Unsaturated Dimer Research Articles

Trithiocarbonate-Mediated RAFT Polymerization Enables the Synthesis of Homotelechelic N-Vinylpyrrolidone Oligomers with Surfactant Properties

Poly(N-vinylpyrrolidone) (PVP) is a well-known biocompatible polymer widely used in cosmetics, pharmaceuticals, and many other applications and is usually synthesized via radical polymerization. High molar mass PVP lacks biodegradability according to the OECD 301 F standard and can lead to permanent accumulation within the body or in the environment. Nowadays, lower molar mass PVP is produced via xanthate-mediated reversible addition–fragmentation chain-transfer (RAFT) polymerization. However, this type of polymerization also leads to a large amount of undesired dimer formation. Herein, various homotelechelic PVP oligomers were prepared via a trithiocarbonate-mediated RAFT polymerization with the production of a minimal amount of unsaturated dimer. These PVP oligomers showed similar surfactant properties as the well-known Lutensol AT50 surfactant, and they were used as a nonionic surfactant in a typical radical aqueous miniemulsion polymerization of methyl methacrylate (MMA) to produce well-defined PMMA nanoparticles. Additionally, PVP oligomers showed no toxicity to the bacterial strain Escherichia coli and to the water fleas Daphnia pulex, which is promising for safe release in wastewater systems.

Triangles and Squares for a Unique Molecular Crystal Structure: Unsupported Two‐Coordinate Lithium Cations and CC Agostic Interactions in Cyclopropyllithium Derivatives

AbstractUnderstanding and controlling the aggregation state is germane to alkyllithium chemistry. Lewis base‐free alkyllithium compounds normally form tetrahedral tetramers or octahedral hexamers in the solid state with the lithium cations being three‐coordinate. We report that the unsupported cyclopropyl derivative 1‐(trimethylsilyl)cyclopropyllithium [{μ‐c‐C(SiMe3)C2H4}Li]4 (1), synthesized by the reduction of 1‐(phenylthio)‐1‐(trimethylsilyl)cyclopropane, crystallizes as a tetramer in the space group I‐4 with the two‐coordinate lithium atoms forming a square. CC agostic interactions complete the coordination sphere around each lithium. The aggregate is preserved in hydrocarbon solution. Furthermore, CC agostic interactions compete intra‐ and intermolecularly with Lewis base donation as in the unsaturated dimer of 1‐(phenylthio)cyclopropyllithium [Li(thf)2{μ‐c‐C(SPh)C2H4}2Li (thf)] (3) which is also fully characterized.

Triangles and Squares for a Unique Molecular Crystal Structure: Unsupported Two-Coordinate Lithium Cations and CC Agostic Interactions in Cyclopropyllithium Derivatives.

Understanding and controlling the aggregation state is germane to alkyllithium chemistry. Lewis base-free alkyllithium compounds normally form tetrahedral tetramers or octahedral hexamers in the solid state with the lithium cations being three-coordinate. We report that the unsupported cyclopropyl derivative 1-(trimethylsilyl)cyclopropyllithium [{μ-c-C(SiMe3 )C2 H4 }Li]4 (1), synthesized by the reduction of 1-(phenylthio)-1-(trimethylsilyl)cyclopropane, crystallizes as a tetramer in the space group I-4 with the two-coordinate lithium atoms forming a square. CC agostic interactions complete the coordination sphere around each lithium. The aggregate is preserved in hydrocarbon solution. Furthermore, CC agostic interactions compete intra- and intermolecularly with Lewis base donation as in the unsaturated dimer of 1-(phenylthio)cyclopropyllithium [Li(thf)2 {μ-c-C(SPh)C2 H4 }2 Li (thf)] (3) which is also fully characterized.

Phosphinoborane-induced fragmentation of the unsaturated hydride H2Re2(CO)8: X-ray structure of HRe(CO)4(κB,P-Ph2PCH2CH2BR2) (where BR2 = 9-borabicyclo[3.3.1]nonanyl) and DFT Evaluation of hydride versus CO coordination by the ancillary borane

