Synthesis Of Lactide Research Articles

Efficient Synthesis of Lactide with Low Racemization Catalyzed by Zinc Lactate and Creatinine and Polycondensation Kinetics

Efficient Synthesis of Lactide with Low Racemization Catalyzed by Zinc Lactate and Creatinine and Polycondensation Kinetics

One-step synthesis of lactide via separation-promoted catalytic self-transesterification reactions of lactates

Lactide is an important building block of biodegradable polylactic acid. Lactide was synthesized via separation-promoted liquid-phase transesterification reactions of lactates. Amberlyst-15 resin exhibited relatively high catalytic activity due to its large number of strong Brønsted acid sites. Methyl lactate was much more reactive than butyl lactate due to its methyl group with smaller steric hindrance. The reactions were promoted by evaporating alcohol products with an open cylinder reactor with an opening degree of 5 %. In addition, the evaporation of substrate could be inhibited by adding a small quantity of γ-valerolactone. The lactide selectivity and yield reached 45.3 % and 18.2 %, respectively. After the recovery of starting materials for additional reaction, the overall yield of lactide reached 21.3 % (state-of-the-art: 45 %). The reaction pathway was clarified: Two methyl lactate molecules combined into an acyclic C7 molecule via self-transesterification, followed by ring-closure reaction of this molecule. The SO3H groups on the resin catalyst were leachable, and coke was deposited on the catalyst, resulting in decrease of catalytic activity in reuse experiment. This direct synthesis method of lactide is much simpler than the conventional lactic-acid-based route, and the reaction conditions were much milder compared to other direct synthesis approaches.

Nanosized “rice ball” like hierarchical beta zeolites with inter-crystalline mesopores for efficient catalytic synthesis of lactide

A series of nanosized “rice ball” like hierarchical beta zeolite aggregates (RBZxAy, x = 6, 9, 12 or 15; y = 2, 4 or 6) with hierarchical structures are successfully synthesized via gel aging and hydrothermal method without mesoporous template. The as-prepared RBZxAy zeolites possess two ranges of inter-crystalline mesoporous that formed by zeolite nanoparticles aggregation compared to the non-aged samples (B12Z4). The effects of Si/Al ratio and crystallization time on the morphology, structure and surface acidic properties of RBZxAy were systematically investigated. Meanwhile, RBZxAy as catalysts were applied in the conversion of lactic acid (LA) to lactide (LT) to investigate their catalytic performance. Benefitting from smaller crystal size, hierarchical structures and higher acid content, the representative catalyst (RBZ12A4) exhibited outstanding catalytic activity that the LA conversion was high to 98 % and the LT yield up to 94 %. In addition, RBZ12A4 presented perfect regeneration ability after 10 times recycles. This work provides an effective and facile route to directly synthesis nanocrystals aluminosilicate zeolite with hierarchal structure, and constructs an approach for efficiently converting LA to LT, it has greatly significance for the development of polylactic acid industry.

Synthesis of L-Lactide from Lactic Acid and Production of PLA Pellets: Full-Cycle Laboratory-Scale Technology.

Lactide is one of the most popular and promising monomers for the synthesis of biocompatible and biodegradable polylactide and its copolymers. The goal of this work was to carry out a full cycle of polylactide production from lactic acid. Process conditions and ratios of reagents were optimized, and the key properties of the synthesized polymers were investigated. The influence of synthesis conditions and the molecular weight of lactic acid oligomers on the yield of lactide was studied. Lactide polymerization was first carried out in a 500 mL flask and then scaled up and carried out in a 2000 mL laboratory reactor setup with a combined extruder. Initially, the lactic acid solution was concentrated to remove free water; then, the oligomerization and synthesis of lactide were carried out in one flask in the presence of various concentrations of tin octoate catalyst at temperatures from 150 to 210 °C. The yield of lactide was 67-69%. The resulting raw lactide was purified by recrystallization in solvents. The yield of lactide after recrystallization in butyl acetate (selected as the optimal solvent for laboratory purification) was 41.4%. Further, the polymerization of lactide was carried out in a reactor unit at a tin octoate catalyst concentration of 500 ppm. Conversion was 95%; Mw = 228 kDa; and PDI = 1.94. The resulting products were studied by differential scanning calorimetry, NMR spectroscopy and gel permeation chromatography. The resulting polylactide in the form of pellets was obtained using an extruder and a pelletizer.

