Alkyl Lactates Research Articles

Ionic Liquid–Catalyzed Annulation of Biomass-Derived Alkyl Lactates: Time-Dependent Tunable Synthesis of Bioactive Dihydroquinoxalines and Quinoxalines

Ionic Liquid–Catalyzed Annulation of Biomass-Derived Alkyl Lactates: Time-Dependent Tunable Synthesis of Bioactive Dihydroquinoxalines and Quinoxalines

Mononuclear and multinuclear O^N^O‐donor Zn(II) complexes as robust catalysts for the production and depolymerization of poly(lactide)

Mononuclear and multinuclear O^N^O‐donor Zn(II) complexes are herein reported as catalysts in the ring‐opening polymerization (ROP) of rac‐lactide (rac‐LA) and depolymerization of poly(lactide) (PLA). Reactions of imino‐phenol proligand 2[((2‐hydroxyethyl)imino)methyl]phenol (L1H2) with ZnCl2 and ZnEt2 afforded the dinuclear and tetranuclear complexes [Zn2(L1H)2Cl2] (Zn1) and [Zn4(L1)4] (Zn2), respectively. Separately, treatments of proligands 2‐[1‐((2‐hydroxyethyl)imino)ethyl]phenol (L2H2) and [((2‐methoxyethyl)imino)methyl]phenol (L3H) with ZnCl2 gave the respective mononuclear complexes [Zn(L2H2)2Cl2] (Zn3) and [Zn(L3H)2Cl2] (Zn4), while the reactions of L3H with ZnEt2 afforded the bis(chelated) mononuclear complex [Zn(L3)2] (Zn5). The complexes were characterized using NMR and IR spectroscopy, elemental analysis and single crystal X‐ray crystallography. All the Zn(II) complexes showed high catalytic activities in the ROP of rac‐LA (kapp of up to 4.18 × 10‐4 s‐1) to give moderate molecular weight PLA (39 960 g mol‑1) with relatively narrow dispersities (Đ = 1.4‐2.1). The complexes produced mainly atactic PLAs with Pr values of 0.51‐0.58. More significantly, complexes Zn1, Zn2 and Zn5 were also active in the depolymerization of commercial PLA in methanol (kapp of up to 2.67 × 10‐4 s‐1) to produce alkyl lactates. The ROP and depolymerization behavior were largely controlled by the structure and nuclearity of the complexes.

Open- and Closed-Loop Recycling: Highly Active Zinc Bisguanidine Polymerization Catalyst for the Depolymerization of Polyesters.

In this study, the aliphatic N,N-bisguanidine zinc complex [Zn(DMEG2ch)2](OTf)2 ⋅ THF is introduced as a promising candidate for the chemical recycling of (bio) polyesters. This catalyst is highly active in the ring-opening polymerization (ROP) of lactide (LA) and ϵ-caprolactone (CL). The combination of polymerization and depolymerization activity creates new pathways towards a sustainable circular economy. The catalytic activity of [Zn(DMEG2ch)2](OTf)2 ⋅ THF for the chemical recycling of polylactide (PLA) via alcoholysis was investigated by detailed kinetic and thermodynamic studies. It is shown that various high value-added alkyl lactates can be obtained efficiently under mild reaction conditions. Catalyst recycling was successfully tested using ethanol for the degradation of PLA. In addition, LA can be recovered directly from PLA, enabling either open- or closed-loop recycling. Selective PLA degradation from mixtures with polyethylene terephthalate (PET) and polymer blends are presented. For the first time, a cascade recycling reaction of a PLA/polycaprolactone (PCL) blend is tested with a zinc-based bisguanidine catalyst, whereby PLA is degraded selectively at first and subsequent modification of the reaction conditions leads to efficient degradation of the remaining PCL. The highly active, universally applicable benign zinc catalyst allows the implementation of a circular plastics economy and thus the reduction of plastic pollution in the environment.

