Claudia G. Adam

Characterization of solvent mixtures. Part 8 — preferential solvation of chemical probes in binary solvent systems of a polar aprotic hydrogen-bond acceptor solvent with acetonitrile or nitromethane. Solvent effects on aromatic nucleophilic substitution reactions

The use of chemical probes for the characterization of chemical properties was explored for completely non-aqueous aprotic binary solvent mixtures. The Dimroth–Reichardt ET(30) betaine dye, 4-nitrophenol, 4-nitroanisole, 4-nitroaniline and N,N-diethyl-4-nitroaniline were used to study preferential solvation in binary mixtures of a polar aprotic hydrogen bond-acceptor solvent (DMSO, DMF, acetone, butanone and ethyl acetate) with acetonitrile or nitromethane at 25 °C over the whole range of solvent composition. The indicators were employed to determine ET(30), π*, α and β solvatochromic parameters of the mixtures. Each solvent system was analysed according to its deviation from ideal behaviour due to the preferential solvation of the indicators and also from the complicated intermolecular interactions of the mixed solvent. The validity of the concept of an intrinsic, absolute property of a solvent mixture and whether such a property can be defined by means of chemical probes is discussed. These results were related to the solvent effects on some aromatic nucleophilic substitution reactions. The kinetics of the reactions between 1-fluoro-2,4-dinitrobenzene and primary or secondary amines were studied in ethyl acetate– acetonitrile and N,N-dimethylformamide–acetonitrile mixtures, respectively, taken as representatives of two clearly different solvation models. Copyright

Solvent effects on aromatic nucleophilic substitution reactions. Part 9. Special kinetic synergistic behavior in binary solvent mixtures

The kinetics of the reactions of 1-fluoro-2,4-dinitrobenzene with morpholine and piperidine were studied at 25 °C in several binary solvent mixtures of the polar aprotic hydrogen bond acceptor solvent + chloroform or dichloromethane type, which, in some cases, exhibit synergism for the ET(30) solvent polarity parameter. In each case, the kinetic response model was analyzed as a function both of the amine concentration and of the solvent mixture composition. The kinetic data show that for some reaction systems under certain experimental conditions, the reactions are faster in binary solvent mixtures than in the corresponding pure solvents, manifesting a special kinetic synergetic behavior. This kinetic effect was attributed to a complex combination of factors related to the variations of the influence of base catalysis with the solvent composition, and to the consequence of specific solvent effects. The kinetic results were related to the ET(30) solvent polarity parameter, analyzing the general validity of the chemical probe for interpreting the solvent effects in the aromatic nucleophilic substitution reactions explored. The applicability of the preferential solvation model allowed the special behavior observed to be attributed to the influence of preferential solvation phenomena. Copyright

Characterization of solvent mixtures: preferential solvation of chemical probes in binary solvent mixtures of polar hydrogen‐bond acceptor solvents with polychlorinated co‐solvents

The use of chemical probes for the characterization of chemical properties is explored for aprotic binary solvent mixtures. The solvatochromic indicators N,N-diethyl-4-nitroaniline, 4-nitroanisole, 4-nitroaniline and 4-nitrophenol were used to characterize binary solvent mixtures of a polar aprotic hydrogen-bond acceptor solvent (ethyl acetate, acetonitrile and dimethyl sulfoxide) with a polychlorinated hydrogen-bond donor solvent (chloroform or dichloromethane). The solvent parameters π*, α and β of the binary mixtures were calculated from the solvatochromic shifts of the indicators. In each case the degree of convergence for a solvent property values obtained from different probes was analyzed. Data obtained by using the non-polar solvatochromic indicator β-carotene are additionally presented. The behavior of the solvent systems was analyzed according to their deviation from ideality due to preferential solvation of the solutes and the complicated intermolecular interactions of the two components of the solvent mixture. The validity of the concept of an intrinsic absolute property of a solvent mixture and whether such a property can be defined by means of chemical probes is discussed. Theoretical equations (preferential solvation models) were used to compute the solvatochromic data. The results were analyzed and related to the solvent effects on some aromatic nucleophilic substitution reactions, comparing the application of single- and multiparametric treatments of solvent effects. Copyright

Solvent effects on aromatic nucleophilic substitution reactions. Part 7. Determination of the empirical polarity parameter ET(30) for dipolar hydrogen bond acceptor–co‐solvent (chloroform or dichloromethane) mixtures. Kinetics of the reactions of halonitrobenzenes with aliphatic amines

