Iron catalyzed polyethylene chain growth on zinc: a study of the factors delineating chain transfer versus catalyzed chain growth in zinc and related metal alkyl systems

The bis(imino)pyridine iron complex, [[2,6-(MeC=N-2,6-iPr2C6H3)2C5H)N]FeCl2] (1), in combination with MAO and ZnEt2 (> 500 equiv.), is shown to catalyze polyethylene chain growth on zinc. The catalyzed chain growth process is characterized by an exceptionally fast and reversible exchange of the growing polymer chains between the iron and zinc centers. Upon hydrolysis of the resultant ZnR2 product, a Poisson distribution of linear alkanes is obtained; linear alpha-olefins with a Poisson distribution can be generated via a nickel-catalyzed displacement reaction. Other dialkylzinc reagents such as ZnMe2 and ZniPr2 also show catalyzed chain growth; in the case of ZnMe2 a slight broadening of the product distribution is observed. The products obtained from Zn(CH2Ph)2 show evidence for chain transfer but not catalyzed chain growth, whereas ZnPh2 shows no evidence for chain transfer. The Group 13 metal alkyl reagents AlR3 (R = Me, Et, octyl, IBu) and GaR3 (R = Et, nBu) act as highly efficient chain transfer agents, whereas GaMe3 exhibits behavior close to catalyzed chain growth. LinBu, MgnBu2 and BEt3 result in very low activity catalyst systems. SnMe4 and PbEt4 give active catalysts, but with very little chain transfer to Sn or Pb. The remarkably efficient iron catalyzed chain growth reaction for ZnEt2 compared to other metal alkyls can be rationalized on the basis of: (1) relatively low steric hindrance around the zinc center, (2) their monomeric nature in solution, (3) the relatively weak Zn-C bond, and (4) a reasonably close match in Zn-C and Fe-C bond strengths.     

Effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases

Lyotropic quaternary mixtures of potassium alkanoates (KCx) and sodium alkyl sulphates (NaCxS), where x is the number of carbon atoms in their alkyl chains, were prepared to investigate the effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases. The lyotropic mixtures investigated were formed by the dissolution of KCx (NaCxS) surfactants in the mixture of Rb₂SO₄/1-decanol/water (Na₂SO₄/1-decanol/water), separately. The uniaxial-to-biaxial nematic phase transitions were identified from the temperature dependence of the birefringences of the nematic phases by means of laser conoscopy. The micelle dimensions were obtained from small-angle X-ray scattering measurements. It was observed that the increase in the surfactant alkyl chain length causes the micellar growth in the plane perpendicular to the main amphiphile bilayer. The surfactant alkyl chain length plays a key role on the shape anisotropy of micelles, which triggers the orientational fluctuations that are responsible for the stabilisation of the different lyotropic nematic phases.     

From crystal structure prediction to polymorph prediction: interpreting the crystal energy landscape

Many organic molecules are emerging as having many crystalline forms, including polymorphs and solvates, as more techniques are being used to generate and characterise the organic solid state. The fundamental scientific and industrial interest in controlling crystallisation is inspiring the development of computational methods of predicting which crystal structures are thermodynamically feasible. Sometimes, computing this crystal energy landscape will reveal that a molecule has one way of packing with itself that is sufficiently more favourable than any other so only this crystal structure will be observed. More frequently, there will be many energy minima that are energetically feasible, showing approximately equi-energetic compromises between the various intermolecular interactions allowed by the conformational flexibility. Such cases generally lead to multiple solid forms. At the moment, we usually calculate the lattice energy landscape, an approximation to the real crystal energy landscape at 0 K. Despite its limitations, many studies show that this is a valuable complement to solid form screening, which helps in discovering new structures as well as rationalising the solid forms that are found in experimental searches. The range of factors that can determine which of the thermodynamically feasible crystal structures are observed polymorphs, shows the many further challenges in developing crystal energy landscapes as a tool for control of the organic solid state.     

