Hydrogen bonding in liquid and supercritical 1-octanol and 2-octanol assessed by near and midinfrared spectroscopy

Abstract

The near and midinfrared spectra of 1-octanol (and 2-octanol) have been measured along the liquid-gas coexistence curve from room temperature up to the critical point and in the supercritical domain along the isotherm T=385 degrees C (and T=365 degrees C) above the critical point of both 1-octanol and 2-octanol for pressure ranging from 0.5 up to 15 MPa. The density values of SC 1- and 2-octanol have been estimated by analysing the near infrared (NIR) spectra in the 3nu(a)(CH) region. A quantitative analysis of the absorption band associated with the OH stretching vibration [nu(OH)] and its first and second overtones [2nu(OH) and 3nu(OH)] was carried out in order to estimate the percentage of "free" OH groups in both alcohols in the whole thermodynamic domain investigated here. Very consistent results have been obtained from the independent analysis of these three different absorption bands which gave us a good confidence in the degree of hydrogen bonding reported here for 1- and 2-octanol. Thus, the percentage of free OH groups which is around 5% in liquid 1-octanol under ambient conditions strongly increase up to 70%-80% at a temperature of about 340 degrees C. Then, in the supercritical domain, upon a decrease of the density from 0.4 to 0.1 g cm(-3), the fraction of free hydroxyl groups is nearly constant presenting a plateaulike regime around 80%. As the density decreases again, this plateau regime is followed by a further increase of X(nb) which reaches a value of 96% for the system in the gaseous phase (0.01 g cm(-3); P=0.45 MPa). Finally, it comes out from this study that the percentage of free OH groups is always greater in 2-octanol than in 1-octanol at the same density.

Phase equilibrium of the CO2/glycerol system: Experimental data by in situ FT-IR spectroscopy and thermodynamic modeling

“…2 shows the spectral changes of the glycerolrich phase occurring with an increase of temperature from 40 to 200 • C at 10.0 MPa as a result of the change in CO 2 concentration in that phase. The peak at 3696 cm −1 , assigned to the combination mode 2 2 + 3 of the CO 2 , decreases with temperature, which results from a decrease of CO 2 concentration in the glycerol-rich phase when temperature increases from 40 to 200 • C. The peak detected at 4740 cm −1 , assigned to the combination of the (OH) + ı(OH) mode of the associated OH of glycerol, presents a shift towards 4865 cm −1 (dashed lines) when temperature increases, which results from a progressive breaking of the hydrogen bond network of glycerol molecules, as previously reported for other alcohols [22]. In fact, glycerol is a highly flexible molecule forming both intra-and inter-molecular hydrogen bonds; molecular dynamics simulations on this molecule have shown that the number of inter-molecular hydrogen bonds decreases when temperature is increased [43,44].…”

“…This method has been previously successfully applied in phase equilibrium studies for the determination of the CO 2 sorption and swelling in liquids [18,19] and in polymers [20,21]. In particular, we would like to stress that molar absorption coefficients of CHstretching vibrational modes and combination bands are expected to exhibit little sensitivity upon temperature and pressure conditions [20,22,23]. For example, Buback et al [24] have shown that the molar absorption coefficient of combination bands of CO 2 were almost independent of the CO 2 density.…”

Electrical Conductivity and Viscosity in Binary Organic Liquid Mixtures: Participation of Molecular Interactions and Nanodomains

“…By comparing activation enthalpies from viscosity and self-diffusion (by NMR) measurements for octanol and octanoic acid in n-decane, Iwahashi et al [51] identified additional restrictions (due to more extensive hydrogen bonding) in the octanol system, the values being −27 and −18 kJ/mol, respectively, from both techniques. The octanol value compares well with the cooperative hydrogen bond enthalpy of −22 kJ/mol obtained by Palombo et al [52].…”

Experimental studies of Debye-like process and structural relaxation in mixtures of 2-ethyl-1-hexanol and 2-ethyl-1-hexyl bromide

“…The assignment made here is in harmony with other (N)IR spectroscopy studies. [51][52][53] As 2E1H contains many CH n groups, the OH overtone region is strongly overlapped with hydrocarbon combination bands. 47,54 Since the contribution of the CH n groups is practically independent of x, we calculated difference spectra, A(λ,x) = A(λ,x) − A(λ,0), by subtracting the spectrum of neat 2E1Br.…”