Surface modified precipitated calcium carbonates at a high degree of dispersion

Calcium carbonates of different degrees of surface hydrophobicity were obtained when sorbic acid or polyoxyethylene glycol were present during the precipitation. In the presence of trace amounts of divalent cations carbonates with high surface hydrophilicity and improved monodisperse character are obtained. Surface modification of the calcium carbonates by several proadhesive compounds can markedly improve the chemical affinity of the carbonates to polymers. Very effective are isostearoyl titanate and two polyoxyethylene compounds. Precipitated calcium carbonates modified with 2 to 3 percent (wt/wt) of isostearoyl titanate increased the tensile strenght of butadiene-styrene rubber by approximately 100%. Polyurethane is only strengthened when 30 wt/wt of a filler are introduced independently of the type proadhesive compounds. The best strength and hysteresis of polyurethanes are obtained with calcium carbonate modified with 2 percent (wt/wt) of polyoxyethylene glycol.     

Methyl-and ethyl carbonates derived from vanillin and vanillal in the synthesis of nitrogen-containing compounds

Reactions of 4-hydroxy-3-methoxybenzaldehyde and 3-ethoxy-4-hydroxybenzaldehyde with methyl and ethyl chloroformates in the presence of pyridine gave the corresponding methyl and ethyl carbonates which were brought into condensation with biphenyl-4-amine, naphthalen-1-and-2-amines, and 3-and 4-aminobenzoic acids to obtain the corresponding Schiff bases. Alkyl 4-(9,9-dimethyl-11-oxo-7,8,9,10,11,12-hexahydrobenzo[a]acridin-12-yl)-2-alkoxyphenyl carbonates were selectively synthesized by cascade heterocyclization of naphthalen-2-amine, 5,5-dimethylcyclohexane-1,3-dione, and 4-formyl-2-methoxy(or ethoxy)phenyl methyl(or ethyl) carbonates. Ammonium salts were obtained from the benzoacridine derivatives and Schiff bases derived from aminobenzoic acids.     

Palladium-catalyzed carbon dioxide elimination-fixation reaction of 4-methoxycarbonyloxy-2-buten-1-ols

A new type of palladium-catalyzed CO(2) recycling reaction using allylic carbonates is described. Reaction of trans-4-methoxycarbonyloxy-2-buten-1-ols in the presence of a palladium catalyst produces cyclic carbonates having a vinyl group via a CO(2) elimination-fixation process. A variety of allylic carbonates participate in the reaction giving cyclic carbonates with high efficiencies. Stereoselective construction of trans-cyclic carbonates is achieved by using nonsymmetric substrates. An enantiospecific reaction proceeds to give chiral cyclic carbonate when a chiral methyl-substituted substrate is subjected to the reaction conditions.     

Thermal stability of some aromatic polyesters and poly(ester carbonates)

The thermal stability of some hydroxyl-terminated poly(bisphenol A tere- or isophthalates) and their corresponding poly(ester carbonates) made by subsequent coupling with phosgene has been investigated by thermogravimetry. Samples have been studied in nitrogen or air using constant rates of temperature rise or isothermal conditions.The isophthalate-containing polyesters are more thermo-oxidatively stable than their terephthalate analogues and molecular weight has a significant effect on stability. In contrast, there is little difference in the thermal stability of the poly (isophthalate carbonates) and the poly(terephthalate carbonates) and the stability of the latter is relatively independent of the ratio of the diester to carbonate group content. The stability of the poly(terephthalate carbonates) is also relatively insensitive to end-group modifications.     

Organocatalytic methods for chemoselective O-tert-butoxycarbonylation of phenols and their regeneration from the O-t-Boc derivatives

Carbon tetrabromide (CBr4) catalyzes O-tert-butoxycarbonylation of functionalized phenols without any side reactions (bromination, addition of CBr3 to a double bond, and formation of symmetrical diaryl carbonates, cyclic carbonates, or carbonic-carbonic anhydrides). The parent phenols are regenerated from the O-t-Boc derivatives by the catalyst system CBr4-PPh3 without affecting other protecting groups (aryl alkyl ether, alkyl ester, and thioacetal) or competitive side reaction such as bromination, nitrene (from NO2) and alpha,alpha-dibromoolefine (with CHO/COMe) formation, and transesterification (with CO2Me/Et) taking place.     

A novel methodology for the synthesis of cyclic carbonates based on the palladium-catalyzed cascade reaction of 4-methoxycarbonyloxy-2-butyn-1-ols with phenols,involving a novel carbon dioxide elimination-fixation process

A palladium-catalyzed CO(2)-recycling reaction has been developed. Reaction of 4-methoxycarbonyloxy-2-butyn-1-ols with phenols, carried out in the presence of a palladium catalyst, produces phenoxy-substituted cyclic carbonates by way of a pathway involving a CO(2) elimination-fixation. A variety of propargylic alcohols and phenols participate in these reactions which yield cyclic carbonates with high efficiencies. Stereoselective construction of trans-cyclic carbonates is achieved by using nonsymmetric substrates. Highly enantioselective reactions occur when (S)-BINAP is used as a ligand. Reaction of 4-phenoxycarbonyloxy-2-butyn-1-ol in the presence of the palladium catalyst yields the corresponding cyclic carbonates via a three-component decomposition-reconstruction process.     

