PHOTO-DEGRADATION OF HYDROPHOBIC DERIVATIVES OF PYRIDINECARBOXYLIC ACID AS COPPER EXTRACTANTS FROM CHLORIDE MEDIA

ABSTRACT

The photo-stability of 2-ethylhexyl pyridine-3-carboxylate and N,N′-di(2-ethylhexyl)pyridine-3,5-dicarboxamide as the model extractants of copper from chloride media were studied and compared with the photo-stability of di(2-ethylhexyl) pyridine-3,5-dicarboxylate, N,N,N′,N′-tetrahexylpyridine-3,5-dicarboxamide and the hydroxyoxime copper extractants. Also the resistance against the UV light the copper(II) complexes of tested extractants were done. The obtained results of photo-degradation indicate that the UV light degraded amide derivatives and esters of pyridine-3,5-dicarboxylic acid and pyridine-3-carboxylic acid. A comparison of the photo-stability of oximes and derivatives of pyridine-3,5-dicarboxylic acid and pyridine-3-carboxylic acid indicates that all tested derivatives of pyridinecarboxylic acid are more stable than hydroxyoxime copper extractants. The copper complexes of derivatives of pyridinecarboxylic acid are less stable than the copper complexes of hydroxyoxime.     

Effect of Hydrophobicity and Interfacial Activity of 2-Hydroxy-5-alkylbenzophenone Oximes upon the Rate of Copper Extraction from Acidic Sulfate Solution

Abstract

The rates of copper extraction from acidic sulfate solutions with 2-hydroxy-5-alkylbenzophenone oximes of various hydrophobicities were measured by means of the drop ascending method, and they are discussed from the view of hydroxyoxime partition between both extraction phases and hydroxyoxime interfacial activity. The measured extraction rates are compared with those predicted from partition and interfacial activity data for various versions of the extraction mechanism. The ratios of specific extraction constants for oximes of various hydrophobicities are estimated for the interfacial mechanism with the preadsorption of hydroxyoximes at the hydrocarbon/water interface. The order of the specific rate constants determined for the interfacial reaction is in agreement with the order of the free energy of hydroxyoxime adsorption at the hydrocarbon/water interface.     

Interfacial Activity of Hydroxyoximes and mechanism and kinetics of palladium(II) extraction

Surface excess isothermers were determined and interpreted for systems containing 2-hydroxy-5-t-nonylbenzaldehyde oxime ( 1 ), 2-hydroxy-5-t-octylacetophenone oxime ( 2 ) and 2-hydroxy-5-t-octylbenzophenone oxime ( 3 ). These surface excess isotherms were used to predict reaction orders with respect to hydroxyoximes for various versions of interfacial process. Agreement with the experimental data was observed both for the interfacial and bulk aqueous mechanism. The surface activity of extractants cannot be recognized as the sole evidence for the interfacial mechanism of extraction. More experimental kinetic data are needed in order to determine the effect of hydroxyoxime concentration upon the reaction order. According to the interfacial mechanism, with the formation of the stable 2:1 complex as the limiting step the reaction order in hydroxyoxime equal to 1 is observed over a large range of hydroxyoxime concentration, but increases to 1.5-2.0 for very low concentrations.     

Discovery of Environmentally Benign Catalytic Reactions of Alcohols Catalyzed by Pyridine-Based Pincer Ru Complexes, Based on Metal–Ligand Cooperation

We have developed a new mode of metal–ligand cooperation, based on aromatization–dearomatization of pyridine-based pincer-type ligands, and have demonstrated it in the activation of H₂ and C–H bonds by PNP Ir complexes. This type of metal–ligand cooperation plays a key role in the recently discovered environmentally benign reactions of alcohols, catalyzed by PNP and PNN pincer complexes of ruthenium, including (a) dehydrogenation of secondary alcohols to ketones (b) dehydrogenative coupling of primary alcohols to form esters and H₂ (c) hydrogenation of esters to alcohols under mild conditions (d) unprecedented amide synthesis: catalytic coupling of amines with alcohols, with liberation of H₂. Ligand modification in the latter reaction has led to unprecedented synthesis of imines with H₂ liberation. These reactions are very efficient, proceed under neutral conditions and produce no waste.     

INTERACTION OF LONG-CHAIN ALCOHOL “MODIFIERS” WITH LIX SOLVENT EXTRACTION REAGENTS

The effect of two long chain alcohols, n-tridecyl alcohol (TDA) and 2-(l,3-trimethylbutyl)-5,7,7-trlinethyloctanol (ODA) on the extraction of Cu by alkylated hydroxyaldoximes in heptane was investigated by extraction equilibrium determination and infrared spectroscopic examination. The formation of an alcohol-extractant association complex quantitatively explains observed decreases in Dcu that accompanies alcohol addition. Further, an examination of Interfacial activity in these systems demonstrates that, whereas alcohol addition decreases the extractant adsorption at the interface, this cannot be attributed to simple displacement (the extractants are significantly more surface active than the alcohols) but rather to its depletion resulting from the formation of the poorly surface active extractant-modifier complex. Values for the Cu-hydroxyaldoxime extraction constants, self-association constants of the extractants, and the alcohols and extractant-modifier complex formation constant are presented. The critical role of infrared spectroscopic measurements in this study is described.     

