levulinic acid

Top PDF levulinic acid:

Transformation of biogenic carbohydrates into levulinic acid and further hydrogenation using supported nanoparticle catalysts synthesized by chemical fluid deposition

Transformation of biogenic carbohydrates into levulinic acid and further hydrogenation using supported nanoparticle catalysts synthesized by chemical fluid deposition

To exploit the large potential of LA as key platform chemical, a large number of chemical industry firms and researchers devoted numerous endeavors to address afore mentioned issues. The first pioneered study on the preparation of LA was reported as early as the 1840s by G. J. Mulder. 35 His group t ried to prepare LA by heating a mixture of sucrose with mineral acid such as HCl. Unfortunately, details on the reaction conditions and the LA yield are unknown. ˝In 1940, the first commercial scale production of levulinic acid in an autoclave was started in United States by Stanley.˝ 35 The pioneered work done by groups of Hanna 36 and Heeres 37 using kernel grain sorghum and starch as starting material for the production of levulinic acid. Notably, the maximum yield of levulinic acid obtained was as high as 50%.
Mehr anzeigen

165 Mehr lesen

Catalytic upgrading of α-angelica lactone to levulinic acid esters under mild conditions over heterogeneous catalysts

Catalytic upgrading of α-angelica lactone to levulinic acid esters under mild conditions over heterogeneous catalysts

Introduction As a result of the massive exploitation of petroleum and its foreseeable depletion, the search for renewable resources is becoming increasingly urgent. 1 Biomass presents a promising example of a sustainable source of energy since it can be uti- lized to produce liquid fuels or fuel additives. 2 Particularly, levulinic acid esters (LAE) are a group of compounds with high potential for use, not only, in the fuel sector, 3–6 but also for polymers, 7–9 green solvents, 10 and fragrances. 11 LAE can be produced through a catalytic conversion of various lignocellulosic-derived intermediates (Scheme 1). 4 The direct conversion of polysaccharides in a one-pot reaction to LAE, although highly attractive, 12 is severely limited by the harsh conditions (e.g. 175 °C for 20 h) required to achieve this reac- tion. 13,14 The one-pot conversion of cellulose to methyl levulinate (ML) is the only example thus far. 15 Other studies have focused on mono- and disaccharides as starting mate- rial. 15,16 These sugars can be obtained through hydrolysis of polysaccharides 17 and less by-products and milder conditions are expected. LAE can be prepared from glucose through acid- catalysed dehydration via 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) and esterification in alcoholic medium. 18
Mehr anzeigen

6 Mehr lesen

Development of modified ZrO2 catalysts for the production of levulinic acid esters

Development of modified ZrO2 catalysts for the production of levulinic acid esters

between the population of Brönsted acidity and catalytic activity could be affirmed. The second part of this work elaborates the production of levulinic esters via addition reaction of alpha-angelica lactone (a-AL) with 1-BuOH over Amberlyst-36. Full conversion with 97% selectivity towards the ester can be achieved by performing the reaction with stoichiometric amount of the reactants at a milder condition. The reaction mechanism for the ester formation has been confirmed revealing that p-BL is the intermediate during the transformation of a-AL to n-BL. Different alcohols have also been studied suggesting the effect of linearity and the length of alkyl chain influence the reaction. This study eventually indicates that a-AL can be used as a better candidate to substitute LA for the synthesis of levulinic acid esters. Different type solid acid catalysts have been tested suggesting that strong acidity is required to allow the addition reaction.
Mehr anzeigen

120 Mehr lesen

Catalytic upgrading of α-angelica lactone to levulinic acid esters under mild conditions over heterogeneous catalysts

Catalytic upgrading of α-angelica lactone to levulinic acid esters under mild conditions over heterogeneous catalysts

Introduction As a result of the massive exploitation of petroleum and its foreseeable depletion, the search for renewable resources is becoming increasingly urgent. 1 Biomass presents a promising example of a sustainable source of energy since it can be uti- lized to produce liquid fuels or fuel additives. 2 Particularly, levulinic acid esters (LAE) are a group of compounds with high potential for use, not only, in the fuel sector, 3–6 but also for polymers, 7–9 green solvents, 10 and fragrances. 11 LAE can be produced through a catalytic conversion of various lignocellulosic-derived intermediates (Scheme 1). 4 The direct conversion of polysaccharides in a one-pot reaction to LAE, although highly attractive, 12 is severely limited by the harsh conditions (e.g. 175 °C for 20 h) required to achieve this reac- tion. 13,14 The one-pot conversion of cellulose to methyl levulinate (ML) is the only example thus far. 15 Other studies have focused on mono- and disaccharides as starting mate- rial. 15,16 These sugars can be obtained through hydrolysis of polysaccharides 17 and less by-products and milder conditions are expected. LAE can be prepared from glucose through acid- catalysed dehydration via 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) and esterification in alcoholic medium. 18
Mehr anzeigen

