Calorimetric study of the relationship between molecular structure and liquid crystallinity of rod-like mesogens II. Heat capacities and phase transitions of 4-(trans-4-propylcyclohexyl)benzonitrile

The molar heat capacity of the rod-like compound 4-(trans-4-propylcyclohexyl)benzonitrile (3-CBCN), purity of 99.8mol%, has been measured with an adiabatic calorimeter at temperatures between 15 and 385K. 3-CBCN is a nematogenic mesogen, whose melting and clearing points are 316.33 and 319.09 K, respectively. The enthalpy and entropy gained at fusion are 20.4 kJmol -1 and 64.4 J K -1 mol -1, respectively; those for the nematic-to-isotropic transition are 1.1 kJmol -1 and 3.5 J K -1 mol -1 respectively. 3-CBCN exhibits a supercooled nematic phase, whose molar heat capacities have been measured from 25 K below the melting point. The molar and transition entropies of 3-CBCN are discussed in relation to those of 4-propylbiphenyl-4-carbonitrile (3-BBCN) and trans,trans-4'-propylbicyclohexyl- 4-carbonitrile (3-CCCN). There seems to exist a correlation between these values and mesophase stability. Finally, Eidenschink's theoretical model for the nematic-to-isotropic transition has been applied to 3-CBCN; the transition enthalpy estimated according to this model agrees well with the observed value.     

Synthesis,crystal structure and thermal behavior of 4-amino-3,5-dinitropyrazole copper salt

A novel energetic combustion catalyst, 4-amino-3,S-dinitropyrazole copper salt （[Cu（adnp）2（H2O）2]）, was synthesized in a yield of 93.6% for the first time. The single crystal of [Cu（adnp）2（H2O）2] was determined by single crystal X-ray diffraction. It crystallizes in a triclinic system, space group p^-1 with crystal parameters a = 5.541（3） A, b = 7.926（4） A, c = 10.231（5） A,β = 101.372（8）°, V = 398.3（3） A3, Z = 1, μ = 1.467 mm^-1, F（0 0 0） = 243, and Dc = 2.000 g cm^-3. The thermal behavior and non-isothermal decomposition reaction kinetics of [Cu（adnp）2（H2O）2] were studied by means of different heating rate differential scanning calorimetry （DSC）. The kinetic equation of major exothermic decomposition reaction for [Cu（adnp）2（H2O）2] was obtained. The entropy of activation （△S≠）, enthalpy of activation （△H≠）, free energy of activation （△G≠）, the self-accelerating decomposition temperature （TSADT） and the critical temperature of thermal explosion （Tb） are 59.42 j mol^-1 K^-1, 169.5 kJ mol^-1, 1141.26 kJ mol ^-1 457.3 K and 468.1 K, respectively.     

4-羟甲基吡啶的热力学性质

用精密自动绝热量热计测定了4-羟甲基吡啶在79～380 K温区的摩尔热容. 实验结果表明, 该化合物在79～301 K温区无相变和热异常现象发生, 在301～331 K, 发生固-液相变, 其熔化温度、摩尔熔化焓及摩尔熔化熵分别确定为：325.12 K, 11.78 kJ•mol^-1 和36.23 J•K^-1•mol^-1. 根据热力学函数关系式, 从热容值计算了4-羟甲基吡啶在80～380 K温区以标准状态（298.15 K）为基准的热力学函数值. 用热重法(TG)对该化合物的热稳定性作进一步考察, 从TG曲线上观察到该化合物在490 K有最大的蒸发失重速率.     

Low-temperature Heat Capacity and Standard Thermodynamic Functions of D-Galactose and Galactitol

The heat capacities of D-galactose and galactitol were measured on a quantum design physical property measurement system(PPMS) over a temperature range of 1.9―300 K, and the experimental data were fitted to a function of T using a series of theoretical and empirical models in appropriate temperature ranges. The fit results were used to calculate thermodynamic function values,C_p,m^θ,Δ₀^TS_m^θ, and Δ₀^TH_m^θfrom 0 K to 300 K. The standard molar heat capacity, entropy and enthalpy values of D-galactose and galactitol at 298.15 K and 0.1 MPa were determined to be C_p,m^θ =(227.96±2.28) and (239.50±2.40) J·K^-1·mol^-1,S_m^θ= (211.22±2.11) and (230.82±2.30) J·K^-1·mol^-1 and = H_m^θ (33.95±0.34) and (36.57± 0.37) kJ/mol, respectively.     

