Salvatore Marullo

Ionic Liquids/[bmim][N3] Mixtures: Promising Media for the Synthesis of Aryl Azides by SNAr

The nucleophilic aromatic substitution of some activated aryl or heteroaryl halides has been performed in ionic liquid solution, using the 1-butyl-3-methylimidazolium azide as a nucleophile. The reaction course was studied varying the structures of both substrates and ionic liquids. In particular, in the latter case, the reaction of 2-bromo-5-nitrothiophene was carried out in five different ionic liquids ([bmim][BF 4], [bmim][PF 6], [bmim][NTf 2], [bm 2im][NTf 2], and [bmpyrr][NTf 2]). Finally, for all the substrates considered, a comparison with data obtained in MeOH solution in the presence of NaN 3 was also performed. Data collected indicate that in some cases it is possible to obtain aromatic or heteroaromatic azide derivatives in satisfactory yield by means of a S NAr reaction using [bmim][N 3] as the nucleophile.

Geminal imidazolium salts: a new class of gelators.

The gelling behavior of some geminal diimidazolium salts was investigated in solvents differing in polarity and hydrogen bond donor ability. The used salts, namely the 3,3-di-n-decyl-1,1(1,4-phenylenedimethylene)diimidazolium dibromide [p-Xyl-(decim)(2)][Br](2) (1), the 3,3-di-n-dodecyl-1,1(1,4-phenylenedimethylene)diimidazolium dibromide [p-Xyl-(dodecim)(2)][Br](2) (2), and the 3,3-di-n-dodecyl-1,1(1,4-phenylenedimethylene)diimidazolium ditetrafluoroborate [p-Xyl-(dodecim)(2)][BF(4)](2) (3), differ in the alkyl chain length and in the anion properties, such as size, shape, and coordination ability. In all cases in which gelation process was observed, the obtained gels were characterized by gel melting temperature determination, resonance light scattering, and UV-vis measurements. On the whole, the investigation allowed to get information about both the thermodynamic stability and the features of the aggregates characterizing the soft materials at the equilibrium. Data collected by us point out that the used organic salts are able to behave as both hydro- and organogelators. In particular, bromide salts formed hydrogels in the presence of α-cyclodextrin allowing to hypothesize that the gelation process is favored by the formation of supramolecular assemblies. To verify this hypothesis, 1D and 2D (1)H NMR measurements were carried out. Both the alkyl chain length and the anion ability to reticulate the three-dimensional network proved to be determinant factors in affecting the gelation process as well as the features of the gel phases. Finally, with the future aim to use the obtained gels as reaction media, the effect of a guest molecule such as the UV-vis active probe Nile Red was studied.

Binary Mixtures of Ionic Liquids: A Joint Approach to Investigate their Properties and Catalytic Ability

The growing interest in the properties and applications of ionic liquids has recently led to research into the possibility of using their binary mixtures. This work reports on the effects of binary mixtures of ionic liquids on the outcome of organic reactions such as the mononuclear rearrangement of heterocycles and the solvatochromic behavior of Nile Red. Binary mixtures formed by ionic liquids differing in the structure of the cation and the anion are taken into account. In particular, ionic liquids such as 1-benzyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, 1-(2,3,4,5,6-pentafluorobenzyl)-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-benzyl-3-butylimidazolium tetrafluoroborate, are studied. To achieve a deep understanding of the properties of ionic-liquid binary mixtures, their three-dimensional organization was analyzed by a combination of resonance light scattering, UV/Vis spectroscopy, and (1)H and (19)F NMR spectroscopy. Data collected herein evidence that the most significant changes in the ionic lattice structure, and consequently the most pronounced effects exerted as solvent media, occur when the studied system involves a blend of different anions.

Aryl Azides Formation Under Mild Conditions: A Kinetic Study in Some Ionic Liquid Solutions

The kinetics of nucleophilic aromatic substitution of three nitrothiophene derivatives in different [1-butyl-3-methylimidazolium][N(3)]/ionic liquid binary mixtures was studied spectrophotometrically at 298 K. Ionic liquids differing for cation structure (imidazolium or pyrrolidinium) and for size, shape, and coordination ability of the anion ([BF(4)(-)], [PF(6)(-)], [SbF(6)(-)], and [NTf(2)(-)]) were used. Furthermore, in order to have a comparison with conventional organic solvents, the target reaction was also carried out in DMF solution at increasing concentration of NaN(3) or [bmim][N(3)]. Data collected show that the reaction occurs faster in DMF than in ionic liquid solution. Furthermore, as a consequence of the ability of all solvent media to favor the leaving group departure, a simple linear dependence of the pseudo-first-order kinetic constant from nucleophile concentration was detected. The results of this kinetic investigation once more underline that ionic liquids are able to exert peculiar effects that can be understood also considering their three-dimensional organization.

Synthesis of aryl azides: A probe reaction to study the synergetic action of ultrasounds and ionic liquids

The combined effect of ultrasounds and ionic liquids was used to perform the synthesis of aryl azides by nucleophilic aromatic substitution in ionic liquid/[1-butyl-3-methylimidazolium][N3] binary mixtures. The ultrasounds efficiency was analyzed as a function of the substrate and of the ionic liquid structure. In the first case, both 6π and 10π electrons aryl halides were considered. As far as the ionic liquid structure is concerned, both aromatic and aliphatic ionic liquids were taken into account. Among aromatic cations, the effects due to different ability in giving hydrogen bond or π-π interactions were considered. The use of a geminal ionic liquid having an aromatic spacer was examined too. On the whole, collected data evidence an activating effect on the target reaction by the combined use of ultrasounds and ionic liquids. The structural order degree of the ionic liquid seems to be the main factor affecting the ultrasounds efficiency. Furthermore, the effects due to changes in the anion structure seem to be more significant than those due to changes in the cation structure.