6 Mehr lesen

Development of modified ZrO2 catalysts for the production of levulinic acid esters

Development of modified ZrO2 catalysts for the production of levulinic acid esters

Chapter 1 5 synthesis leading to the formation of larger pore opening, which is advantageous for catalysis [47–50]. Furthermore, the resulting ZrO2 crystal is highly influenced by the existence of SO4 2- ions. The addition of SO4 2- anions can reduce the particle size. Consequently, the unstable tetragonal phase will be predominately present in ZrO2 even at low temperatures. Indeed, the presence of anions can delay the particle growth during calcination. However, stabilized tetragonal zirconia can be transformed to monoclinic zirconia at a harsh calcination temperature of 800 °C due to sintering and agglomeration [51]. Although tetragonal ZrO2 is reported to be less acidic compared to monoclinic zirconia, the presence of SO4 2- ions appreciably increases its acidity. Ward et al suggested that a SO4 2- ion attached on a Zr atom can increase the ability of the adjacent Zr atoms to donate the proton [52]. In line, strong Brönsted acidity is generated. In contrast, a less coordinated Zr atom has a tendency to withdraw electrons, which is a characteristic of Lewis acidity as illustrated in Figure 1-1. One of the most crucial problems of using SZr is the instability during reaction and regeneration. During reaction, H2S is produced by SO4 2- reduction accompanied by coke production due to the formation of aromatics via dehydrogenation [12]. The carbon deposits covering the catalyst have to be removed via combustion with air oxygen accompanied by the conversion of SO4 2- to SO2. The addition of Pt on SZr (Pt-SZr) catalyst can facilitate H2 spillover which is able to reduce and remove carbonaceous deposit on the surface leading to higher catalyst stability. Additionally, Ebitani et al proposed that the dissociative H atom on Pt surface could migrate and transfer an electron to the Lewis acid sites (unsaturated Zr 4+ ) to form H + responsible to the enhanced Brönsted acidity [53,54]. Despite more stable SZr catalysts can be obtained by Pt doping, suitable alternatives possessing higher stability and facilitated regeneration are desirable.
Mehr anzeigen

120 Mehr lesen

Synthesis of 5-AminoIevulinic Acid 

Synthesis of 5-AminoIevulinic Acid 

T herefore, it is often used for biochem ical investiga­ tions and a sim ple synthesis would be useful. Till now , a number o f synthesis have been described, which are m ostly tim e-consum ing or result in difficult to clean product(s) (for a com plete list see [1 — 3]). Som e years ago, M cD onald [4] published the bromi- nation o f levulinic acid yielding 3-bromo- and 5-brom olevulinic acid which can be separated by dis­ tillation. We obtained 5-am inolevulinic acid from 5-brom olevulinic acid by a 2-step sequence (Gabriel- synthesis and hydrolysis) in 33% overall yield (Fig. 2).
Mehr anzeigen

2 Mehr lesen

Electrocatalytic upgrading of itaconic acid to methylsuccinic acid using fermentation broth as a substrate solution

Electrocatalytic upgrading of itaconic acid to methylsuccinic acid using fermentation broth as a substrate solution

Beside conventional chemo-catalysis, electrocatalysis poses an e fficient methodology for the production of bio-derived chemicals. 26–35 In this regard, in particular the hydrogenation (or reduction) of levulinic acid into valeric acid and γ-valerolactone reported by Nilges, Xin, Qiu and Dos Santos et al. revealed that electrochemistry represents a feasible tool for the effective and sustainable production of promising chemicals. 26,28,31,33 The mentioned reaction was carried out in aqueous acidic solutions and at room temperature, using Pb electrodes for high valeric acid selectivities and glassy carbon electrodes for high γ-valerolactone selectivities. 28 Among these electrochemical approaches also the mild electrosynthesis of 2,5-furandicarboxylic acid from HMF has received attention, as it does not require high temperatures and oxygen pressure. 29,36 The mild process conditions fulfil the major criteria of green chemistry and open a window of opportunity to integrate renewable electrical energy into biomass valorization.
Mehr anzeigen

8 Mehr lesen

Extracellular Production of Abscisic Acid by Soil Algae under Salt, Acid or Drought Stress 

