Kinetics of esterification of the levulinic acid with n‐hexanol,n‐octanol,and 2‐ethylhexanol in the presence of methanesulfonic acid as a catalyst under nonisothermal conditions

The levulinic acid was esterified with alcohol at an alcohol to acid molar ratio of 3:1, 5:1, and 10:1 in the presence of a 0.1 wt% methanesulfonic acid catalyst. During esterification, the temperature was changed linearly from 373 to 428 K and its average change was 4.5 K/min. The authors stated that reactions were of second order and that the activation energy (E) decreased from 61 to 46 kJ/mol in the following alcohol sequence: n‐hexanol > n‐octanol > 2‐ethylhexanol. The fitting errors varied between 3.8% and 6.4%. The time of experiment carried out under nonisothermal condition is five to 15 times shorter than that conducted under isothermal conditions. A smaller number of experimental series also determines a significantly lower cost of such research. The results of such study are the precise form of the kinetic equation, which is indispensable in design and optimization of industrial‐scale chemical reactors.     

水热条件下酸催化氧化木质纤维生物质制取乙酸

木质纤维基生物质是一类新的能够生产液体燃料和化学品的可再生资源. 本文研究了木质纤维生物质在水热条件下, 以少量无机酸作为酸催化剂, 氧气作为氧化剂(2.0 MPa), 经过"一锅两步法"转化成乙酸的反应. 以玉米秸秆作为反应原料时, 最高可以获得21.3 wt%的乙酸, 占据整个液体产物质量比例的84.6% (选择性). 同时, 将反应推广到玉米芯, 甘蔗渣, 竹子, 杨木和松木等多种生物质原料的转化, 同样取得了较高的乙酸产率. 最后, 我们对木质纤维生物质转化到乙酸的反应过程进行了研究. 研究表明木质纤维生物质中的碳水化合物六碳糖是乙酸的主要来源, 六碳糖经过脱水和水解生成乙酰丙酸中间体, 乙酰丙酸在氧化条件下断裂C-C键生成乙酸.     

Palladium/Zinc Co-Catalyzed Asymmetric Hydrogenation of γ-Keto Carboxylic Acids

A palladium-catalyzed asymmetric hydrogenation of levulinic acid has been successful developed by using Zn(OTf)₂ as co-catalyst. The present method not only has provided a strategy in the palladium-catalyzed asymmetric hydrogenation of ketone, but also allowed the preparation of a wide range of chiral γ-valerolactones in good yields with excellent enantioselectivities.     

Efficient Extraction of Fermentation Inhibitors by Means of Green Hydrophobic Deep Eutectic Solvents

The methods for hydrogen yield efficiency improvements, the gaseous stream purification in gaseous biofuels generation, and the biomass pretreatment are considered as the main trends in research devoted to gaseous biofuel production. The environmental aspect related to the liquid stream purification arises. Moreover, the management of post-fermentation broth with the application of various biorefining techniques gains importance. Chemical compounds occurring in the exhausted liquid phase after biomass pretreatment and subsequent dark and photo fermentation processes are considered as value-added by products. The most valuable are furfural (FF), 5-hydroxymethylfurfural (HMF), and levulinic acid (LA). Enriching their solutions can be carried with the application of liquid–liquid extraction with the use of a suitable solvent. In these studies, hydrophobic deep eutectic solvents (DESs) were tested as extractants. The screening of 56 DESs was carried out using the Conductor-like Screening Model for Real Solvents (COSMO-RS). DESs which exposed the highest inhibitory effect on fermentation and negligible water solubility were prepared. The LA, FF, and HMF were analyzed using FT-IR and NMR spectroscopy. In addition, the basic physicochemical properties of DES were carefully studied. In the second part of the paper, deep eutectic solvents were used for the extraction of FF, LA, and HMF from post-fermentation broth (PFB). The main extraction parameters, i.e., temperature, pH, and DES: PFB volume ratio (V_DES:V_PFB), were optimized by means of a Box–Behnken design model. Two approaches have been proposed for extraction process. In the first approach, DES was used as a solvent. In the second, one of the DES components was added to the sample, and DES was generated in situ. To enhance the post-fermentation broth management, optimization of the parameters promoting HMF, FF, and LA extraction was carried under real conditions. Moreover, the antimicrobial effect of the extraction of FF, HMF, and LA was investigated to define the possibility of simultaneous separation of microbial parts and denatured peptides via precipitation.     