Zn/Ni catalyst facilitates the oxidation of ethyl lactate to ethyl pyruvate by selective progressions on mesoporous SBA-15 support by a continuous processing approach

The solid-state catalyst-mediated oxidation of alkyl lactate produced from biomass to alkyl pyruvate is an intriguing approach to manufacture valuable resources compounds. In this study, several types of SBA-15/Zn/Ni catalysts containing different nickel loadings have been developed and used in a molecular oxygen environment to oxidize ethyl lactate (EL) compound to ethyl pyruvate (EP). The aforementioned catalyst was comprehensively characterised by employing XRD, ICP, FTIR, N2 physisorption, NH3-TPD, HR-SEM and HR-TEM. As more of nickel was loaded onto the Ni/Zn/SBA-15 catalyst, the EL conversion improved, but the selectivity of EP consistently exceeded greater than 95 %, regardless of the 15 % nickel loading. Assuming maximum conditions for the reaction (90 °C, 2 h in O2) over the Ni/Zn/SBA-15 catalyst, the selectivity of 99.5 % for EP and a conversion of 97.7 % for EL were achieved. A selectivity of 99.5 % for EP and a conversion of 97.7 % for EL were achieved. The catalytic combination of SBA-15 and Zn/Ni exhibited a significant reducing capacity due to the significant connection between both of them, as demonstrated by the NH3-TPD data.

One-pot catalytic conversion of sugars to methyl lactate over acid-base bifunctional Sn/MgO catalysts

Alkyl lactates represent such green added-value chemicals that commonly used as biodegradable green solvents, detergents, pharmaceutical intermediates et al. Catalytic conversion of carbohydrates to methyl lactate (MLA) is a representative way for high-value utilization of biomass and the key lies in the development of highly efficient catalysts. In methanol, strong acid or alkaline catalysts are usually used under high temperature and high pressure, suffering from problems such as low selectivity, high cost or contamination of environment. This study aims to develop an acid-base bifunctional heterogeneous catalyst for the one-pot conversion of sugars to MLA under mild conditions. Sn/Mg composite oxides was synthesized by a coprecipitation method and further modified by poly (vinyl imidazole) ([PVIM]) to tune the hydrophilicity. Effect of polymer and Sn amount, calcination temperature, reaction temperature, catalyst dosage, and substrate concentration were investigated. The acid-base properties were characterized by NH3-TPD, pyridine-FTIR and CO2-TPD analysis. It was found that the presence of medium acid sites and medium base sites played an important role to the cascade reactions of carbohydrates to MLA. An optimum MLA yield of 55.4% was achieved over 10[PVIM]-5Sn/MgO (0.05 g) with complete conversion of glucose (28 mM) at 140 ℃, 2 MPa N2 for 10 h. The reaction conditions are mild and no strong acid or strong base catalyst is required. Furthermore, a possible reaction mechanism was proposed that the introduction of [PVIM] effectively regulated the local microenvironment of active sites and the acid base synergism greatly promoted the retro-aldol condensation, dehydration and hydrogen transfer reactions during the conversion of glucose to MLA.

One-pot FeCl3-catalyzed sustainable synthesis of pyrimidines using ammonium iodide, aldehydes and alkyl lactate as raw materials

Iron(iii)- and iodide-promoted efficient synthesis of pyrimidines from biomass-based alkyl lactates, inorganic ammonium, and aldehydes was carried out.

Bifunctional Au-Sn-SiO2 catalysts promote the direct upgrading of glycerol to methyl lactate.