Extracellular Production of Abscisic Acid by Soil Algae under Salt, Acid or Drought Stress 

was passed through a preconditioned (with m eth­ anol, water and 0.2 m acetic acid) Sep-Pak C18 cartridge (Millipore W aters, U.S.A.). The cartridge was washed with 0.2 m acetic acid and 10% MeOH; ABA was eluted with 5 ml of M eC )H -0.2M acetic acid (3:2, v/v). The eluate was evaporated at 35 °C with a stream of N 2, the residue was dissolved in 500 (il M eO H and used for ABA quantification by high perform ance thin layer chrom atography (H PTLC) and scanning densitom etry using TLC Scanner II by Cam ag (Switzerland).
Mehr anzeigen

4 Mehr lesen

Aspartic Acid-Aspartate and Glutamic Acid-Glutamate Hydrogen Bonds Having Great Proton Polarizability — IR Investigations 

Aspartic Acid-Aspartate and Glutamic Acid-Glutamate Hydrogen Bonds Having Great Proton Polarizability — IR Investigations 

The protected am ino acids N-benzyloxycarbonyl- aspartic acid-O -m ethylester (Z-asp-OM e) and N- benzyloxycarbonyl-glutamic acid-O -benzylester (Z- glu-OBzl) were obtained from the M ax-Planck- Institut für Biochemie, M artinsried, B undesrepublik Deutschland.

3 Mehr lesen

Studies of the Reaction of Various 1,2-Disubstituted Benzenes with Crotonic Acid in Polyphosphoric Acid 

Studies of the Reaction of Various 1,2-Disubstituted Benzenes with Crotonic Acid in Polyphosphoric Acid 

This work has been digitalized and published in 2013 by Verlag Zeitschrift für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative[r]

6 Mehr lesen

Chemistry of Fenchonesulfonic Acid Derivatives 

Chemistry of Fenchonesulfonic Acid Derivatives 

The application of derivatives of cam phor as chiral auxiliaries [1, 2] and starting m aterials [3-6] is a well investigated area in organic chemis­ try, and num erous reports on the general chemis­ try of this ketone exist. Surprisingly, only little work has been done on the isomeric fenchone (l,3,3-trimethylbicyclo[2.2.1]heptan-2-one) (1), al­ though it is available from the natural chiral pool in almost enantiom erically pure form as well. The main drawback, com pared with camphor, for the developm ent of its chemistry, is w ithout doubt the position of its carbonyl group betw een quaternary carbon atoms, first established by Semmler [7], which excludes derivatization in the a-position. Notew orthy among its reactions are the form ation of 3-isopropyl-toluene by treatm ent with phos­ phorus pentoxide above 100 °C [8], and of 3,4-di- m ethylacetophenone by heating with sulfuric acid [9]. The mechanism of the latter rearrangem ent has been elucidated by means of labeling with 14C and involves a primary 1,2-methyl shift of the car- bocation formed by protonation of the carbonyl group [10]. The isomeric cam phor is a by-product of this reaction. Thus, rearrangem ents can be ex­
Mehr anzeigen

6 Mehr lesen

Activation of the Glutamic Acid-Dependent Acid Resistance System in Escherichia coli BL21(DE3) Leads to Increase of the Fatty Acid Biotransformation Activity

Activation of the Glutamic Acid-Dependent Acid Resistance System in Escherichia coli BL21(DE3) Leads to Increase of the Fatty Acid Biotransformation Activity

Fatty acid biotransformation activity of E. coli BL21(DE3) pCOLA-RcsB-DsrA The effect of the GDAR system engineering on the whole-cell fatty acid biotransformation activity was investigated by conducting the bioconversion of ricinoleic acid (i.e., 12-hydroxyoc- tadec-9-enoic acid (1)) into n-heptanoic acid (5) and 11-hydroxyundec-9-enoic acid (4) ( S1 Scheme ), which was described in our previous study [ 15 ]. When ricinoleic acid was added into the culture broth of the recombinant E. coli BL21(DE3) pACYC-ADH, pET-BVMO, pCOLA or E. coli BL21(DE3) pACYC-ADH, pET-BVMO, pCOLA-RcsB-DsrA expressing the alcohol dehydrogenase (ADH) of Micrococcus luteus and the Baeyer-Villiger monooxygenase (BVMO) of Pseudomonas putida, the final product formation rates of the both cells were similar to at t < 4 h ( Fig 6 ). However, the final product formation rate of E. coli BL21(DE3) pACYC-ADH, pET-BVMO, pCOLA ceased resulting in an accumulation of the reaction intermediate (2) in the culture medium at t > 4 h, when the product concentration and bioconversion yield reached over 6 mM and 45%, respectively ( Fig 6A ). This might be ascribed to the toxicity of n- heptanoic acid ( Fig 5B ). In contrast, the final product formation rate of E. coli BL21(DE3) pACYC-ADH, pET-BVMO, pCOLA-RcsB-DsrA was further maintained resulting in a final product concentration of over 10 mM (conversion yield, 68%), which was 1.6-fold higher as compared to the E. coli BL21(DE3) pACYC-ADH, pET-BVMO, pCOLA. This value was also Fig 4. The relationship between GadA/B activity and cultivation pH (A) or n-heptanoic acid concentration (B). The GadA/B
Mehr anzeigen

