Search

This work aims to provide reliable heat capacities for ethylene glycol and selected oligo(ethylene glycol)s (diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and h...

Isobaric heat capacities of ten selected aliphatic octanols (3-octanol, CAS RN: 589-98-0; 2,2,4-trimethyl-3-pentanol, CAS RN: 5162-48-1; 2,2-dimethyl-3-hexanol, CAS RN: 4209-90-9; 2,3-dimethyl-3-hexanol, CAS RN: 4166-46-5; 2,4-dimethyl-3-hexanol, CAS RN: 13432-25-2; 2,5-dimethyl-3-hexanol, CAS RN: 19550-07-3; 3,5-dimethyl-3-hexanol, CAS RN: 4209-91-0; 4-ethyl-3-hexanol, CAS RN: 19780-44-0; 3-methyl-4-heptanol, CAS RN: 1838-73-9; 4-methyl-4-heptanol, CAS RN: 598-01-6) were measured with a Tian–Calvet calorimeter in the temperature range from 257 to 358 K; this temperature range was extended up to 423 K with a heat-flux DSC. For all studied compounds, a maximum on temperature dependence of heat capacity was observed; this feature was corroborated by FTIR spectroscopy performed from 303 K to a maximum of 463 K. Such maxima are related to disintegration of oligomers kept together by hydrogen bonds. The role of steric hindrance on hydrogen bonding is discussed. It is apparent that temperature of maxima is very sensitive to steric hindrance; however, further effort is required for full understanding of hydrogen bonding in aliphatic octanols.

The heat capacity and thermal behavior trend along the 1-alkyl-3-methylimidazolium hexafluorophosphate [C n C 1 im][PF 6 ] (with n = 2–10, 12) ionic liquids series, is used to explore the effect of the alkyl chain length in the nanostructuration. The heat capacities of the studied ILs were measured with an uncertainty better than ± 0.15% and are in excellent agreement with the available data in the literature. An odd-even effect for the specific and volumic heat capacities of the [C n C 1 im][PF 6 ] series was found. The observed odd-even effect in the liquid heat capacity was rationalized considering the preferential orientation of the terminal CH 3 group. The higher specific/volumic heat capacities shown for the [C 6 C 1 im][PF 6 ] and [C 8 C 1 im][PF 6 ] are an indication of an additional conformational disorder increase in the liquid phase that could be related with a weaker alkyl chain interdigitation capability of the even number chain ILs. The melting temperatures and consequent ∆ s l H m o and ∆ s l S m o trend along the alkyl series present a V-shape profile that is explained based on the analysis of the balance between the initial decrease of the electrostatic interaction potential and the increase of the van der Waals interactions with the increasing size of the alkyl side chain of the cation. The inhibition of crystallization for intermediate alkyl chain size (from [C 5 C 1 im][PF 6 ] to [C 8 C 1 im][PF 6 ]) seems to arise from the overlapping of the hypothetical cold crystallization temperature by the melting temperature. Above the critical alkyl size, CAS, a regular increase in the entropy and enthalpy profiles presents a similar shape than the observed in other alkane series and is a strong support of the intensification of the ILs nanostructuration.

Three pure heptanol isomers were studied using infrared spectroscopy: n -heptanol, 2,4-dimethyl-3-pentanol, and 3-ethyl-3-pentanol. In order to analyze the branching effect of heptanol, investigations on the two symmetric branched isomers have been performed. Branching and steric hindrance highly influence the aggregation in associating systems. Therefore, a systematic comparison with the linear molecule n -heptanol is performed to better understand the experimental data. The vibrational structures were studied in the spectral range from 650 to 4000 cm − 1 and the individual peaks were assigned to the corresponding vibrational modes of the molecules. The OH-stretching band is significantly narrower in the spectra of the branched alcohols compared to n -heptanol. In particular, the low frequency components of the band are absent. This is a result of the steric hindrance leading to a less pronounced hydrogen bonding network.

Isobaric liquid phase heat capacities of nine selected aliphatic heptanols (1-heptanol, CAS RN: 111-70-6; 3-heptanol, CAS RN: 589-82-2; 4-heptanol, CAS RN: 589-55-9; 2-methyl-2-hexanol, CAS RN: 625-23-0; 5-methyl-2-hexanol, CAS RN: 627-59-8; 2-methyl-3-hexanol, CAS RN: 617-29-8; 3-ethyl-3-pentanol, CAS RN: 597-49-9; 2,2-dimethyl-3-pentanol, CAS RN: 3970-62-5; 2,4-dimethyl-3-pentanol, CAS RN: 600-36-2) were measured with a highly sensitive Tian-Calvet calorimeter in the temperature range from 261 K to 382 K. Experimental heat capacity data were correlated as a function of temperature. For eight compounds, a maximum on temperature dependence of heat capacity was observed. The phase behavior was investigated with a differential scanning calorimeter. Calorimetric measurements were complemented by FTIR spectroscopy from room temperature to a maximum of 428 K. The main aim of this work was to fill the gap in reliable heat capacity data for these compounds and to extend the knowledge base required for a better understanding of alcohols self-association.

The thermal behavior, solid and liquid heat capacities of the 1-benzyl-3-methylimidazolium, [Bzmim]+, based ionic liquid series with Cl−, PF6−, BF4−, CHF2CF2SO3− and NTf2− as anions were used to evaluate the effect of the insertion of an aromatic character (benzyl group) and the expected increase of the π–π interactions as well as the impact in the cation–anion hindrance and charge delocalization in the ionic liquid properties. It was found that the molar liquid heat capacities of [Bzmim][X] are in the same order as the 1-pentyl-3-methylimidazolium, [C5C1im][X] analogs. A good correlation between the molar (solid and liquid) heat capacity and the number of atoms of the anion was found. Two different crystalline forms for [Bzmim][BF4] differing by 10 K in the melting temperature and about 10% in the heat capacity were found. The crystallization behavior, melting temperatures, and enthalpies and entropies of fusion show that the insertion of an aromatic character (benzyl group) in the imidazolium cation leads to a significant and systematic change of the thermophysical properties of the ionic liquids associated with an increase of the glass transition and melting temperatures arising from the additional π–π interactions.

Isobaric heat capacities of selected cycloalcohols (cyclobutanol, CAS RN: 2919-23-5; cyclopentanol, CAS RN: 96-41-3; cyclohexanol, CAS RN: 108-93-0; cycloheptanol, CAS RN: 502-41-0; cyclooctanol CAS RN: 696-71-9) were measured with a highly sensitive Tian–Calvet calorimeter in the temperature range from 254 K to 352 K. Experimental heat capacity data were correlated as a function of temperature. The phase behavior was investigated with a differential scanning calorimeter. Calorimetric measurements were complemented by FTIR spectroscopy for less volatile compounds (cyclohexanol, cycloheptanol, cyclooctanol). The main aim of this work was to fill the gap in reliable heat capacity data for these compounds and to extend the knowledge base required for a better understanding of alcohols self-association.