A response surface methodology for the use of MIL‐101 as a catalyst for the one‐step synthesis of lactide

Lactide is a vital monomer for producing high molecular weight polylactic acid (PLA) through ring‐opening polymerization. This study synthesized crude lactide from L‐lactic acid with MIL‐101 as the catalyst. MIL‐101 is a metal‐based catalyst with organic ligands (MOF) that was prepared by reacting Cr(NO3)3.9H2O with terephthalic acid (BDC). The formation of MIL‐101 was confirmed from Fourier‐transform infrared (FTIR) analysis. The role of MIL‐101 and the effect of temperature, time, and MIL‐101 loading, as well as their interactions in the conversion of lactic acid to crude lactide, were then investigated using the response surface method (RSM). Crude lactide was analyzed using 1H‐nuclear magnetic resonance (NMR) spectroscopy to confirm the presence of lactide. The RSM results indicated that the highest conversion of 22.84% can be obtained using a temperature of 175 °C, 1.5% w/w MIL‐101 loading, and a reaction time of 5 h. The RSM model showed that the interaction of MIL‐101 loading and reaction time strongly affected the conversion of lactic acid to lactide, with a P‐value of 0.0021 and an F‐value of 50.45. In contrast, the interaction of catalyst loading and temperature did not significantly affect the conversion of lactic acid to lactide, with a P‐value of 0.2565 and an F‐value of 1.75.

Detection and elimination of trace d-lactic acid in lignocellulose biorefining chain: Generation, flow, and impact on chiral lactide synthesis.

High chiral purity of lactic acid is a crucial indicator for the synthesis of chiral lactide as the primary intermediate chemical for ring-open polymerization of high molecular weight polylactic acid (PLA). Lignocellulose biomass is the most promising carbohydrate feedstock for commercial production of PLA, but the presence of trace d-lactic acid in the biorefinery chain adversely affects the synthesis and quality of chiral lactide. This study analyzed the fingerprint of trace d-lactic acid in the biorefinery chain and found that the major source of d-lactic acid comes from lignocellulose feedstock. The naturally occurring lactic acid bacteria and water-soluble carbohydrates in lignocellulose feedstock provide the necessary conditions for d-lactic acid generation. Three strategies were proposed to eliminate the generation pathway of d-lactic acid, including reduction of moisture content,conversion of water-soluble carbohydrates to furan aldehydes in pretreatment, and conversion to l-lactic acid by inoculating engineered l-lactic acid bacteria. The natural reduction of lactic acid content in lignocellulose feedstock during storage was observed due to the lactate oxidase-catalyzedoxidation of l- and d-lactic acids. This study provided an important support forthe production of cellulosic l-lactic acid with high chiral purity.

Synthesis of lactide from L-Lactic acid over iso-reticular zeolites derived from Al-UTL

Controlling the reaction selectivity by use of rationally designed catalysts provides high yields of desired products rendering the process more efficient and sustainable. In this study, we investigated a series of isoreticular zeolites (Al-IPC-n, n = 2, 4, 6, and 7), in the synthesis of lactide from L-Lactic acid as an intermediate for the polylactic acid production. Catalytic tests allowed a thorough understanding of the structure-acidity-activity relationship and the control of the shape selectivity. The lactide and the dimers of the lactic acid were obtained in one step with a high selectivity (>55% for lactide and >70% for the dimer of the lactic). The selectivity to L,L-lactide was comparable with that on more acidic commercial BEA. A balance between the acidity and the pore size afforded high yields of the dimer, avoiding the poisoning of the catalyst and the production of the larger oligomers.