20 Mehr lesen

Docosahexaenoic acid suppresses arachidonic acid-induced proliferation of LS
174T human colon carcinoma cells

Docosahexaenoic acid suppresses arachidonic acid-induced proliferation of LS 174T human colon carcinoma cells

In this context it has been proposed that the human genetic profile was originally established on a n-6 to n-3 PUFA ratio of approximately 1:1 as found in “ancient” diets, whereas today’s Western diet has been estimated to provide n-6 to n-3 PUFAs in a ratio of 15:1–20:1. It has been hypothesized that this may contribute to many serious health issues typically found in Western societies, including CRC. However, previous in vitro observations have led to some uncertainty regarding differential roles of n-3 and n-6 PUFAs in CRC cells. While the majority of investigations conducted in this field addressed neither the effects of n-6 PUFAs nor the impact of a balanced n-6 to n-3 PUFA ratio, several other studies reported n-3 and n-6 PUFAs to exert anti-cancerous effects in vitro. Hence, it was the aim of the present study to investigate the impact of n-3 PUFA docosahexaenoic acid (DHA) and n-6 PUFA AA and their combination on CRC cell line LS 174T in vitro.
Mehr anzeigen

82 Mehr lesen

Interaction of Ascorbic Acid with Disulfides 

Interaction of Ascorbic Acid with Disulfides 

observed binding o f several m olecules o f A H 2 to each BSA m olecule; SH blocking agents (e.g. / 7 -chlorom ercuri benzoate) p revented this. U sing EPR m ethodology, a spectrum was o b ta in e d w ith dithiobutyric acid (Fig. 2) w hich was id en tical to that generated by the b in d in g o f A H 2 w ith ce r­ tain biological m olecules [ 1 ] and w ith th e o th e r disulfides investigated. Since nitrogen is not present in dithiobutyric acid, it is reaso n ab le to assign the S - S group a role in the in te rm o lec u la r bo n d fo rm a ­ tion. This bond m ay be an in te rm e d ia te com plex sim ilar in type to th a t form ed betw een A and reduced glutathione, cysteine o r th ioglycolic acid [10]. In this case, D ra k e et al. h ad show n th a t w hen dehydroascorbic acid is red u ced to ascorbic acid in the presence o f SH groups, co n co m itan t o x id a tio n o f these SH groups occurs w ith the fo rm a tio n o f interm olecular com plexes.
Mehr anzeigen

3 Mehr lesen

Gutenberg Open Science: Branched and star copolymers based on poly(glycolic acid) and poly(lactic acid)

Gutenberg Open Science: Branched and star copolymers based on poly(glycolic acid) and poly(lactic acid)

4 to 9 glycolic acid units per arm, was adjusted via the monomer/OH group ratio. This strategy permits the incorporation of 13 to 62 wt% PGA into the copolymer. In general, poly(glycolide) and PEG themselves are purified by precipitation into a non‐common solvent (methanol for PGA, diethyl ether for PEG). Graft copolymers with high PEG content were soluble in methanol as well as the glycolide monomer. Precipitation into diethyl ether resulted in precipitation of both the monomer and the polymer. Therefore, precipitation in ethyl acetate was performed to ensure complete removal of residual glycolide monomer. Depending on the PEG/PGA ratio, the obtained graft copolymers were soluble in a broad range of solvents including methanol, water, dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF), indicating the absence of precipitated PGA homopolymer. Hence, the PEG block contributes to an increase in solubility of the graft copolymer via its hydrophilic character and the PG block gives access to higher incorporation of PGA molar content with limited chain length. The PEG precursors (Table 1, 1‐5) and the corresponding graft copolymers (Table 2, 1a‐5d) have been characterized with respect to their molar composition, molecular weight and polydispersity (M w /M n )
Mehr anzeigen