Valuable alkyl lactates can be obtained from (waste) glycerol, through a two-step process that entails (i) the oxidation of glycerol to dihydroxyacetone (DHA) catalyzed by support Au nanoparticles and (ii) a rearrangement of DHA with an alcohol effectively catalyzed by Sn-based heterogeneous catalysts. To solve selectivity and processing issues we propose to run the process as a cascade reaction, in one step, and with a single bifunctional catalyst. Tackling the challenge associated with the preparation of such bifunctional catalysts, here, an aerosol-assisted sol-gel route is exploited. The catalysts feature small Au nanoparticles (3-4 nm) embedded at the surface of mesoporous Sn-doped silica microspheres. The preparation successfully leads to insert both active sites in their most active forms, and in close proximity. With the bifunctional catalysts, the yield for the final product of the cascade reaction (methyl lactate) is higher than the DHA yield when only the first reaction is carried out. This highlights a beneficial substrate channeling effect which alleviates side reactions. Interestingly, the bifunctional catalysts also markedly outcompeted mechanical mixtures of the corresponding monofunctional Au- and Sn-based catalysts. Thus, the spatial proximity between the two active sites in bifunctional catalysts is identified as a key to stir the cascade reaction towards high lactate yield.

Synthesis and Catalytic Applications of Advanced Sn- and Zr-Zeolites Materials.

The incorporation of isolated Sn (IV) and Zr (IV) ions into silica frameworks is attracting widespread attention, which exhibits remarkable catalytic performance (conversion, selectivity, and stability) in a broad range of reactions, especially in the field of biomass catalytic conversion. As a representative example, the conversion route of carbohydrates into valuable platform and commodity chemicals such as lactic acid and alkyl lactates, has already been established. The zeotype materials also possess water-tolerant ability and are capable to be served as promising heterogeneous catalysts for aqueous reactions. Therefore, dozens of Sn- and Zr-containing silica materials with various channel systems have been prepared successfully in the past decades, containing 8 membered rings (MR) small pore CHA zeolite, 10-MR medium pore zeolites (FER, MCM-56, MEL, MFI, MWW), 12-MR large pore zeolites (Beta, BEC, FAU, MOR, MSE, MTW), and 14-MR extra-large pore UTL zeolite. This review about Sn- and Zr-containing metallosilicate materials focuses on their synthesis strategy, catalytic applications for diverse reactions, and the effect of zeolite characteristics on their catalytic performances.

Hierarchical zeolite with open tin sites stabilized by metal ions catalyze the conversion of polysaccharides to alkyl lactates

The high yield of alkyl lactate from polysaccharides is attractive and challenging. Here, we report the remarkable catalytic ability of hierarchical tin-containing Beta zeolites for this process. The hierarchical structure, mediated by polystyrene microspheres or starch, improves mass transfer in the polysaccharide conversion. Two types of acidic sites in the zeolite achieved cooperation in the cascade conversion. Brønsted acid associated with Al promoted the hydrolysis of polysaccharides to monosaccharides; the abundant open Sn site stabilized by Ni2+ converted the monosaccharides to alkyl lactate. Polydextrose was used as a substrate in various alcohols, yielding up to 44% for methyl lactate, 37% for ethyl lactate, and 36% for propyl lactate, and the catalytic yields were consistent throughout three runs. More than 90% of the catalytic capability was recovered by the ion exchange and calcination procedures.

Hydrothermal conversion of fructose to lactic acid and derivatives: Synergies of metal and acid/base catalysts

With increasing strict regulation on single-use plastics, lactic acid (LA) and alkyl lactates, as essential monomers for bio-degradable polylactic acid (PLA) plastic products, have gained worldwide attention in both academia and industry. While LA is still dominantly produced through fermentation processes from start, chemical synthesis from cellulosic biomass remains a grand challenge, owing to poor selectivity in activating C-H and C-C bonds in sugar molecules. To our best knowledge, recent publications have been focused on hydrothermal conversion of glucose to LA, while this review summarizes the highlights on direct thermal conversion of fructose as starting material to LA and derivatives. In particular, the synergies of metal/metal cations and acid/base catalysts will be critically revised on retro-aldol and dehydration reactions. This work will provide insights into rational design of active and selective catalysts for the production of carboxylic acids from biomass feedstocks.