Empirical solvent polarity parameters ET(30) were determined by UV/VIS spectroscopy, using Dimroth–Reichardts betaine dye, as a function of composition, for several binary solvent mixtures [i.e. polar hydrogen bond acceptor (PHBA) solvents+chloroform or dichloromethane]. Each solvent system was analyzed according to its deviations from additivity due to preferential solvation of the chemical probe and also from complicated intermolecular interactions of the mixed solvents. The ET(30) parameter of many of these mixtures has presented synergism. The synergetic effects were more significant for those binary solvent systems in which chloroform is the co-solvent. These results were related to the solvent effects on some aromatic nucleophilic substitution reactions. The kinetics of the reactions between 1-halo-2,4-dinitrobenzenes and primary or secondary aliphatic amines were studied in three solvent systems (PHBA+chloroform) where the synergism for the ET(30) polarity parameter is the rule. In all the aminodehalogenation reactions discussed the formation of the intermediate is the rate-determining step. The kinetic data show a tendency to decrease with decrease in the overall solvation capability of the binary mixture. In general, the reaction rates presented a gradual decrease in the PHBA solvent-rich zone and a large decrease at high co-solvent concentrations. The ET(30) values corresponding to binary dipolar hydrogen bond acceptor–hydrogen bond donor mixtures may be not generally valid for interpreting solvation effects on the reactions under consideration.

Ionic Liquids as Binary Mixtures with Selected Molecular Solvents, Reactivity Characterisation and Molecular-Microscopic Properties

This chapter presents the design and analysis of the microscopic features of binary solvent systems formed by ionic liquids, particularly room temperature ionic liquids with molecular solvents. Protic ionic liquids, ethylammonium nitrate and 1-n-butyl-3-methylmidazolium (bmim)-based ILs, were selected considering the differences in their hydrogen-bond donor acidity. The molecular solvents chosen were aprotic polar (acetonitrile, dimethylsulphoxide and N,N-dimethylformide) and protic (different alcohols). The empirical solvatochromic parameters E T N , π*, α and β were employed in order to analyse the behaviour of each binary solvent system. The study focuses on the identification of solvent mixtures of relevant solvating properties to propose them as ‘new solvents’. Kinetic study of aromatic nucleophilic substitution reactions carried out in this type of solvent systems is also presented. On the other hand, this is considered as a new approach on protic ionic liquids. Ethylammonium nitrate can act as both Bronsted acid and/or nucleophile. Two reactions (aromatic nucleophilic substitution and nucleophilic addition to aromatic aldehydes) were considered as model reactions.

Solvatochromic and Kinetic Response Models in (Ethyl Acetate + Chloroform or Methanol) Solvent Mixtures

The present work analyzes the solvent effects upon the solvatochromic response models for a set of chemical probes and the kinetic response models for an aromatic nucleophilic substitution reaction, in binary mixtures in which both pure components are able to form intersolvent complexes by hydrogen bonding.

Determination of glyphosate, AMPA and glufosinate in dairy farm water from Argentina using a simplified UHPLC-MS/MS method

Argentina, together with the USA and Brazil, produces approximately 80% of the total worldwide glyphosate loadings. The development of a simplified ultra-high performance liquid chromatographic tandem mass spectrometric method (UHPLC-MS/MS) for the determination of glyphosate, aminomethylphosphonic acid (AMPA) and glufosinate in water is described, including studies of several alternatives of 9-fluorenylmethylchloroformate (FMOC-Cl) derivatization and pretreatment steps. The proposed method includes acidification and neutralization of a low sample volume (3 mL), 2 hours derivatization step, cleanup with dichloromethane, followed by reverse phase UHPLC-MS/MS determination of the analytes. Figures of merit were satisfactory in terms of linearity, selectivity, accuracy and intermediate precision (%REC 70-105% with RSD < 15%). Limits of quantification (LOQ) were suitable for monitoring purposes (0.6, 0.2, 0.1 μg/L for glyphosate, AMPA and glufosinate respectively). The validated methodology was applied for the analysis of livestock wells waters from 40 dairy farms located in the central region of Argentina. Glyphosate and AMPA were quantified in 15% and 53% of the analyzed samples with concentrations ranging from 0.6-11.3 μg/L and 0.2-6.5 μg/L respectively. Greater concentrations of glyphosate were also verified in waters from open-reservoir tanks, which are directly exposed to the farm environment. In these cases glyphosate and AMPA occurrence increased, being quantified in the 33% and 61% of the samples with values ranging 0.6-21.2 μg/L and 0.2-4.2 μg/L respectively. Also in this case glufosinate was found in 52% samples at <LOQ levels and was quantified in one sample at 0.1 μg/L. This new information constitutes an important contribution to authorities and scientists for further research, control and risk analysis purposes.

Ionic liquid based-alkylammonium cations: analysis of their behavior as nucleophile and acid catalyst in reactive systems.

The investigation in ionic liquids (Lis) is in continuous growth, nevertheless many of their results are being reviewed. Our interest is to analyze the behavior of Lis alkylammonium derivatives in cycloaddition reactions analyzing their participation as catalyst and potential nucleophilic generated in situ.