283 Mehr lesen

Itaconic acid production by ustilago maydis

Itaconic acid production by ustilago maydis

7KHXWLOL]DWLRQRIVHFRQGJHQHUDWLRQIHHGVWRFNIRUWKHSURGXFWLRQRIELRIXHOVRUELRFKHPLFDOVLV FKDOOHQJLQJ7KHK\GURO\VLVRIOLJQRFHOOXORVLFPDWHULDOWRJOXFRVHDQGRWKHUIUHHVXJDUV[r]

152 Mehr lesen

Itaconic acid production by ustilago maydis

Itaconic acid production by ustilago maydis

%HVLGHV WKHVH WUDQVSRUWHUV DOVR ZHDN H[SUHVVLRQ OHYHOV RU GLIIHUHQW SRVWWUDQVODWLRQDO PRGLILFDWLRQVHJJO\FRV\ODWLRQRIWKHIXQJDOELRV\QWKHWLFHQ]\PHVE\6FHUHYLVLDH[r]

152 Mehr lesen

Retinoic acid signaling after nerve injury

Retinoic acid signaling after nerve injury

trypsinated. The serum protease trypsin disrupts peptide chains of amino acid residues of L- arginine and L-lysine. Cells were incubated for about 2 min with 1.5 ml of a 0.25% trypsine/EDTA-solution at 37°C and cell disruption was controlled under a microscope. Again, serum terminated the enzymatic reaction. The cell suspension was transferred into 8 ml FCS containing medium and centrifuged. Pellet was resuspended in 1 ml of fibroblast- binding monoclonal anti-mouse Thy 1.1 antibody (Sigma M7898), diluted 1/40 in PBS, and 1 ml DMEM and incubated at 37°C for 30 min. Lyophilized baby rabbit complement (Linaris CL 3441), dissolved in 1 ml sterile water was added for another 30 min. Complement proteins bind to Thy 1.1 antibody labeled fibroblasts and induce the formation of pores in the cell membrane and by this lysis of the tagged cells. Lysis was blocked by adding serum containing medium. Pure Schwann cells were centrifuged, resuspended in 5 ml DMEM containing 10% FCS, 2 µM forskolin (ICN Biomedicals) and 100 µg/ml bovine pituitary extract (Invitrogen) and cultured in poly-L-lysine (Sigma) coated (200µg/ml in sterile water) T25-culture dishes. Confluent Schwann cells were expanded on poly-L-lysine coated T75-culture dishes with DMEM containing 10% FCS and 2 µM forskolin. Forskolin activates the adenylyl cyclase, thus raises the level of cyclic adenosine mono-phosphate (cAMP). During experiments cells were kept in medium without forskolin 24 hrs before RA treatment. Confirmation of Schwann cell identity was given by immunohistochemical staining with the S-100 antibody (Sigma).
Mehr anzeigen

84 Mehr lesen

Synthese des Indolalkaloids α-Cyclopiazonic Acid

Synthese des Indolalkaloids α-Cyclopiazonic Acid

Benzoesäureanhydrid (471 mg, 2.08 mmol) gelöst in DMF (1.6 ml) wird tropfenweise bei 0 °C unter Stickstoffatmosphäre über eine Glasspritze zugegeben und die Reaktion anschließend noch [r]

214 Mehr lesen

Therapeutic drug monitoring of mycophenolic acid

Therapeutic drug monitoring of mycophenolic acid

high MPAG exposure in plasma. The function of MRAP-2 is not only the excretion of MPAG into the bile but also other endogenous (e.g. Bilirubin) and exogenous (e.g. diclofenac and valproic acid) conjugates. CsA is clinically relevant because it can reduce the MPA exposure upto 30-40% and it is nephrotoxic [27, 60]. In a 2-year, randomized study, L Frimat et al showed an improvement in the kidney function without increasing the risk for graft rejections on 50% CsA dose reduction in combination with MMF [24]. There also exists a recommendation to measure MPA plasma levels dependent on co-mediaction, such as CyA or Tacrolimus. According to Shaw LM et al and if MPA is prescribed together with CyA, the trough MPA levels should range between 1.0-3.5 μg/mL. The AUC target is between 30-60 μg*h/mL [67] after renal or heart transplantation. And if prescribed together with Tacrolimus then trough levels differ a lit bit (> 1.9 ug/mL) [71].
Mehr anzeigen

65 Mehr lesen

Show all 1141 documents...