2-(4-Alkylphenyl)-5-(alkenyloxy)pyrimidines: Synthesis,liquid crystal transition temperatures and some physical properties

Abstract

We have recently reported the introduction of a carbon-carbon double bond into a wide variety of 5-n-alkyl-2-(4-n-alkoxyphenyl)pyrimidines to produce the corresponding alkenyloxy derivatives. The position and nature (E/Z) of the double bond were varied systematically and the effect on the liquid crystal transition temperatures studied. The position and nature (E/Z) of the double bond changed the conformation of the alkenyloxy chain substantially. This resulted in higher smectic C and nematic transition temperatures for compounds with a trans-double bond (E) at an even number of carbon atoms from the molecular core. Significantly lower transition temperatures (including the melting point) were observed for materials with a cis-double bond (Z) at an odd number of carbon atoms from the molecular core. We have now performed the same operation on the related 2-(4-n-alkylphenyl)-5-n-alkoxypyrimidines to produce the corresponding alkenyloxy derivatives. An interesting feature of the new results is the high melting points of the trans-substituted materials and the low melting points of the terminally substituted compounds. The smectic C transition temperatures of both series are high. No nematic phases could be observed. However, in admixture with other smectic C components, the new compounds lead to surprisingly fast switching times, high smectic C transition temperatures and low melting points/crystallization temperatures in experimental mixtures designed for electro-optic display devices based on ferroelectric effects.     

Thermal stability of new vanadyl complexes with flavonoid derivatives as potential insulin-mimetic agents

A series of new complexes of the type VO(OH)L·nH₂O ((1) L: fisetin, n = 3; (2) L: quercetin, n = 2; (3) L: morin, n = 4) were synthesised and characterised by analytical as well as IR and electronic data. The modification evidenced in IR spectra was correlated with the presence of flavonoid as bidentate in all complexes. The electronic reflectance spectra showed the d–d transition characteristic for the square-pyramidal stereochemistry of vanadium (IV) ion. The thermal analysis (TG, DTA) in synthetic air flow elucidated the composition and also the number and nature of the water molecules. The TG curves show three well-separated thermal events. The first corresponds to the water loss at lower temperatures, which is followed by flavonoid derivative decomposition and pyrolysis at higher temperatures. The final product is vanadium (V) oxide.     

FISSION OF AS-AS BONDS IN ELEMENTAL ARSENIC BY ALKALI METALS IN LIQUID AMMONIA. A ROUTE TO MONOALKYL ARSINES

Abstract

Addition of two mol equivalents of t-butyl alcohol to a mixture of powdered arsenic and three mol equivalents of lithium in liquid ammonia gives a suspension of lithium arsenide LiAsH₂. Subsequent addition of a large excess of t-butyl alcohol and n-octyl iodide at very low temperatures affords n-octyl arsine in -65% yield.     

Hydrogen bond-induced ferroelectric liquid crystals

Abstract

Hydrogen-bonded dimers of 4-alkoxy-4′-stilbazole homologues (C _n OSB, proton acceptors) and the mono-(2-methylbutyl)ester of terephthalic acid (MBTA, proton donor) behaved like conventional thermotropic mesogens. For chiral MBTA mixtures, chiral nematic and blue phases were observed with n = 1 and 2, and chiral smectic C phases were observed with n ≥ 5. Achiral phases were observed for mixtures with racemic MBTA as proton donor. Transition temperatures and enthalpies are similar for the chiral and achiral systems.     

Formation of micelles of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide in N-methyl acetamide—alcohol and N,N-dimethyl acetamide—alcohol mixtures

The critical micelle concentrations of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide in solutions of in N-methylacetami de and in N,N-dimethyl acetamide with added methanol, ethanol, n-propanol, n-butanol and n-pentanol were determined using electrical conductivity and surface tension measurements at various temperatures. Both methods show that micelles are formed in N-methyl acetamide and N, N-dimethyl acetamide solutions in a presence of n-alcohols. Critical micelle concentrations were also determined as functions of concentration of added alcohol. The data suggest that alcohol adding leads to an enhancement of penetration of alcohol into the micelle external shell that depends on the alcohol chain length. Thermodynamic parameters for micellar systems in a presence of n-alcohols were also calculated.     

Adiabatic scanning calorimetry of the nematic-smectic A1 and the smectic A1–smectic A transitions in frustrated smectic mixtures at low temperatures

Abstract

Phase diagram results and high resolution adiabatic scanning calorimetric data are presented for several binary mixtures of 4-cyanocyclohexyl-4'-n-butyl-cyclohexane and 1 amino-9-fluorenone showing smectic A₁ and smectic à phases at low temperatures. Contrary to present theoretical expectations and experimental evidence for other systems, we find strongly first order nematic to smectic A₁ transitions with a latent heat of about 2 kJ/mol for all the mixtures investigated. The enthalpy change related to the smectic A₁ to smectic à transitions is two orders of magnitude smaller and corresponds most likely to a fluctuation induced first order transition.     

