Vapor pressure measurements in the range 10 Pa to 1 Pa of four pentaerythritol esters: Density and vapor–liquid equilibria modeling of ester lubricants

Vapor pressures of four pure pentaerythritol esters, PE, pentaerythritol tetrapentanoate, pentaerythritol tetraheptanoate, pentaerythritol tetranonanoate and pentaerythritol tetra 2-ethylhexanoate were measured between 334 and 476 K in a recently developed gas saturation apparatus. The experimental vapor pressure values for the four polyolesters range from 5.6 × 10⁻⁵ Pa to 0.94 Pa. These data together with density values were used to determined SAFT and PC-SAFT characteristic parameters. The linearity of molecular parameters for both models with the molecular weight permits to interpolate and extrapolate these parameters for pentaerythritol ester with linear chains. For pentaerythritol esters with ethyl-alkanoic chains, the parameters of SAFT and PC-SAFT have been estimated assuming that the slope of these straight lines is the same for PEs with linear chains that for PE with branched chains. This procedure was used to predict density of commercial POEs, estimating the molecular weight when it is not available from the viscosity at 313.15 K. PC-SAFT gives better performances than SAFT to predict density data for these four compounds at high pressures and for other PEs at atmospheric pressure. Furthermore, characteristic parameters for Soave-Redlich-Kwong and Peng Robinson EoSs were also estimated from the experimental vapor pressures and literature density values.     

A Surprising Solid-Phase Effect: Development of a Recyclable “Traceless” Linker System for Reactions on Solid Support

Triazenes as “traceless” linkers for solid-phase synthesis have been utilized for the attachment of arenes to a solid support and yield the corresponding products after various organometallic reactions (Heck reaction and asymmetric dihydroxylation, see the reaction scheme) and cycloadditions (Diels–Alder reaction). The triazene linker is distinguished by its accessibility, thermal robustness, and capability to undergo regeneration.     

A Constrained Disorder Refinement: “Reinvestigation of “Single‐Crystal X‐ray Structure of 1,3‐Dimethylcyclobutadiene” by M. Shatruk and I. V. Alabugin”

Shatruk and Alabugin propose an alternative structural model for the observed electron density that we have attributed to the photochemical formation of 1,3‐dimethylcyclobutadiene in a protective solid crystalline matrix. The main criticism from Shatruk and Alabugin concerns the modeling of the disorder in the calixarene cavity and in particular the neglect of a residual electron density close to the O1 atom. We published (Chem. Eur. J. 2011 , 17, 10021) our opinion concerning this “ignored peak” in the Supporting Information of the paper. The current response to the Correspondence demonstrates that Shatruk and Alabugin have over‐modeled our data by assigning a small electron density peak, which is hardly more than the density corresponding to a hydrogen atom, to an under‐occupied oxygen site, using inappropriate refinement contraints.     

Generation of “Sumanenylidene”: A Ground‐State Triplet Carbene on a Curved π‐Conjugated Periphery

We have observed the generation of sumanenylidene ( 2 ), a divalent, neutral‐carbon species at the benzylic position of sumanene ( 1 ). We also clarified both experimentally and theoretically that the ground state of compound 2 was a triplet state and that its singlet–triplet energy gap (ΔE_ST) was similar to that in fluorenylidene. The curved structure of compound 2 led to slightly better spin delocalization over the two adjacent aromatic rings than in planar systems, because of the unpaired spins on the σ and π orbitals. Synthetic application of the carbene precursor, diazosumanene ( 5 ), with a variety of thiocarbonyl compounds revealed its utility for the preparation of tetrasubstituted alkene compounds (e.g., that contain a strongly electron‐donating unit) that are directly conjugated to the sumanene ( 1 ) moiety.     

Novelties of cyanide displacement reaction in ibuprofen amide process by phase transfer catalysis: Solid–liquid versus solid–liquid (omega)–liquid systems

This work deals with the phase transfer catalysed cyanide displacement reaction on 1-(4-isobutyl phenyl) ethyl chloride to synthesize 2-(4-isobutyl phenyl) propionitrile, which is an intermediate for the synthesis of ibuprofen analogs, belonging to a class of NSAID (nonsteroidal anti-inflammatory drugs). The reaction was studied using solid–liquid phase transfer catalysis (S-L PTC) with trace quantities of water, forming the so-called omega phase at 90 °C. The rates of reaction and selectivity to the product are enhanced in the S-L(org.)-L (ω) PTC in comparison with S-L PTC, which in turn is superior to L-L PTC; the latter suffers from the disadvantage of side reactions in the aqueous phase. In the current work, the effects of various parameters such as catalyst structure, catalyst loading, substrate loading and temperature were studied on the conversion and rates of reaction of 1-(4-isobutyl phenyl) ethyl chloride with solid sodium cyanide under S-L and S-L(ω)-L PTC at 90 °C with toluene as the organic solvent. Tetrabutylammonium bromide (TBAB) was found to be the best catalyst. The role of omega liquid phase in intensification of the S-L PTC was theoretically and experimentally investigated. The kinetic constants have been determined and the apparent activation energy is found as 4.2 kcal/mol, which suggests that the reaction is quite fast, which is likely to bring in mass transfer effects.     

