Hydroxyl Groups Of Glycerol Research Articles

Cooperativity of Brønsted and Lewis Acid Sites on Zeolite for Glycerol Dehydration

Selective dehydration of glycerol, a byproduct from the biodiesel industry, on solid acids is an important reaction in the production of the value-added chemical acrolein for economic-sustainable biorefinery. Most efforts have been made on the development of strong Brønsted acid sites (BAS) to improve the production of acrolein, because the Lewis acid sites (LAS) generally promote the generation of the byproduct acetol. However, exclusively tuning the properties of BAS or LAS did not well-promote the acrolein production from glycerol as indicated in this work. We provide a new route for efficient and selective glycerol transformation to acrolein via the cooperative dehydration between the BAS and LAS. The role of LAS (extra-framework aluminum species on zeolites) was altered from competition with BAS to generate the byproduct acetol to cooperation with the neighboring BAS. It is very beneficial for the sequential two-step dehydration of the internal and terminal hydroxyl groups of glycerol to value-added acrolein. This cooperativity of BAS and LAS significantly improved the yield of acrolein from the selective glycerol dehydration.

Collisions of Sodium Atoms with Liquid Glycerol: Insights into Solvation and Ionization

The reactive uptake and ionization of sodium atoms in glycerol were investigated by gas-liquid scattering experiments and ab initio molecular dynamics (AIMD) simulations. A nearly effusive beam of Na atoms at 670 K was directed at liquid glycerol in vacuum, and the scattered Na atoms were detected by a rotatable mass spectrometer. The Na velocity and angular distributions imply that all impinging Na atoms that thermally equilibrate on the surface remain behind, likely ionizing to e(-) and Na(+). The reactive uptake of Na atoms into glycerol was determined to be greater than 75%. Complementary AIMD simulations of Na striking a 17-molecule glycerol cluster indicate that the glycerol hydroxyl groups reorient around the Na atom as it makes contact with the cluster and begins to ionize. Although complete ionization did not occur during the 10 ps simulation, distinct correlations among the extent of ionization, separation between Na(+) and e(-), solvent coordination, and binding energies of the Na atom and electron were observed. The combination of experiments and simulations indicates that Na-atom deposition provides a low-energy pathway for generating solvated electrons in the near-interfacial region of protic liquids.

Effect of glycerol on the preparation of phosphogypsum-based CaSO4·0.5H2O whiskers

Phosphogypsum-based CaSO4·0.5H2O whiskers were successfully prepared in the presence of glycerol by hydrothermal method. The action mechanism of glycerol on the morphology of CaSO4·0.5H2O whiskers was investigated and discussed in detail. The as-prepared products were characterized by X-ray powder diffraction spectrometer, scanning electron microscopy, Fourier transform infrared spectrometer, and thermal analyzer. The main phase of the as-prepared products was CaSO4·0.5H2O, and the morphology was uniform fiber. Moreover, the aspect ratio and productivity of the as-prepared CaSO4·0.5H2O whiskers increased with the concentration of glycerol. Even whiskers with mean length of 38–83 μm, mean width of 1.33–0.73 μm, aspect ratio of 29–118, and productivity of 89–96 % were obtained under the condition of glycerol/water volume ratio of 10–100 %. As far as mechanism was concerned, the hydroxyl groups of glycerol adsorbed and occupied the vacancies of Ca sites on (001) plane of CaSO4·0.5H2O whiskers, and however, on (100) plane, hydroxyl groups of glycerol adsorbed mainly on Ca sites and formed hydrogen bond layered structure on both sides of that, which should be the reason that CaSO4·0.5H2O whiskers grew along the c-axis observed in this study.

Highly Improved Thermal Properties of Hydroxyl‐Containing Polymers via Modification by Benzoxazine Groups

AbstractIsocyanate functional benzoxazine (NCO‐4HBA‐a) is used for coupling with hydroxyl‐group‐containing molecules. Glycerol is used in a model reaction to study the urethane bonds formed between the NCO‐4HBA‐a and the glycerol's hydroxyl groups. The model supports a reaction between NCO‐4HBA‐a and poly(vinyl alcohol) (PVA), which leads to an improved char yield, determined by thermogravimetric analysis. Glycerol‐based benzoxazine is also an attractive benzoxazine synthesized from the products of biofuel production. Upon functionalization with benzoxazine and subsequent thermal treatment, the hydroxyl‐containing polymer gains thermal stability shown by improved char yield of polybenzoxazine cross‐linked PVA.magnified image