A new polymorph of the gastrokinetic drug cisapride monohydrate

Cisapride monohydrate (systematic name: 4‐amino‐5‐chloro‐N‐{(3RS,4SR)‐1‐[3‐(4‐fluorophenoxy)propyl]‐3‐methoxypiperidin‐4‐yl}‐2‐methoxybenzamide monohydrate), C₂₃H₂₉ClFN₃O₄·H₂O, is a nondopamine‐blocking gastrokinetic drug. A new polymorph of cisapride monohydrate has been reported nearly three decades after the report of its first known crystal structure [Collin et al. (1989). J. Mol. Struct. 214 , 159–175]. The second polymorph is also monoclinic, but with different unit‐cell parameters. A comparison of both polymorphic forms shows that the difference is thus not in the molecular conformation but in the arrangements of molecules in the crystal packing. The crystal morphology of two forms was predicted with the BFDH model in Materials Studio and inferred that the powder of the new polymorph has better flowability than the original polymorph. The results of DSC (differential scanning calorimetry) analysis and slurry experiments show that both polymorphs are stable at room temperature.     

Effects of a flexible alkyl chain on a ligand for CuAAC reaction

Imidazole derivatives substituted by a normal alkyl group are shown to be efficient as a ligand for the copper(Ι)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. An alkyl chain on the imidazole ligands shows an efficient steric effect and benefits the reaction. Such functionalities of an alkyl chain allow a rapid CuAAC reaction of even a bulky alkyne, which has been difficult to perform under conventional conditions.     

Effect of alkyl chain asymmetry on catanionic mixtures of hydrogenated and fluorinated surfactants

In this work we studied and compared the physicochemical properties of the catanionic mixtures cetyltrimethyl-ammonium bromide–sodium dodecanoate, cetyltrimethyl-ammonium bromide–sodium perfluorodacanoate, octyltrimethylammonium bromide–sodium perfluorodacanoate and cetyltrimethyl-ammonium bromide–sodium octanoate by a combination of rheological, transmission electron microscopy (TEM) and polarized optical microscopy measurements. The binary mixtures of the surfactants have been analyzed at different mixed ratios and total concentration of the mixture. Mixtures containing a perfluorinated surfactant are able to form lamellar liquid crystals and stable spontaneous vesicles. Meanwhile, system containing just hydrogenated surfactants form hexagonal phases or they are arranged in elongated aggregates.     

Synthesis, characterization and crystal structure of 1-ferrocenesulfonyl-2-long carbon chain alkyl benzimidazole

Six new 1-ferrocenesulfonyl-2-benzimidazole derivatives were prepared by the reaction of ferrocenesulfonyl chloride with benzimidazole derivatives in the presence of dichloromethane and n-tetrabutylammonia bromide. The yields of these six new ferrocenesulfonyl benzimidazole derivatives were about 80%. The structures characteristic were confirmed by IR, ¹H-NMR, Elemental analysis and MS. The crystal structure of compound a₂ was determined via X-ray single crystal diffraction and it belongs to monoclinic system with space group C2/c, and the unit cell parameters are α = 2.8252(2) nm, b = 0.97696(7) nm, c = 1.64828(12) nm, α = 90°, β = 92.053(2)°, γ = 90°, V = 4.5466(6) nm³, Z = 8, F (000) = 2024, Mr = 481.40, Dc = 1.407 g/cm³, μ = 0.784 mm⁻¹, R ₁= 0.0495, wR ₂= 0.1517. The results show that the reactions of 2-alkylbenzimidazoles containing active hydrogen with ferrocenesulfonyl chloride gave 1- ferrocenesulfonyl-2-alkylbenzimidazoles in good yields. __________ Translated from Chinese Journal of Applied Chemistry, 2007, 24(11) (in Chinese)     

The effects of a second branched alkyl chain and double chiral centres on the phase transition and spontaneous polarization of a chiral smectic liquid crystal