Esterification and ketalization of levulinic acid with desilicated zeolite β and pseudo-homogeneous model for reaction kinetics

To maximize the production of esters (E), keto (K) and keto-ester (KE) by esterification and ketalization of levulinic acid (LA) has been reacted using diols such as 1,2-propane diol (PDOL),1,2-ethane diol (EDOL), and 1,2,3-propane triol or glycerol (TRIOL) with desilicated Hβ. This work aims to assess the conversion and selectivity for the production of esters using conventional and microwave-irradiated (MWI) reactors. Catalysts characterizations were performed using NH₃-temperature programme desorption, Brunauer, Emmett and Teller surface area (BET), Barrett, Joyner, and Halenda (BJH), scanning electron microscope, transmission electron microscope, and dynamic light scattering. Operating parameters such as reaction temperature (170–180°C), reaction time (20–80 min), feed composition (LA:PDOL/EDOL/TRIOL, 1:8/10/12), and microwave energy (300–500 watt) have been systematically investigated. Note that 99–100% conversion was achieved with the product selectivity of E (40%), K (30%), and KE (30%) with1,2-EDOL; E (56%), K (2%), and KE (17%) with 1,2-PDOL; E (69%), K(0%), and KE (22%) with TRIOL using D-Hβ as a solid catalyst in an MWI reactor. Reaction paths and kinetics were studied using pseudo-homogeneous (PH) model.     

Vibrational properties of levulinic acid and furan derivatives: Raman spectroscopy and theoretical calculations

In this work, the Raman spectra of furan, furfuryl alcohol (FA), furfural, hydroxymethylfurfural (HMF), and levulinic acid were obtained in the 500 to 4000 cm⁻¹ spectral region at room temperature. Vibrational wavenumbers were calculated for these compounds with the B3LYP method using the 6‐31 + G(2df,p) basis set. The experimentally determined CC and C C wavenumbers for furan and furan derivatives were in good agreement with the calculated wavenumbers without scaling factor, while the calculated CO and C H wavenumbers at ∼1660 and 3000 cm⁻¹, respectively, showed larger deviations from the measured ones. The Raman spectra for furan and furan derivatives showed intense CC bands, whereas the levulinic acid spectrum showed intense C H vibrations with broad doublet CO bands. We also found that an empirical method based on the chemical structure similarities is able to predict the HMF Raman spectrum from the combined furfural and FA spectra. Copyright © 2011 John Wiley & Sons, Ltd.     

Efficient Hydrogenation of Biomass Oxoacids to Lactones by Using NHC–Iridium Coordination Polymers as Solid Molecular Catalysts

A series of NHC–iridium coordination polymers have proven to be robust, efficient and recyclable solid molecular catalysts toward the hydrogenation of biomass levulinic acid (LA) to γ‐valerolactone. Along with quantitative yields attained at 0.01 mol % catalyst loading under 50 atm of H₂, the solid molecular catalyst was readily recovered and reused for 12 runs without obvious loss of the selectivity and activity. Remarkably, up to 1.2×10⁵ TON, an unprecedented value could be achieved in this important transformation. In addition, a number of LA homologues, analogues and derivatives were well tolerated to deliver various intriguing and functional lactones in good to excellent yields, which further confirmed the feasibility of the solid molecular catalysts.     

Study of organic acids in Schisandrae Chinensis Fructus after vinegar processing

The ripened fruit of Schisandrae Chinensis Fructus has unique medical properties in Chinese medicine. It is commonly used after vinegar steaming. Vinegar steaming changes the color of Schisandrae Chinensis Fructus from red to black and enhances its acidic and astringent properties. Lignans are the well‐investigated components in this herb. However, Schisandrae Chinensis Fructus is acidic in the theory of Chinese medicine, and whether vinegar processing changes its organic acid components remains largely unknown. In this study, the organic acids in this herb were derived by the method of methyl esterification, and further analyzed by gas chromatography with mass spectrometry. A total of 39 organic acid compounds were identified. Interestingly, Schisandrae Chinensis Fructus after vinegar processing showed a significant increase in the content of levulinic acid as compared to the unprocessed ones. Pharmacological experiments demonstrated that levulinic acid inhibited the contractility of isolated intestine and had an inhibitory effect on the excessive hyperfunction of small intestinal propulsion. Moreover, the extracts of vinegar‐processed Schisandrae Chinensis Fructus had a stronger inhibitory on the excessive hyperfunction of small intestinal propulsion than that of unprocessed ones. Taken together, this study offers novel insight into the effect of Schisandrae Chinensis Fructus after vinegar processing.