ChemInform Abstract: Efficient Solvent‐Free Microwave‐Assisted Esterification of Fusel Oil Using p‐TsOH and H3PW12O40 as Catalysts.

Pérez, Eliseo García; Carnevalli, N. C.; Cordeiro, Paulo Jorge Marques; Rodrigues-Filho, Ubirajara P.; Franco, Douglas Wagner

doi:10.1002/chin.200143068

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“…Keggin-type heteropolyacids have remarkable physical and chemical properties, such as high polarizability and surface charge distribution, high acidity, , high solubility in aqueous and nonaqueous solvents, suitable redox potentials for electron and proton transfer/storage, − high miscibility with sol–gel and polymer matrices, − and the ability to form supramolecular complexes with organic compounds. , Applications for these compounds have been developed in a variety of fields, acting as catalyzers, sensors, fuel cells electrolytes, and electrochromic devices. − Some of these Keggin compounds, such as the 12-tungstophosphoric acid (PW 12 O 40 H 3 , HPW), show photochromic and photochemical properties. ,− Recent studies show the possibility of developing organically modified silica (ormosil) photochromic materials with HPW, which might be used for dosimetry in the UV range. − These materials are prepared by sol–gel methods and can be cast as films. Some of the properties relevant for the photochromic response may be tuned, varying the concentration and type of the organic functionalities.…”

Section: Introductionmentioning

confidence: 99%

Thermal Transformations and Proton Species in 12-Phosphotungstic Acid Hexahydrate Studied by ¹H and ³¹P Solid-State Nuclear Magnetic Resonance

2014

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The hydration environments around the heteropolyanion in 12-phosphotungstic acid (PW 12 O 40 H 3 , HPW) were analyzed as a function of temperature in the hexahydrated form (HPW•6H 2 O). Samples were obtained drying HPW•nH 2 O with n ∼ 22 at 358 K for 2 h in a furnace with either uncontrolled air atmosphere or saturated with N 2 . The existence of a phase transition in HPW•6H 2 O and the change in the thermal balance of hydrated species were tested using a set of multinuclear NMR techniques: high-resolution 31 P and 1 H NMR, 31 P{ 1 H} spin−echo double resonance, and { 1 H}-31 P cross-polarization. Differences in the proton dynamics were also probed measuring the spin−lattice relaxation time in the rotating frame ( 1 H-T 1ρ ), using direct excitation of all 1 H species or selecting only those in the neighborhood of the polyanion with cross-polarization techniques. Experiments were conducted between 223 and 358 K to induce appreciable variations in the dynamic equilibrium of hydrated species. Although XRD and TGA showed the same results for both samples, consistent with HPW•6H 2 O, structural differences were detected with NMR, indicating that the material obtained from the drying process under N 2 is more compatible with the hexahydrate. 1 H NMR confirmed the existence of an equilibrium balance between hydration species as a function of temperature: H 5 O 2 + ↔ H 3 O + + H 2 O ↔ H + + 2H 2 O. Proton exchange was detected in H 3 O + and also in hydrogen bonds in H 5 O 2 + at a very fast rate, even at low temperatures. No evidence of a structural phase transition was found in this sample. For the sample dried in uncontrolled atmosphere, the presence of mobile water in clusters was detected. Heating from room temperature, the hydrated species undergo a transformation at 318 K, related to rearrangement/removal of interstitial H 2 O. A complex sequence of metastable states and hysteresis effects is observed when this sample is cooled down to room temperature. These results indicate that the transformation at 318 K is not an intrinsic property of the HPW hexahydrate structure, but it is related to the rearrangement of interstitial H 2 O.

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Section: Introductionmentioning

confidence: 99%

Thermal Transformations and Proton Species in 12-Phosphotungstic Acid Hexahydrate Studied by ¹H and ³¹P Solid-State Nuclear Magnetic Resonance

2014

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ChemInform Abstract: Efficient Solvent‐Free Microwave‐Assisted Esterification of Fusel Oil Using p‐TsOH and H₃PW₁₂O₄₀ as Catalysts.

Cited by 1 publication

References 1 publication

Thermal Transformations and Proton Species in 12-Phosphotungstic Acid Hexahydrate Studied by ¹H and ³¹P Solid-State Nuclear Magnetic Resonance

Thermal Transformations and Proton Species in 12-Phosphotungstic Acid Hexahydrate Studied by ¹H and ³¹P Solid-State Nuclear Magnetic Resonance

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ChemInform Abstract: Efficient Solvent‐Free Microwave‐Assisted Esterification of Fusel Oil Using p‐TsOH and H3PW12O40 as Catalysts.

Cited by 1 publication

References 1 publication

Thermal Transformations and Proton Species in 12-Phosphotungstic Acid Hexahydrate Studied by 1H and 31P Solid-State Nuclear Magnetic Resonance

Thermal Transformations and Proton Species in 12-Phosphotungstic Acid Hexahydrate Studied by 1H and 31P Solid-State Nuclear Magnetic Resonance

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ChemInform Abstract: Efficient Solvent‐Free Microwave‐Assisted Esterification of Fusel Oil Using p‐TsOH and H₃PW₁₂O₄₀ as Catalysts.

Thermal Transformations and Proton Species in 12-Phosphotungstic Acid Hexahydrate Studied by ¹H and ³¹P Solid-State Nuclear Magnetic Resonance

Thermal Transformations and Proton Species in 12-Phosphotungstic Acid Hexahydrate Studied by ¹H and ³¹P Solid-State Nuclear Magnetic Resonance