A “one-step” approach to the highly efficient synthesis of lactide through the confinement catalysis of covalent organic frameworks

The precision confinement effect of the highly ordered channels with functional moieties in the designed 2D COFs realizes the highly efficient conversion from the lactide acid to the cyclic dimer lactide directly and avoids oligomerization.

Direct Synthesis of Lactide from Lactic Acid by Sn-beta Zeolite: Crucial Role of the Open Sn Site

Direct Synthesis of Lactide from Lactic Acid by Sn-beta Zeolite: Crucial Role of the Open Sn Site

Direct synthesis of lactide from concentrated lactic acid catalyzed by hierarchical Sn-beta zeolite

<p indent="0mm">Direct synthesis of lactide from concentrated lactic acid (LA) is an energy-efficient method, which is of great significance to reduce the cost of polylactic acid production. It is difficult to produce lactide with high yield from commercial concentrated LA due to the great quantity of LA oligomers. Herein, the hierarchical Sn-beta (Sn-beta-M) zeolite was prepared as a catalyst for the conversion of 97 wt% LA to lactide with yield of 86.5% in 3 h. The mesoporosity in Sn-beta-M characterized by N₂ adsorption/desorption test shortened the diffusion path way in the micropores, which facilitated the fast escape of lacide avoiding decyclization and oligomerization. L₃A and L_{<italic>n</italic>}A’s conversion to lactide may be attributed to the Sn sites present in mesopores. The Sn⁴⁺ coordinated in Sn-beta-M framework, exhibited strong Lewis acidity and could act as the active center for the synthesis of lactide. We speculated that the Sn and the surrounding O in Sn-beta-M acted as strong Lewis acid sites and weak base sites respectively in mediating C–O bond formation of lactide from L₂A and L_{<italic>m</italic>}A (<italic>m</italic>≥3).

Simple and Rapid Mechanochemical Synthesis of Lactide and 3S-(Isobutyl)morpholine-2,5-dione-Based Random Copolymers Using DBU and Thiourea.

There is a growing interest surrounding morpholine-2,5-dione-based materials due to their impressive biocompatibility as well as their capacity to break down by hydrolytic and enzymatic pathways. In this study, the ring-opening (co)polymerization of leucine-derived 3S-(isobutyl)morpholine-2,5-dione (MD) and lactide (LA) was performed via ball-milling using a catalytic system composed of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 3-[3,5-bis(trifluoromethyl)phenyl]-1-cyclohexylthiourea (TU). Once the homopolymerizations of MD and LA optimized and numerous parameters were studied, the mechanochemical ring-opening copolymerization of these monomers was explored. The feasibility of ring-opening copolymerizations in mechanochemical systems was demonstrated and a range of P(MD-co-LA) copolymers were produced with varying proportions of MD (23%, 48%, and 69%). Furthermore, the beneficial cocatalytic effects of TU with regards to ROP control were found to be operative within mechanochemical systems. Further parallels were observed between solution- and mechanochemical-based ROPs.

Controlled Synthesis of l-Lactide Using Sn-Beta Zeolite Catalysts in a One-Step Route

Polylactic acid (PLA), as a biodegradable and renewable polymer, has been widely used in biomedical and commercial applications. The energy-efficient synthesis of lactide from lactic acid (La) via a one-step route is highly desired for megaton-scale PLA production. In this work, stereo-pure l-lactide was synthesized with high yield (88.2–95.8%) via a one-step route catalyzed by Sn-beta zeolites. Sn–O–Si bonds on tin–silica catalysts are indeed important for a high l-lactide yield. The Sn4+ ions with four isolated coordinates in tetrahedral configuration of Sn-beta zeolites are more active for l-lactide synthesis than those with hexacoordinated polymeric Sn–O–Sn-type species. l-La was first converted into a lactic acid dimer (L2a) and then formed l-lactide catalyzed by a Sn-beta zeolite, and the average reaction rate in first 20 min (R20minav) increased linearly with increasing Sn content. Importantly, lactic acid trimers (L3a) formed during the reaction could also be converted to l-lactide in the later stage of the reaction, and the diffusion of L3a to the active site within the Sn-beta zeolite pore is the rate-limiting step. The lactic acid oligomer (Lna, n ≥ 4) was limited to form lactide with an R20minav of only 0.013 mmol min–1 gcat–1.

