Thermal degradation behaviour and kinetic analysis of unsaturated polyester-based composites and IPNs by conventional and modulated thermogravimetric analysis

The thermal degradation behaviour of epoxy/unsaturated polyester based polymer interpenetrating networks (IPNs), and unsaturated polyester containing various flame-retardants have been investigated by TGA and Py/GC/MS. The kinetic parameters of various polymers were analysed by conventional and modulated thermogravimetric analysis (MTGA) methods. The activation energies of degradation were calculated by the Coats-Redfern and MTGA methods, respectively. The results of both conventional and MTGA analyses reveal that the decomposition of IPNs consists of two non-interfering decomposition processes for epoxy polymer and cured unsaturated polyester, respectively. For the flame-retardant containing unsaturated polyesters, ammonium polyphosphate (APP) played an important role in the second-step of the pyrolysis reaction of APP-containing samples. It is important to note that the possibilities of reaction order for these pyrolysis processes are significantly distinguishable by Coats-Redfern method. Furthermore, the activation energies for various samples calculated by MTGA method are on average larger than those calculated from the Coats-Redfern method. The results also reveal that when either the flame-retardant or the epoxy was added to the unsaturated polyester, the heat resistance of the unsaturated polyester was enhanced.     

Aryloxide‐Facilitated Catalyst Turnover in Enantioselective α,β‐Unsaturated Acyl Ammonium Catalysis

A new general concept for α,β‐unsaturated acyl ammonium catalysis is reported that uses p‐nitrophenoxide release from an α,β‐unsaturated p‐nitrophenyl ester substrate to facilitate catalyst turnover. This method was used for the enantioselective isothiourea‐catalyzed Michael addition of nitroalkanes to α,β‐unsaturated p‐nitrophenyl esters in generally good yield and with excellent enantioselectivity (27 examples, up to 79 % yield, 99:1 er). Mechanistic studies identified rapid and reversible catalyst acylation by the α,β‐unsaturated p‐nitrophenyl ester, and a recently reported variable‐time normalization kinetic analysis method was used to delineate the complex reaction kinetics.     

Densitometric determination of unsaturated fatty acids with p-hydroxybenzaldehyde by HPTLC

A rapid method for the detection and quantltatlve determlnation of unsaturated fatty acids by TLC is presented. After separation on HPTLC-RP₁₈-plates, reaction wlth p-hydroxybenzaldehyde is carried out by a dipping procedure. Nanogram amounts of unsaturated fatty acids can be determined with good reproducibility.     

Reaction of unsaturated compounds with ethyl benzenesulfenate and trimethylsilyl isothiocyanate

A new method for the synthesis of thiocyanato- and isothiocyanatoalkyl phenyl sulfides by the reaction of unsaturated compounds with ethyl benzenesulfenate and trimethylsilyl isothiocyanate has been suggested. Regio- and stereoselectivity of the reaction was studied, having taken alkenes, dienes, and alkynes as examples.     

Étude de l'addition des organozinciques α-éthyléniques aux amines éthyléniques,acétyléniques et alléniques

The general features and the field of application of a new reaction, that of addition of α-ethylenic organozinc compounds to unsaturated (ethylenic, acetylenic and allenic) amines, have studied. It is shown by numerous examples that this reaction constitutes a general method of synthesis for mono- and di-ethylenic amines.     

Tandem Reaction of Deprotonation-Oxidation-Wittig Reaction: Stereoselective Synthesis of (E)-α,β-Unsaturated Enoates

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Syntheses of protected vinylic amino acids by intermolecular Lewis acid catalyzed ene reactions

Intermolecular ene reaction between ethylglyoxylate and allylic amino acid derivatives gave highly functionalized unsaturated pimelic acids in one step. This synthetic approach appears as a new efficient method for the synthesis of vinylic amino acids.     

Domino‐Hydroformylation/Aldol Condensation Catalysis: Highly Selective Synthesis of α,β‐Unsaturated Aldehydes from Olefins

A general and highly chemo‐, regio‐, and stereoselective synthesis of α,β‐unsaturated aldehydes by a domino hydroformylation/aldol condensation reaction has been developed. A variety of olefins and aromatic aldehydes were efficiently converted into various substituted α,β‐unsaturated aldehydes in good to excellent yields in the presence of a rhodium phosphine/acid–base catalyst system. In view of the easy availability of the substrates, the high atom‐efficiency, the excellent selectivity, and the mild conditions, this method is expected to complement current methodologies for the preparation of α,β‐unsaturated aldehydes.     

