Reaction of lithium diethylamide with an alkyl bromide and alkyl benzenesulfonate: origins of alkylation, elimination, and sulfonation

A combination of NMR, kinetic, and computational methods are used to examine reactions of lithium diethylamide in tetrahydrofuran (THF) with n-dodecyl bromide and n-octyl benzenesulfonate. The alkyl bromide undergoes competitive S(N)2 substitution and E2 elimination in proportions independent of all concentrations except for a minor medium effect. Rate studies show that both reactions occur via trisolvated-monomer-based transition structures. The alkyl benzenesulfonate undergoes competitive S(N)2 substitution (minor) and N-sulfonation (major) with N-sulfonation promoted at low THF concentrations. The S(N)2 substitution is shown to proceed via a disolvated monomer suggested computationally to involve a cyclic transition structure. The dominant N-sulfonation follows a disolvated-dimer-based transition structure suggested computationally to be a bicyclo[3.1.1] form. The differing THF and lithium diethylamide orders for the two reactions explain the observed concentration-dependent chemoselectivities.     

Bingel-Hirsch reactions on non-IPR Gd3N@C2n (2n = 82 and 84)

The Bingel-Hirsch reactions on non-isolated pentagon rule (non-IPR) Gd(3)N@C(2n) (2n = 82, 84) are studied. Computational results show that the two metallofullerenes display similar reactivity according to their related topologies. Long C-C bonds with large pyramidalization angles lead to the most stable adducts, the [5,6] bonds in the adjacent pentagon pair being especially favored. The lesser regioselectivity observed for Gd(3)N@C(82) is probably due to the activation of some C-C bonds by means of the metal cluster.     

Reactivity of ortho‐Substituted Aryl–Palladium Complexes towards Carbodiimides,Isothiocyanates, Nitriles,and Cyanamides

Complexes [Pd(C₆H₃XH‐2‐R′‐5)Y(N^N)] (X=O, NH; Y=Br, I; R′=H, NO₂; N^N=N,N,N′,N′‐tetramethylethylenediamine (tmeda), 2,2′‐bipyridine (bpy), 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine (dtbbpy)) react with RN?C?E (E=NR, S) or RC≡N (R=alkyl, aryl, NR′′₂) and TlOTf (OTf=CF₃SO₃) to give, respectively, 1) products of the insertion of the C?E group into the C? Pd bond, protonation of the N atom, and coordination of X to Pd, [Pd{κ²‐X,E‐(XC₆H₃{EC(NHR)}‐2‐R′‐4)}(N^N)]OTf or [Pd(κ²‐X,N‐{ZC₆H₃(NH?CR)‐2‐R′‐4})(N^N)]OTf, or products of the coordination of carbodiimides and OH addition, [Pd{κ²‐C,N‐(C₆H₄{OC(NR)}NHR‐2)}(bpy)]OTf; or 2) products of the insertion of the C≡N group to Pd and N‐protonation, [Pd(κ²‐X,N‐{XC₆H₃(NH?CR)‐2‐R′‐4})(N^N)]OTf.     

Limitations of electrospray ionization in the analysis of a heterogeneous mixture of naturally occurring hydrophilic and hydrophobic compounds

A model heterogeneous mixture of a hydrophilic tripeptide (phenylalanine-glycine-glycine, PGG) and hydrophobic organic acids ((12)C- and (13)C-octanoic acid and pentadecanoic acid) was subjected to electrospray ionization mass spectrometry (ESI-MS). The objective was to verify the previously noted inconsistencies in ESI-MS of complex environmental samples such as humic materials from either aquatic or terrestrial origins. The hydrophobic organic acids, either alone or together, reduced significantly the ESI-MS detection of the tripeptide molecular and self-associated ions at a concentration that was an order of magnitude lower than that of PGG. The most intense peaks were invariably those of the octanoic acid as either deprotonated, self-associated, or acetate-clustered molecules. The presence of equimolar amounts of PGG and organic acids yielded similar results, but with a significant increased detection of PDA and a smaller depression of the PGG signals. This behaviour is attributed to a different electrospray ionization of the mixture compounds depending on their most probable positioning at the surface of the evaporating droplet. The most favoured positioning of hydrophobic molecules at the aqueous-gas interphase allows preferential evaporation of hydrophobic ions whereas the hydrophilic molecules are retained in the droplet interior, and, their ESI-MS detection depressed. These findings suggest that the electrospray ionization of different molecules present in complex heterogeneous mixtures of environmental significance such as humic substances is limited by their concentration and reciprocal attracting forces.     

Thermo-mechanical properties of microfibrillated cellulose-reinforced partially crystallized PLA composites

Polylactic acid (PLA) in a crystallized state has mechanical properties at high temperatures superior to PLA in an amorphous state. However, a long annealing time is required to fully crystallize PLA. In this study, microfibrillated cellulose (MFC)-reinforced partially crystallized PLA composites were produced, with the goal of reducing the time required to fabricate PLA parts. A series of PLA/MFC composites at a fiber content of 10 wt% from degree of crystallinity (Xc) 0 to 43% was obtained by annealing at 80 °C. Although the annealing time required to obtain a composite (Xc: 17%) was only around one-seventh of the 20 min needed to fully crystallize neat PLA (Xc: 41%), both materials had comparable rigidity above the glass transition temperature (T _g) and creep deformation at around T _g. These results showed that partially crystallized PLA/MFC composite can replace fully crystallized neat PLA.     