The effects of a second branched alkyl chain, lateral substitution, and double chiral centres on the phase transition and spontaneous polarization of the ferroelectric liquid crystal having a 2-methylalkanoyl group have been investigated. The introduction of another branched alkyl chain away from the 2-methylalkanoyl group causes a sharp S_C*-S_A transition peak and also enhances the ferroelectric properties in the S_C* phase. Since the order within the layers is liquid-like in the S_C* phase, the alkyl chain branching away from both the chiral centre and a polar group affects the overall motion of the molecule in the S_C* phase. In the system of a compound with double chiral centres, the existence of the chiral centre in the 2-methylalkanoyl group affects the phase transition temperatures and the magnitude of the spontaneous polarization in the S_C* phase. On the other hand, the existence of the chiral centre in the 2-methylbutyl group only affects the stability of a more highly ordered smectic phase appearing below the S_C* phase.     

Microemulsions: Effect of alkyl chain length of alcohol and alkane

In microemulsions consisting of four components, i.e. detergent — water — oil — cosurfactant, the free energy of transfer from the continuous oil phase to the interfacial region for the cosurfactant is reported. From the effect of temperature on the free energy, the entropy and the enthalpy values are also reported. The effect of chain length of the alcohol (cosurfactant) is also described. It is further shown, that if the oil phase consists of hexadecane, then the free energy changes as a linear function of the number of carbon atoms in the cosurfactant. On the other hand, if the oil phase is benzene, the cosurfactant chain length has very little effect. These data are analyzed with respect to the microemulsion structure and stability.     

Effect of the conformation of the alkyl chain on the catalytic miniemulsion copolymerization of ethylene and acrylates

The catalytic copolymerization of ethylene and acrylic monomers is a promising way of incorporating polar functionality into polyolefins and therefore enlarging the range of properties of these materials. This work shows that for the copolymerization of ethylene and C4 acrylates using a sterically encumbered Pd catalyst, the degree of incorporation of the acrylic monomer decreases with the degree of branching of the alkyl chain of the acrylate, the main reason being the difficulty for coordination of bulky acrylates to the catalytic site. This strongly affects the polymerization rate as well as the molecular weight, crystallinity and melting point temperature of the copolymers.     

Inversion twinning in a second polymorph of the hydrochloride salt of the recreational drug ethylone

A second polymorph of the hydrochloride salt of the recreational drug ethylone, C₁₂H₁₆NO₃⁺·Cl⁻, is reported [systematic name: (±)‐2‐ethylammonio‐1‐(3,4‐methylenedioxyphenyl)propane‐1‐one chloride]. This polymorph, denoted form (A), appears in crystallizations performed above 308 K. The originally reported form (B) [Wood et al. (2015). Acta Cryst. C 71 , 32–38] crystallizes preferentially at room temperature. The conformations of the cations in the two forms differ by a 180° rotation about the C—C bond linking the side chain to the aromatic ring. Hydrogen bonding links the cations and anions in both forms into similar extended chains in which any one chain contains only a single enantiomer of the chiral cation, but the packing of the ions is different. In form (A), the aromatic rings of adjacent chains interleave, but pack equally well if neighbouring chains contain the same or opposite enantiomorph of the cation. The consequence of this is then near perfect inversion twinning in the structure. In form (B), neighbouring chains are always inverted, leading to a centrosymmetric space group. The question as to why the polymorphs crystallize at slightly different temperatures has been examined by density functional theory (DFT) and lattice energy calculations and a consideration of packing compactness. The free energy (ΔG) of the crystal lattice for polymorph (A) lies some 52 kJ mol⁻¹ above that of polymorph (B).     