Design and characterization of novel supramolecular liquid crystals involving multiple hydrogen bonds

A novel type of liquid crystalline system, namely 5-[4-(4-methoxyphenylazo)phenyloxyalkyloxy]isophthalic acidhydrazides (Dn , n = 3, 6, 10) was designed and synthesized. The FTIR spectra of the Dn compounds were examined in the range 4000-1000 cm^?1 at different temperatures. The results showed that the stretching vibration frequencies of the NH and C=O groups, and the NH₂ deformation shifted to lower frequencies with decrease of temperature, while out-of-plane NH bending shifted slightly to higher frequency. Intermolecular hydrogen bonding between NH, NH₂ and C=O groups is proposed and the schematic supramolecular Dn structure is given. This may explain the higher Dn transitional temperatures and their smectic phase behaviour compared with that of 5-[4-(4-methoxyphenylazo)phenyloxyalkyloxy]isophthalic acid diethyl esters.     

Analysis of Excess Molar Volumes of the Ternary Systems Containing a Propyl Alkanoate and Two Alkanes with Some Predictive Methods

Abstract

Excess molar volumes at 298.15 K of the ternary mixtures (propyl ethanoate + n-heptane + n-decane), (propyl propanoate + n-heptane + n-decane) and (propyl butanoate + n-heptane + n-decane) were determined using a DMA 60/602 Anton Paar densimeter. All the experimental values were compared with the results obtained with empirical expressions for estimating ternary properties from binary data and with the Nitta-Chao group-contribution model. For these ternary mixtures the same behaviour that had been observed in ester + n-alkane binary systems was found: excess volumes decrease when the ester length increases.     

Phase diagrams of (R4N)2[Nd(NO3)5]-carbon tetrachloride-n-octanol (n-butanol, n-decanol, cyclohexanol) liquid ternary systems at various temperatures

Phase diagrams are studied for (R₄N)₂[Nd(NO₃)₅]-CCl₄ n-octanol (n-butanol, n-decanol, cyclohexanol) ternary liquid systems, where R₄N⁺ stands for trialkylbenzylammonium, at T = 298.15–333.15 K. The (R₄N)₂[Nd(NO₃)₅]-CCl₄ binary system at all temperatures is a two-phase liquid. One phase (phase I) is almost neat carbon tetrachloride; the other (phase II) is enriched in (R₄N)₂[Nd(NO₃)₅]. The CCl₄ solubility in phase II increases with rising temperature. The liquid ternary systems are characterized by homogeneous and two-phase liquid solution fields. One phase is enriched in (R₄N)₂[Nd(NO₃)₅] and n-octanol (n-butanol, n-decanol, cyclohexanol) and the other in CCl₄. Miscibility fields in the ternary liquid systems narrow with rising temperature.     

(Liquid + liquid) equilibria for ternary mixtures of (ethylene glycol + toluene + n-octane)

Tie-line data for ternary systems of (ethylene glycol + toluene + n-octane) at three temperatures (295.15, 301.15, and 307.15) K are reported. The compositions of liquid phases at equilibrium were determined and the results were correlated with the UNIQUAC and NRTL activity coefficient models. The partition coefficients and the selectivity factor of ethylene glycol are calculated and compared to suggest which ethylene glycol is more suitable for extracting of toluene from n-octane. The phase diagrams for the studied ternary mixtures including both the experimental and correlated tie lines are presented. From the phase diagrams and the selectivity factors, it is concluded that ethylene glycol may be used as a suitable solvent in extraction of toluene from n-octane mixtures.     

Excess Molar Volumes of n-Pentanol + Cumene,n-Pentanol + 1,4-Dioxane and Cumene + 1,4-Dioxane at Different Temperatures

Abstract

Molar excess volumes (V^E ) and partial molar excess volumes ( ^VE ) are reported for non-electrolyte binary mixtures of n-pentanol + cumene, n-pentanol + 1,4-dioxane and cumene + 1,4-dioxane at four temperatures and over the whole concentration range. In these systems, the n-pentanol is a highly polar molecule with association in its pure state, while the others two show little polarity without association in their pure states. The results of V^E are discussed in terms of the interactions between components. The Prigogine–Flory–Patterson model of solution thermodynamics has been used to predict V^E . This work shows the importance of the three contributions δV _int, δV _p? and δV_F to V^E .     