Synthesis and Characterization of Picket Porphyrin Receptors That Bind Phosphatidylglycerol, an Anionic Phospholipid Found in Bacterial Membranes

The lipid binding ability of four urea-picket porphyrins designed to bind to both the phosphate anion portion as well as the glycerol hydroxyl groups of phosphatidylglycerol (PG) has been investigated. Isothermal titration calorimetry (ITC) and (1)H NMR were used to determine the receptor's stoichiometry of binding, association constants, and both the enthalpy and entropy of binding with the PG anion. Spectral evidence shows that the phosphate anion portion of PG is hydrogen bonded to the urea groups of the receptors. This binding interaction orients the PG anion in the receptor pocket such that its glycerol hydroxyl groups can align with a third urea picket, and results are furnished that suggest this multifunctional interaction does occur. The structure of the entire picket was found to influence the enthalpy and entropy of lipid binding. The synthesis of tetrabutlyammonium phosphatidylglycerol (TBAPG), and a detailed spectral characterization of its headgroup, is also presented.

Study of Micro-Arc Oxidation Process in Magnesium Surface

This study selected sodium silicate, sodium fluoride, glycerol hydroxyl acid, potassium hydroxide and phosphine oxide (LAP) as the stabilizer electrolyte, and then on micro-arc oxidation of magnesium with constant current density. The microstructure, corrosion resistance, chemical composition, structure and characterization of micro-arc oxidation film were determined by SEM and anodic oxidation methods. Experimental results indicated that the test pieces of magnesium would formed an silver-gray uniform densification oxide film on the surface by micro-arc oxidation treatment, and the corrosion resistance of magnesium film-formed had increased by potentiodynamic polarization curve testing.

Novel Tetraspiroorthocarbonates as Successful Anti-shrinking Agents for the Photopolymerization of Epoxy Monomers

A pair of novel tetrafunctional spiroorthocarbonates (TETRASOC) was prepared in three stages. First, glycerol was reacted with tetraethyl orthocarbonate to form a pair of isomeric hemi spiroorthocarbonates (HEMI SOC-OLs) by monocyclization of glycerol. Formation of these two isomers depends on terminal or adjacent hydroxyl groups of glycerol reacting with the tetraethylorthocarbonate to form five and six-membered ring HEMI SOC-OLs. Second, the HEMI SOC-OLs were made to undergo another cyclization reaction by reacting with 1,3-propanediol, to form a pair of spiroorthocarbonates with one hydroxyl group (SOC-OL). In the third stage, the SOC-OL was used as nucleophylic reactant to displace the bromine atom of pentaerythritol bromide to form the final product TETRASOC. A volume change study was carried out to determine the efficiency of TETRASOC as an anti-shrinking additive finding that even at a low concentration of 7 mol%, it caused a 2.18% expansion of the polymeric volume of a bis epoxycyclohexane monomer (3,4-EP). Dynamic Mechanical Analysis (DMA) determined that the flexibilization induced by the TETRASOC in the polyether derived from 3,4-EP did not adversely impact the mechanical properties of the polymer.

Novel Process for 1,3-Dihydroxyacetone Production from Glycerol. 1. Technological Feasibility Study and Process Design

A novel and efficient conversion process of glycerol to 1,3-dihydroxyacetone (DHA) via indirect oxidation was developed. The idea is to oxidize the middle hydroxyl group of glycerol to a carbonyl group with the help of a group protection technique, and then the protection reagent is removed by hydrolysis. With this new process, the conversion is conducted in three steps, namely, acetalization, oxidation, and hydrolysis. The oxidation step is the focus of this conversion process. In our work, three oxidant systems (CrO3 anion resin oxidant system, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)/NaBr/NaClO system, and TEMPO/NaBr/Air system) were experimentally examined to verify the feasibility of this new process. The process of this conversion is also preliminarily designed on the basis of the laboratory procedure described in the experimental section, which offers a potential foundation for the large-scale production of DHA from glycerol.

