) Catalyst Synthesis

(13) Adding compound A 0.6 mmol and compound B 0.9 mmol in a heat-proof glass tube, adding mesitylene 4 ml and 1,4-dioxane 16 ml, mixing evenly by ultrasonic treatment, adding 3 M acetic acid 6 ml, de-aerating for three times by freeze-pump-thaw cycling, vacuum sealing, putting in a drying oven at 80? C. for three days, filtering precipitates, washing with a Soxhlet extractor by THF and acetone for respectively 4 hours, vacuum drying at 80? C. overnight, and solid catalysts COF-Z with a yield rate of 93% is obtained;

(14) Wherein a structural formula of the compound A is

(15) ##STR00005##

(16) A structural formula of the compound B is

(17) ##STR00006##

(18) A reaction formula showing synthesis of the catalyst is:

(19) ##STR00007##
(II) Confinement Effect Catalysis for Synthesis of Lactide

(20) Adding the catalyst COF-Z 10 mg obtained in step (I) in a round bottom flask 25 ml, 90 wt % L-LA 100 mg, mesitylene or ortho-xylene 10 ml, adding a water knockout vessel on the flask, connecting a condenser tube on the water knockout vessel, reacting for 5 h, cooling slowly, filtering, washing with acetonitrile, removing solvents at low pressure, calculating yield with HPLC and 1H-NMR, it is found that the yield after catalysis with COF-Z-1 is the highest, which is 85.6%. The nuclear-magnetism data after catalysis treatment by COF-Z-1 are shown in FIG. 1.

(21) (III) Lactide Purification

(22) After removing solvents at low pressure (it can be seen that obviously a lot of crystalloid is at a bottom portion of the flask), coarse lactide is obtained, conducting liquid liquid extraction with methylbenzene and water, taking organic phases, removing solvents therein and L-lactide with a purity of 98.5% is obtained.

(23) Repeated Test

(24) Repeated tests are done at the same conditions as those for embodiment 1. Experiment conditions of the repeated trials are the same as those for embodiment 1, the same catalyst is used in the repeated trials, catalysts recovered from last experiment are used, masses of L-lactic acid used in the present experiment are decided by masses of the catalysts recovered, wherein the mass of L-lactic acid shall be 10 times the mass of the catalyst, specifically, the data are shown in the following table.

(25) TABLE-US-00001 Remaining mass of the catalyst (COF-Z) after L-lactic Yield of S. N. loss in the previous reaction/mg acid/mg lactide 1 50 100 85.6 2 48.3 96.6 82.4 3 45.8 91.6 83.5 4 42.3 84.6 75.7 5 40.0 80 73.1 6 38.3 76.6 73.0 7 37.0 74 70.09

(26) From the foregoing experimental data and FIGS. 2-9, it can be known that, the catalyst COF-Z-1 can have a yield of over 70% after catalysis of consecutive 7 times in ortho-xylene, and by XRD comparison, structure thereof is still complete, so the catalyst COF-Z-1 has high stability and reproducibility.

(27) Reaction Principles of the Present Invention:

(28) (I) Catalyst Synthesis

(29) ##STR00008## ##STR00009## ##STR00010##

(30) As the catalyst COF-Z has a large number of carboxyl and hydroxyl functional groups, hydrogen ions can be ionized from methylbenzene and ortho-xylene, and pore diameters of COF-Z are around 2.1 nm, a length of L-lactic acid is around 0.4 nm, COF-Z can make shape-selective catalysis and the ionized hydrogen ions promote cyclization of the dimers to form the lactide.

(31) The applicant declares that, the foregoing are only some specific embodiments of the present invention, the protection scope of the present invention is not limited to these embodiments disclosed here, those skilled in the art shall appreciate that, any change or replacement that one of ordinary skill in the art can easily come up with within the technical scope disclosed in the present invention falls into the protection scope of the present invention.