Effect of Temperature on Phase Separation in Liquid Binary System Constituted by Tetradecane and Samarium(III) Nitrate Solvate with Tri-n-Butyl Phosphate and Ternary System Constituted by Tetradecane,Tri-n-Butyl Phosphate,and Samarium(III) Nitrate Solvate with Tri-n-Butyl Phosphate

The phase diagrams of a binary liquid system constituted by tetradecane and samarium(III) nitrate solvate with tri-n-butyl phosphate and a ternary system constituted by tetradecane, tri-n-butyl phosphate, and samarium(III) nitrate solvate with tri-n-butyl phosphate were studied at 298.15-355.15 K. The distribution of components between the phases was considered. The points of critical compositions of the ternary system at various temperatures and the upper critical temperature of mixing of the binary and ternary systems were estimated.     

Density studies in terephthalylidene-bis-p-n-alkylanilines

Abstract

The temperature dependence of density in terephthalylidene-bis-p-n-alkylanilines (TBAA5 and 6) is studied to investigate the phase transitions, associated volume jumps, order of the transitions, estimated pressure dependence of transition temperatures, and pretransitional effects. The compounds exhibit nematic, smectic A, smectic C, smectic F, smectic G and smectic H phases with higher clearing temperatures. The smectic A to smectic C transition, which is a fluctuation induced first order transition in TBAA5, is found to be a second order transition in TBAA5 and 6. The results are discussed in the light of other experimental reports. The estimated pressure dependence of transition temperatures along with the reported experimental P[sbnd]T data are discussed. The N[sbnd]S_A transition is first order in TBAA5 and 6. The studies across other transitions are also discussed.     

Curing behavior of epoxy resins with a series of novel curing agents containing 4,4′-biphenyl and varying methylene units

A new homologous series of curing agents (LCECAn) containing 4,4′-biphenyl and n-methylene units (n = 2, 4, 6) were successfully synthesized. The curing behaviors of a commercial diglycidyl ether of bisphenol-A epoxy (E-51) and 4,4′-bis(2,3-epoxypropoxy)biphenyl (LCE) by using LCECAn as the curing agent have been investigated by differential scanning calorimetry (DSC), respectively. The Ozawa equation was applied to the curing kinetics based upon the dynamic DSC data, and the isothermal DSC data were fitted using an autocatalytic curing model. The glass transition temperatures (T _g) of the cured epoxy systems were determined by DSC upon the second heating, and the thermal decomposition temperatures (T _d) were obtained by thermogravimetric (TG) analyses. The results show that the number of methylene units in LCECAn has little influence on the curing temperatures of E-51/LCECAn and LCE/LCECAn systems. In addition, the activation energies obtained by the dynamic method proved to be larger than those by the isothermal method. Furthermore, both the T _g and T _d of the cured E-51/LCECAn systems and LCE/LCECAn systems decreased with the increase in the number of methylene units in LCECAn.     

Side-chain crystallinity. III. Influence of side-chain crystallinity on the glass transition temperatures of selected copolymers incorporating n-octadecyl acrylate or vinyl stearate

The influence of side-chain crystallinity on the glass transition temperatures of selected copolymers was investigated. The copolymers were selected, in part, from those whose crystallinity was treated in the preceding paper. These included the lower amorphous acrylate esters, such as methyl, ethyl, n-butyl, and 2-ethylhexyl acrylates, together with methyl methacrylate and acrylonitrile, each copolymerized with n-octadecyl acrylate over the range of composition. The decline in the glass transition temperature was linear with increasing weight fraction of n-octadecyl acrylate for all systems in the composition range where the copolymers were essentially amorphous. The extrapolated T_g for the amorphous state of poly(n-octadecyl acrylate), and for amorphous poly(oleyl acrylate), was close to ?111°C. This coincided with a value previously obtained by an extrapolation of data on homologs. Beyond a critical fraction of octadecyl acrylate (0.3 to 0.5), developing side-chain crystallinity in n-octadecyl acrylate raised the glass temperature steadily for all systems, up to a value of 17-C, obtained for the crystalline homopolymer. Crystallinity did not develop in stiff copolymers until T_g was about 30°C below the melting point of the most perfect crystals. In compositionally heterogeneous copolymers incorporating vinyl stearate, blocks of crystalline units appeared to be dispersed in a glassy matrix of amorphous co-units. An empirical equation was derived which fitted the experimental data for random copolymers, over all composition ranges, with fair accuracy.     

Liquid–Liquid Equilibria of Oxygenate Fuel Additives with Water at 298.15 K: Ternary and Quaternary Aqueous Systems of Diisopropyl Ether and Hydrocarbons with 2-Propanol

Experimental tie-line data were determined for one ternary system, water + diisopropyl ether + n-heptane and two quaternary systems, water + diisopropyl ether + 2-propanol + n-heptane or toluene at 298.15 K and ambient pressure. The experimental liquid–liquid equilibrium data were successfully correlated using a modified UNIQUAC model with ternary and quaternary mixture parameters, in addition to the binary ones. The calculated results were also compared with those obtained from an extended UNIQUAC model of Nagata [Fluid Phase Equilib. 54, 191 (1990)].     

