Experimental Study of Asphaltenes Flocculation Onset in Crude Oils Using the Densitometry Measurement Technique

The asphaltenes flocculation proceeds with changes of oil composition and causes significant losses in petroleum industry operations. The main objective of this work is to evaluate the reliability of the densitometry technique in studying experimentally the mechanism of aggregation and flocculation of asphaltenes occurring in crude oils. As asphaltene flocculation threshold in crude oils or mixture can be achieved by addition of n-heptane, various n-heptane concentrations were added to crude oil, and their effects have been investigated trough density measurements. Thereby, measurements were based on mixture of crude oil + toluene and cyclohexane + n-heptane, respectively. While asphaltene aggregates form clusters and flocculate, the mixture volumetric mass change and the reduced density of non-Newtonian fluids under investigation have been pointed out as one of appropriate measures of flocculation process. In particular, the curve representing the reduced density as function of the ratio between n-heptane concentration and concentration of crude oil under study featured a break point that well characterizes the flocculation threshold. Besides the quantity needed to initiate and to aggregate asphaltenes within crude oils, the amount required to completely achieve deposition of asphaltenes has also been identified. A quantity of 4 and 20 g of n-heptane per gram of crude oil was found necessary.     

An Improved Synthesis and NMR Spectra of Benzylated Glycals

Abstract

Benzylated glycals, unlike their acylated congeners which easily undergo allylic rearrangement, are frequently employed as reactive enol ether type substrates in a variety of electrophilic addition reactions.^1–4 Although these compounds are considered to be readily available substrates, reported procedures for their syntheses involve some steps of limited efficiency, chromatographic separations or costly reagents,^5–7 and experimental requirements not amenable for large scale preparations. In view of the recent applications of benzylated glycals to syntheses of O-glycosides,^1,2 C-glycosyl compounds,³ and β-lactams,⁴ we have undertaken a study aimed at efficient one step benzylation procedures applicable to pyranoid 1-enitols as well as to their acylated derivatives. This goal was eventually achieved by employing a catalytic phase transfer alkylation system with     

Probing the Coordination Environment of the Human Copper Chaperone HAH1: Characterization of HgII‐Bridged Homodimeric Species in Solution

Although metal ion homeostasis in cells is often mediated through metallochaperones, there are opportunities for toxic metals to be sequestered through the existing transport apparatus. Proper trafficking of Cu^I in human cells is partially achieved through complexation by HAH1, the human metallochaperone responsible for copper delivery to the Wilson and Menkes ATPase located in the trans‐Golgi apparatus. In addition to binding copper, HAH1 strongly complexes Hg^II, with the X‐ray structure of this complex previously described. It is important to clarify the solution behavior of these systems and, therefore, the binding of Hg^II to HAH1 was probed over the pH range 7.5 to 9.4 using ¹⁹⁹Hg NMR, ^199mHg PAC and UV–visible spectroscopies. The metal‐dependent protein association over this pH range was examined using analytical gel‐filtration. It can be concluded that at pH 7.5, Hg^II is bound to a monomeric HAH1 as a two coordinate, linear complex (HgS₂), like the Hg^II–Atx1 X‐ray structure (PDB ID: 1CC8). At pH 9.4, Hg^II promotes HAH1 association, leading to formation of HgS₃ and HgS₄ complexes, which are in exchange on the μs–ns time scale. Thus, structures that may represent central intermediates in the process of metal ion transfer, as well as their exchange kinetics have been characterized.     

Dehydrogenation Mechanism of Liquid Organic Hydrogen Carriers: Dodecahydro‐N‐ethylcarbazole on Pd(111)

