Self-Association of Medium-Chain Alcohols in n-Decane Solutions

Abstract

Self-association of medium-chain alcohols in n-decane solutions has been studied by infrared absorption of the fundamental OH stretching vibration. The alcohols investigated were 1-propanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-butanol, 1-pentanol, and 1-hexanol. Infrared spectra were acquired for varying alcohol molalities, the highest concentration being 0.2 mol/kg. The spectra for each alcohol were collected in a data matrix. The bilinear multicomponent data were successfully resolved into spectra and concentration profiles by a multivariate method. The result indicates that monomers dominate the spectral variance in the low-molality region, while cyclic oligomers dominate in the upper concentration range. It further indicates that minor amounts of open-chain aggregates may be present. The monomer and cyclic tetramer appear to be the dominant species, while the amount of open-chain aggregates was negligible even in the low-molality region. The equilibrium constants for the monomer–tetramer association reactions ( K1–4) were calculated by a least-squares method. The calculated values for the equilibrium constants, based on the molality, range from 138 to 106 for the linear alcohol molecules. The result shows that 1-butanol, 1-pentanol, and 1-hexanol have similar constants, while 1-propanol displays a markedly higher value. The equilibrium constants obtained for 2-methyl-1-propanol and 2-methyl-2-propanol were 77 and 39, respectively. The considerably lower values for the branched alcohol molecules indicate that steric interaction between the chain prevents self-association into larger aggregates.

Novel method for rapid monitoring of lipid oxidation by FTIR spectroscopy using disposable IR cards

“…Guillén and Cabo (12) also reported a shift of the ROOH band toward lower wavenumbers as oils underwent oxidation at 60°C, but to a somewhat lesser extent. Similar band shifts observed in the FTIR spectra of alcohols at high concentrations in n-decane have been attributed to cluster formation (19); thus, it may be postulated that the ROOH band shift is due to extensive intermolecular hydrogen bonding of hydroperoxides resulting from their accumulation at high concentrations in the card matrix at the moderate temperatures used. In experiments performed to investigate this further, sunflower oil was oxidized at 60°C for 6 d and then serially diluted with fresh sunflower oil to produce seven standards ranging from 10 to 100% oxidized oil.…”

Aggregate formation in oil and adsorption at oil/water interface: thermodynamics and its application to the oleyl alcohol system

“…(52). Since the activity coefficient of oleyl alcohol can be estimated approximately at 298.15 K in the terms of the ratio of the monomer fraction to the total concentration of oleyl alcohol [22], we adopted the method proposed by Aveyard et al and calculated the monomer concentration at 298.15 K by IR spectroscopy [3,38] as follows: The infrared spectra showed the same aspect as the ones in the previous studies [11]; only one band at 3644 cm −1 assigned to the free-OH stretching vibration appeared at a lower concentration and the bands assigned to the OH stretching vibration in aggregates appeared at high concentrations [8,10]. Then we can estimate the monomer concentration by the dependence of the absorbance maximum around 3644 cm −1 on the concentration [11].…”

“…The properties of oil solutions of long-chain alcohols have been studied from the different points of views and it has been known that alcohol molecules gather together to form aggregates in oil solutions [1][2][3][4][5][6][7][8][9][10]. Also, in our previous paper [11], the enthalpy of mixing of oleyl alcohol and oils was measured by a high-accuracy isothermal calorimeter and the aggregation behavior of the alcohol molecules has been elucidated.…”

Solvation of Alcohols in n-Heptane and n-Propanol from the Acoustic Passynski Method

“…(2), valid in the region of very low solute contents, where specific or non-specific solute-solute interactions can be neglected [11]. The final results are collected in Table and illustrated in Fig.…”