Applications of protecting groups in the synthesis of surfactants, lipids, and related compounds

Several types of alkyl ether lipids were prepared in high yield and high purity using protecting groups such as 1,3-dioxolane compounds or allyl ethers. We also succeeded in the industrial production of alkyl glyceryl ethers using the reaction of alkyl glycidyl ethers with acetone to give 1,3-dioxolane compounds, from which the desired alkyl glyceryl ethers were obtained in high quantities. 1,3-Dioxolane (ketal) compounds based on acetone were used in the enzymatic preparation of monoglyceride on an industrial scale. On the basis of these protecting groups, we extended our studies concerning both the preparations and properties of novel polyol ether compounds, beginning with alkyl glycidyl ethers. Another typical property of surfactants containing 1,3-dioxolane units and acetal is degradability under acidic conditions. Several types of destructible/cleavable surfactants based on polyols, such as carbohydrates and polyethyleneglycol, were prepared. As for natural products containing polyol skeletons, much attention has been paid to their molecular design, in which protecting groups such as 1,3-dioxolane compounds or allyl ether have contributed to synthetic strategies.     

Brominative Deoxygenation of some aldehydes and ethers

Three aldehydes ( 4a–c ) are transformed into 1,1-dibromides ( 6a–c ) by 2,2,2-tribromo-2,2-dihydro-1,3,2-benzodioxaphosphole ( 2 ). This reagent ( 2 ) is also very active in the cleavage of ethers; its reactions may show some features of carbonium as well as of S_N2 character.     

Cyclic ureas as solvents for poly(aryl ether) synthesis

Summary The synthesis of various poly(aryl ethers) and related small molecule compounds were examined using the cyclic urea 1,3-Dimethyl-3,4,5,6-tetrahydro-2(IH)-pyrimidinone (N,N′-dimethylpropylene urea, DMPU) as the solvent. The results showed that generally higher molecular weight or yields were obtained under less stringent conditions, as compared to other common polymerization solvents. The enhancement was most notable for polymerizations involving aryl fluorides with a lower reactivity than conventionally activated dihalide monomers, e.g. ketones, sulfones. Poly(aryl ethers) displayed excellent solubility in DMPU, which was beneficial in the cases where more rigid heterocyclic-aryl ether polymers are formed.     

Molecular dynamics study on growth of carbon dioxide and methane hydrate from a seed crystal

In the current work, molecular dynamics simulation is employed to understand the intrinsic growth of carbon dioxide and methane hydrate starting from a seed crystal of methane and carbon dioxide respectively. This comparison was carried out because it has relevance to the recovery of methane gas from natural gas hydrate reservoirs by simultaneously sequestering a greenhouse gas like CO₂. The seed crystal of carbon dioxide and methane hydrate was allowed to grow from a super-saturated mixture of carbon dioxide or methane molecules in water respectively. Two different concentrations (1:6 and 1:8.5) of CO₂/CH₄ molecules per water molecule were chosen based on gas–water composition in hydrate phase. The molecular level growth as a function of time was investigated by all atomistic molecular dynamics simulation under suitable temperature and pressure range which was well above the hydrate stability zone to ensure significantly faster growth kinetics. The concentration of CO₂ molecules in water played a significant role in growth kinetics, and it was observed that maximizing the CO₂ concentration in the aqueous phase may not result in faster growth of CO₂ hydrate. On the contrary, methane hydrate growth was independent of methane molecule concentration in the aqueous phase. We have validated our results by performing experimental work on carbon dioxide hydrate where it was seen that under conditions appropriate for liquid CO₂, the growth for carbon dioxide hydrate was very slow in the beginning.     

New aspects in acceleration of glycidyl ether oligomerization by imidazole compounds

Summary Using simple model compounds the oligomerization of glycidyl ethers accelerated by imidazole and imidazole derivatives was investigated. The formation of oligomers depending on 1,3-diphenoxy-2-hydroxypropane as their starting compound was predominant.In the case of imidazole 1,2-dihydroxy-3-phenoxypropane and the resulting oligomers are further formed. It seems to be obvious that this reaction also occurs in the absence of water.An over-all reaction mechanism including both the main products of the glycidyl ether oligomerization formed and the different imidazole compounds investigated is proposed.     