Synthesis of comb type and semi-interpenetrating networks of acryloyl-l-proline methyl ester and poly (acrylic acid) for Cu (II) immobilization

Graft copolymer hydrogels and semi-interpenetrating networks (s-IPN) of acryloyl-l-proline methyl ester (A-ProOMe) and poly (acrylic acid) (PAAc) were synthesized in methanol solutions, by ionizing radiation (γ rays from a Co⁶⁰ source at room temperature). These systems are thermo and pH-sensitive and the pH sensitivity increases from acidic to basic solutions. The Lower Critical Solution Temperature (LCST), due to presence of poly (acryloyl-l-proline methyl ester) (PA-ProOMe) has been found between 18 and 20 °C and an unexpected Upper Critical Solution Temperature (UCST) due to poly acrylic acid (PAAc) has been found between 21 and 22 °C. Preliminary studies on the immobilization of Cu²⁺ for both hydrogels were done at several pH values at room temperature. Other techniques employed to characterize the comb type hydrogels and sIPN included scanning electronic microscopy (SEM) and infrared (FTIR-ATR).     

Experimental methodology for precise determination of density of RTILs as a function of temperature and pressure using vibrating tube densimeters

A specific calibration procedure that allows the accurate determination of densities of room temperature ionic liquids, RTILs, as a function of temperature and pressure using vibrating tube densimeters is presented. This methodology overcomes the problems of common calibration methods when they are used to determine the densities of high density and high viscosity fluids such as RTILs. The methodology is applied for the precise density determination of RTILs 1-ethyl-3-methylimidazolium tetrafluoroborate [Emim][BF₄], 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF₄], 1-hexyl-3-methylimidazolium tetrafluoroborate [Hmim][BF₄], and 1-octyl-3-methylimidazolium tetrafluoroborate [Omim][BF₄] in the temperature and pressure intervals (283.15 to 323.15) K and (0.1 to 60) MPa, respectively. The viscosities of these substances, needed for the estimation of the viscosity-induced errors, were estimated at the same conditions from the experimental measurements in the intervals (283.15 to 323.15) K and (0.1 to 14) MPa and from a specific extrapolation procedure. The uncertainty in the density measurements was estimated in ±0.30 kg · m^?3 which is an excellent value in the working intervals. The results of these RTILs have demonstrated that viscosity-induced errors are relevant and they must be taken into account for a precise density determination. Finally, an alternative tool for a simpler application of this procedure is presented.     

Carbon nanotubes: Solid-phase extraction

Since the first report in 1991, carbon nanotubes (CNTs) have shown great possibilities for a wide variety of processes and applications, which include their use as electrodes, sensors (gas, enzymatic, etc.), nanoprobes, electronic materials, field emitters, etc. The combination of structures, dimensions and topologies has provided physical and chemical attractive properties that are unparalleled by most known materials. Their applications have also reached the Analytical Chemistry field in which CNTs are being used as matrices in matrix assisted laser desorption ionization, stationary phases in either gas chromatography, high performance liquid chromatography or capillary electrochromatography, also as pseudostationary phases in capillary electrophoresis, etc. as well as new solid-phase extraction (SPE) materials. Concerning this last application the number of works has considerably increased in the last five years. This review article pretends to focus on the most important features and different applications of SPE using CNTs (including matrix solid-phase dispersion and solid-phase microextraction) covering articles published since their introduction up to now (September 2009).     

Enantiomeric separation of chiral polycyclic musks by capillary electrophoresis: Application to the analysis of cosmetic samples

The enantiomeric separation of four chiral polycyclic musks (Galaxolide, Tonalide, Traseolide and Phantolide) using CE was achieved for the first time in this work. Two chiral methodologies were developed by CD-MEKC using SDS as surfactant in a CHES buffer (pH 9.0). One methodology enabled the fast enantiomeric separation of individual polycyclic musks with analysis times lower than 10 min for Tonalide, 13 min for Traseolide and Phantolide, and 17 min for Galaxolide. Enantiomeric resolutions obtained were higher than 1.5 using different separation media for each compound. A second methodology was also developed enabling the simultaneous enantioseparation of the four musks. In this case, the use of a dual CD system containing two neutral CDs was necessary to achieve the separation of all enantiomers from three out of four musks in 45 min. Although a coelution between Galaxolide and Phantolide was observed, the use of different UV absorption wavelengths allowed the simultaneous analysis of both musks. In addition, a sweeping strategy was performed in order to increase the sensitivity of the method. Appropriate analytical characteristics (linearity, LOD and LOQ, precision and absence of matrix interferences) were obtained for conventional and sweeping methodologies. Finally, the usefulness of the method was demonstrated in the determination of the enantiomers of the polycyclic musks in personal care products as perfumes.