VARIATIONS IN THE SOLVENT EXTRACTION BEHAVIOR OF BIFONCTIONAL PHOSPHORUS-BASED COMPOUNDS MODIFIED WITH TBP

ABSTRACT

The solvent extraction of americium from nitric acid by several modified bifunctional extractants in CCl₄has been investigated. For all the compounds examined, addition of a modifier such as tributylphosphate (TBP) enhances distribution ratios at high aqueous acidities. The effect of the modifier at lower acidities varies depending on the basicity of the bifunctional extractant. While the most basic extractants show significantly reduced distribution ratios from lower acid solutions upon TBP addition, for the less basic compounds only slight reductions or, in some cases, even moderate increases in extraction are observed. Studies of the effect of modifier basicity on extraction behavior have also been carried out. The changes in distribution ratios with modifiers fall within the range of variations observed for diluent effects with extractants of this type. Increases in high acid distribution ratios upon TBP addition to an extractant as simple as trioctylphosphine oxide indicate that this modification of extraction behavior may be of general use for a wide range of neutral extractants     

KINETICS MODEL FOR INTERFACIAL REACTION OF COPPER EXTRACTION WITH 1-(2'-HYDROXY-5'-NONYLPHENYL)-l-ETHANONE (E)-OXIME AND 1-(2'-HYDROXY-5'-METHYLPHENYL)-1-DECANONE (E)-OXIME

Abstract

A kinetic model for the interfacial reaction of copper extraction with Individual 1-(2'-hydroxy-5'-nonylphenyl)-1-ethanone (E)-oxime and 1-(2'-hydroxy-5'-methylphenyl)-1-decanone (E)-oxime having the same hydrophobicity was used to interpret the effect of hydroxyoxime partition and interfacial activity upon the rate of copper extraction from acidic sulfate solutions. Due to similar hydrophobicity of studied extractants the proposed model, which is very sensitive to the errors of the partition coefficient determination, cannot support any version of extraction mechanism.     

SEMI-EMPIRICAL (PM3) COMPUTATIONAL STUDIES OF THE ASSOCIATION OF ALKYL PYRIDINE MONOCARBOXYLATES WITH METHANOL AND WATER IMPLICATION FOR INTERFACIAL ACTIVITY AND THE EFFECT OF PHASE MODIFIERS

ABSTRACT

Alkyl pyridine monocarboxylates can form associates with alcohols. The alcohol hydroxyl group is mainly bonded with oxygen atoms of the ester group, while the pyridine nitrogen is only slightly blocked. The degree of hydrogen-bonding at the different acceptor sites depends significantly on the position of the carboxyl group in the pyridine ring. Alkyl pyridine monocarboxylates can form hydrates with water molecules. Again the hydrogen bonds are mainly formed with the oxygen atoms of the ester group. Such hydration is limited in extraction systems containing alkyl isonicotinate and alkyl nicotinate, and only weak monohydrates with one water molecule bonded with the pyridine nitrogen can be formed. The oxygens of the ester group of alkyl picolinate can be, however, easily hydrated. This phenomenon is reflected in interfacial activity and interfacial concentration of the considered extractants.     

EXTRACTION OP LANTHANIDE IONS BY 2-HETHYL-8-QOINOLINOL

The equilibrium extraction behavior of a series of tervalent lanthanides (La, Pr, Eu, Ho, and Yb) with 2-methyl-8-quinolinol(HL) in chloroform has been studied. Although the sterically hindered extractant does not form neutral LnL₃, complexes, ion pair complexes of intermediate chelates with either perchlorate or thio-cyanate ions are extractable. The extraction constants of such species are smaller than those of other 8-quinolinols and closer together because the adverse steric influence of the 2-methyl group is greater on the heavier lanthanide ions. The rates of extraction of the complexes were found to be unusually slow.     

A Review of New Developments in Amine Solvent Extraction Systems for Hydrometallurgy

Abstract

Amine extractants, regardless of structure, have been of limited utility for the extraction of complex metallic anions from alkaline solution due to an inability to increase the amine's basicity. This situation is contrasted to acid extractants in which case such control of extractant strength is possible. Recent studies with amine extractants have shown that the use of specific modifiers allows for the control of amine basicity over an appreciable pH range for certain anions. Particularly significant is the potential for the extraction of gold from alkaline cyanide solutions.     