NHC‐Catalyzed Chemoselective Reactions of Enals and Aminobenzaldehydes for Access to Chiral Dihydroquinolines

An N‐heterocyclic carbene (NHC)‐catalyzed reaction between α‐bromoenals and 2‐aminoaldehydes has been developed. Key steps include chemoselective reaction of the NHC catalyst with one of the aldehyde substrates (the bromoenal) to eventually generate an α,β‐unsaturated acylazolium intermediate. Addition of the nitrogen atom of aminoaldehyde to the unsaturated azolium ester intermediate followed by intramolecular aldol reaction, β‐lactone formation, and decarboxylation leads to chiral dihydroquinolines with high optical purity. The dihydroquinoline products, which are quickly prepared by using this method, can be readily transformed into a diverse set of functional molecules such as pyridines and chiral piperidines.     

BuLi—AlCl3—CH2I2 as a new reagent system for olefin cyclopropanation

Russian Chemical Bulletin - A new method for cyclopropanation of olefins with the BuLi—AlCl3—CH2I2 reagent system was developed. The reaction is tolerant of a wide range of unsaturated...     

Palladium‐catalyzed decarboxylative coupling of α,β‐unsaturated carboxylic acids with aryl tosylates

We report a general method for selective cross‐coupling of α,β‐unsaturated carboxylic acids with aryl tosylates enabled by versatile Pd(II) complexes. This method features the general cross‐coupling of ubiquitous α,β‐unsaturated carboxylic acids by decarboxylation. The transformation is characterized by its operational simplicity, the use of inexpensive, air‐stable Pd(II) catalysts, scalability and wide substrate scope. The reaction proceeds with high trans selectivity to furnish valuable (E)‐1,2‐diarylethenes.     

The use of ion-molecule reactions in the mass spectrometric location of double bonds

A method for the location of the positions of carbon-carbon double bonds using high pressure mass spectrometry is proposed. A known olefinic molecular ion reacts with a second, unknown olefin to form a four-centre complex, which fragments with retention of the structural identity of methylene and substituted methylene groups to eliminate a new olefin molecule and to form an unsaturated ion from which the position of the double bond in the unknown olefin can be inferred. Vinyl methyl ether proved to be a convenient reagent gas and its molecular ion undergoes the required reaction with several classes of olefinic compound. Conjugated dienes and unsaturated compounds containing electronegative groups do not undergo this reaction.     

Quinine-catalyzed asymmetric domino Michael-cyclization reaction for the synthesis of spirocyclic oxindoles bearing two spiro quaternary centers and three consecutive stereocenters

An efficient organocatalytic diastereo- and enantioselective method for the construction of spirocyclic oxindole derivatives bearing two spiro quaternary centers and three consecutive stereocenters via a domino Michael/cyclization process has been developed. Using commercially available quinine as catalyst, the reactions of 3-isothiocyanato oxindoles with unsaturated pyrazolones and unsaturated isoxazolones proceeded smoothly under mild reaction conditions for giving two classes of spirocyclic oxindole compounds in high to excellent yields with moderate to good diastereoselectivities and enantioselectivities. A plausible dual activation working model was tentatively proposed to account for the stereochemistry of the domino Michael/cyclization process.     

A general organocatalyzed Michael-Michael cascade reaction generates functionalized cyclohexenes

Although β-dicarbonyl compounds are regularly employed as Michael donors, intermediates arising from the Michael addition of unsaturated β-ketoesters to α,β-unsaturated aldehydes are susceptible to multiple subsequent reaction pathways. We designed cyclic unsaturated β-ketoester substrates that enabled the development of the first diphenyl prolinol silyl ether catalyzed Michael-Michael cascade reaction initiated by a β-dicarbonyl Michael donor to form cyclohexene products. The reaction conditions we developed for this Michael-Michael cascade reaction were also amenable to a variety of linear unsaturated β-ketoester substrates, including some of the same linear unsaturated β-ketoester substrates that were previously ineffective in Michael-Michael cascade reactions. These studies thus revealed that a change in simple reaction conditions, such as solvent and additives, enables the same substrate to undergo different cascade reactions, thereby accessing different molecular scaffolds. These studies also culminated in the development of a general organocatalyzed Michael-Michael cascade reaction that generates highly functionalized cyclohexenes with up to four stereocenters, in up to 97% yield, 32:1 dr, and 99% ee, in a single step from a variety of unsaturated β-ketoesters.     