Dodecahydro‐N‐ethylcarbazole (H₁₂‐NEC) has been proposed as a potential liquid organic hydrogen carrier (LOHC) for chemical energy storage, as it combines both favourable physicochemical and thermodynamic properties. The design of optimised dehydrogenation catalysts for LOHC technology requires a detailed understanding of the reaction pathways and the microkinetics. Here, we investigate the dehydrogenation mechanism of H₁₂‐NEC on Pd(111) by using a surface‐science approach under ultrahigh vacuum conditions. By combining infrared reflection–absorption spectroscopy, density functional theory calculations and X‐ray photoelectron spectroscopy, surface intermediates and their stability are identified. We show that H₁₂‐NEC adsorbs molecularly up to 173 K. Above this temperature (223 K), activation of C? H bonds is observed within the five‐membered ring. Rapid dehydrogenation occurs to octahydro‐N‐ethylcarbazole (H₈‐NEC), which is identified as a stable surface intermediate at 223 K. Above 273 K, further dehydrogenation of H₈‐NEC proceeds within the six‐membered rings. Starting from clean Pd(111), C? N bond scission, an undesired side reaction, is observed above 350 K. By complementing surface spectroscopy, we present a temperature‐programmed molecular beam experiment, which permits direct observation of dehydrogenation products in the gas phase during continuous dosing of the LOHC. We identify H₈‐NEC as the main product desorbing from Pd(111). The onset temperature for H₈‐NEC desorption is 330 K, the maximum reaction rate is reached around 550 K. The fact that preferential desorption of H₈‐NEC is observed even above the temperature threshold for H₈‐NEC dehydrogenation on the clean surface is attributed to the presence of surface dehydrogenation and decomposition products during continuous reactant exposure.     

The 2,2′-Coupled Pyrrolidine-Phospholane Ring System: A Highly Enantioselective Synthesis and Kinetic Resolution of the Phosphorus Centre

Abstract

Enantiopure five-membered ring nitrones derived from L-tartaric acid and from L-malic acid undergo highly regio- and stereoselective cycloaddition reactions with an excess of racemic 2,3-dihydro-1-phenyl-1H-phospholes producing two readily separable tricyclic cycloadducts and concomitantly effecting kinetic resolution of the dihydrophosphole derivative (diastereomeric ratio up to 10:l; stereoselectivity factor s = kS/kR = 14). The tricyclic cycloadducts feature 2,2′-connection of pyrrolidine and phospholane rings and five to seven contiguous stereogenic centers of which three are induced and one or two are kinetically resolved during the cycloaddition process.     

New Chemistry of Enol Phosphates

Applications of enol phosphates in the synthesis of novel bicyclic 1,3-dienes, bi- and polycyclic aromatic derivatives, and f -hydroxy ketones are described.     

THE STEREOCHEMISTRY OF DEALKYLATION STEP IN THE ARBUZOV REACTION INVOLVING FIVE-COORDINATE INTERMEDIATE. EVIDENCE FOR EQUILIBRIUM BETWEEN PHOSPHORANE AND PHOSPHONIUM SPECIES

Abstract

The oxidative addition of molecules X–Y to three-coordinated phosphorus compounds is of considerable general interest. If one of the groups attached to the phosphorus atom is an alkoxy, OR, the final product is almost always > P(O)Y with the formation of an alkyl halide RX. The above process is known as Arbuzov reaction, the mechanism of which can be represented, in the light of our present knowledge, as follows: mental mechanistic problem for the Arbuzov reaction.

The R(?)phosphite (4) was prepared from R(+)2-octanol of 95% opt. purity, [α]²⁰ _D + 9.4° (neat) and the chlorophosphite (3) by standard condensation in the presence of tertiary amine and purified by distilla tion in vacuo, δ³¹P ?127.5 ppm, [α]^D ₂₀ ?25.6° (neat). Equimolar amounts of the phosphite (4) and the corresponding halogen in CH2 C12 solution were allowed     

31P High Resolution Solid State NMR Spectroscopy as a Tool for Structural Studies of Organothiophosporyl Compounds

Abstract

Employing 1,6-anhydro-2-0-(tosyl)-4-S-(5,5-dimethyl-2-tioxa-1,3,2-dioxaphosphorinan-2-yl) β-D-glucopyranose 1, bis-imidazole 5,5-dimethyl-1,3,2-dioxaphosphorinan-2-tioxa-2-hydroxy complex II and bis (organothiophosphoryl) dichalcognides III as models this report presents power of ¹³C and ³¹P CP/MAS experiment in structural studies organothiophosphoryl compounds [1,2,3].     

An Investigation of the Structure of Copolymers of lsobutylene and Diene Prepared by Initiation with VCI4 in the Dark and with Visible Light

¹H-NMR spectra of copolymers of isobutylene and 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene were investigated in connection with the elucidation of the formation of soluble and insoluble copolymers. For copolymers soluble in heptane, benzene, and CCI₄ it was found that the incorporation of diene into the polymer chain proceeds by 1,4-addition in the case of copolymerizations conducted both in the dark and with visible light using VC1₄ as initiator. The formation of a soluble and an insoluble copolymer is attributed to a different type of initiation, either with radical-cations of isobutylene, if soluble copolymers are formed, or with radical-cations of diene, if the arising copolymers are insoluble.