Outlook on the Phase Equilibria of the Innovative System of “Protected Glycerol”: 1,4-Dioxaspiro[4.5]decane-2-methanol and Alternative Solvents

Fundamental data on 1,4-dioxaspiro[4.5]decane-2-methanol are scarce. This work presents the foremost systematic data on the solubility of 1,4-dioxaspiro[4.5]decane-2-methanol in sustainable solvents such as water and ionic liquids accompanied by the interpretation of interactions occurring in such binary systems. 1,4-Dioxaspiro[4.5]decane-2-methanol, here called protected glycerol, has been synthesized in order to protect the two hydroxyl groups of glycerol, thus avoiding the formation of side products in a specific process. A series of imidazolium salts accompanied by pyridinium, phosphonium, and ammonium ones with various types of counterions were used in this study. The liquid-liquid and solid-liquid equilibrium measurements in binary systems were carried out by using a dynamic method at atmospheric pressure over the temperature range from 273.00 to 378.30 K or below the boiling point of the solvent. Among all tested sustainable solvents, protected glycerol exhibited limited solubility, with only a few of them in the temperature range studied. The majority of the examined ionic liquids, either hydrophilic or hydrophobic, showed complete miscibility with this monohydroxyol. The Fourier-transform infrared (FTIR) spectroscopy studies of solute and solvents showing a miscibility gap and of their mixtures were performed to obtain insight into major inter- and intramolecular interactions in the investigated systems. Furthermore, the differential scanning calorimetry was used for the first time to determine the melting point, the enthalpy of melting, and the temperature and enthalpy of the solid-solid phase transition of 1-allyl-3-methylimidazolium chloride [Amim][Cl]. The results for the solubility of protected glycerol in sustainable solvents can be used to design future alternative reactions, such as telomerization with protected glycerol in ionic liquids for more specific building blocks and extraction/or separation that involves these mixtures.

On-line concentration and separation of cationic and anionic neurochemicals by capillary electrophoresis with UV absorption detection

This paper presents on-line simultaneous concentration and separation of cationic and anionic neurochemicals by capillary electrophoresis (CE) with UV absorbance spectroscopy. Neurochemical stacking exploits differences in local electric field and viscosity between the sample zone and the background electrolyte (BGE). To achieve these discontinuous conditions for CE, neurochemicals were prepared in a solution containing 1mM formic acid and 20% (v/v) acetonitrile (ACN). The capillary was filled with a solution of 500mM Tris–borate (TB) and 10% (v/v) glycerol. The buffer vial contained 500mM TB and 0.5% (v/v) polyethylene oxide (PEO). After injecting a large sample volume, PEO enters the capillary by electro-osmotic flow (EOF). Anionic neurochemicals stacked at the sample zone and PEO-containing BGE boundary. Simultaneously, cationic neurochemicals were concentrated at the boundary between the sample zone and the glycerol-containing BGE. The concentrated cationic neurochemicals were baseline separated in the presence of glycerol, mainly due to hydrogen bonding interactions between glycerol hydroxyl groups and the neurochemical's hydroxyl and amino groups. Under optimal stacking conditions, we observed the following: (a) the maximum sample injection volume was 720nL; (b) the limit of detection for signal-to-noise ratio of 3 ranged from 14.7 to 313.4nM; and (c) sensitivity enhancements compared to normal injection (15nL) ranged from 116 to 281-fold. We evaluated the proposed method by the determination of neurochemicals in urine samples.

Process advantages and product benefits of interesterification in oils and fats

The physical properties of oils and fats depend on their chemical properties, such as unsaturation, saturation, chain length, and distribution of the three hydroxyl groups of glycerol in the fatty acids. These characteristics change by hydrogenation, fractionation, blending, and interesterification (IE), hence improving the spectrum for the application of the oils and fats. IE is a process where the fatty acids have been moved from one triglyceride molecule to another and it does not alter the fatty acids. IE (chemical and enzymatic) is used to deal with the problems of plastic fat products such as granular development, texture breakdown, lumpy appearance, post hardening, consistency, melting point, and rancidity and create oil more suitable for deep frying or making margarine with good taste and low content of saturated fatty acids, etc. Nutritionally, IE contributes in eliminating or reducing trans fatty acids, providing a higher essential fatty acid activity. Trans and hydrogenated fats increase the coronary heart disease risk factors.

Preparation and properties of starch-based biopolymers modified with difunctional isocyanates

The present work reports on the preparation of thermoplastic starch (TPS) modified in situ with a diisocyanate derivative. Evidence of the condensation reaction between the hydroxyl groups of starch and glycerol with the isocyanate function (NCO) was confirmed by FTIR analysis. The evolution of the properties of the ensuing TPS, in term of mechanical properties, microstructure, and water sensitivity, was investigated using tensile mechanical, dynamic mechanical thermal analysis (DMTA), X-ray diffraction (XRD), and water uptake. The results showed that the addition of isocyanate did not affect the crystallinity of the TPS and slightly reduced the water uptake of the material. The evolution of the mechanical properties with ageing became less pronounced by the addition of the isocyanate as their amount exceeded 4 to 6wt%.

