Isomeric Picolines Research Articles

Adsorptive separation of picoline isomers by adaptive calix[3]acridan crystals.

The exploration of macrocycle-based nonporous adaptive crystals (NACs) for adsorption and separation has been one of the hotspots in supramolecular chemistry and crystal engineering. Herein, we developed calix[3]acridan-based NACs to separate industrially important 4-picoline from its isomer mixtures with over 93.8% purity.

Thermodynamic properties of liquid mixtures containing cyclic amines and isomeric picolines: excess molar volumes and excess isentropic compressibilities and excess heat capacities

The present study reports densities, ρ, speeds of sound, u, molar heat capacities, CP of binary piperidine or 1-methylpiperidine (1) + 2- or 3- or 4-picolines (2) mixtures over entire composition range by varying temperature range from 293.15 to 308.15 K with step of 5 K interval. Experimental data have been used to access excess molar volumes, VE, excess isentropic compressibilities, $$\kappa_{{\rm S}}^{\text{E}}$$ and excess heat capacities, $$C_{{\rm P}}^{\text{E}}$$ . The VE, $$\kappa_{{\rm S}}^{\text{E}}$$ and $$C_{{\rm P}}^{\text{E}}$$ data have been fitted to Redlich–Kister polynomial equation to evaluate the adjustable parameters and standard deviations. The $$C_{{\rm P}}^{\text{E}}$$ data of piperidine (1) + 2- or 3- or 4-picolines (2); 1-methylpiperidine (1) + 3- or 4-picolines (2) are positive and those for 1-methylpiperidine (1) + 2-picoline (2) mixture, sign and magnitude of $$C_{{\rm P}}^{\text{E}}$$ values change with increase in mole fraction of 1-methylpiperidine. Further, VE and $$\kappa_{{\rm S}}^{\text{E}}$$ of 1-methylpiperidine (1) + 2- or 3- or 4-picolines (2); piperidine (1) + 2- or 3-picolines (2) are negative; and those for piperidine (1) + 4-picoline (2) are positive across full range of composition. The VE, $$\kappa_{{\rm S}}^{\text{E}}$$ and $$C_{{\rm P}}^{\text{E}}$$ data have been utilized to test the applicability of Graph theory. It has been observed that VE, $$\kappa_{{\rm S}}^{\text{E}}$$ and $$C_{{\rm P}}^{\text{E}}$$ values calculated from the Graph theory compare reasonably well with their corresponding experimental values. The Quantum mechanical calculations and IR spectral studies on the aforesaid mixtures support the presence of various molecular entities (estimated by analyses of VE data) in pure and mixed state.

Characterization of multicomponent mixtures containing piperidine, 1-methylpiperidine, 2-pyrrolidinone and isomeric picolines

The paper reports densities, speeds of sound of binary 2-pyrrolidinone (2) + 2-, 3-, 4- picoline (3) and ternary piperidine, 1-methylpiperidine (1) + 2-pyrrolidinone (2) + 2-, 3-, 4-picoline (3) mixtures over full composition of x1; x1 and x2 within range 293.15–308.15 K with 5 K footstep at atmospheric pressure. The molar heat capacities of the same set of binary mixtures have also been measured at the above said temperatures. Excess molar volumes, VE, V123E; excess isentropic compressibilities, κSE, (κSE)123 and excess heat capacities, CPE for the current mixtures have been determined from the measured data and derived properties have been correlated to composition using Redlich–Kister equation. VE, V123E, κSE, (κSE)123, CPE; IR spectral studies and estimated internuclear distances among interacted atoms (using quantum concepts) have been used to characterize interactions in mixtures taking into consideration effect of composition and temperature.

A Versatile VMPO Catalyst Prepared In Situ for Oxidative Ammonolysis of Isomeric Picolines and Xylenes

The V2O5–MoO3–P2O5 (VMPO) catalyst has been prepared in situ by thermal decomposition of vanado-molybdophosphoric acid (PMoV) on TiO2 support at 475°C. The TiO2 supported VMPO catalysts are characterized by FT–IR, XRD, BET surface area, NH3–TPD, and H2–TPR. Morphology of the catalyst has been studied by TEM. The accumulated data indicate decomposition of PMoV and presence of phosphate and pyrophosphate phases of molybdenum and vanadium after calcination. TPD and TPR studies exhibit the moderate acidity and presence of V4+ in the material, respectively. The VMPO catalyst has been used for ammoxidation of six different compounds including three isomeric picolines and three isomeric xylenes to the corresponding nitriles with the yield of 90–96%.