Researches on heterogeneous acid-base catalysis in Institute for sorption and problems of endoecology of the National Academy of Sciences of Ukraine

In chronological order, the reaseach results of Department of heterogeneous acid-base catalysis at Institute for sorption and endoecology problems in 2003-2023 are described. It relates to the synthesis, study and application of solid superacids WO3/ZrO2, WO3/ZrO2-SiO2, ZrO2-SiO2-Al2O3, ZrO2-SiO2-SnO2, as catalysts, in vacuum gas oil cracking, alkylation of isobutane with isobutanol, acylation toluene, oligomerization of tetrohydrofuran, acylation of methyl tert-butyl ether and other. Some study deals with a search of the correlations between of acid site strength of a catalyst and its activity, in particular, in dehydration reaction of C2-C4 alcohols, and the correlations between ability of primary and secondary alcohols to dehydrogenation and oxidation and their chemical shifts δ (R17OH) and δ (R13СОH ). For the first time, the values of Hammett's acidity function have been measured at elevated (up to 200 °C) temperatures for solid acids. In particular, for H-Y faujasite, H0 reaches superacidic value H0 at 160 °С. Since 2010, the main focus has been on the catalytic conversion of renewable raw materials, mainly bioalcohols (ethanol, glycerol) and C6 carbohydrates, into important products of organic synthesis (ethyl acetate, 1,1 diethoxyethane, n-butanol, propylene glycol, alkyl lactates, lactide, glycolide). In cooperation with “Techinservice Manufacturing Group”, new processes for obtaining ethyl acetate, 1,1 diethoxyethane, n-butanol from bioethanol and racemic lactide from glycerol were developed. Also, new technologies for obtaining propylene oxide from propylene and hydrogen peroxide (НРPОа-process), vapor phase hydrogenation of the pyrolysis C4-5 fraction, and direct high-temperature chlorination of ethylene to vinyl chloride have been developed for Kalush “Karpatnaftochim” plant. The HHPOa installation (2000 t/y) has been started at “Karpatnaftochim” in 2020.

In vitro safety assessment of alkyl lactate esters in human umbilical vein endothelial cells (HUVECs).

Safety assessment requires information on both the chronic and acute effects of chemicals. Chemical materials such as food additives have become one of the most critical and compelling issues in the continuing debate on food safety. Calcium lactate (CL) and Sodium lactate (SL) are approved chemicals used in various products. The present study, in vitro study, was designed to evaluate the cyto-genotoxicity effects of CL and SL on human umbilical vein endothelial cells (HUVECs). The cytotoxicity effect of these additives was determined by MTT and Annexin V-FITC apoptosis assays. Besides, genotoxicity parameters such as morphological change of DNA and DNA fragmentation were studied with DAPI staining and DNA ladder assays, respectively. The results showed that the growth of HUVECs decreased upon treatment with CL at higher concentrations, but SL did not significantly alter HUVECs cell number. Annexin V-FITC apoptosis assays revealed that CL could induce cell death based on necrosis rather than apoptosis. In SL, the early and late apoptosis was not considerable in treated cells. Exposure to CL and SL did not lead to morphological change and DNA fragmentation in the HUVECs cell line. Overall, it is concluded from these results that CL and SL have not been cytotoxic and genotoxic effects in low concentrations in human umbilical vein endothelial cells in vitro.

Surface Tensions of Alkyl Lactates with n-Alkanols or Branched Alkanols.

The surface behavior of 18 binary mixtures at T = 298.15 K and at atmospheric pressure (p = 0.1 MPa) was measured with a drop volume tensiometer. These mixtures are formed by alkyl lactates (methyl lactate and ethyl lactate) and alcohols (n-alkanols from methanol to 1-hexanol and isomeric butanols). Surface tension deviations for all these systems were calculated and correlated with the mole fraction using the Myers-Scott equation. For the mixtures alkyl lactate with methanol, the surface tension deviations are positive. With regard to the mixtures containing ethanol, the surface tension deviation is positive for methyl lactate and slightly negative in the lactate-poor region for ethyl lactate. For the rest of the mixtures, the surface tension deviations are negative. A molecular interpretation of the different behaviors observed was proposed.