Kinetically controlled synthesis of monoglyceryl esters from chiral and prochiral acids methyl esters catalyzed by immobilized Rhizomucor miehei lipase

Partial acylation of only one primary hydroxyl group of glycerol generates a chiral center at position 2. Rhizomucor miehei lipase (RML) catalyzes the kinetically controlled transesterification of different aromatic carboxylic acids methyl esters with glycerol. High synthetic yields of glyceryl esters (around 70-80%) were obtained even in the presence of significant concentrations of water (from 5% to 20%). After a long incubation of the reaction mixture in the presence of the biocatalyst only pure free acid was obtained. Other lipases (from Geobacillus thermocatenulatus and from Thermomyces lanuginose) also catalyzed similar kinetically controlled transesterifications although less efficiently. RML immobilized on Sepharose-Q showed a high activity and specificity, compared to the immobilization by other techniques, only producing monoglyceryl esters with all substrates. In particular, monoglyceryl-phenylmalonate product was synthesized in 82% overall yield and >99% diastereomeric excess at pH 7.0 and 37°C and 90% glycerol.

Phase equilibria modeling of biodiesel related mixtures using the GCA-EoS model

In this work, a group-contribution equation of state that takes into account association effects (GCA-EoS) is extended to model the phase behavior of fatty esters (biodiesel) in binary mixtures with glycerol, alcohols and water and ternary mixtures with glycerol and methanol. A new associating group (glycerol hydroxyl group: OH Gly) was defined to take into consideration the association effects in the glycerol molecule. Self-association of methanol, water and glycerol and cross-association between methanol–glycerol, alcohol–ester, water–ester and glycerol–ester groups were considered. New pure-group, binary interaction and association parameters have been determined. The correlations and predictions of the model are found in acceptable agreement with selected experimental data reported in the literature.

Biocatalytic Approach for the Synthesis of Glycerol‐Based Macroamphiphiles and their Self‐Assembly to Micellar Nanotransporters

AbstractGlycerol is one of the most versatile and valuable chemical substances and is utilized in a variety of commercial products with no known adverse pharmacological or environmental effects. Moreover, it exhibits good chemical stability and inertness under biological conditions. We have designed and developed Candida antarctica lipase (CAL B) catalyzed biocatalytic method to synthesize novel polymeric systems using glycerol and poly[ethylene glycol bis(carboxymethyl) ether] dimethylester. Both synthons are biocompatible, non‐toxic, and are readily available. The polymerization occurs regioselectively through the primary hydroxyl groups of glycerol leaving the secondary hydroxyls for post‐polymerization chemical modifications and also for attaching drugs/bioactive molecules. We have utilized these sites for the synthesis of amphiphilic polymers by attaching alkyl chains at the secondary hydroxyl groups simply by acylation. The drug encapsulation abilities of the resulting polymers have been evaluated for potential biomedical applications.magnified image

Flexible cross-linking of shape memory polyurethane by a long polyethyleneglycol spacer

Flexible linking of shape memory polyurethane (SMPU) was tried with a long polyethyleneglycol (PEG) spacer (PEG-600 or PEG-1000) longer than the one tested before (PEG-200). The SMPU was composed of MDI, polytetramethyleneglycol (PTMG), 1,4-butanediol (BD), glycerol, and PEG as a spacer. PEG connected the glycerol hydroxyl group of polyurethane chain via MDI as a connecting agent. Significant increase in both maximum stress and strain at break was attained simultaneously, because of the flexible structure of PEG. Especially, it was shown in the stress-strain curve that the PEG-linked SMPU showed similar behavior and superior tensile mechanical properties to natural rubber. Shape recovery of the PEG-linked SMPU went up to 96 %, and shape retention remained low compared to linear one. PEG-1000 was better than PEG-600 in enhancing the overall tensile strength and shape memory of SMPU.