Enclathration of Picoline Isomers by (rac)-TADDOLs: Structures, Selectivity, and Thermal Analysis

In this investigation, we studied the preferences of three α,α,α′,α′-tetraphenyl-l,3-dioxolane-4,5-dimethanol (TADDOL)-derived host compounds toward the isomers of methyl-pyridines (picolines). Ten novel inclusion compounds were synthesized, and their structural and thermal properties were further characterized. Binary competition experiments were performed, and all three hosts discriminate between the picoline isomer guests. Interestingly, all three hosts display different preferences toward the isomers, and these results were rationalized by their resulting crystal structures and packing analysis and correlated to their differential scanning calorimetry (DSC) results. DSC results showed a correlation between the thermal stability of an inclusion compound and the preference of the host toward a given isomer.

FTIR study of the role of surface complexes in a transformation of picoline isomers on vanadium-titanium oxide catalysts

Surface complexes of 2-, 3- and 4-picoline on the VTi oxide catalysts were studied by FTIR spectroscopy. The sequence of its transformations has been studied in the temperature range 100–260°C. In the first step, isomers of picoline interact with the strong Brönsted acid sites of the catalysts to form the corresponding methylpyridinium ions. Further, these complexes are transformed into the corresponding surface complexes of pyridinecarbaldehyde. The latter are transformed further into the corresponding carboxylates. The carboxylates are the direct precursors of picolinic, nicotinic, and isonicotinic acids. 2-Pyridine carbaldehyde complex are transformed also into α-pyridoin complex via the condensation. This fact explains the low yield of picolinic acid. Published data on the order of activity in oxidation and ammonolysis of the picoline isomers (2≈4>3) can be explained by the values of the basicity of isomeric picolines and by values of pKa of the methyl group deprotonation.

Nanoclusters formation in ion mobility spectrometry and change separation selectivity of picoline isomers

Ion mobility spectrometry (IMS) was applied to determine the influence of structural features of nanocluster formation of picoline isomers in ion mobility spectrometry. Since the results of our studies show that different isomers have the same mobilities in pure nitrogen buffer gas and their corresponding peaks are totally overlapped, 2-butanol vapor was introduced into buffer gas by means of an online system from 0 to 300 mL min−1. We found different structural features of these isomeric compounds which cause distinct differences in ion mobility spectra. These differences result from the formation of different nanocluster product ions (~1 nm3) with different cross section areas formed depending on the occurrence of certain structural features (position of the methyl group on the pyridine ring). The size of cluster product ions formed was determined using cross section area measurements. The effects of temperature in the range from 80 to 200 °C and electric field strength have also been investigated. At 140–160 °C and 636 V cm−1, optimum peak-to-peak resolution can be obtained.

Inclusion of picolines by a substituted binaphthyl diol host: selectivity and structure

The host compound 3,3′-bis(9-hydroxy-9-fluorenyl)-2,2′-binaphthyl forms inclusion compounds with the isomers of picoline. Competition experiments show that the preferred selectivity is in the order 4PIC > 3PIC > 2PIC. The structures of the inclusion compounds formed with each picoline, as well as representative samples from the competition experiments, have been elucidated. The thermal stabilities of the inclusion compounds correlate with the selectivity results.

Topological investigations of binary mixtures containing ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate and pyridine or isomeric picolines

The densities, ρ, speeds of sound, u of {1-ethyl-3-methylimidazolium tetrafluoroborate (i)+pyridine or α- or β- or γ-picoline (j)} at T/K=(293.15, 298.15, 303.15, and 308.15) and excess molar enthalpies, HE of the same set of mixtures at T/K=(298.15) have been measured over entire mole fraction range using DSA-5000 and 2-drop microcalorimeter. Excess molar volumes, VE and excess isentropic compressibilities, κSE values have been predicted by utilizing the measured densities and speeds of sound data. It has been observed that VE, HE, and κSE values for the studied mixtures are negative over entire composition. The connectivity parameter of third degree of a molecule, 3ξ (which in turn depends upon its topology) have been applied to predict (i) state of components of ionic liquid mixtures in their pure and mixed state; (ii) nature and extent of interactions existing in mixtures; and (iii) VE, HE, and κSE values. The analysis of VE data in terms of Graph theory (which deals with topology of a molecule) suggest that while 1-ethyl-3-methylimidazolium tetrafluoroborate is characterised by electrostatic forces of attraction and exist as monomer; α- or β- or γ-picoline exist as associated molecular entities. Further, (i+j) mixtures are characterized by interactions between nitrogen and florine atoms of 1-ethyl-3-methylimidazolium tetrafluoroborate with nitrogen and carbon atoms of pyridine or isomeric picolines to form 1:1 molecular complex. The IR studies also support to this view point. The VE, HE, and κSE values predicted by Graph theory compare well with experimental values.