用恒温热重法测定1-己基-3-甲基咪唑苏氨酸离子液体[C6mim][Thr]蒸汽压和蒸发焓

用中和法合成了氨基酸离子液体(AAIL)1-己基-3-甲基苏氨酸盐[C₆mim][Thr],并用核磁共振氢谱(¹H NMR)和核磁共振碳谱(¹³C NMR)进行了表征。以苯甲酸为参考物质,用恒温热重法确定了AAIL[C₆mim][Thr]的蒸汽压和在平均温度下(T_av= 438.15 K)的蒸发焓(Δ^g_lH_m^? (T_av) =128.5 ± 6.0 kJ·mol^-1)。利用Verevkin等人提出的方法计算得到AAIL[C₆mim][Thr]气态和液态的恒压热容差(Δ^g_lC_pm^? = -70.8 J·K^-1·mol^-1),进而计算了不同温度的蒸发焓,其中参考温度(298.15 K)下的蒸发焓Δ^g_lH_m^? (298.15 K) = 138.4 kJ·mol^-1,只比应用我们提出的蒸发焓理论模型估算值大1.6 kJ·mol^-1,小于恒温热重法的实验误差3.0 kJ·mol^-1,说明这个蒸发焓的理论模型有一定的合理性。借助Clausius-Clapeyron方程估算了AAIL[C₆mim][Thr]的假想的正常沸点T_b= 522.07 K,以及沸点的蒸发熵Δ^g_lS_m^? (T_b) = 228.5 J·K^-1·mol^-1,进一步得到了不同温度的蒸发熵和蒸发自由能Δ^g_lG_m^? (T),其结果表明蒸发自由能随着温度的上升而减小,达到沸点温度T_b时变为零,而蒸发熵则随着温度上升而增大,是AAIL[C₆mim][Thr]蒸发过程的驱动力。     

CTAB对四磺酸基酞菁钴与Na2S反应的影响

研究了十六烷基三甲基溴化铵（CTAB）对四磺酸基酞菁钴(CoTsPc)与Na₂S反应的影响，发现在CTAB存在下CoTsPc与Na₂S更易发生氧化还原反应生成轴向配合物HSCo(I)TsPc. 讨论了CTAB对该反应的作用机理. 采用多波长、双系数法解析反应平衡混合物的紫外吸收光谱，计算了该反应生成物的组成和反应的平衡常数. 从温度对反应平衡常数影响，得到了该反应的热力学数据. 在CTAB浓度为8.36×10^-3 mol•L^-1及303 K时，反应的ΔGΘ、ΔHΘ和ΔSΘ分别为－17.28 kJ•mol^-1、84.1 kJ•mol^-1 和335 J•mol^-1•K^-1.     

Synthesis and Thermal Behavior of 1,8-Dihydroxy- 4,5-dinitroanthraquinone Manganese Salt

A novel energetic combustion catalyst, 1,8-dihydroxy-4,5-dinitroanthraquinone manganese salt （DHDNEMn）, was synthesized by virtue of the metathesis reaction in a yield of 91%, and its structure was characterized by IR, element analysis and differential scanning calorimetry（DSC）. The thermal decomposition reaction kinetics was studied by means of different heating rate DSC. The results show that the apparent activation energy and pre-exponential factor of the exothermic decomposition reaction of DHDNEMn obtained by Kissinger＇s method are 162.3 kJ/mol and 1011.8 s^-1, respectively. The kinetic equation of major exothermic decomposition reaction of DHDNEMn is dα/dT= 10^118/β 2/5（1-α）[-ln（1-α）[-ln（1-α）]^3/5 exp（-1.623×10^5/RT）. The entropy of activation（△S^≠）, enthalpy of activation（△H^≠） and free energy of activation（A△G^≠） of the first thermal decomposition are -24.49 J·mol^-1·K^-1, 185.20 kJ/mol and 199.29 kJ/mol（T=575.5 K）, respectively. The self-accelerating decomposition temperature（TSADT） and critical temperature of thermal explosion（Tb） are 562.9 and 580.0 K, respectively. The above-mentioned information on the thermal behavior is quite useful for analyzing and evaluating the stability and thermal safety of DHDNEMn.     