Trimeric liquid crystals containing lateral alkyl chains

Abstract

The first twelve members of the n-alkyl 2,5-bis-(4′-cyanobiphenyloxybutyloxy)-benozates have been prepared. The compounds are nematogenic; in addition the first three members exhibit a smectic A phase. The nematic-isotropic transition temperatures decrease with little or no alternation on increasing the number of methylene groups in the lateral chain; this is analogous to the behaviour found in monomeric and polymeric mesogens possessing lateral alkyl chains.     

The synthesis and liquid crystalline behaviour of alkoxy‐substituted derivatives of 1,4‐bis(phenylethynyl)benzene

Despite the prevalence of organised 1,4‐bis(phenylethynyl)benzene derivatives in molecular electronics, the interest in the photophysics of these systems and the common occurrence of phenylethynyl moeties in molecules that exhibit liquid crystalline phases, the phase behaviour of simple alkoxy‐substituted 1,4‐bis(phenylethynyl)benzene derivatives has not yet been described. Two series of 1,4‐bis(phenylethynyl)benzene derivatives, i.e. 1‐[(4′‐alkoxy)phenylethynyl]‐4‐(phenylethynyl)benzenes (5a–5f) and methyl 4‐[(4″‐alkoxy)phenylethynyl‐4′‐(phenylethynyl)] benzoates (18a–18f) [alkoxy = n‐C₄H₉ (a), n‐C₆H₁₃ (b), n‐C₉H₁₉ (c), n‐C₁₂H₂₅ (d), n‐C₁₄H₂₉ (e), n‐C₁₆H₃₃ (f)] have been prepared and characterised. Both series have good chemical stability at temperatures up to 210°C, the derivatives featuring the methyl ester head‐group (18a–18f) offering rather higher melting points and generally stabilising a more diverse range of mesophases at higher temperatures than those found for the simpler compounds (5a–5f). Smectic phases are stabilised by the longer alkoxy substituents, whereas for short and intermediate chain lengths of the simpler system (5a–5c) nematic phases dominate. Diffraction analysis was used to identify the SmB_hex phase in (5d–5f) that is stable within a temperature range of approximately 120–140°C. The relationships between the organisation of molecules within these moderate temperature liquid crystalline phases and other self‐organised states (e.g. Langmuir‐Blodgett films) remain to be explored.     

Side-chain crystallinity. V. Heats of fusion and melting temperatures on monomers whose homopolymers have long side chains

Heats of fusion and melting temperatures were obtained for selected monomeric n-alkyl acrylates, N-n-alkylacrylamides, and vinyl esters. The corresponding thermodynamic parameters for homopolymers, derived from these monomers, had been reported previously from this laboratory. The α-hexagonal crystal modification was indicated near the melting point for the higher n-alkyl acrylates, but a β form was stable at low temperatures for the entire series. The magnitude of the heats of fusion indicated β polymorphs for vinyl esters in support of x-ray diffraction analysis from the literature. Because hexagonal crystal geometry prevailed in all reported homopolymers having long side chains, greater emphasis was placed on thermodynamic data for monomers exhibiting this crystal modification. Accordingly, a convergence temperature was estimated statistically for the α-hexagonal crystal modification of these systems and appropriate literature values of the n-alkanes and ethyl esters. The convergence temperature was computed to be 135°C, uncorrected for the entropy of disorientation. The anomalously large interfacial end-packing-defect energy of the poly(n-alkyl acrylates) and the poly-N-n-alkylacrylamides was shown to be associated with a high energy barrier to molecular transport in the melt as the vitreous state was approached. In support of this conclusion, similarity of the glass and melting transition temperatures of these homopolymer homologs occurred near their critical side-chain lengths, below which the homopolymers are amorphous. A special critical requirement of nucleus length was not indicated from rough estimations of nucleation parameters for the poly(n-alkyl acrylates). These findings lent increased, but still not unqualified, support to an x-ray diffraction study from the literature. The latter had specified the inclusion of the entire side chain and the main-chain units in the crystal lattices of the higher poly(n-alkyl acrylates).     

Critical temperatures and pressures of linear alk-1-enes with 13 to 20 carbon atoms using the pulse-heating technique

The paper presents experimental critical temperatures and critical pressures of thermally unstable alk-1-enes C_nH_2n with a number of carbon atoms n=13–20. The method of pulse heating of a wire probe placed in the liquid under investigation has been used. Equations for correlation of the critical temperatures and pressures of alk-1-enes with a number of carbon atoms in a molecule have been obtained. The acentric factors of alk-1-enes have been calculated.