Energetics and rearrangements of the isomeric picoline dications

The second ionization energy of β-picoline was determined from photoionization experiments as 2 IE β = (24.05 ± 0.1) eV and the threshold for the dehydrogenation of the dication generated by photoionization as AE(–H 2) β = (25.0 ± 0.2) eV. The second ionization energy is about 0.5 eV lower than values recently determined for α- and γ-picoline, whereas the energies required for dehydrogenation are similar. In order to rationalize the different behavior of dications generated from these isomeric picolines, we have performed a mass spectrometric investigation of the fragmentation patterns of the individual picoline dications and an extensive series of DFT calculations to explain the observed spectra.

Thermodynamic properties of binary mixtures of tetrahydropyran with pyridine and isomeric picolines: Excess molar volumes, excess molar enthalpies and excess isentropic compressibilities

Densities, ρ and speeds of sound, u of tetrahydropyran (i) + pyridine or α-, β- or γ- picoline (j) binary mixtures at 298.15, 303.15 and 308.15 K and excess molar enthalpies, H E of the same set of mixtures at 308.15 K have been measured as a function of composition using an anton Parr vibrating-tube digital density and sound analyzer (model DSA 5000) and 2-drop micro-calorimeter, respectively. The resulting density and speed of sound data of the investigated mixtures have been utilized to predict excess molar volumes, V E and excess isentropic compressibilities, κ S E . The observed data have been analyzed in terms of (i) Graph theory; (ii) Prigogine–Flory–Patterson theory. It has been observed that V E , H E and κ S E data predicted by Graph theory compare well with their experimental values.

Gossypol clathrates: Structure and thermal behavior of gossypol solvates with two picoline isomers

Gossypol forms stable solvates with 4- and 2-picolines at room temperature. The solvates are investigated by single crystal X-ray diffraction and thermal analysis. Solvate crystals of gossypol with 4-picoline (1) have the 1:3 composition (gossypol:4-picoline) and crystallize in the P21/c space group. This substance is isostructural to a trisolvate of gossypol with pyridine. Solvate crystals of gossypol with 2-picoline (2) have the 1:4 composition (gossypol:2-picoline) and crystallize in the P-1 space group. The unit cell parameters for the investigated structures are as follows: 1 monoclinic crystals, C30H30O8·3C6H7N, a = 10.7530(1) A, b = 20.7834(3) A, c = 19.1166(2) A, β = 95.537(1)°, V = 4252.32(9) A3, M = 797.92, Z = 4, dx = 1.246 g/cm3, and R = 0.0489 for 4102 reflections; 2 triclinic crystals, C30H30O8·4C6H7N, a = 11.467(1) A b = 14.962(2) A, c = 15.570(3) A, α = 75.62(1)°, β = 69.83(1)°, γ = 79.58(1)°, V = 2414.6(7) A3, M = 891.04, Z = 2, dx = 1.226 g/cm3, and R = 0.0528 for 3779 reflections. The results of the single crystal XRD and thermal analysis confirm that gossypol with 4-picoline forms a trisolvat, and a tetrasolvate with 2-picoline. The transition from 4-picoline to 2-picoline proves to change the type of the host-guest association from one-dimensional to zero-dimensional, i.e., to lead to a new crystal structure. Desolvation of compound 2 begins at a lower temperature than that for compound 1, which is explained by their different crystal structures. Keywords: gossypol, 4-picoline, 2-picoline, clathrate formation, crystal structure.

Enclathration of bases by a fluorenyl host: structure, stability and selectivity

The host compound 9,9′-(1,4-phenylene)-bis-(fluoren-9-ol) forms inclusion compounds with pyridine, the isomers of picoline and morpholine. The structures of the inclusion compounds are stabilised by (Host)O–H⋯N(Guest) hydrogen bonds. Unusually, the structure of the host containing 4-picoline and morpholine displays both cis- and trans-conformation. The enthalpy of enclathration of these guests was estimated by packed-column chromatography.

Selective enclathration of picoline isomers by a resorcinarene host

The resorcinarene host 14,16,54,56-tetrahydroxy-2,4,6,8-tetrapentyl-34,36,74,76-tetra(p-toluene-sulfonyl-oxy)-1,3,5,7(1,3)-tetrabenzenacyclooctaphane forms inclusion compounds with 2-, 3- and 4-picoline. The structures of these inclusion complexes have been elucidated and compared, with some being found to additionally include water molecules as guests. Competition experiments were carried out to determine whether this host would selectively enclathrate any of the picolines and thus investigate the capability of this host for the separation of picoline isomers. A very interesting result was obtained for the 3-picoline versus 4-picoline competition experiment, which displays a concentration dependent selectivity, but instead of selective inclusion of the guest of higher concentration, it was in fact the guest of lower concentration in the solution which was preferentially enclathrated. This unusual result was explained in terms of solubilities of the clathrates in the two guests.