TEMPO-initiated oxidation of 2-aminophenol to 2-aminophenoxazin-3-one

The oxidation reaction of 2-aminophenol (OAP) to 2-aminophenoxazin-3-one (APX) initiated by 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) has been investigated in methanol at ambient temperature. The oxidation of OAP was followed by electronic spectroscopy and the rate constants were determined according to the rate law −d[OAP]/dt=k_obs[OAP][TEMPO]. The rate constant, activation enthalpy and entropy at 298 K are as follows: k_obs (dm³ mol⁻¹ s⁻¹)=(1.49±0.02)×10⁻⁴, E_a=18±5 kJ mol⁻¹, ΔH^‡=15±4 kJ mol⁻¹, ΔS^‡=−82±17 J mol⁻¹ K⁻¹. The results of oxidation of OAP show that the formation of 2-aminophenoxyl radical is the key step in the activation process of the substrate.     

Temperature dependence of the rate constant for reactions of hydrated electrons with H, OH and H2O2

The temperature dependence of the rate constants, for the reactions of hydrated electrons with H atoms, OH radicals and H₂O₂ has been determined. The reaction with H atoms, studied in the temperature range 20–250°C gives k(20°C) = 2.4 × 10¹⁰M^-1s¹ and the activation energy E_A = 14.0 kJ mol^-1 (3.3 kcal mol^-1). For reaction with OH radicals the corresponding values are, k(20°C) = 3.1 × 10¹⁰M^-1s^-1 and E_A = 14.7 kJ mol^-1 (3.5 kcal mol^-1) determined in the temperature range 5–175°C. For reaction with H₂O₂ the values are, k(20°C) = 1.2 × 10¹⁰M^-1s^-1 and E_A = 15.6 kJ mol^-1 (3.7 kcal mol^-1) measured from 5–150°C. Thus, the activation energy for all three fast reactions is close to that expected for diffusion controlled reactions. As phosphates were used as buffer system, the rate constant and activation energy for the reaction of hydrated electron with H₂PO₄^- was determined to k(20°C) = 1.5 × 10⁷M^-1s^-1 and E_A = 7.4 kJ mol^-1 (1.8 kcal mol^-1) in the temperature range 20–200°C.     

铝基离子液体BMIAlCl4的热力学性质

在高纯氩气氛下, 直接将摩尔比为1:1的高纯无水AlCl₃和BMIC(氯化1-甲基-3-丁基咪唑)搅拌混合, 得到一种无色透明的离子液体BMIAlCl₄. 在278.2～343.2 K范围内, 用最大气泡法测定了BMIAlCl₄的表面张力, 用Westphal天平法测定了该离子液体的密度；利用Glasser经验方程讨论了该离子液体的热力学性质, 并与其它离子液体作了比较. 根据空隙模型计算了BMIAlCl₄离子液体的恒压热膨胀系数, 与本文实验值基本一致, 说明空隙模型具有一定的合理性.     

Phase behavior, conformations, thermodynamic properties, and molecular motion of multicomponent paraffin waxes: A Raman spectroscopy study

Variable-temperature (72–20 °C) studies of Raman spectra (3100–800 cm⁻¹) and thermal analysis of multicomponent paraffin wax have been carried out. The disorder–order transition under liquid–solid transition was observed and their temperature ranges were obtained through the S_lateral order parameter as a function of temperature. From 56 to 43 °C, the paraffin undergoes a conformational state transition of non-extended chain state (NECS) to extended chain state (ECS). The enthalpy and entropy change for the transition obtained by van’t Hoff analysis were 214.286 ± 21 kJ/mol and 0.661 ± 0.066 kJ/mol/K, respectively. The enthalpy determined by differential scanning calorimetry (DSC) was 52.165 ± 5.2 kJ/mol, which is smaller than the van’t Hoff enthalpy due to larger effective non-extended chain state. The variation of Raman spectra with decreasing temperature presents the structure evolution and molecular motion during the crystallization of paraffin wax.     

Dipolar coupling study of the conformations and ordering of 4-chloroethoxybenzene in a nematic solvent

The observed dipolar couplings of 4-chloroethoxybenzene in a nematic solvent are used to study the internal rotations about the O-C(H₂) bond. Accurate theoretical reproductions of these couplings are obtained using the standard three state (trans, gauche^±) rotational isomer model with gauche rotation angle φ^g = 96° and the trans—gauche energy difference E_tg, = 5·52kJ mol^-1. The probabilities and ordering matrix components of the trans and gauche forms are calculated.     