A study on highly concentrated lactic acid and the synthesis of lactide from its solution

Lactic acid is an important platform compound used as raw material for the production of lactide and polylactic acid. However, its concentration and composition distribution are not as simple as those of common compounds. In this work, the mass concentration distribution of highly concentrated lactic acid is determined by back titration. The components of highly concentrated lactic acid, crude lactide, and polymer after the reaction are analyzed by HPLC. Different concentrations of lactic acid solution were prepared for the synthesis of lactide and its content in the product was determined by 1H NMR analysis. We found that lactide is more easily produced from high-concentration lactic acid solution with which the condensed water is easier to release. Hence, the removal of condensed water is crucial to the formation of lactide, although it is not directly formed by esterification of two molecules of lactic acid.

Efficient Synthesis of Lactide with Low Racemization Catalyzed by Sodium Bicarbonate and Zinc Lactate

Lactide is an important monomer in the industrial production of PLA, which is one of the materials with the greatest potential for replacing petroleum-based polymers. In view of the low yields of l...

Phosphasalen group IV metal complexes: synthesis, characterization and ring opening polymerization of lactide.

We report the synthesis of a series of Zr and Ti complexes bearing phosphasalen which differs from salen by the incorporation of two P atoms in the ligand backbone. The reaction of phosphasalen proligands (1a-1c)H2 with Zr(CH2Ph)4 led to different products depending on the nature of the N,N-linker in the ligand. In the case of ethylene-linked phosphasalen, octahedral Zr complex 2a formed as a single stereoisomer in trans geometry. With the phenylene linker, it was shown by dynamic NMR spectroscopy that complex 2b exists as a mixture of trans and cis-β isomers in solution, both enantiomers (Δ and Λ) of the cis-β isomer being in fast equilibrium with respect to the NMR time-scale. The use of a propylene-linked phosphasalen proligand 1cH2 led to a mixture of complexes among which a binuclear Zr complex 2c bridged only by one phosphasalen ligand could be isolated and characterized. Addition of 2 equiv. of iPrOH to 2a and 2b afforded diisoproxy Zr complexes 3a and 3b as a mixture of trans and cis-β isomers, the latter undergoing fast Δ/Λ isomerization in solution. Addition of B(C6F5)3 to 2a and 2b gave cationic monobenzyl Zr complexes 4a and 4b which have been further converted into cationic alkoxy Zr complexes 5a-b and 6a-b by alcoholysis with iPrOH and (S)-methyl-lactate, respectively. The reaction of the phosphasalen proligands with Ti(NMe2)4 proceeded diastereoselectively giving rise to Ti complexes 7a-c in octahedral geometry with cis-β wrapping of the ligand. The complexes have been tested for the ROP of rac-lactide. The neutral phosphasalen Ti and Zr complexes showed only poor activity probably due to the encumbered and electron donating nature of the phosphasalen ligand. In contrast, the cationic Zr alkoxides 5a, 6a and 6b are effective initiators for the controlled and hetero-selective ROP of rac-lactide.

Synthesis of lactide from alkyl lactates catalyzed by lanthanide salts

Cerium salt exhibited a highest catalytic activity in the conversion of ethyl and isopropyl oligolactates into lactide. A maximum yield of the target product was reached at the concentration of CeCl3·7H2O ranging from 1 to 4 mol% relative to the lactide units in ethyl and isopropyl oligolactates. A gradual reduction of the pressure from 50 to 5 Torr along with the temperature increase from 180 to 230 °C during depolymerization resulted in the product containing up to 94% lactide.