Site‐Specific Solid‐State NMR Studies of “Trigger Factor” in Complex with the Large Ribosomal Subunit 50S

Co‐translational protein folding is not yet well understood despite the availability of high‐resolution ribosome crystal structures. We present first solid‐state NMR data on non‐mobile regions of a prokaryotic ribosomal complex. Localized chemical shift perturbations and line broadening are observed for the backbone amide resonances corresponding to the regions in the trigger factor ribosome‐binding domain that are involved in direct contact with the ribosome or undergo conformational changes upon ribosome binding. This large asymmetric protein complex (1.4 MDa) becomes accessible for NMR investigations by the combined use of proton detection and high MAS frequencies (60 kHz). The presented results open new perspectives for the understanding of the mechanism of large molecular machineries.     

The “True” Affinities of Metal Cations to p‐Sulfonatocalix[4]arene: A Thermodynamic Study at Neutral pH Reveals a Pitfall Due to Salt Effects in Microcalorimetry

A microcalorimetric study on the inclusion of monovalent and divalent metal cations by p‐sulfonatocalix[4]arene was performed. The thermodynamic parameters for the complexation of alkali metal cations and Ag⁺ were obtained for the first time at neutral pH. The Na⁺ cation is routinely present as counterion of the calixarene in neutral aqueous solution, and this must be taken into account in the determination of the thermodynamic parameters for the complexation of Na⁺ and the other cations by considering a sequential or a competitive binding scheme. The ΔH° and ΔS° values show that the inclusion process is entropically driven, although an influence of the temperature on the complexation reaction indicates that the enthalpic term is also an important contributor. The results also reveal that enthalpy/entropy compensation balances the gain in one contribution against a corresponding loss in the other. The obtained thermodynamic data are in contrast to the results from previous microcalorimetric studies, which showed binding constants that were orders of magnitude smaller and complexations, which were in part enthalpically driven but which neglected the influence of the alkali metal counterions.     

A Poly(9‐Borafluorene) Homopolymer: An Electron‐Deficient Polyfluorene with “Turn‐On” Fluorescence Sensing of NH3 Vapor

A substituted poly(9‐borafluorene) (P9BF) homopolymer, a boron congener of polyfluorene, is prepared by Yamamoto coupling of a triisopropylphenyl substituted borafluorene (1). As predicted by prior density functional theory (DFT) studies, P9BF has a reduced optical bandgap (E_g,opt = 2.28 eV) and a significantly lowered LUMO level (−3.9 eV, estimated by cyclic voltammetry (CV)) compared to polyfluorene. In addition to binding fluoride in solution, films of P9BF exhibit a reversible, simultaneous turn‐off/turn‐on fluorescence response to NH₃ vapor. A 9‐borafluorene‐vinylene copolymer (P9BFV) is synthesized via Stille coupling, demonstrating that 1 can readily be incorporated into copolymers. The extended conjugation of P9BFV due to the inclusion of the vinylene group results in a reduced optical bandgap (2.12 eV) and LUMO (−4.0 eV, estimated by CV) compared to the homopolymer P9BF.

     

Molecular engineering of liquid crystalline polymers by “living” polymerization. XXXII. Synthesis and “living” cationic polymerization of 3-fluoro-4′-(ω-vinyloxyalkoxy)-4-biphenylyl (2r,3s)-2-fluoro-3-methylpentanoate with undecanyl and octyl alkyl groups

The synthesis and “living” cationic polymerization of 3-fluoro-4′-(11-vinyloxyundecany-loxy)-4-biphenylyl (2R,3S)-2-fluoro-3-methylpentanoate ( 12-11 ) and 3-fluoro-4′-(8-vi-nyloxyoctyloxy)-4-biphenylyl (2R,3S)-2-fluoro-3-methylpentanoate ( 12-8 ) are presented. Poly ( 12-11 )s and poly ( 12-8 )s with degrees of polymerization from 4.0 to 16.5 and poly-dispersities ≤ 1.13 have been synthesized and characterized by differential scanning cal-orimetry (DSC) and thermal optical polarized microscopy. Over the entire range of molecular weights poly ( 12-11 )s and poly ( 12-8 )s exhibit an enantiotropic S_A and an unidentified S_X phase. In addition, regardless of its molecular weight, poly ( 12-8 ) exhibits a S^*_c phase in between the S_A and S_x phases. Poly ( 12-11 ) and poly ( 12-8 ) show lower transition tem-peratures and broader temperature ranges of all their mesophases as compared to the corresponding polymers without a fluorine atom on the biphenyl group. The role of the connecting group between the biphenyl and chiral group of the mesogenic unit on the phase behavior of these polymers is also discussed. Copolymers of 12-8 with (2R,3S)-2-fluoro-3-methylpentyl 4′-(11-vinyloxyundecanyloxy)biphenyl-4-carboxylate ( 13-11 ) {i.e., poly-[( 12-8 )-co-( 13-11 )] (X/Y), where X/Y represents the molar ratio of monomer 12-8 to monomer 13-11 } with DP of ca. 11 and polydispersities lower than 1.23 were also syn-thesized and characterized. Their S_A and S^*_c mesophases exhibit continuous dependences of composition and this support the assignment of the mesophases exhibited by poly ( 12-8 ). © 1995 John Wiley & Sons, Inc.     

