Handbook of Solvents - George Wypych - ChemTech - Ventech!

538 Y. Y. Fialkov, V. L. Chumak
Possibility of management of the products` output may by illustrated by the data from
reaction equilibrium [9.84]. As follows from Figure 9.8, maximum equilibrium constant (in
investigated solvents) is for pure chloroheptane; the adducts output in this solvent equals to
86% (at initial concentration of reagent 0.1 M). Minimum equilibrium constant of the process
is in pure ethyl acetate, where the products` output equals to 18 % (at initial concentration
of reagent 0.1 M). Thus the products` output of the reaction [9.84] can be changed
directionally in the range 90 up to 20% by means of choice of corresponding binary or individual
solvent. If selected solvent is more basic than ethyl acetate or more acidic than
nitromethane, the process is not possible.
Heteromolecular association process of o-nitrophenol and triethylamine can be an example
of the management of products` output. Association constant of this process has been
determined for some solvents. 35 Use of hexane instead of 1,2-dichloroethane, DHLE, increases
products’ output from 6% to 93%.
When both components of the mixed solvent are solvate-active towards the reagents
of equilibrium [9.64], the following interactions take place:
E + A ↔ EA; F + A ↔ FA; E + B ↔ EB; F + B ↔FB
[9.87]
The process of heteromolecular association [9.64] is due to displacement of the solvent
components and formation of completely or partially desolvated adduct:
( ) () ()
xEA + yFA + m −xEB ↔ E F + A + B
[9.88]
m n
It is easy to develop the equation for binary solvent formed from two solvate-active
components similar to [9.90] by using the above scheme for the binary solvent with one
solvate active component (equations [9.76 - 9.80]) and introducing equilibrium constant of
the process [9.88] such as K us:
( )( )( )( )
K = K 1+ K 1+ K 1+ K 1 + K
[9.89]
EF us EA FA EB FB
where:
Ki equilibrium constant of the processes [9.87]
9.4.4.1 Selective solvation. Resolvation
When component B is added to solution E in solvent A (E is neutral molecule or ion),
resolvation process takes place:
EAP + qB = EB q + pA
[9.90]
Equilibrium constant of this process in ideal solution (in molar parts of the components)
equals to:
p
q
K = m m / m m
[9.91]
us EBq A EAp B
where:
mi a number of moles
p, q stoichiometric coefficients of reaction
On the other hand, resolvation constant Kus equals to the ratio of equilibrium constants of
solvation processes E+pA↔EAp(I);E+qB↔EBq(II):