One-step synthesis of stereo-pure l,l lactide from l-lactic acid

Poly (lactic acid) (PLA) is extensively used as an eco-friendly compound for many applications. The synthesis of stereo-pure lactide, specifically l,l-lactide which is the most desired isomer for the synthesis of high-quality PLA is very important. In this work, various materials including MOFs and simple bases have been applied as catalysts for the Lactide synthesis. Herein we report the one-step synthesis of l,l-lactide with high selectivity and yield (99%) in the absence of racemization by applying a cost-effective Cs2CO3 catalyst. The novel described procedure is even expected to be very efficient for industrial applications.

Economically Efficient Synthesis of Lactide Using a Solid Catalyst

An economically efficient one-step lactide synthesis process has been developed by using a low-price commercialized catalyst of SiO2/Al2O3 in a packed-bed reactor. Under the optimized conditions of preheater temperature 160 ℃, reactor temperature 240 ℃ and WHSV 3 h-1, 90% lactic acid conversion and 99% lactide selectivity were obtained. Filling of glass beads underneath the catalyst bed proved to be quite effective in improving reaction performance. The catalyst stably maintained its activity for as long as 120 hours showing no noticeable changes in its structure and chemical composition of the surface although a small amount of byproduct oligomers covered the surface. Oligomers deposited on the catalyst surface could be effectively removed by calcination at 600 ℃.

Bimetallic aluminum complexes supported by bis(salicylaldimine) ligand: Synthesis, characterization and ring-opening polymerization of lactide

Two types of bifunctional bis(salicylaldimine) ligands (syn-L and anti-L) were designed and synthesized to support bimetallic aluminum complexes. Owing to the rigid anthracene skeleton, syn-L and anti-L successfully locked two Al centers in close proximity (syn-Al2) and far apart (anti-Al2), respectively. The distance between two Al centers in syn-Al2 was defined by X-ray diffraction as 6.665 A, which is far shorter than that in anti-Al2. In the presence of stoichiometrical BnOH, syn-Al2 and anti-Al2 were both efficient for ring-opening polymerization (ROP) of rac-LA with the former being more active. In the presence of excess BnOH, syn-Al2 showed an efficient and immortal feature, consistent with high conversions, matched Mns, narrow molecular weight distributions and end group fidelity, while anti-Al2 had a much lower activity or even became entirely inactive due to rapid decomposition, indicated by in situ1H-NMR experiments of Al complexes with BnOH.

Synthesis of lactide/ɛ‐caprolactone quasi‐random copolymer by using rationally designed mononuclear aluminum complexes with modified β‐ketiminato ligand

ABSTRACTA series of novel aluminum complexes containing bulky aryl‐β‐ketiminato ligands [ArNCHC10H7C6H5O]Al(CH3)2 (3a, Ar = C6F5; 3b, Ar = C6H5; 3c, Ar = 2,6‐iPr2C6H3) have been synthesized in high yields. These complexes were identified by 1H and 13C NMR spectroscopy, elemental analysis, and X‐ray structural analysis. All the aluminum complexes could efficiently catalyze the ROP of ɛ‐caprolactone (ɛ‐CL) and Lactide (LA) in a controlled manner. It was found that the steric effect of the ligand has less effect on the ROP of CL, while the polymerization rate of L‐LA was suppressed significantly. More interestingly, this kind of catalysts can promote the random copolymerization of ɛ‐CL and L‐LA. The transesterification side reaction and the polymer composition could be adjusted by modulating the electronic and steric effects of the ligand. In paticular, compound 3c could produce quasi‐random copolymers without transesterification side reactions, as indicated by both the values of the reactivity ratios of the two monomers (rLA = 1.31; rCL = 0.99) and the similar average lengths of the caproyl and lactidyl sequences (LCL = 2.34; LLA = 2.44). Finally, a drug‐random copolymer conjugates could be easily prepared by using 3c, indicating a potential application of 3c in pharmacutical and biomedical field. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 203–212