Theoretical Study on the Role of Surface Basicity and Lewis Acidity on the Etherification of Glycerol over Alkaline Earth Metal Oxides

Alkaline earth metal oxides (MO) are catalytically active in the etherification of glycerol. Density Functional Theory (DFT) calculations have been used to examine the reactivity of glycerol with MO surfaces with M=Mg, Ca, Sr or Ba. More specifically, the optimum glycerol adsorption mode and the strength of glycerol interaction with regular MO (001) surfaces and a stepped CaO surface have been investigated and involves the interaction with acid-base surface sites. The basicity of lattice oxygen atoms is correlated with the adsorption energy: BaO (-3.02 eV) > SrO (-2.85 eV) > CaO (-2.05 eV) > MgO (-1.35 eV). The interactions have an exothermic character, that is, the more basic the alkaline earth metal oxide, the more exothermic is the adsorption process and the higher the dissociation extent. Thus, the dissociation of glycerol increases in the order: MgO (not dissociated) < CaO (partially dissociated < SrO (partially dissociated) < BaO (completely dissociated). The presence of defects is found to play a key role in the mechanism: glycerol interaction with a stepped CaO surface presents the highest adsorption energy (-3.78 eV), and the molecule is found to dissociate at the step. The calculated structural parameters are found to be in good agreement with experimental data on catalyst reactivity. Moreover, the earlier postulated reaction mechanism, which also involves the additional involvement of Lewis acid sites proved to be feasible for CaO and SrO regular surfaces, and for the stepped CaO surface. It was found that for these oxides one of the most favored adsorption modes involves a non-dissociative adsorption of one hydroxyl group of glycerol, which as a result becomes a better leaving group. Therefore, theoretical evidence was found for the possible direct involvement of Lewis acid sites in the catalytic etherification of bio-derived alcohols, such as glycerol, as it is anticipated that these observations can be extended to sugar alcohols as well.

Detection and Quantification of Free Glycerol in Virgin Olive Oil by 31P‐NMR Spectroscopy

Abstract31P‐Nuclear magnetic resonance (NMR) spectroscopy was employed to detect and quantify free glycerol in virgin olive oils originating from various regions of Greece. This analytical method was based on the derivatization of the hydroxyl groups of glycerol with the tagging reagent 2‐chloro‐4,4,5,5‐tetramethyldioxaphospholane, and identification of the phosphitylated compound on the basis of 31P chemical shifts. Quantification of glycerol in olive oils was accomplished by integration of the appropriate signals in the 31P NMR spectrum and the use of the phosphitylated cyclohexanol as internal standard. A linear correlation was observed between the glycerol content and 1,3‐diacylglycerols and free acidity indicating that glycerol is the final product of the partial hydrolysis of triacylglycerols.

Trafficking pathways of mycolic acids: structures, origin, mechanism of formation, and storage form of mycobacteric acids

Mycolic acids, the hallmark of mycobacteria and related bacteria, are major and specific components of their cell envelope and essential for the mycobacterial survival. Mycobacteria contain structurally related long-chain lipids, but the metabolic relationships between these various classes of compounds remain obscure. To address this question a series of C(35) to C(54) nonhydroxylated fatty acids (mycobacteric acids), ketones, and alcohols structurally related to the C(70-80) dicyclopropanated or diethylenic mycolic acids were characterized in three mycobacterial strains and their structures compared. The relationships between these long-chain acids and mycolic acids were established by following the in vivo traffic of (14)C labeled alpha-mycolic acids purified from the same mycobacterial species. The labeling was exclusively found in mycobacteric acids. The mechanism of this degradation was established by incorporation of (18)O(2) into long-chain lipids and shown to consist in the rupture of mycolic acids between carbon 3 and 4 by a Baeyer-Villiger-like reaction. We also demonstrated that mycobacteric acids occur exclusively in the triacylglycerol (TAG) fraction where one molecule of these acids esterifies one of the three hydroxyl groups of glycerol. Altogether, these data suggest that these compounds represent a pathway of metabolic energy that would be used by mycobacteria in particular circumstances.

Phosphitylation and quantitative 31P NMR analysis of partially substituted biodiesel glycerols

The main step during biodiesel production is the catalytic transesterification of triglycerides. Glycerol and fatty acids are by-products of the biodiesel production and considered as contaminants in the final product. By selectively measuring the amount of fatty acids and glycerol with different substitution levels, the yield of this step and the quality of the final biodiesel can be determined. This study examines the application of phosphitylation of glycerol hydroxyl groups with 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane followed by 31P NMR analysis to provide a rapid quantitative analytical technique for the determination of substitution patterns on partially esterified glycerols, alcohols and the detection of fatty acids. 31P NMR chemical shift data was established with a series mono and di-substituted esters of glycerol, fatty acids and alcohols, then utilized to characterize commercial glycerol and biodiesel samples.