Solution of the “Classical” Schrödinger equation for a driven symmetric triple well: A comparison with its classical counterpart

The behavior of a driven symmetric triple well potential has been studied by developing an algorithm where the well‐established Bohmian mechanics and time‐dependent Fourier Grid Hamiltonian method are incorporated and the quantum theory of motion (QTM) phase space structures of the particle are constructed, both in “nonclassical” and “classical” limits. Comparison of QTM phase space structures with their classical analogues shows both similarity as well as dissimilarities. The temporal nature and the spatial symmetry of applied perturbation play crucial roles in having similar phase space structures. © 2016 Wiley Periodicals, Inc.     

Covalently Linked Plasticizers: Triazole Analogues of Phthalate Plasticizers Prepared by Mild Copper‐Free “Click” Reactions with Azide‐Functionalized PVC

Copper‐free azide‐alkyne click chemistry is utilized to covalently modify polyvinyl chloride (PVC). Phthalate plasticizer mimics di(2‐ethylhexyl)‐1H‐triazole‐4,5 dicarboxylate (DEHT), di(n‐butyl)‐1H‐1,2,3‐triazole‐4,5‐dicarboxylate (DBT), and dimethyl‐1H‐triazole‐4,5‐dicarboxylate (DMT) are covalently attached to PVC. DEHT, DBT, and DMT have similar chemical structures to traditional plasticizers di(2‐ethylhexyl) phthalate (DEHP), di(n‐butyl) phthalate (DBP), and dimethyl phthalate (DMP), but pose no danger of leaching from the polymer matrix and forming small endocrine disrupting chemicals. The synthesis of these covalent plasticizers is expected to be scalable, providing a viable alternative to the use of phthalates, thus mitigating dangers to human health and the environment.

     

Ion–Molecule Reactions of “Rollover” Cyclometalated [Pt(bipy−H)]+ (bipy=2,2′‐bipyridine) with Dimethyl Ether in Comparison with Dimethyl Sulfide: An Experimental/Computational Study

The ion–molecule reactions of dimethyl ether with cyclometalated [Pt(bipy?H)]⁺ were investigated in gas‐phase experiments, complemented by DFT methods, and compared with the previously reported ion–molecule reactions with its sulfur analogue. The initial step corresponds in both cases to a platinum‐mediated transfer of a hydrogen atom from the ether to the (bipy?H) ligand, and three‐membered oxygen‐ and sulfur‐containing metallacycles serve as key intermediates. Oxidative C? C bond coupling (“dehydrosulfurization”), which dominates the gas‐phase ion chemistry of the [Pt(bipy?H)]⁺ ion with dimethyl sulfide, is practically absent for dimethyl ether. The competition in the formation of C₂H₄ and CH₂X (X=O, S) in the reactions of [Pt(bipy?H)]⁺ with (CH₃)₂X (X=O, S) as well as the extensive H/D exchange observed in the [Pt(bipy?H)]⁺/(CH₃)₂O system are explained in terms of the corresponding potential‐energy surfaces.     

The “comonomer effect” in ethylene/α‐olefin copolymerization using homogeneous and silica‐supported Cp2ZrCl2/MAO catalyst systems: Some insights from the kinetics of polymerization,active center studies,and polymerization temperature

Homogeneous and silica‐supported Cp₂ZrCl₂/methylaluminoxane (MAO) catalyst systems have been used for the copolymerization of ethylene with 1‐butene, 1‐hexene, 4‐methylpentene‐1 (4‐MP‐1), and 1‐octene in order to compare the “comonomer effect” obtained with a homogeneous metallocene‐based catalyst system with that obtained using a heterogenized form of the same metallocene‐based catalyst system. The results obtained indicated that at 70 °C there was general rate depression with the homogeneous catalyst system whereas rate enhancement occurred in all copolymerizations carried out with the silica‐supported catalyst system. Rate enhancement was observed for both the homogeneous and the silica‐supported catalyst systems when ethylene/4‐MP‐1 copolymerization was carried out at 50 °C. Active center studies during ethylene/4‐MP‐1 copolymerization indicated that the rate depression during copolymerization using the homogeneous catalyst system at 70 °C was due to a reduction in the active center concentration. However, the increase in polymerization rate when the silica‐supported catalyst system was used at the same temperature resulted from an increase in the propagation rate coefficient. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 267–277, 2008