Novel methodologies for the synthesis of cyclic carbonates

Cyclic carbonates are valuable compounds that have applications in a variety of chemical fields. Methodologies for the synthesis of cyclic carbonates are well investigated in recent years, and the most successful and popular procedure is the utilization of CO(2). This paper presents recent progress in the synthesis of cyclic carbonates by a CO(2)-fixation process, which involves novel palladium-catalyzed CO(2)-recycling reactions.     

Palladium-catalyzed divergent reactions of 1,6-enyne carbonates: synthesis of vinylidenepyridines and vinylidenepyrrolidines

A method for preparing five- or six-membered heterocyclic compounds from enyne carbonates via palladium catalysis was developed. Enyne carbonates were transformed into 3-vinylidene-1-tosylpyridines 2 in the presence of PdI(2) as the catalyst. Using Pd(dba)(2) as the catalyst, 3-vinylidene-1-tosylpyrrolidines 3 were obtained. Further functionalizations of compounds 3 were carried out in a one-pot manner.     

A useful synthetic equivalent of a hydroxyacetone enolate

Indium promoted allylation of carbonyl compounds with 4-(bromomethyl)-1,3-dioxol-2-one diastereoselectively affords anti-α,β-dihydroxyketones, protected as enol carbonates. These initial products can be deprotected to free dihydroxyketones or transformed under mild conditions into the corresponding cyclic carbonates, which constitutes a useful approach to hydroxyacetone aldols.     

New synthesis and reactions of perfluoro-tert-butyl chloroformate

A new synthesis of perfluoro-tert-butyl chloroformate (perfluoro-tert- butoxycarbonyl chloride) is based on the reaction of potassium perfluoro- tert-butoxide with one equivalent of phosgene in xylene or mesitylene. Perfluoro-tert-butyl chloroformate reacts readily with hydroxy, sulfhydryl and amino compounds to give the corresponding perfluoro-tert-butyl alkyl carbonates, thiolcarbonates or carbamates, respectively. Dialkyl carbonates, diaryl carbonates, and symmetrically substituted ureas are formed as by-products and, with some compounds, as exclusive products. Primary amines form isocyanates.     

Reactions of singly-reduced ethylene carbonate in lithium battery electrolytes: a molecular dynamics simulation study using the ReaxFF

We have conducted quantum chemistry calculations and gas- and solution-phase reactive molecular dynamics simulation studies of reactions involving the ethylene carbonate (EC) radical anion EC(-) using the reactive force field ReaxFF. Our studies reveal that the substantial barrier for transition from the closed (cyclic) form, denoted c-EC(-), of the radical anion to the linear (open) form, denoted o-EC(-), results in a relatively long lifetime of the c-EC(-) allowing this compound to react with other singly reduced alkyl carbonates. Using ReaxFF, we systematically investigate the fate of both c-EC(-) and o-EC(-) in the gas phase and EC solution. In the gas phase and EC solutions with a relatively low concentration of Li(+)/x-EC(-) (where x = o or c), radical termination reactions between radical pairs to form either dilithium butylene dicarbonate (CH(2)CH(2)OCO(2)Li)(2) (by reacting two Li(+)/o-EC(-)) or ester-carbonate compound (by reacting Li(+)/o-EC(-) with Li(+)/c-EC(-)) are observed. At higher concentrations of Li(+)/x-EC(-) in solution, we observe the formation of diradicals which subsequently lead to formation of longer alkyl carbonates oligomers through reaction with other radicals or, in some cases, formation of (CH(2)OCO(2)Li)(2) through elimination of C(2)H(4). We conclude that the local ionic concentration is important in determining the fate of x-EC(-) and that the reaction of c-EC(-) with o-EC(-) may compete with the formation of various alkyl carbonates from o-EC(-)/o-EC(-) reactions.     

Gold-catalyzed rearrangement of propargylic tert-butyl carbonates

Diversely substituted 4-alkylidene-1,3-dioxolan-2-ones are efficiently synthesized by a gold(I)-catalyzed rearrangement of propargylic tert-butyl carbonates. The substrates are readily accessible and the transformation, which is performed under mild reaction conditions using a low loading of catalyst, allows the synthesis of cyclic carbonates, which would be less efficiently obtained using traditional methods. This procedure has also been applied to the stereoselective synthesis of (E)- or (Z)-4-halomethylene-1,3-dioxolan-2-ones, which proved to be suitable substrates for palladium-catalyzed cross-coupling reactions.     