Dimesitylborane monomer-dimer equilibrium in solution, and the solid-state structure of the dimer by single crystal neutron and X-ray diffraction

Dimesitylborane dimer has been shown to exist in equilibrium with dimesitylborane monomer in solution. This equilibrium has been investigated by variable concentration and variable temperature multinuclear NMR spectroscopy and values for the dissociation constant, enthalpy and entropy of dissociation were found to be K_diss=(3.2±0.4)×10⁻³ M, ΔH=70 kJ mol⁻¹, and ΔS=212 J K⁻¹mol⁻¹, respectively. Ab initio methods have been used to investigate the gas-phase structures and energies of both monomer and dimer, and calculated ¹¹B-NMR shifts are also presented. The solid-state structure of dimesitylborane dimer has been investigated by single crystal X-ray diffraction at 100 K and the position of the bridging hydrogen atoms (B---H=1.340(2), 1.342(2) Å, H---B---H=92.46(14)°) has been determined accurately, for the first time, by single crystal neutron diffraction at 20 K.     

Thermal stability and related thermodynamic properties of N-ethylthiourea

The enthalpy and entropy of sublimation of N-ethylthiourea were obtained from the temperature dependence of its vapour pressure measured by both the torsion–effusion and the Knudsen effusion method in the temperature range 360–380 K. The compound undergoes no solid-to-solid phase transition or decomposition below 380 K. The pressure against reciprocal temperature resulted in lg(p, kPa) = (13.40 ± 0.27) − (6067 ± 102) /T(K). The molar sublimation enthalpy and entropy at the mid interval temperature were Δ_subH_m(370 K) = (116.1 ± 2.0) kJ mol⁻¹ and Δ_subS_m(370 K) = (218.0 ± 5.2) J mol⁻¹ K⁻¹, respectively. The same quantities derived at 298.15 K were (118.8 ± 2.1) kJ mol⁻¹ and (226.1 ± 5.5) J mol⁻¹ K⁻¹, respectively.     

The High-spin↔Low-spin Equilibrium of Iron(Ⅱ) Complexes with Schiff Base Ligand:Optical,Magnetic and Spectroscopic Properties

Spin transition compounds are of great interest because of their potential application in molecular based electronic devices such as optical memoty and switch, display and data record^[1]. The occurrence of iron(Ⅱ) spin crossover systems depends on the ligand field strength. Iron(Ⅱ) spin crossover compounds mainly have sixfold nitrogen coordination and the range of lODq is very narrow:10Dq^HS≈11500-12500 cm^-1 and 10Dq^LS≈19000-21000 cm^-1[2]. The sensitivity of the spin state to small perturbations suggests that new coordination complexes exhibiting spin transition phenomena could be designed through a fine tuning of the ligands surrounding the metal. The derivatives of 1,2,4-triazole have been found to generate an intermediate ligand field force and the iron(Ⅱ) compounds containing such ligands which yielded spin-crossover materials exhibiting cooperative behavior have been reported recently^[3]. In this paper we present two new iron(Ⅱ) compounds FeL₃(ClO₄)₂·2H₂O (1) and FeL₃(BF₄)₂·3H₂O (2),where L is the Schiff base ligand derived from 4-amino-l,2,4-triazole and benzaldehyde. The compounds appear as white (HS) powders at room temperature and the color changes to pink (LS) upon decreasing the temperature to liquid nitrogen. 1 and 2 are investigated by the optical setup (520 nm, 293-77 K), ⁵⁷Fe Mössbauer Spectroscopy (293-77 K) and magnetic susceptibility (293-4 K). The HS→LS and LS→HS transitions were observed at Tc↓=135 K (1) and 169 K (2), and Tc↑=150 K (1) and 180 K (2), respectively. The thermal hysteresis is found to be 15 K and 11 K for 1 and 2. The area fractions are calculated to be 57% for 1 and 43% for 2. Variable temperature magnetic susceptibility data were fitted to magnetic susceptibility equations derived from domain model, two level Ising-type model and regular solution model. The calculated variations of enthalpy and entropy of the compounds fall within the limits ΔH≈8.1-10.9 kJ·mol^-1 and ΔS≈47-61 J·K^-1·mol^-1 found for mononuclear iron(Ⅱ) spin transition compounds from calorimetric measurements. The cooperativity parameter y determines the occurrence of hysteresis.     