The reactivity of the unsaturated dimer H2Re2(CO)8 (1) with the ambiphilic phosphinoborane Ph2PCH2CH2BR2 (2; where BR2 = 9-borabicyclo[3.3.1]nonanyl) has been explored. Coordination of the ambiphilic ligand to 1 is rapid at room temperature, leading to the fragmentation of 1 and formation of HRe(CO)4(κB,P-Ph2PCH2CH2BR2) (3) in high yield. 3 has been characterized in solution by IR and NMR spectroscopy, and the molecular structure established by X-ray diffraction analysis. The solid-state structure confirms the presence of a chelated phosphinoborane ligand through coordination of the phosphine to the rhenium center and the formation of a three-center, two-electron (3c,2e) Re–H–B interaction. The nature of the Re–H–B interaction in 3 has been investigated by DFT, and the energetics for borane dissociation and hydride abstraction by the coordinated Lewis acid in 3 have also been computationally evaluated. The coordination of an oxygen in one of the ancillary CO groups by the pendant borane in HRe(CO)4(κP-Ph2PCH2CH2BR2) is thermodynamically unfavorable relative to the formation of the 3c,2e Re–H–B bond.

Unexpected reactions associated with the xanthate‐mediated polymerization of N‐vinylpyrrolidone

AbstractThe monomer N‐vinylpyrrolidone (NVP) undergoes side reactions in the presence of R group functional xanthates and impurities. The fate of the monomer NVP and a selection of six O‐ethyl xanthates during xanthate‐mediated polymerization were studied via NMR spectroscopy. A high number of by‐products were identified. Significant side reactions affecting NVP include the formation of an unsaturated dimer and hydration products in bulk or in solution in C6D6. In addition, the xanthate adjacent to a NVP unit was found to undergo elimination at moderate temperature (60–70 °C), resulting in unsaturated species and the formation of new xanthate species. The presence of the chlorinated compound α‐chlorophenyl acetic acid, ethyl ester, a precursor in the synthesis of the xanthate S‐(2‐ethyl phenylacetate) O‐ethyl xanthate, resulted in a dramatic increase in the rate of side reactions such as unsaturated dimer formation and a high ratio of unsaturated chain ends. The conditions for the occurrence of such side reactions are discussed in this article, with relevance to increasing the control over the polymerization kinetics, endgroup functionality, and control over the molar mass distribution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6575–6593, 2008

Effect of ambient pressure and nickel contamination on the dimer-dangling-bond surface state of Si(001)2×1

The well known dimer-dangling-bond surface state of the Si(001)2×1 surface is very sensitive to even a small amount of adsorption from the ambient pressure in an UHV chamber. The authors show the decay of the surface state intensity, obtained with ultraviolet photoelectron spectroscopy (UPS), as a function of time for two different ambient UHV chamber pressures typically considered to be sufficiently low for carrying out surface sensitive experiments. In ambient pressures greater than 1×10−10Torr, the dimer-dangling-bond surface state decays completely in less than 1h, even at the relatively “good” pressure of 4×10−10Torr. The reason for the decay is likely due to the passivation of the dimer dangling bonds predominantly as a result of H adsorption from the ambient pressure in the UHV chamber. Furthermore, Ni-contamination-induced defects on the Si(001)2×1 surface alone do not cause the decay of the surface state. As long as unsaturated dimer dangling bonds remain on the surface, even in the presence of l...

Time-resolved infrared study of reactive species produced by flash photolysis of the hydroformylation catalyst precursor Co 2(CO) 6(PMePh 2) 2

Flash photolysis with time-resolved infrared (TRIR) spectroscopy was used to elucidate the photochemical reactivity of the hydroformylation catalyst precursor Co 2(CO) 6(PMePh 2) 2. Depending on reaction conditions, the net products of photolysis varied significantly. A model is presented that accounts for the net reactivity with two initial photoproducts, the 17-electron species Co(CO) 3(PMePh 2) and the coordinatively unsaturated dimer Co 2(CO) 5(PMePh 2) 2. No evidence was found for photochemical formation of Co 2(CO) 6(PMePh 2). Time-resolved spectroscopic studies allowed for the direct observation of transient species and for kinetics studies of certain reactions; for example, the reactions of Co(CO) 3PMePh 2 with CO and with PMePh 2 gave the respective rate constants 1.5 × 10 5 and 1.2 × 10 7 M −1 s −1, while the analogous reactions with Co 2(CO) 5(PMePh 2) 2 gave the rate constants of 2.6 × 10 6 M −1 s −1 and 3.9 × 10 7 M −1 s −1.

