**3.1 SNAr reactions in ionic liquids**

A series of reaction have been studied in RTILs and mixtures of them with water or COS. The criteria to select the RTILs were based on the following: (i) the solubility of substrates and nucleophiles; (ii) to have a reasonable number of anions and cations to assess anion and cation effects; and (iii) to ensure that these RTILs do not interfere with the reaction [12]. Solvent effects in RTILs are a complex problem, because the solute-solvent interactions will be masked by the leading solvent-solvent interactions that are coulombic in nature. Some strategies to study

**233**

*Solvent Effect on a Model of SNAr Reaction in Conventional and Non-Conventional Solvents*

role of the RTIL structure on the reaction rates of SNAr reactions [41, 42].

The use of RTILs or ionic liquid binary mixtures could give variations in the structure of the ionic lattice of neat ILs after mixing [43–45]. This fact may have significant repercussions on the nature and strength of the interactions that contribute mainly to coulomb interactions that determine the 3D structure of ILs [46, 47]. Studies of binary mixtures with common anions, for instance, the same cation but different anions, have shown how the presence of random co-networks or block co-networks depends on the size of the anions [4, 47, 48]. Seddon suggests the use of IL mixtures to expand the range of room temperatures in ILs [49]. Initially, the hygroscopic nature of the ILs was a problem; however the high capacity of the ILs to solubilize water opens a wide spectrum of reaction media, mainly based on the role of the hydrogen bond (HB) and electrostatic interactions between molecules in the mixture. Reports have shown that the addition of COS to ILs may affect significantly the density, viscosity, and conductivity with respect to pure ILs. For instance, the direct relationships between the viscosity of the IL/COS mixtures with the solvent dielectric constant (ε) of the COS pure [50, 51]. It may be attributed to the difference in the ion-dipole interactions between the ions and solvents. The addition of water to ILs may change the molecular structure of pure ILs probably due to HB between the water molecules and the anions of the ILs [52, 53]. Sanchez et al. studied solvent mixtures between 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIMBF4)/water at different molar fractions, observing on the studied range of compositions, a border line located close to χ = 0.2. Before this value indicates that the added RTIL promotes the reactivity of the substrate by preferential solvation. After this value, the rate coefficients remain approximately constant. At low concentrations the water begins to break down the 3D

**3.2 Binary mixtures based on ionic liquids**

solvent effects in RTILs consider a reasonable large number of these and to evaluate their performance by fixing the anion and varying the cation and vice versa. For instance, a complete study based on the reaction of DNBSCl with piperidine was performed in 17 RTILs considering water as a solvent reference. This study identified three groups of RTILs showing 1-ethyl-3-methylimidazolium dicyanamide (EMIMDCN) as the best solvent considering all the studied RTILs and 21 COS [12, 40]. EMIMDCN shows a catalytic behavior attributed to its high polarizability given by the dicyanamide anion (DCN<sup>−</sup>), which presents a highly rich π electron density, and its size could be in relationship with steric hindrance effects. Note that ethylammonium nitrate (EAN) was the only protic RTIL that decreased the reaction time in comparison to water and EMIMDCN, respectively. Then, a comparative study of the reaction of DNBSCl and propylamine in COS and RTILs, respectively, was performed in order to analyze the nature of the nucleophile. Piperidine showed to be more active than propylamine in polar solvents with the ability to donate and accept HB, while the reaction of propylamine was favored only with solvent that can accept HB, being the best COS solvent: N,N-dimethylformamide (DMF). Note that, in all the studied RTILs for propylamine, the reactivities of the reactions were lower than piperidine. This response was attributed to the capacity of the RTILs to donate/accept HB in agreement with the COS behavior [12]. On the other hand, propylammonium nitrate (PAN) was able to emulate the HB behavior of water toward the reaction between 4-chloroquinazoline and aniline [39]. PAN could be donating an HB by the ammonium moiety of PAN toward the substrate emulating an electrophilic solvation suggested in aqueous media improving its reactivity toward the nucleophile. These results are in agreement with the report of Welton et al. [2] based on the task-specific design of RTILs in order to optimize those properties that enhanced the reaction reactivities. Harper et al. reported the main

*DOI: http://dx.doi.org/10.5772/intechopen.89838*

*Solvent Effect on a Model of SNAr Reaction in Conventional and Non-Conventional Solvents DOI: http://dx.doi.org/10.5772/intechopen.89838*

solvent effects in RTILs consider a reasonable large number of these and to evaluate their performance by fixing the anion and varying the cation and vice versa. For instance, a complete study based on the reaction of DNBSCl with piperidine was performed in 17 RTILs considering water as a solvent reference. This study identified three groups of RTILs showing 1-ethyl-3-methylimidazolium dicyanamide (EMIMDCN) as the best solvent considering all the studied RTILs and 21 COS [12, 40]. EMIMDCN shows a catalytic behavior attributed to its high polarizability given by the dicyanamide anion (DCN<sup>−</sup>), which presents a highly rich π electron density, and its size could be in relationship with steric hindrance effects. Note that ethylammonium nitrate (EAN) was the only protic RTIL that decreased the reaction time in comparison to water and EMIMDCN, respectively. Then, a comparative study of the reaction of DNBSCl and propylamine in COS and RTILs, respectively, was performed in order to analyze the nature of the nucleophile. Piperidine showed to be more active than propylamine in polar solvents with the ability to donate and accept HB, while the reaction of propylamine was favored only with solvent that can accept HB, being the best COS solvent: N,N-dimethylformamide (DMF). Note that, in all the studied RTILs for propylamine, the reactivities of the reactions were lower than piperidine. This response was attributed to the capacity of the RTILs to donate/accept HB in agreement with the COS behavior [12]. On the other hand, propylammonium nitrate (PAN) was able to emulate the HB behavior of water toward the reaction between 4-chloroquinazoline and aniline [39]. PAN could be donating an HB by the ammonium moiety of PAN toward the substrate emulating an electrophilic solvation suggested in aqueous media improving its reactivity toward the nucleophile. These results are in agreement with the report of Welton et al. [2] based on the task-specific design of RTILs in order to optimize those properties that enhanced the reaction reactivities. Harper et al. reported the main role of the RTIL structure on the reaction rates of SNAr reactions [41, 42].