High-Pressure Depolymerization of Poly(lactic acid) (PLA) and Poly(3-hydroxybutyrate) (PHB) Using Bio-Based Solvents: A Way to Produce Alkyl Esters Which Can Be Modified to Polymerizable Monomers.

The polyesters poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) used in various applications such as food packaging or 3D printing were depolymerized by biobased aliphatic alcohols-methanol and ethanol with the presence of para-toluenesulphonic acid (p-TSA) as a catalyst at a temperature of 151 °C. It was found that the fastest depolymerization is reached using methanol as anucleophile for the reaction with PLA, resulting in the value of reaction rate constant (k) of 0.0425 min-1 and the yield of methyl lactate of 93.8% after 120 min. On the other hand, the value of constant k for the depolymerization of PHB in the presence of ethanol reached 0.0064 min-1 and the yield of ethyl 3-hydroxybutyrate was of 76.0% after 240 min. A kinetics study of depolymerization was performed via LC-MS analysis of alkyl esters of lactic acid and 3-hydroxybutanoic acid. The structure confirmation of the products was performed via FT-IR, MS, 1H NMR, and 13C NMR. Synthesized alkyl lactates and 3-hydroxybutyrates were modified into polymerizable molecules using methacrylic anhydride as a reactant and potassium 2-ethylhexanoate as a catalyst at a temperature of 80 °C. All alkyl esters were methacrylated for 24 h, guaranteeing the quantitative yield (which in all cases reached values equal to or of more than 98%). The methacrylation rate constants (k') were calculated to compare the reaction kinetics of each alkyl ester. It was found that lactates reach afaster rate of reaction than 3-hydroxybutyrates. The value of k' for themethacrylated methyl lactate reached 0.0885 dm3/(mol·min). Opposite to this result, methacrylated ethyl 3-hydroxybutyrate's constant k' was 0.0075 dm3/(mol·min). The reaction rate study was conducted by the GC-FID method and the structures were confirmed via FT-IR, MS, 1H NMR, and 13C NMR.

Synergetic Effect of Mo, Mg-Modified Sn-β Over Moderate-Temperature Conversion of Hexose to Alkyl Lactate.

The thermocatalytic conversion of hexose into valuable chemicals such as methyl lactate under mild conditions is very appealing. Here, we report that Mo, Mg co-modified Sn-β catalyst can effectively catalyze the transformation of glucose and fructose into alkyl lactate at moderate temperatures. A maximum yield of around 35% of methyl lactate was achieved from the conversion of glucose in methanol at 100°C over Sn-β catalyst modified with 3 wt% Mo and 0.5 wt% Mg. However, up to 82.8% yield of ethyl lactate was obtained in the case of fructose in ethanol upon the same catalytic condition, suggesting a significant solvent effect. The Mo species plays a key role to enable the retro-aldol condensation of fructose, in which the competing side reactions are significantly suppressed with the assistance of neighboring Mg species probably through a synergetic effect of Lewis acid-base.

Methanolysis of Poly(lactic Acid) Using Catalyst Mixtures and the Kinetics of Methyl Lactate Production

Polylactic acid (PLA) is a leading bioplastic of which the market share is predicted to increase in the future; its growing production capacity means its end-of-life treatment is becoming increasingly important. One beneficial disposal route for PLA is its chemical recycling via alcoholysis. The alcoholysis of PLA leads to the generation of value-added products alkyl lactates; this route also has potential for a circular economy. In this work, PLA was chemically recycled via methanolysis to generate methyl lactate (MeLa). Four commercially available catalysts were investigated: zinc acetate dihydrate (Zn(OAc)2), magnesium acetate tetrahydrate (Mg(OAc)2), 4-(dimethylamino)pyridine (DMAP), and triazabicyclodecene (TBD). Dual catalyst experiments displayed an increase in reactivity when Zn(OAc)2 was paired with TBD or DMAP, or when Mg(OAc)2 was paired with TBD. Zn(OAc)2 coupled with TBD displayed the greatest reactivity. Out of the single catalyst reactions, Zn(OAc)2 exhibited the highest activity: a higher mol% was found to increase reaction rate but plateaued at 4 mol%, and a higher equivalent of methanol was found to increase the reaction rate, but plateaued at 17 equivalents. PLA methanolysis was modelled as a two-step reversible reaction; the activation energies were estimated at: Ea1 = 25.23 kJ∙mol−1, Ea2 = 34.16 kJ∙mol−1 and Ea-2 = 47.93 kJ∙mol−1.