Electronic and steric effects: how do they work in ionic liquids? The case of benzoic acid dissociation.

The need to have a measure of the strength of some substituted benzoic acids in ionic liquid solution led us to use the protonation equilibrium of sodium p-nitrophenolate as a probe reaction, which was studied by means of spectrophotometric titration at 298 K. In order to evaluate the importance of electronic effect of the substituents present on the aromatic ring, both electron-withdrawing and -donor substituents were taken into account. Furthermore, to have a measure of the importance of the steric effect of the substituents both para- and ortho-substituted benzoic acids were analyzed. The probe reaction was studied in two ionic liquids differing for the ability of the cation to give hydrogen bond and pi-pi interactions, namely [bm(2)im][NTf(2)] and [bmpyrr][NTf(2)]. Data collected show that benzoic acids are less dissociated in ionic liquid than in water solution. Furthermore, the equilibrium constant values seem to be significantly affected by both the nature of ionic liquid cation and the structure of the acid. In particular, the ortho-steric effect seems to operate differently in water and in the aromatic ionic liquid, determining in this solvent medium a particular behavior for ortho-substituted benzoic acids.

Aggregation Processes of Perylene Bisimide Diimidazolium Salts

The supramolecular aggregation of three diimidazolium-functionalized perylene bisimides, differing in the alkyl chain length was investigated. These salts form aggregates in solvents like chloroform, dichloromethane, and glycerol. Solvent-, concentration-, and temperature-dependent spectroscopic studies were carried out, evidencing the occurrence of an isodesmic, enthalpy-driven aggregation process, underpinned by π-π stacking and hydrogen bonding. Moreover, dynamic light scattering (DLS) measurements and SEM images revealed that these salts aggregate in chloroform into elongated structures.

Task Specific Dicationic Ionic Liquids: Recyclable Reaction Media for the Mononuclear Rearrangement of Heterocycles

Nine functionalized dicationic ionic liquids were used to study the base catalyzed mononuclear rearrangement of (Z)-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into the corresponding triazole at 363 K. Ionic liquids were characterized by the presence of 1-(1-imidazolylmethyl)-3,5-di[1-(3-octylimidazolylmethyl)]benzene cation, bearing on the structure a neutral imidazole unit as basic functionality. Besides anions generally used for monocationic ionic liquids, such as [Br(-)], [BF4(-)], and [NTf2(-)], also dianions having a rigid aromatic spacer such as 1,4-benzenedicarboxylate, 2,6-naphthalenedicarboxylate, and 1,5- and 2,6-naphthalenedisulfonate were taken into account. Furthermore, to have information about the effect deriving from the spacer rigidity also dianions such as 1,4-butanedicarboxylate and 1,6-hexanedicarboxylate were used. The basic strength of dicationic ionic liquids was determined using the Hammett indicator method. Data collected gave evidence that the outcome of the target reaction was affected by the nature of interactions operating between cation and anion of the ionic liquid used. Quite interestingly, solvent systems used had a good recyclability. Indeed, in some cases, they were reused for four cycles without significant loss in yield.

Acid- and Base-Catalysis in the Mononuclear Rearrangement of Some (Z)-arylhydrazones of 5-Amino-3-benzoyl-1,2,4-oxadiazole in Toluene: Effect of Substituents on the Course of Reaction

The reaction rates for the rearrangement of eleven (Z)-arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole 3a-k into the relevant (2-aryl-5-phenyl-2H-1,2,3-triazol-4-yl)ureas 4a-k in the presence of trichloroacetic acid or of piperidine have been determined in toluene at 313.1 K. The results have been related to the effect of the aryl substituent by using Hammett and/or Ingold-Yukawa-Tsuno correlations and have been compared with those previously collected in a protic polar solvent (dioxane/water) as well as with those on the analogous rearrangement of the corresponding (Z)-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole 1a-k in benzene. Some light can thus be shed on the general differences of chemical reactivity between protic polar (or dipolar aprotic) and apolar solvents.

Molecular "pincer" from a diimidazolium salt: a study of binding ability.

The anion recognition ability of the dicationic imidazolium salt 3,3-di-n-octyl-1,1-(1,3-phenylenedimethylene)diimidazolium 1,5-naphthalenedisulfonate ([m-Xyl-(oim)2][1,5-NDS]) was investigated in acetonitrile solution by means of proton NMR titrations. A wide range of anions, comprising simple inorganic ions, halides, and mono- and dicarboxylates was taken into account. The study showed that this receptor binds carboxylate anions more strongly than halides. Moreover [m-Xyl-(oim)2][1,5-NDS] displays selectivity for di- over monocarboxylate anions. The complex stability was mainly affected by the anion basicity in the presence of monocarboxylates, whereas the flexibility of the alkyl chain linking the two carboxylate moieties appeared to play a major role in the presence of dicarboxylate anions.