Enzyme-mediated enantioselective hydrolysis of poly(ethylene glycol)-supported carbonates

Kinetic resolution of poly(ethylene glycol)(PEG)-supported carbonates by enzymatic hydrolysis is discussed. Water-soluble carbonates are prepared by immobilization of racemic secondary alcohols onto low-molecular weight monomethoxy PEG (MPEG) through a carbonate linker. Porcine pancreas lipase (PPL) enantioselectively catalyzes the hydrolysis of the substrates to give optically active compounds. In this system, the separation of the resulting alcohols and the remaining substrates is achieved by an extraction process without laborious column chromatography. The carbonates are easily hydrolyzed with K₂CO₃ to afford the corresponding alcohols.     

碳酸盐炼制共热耦合甲烷干重整制高附加值化学品发展展望

传统过程工业,诸如我国水泥、钢铁、耐材和电石等行业,都涉及碳酸盐高温热分解过程,其导致的CO₂排放量超过了全国工业碳排放总量的50%,大量CO₂排放对全球气候产生了不可逆转的影响。因此,如何减少过程工业排放的CO₂并且充分利用碳酸盐热分解的余热面临着巨大挑战。为进一步降低该类过程工业的CO₂排放量同时降低其热分解的能耗,通过利用地球上储量丰富的温室气体CH₄,对碳酸盐进行共热耦合重整制备合成气等高附加值产品,有望成为一种环保经济的技术路线。本文总结了(光/热)碳酸盐炼制耦合甲烷干重整反应、醇类重整反应以及CO₂捕获反应的最新进展,并且对碳酸盐炼制耦合甲烷干重整反应在理论计算方面的研究进展进行了介绍,进一步结合本课题组近期关于碳酸盐共热耦合甲烷重整的最新结果,我们提出了该类耦合反应的发展展望,为实现CO₂的高效转化和减排增效提供了思路。     

绿色催化二氧化碳、炔丙醇和亲核试剂的三组分反应

近些年来,将CO₂转化为高附加值化学品受到广泛关注。其中,CO₂、炔丙醇和亲核试剂的三组分反应可用于制备用途广泛的羰基化合物,该方法具有步骤经济性、原子经济性等优点。由于CO₂分子具有热力学稳定性和动力学惰性,多数CO₂参与的化学反应在热力学上不支持。然而,CO₂、炔丙醇和双亲核试剂三组分反应是热力学有利的CO₂转化反应,实现了邻二醇或氨基醇和CO₂到环状碳酸酯以及2-噁唑啉酮的高效转化。本综述旨在于总结并讨论近年来CO₂、炔丙醇和亲核试剂三组分反应制备多种羰基化学物的主要进展。     

环状碳酸酯低聚物的合成及其开环聚合的研究

环状碳酸酯低聚物的合成及其开环聚合的研究陈雨萍魏玮李革（中国科学院化学研究所工程塑料国家重点实验室北京１０００８０）关键词环状碳酸酯低聚物，聚碳酸酯，开环聚合环状单体的开环聚合在合成高聚物方面具有突出的优点，即在聚合过程中没有副产物、热效应低、聚合...     

Allylation of erythromycin derivatives: introduction of allyl substituents into highly hindered alcohols

Functionalized erythromycin 9-oxime derivatives are 6-O-allylated under mild conditions using substituted allyl tert-butyl carbonates under palladium(0) catalysis. This allylation works well where traditional ether-forming protocols function poorly. Allyl tert-butyl carbonates provide higher yields in this reaction than lesser substituted carbonates such as ethyl or isopropyl. Aryl-substituted allyl carbonates or carbamates may be employed as well and, when used, produce trans-olefinic products.     

碳酸盐标准生成焓的计算

碳酸盐标准生成焓的计算戴长文，王振民，徐琰，戴晓弘（郑州大学化学系，郑州，４５００５２）（郑州高新技术开发区，郑州，４５０００１）关键词热力学性质，标准生成焓，碳酸盐预测无机化合物生成热的计算方法已见报道［１，２］，但引入经验参数过多，且计算偏差亦较...     

Facile synthesis of bisphosphine monoxides from Morita–Baylis–Hillman carbonates

A facile two-step synthesis of bisphosphine monoxides (BPMOs, with both the phosphine and phosphine oxide moieties within one molecule) from readily available Morita–Baylis–Hillman (MBH) carbonates was realized. Under the catalysis of DABCO, the MBH carbonates undergo allylic phosphorylation reaction with diphenylphosphine oxide or diethyl phosphonate to give monophosphine oxides bearing an activated alkene moiety; subsequent base-catalyzed hydrophosphination of the prepared monophosphine oxide with HPPh₂ readily affords the BPMOs.     

Halogen-free processes for organic carbonate synthesis from CO2

Recent progress on the synthesis of organic carbonates by halogen-free processes has been reviewed. With CO₂ as a cheap and non-toxic feedstock, alcohols, epoxides and olefins can convert to abundant organic carbonates, e.g. dialkyl carbonates, five- or six-membered cyclic carbonates and polycarbonates. To avoid environmental pollution and equipment corrosion, new synthesis routes which exclude traditional halogen-containing catalysts and solvents have caused much attention. Effective alternatives mainly include the organic/inorganic bases and metal-complexes catalysts. In addition, novel carriers for the catalysts are being applied in these processes to improve the activity and facilitate the recovery.