Ranking of polymorph stability for a pharmaceutical drug using the Noyes-Whitney titration template method

A further refinement to the screening process of candidate selection in early drug development is the selection of a polymorphic form on the bases of solid state stability. The Noyes-Whitney titration template method has been used routinely by others to determine the intrinsic solubility of sparingly soluble materials. This method uses potentiometric measurements whilst titrating over a pH range to determine the pH-solubility profile of a drug substance. Using a novel modification to the conventional Noyes-Whitney titration template method, this paper describes an application for the determination of the relative stability between polymorphic forms of materials. Such an assessment can be deduced from the change in Gibbs energy that accompanies the physical changes in materials when going from a solid to a solution phase and will be shown to be derived from the intrinsic solubility measurements. In addition, it will be shown that solution calorimetry was used to good effect to help in the interpretation of the solubility results.Three crystalline polymorphic modifications, a hydrate and two anhydrate forms, and an amorphous form of a pure drug substance currently in development in GSK were ranked in terms of physical stability. Stability measurements were made as a function of temperature and a phase diagram over a narrow temperature range was constructed.     

外缘烷基链长对共轭有机小分子聚集行为及光电性质影响

改变分子化学结构和调控分子结构聚集态行为从而影响或改变材料的化学和物理性质, 是开发新型高效有机光电功能材料的重要手段. 在共轭有机分子外缘引入烷基链一般是为了改进材料溶解性能, 但近来的一些研究表明, 烷基链长对一些共轭有机小分子固态聚集行为和光电性质具有重要影响, 烷基链扮演着显著调控材料光电性质的“功能基团”作用. 本文以聚集诱导发光（aggregation-induced emission, AIE）/聚集强化荧光（aggregation enhanced emission, AEE）发射共轭有机小分子为重点, 对近年来有关烷基链长对共轭有机分子聚集形态和光电性质影响的一些典型事例进行评述, 旨在使人们在进行共轭有机分子设计合成及其结构与性能关系研究中能够关注烷基链的因素, 使烷基链变化作为功能导向晶态共轭有机材料设计合成及其可控制备的一种手段.     

Effect of alkyl chain length on the surface dilational rheological and foam properties of N-acyltaurate amphiphiles

The dynamic dilational properties of sodium 2-(2-(alkylaryloxy)-alkylamido)ethanesulfonates (12+nB-Ts) at the air–water interfaces were investigated by drop shape analysis, and their foam properties were also measured. The influences of time and bulk concentration on surface dilational properties were expounded. The results show that the molecular interaction controls the nature of adsorption film during lower concentration range, and the film behaves elastic in nature. During higher concentration range, the diffusion exchange process controls the dynamic dilational properties and the surface film shows remarkable viscoelasticity. An increase in hydrophobic chain length enhances the molecular interaction at low concentration and speeds up the diffusion exchange process at high concentration, which results in the different variations of modulus at different concentration regions. For 12+nB-Ts, too short a chain probably produces bad film elasticity, whereas too great a length produces too fast liquid drainage. Therefore the optimal length in the branched chain leads to the best foam stability.     

Effect of electrostatic field on the polymer chain in the quaternized reaction of polyvinylpyridine with alkyl halides

In order to discuss the electrostatic-field effect on a polymer reaction, the quaternization of poly-4-vinylpyridine–benzyl chloride (system I) was compared to that of poly-γ-chloromethylstyrene–γ-picoline (system II). In these two systems, the reaction initially proceeded according to the simple second-order kinetics. However, after the degree of quaternization exceeded 20–30 mole-%, a deviation from simple second-order kinetics occurred. In system I negative deviation occurred, while in system II positive deviation occurred. These phenomena occurred even though the solvent or the initial concentrations of the reactants were changed. The reasons for these phenomena are given below. In system I, the quaternized pyridine nitrogens prevented the benzyl chloride from approaching the unquaternized pyridine nitrogens. However, in system II the free γ-picoline was attracted by the quaternized chloro-γ-methyl site. Furthermore, the point at which the deviation occurred was determined by the degree of chloromethylation. All these results suggest that the effect of an electrostatic field must be presumed in these two systems.