Preparation of macromonomers by copolymerization of methyl acrylate dimer involving β fragmentation

AbstractThe unsaturated dimer of methyl acrylate [CH2C(CO2CH3)CH2CH2CO2CH3, or MAD] was copolymerized with various monomers to prepare copolymers bearing the ω‐unsaturated end group [CH2C(CO2CH3)CH2] arising from β fragmentation of the MAD propagating radical. Copolymerizations of MAD with cyclohexyl and n‐butyl acrylate resulted in copolymers with ω‐unsaturated end groups, and increasing the temperature up to 180 °C resulted in an increase in the rate of β fragmentation of MAD radicals relative to propagation. Only a small amount of unsaturated end groups was introduced by copolymerization with ethyl methacrylate (EMA), and the EMA content in the copolymer increased with temperature. These findings could be explained by the reversible addition of the poly(EMA) radical to MAD. The copolymerization with ethyl α‐ethyl acrylate (EEA) did yield a copolymer containing unsaturated end groups with MAD units as part of the main chain, although the steric hindrance of the ethyl group suppressed homopropagation and crosspropagation of EEA, resulting in low polymerization rates. Therefore, the copolymerization of MAD with acrylic esters at high temperatures was noted as a convenient route for obtaining acrylate–MAD copolymers bearing unsaturated end groups at the ω end (macromonomer). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 597–607, 2004

Detailed studies of the initiation step in free radical polymerization of α-(substituted methyl)acrylates by electron paramagnetic resonance spectroscopy

Reactions of the adduct radical obtained by addition of the initiator-derived 2-carbomethoxy-2-propyl radical to methyl α-[(2-methyl-2-carbomethoxy)propyl]acrylate (the unsaturated dimer of methyl methacrylate (MMAD)) have been monitored by electron paramagnetic resonance spectroscopy. Rate constants for addition of the 2-carbomethoxy-2-propyl radical to MMAD, mutual reactions between the adduct radicals, and reactions of the adduct radical and the 2-carbomethoxy-2-propyl radical, and β-fragmentation of the adduct radical were evaluated by steady-state and non-steady-state kinetic analysis in tandem with computer modeling and simulations involving parameter optimization procedures. The resulting rate constants showed that addition and radical–radical reactions between low molecular weight radicals are suppressed due to the marked steric congestion of the carbon-carbon double bond and radical center, respectively, and that β-fragmentation can compete with radical–radical reactions of the adduct radicals depending on the radical concentration.

Analysis of oligoguluronic acids with NMR electrospray ionization–mass spectrometry and high-performance anion-exchange chromatography

Oligoguluronates were prepared by enzymatic hydrolysis of homopolymeric blocks of guluronic acids. Two different oligosaccharides were prepared by separating final hydrolysates on Q-Sepharose FF ion chromatography. High-performance anion-exchange chromatography analysis showed the high purity of these oligosaccharides. The molecular masses of these two oligosaccharides, determined by electrospray ionization–mass spectrometry, were 396 and 594, respectively. 1H, 13C NMR, H-H COSY and HSQC analysis proved that they were the unsaturated dimer and trimer oligoguluronates. The 1H and 13C NMR chemical shifts of these two oligosaccharides are also reported.

Modes of action of five different endopectate lyases from Erwinia chrysanthemi 3937.

Five endopectate lyases from the phytopathogenic bacterium Erwinia chrysanthemi, PelA, PelB, PelD, PelI, and PelL, were analyzed with respect to their modes of action on polymeric and oligomeric substrates (degree of polymerization, 2 to 8). On polygalacturonate, PelB showed higher reaction rates than PelD, PelI, and PelA, whereas the reaction rates for PelL were extremely low. The product progression during polygalacturonate cleavage showed a typical depolymerization profile for each enzyme and demonstrated their endolytic character. PelA, PelI, and PelL released oligogalacturonates of different sizes, whereas PelD and PelB released mostly unsaturated dimer and unsaturated trimer, respectively. Upon prolonged incubation, all enzymes degraded the primary products further, to unsaturated dimer and trimer, except for PelL, which degraded the primary products to unsaturated tetramer and pentamer in addition to unsaturated dimer and trimer. The bond cleavage frequencies on oligogalacturonates revealed differences in the modes of action of these enzymes that were commensurate with the product progression profiles. The preferential products formed from the oligogalacturonates were unsaturated dimer for PelD, unsaturated trimer for PelB, and unsaturated tetramer for PelI and PelL. For PelA, preferential products were dependent on the sizes of the oligogalacturonates. Whereas PelB and PelD displayed their highest activities on hexagalacturonate and tetragalacturonate, respectively, PelA, PelI, and PelL were most active on the octamer, the largest substrate used. The bond cleavage frequencies and reaction rates were used to estimate the number of subsites of each enzyme.