2, 6-二甲氧基-2-嘧啶氧基-N-芳基苄胺衍生物的酸催化Smiles重排反应动力学

研究了酸催化下的2, 6-二甲氧基-2-嘧啶氧基-N-芳基苄胺衍生物Smiles重排反应的动力学,考察了盐酸的初始浓度、溶剂、反应温度和取代基对反应速率的影响。结果表明,盐酸的初始浓度增加,重排反应速率加快;在单一溶剂中反应速率的顺序为:甲醇>乙醇>二甲基亚砜>乙腈,而在甲醇/水(1:1, V/V)的混合溶剂中反应速率明显增加,其表观反应速率常数(k_obs)值是甲醇溶剂中的5.27倍;在25-45 ℃温度范围内,各衍生物的反应速率随着温度的升高而加快,其活化能(73.99-76.92 kJ·mol^-1)、活化焓(71.57-74.38 kJ·mol^-1)及Gibbs自由能(81.51-85.77 kJ·mol^-1)数值相近,仅活化熵(-24.38 --47.11 J·K^-1·mol^-1)有一定的差别;取代基常数和表观速率常数之间呈现一定的线性关系,环上吸电子基团的存在有利于反应速率的提高;实验验证了反应机理的合理性。     

Determination of the free activation energy for the breaking of the P---Ag bond in [(η-p-cymene)Ru(μ-pz)3Ag(PPh3)]

The Arrhenius equation corresponding to the process P---Ag+P*---Ag*→---P---Ag*+P*---Ag has been determined for [(η⁶-p-cymene)Ru(μ-pz)₃Ag(PPh₃)] (1) by complete line-shape analysis of the ³¹P NMR spectra between −40°C and +30°C. It has the form K = 10^11.8± e^{(−46±5 kJ mol−1/RT)}. The preexponential term, log A = 11.8 corresponds to a small activation entropy, whereas the activation energy, 46 kJ mol⁻¹ is comparable to those determined for other phosphorus—metal compounds.     

Heat capacity and thermodynamic properties of N-(2-cyanoethyl) aniline (C9H10N2)

The low temperature heat capacities of N-(2-cyanoethyl)aniline were measured with an automated adiabatic calorimeter over the temperature range from 83 to 353 K. The temperature corresponding to the maximum value of the apparent heat capacity in the fusion interval, molar enthalpy and entropy of fusion of this compound were determined to be 323.33 ± 0.13 K, 19.4 ± 0.1 kJ mol⁻¹ and 60.1 ± 0.1 J K⁻¹ mol⁻¹, respectively. Using the fractional melting technique, the purity of the sample was determined to be 99.0 mol% and the melting temperature for the tested sample and the absolutely pure compound were determined to be 323.50 and 323.99 K, respectively. A solid-to-solid phase transition occurred at 310.63 ± 0.15 K. The molar enthalpy and molar entropy of the transition were determined to be 980 ± 5 J mol⁻¹ and 3.16 ± 0.02 J K⁻¹ mol⁻¹, respectively. The thermodynamic functions of the compound [H_T − H_298.15] and [S_T − S_298.15] were calculated based on the heat capacity measurements in the temperature range of 83–353 K with an interval of 5 K.     

A thermodynamic investigation on the binding of mercury ion with myelin basic protein at different temperatures

A thermodynamic study on the interaction of myelin basic protein with mercury ion was studied by using isothermal titration calonmetry,ITC,at 300.15,310.15 and 320.15 K in Tris buffer solution at pH 7.The enthalpies of MBP + Hg²⁺ interaction are reported and analysed in terms of the extended solvation model.It was found that MBP has two identical and non-cooperative binding sites for Hg²⁺ ions.The intrinsic dissociation equilibrium constants are 99.904,112.968 and 126.724μmol/L,and the molar enthalpy of binding are -11.634,-10.768 and -10.117kJ mol^-1 at 300.15,310.15 and 320.15 K,respectively.     

Alkyl group as entropy reservoir in an MMX chain complex, Pt2(n-PenCS2)4I

Heat capacity of halogen-bridged one-dimensional binuclear metal complex (so-called MMX chain) having four n-pentyl groups, Pt2(n-PenCS2)4I, was measured by adiabatic calorimetry. A first-order phase transition was observed at 207.4 K when measurement was made after cooling from room temperature. The enthalpy and entropy of transition were determined to be 10.19 kJ mol(-1) and 49.1 J K(-1) mol(-1), respectively. A monotropic phase transition was observed at 324 K on heating, and the entropy of transition was essentially null. The sample once heated above 324 K never returned to the initial phase at room temperature and underwent a higher-order phase transition at 173 K and a first-order phase transition at 220.5 K. The enthalpy and entropy of the first-order phase transition were estimated to be 11.6 kJ mol(-1) and 52.4 J K(-1) mol(-1), respectively. The magnitude of the entropy gain at the phase transition from the initial room-temperature phase to the high-temperature phase at 324 K shows that in Pt2(n-PenCS2)4I a large amount of entropy reserved in alkyl chain is transferred to dithiocarboxylato groups upon the phase transition, as in the cases of Pt2(n-PrCS2)4I and Pt2(n-BuCS2)4I.