Enantiospecific synthesis of α-amino acid semialdehydes: a key step for the synthesis of unnatural unsaturated and saturated α-amino acids

The enantiospecific synthesis of unnatural unsaturated and saturated α-amino acids based on a Wittig type reaction is described. The versatile synthetic intermediates, l-glutamic and l-aspartic acid semialdehydes, are obtained from the corresponding N,N-di-Boc-diesters, by the selective reduction of the ω-ester with DIBAL^® under controlled conditions. The semialdehydes are chemically stable for a prolonged time and react with various phosphorous ylides, under controlled conditions, to produce the enantiomerically pure unsaturated α-amino acids in high yields. The method is equally applicable to homologated diesters obtained by the presented methodology providing unsaturated amino acids with variable unsaturated positions and geometries. The corresponding saturated products can be obtained by simple hydrogenation.     

铜-有机配位体不饱和配合物的催化化学发光活性及其分析应用

铜(Ⅱ)离子与许多有机配位体组成饱和配合物后, 均导致铜(Ⅱ)在Luminol-H2O2和o-Phen-H2O2体系中催化化学发光活性的消失。本文首次发现, 当铜(Ⅱ)离子与某些有机配位体组成1:1不饱和配位化合物时, 它们非但不抑制化学发光,而且比铜(Ⅱ)离子具有更高的催化化学发光活性, 据此, 本文建立了用配合溶解Cu(OH)2, 流动注射化学发光技术测定氨基酸的新方法, 检测限均可达pmol级,比文献普遍使用的抑制化学发光法灵敏度高10~150倍, 线性范围达三个数量级,相对偏差在5.4%以下。     

The Chemistry of Bunte Salts

Bunte salts can be obtained, not only from alkyl halides and sodium thiosulfate, but also from compounds containing activated multiple bonds, and sodium thiosulfate. The Bunte salts prepared by the new method, contrary to earlier observations, are cleaved by alkalis into the unsaturated starting compounds and sodium thiosulfate. This reaction, which is used for the fixation of unsaturated compounds (e.g. to cellulose), and other reactions of the Bunte salts are discussed. The industrial applications and biological properties of the Bunte salts are also mentioned.     

Synthesis and characterization of a chlorofunctionalized unsaturated carbosilane oligomer

Acyclic diene metathesis (ADMET) polymerization offers a viable route for the synthesis of chlorofunctionalized unsaturated carbosilane oligomers. The Si Cl bond in unsaturated carbosilane monomers remains inert during metathesis and the use of a highly reactive molybdenum-based, Lewis acid-free alkylidene catalyst affords unsaturated chlorofunctionalized carbosilane oligomers with known vinyl end groups. The first synthesis of an unsaturated carbosilane oligomer functionalized with a Si Cl bond was performed. A chlorofunctionalized silacyclopentene product was also observed, due to a backbiting reaction. This new class of functionalized oligomers has a low glass transition temperature and sites of unsaturation which may be used for further reaction. ADMET chemistry now provides access to a variety of chlorofunctionalized unsaturated carbosilanes which can be used to tailor make hydrolytically stable carbosilane oligomers and polymers via nucleophilic grafting reactions.     

Solvent-free synthesis of unsaturated amino esters in a ball-mill

The ball-milling technique was used under solvent-free conditions to perform a Horner-Wadsworth-Emmons reaction in the presence of a mild carbonate base. Starting from a phosphonate-substituted glycine, this method gave access to Boc-protected unsaturated amino esters in excellent yield and selectivity in many cases. The scope of the reaction was delineated.     

Pd(0)-Mediated Cross-Coupling of Reformatsky Reagents with Vinyl and Aryl Triflates

Pd(0)-Mediated cross-coupling reaction between Reformatsky reagents and vinyl/aryl trifla tes is reported. The method represents a procedure for the synthesis of β - γ unsaturated esters and aryl acetic esters.