Cost-effective and fast synthesis of Sn-β zeolite with less silanol defects for efficient conversion of glucose to methyl lactate

Sn-β with strong Lewis acid sites is considered as the state-of-the-art solid catalyst for converting glucose to alkyl lactate. However, the extensive use of organic template and mineralizing agent and long preparation period in the synthesis of Sn-β brought serious environmental pollution and high synthesis cost. Herein, a cost-effective and fast synthesis strategy using fewer organic template and mineralizing agent, fumed silica as Si source, Mg2+ cation as crystallization promoter and without additional solvent, is proposed to alleviate the aforementioned shortcomings. The results reveal that highly crystalline Mg-Sn-β can be synthesized in 3 days from the gel of 0.005MgO/0.005SnO2/SiO2/0.15TEAOH/0.15NH4F/3.75H2O. Besides accelerating the crystallization, it is found that Mg2+ cation facilitated Sn4+ incorporation into the framework site and lessened the silanol defects of zeolite notably. For conversion of glucose to methyl lactate (MLA), a higher yield of MLA was obtained over 1Mg-Sn-β-3d (54.4%) compared with Sn-β-H-7d (37.2%) and Sn-β-7d (41.3%).

Metal-free three-component assemblies of anilines, α-keto acids and alkyl lactates for quinoline synthesis and their anti-inflammatory activity.

A new and metal-free three-component method for the synthesis of 2,4-disubstituted quinolines via the reactions of anilines, α-keto acids and alkyl lactates is reported. The reactions proceed in the presence of p-toluene sulfonic acid (p-TSA) and tert-butyl peroxybenzoate (TBPB) to provide diverse quinoline products via the construction of new CC double, C-C single and CN double bonds without producing any organic mass-based side product. Notably, the anti-inflammatory activity of the quinolines has been investigated by measuring their ability to inhibit NO release by lipopolysaccharide (LPS) induced RAW264.7 cells, leading to the identification of 4i, 4t and 4x as potent anti-inflammatory compounds in vitro.

A recyclable process between a monomer and polyester with a natural catalyst

Catalysts from nature promoted a circular process for polylactide chemistry, including the polymerization of lactide to polylactide, the depolymerization of polylactide to alkyl lactate, and finally the conversion of alkyl lactate back to lactide.

How substituent effects influence the thermodynamics and kinetics of gas-phase transesterification of alkyl lactates to lactide using TiO2/SiO2

Lactide, a crucial precursor of the bioplastic polylactic acid, was obtained through the gas-phase transesterification of alkyl lactates using a 5 wt% TiO2/SiO2 catalyst as an alternative to the conventional liquid-phase process. Lactide selectivity above 80% was achieved at 220 °C but conversion was thermodynamically limited at around 50% for all alkyl lactates. The nature of the ester alkyl chain had minimal impact of the thermodynamics of the reaction, but significantly influenced its kinetics. The Taft equation indicated that this kinetic effect was due to the polarity of the alkyl chain. Mechanistic studies indicated that lactide formed via a Langmuir-Hinshelwood mechanism involving two lactate molecules. The derived kinetic expression was fitted to experimental data of methyl lactate transesterification, resulting in a reduced chi-squared of 0.99 and an activation energy of 89.8 kJ·mol−1. Initial rate kinetics confirmed that the proposed mechanism was valid for other alkyl lactate species.