Interphase distribution of weak acids in systems with binary extractants

General dependences of interphase distribution of weak acids in systems containing binary extractants were studied. Substantial differences in the extraction dependences of the composition of the organic and aqueous phases were shown for weak acids compared to systems that contain strong acids and binary extractants, as well as weak acids and neutral extractants. The influence of hydrogen bonding between two extracted compounds was observed when low-molecular monocarboxylic acids were extracted with agents based on quaternary ammonium bases and organic hydroxy acids.     

Lithium Perchlorate‐Catalyzed Boc Protection of Amines and Amine Derivatives

A new mild and chemoselective method for mono‐N‐protection of amines and amine derivatives as tert‐butoxycarbonyl derivatives is reported. The reaction proceeds with lithium perchlorate (20 mol %) and pyrocarbonates, and shows general applicability. The catalytic action of LiClO₄ is specific for the activation of Boc₂O, thus acid‐sensitive functionalities of the starting materials remain unchanged in the protection process. This procedure works well for sterically hindered primary amine as well as electron‐deficient primary arylamines, primary and secondary amino alcohols, α‐amino acid esters, hydroxylamines, hydrazines and sulfonamides.     

Solvent Extraction of Weak Acids in Binary Extractant Systems

The interphase distribution of weak acids in systems involving salts of quaternary ammonium bases with organic acids (binary extractants) has been analyzed. Significant differences in the extraction depending on the composition of the aqueous and organic phases for weak acids compared with that for strong acids in binary extractant systems have been shown. The difference in the extraction of weak acids with binary extractants compared with neutral extractants has been also revealed. The experimental data were interpreted by two variants of distribution processes, when two extracted species are formed (R₄NX and HA) and for the case of forming extracted species with strong H-bonds (R₄NX · HA). The least square regression method showed that the proposed mechanisms well describe the extraction of monocarboxylic acids with the binary extractant (the smallest sum of squares of relative deviations was 0.025) at their low initial concentrations (<0.05 mol · L^?1). It was shown that the most effective extraction of monocarboxylic acids takes place from acidic solutions (at pH < 2) that indicates the possibility of their effective stripping from organic solutions with water.     

Cyanuric chloride/dimethylformamide promoted one-pot conversion of primary alcohols into alkyl thiocyanates

A convenient and efficient procedure for one-pot conversion of alcohols into corresponding alkyl thiocyanates in the presence of cyanuric chloride/dimethylformamide mixed reagent is described. This approach is efficient and selective for primary alcohols especially substituted benzyl alcohols. This method can be easily applied for the facile conversion of primary alcohols into corresponding thiocyanates, but sterically hindered alcohols produced corresponding thiocyanates in very low yields.     

Metal-ligand cooperation by aromatization-dearomatization: a new paradigm in bond activation and "green" catalysis

In view of global concerns regarding the environment and sustainable energy resources, there is a strong need for the discovery of new, green catalytic reactions. For this purpose, fresh approaches to catalytic design are desirable. In recent years, complexes based on "cooperating" ligands have exhibited remarkable catalytic activity. These ligands cooperate with the metal center by undergoing reversible structural changes in the processes of substrate activation and product formation. We have discovered a new mode of metal-ligand cooperation, involving aromatization-dearomatization of ligands. Pincer-type ligands based on pyridine or acridine exhibit such cooperation, leading to unusual bond activation processes and to novel, environmentally benign catalysis. Bond activation takes place with no formal change in the metal oxidation state, and so far the activation of H-H, C-H (sp(2) and sp(3)), O-H, and N-H bonds has been demonstrated. Using this approach, we have demonstrated a unique water splitting process, which involves consecutive thermal liberation of H(2) and light-induced liberation of O(2), using no sacrificial reagents, promoted by a pyridine-based pincer ruthenium complex. An acridine pincer complex displays unique "long-range" metal-ligand cooperation in the activation of H(2) and in reaction with ammonia. In this Account, we begin by providing an overview of the metal-ligand cooperation based on aromatization-dearomatization processes. We then describe a range of novel catalytic reactions that we developed guided by these new modes of metal-ligand cooperation. These reactions include the following: (1) acceptorless dehydrogenation of secondary alcohols to ketones, (2) acceptorless dehydrogenative coupling of alcohols to esters, (3) acylation of secondary alcohols by esters with dihydrogen liberation, (4) direct coupling of alcohols and amines to form amides and polyamides with liberation of dihydrogen, (5) coupling of esters and amines to form amides with H(2) liberation, (6) selective synthesis of imines from alcohols and amines, (6) facile catalytic hydrogenolysis of esters to alcohols, (7) hydrogenolysis of amides to alcohols and amines, (8) hydrogenation of ketones to secondary alcohols under mild hydrogen pressures, (9) direct conversion of alcohols to acetals and dihydrogen, and (10) selective synthesis of primary amines directly from alcohols and ammonia. These reactions are efficient, proceed under neutral conditions, and produce no waste, the only byproduct being molecular hydrogen and/or water, providing a foundation for new, highly atom economical, green synthetic processes.     