Hydrogen bond activation strategy for cyclic carbonates synthesis from epoxides and CO2: current state-of-the art of catalyst development and reaction analysis

Chemical fixation of CO₂ into useful organic compounds has been attracting much attention from the viewpoint of CO₂ emission reduction and energy structure reformation. A useful and widely investigated chemical utilization of CO₂ is the cycloaddition of CO₂ to epoxides for the synthesis of cyclic carbonates. Efforts have been paid to the design and preparation of various catalyst systems that are active and selective to the production of the desired products under mild conditions and in green processes. This article is to review the current state of the catalyst development and the experimental and theoretical analysis of reaction mechanism for the cyclic carbonate synthesis from epoxides, one of currently important reactions involving CO₂ as a reactant with 100% atom economy. Particular attention is given to the catalysis of multifunctional catalyst systems such as metal- and hydrogen-bond donor (HBD)-based catalysts.     

Preparation of 1,3-diacylglycerols and 1-alkyl-3-acylglycerols in the presence of quaternary ammonium salt

A series of symmetrical and racemic 1,3-diacylglycerols and 1-alkyl-3-acylglycerols were prepared simply, and in high yields, by the reaction of carboxylic acids with glycidyl esters or glycidyl ethers in the presence of quaternary ammonium salt. The effect of reaction conditions on the yield, the ratio of 1,3- and 1,2-diacylglycerols, and the stability of 1,3-diglycerides are also discussed.     

3,5-二氯-α-(三氟甲基)苯乙烯合成工艺的改进

以3,5-二氯溴苯为起始原料,在镁和二异丁基氢化铝等条件下制成格氏试剂后,再与三氟乙酸乙酯发生取代反应制得3',5'-二氯-2,2,2-三氟苯乙酮。然后,3',5'-二氯-2,2,2-三氟苯乙酮与甲基三苯基碘化磷在叔丁醇钾作用下发生Witting反应,制得标题化合物。通过对3',5'-二氯-2,2,2-三氟苯乙酮和标题化合物进行IR、MS、UV、1HNMR和13CNMR等表征,确认了化合物的结构。该合成路线具有操作简单、反应条件温和、原料易得、绿色环保、成本低等优势。     

Developing a molecular platform for potential carbon dioxide fixing

This paper presents an attempt to develop a new system for fixing carbon dioxide from the atmosphere. The proposed molecular system has been designed to have the capacity to spontaneously bind CO₂ from the atmosphere with high affinity. The molecular system is furthermore designed to have the ability to liberate CO₂ at a later stage in the process, i.e., in a separate compartment. The liberated CO₂ presents a carbon neutral way of obtaining pure CO₂. The proposed molecular system is based on a small stable organic molecule that potentially have two forms: one without bound CO₂ and one with bound CO₂. One class of molecules that undergo a reaction compatible with our purposal is the merocyanine dyes that exhibit photochromic properties. Based on this structural class of molecules, a system for the potential fixing of CO₂ has been developed.     

Phase Behavior of Supercritical CO2 Microemulsion with AOT and its Solubilization Properties of 1,3-propanediol

The phase behaviors of three microemulsion systems were studied in a custom-made volume-variable view cell, including the ternary system of CO₂/EtOH (ethanol)/1,3-PDO (1,3-propanediol), quaternary system of CO₂/EtOH/H₂O/1,3-PDO and quinary system of AOT/CO₂/EtOH/H₂O/1,3-PDO, using 1,3-PDO as the model compound, AOT (sodium bis(2-ethylhexyl) sulfosuccinate) as surfactant and ethanol as co-solvent in the CO₂ continuous phase. The phase behaviors of the AOT/CO₂/EtOH/H₂O/1,3-PDO quinary system were mainly discussed in the temperature range of 29.1°C–44.3°C and pressure range of 6.41 MPa-15.95 MPa. The result shows that a thermodynamically stable microemulsion can be formed by controlling the operating pressures and temperatures, which can provide basic thermodynamics data for industrial design and proper operating conditions for selectively solubilizing 1,3-PDO from dilute aqueous solution.     

Generation of microcellular polyurethane foams via polymerization in carbon dioxide. I: Phase behavior of polyurethane precursors

On investigating the generation of microcellular polyurethane foam via reaction in carbon dioxide, we have observed that common polyurethane precursors are CO₂ miscible, whereas typically fluorinated compounds or specially designed surfactants are needed to solubilize polymers in CO₂. Both isocyanates and polyols are CO₂-miscible at workable pressures and temperatures and in useful concentrations to allow generation of polyurethane foams in CO₂. By characterizing the phase behavior of several series of propylene oxide and ethylene oxide polyols, we have observed that the combined effects of molecular weight and hydroxyl number fix the location of the phase separation pressures. In general, lower molecular weights and lower hydroxyl mole fractions produce phase boundaries at relatively lower pressures in carbon dioxide. It also has been shown that CO₂-soluble compounds may have a com̀patibilizing effect on less CO₂-soluble materials.     

Interfacial Tension of CO2 and Organic Liquid under High Pressure and Temperature

In order to investigate the effect of organic liquid molecular structure and the intermolecular force operating with CO₂ molecules and organic liquid molecules on interfacial tension (IFT) between CO₂ and organic liquid at the first contact, the interfacial tension between CO₂ and hexane, octane, ethanol and cyclohexane at different temperatures and pressures is measured by using the pendant drop method and the axisymmetric drop shape analysis (ADSA). The results show that the interfacial tension between CO₂ and organic liquids is affected by the polarity and the structure of the organic liquid molecule obviously. The intermolecular force operating within CO₂ molecules or organic liquid, and that between CO₂ and organic liquids molecules play a dominate role on the interfacial tension between CO₂ and the organic liquids.     

新型卡宾前体1, 3-二取代-2-羧基咪唑(啉）

性质稳定的1,3-二取代-2-羧基咪唑（啉）（NHC－CO₂）是一类重要的卡宾前体,以3条路线合成了一系列含有不同取代基结构的NHC-CO₂。通过核磁共振（¹H NMR）、元素分析以及红外光谱（IR）对产物进行了结构表征。利用热重/微商热重分析（TG/DTG）对产物的热脱羧性能进行了研究。结果表明：随着温度升高,NHC-相似文献   

Synthesis of 2-imino-1,3-dithiolanes containing trimethylsilylethynylthiolato groups

An efficient, eco-friendly, and simple one-pot approach for the synthesis of 2-imino-1,3-dithiolanes via reaction of allyl chloride, primary amines, carbon disulfide, and I₂ under solvent-free conditions is presented. The obtained 5-iodomethyl-2-imino-1,3-dithiolanes were converted into silyl-protected terminal alkynyl sulfides substituted 2-imino-1,3-dithiolanes by treatment with lithium 2,2,2-tris(trimethylsilyl)ethanedithioate, produced by the reaction of tris(trimethylsilyl)methyllithium (TsiLi) with CS₂.     

Sequestration of CO2 using microorganisms and evaluation of their potential to synthesize biomolecules

ABSTRACT

Microalgae are the unicellular or multicellular photosynthetic microorganisms that can efficiently fix carbon dioxide (CO₂) from various sources such as the environment, industrial flue gas, and some carbonate salts. In the present study, one green microalgal strain and a cyanobacterial consortium were used separately for the sequestration of CO₂ at different pHs (7–11), at different initial concentrations of CO₂ (5–20%), and at various inoculum sizes (5–12.5%). The maximum sequestration of CO₂ was found to be 74.37 ± 0.49% and 71.12 ± 0.05% at 5% and 15% CO₂ for green algae and cyanobacterial consortium. The biomass generated after sequestration of CO₂ was utilized for the synthesis of biomolecules.     

Assessment of the flotation activity of reagents in terms of the hydrogen bond energy in molecular complexes with active sites of the coal surface

The hydrogen bond energy of molecular complexes between a flotation reagent and coal’s organic mass is calculated for the first time. The electron density distribution in molecules of 2-methyl-1,3-dioxane and 2-methyl-1,3-dioxa-2-silacyclohexane is determined. It is shown that the silicon atom in the molecule of 2-methyl-1,3-dioxa-2-silacyclohexane increases the electron density at oxygen atoms from ?0.279 to ?0.424 and ?0.432 in positions 1 and 3 of the molecule, respectively. This increases the hydrogen bond energy of the reagent in molecular complexes with water and model compounds of the coal’s organic mass. In molecular complexes of 2-methyl-1,3-dioxa-2-silacyclohexane with model compounds of the coal’s organic mass, the hydrogen bond energy is considerably higher than in corresponding complexes of 2-methyl-1,3-dioxane. As a result, the adsorption of 2-methyl-1,3-dioxa-2-silacyclohexane on the coal surface is 35–45% greater than for 2-methyl-1,3-dioxane. Consequently, the coal grains become more hydrophobic, and their flotation is improved. With the same consumption of reagents, the use of 2-methyl-1,3-dioxa-2-silacyclo-hexane rather than 2-methyl-1,3-dioxane increases the concentrate yield and reduces the losses of the coal’s organic mass with the wastes. Analogous flotation properties of coal are found for other cyclic acetals and their silicon analogs. Experimental data confirm that the hydrogen bond energy in complexes between the flotation reagent and the coal’s organic mass may be used to assess its effectiveness.     

Carbon dioxide: a renewable feedstock for the synthesis of fine and bulk chemicals

The syntheses of carbon dioxide (CO₂) based industrially important chemicals have gained considerable interest in view of the sustainable chemistry and “green chemistry” concepts. In this review, recent developments in the chemical fixation of CO₂ to valuable chemicals are discussed. The synthesis of five-member cyclic carbonates via, cycloaddition of CO₂ to epoxides is one of the promising reactions replacing the existing poisonous phosgene-based synthetic route. This review focuses on the synthesis of cyclic carbonates, vinyl carbamates, and quinazoline-2,4(1H,3H)-diones via reaction of CO₂ and epoxide, amines/phenyl acetylene, 2-aminobenzinitrile and other chemicals. Direct synthesis of dimethyl carbonate, 1,3-disubstituted urea and 2-oxazolidinones/2-imidazolidinones have limitations at present because of the reaction equilibrium and chemical inertness of CO₂. The preferred alternatives for their synthesis like transesterification of ethylene carbonate with methanol, transamination of ethylene carbonate with primary amine and transamination reaction of ethylene carbonate with diamines/β-aminoalcohols are discussed. These methodologies offer marked improvements for greener chemical fixation of CO₂ in to industrially important chemicals.     

Recovery of Phenol through the Decomposition of Tar under Hydrothermal Alkaline Conditions

Decomposition of the tar residue from oil distillation was carried out under hydrothermal conditions using a batch reactor at 623–673 K and 25–40 MPa, with and without K₂CO₃ as a catalyst. The reaction scheme for tar decomposition was determined as follows: the liquefaction and dissolution process of tar occur first and then intermediate chemical compounds are transformed into lighter molecular weight species. The presence of K₂CO₃ activates the dissociation of molecular hydrogen to facilitate hydrogenation reactions. The main products from the decomposition of tar were phenol, biphenyl, diphenylether (DPE), and diphenylmethane (DPM). These results indicate that hydrolysis was important in the cleavage of the macromolecular structure of tar under both catalytic and non‐catalytic hydrothermal conditions. This method can be developed for efficient tar liquefaction to generate high yields of valuable chemicals in an environmentally friendly way.     

Molecular design of nanohybrid gas separation membranes for optimal CO2 separation

Organic-inorganic materials comprising CO₂-philic components may yield superior CO₂ transport properties and good CO₂/H₂ gas selectivity. We report that a fine balance in size heterogeneity in the silicon-based structures is essential and a mixture of sizes up to 50 nm surrounded by 5–15 nm silicon-based nanostructures is the preferred inorganic phase morphology that yields optimal nanohybrid membranes. The combination of optimal synthesis conditions i.e. water/silicon ratio, condensation and ozone pre-treatment durations yields a nanohybrid membrane with a CO₂ permeability of 2000 Barrer while achieving a CO₂/H₂ selectivity of 11. The findings of this work are important for the design of gas separation membranes using green materials.     

Amplifying the molecular sieving capability of polyimide membranes via coupling of diamine networking and molecular architecture

The integration of molecular design with diamine modification generates synergistic effects for enhancing and fine tuning the molecular sieving potential of polyimide membranes. Polymer free volume and rigidity represent crucial conformational parameters that influence the effectiveness of diamine modification for elevating the H₂/CO₂ permselectivity of polyimide membranes. Experimental and molecular dynamics simulation results suggest that polyimides with higher intrinsic free volume and rigidity are ideal for diamine treatment, yielding greater increment in H₂/CO₂ selectivity. A series of copoly(4,4′-diphenyleneoxide/1,5-naphthalene-2,2′-bis(3,4-dicarboxylphenyl) hexafluoropropane diimide) (6FDA-ODA/NDA) membranes are modified with 1,3-diaminopropane (PDA). Polyimides with higher free volume intensify the methanol swelling effect which facilitates the transport and subsequent reaction of the diamine molecules. Gel content analyses of the PDA-modified films prove that the penetration depth of the diamine molecules and the extent of crosslinking are higher for polyimides with greater NDA content. 6FDA-NDA has the highest free volume and rigidity, thus exhibiting impressive improvement in ideal H₂/CO₂ selectivity from 1.8 to 120 after PDA modification. Conversely, 6FDA-ODA which is deficient in terms of free volume and rigidity, demonstrates a much lower increment in H₂/CO₂ selectivity from 2.5 to 8.2. The inherent heterogeneity of the PDA-modified polyimide films results in thickness-dependent gas permeability and selectivity. The potential of merging macromolecular tailoring with diamine networking to enhance the H₂/CO₂ separation performance of polyimide membranes is evident.