Synthesis and characterization of polyamide resins from soy-based dimer acids and different amides

A series of soy-based polyamides with different dimer acids and diamines were synthesized using a condensation polymerization technique. The molecular weight of polyamides prepared from 1,4-phenylenediamine increases greatly with a reaction temperature above 260°C. The physical properties of the polyamides, such as glass transition temperature (Tg), melting point (Tm), decomposition temperature (Td), crystalline behavior, and mechanical strength strongly depend on their molecular weight and flexibility of diamines used. The aromatic-based polyamides have a higher Tg, Tm, Td, and stronger mechanical strength than that of aliphatic-based polyamides. X-ray diffraction patterns of the samples indicate that all of the resins synthesized present a typical semicrystalline morphology. Polyamides made from hydrogenated dimer acid possess lower Tg and higher mechanical strength, compared with polyamides from unsaturated dimer acid with different dimer and trimer ratios. These results are analyzed and discussed in accordance with the influence of rigid aromatic segments and the microstructure of different dimer acids. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:305–314, 1998

Synthesis and characterization of polyamide resins from soy‐based dimer acids and different amides

A series of soy-based polyamides with different dimer acids and diamines were synthesized using a condensation polymerization technique. The molecular weight of polyamides prepared from 1,4-phenylenediamine increases greatly with a reaction temperature above 260°C. The physical properties of the polyamides, such as glass transition temperature (Tg), melting point (Tm), decomposition temperature (Td), crystalline behavior, and mechanical strength strongly depend on their molecular weight and flexibility of diamines used. The aromatic-based polyamides have a higher Tg, Tm, Td, and stronger mechanical strength than that of aliphatic-based polyamides. X-ray diffraction patterns of the samples indicate that all of the resins synthesized present a typical semicrystalline morphology. Polyamides made from hydrogenated dimer acid possess lower Tg and higher mechanical strength, compared with polyamides from unsaturated dimer acid with different dimer and trimer ratios. These results are analyzed and discussed in accordance with the influence of rigid aromatic segments and the microstructure of different dimer acids. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:305–314, 1998

Dimersäure- und Estersulfonate / Sulphonates derived from dimer acids and esters

Several fatty acids, dimer acids - especially unsaturated ones - and some of their derivatives were sulphonated in a batch reactor with liquid sulphur trioxide or chlorosulphonic acid. The main raw materials were stearic and oleic acids and dimers of the latter, they were used as free carboxylic acids or as methyl, 2-ethylhexyl or n-decyl esters. Sulphonation products were neutralized with various alkaline or organic bases, leading to anionic surfactants; several of these have not yet been reported in the literature. Three physical-chemical properties of these sulphonates, related to their adsorption at the air-water interface or to their aggregation, were investigated: surface tension decrease, foaming power and critical micelle concentration (c. m. c.). Due to the presence of several hydrocarbon chains, solubility and c. m. c. are much higher than expected for sulphonates with such a high number of carbon atoms. The surface tension decrease of unsaturated dimer products is very favourable but sodium sulphonate of oleic acid n-decyl ester, also studied in this work, shows the most remarkable decrease. The foaming power of sulphonated unsaturated dimers is about half that of the corresponding sulphonated monomers. According to the physical-chemical properties of sulphonated quasisaturated dimers and to the evolution of these properties with surfactant structure, sulphonated unsaturated dimer acids and esters perform better than similar saturated sulphonates

Conversion of Fatty Acids and Derivatives, IV. Conversion of Fatty Acid Methyl Esters into Dialkylated Succinic Esters by Oxidative Coupling of their Enolates

AbstractThe enolates of fatty acid methyl esters 1a–g are dimerized in good yields (56 to 73%) by means of oxidative coupling with copper(II) bromide to dialkylated succinic esters 2a–g. The configuration of meso‐2a was established by independent synthesis. On treatment with ozone the unsaturated dimer 2c is converted to the tetracarboxyl compound 6. Epoxidation of 2g leads to the corresponding bisepoxy diester 7.