Recovery of volatile organic compounds condensed out of waste gas-streams by selected high boiling point extractants

Recovery of volatile organic compounds (VOCs) condensed-out of waste gas streams has been carried out using re-cyclable high boiling point extractants (HBEs). HBEs were selected using an extractant screening program (ESP) which calculated multi-component liquid–liquid equilibria and then generated a ranking of extractants in terms of either mass partition coefficient or selectivity. Investigated was recovery from condensed VOC/water mixtures of firstly 1-butanol, a solvent used in protective coatings and secondly, alcohols and esters (fusel oils) carried over in the off-gas (CO₂) of alcoholic beverage fermentations. The latter are of particular interest, as they are a potential source of natural flavour and aroma compounds. With the most efficient HBE, VOC recovery in single-stage extraction was in excess of 90% for 1-butanol and 100% for the fusel oils.     

INTEKFACIAL ACTIVITY OF 2-HYDH0XY-5-ALKYLBEKZALDEHYDE OXIMES AHD MECHANISM AND KINETICS OF COPPER EXTRACTION

Different adsorption isotherms such as the Gibbs, Szyszkowski,Frumkln and Temkin and polynomial were found as fits well to experimental interfacial tension isotherms for 2-hydroxy-5-alkylbenzaldehyde oximes at octane/water and xylene/water interfaces. The values of surface excess computed according to them increase as the length of the alkyl chain length increases for xylene/water system. Different behaviour was found at octane/water interface.

The interfacial activity data were used to predict reaction orders against hydroxyoxime for different proposed mechanisms of copper extraction from acid sulphate solution.It was shown that an interfacial mechanism is very probable for compounds with long alkyl chains. For these compounds the extraction limiting step is the reaction between hydroxyoxime molecules present near the interface and the intermediate 1:1 complex.     

A State-of-the-Art Discussion on the Solvent Extraction Reagents Used for the Recovery of Copper from Dilute Sulfuric Acid Leach Solutions

Abstract

The recovery of copper from dilute sulfuric acid leach solutions has been a commercial reality since 1968 (1), and since then the technology has gained worldwide acceptance. Only one chelating functionality, the hydroxy oxime group, has been used commercially for this task. There are, however, two distinct classes of extractants based on the hydroxy oxime group: the salicylaldoximes, which are very strong copper extractants and the ketoximes, which are mo derate copper extractants. A third class of extractants combines a ketoxime with a salicylaldoxime in about a 1/1 mole ratio and results in some surprising advantages. This paper will discuss each reagent class, showing their advantages and disadvantages and will also introduce two new reagents, LIX¯ 84 and LIX 984, showing their behavior with respect to copper extraction, and discussing where they may be used to advantage.     

Ring-opening of 1,2-epoxyalkane with alcohols over H-ZSM-5 in liquid phase

H-ZSM-5 readily catalyzed the ring-opening of 1,2-epoxyalkane with alcohols to give alkoxy alcohols. The reaction proceeded accompanying the shape-selective properties of H-ZSM-5. The rate of the ring-opening was retarded by use of alcohols with larger numbers of carbon atoms such as hexanol. The selectivities for the substitution of nucleophile alcohols at the sterically more hindered position of the epoxide were improved to be almost higher than those under basic conditions.     

脱芳复合萃取剂的研究进展

复合萃取剂包括传统复合溶剂和新型复合溶剂。前者是有机溶剂与有机溶剂或无机盐的复配,后者则是不同种类的离子液体复配,它们不仅具有对芳烃的溶解性好、选择性高的优点,而且萃取后,萃余油的收率相对较高,已经成为继单一萃取剂用于油品（石脑油、重整汽油和模拟油等）脱芳烃研究之后又一新的研究热点。本文综述了国内外脱芳烃复合萃取剂的研究进展,重点介绍了两类复合萃取剂（萃取剂与醇类、胺类溶剂或无机盐复配和离子液体复配）在油品萃取脱芳烃中的应用;根据复合萃取剂中助萃取剂的种类不同,对用于萃取脱芳烃的复合萃取剂进行了分类总结;介绍了不同种类的萃取剂复配与不同种类的离子液体复配的研究进展;最后指出复合萃取剂在分离芳烃应用中具有选择性高、分配系数高、操作工艺简单有效且成本低廉等优点,是工业上萃取脱芳烃今后的发展趋势。