Effect of Ether Oxygen on Proton Transfer and Aggregation Reactions of Amines in Water by Ultrasonic Absorption Method

Abstract

Ultrasonic absorption coefficients in the frequency range from 6.5 to 220 MHz have been measured in aqueous solutions of 3-ethoxy- and 3-butoxypropylamine as functions of their concentrations along with the sound velocity at 2.5 MHz and the density. In a 3-ethoxypropylamine solution, only one relaxational absorption has been observed up to 3.0 mol dm−3. The cause has been clarified to be due to a proton-transfer reaction of the amine from the concentration dependences of the relaxation frequency and the relaxational amplitude. The rate and thermodynamic parameters have been determined and reasonable values have been obtained as a diffusion-controlled reaction. In the solution of 3-butoxypropylamine, another relaxation process in addition to that due to the proton-transfer reaction has been observed in the concentrations of more than 0.5 mol dm−3. This relaxation process has been attributed to a perturbation associated with an aggregation reaction, 4A↔A4, from the concentration dependences of the relaxation frequency and the relaxational amplitude of the absorption. The rate and thermodynamic constants for the proton-transfer and aggregation reactions have been determined. It has been found from a comparison of the results for the two solutions and others reported previously that the introduction of ether oxygen into amine molecules has little influence on the proton-transfer reaction, but prevents the formation of aggregates due to the hydrophobic interaction. It has also been seen from the results of 3-butoxypropylamine solutions that the butoxyl group has a fairly high ability of hydrophobic interaction and that nonionized molecules form aggregates in the aqueous solution.

Volumetric Study of 3-Butoxypropan-1-amine + Water Mixtures between 283.15 and 303.15 K

“…A procedure previously used by various authors including us ,− was adopted. Dissociation degree values, α, were determined from the basicity constant K b = 2.0 × 10 –4 at 298.15 K . The limiting partial molar volume of cation BH + , V BH + ∞ , was obtained from the group contribution values for groups CH 3 , CH 2 , −O–, and NH 3 + , as published by Gianni and Lepori and related to the convention V H + ∞ = −5.4 cm 3 ·mol –1 .…”

“…A procedure previously used by various authors including us 9,17−19 was adopted. Dissociation degree values, α, were determined from the basicity constant K b = 2.0 × 10 −4 at 298.15 K. 20 The limiting partial molar volume of cation BH + , V BH + ∞ , was obtained from the group contribution values for groups CH 3 , CH 2 , −O−, and NH 3 + , as published by Gianni and Lepori 21 and related to the convention V H + ∞ = −5.4 cm 3 •mol −1 . To refer all the limiting partial molar volumes to the same convention (V H + ∞ = −5.4 cm 3 •mol −1 ), V OH − ∞ was obtained from V OH − ∞ = −4.04 cm 3 •mol −1 as published by Millero 22 and related to the convention V H + ∞ = 0, subtracting −5.4 to −4.04…”

Molecular relaxation dynamics and self-association of dexamethasone sodium phosphate solutions

“…Considering that Eq. ( 1 ) describes the above mechanism in one mean stage, we can express the relation between the relaxation frequency f r in MHz and the reactant concentration [DSP] as (Nishikawa et al 1991 ; Nishikawa and Kamimura 2011 ): where n is the aggregation number, while constants k f and k b represent the forward and backward rate constants, respectively. Several values on n were tested in order to receive the least error of plots of .…”

“…Deep understanding of the DSP self-association and its thermodynamic profile is crucial for predicting the docking properties of this molecule, which has important implications in effective drug design. Ultrasonic relaxation spectroscopy has been proved as an effective tool in studying association-dissociation mechanisms (Nishikawa et al 1991 ), proton-transfer reactions (Nishikawa et al 1973a , b , 1996 ; Nishikawa and Kamimura 2011 ; Huang et al 1999 ; Tsigoias et al 2020 a), conformational changes (Bae et al 2001 ; Bae et al 2002 ; Kalampounias 2020 ; Stogiannidis et al 2020 ), complexation (Tamm 1961 ; Petrucci 1971 ), backbone segmental motion and normal mode relaxation in polymers (Kouderis et al 2021 ; Siafarika et al 2021 ) and reaction engineering in general (Bernasconi 1976 ). Furthermore, in several cases systematic analysis of the acoustic spectra permits disentangling between different processes taking place in close time scales (Kouderis et al 2021 ).…”

Excess Partial Molar Enthalpies of 3-Ethoxypropan-1-amine and 3-Butoxypropan-1-amine in Water at 298.15 K

“…In fact, Figure shows a very good symmetrical correlation and x B = 0.003 is the composition beyond which both quantities become almost constant. α values were determined in a previous work, based on the basicity constant K b = 1.3 × 10 –4 at T /K = 298.15 …”