Structural organization of chemically modified rolivsan MV-1 cured by a catalytic method

The Rolivsan MV-I monomer-oligomer system (MOS) contains aromatic esters with several species of unsaturated groups, for example, CH 2 = CHC6H40....... -OC6H4CH(CH3)-~HC6H40-... [i-3]. It was.previously shown that aralkylation reactions take place when model compounds containing side groups [styrene, bis(4-vinylphenyl) ether, unsaturated styrene dimer, unsaturated linear oligomers of bis(4-vinlyphenyl) ether, are heated to I00-120~ with aromatic compounds in the presence of acid catalysts, resulting in the formation of products of addition [4]. It was shown that addition of aromatic oligoesters to the unsaturated components of Rolivsan MV-I takes place analogously, causing (after curing of the composite) a decrease in the density of the polymer network and an increase in the elasticity of the material. Incorporation of small amounts of oligomer in the system is another way of increasing the elasticity of Rolivsan MV-I [2]. The presence of reactive functional groups in it also causes chemical reaction with Rolivsan MV-I. This chemical modification of Rolivsan MV-I can be used to obtain thermostable elastic materials.

Synthesis of functionalized linear poly(divinylbenzene). III. Synthesis of polymeric delocalized carbanion of poly(divinylbenzene) and its reactions

AbstractA polymeric delocalized carbanion of poly(divinylbenzene) [poly(DVB)] (2) was obtained by the proton abstraction with alkyllithium from the acidic methine moieties (HA) of linear poly(DVB) (1), which was prepared by the polymerization of DVB initiated by acetyl perchlorate. The formation of polyanion 2 was confirmed by UV–visible spectroscopy (λmax = 630 nm) and the reaction with methyl iodide to give methylated poly(DVB). Delocalized polyanion 2 reacted with various electrophilic reagents in THF at 60°C, to yield poly(DVB) derivatives having pendant trimethylsilyl, vinyl, vinyloxyl, hydroxyl, and carboxyl groups. Proton abstraction with base and subsequent reactions with electrophiles were also studied with the linear unsaturated dimer of styrene (1,3‐diphenyl‐1‐butene), as a model for poly(DVB) 1.

On the unexpected cathodic electrodimerization of phenyl vinyl sulphone in slightly protic media: the formation of 1,4-bisphenylsulphonylbut-2-ene

Phenyl vinyl sulphone exhibits unusual cathodic behaviour in organic media containing a small excess of a proton donor such as acetic acid or phenol; both the saturated sulphone and an unsaturated dimer are isolated, the formation of which may be explained by hydrogen atom transfer between the organic free radicals formed at the interface.

Mechanism of ruthenium-catalyzed linear dimerization of acrylonitrile: a kinetic study

A detailed kinetic study of the RuCl 2(AN) 3-catalyzed linear dimerization of acrylonitrile reveals that the reaction is first order in Ru and H 2, and zero order in acrylonitrile. A reaction model is proposed which is consistent with the observed kinetic behavior and product distribution data, including our previous deuterium-labelling study [4]. It is visualized that two equivalents of base are first utilized to facilitate the generation of the active catalyst, a zero-valent Ru complex. The Ru(0) complex interacts reversibly with H 2 to give a ruthenium dihydride, which then enters into the dimer-forming catalytic cycle. Two subsequent acrylonitrile insertions, the first into one of the Ru—H bonds followed by another into the Ru—C bond formed in the first insertion, and a β-hydride elimination produce the observed linear dimer. The major side product, propionitrile, is formed by a competing reductive elimination from the hydrido(α- or β-cyanoethyl)ruthenium intermediate. Detailed product distribution analysis reveals the presence of one base ligand in the coordination sphere of the Ru. The coordination of base favors the production of saturated dimer vs. unsaturated dimer, but has no effect on the propionitrile: linear dimer ratio.

New quinolinone and bis-quinolinone alkaloids from Euxylophora paraensis

Three quinolin-2-one alkaloids were isolated from the heartwood of Euxylophora paraensis andidentified by spectroscopic methods as 2,3,3-trimethyl-2,3,4,5-tetrahydrofurano[3,2-c]quinolin-4-one(2a), its N-methyl derivative (2b), and 3-(1,2-dimethyl-2-hydroxypropyl)-4-hydroxy-1-methylquinolin-2(1 H)-one (3). Four new dimers, E, F, G and B, were also isolated and identified as the bisquinolin-2-ones (5c), (5d), (6) and (9). The unsaturated dimer G and an isomer have been prepared by oxidationof paraensidimerin A and C.