Relaxation Dynamics of Highly Vibrationally Excited Picoline Isomers (Evib= 38 300 cm-1) with CO2: The Role of State Density in Impulsive Collisions

Strong collisions of highly vibrationally excited picoline isomers and CO2 (00(0)0) were investigated using high resolution transient IR absorption probing to investigate the role of donor state density. Vibrationally excited 3-picoline and 4-picoline (3-methylpyridine and 4 methylpyridine) with E(vib) = 38300 cm(-1) were prepared by 266 nm excitation followed by rapid internal conversion. Transient IR probe measurements of the nascent rotational and translational energy gain in CO2 (00(0)0) show that large DeltaE collisions for 3- and 4-picoline are similar to those for excited 2-picoline. The probability distributions for the large DeltaE energy transfer of the three isomers have similar dependence on DeltaE. The results are compared with other earlier results demonstrating that the shape of the large DeltaE probability distribution correlates with the DeltaE dependence of the donor vibrational state density. The results are discussed in terms of the GRETCHEN model for collisional relaxation.

Ammoxidation of isomeric picolines on molybdenum phosphate catalyst

Ammoxidation of 2-, 3-, and 4-picolines to their nitrile compounds has been studied on an amorphous molybdenum phosphate (MoPO) catalyst with P/Mo=1.0. The overall catalytic results of this study reveal that the conversion is in the order 2-picoline>4-picoline>3-picoline, which can be rationalized neither by the steric effects nor by the thermodynamic point of view. However, the MoPO catalyst prepared here was found to be very effective for the ammoxidation reaction of picolines. Even at almost 100% conversion levels of all three picoline isomers, selectivities to their nitrile compounds on this MoPO catalyst were higher than 90% or so.

Weak Hydrogen Bonding as a Basis for Concentration-Dependent Guest Selectivity by a Cyclophane Host

Crystalline inclusion complexes between the cyclophane 1 and three isomers of picoline and lutidine were grown and their properties and structures were studied by X-ray analysis, thermal gravimetry (TG), and differential scanning calorimetry (DSC). In competition experiments, the cyclophane host, which by itself is only able to form weak Cbond;H.acceptor hydrogen bonds, is able to discriminate between the different picoline or lutidine isomers, although in some cases a strong concentration dependence of the preferred isomer is observed. In the three-component experiments, inclusion of 4-picoline is strongly favored when X(4-picoline)>0.35-0.39. Very similar results were obtained in the lutidine series. The fact that 2,4-lutidine is favored when X(2,4-lutidine)>0.2 indicates that the host prefers the isomer with the methyl group in 4-position relative to the nitrogen atom. The selectivities observed can be explained based on the assignment of the inclusion complexes to different adduct classes. In the case of the picoline isomers, the preference of 4-picoline was in good agreement with the calculated lattice energies for this series. The present work also shows that caution is advisable when deducing selectivity of crystalline inclusion compounds from guest competition experiments.

Open-tubular capillary electrochromatography using capillary columns chemically bonded with the new host molecules calix[6]crown, calix[6]arene.

Two host molecules, p-tert-butylcalix[6]-1,4-crown-4 and p-tert-butylcalix[6]arene were prepared and attached onto the inner surfaces of capillaries for open-tubular electrochromatography with the aid of gamma-glycidoxypropyl-trimethoxysilane (KH-560) as bridging agent. The successful bonding was confirmed by infrared (IR) results and greatly decreased electroosmotic flow (EOF). Parameters affecting separation, such as buffer pH and organic modifier were studied. The two novel stationary phases were evaluated by the separation of isomeric toluidines, a mixture of pyridine and isomeric picolines, and isomeric dihydroxybenzenes; comparisons between capillaries coated with the two stationary phases and bare capillary were investigated. The special selectivity of these two novel stationary phases showed a certain extent of supramolecular interactions between stationary phases and solutes.

Inclusion compounds of binaphthol with picolines: structures, selectivity and kinetics of desolvation.

The crystal structures of the inclusion compounds formed between the host 2,2'-dihydroxy-1,1'-binaphthyl and the three picoline isomers have been elucidated and their lattice energies calculated. The selectivities of enclathration by the host have been measured by competition experiments. The thermal stabilities and activation energies of desolvation of the compounds have been determined. The kinetics of desolvation are correlated to the structures.

Reactivity of Isomeric Picolines in Oxidative Ammonolysis on a Vanadium Oxide Catalyst

The reactivity of isomeric picolines in their oxidative ammonolysis on a vanadium oxide catalyst, as measured by the rate constants of cyanopyridine formation, increases in the order 3-picoline < 2-picoline < 4-picoline. Correlations were found between the mentioned rate constants and the gas-phase basicities of the starting compounds, with σ constants characterizing electron-acceptor properties of the nitrogen atoms, as well as the deprotonation constants of the methyl groups of picolines in the gas phase or bound via the nitrogen atoms with clasters modeling Bronsted acid centers of the vanadium oxide surface.