Asphaltene precipitation from latin american heavy crude oils. Effects of solvent aromaticity and agitation on particle size reduction

Asphaltenes from three crudes were precipitated with a mixture of n-heptane and toluene, the size of the particles formed under different solvent mixtures and different agitation regimes were studied. The kinetic size reduction of aggregates formed with an excess of precipitant agent is followed, contrary to other published studies where the kinetic followed is of growing particles. It was found that the particle size of precipitated asphaltenes decreases as precipitant aromaticity increases and agitation energy rises, which indicates the formation of aggregates bonded by weak forces, since the agitation applied was not of high energy, except for the ultrasonic device.     

Novel 4,5-bis(trifluoromethyl)-1H-pyrazoles through a concise sequential iodination-trifluoromethylation reaction

An efficient protocol for the assembly of a new series of 1,3-disubstituted 4,5-bis(trifluoromethyl)-1H-pyrazoles – through a concise sequential iodination-trifluoromethylation reaction at the C-4 position of an initial series of 1-aryl-3-(alkyl/aryl)-5-trifluoromethyl-1H-pyrazoles (electronically deactivated heterocycles), using NIS and MFSDA, at good conversion yields and in short reaction times – is reported.     

Chemoselective synthesis of 6-amino(alkoxy)-1,4,5,6-tetrahydropyridines from cyclic β-alkoxyvinyl α-ketoester

The synthetic versatility of ethyl 2-(2-ethoxy-3,4-dihydro-2H-pyran-5-yl)-2-oxoacetate for the synthesis of ethyl 2-oxo-2-(1-alkyl/aryl-6-(amino/ethoxy)-1,4,5,6-tetrahydropyridin-3-yl)acetates, from the reaction with primary amines, is presented. The methodology proposed herein is highly chemoselective, and twenty products were obtained in moderate to good yields (up to 87%).     

One‐pot synthesis of aryl and heteroaroyl‐substituted hydroxypyrazolines from the reactions of β‐alkoxyvinyl trichloromethyl ketones with heteroarylhydrazides

The one‐step regiospecific synthesis of a novel series of 10 trichloromethyl‐, aryl‐, and heteroaroyl‐substituted 5‐hydroxy‐2‐pyrazolines affords 1‐(2‐thenoyl)‐, 1‐(2‐furoyl)‐, and 1‐(isonicotinoyl)‐3‐aryl‐5‐hydroxy‐5‐trichloromethyl‐4,5‐dihydro‐1H‐pyrazoles in 63–92% yields from the cyclocondensation reactions of 1,1,1‐trichloro‐4‐methoxy‐4‐aryl‐3‐buten‐2‐ones (where aryl substituents are –C₆H₅, 4‐CH₃C₆H₄, 4‐OCH₃C₆H₄, 4‐FC₆H₄, 4‐ClC₆H₄, 4‐BrC₆H₄) with 2‐thiophenecarboxylic hydrazide, furoic hydrazide, and isonicotinic acid hydrazide, respectively. Dehydration reaction of two 2‐pyrazolines with P₂O₅ furnished the corresponding 1H‐pyrazoles in low yields (21–29%). © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:685–691, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20261     

Debye to non-Debye scaling of the Boson peak dynamics: critical behavior and local disorder in vitreous germania

We report on the observation of a significant softening of the Boson peak (BP) frequency of vitreous GeO(2) above the glass transition temperature. The softening reminds a critical trend, with a transition temperature intermediate between the glass transition temperature, T(g), and the melting point. The softening of the BP frequency corresponds to a transition from a region dominated by Debye scaling to a non-Debye one. Below T(g) the density of vibrational states varies according to the modification of the elastic continuum medium. Above T(g) the relevant softening of the BP modes can be explained by a broadening of the distribution of elastic constants between neighboring atoms, induced by the structural rearrangement. These findings are discussed together with recent experimental and theoretical results on the low frequency vibrations in glasses.     

W/O/W Multiple Emulsions Obtained by One‐Step Emulsification Method and Evaluation of the Involved Variables

The effects of some composition variables on the development of multiple emulsions by one‐step method were evaluated and their morphology characterized. The formulations that remained stable during the period of the test were submitted to centrifugation and thermal stress tests. The stability and the morphology of multiple droplets were affected not only by the type and concentration of the surfactants employed, but also by the water/oil ratios used. The results suggest that the formation of multiple droplets could involve a combination of transitional and catastrophic phase inversions. The results provide improved knowledge about the one‐step emulsification method, a simplified process to prepare multiple emulsions when compared to the two‐steps method.     

Synthesis and structural study of a new series of 2‐methylsulfanyl‐tetrahydropyrimidines from β‐alkoxyvinyl trihalomethyl ketones

This work describes the synthesis of a novel series of 2‐methylsulfanyl‐tetrahydropyrimidines, from the cyclocondensation reaction of β‐alkoxyvinyl trihalomethyl ketones with 2‐methyl‐2‐thiopseudourea sulfate, in good yields. A detailed ¹H‐ and ¹³C‐NMR study was performed on the 2‐methylsulfanyl‐tetrahydropyrimidines obtained and 3D structures were proposed based on AM1 calculations supported by ¹H NMR coupling constants and NOESY experiments.     

An efficient synthesis of 1-cyanoacetyl-5-halomethyl-4,5-dihydro-1H-pyrazoles in ionic liquid

The synthesis of eleven 1-cyanoacetyl-5-hydroxy-5-halomethyl-4,5-dihydro-1H-pyrazoles from the reaction of 4-alkoxy-3-alken-2-ones f(R ³C(O)C(R ²) = C(R ¹)OR, where R ³ = CF₃, CCl₃, CHCl₂, CO₂ Et; R ²/R ¹ = H/H, H/Me, H/Et, -(CH₂)₄-, Me/H, H/Pr, and R = Me, Et) with cyanoacetohydrazide is reported. The reaction was carried out in the ionic liquid ([bmim][BF₄]) and molecular solvents. The results showed that when the ionic liquid was used as reaction medium, the reaction time was drastically decreased and the yield was improved.     

An ionic liquid as reaction medium for the synthesis of halo-containing β-enaminones at room temperature

A series of twenty halomethylated β-enaminones [RC(O)CH=C(R ¹)NR ³ R ⁴, where R = CF₃,CCl₃, CHCl₂; R ¹ = H, Me, Ph; R ³ = H, Me, Bu, Et; R ⁴ = Me, Et, Bu, allyl, tert-amyl, CH₂CH₂OH, Bn, Ph] were synthesized using the ionic liquid [bmim]BF₄ at room temperature. It is demonstrated that this ionic liquid is a reaction medium suitable for the amination of β-alkoxyvinyl halomethyl ketones. The advantages of this method are the absence of solvents, short reaction times, and good yields. Correspondence: Marcos A. P. Martins, Núcleo de Química de Heterociclos – NUQUIMHE, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil.