Influence of acoustic vibrations on the kinetics of liquid-phase chemical reactions involving associates

doi:10.15406/mojboc.2018.02.00074

MOJ

eISSN: 2574-819X

Bioorganic & Organic Chemistry

Mini Review Volume 2 Issue 3

Influence of acoustic vibrations on the kinetics of liquid-phase chemical reactions involving associates

Kulagina TP,

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Smirnov LP, Andrianova ZS

Institute of Problems of Chemical Physics RAS, Russia

Correspondence: Kulagina TP, Institute of Problems of Chemical Physics RAS, Semenov prospect, Chernogolovka, Moscow region, 142432, Russia

Received: May 15, 2018 | Published: June 18, 2018

Citation: Kulagina TP, Smirnov LP, Andrianova ZS. Influence of acoustic vibrations on the kinetics of liquid-phase chemical reactions involving associates. MOJ Biorg Org Chem. 2018;2(3):163-164. DOI: 10.15406/mojboc.2018.02.00074

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Introduction

In this communication, we report on the effect of external low-frequency periodic mechanical influence on the stability of liquid-phase bimolecular reactions with account for the association of both reagents.^1,2 It is shown that a change in the character of oscillations of intermediate concentrations happens upon an increase in both the applied frequency and amplitude up to some critical values. Above critical amplitude, the reaction mixture no more contains trimers and the reaction is terminated. Our calculations have shown a possibility of controlling reaction rate in conditions of low-frequency acoustic influence.

Mathematical model

The kinetics of bimolecular reactions is described by non-linear differential equations that admit the formation of dissipative structures of intermediate concentration.^3,4 We assumed that in solution reagent A could form dimmer A₂ and trimmer A₃; while reagent B, monomer B and dimmer B₂. Reaction product C is formed in the reaction B₂ + A₃ → C + B + 2A.²

The system of kinetic equations for this reaction can be written in the form:

d[A₂]/dt=k₁[A]²–k_–1[A₂]–k₂[A][A₂]+k_–2[A₃]–k₃[A][A₂][A₃],----- (1)

d[A₃]/dt = k₂[A][A₂] + k₃[A][A₂][A₃] – k_–2[A₃] – k₄k₅[B]₂[A₃]{k_–4+ k₅[A₃]}^–1

The action of acoustic wave with frequency v can be described by taking into account the stretching (σ) developed in the system according to the following expression for rate constants k(v)_–i responsible for decomposition of associates:^1,5

k(v)–i = k_–0iexp[(–E_–i + γσ)/RT]] (i = 1, 2) ------ (2)

Where γ is some structure-sensitive coefficient and σ changes as σ=Р₀sin(2πvt). At the initial stage, the formation of dimmers is governed by the value of k(v)_–i. It is almost convenient to create in a reaction system the density fluctuation, uniform in space, at the expense of external periodic force, influencing system an acoustic wave. At the action of a acoustic wave with a frequency v the stretching σ and compression created in system lead to change of kinetic constants k(v)-and destruction of associates. This constant has view:

k(v)_-i = k_-0iexp[(-E_-i + γσ)/RT]], (i = 1, 2)-------- (2)

Where γ –is a structure-sensitive coefficient, σ – is the strenuous which changes under the law σ=Р₀sin(2πvt). At the initial stage, the formation of dimmers is governed by the value of k(v)_–i.

Results and discussion

The problem was solved by mathematical modeling for the case [A]=[B]=const as described elsewhere.² The result is exemplified in Figure 1. An increase in oscillation frequency was found to suppress the oscillations in the concentration of intermediate and finally to terminate the reaction. The model parameters used in calculations² that yielded the data shown in Figure 1 were as follows: μ=k₁[A]²=35mol(ls)^–1, k_-2=1s^–1, u=k₃[A]=0l²mol^–2s^–1, m=k₄[B]²=200mol (l s)^–1, k_-1=0.005s^–1, a=k₂[A]=0.5mol (ls)^–1, and g=k_-4k₅-1=1.6mol l^–1. In all calculations, it was adopted that x(0)=1.8mol s^–1 and y(0)=0.23mols^–1

The results have shown that the frequency and amplitude of external influence can be used as a tool for controlling the kinetics of chemical reactions, as well as for strengthening or weakening the self-oscillation of intermediate concentration, up to termination of the reaction. In our opinion, the influence of reagents association on the kinetics of chemical reactions deserves further basic and applied research. Advances in this line of research can be expected to provide theoretical backgrounds for controlling chemical kinetics and hence the structure/properties of products.