Determination of heavy metal concentration in feed and permeate streams of polymer enhanced ultrafiltration process

Polymer enhanced ultrafiltration (PEUF) is a newly developed method for the removal of heavy metals from aqueous solutions. This method was applied for the removal of mercury and cadmium with the presence of polyethyleneimine (PEI) as a water soluble polymer. After ultrafiltration experiments for metal–polymer mixtures, two separate streams, namely, retentate and permeate, former of which contains mainly metal–polymer complex and free polymer molecules while latter of which mainly contains free metal ions, were obtained. At the end of PEUF experiments, performance of operation was determined by concentration analyses which was achieved by atomic absorption spectroscopy (AAS) applied in a different way for permeate and retentate streams considering the effect of presence of polymer. For mercury analysis, cold vapor AAS was applied. It was observed that the presence of PEI did not affect the atomic absorption signal when 10% HCl was added to the sample solutions. For calcium and cadmium, flame AAS was used. It was observed that change in PEI concentration results in change in measured concentration of calcium and cadmium. Therefore, two new approaches were developed for accurate measurement of concentrations of calcium and cadmium. It was also observed that presence of other metals did not affect the accuracy of the measurement of a particular metal in the concentration range studied.     

Modern Analysis

The important advances being made in modern analytical methods are indicative of the fundamental changes that are occuring in the theory and practice of “analytical chemistry”. “Information optimization” demands a new approach in teaching and research, and calls for the intergration of chemistry with other scientific and technical disciplines.     

Catalyzed Addition of Aldehydes to Activated Double Bonds—A New Synthetic Approach

In the presence of cyanide ions as catalyst, aromatic and heterocyclic aldehydes can be smoothly added to α,β-unsaturated ketones, esters, and nitriles in aprotic solvents to form γ-diketones, 4-oxo carboxylic esters, and 4-oxo nitriles. Thiazolium salts in the presence of bases are also suitable catalysts; they permit not only addition of aromatic and heterocyclic aldehydes but also the addition of aliphatic aldehydes.     

The Synthesis of Unusual Organic Molecules Using Cyclic Peroxides. New synthetic methods (3)

The photodecarboxylation of malonyl peroxides into α-lactones^[1] and the thermal conversion of the 1,4-endo-peroxide 4,5-epoxy-3,6-epidioxy-1-cyclohexene into the novel benzene trioxide^[2] are two recent examples of the potential of cyclic peroxides in the synthesis of unusual organic molecules. The former transformation entails a fragmentation, the latter a rearrangement process. Most reported examples fall into one of these two gross reaction types. Of the numerous examples that have been reported in the literature during the last two decades, only those shall be focused on that lead to unusual compounds or constitute efficient syntheses of known compounds, in order to stress the convenience of cyclic peroxides in the synthesis of organic compounds.     

Intramolecular,Stoichiometric (Li,Mg, Zn) and Catalytic (Ni,Pd, Pt) Metallo-Ene Reactions in Organic Synthesis [New Synthetic Methods (75)]

Metallo-ene reactions, hardly recognized until very recently, have experienced a breathtaking development when applied in an intramolecular sense. Efficient regio- and stereoselective magnesium-ene cyclizations have served as a cornerstone for numerous syntheses of structurally diverse natural products (e.g., sesquiterpenes of marine or plant origin, alkaloids, fragrances, insect defense compounds, and a fungitoxin). A brilliant example is the synthesis of the elusive odorant (+)-khusimone which outshines 20 years of work in the field of tricyclovetivane synthesis. Palladium-, platinum-, and nickel-catalyzed versions of the metallo-ene reaction are in a comparatively early stage of exploration, but, nevertheless, reveal intriguing potential. Hence an almost 100% stereospecific C? O→C? ;Pd-→ C? C chirality transfer permits simple and selective, cis- or trans-annelation processes. The mild cyclization conditions are compatible with various functional groups, such as nitrogen moieties, which offer interesting perspectives for the preparation of heterocycles (e.g., alkaloids) difficult to obtain by other methods. Carbon monoxide insertion reactions of the cyclized σ-metal intermediates were shown to afford annelated cyclopentanones and cyclopentenones with concomitant stereocontrolled formation of four carbon–carbon bonds. These and other observations, highlighted in this article, provide a platform for further extensions and applications of this powerful method in organic synthesis.     

The Formation of C?C Bonds with the Aid of α-Halogeno Ethers,Sulfides, and Amines

α-Halogeno ethers, sulfides, and amines are reactive compounds which can be used for the formation of new C? C bonds, either as nucleophilic or as electrophilic reagents, or by α-elimination. The use of these compounds in the synthesis of many classes of organic compounds is reviewed.     

Fluorescence monitoring of ultrasound degradation processes

Ultrasound-based water treatment is often applied for degradation of stable organic pollutants, such as polycyclic aromatic hydrocarbons and halogenated compounds. Monitoring the degradation process, during the application of ultrasound radiation, is of considerable economical interest. In this work, the possibility of performing on-line spectral analysis during sonication was examined and it was found that direct absorption or fluorescence readings are misleading. Optical monitoring is strongly affected by the absorption and scattering of light by cavitation micro-bubbles and ultrasound induced particulates. A model was developed to account for these effects and to allow for on-line fluorescence analysis. The model takes into account the absorption and scattering coefficients of the micro-bubbles and particulates, as well as their time dependent concentration. The model parameters are found from independent measurements where the pollutants are added to already sonicated pure water. Then, the model is tested for predicting the actual fluorescence behavior during the sonication process. It has been shown that the model allows for recovery of the true degradation data, as obtained by off-line HPLC measurements.     

Phosphaalkynes—Syntheses,Reactions, Coordination Behavior [New Synthetic Methods (73)]

Organophosphorus compounds have been applied in two ways in chemical synthesis. They can either be used as a reagent in a step of the synthesis (for example, in the Wittig reaction) or they can be incorporated directly into the target molecule. This second application, in particular, has expanded greatly in the last few years with the preparation of low-coordination phosphorus compounds. These include the phosphaalkynes, which are of great interest to organic and inorganic chemists. Phosphaalkynes have been employed in the synthesis of heterocyclic compounds, phosphaarenes and their valence isomers, and polycyclic compounds. Further applications have been the use of phosphaalkynes as new ligand systems in complex chemistry and their cyclooligomerization with organometallic reagents. While the chemical properties of phosphaalkynes have little in common with those of nitriles, they are in many ways very similar to those of the isoelectronic acetylenes.     

Prescriptions and Ingredients for Controlled CC Bond Formation with Organometallic Reagents. New synthetic methods (5)

Merits and drawbacks of known carbon-carbon linking procedures are outlined. Two novel methods are discussed in some detail: the copper-catalyzed alkylation of Grignard reagents and reactions with allylpotassium compounds. Both methods provide a very efficient access to saturated, unsaturated, as well as functionally substituted hydrocarbons and moreover permit an astonishing degree of regio- and stereoselective control of olefin synthesis.     

合成云母蒙脱石及其交联物在乙醇氨化反应中的催化行为

用水热法合成了云母蒙脱石,并与羟基铝齐聚物交联,DTA和IR结果表明,由于柱的引进,高温焙烧时层内八面体上羟基脱除变得较为容易。由NH_3-TPD和吡啶吸附测得的表面酸性表明Al-CLS具有较SMM更多的弱酸和强酸中心。催化剂上弱酸中心有利于醇的脱水,而吸附在强酸中心上的NH_3有利于醇的胺化。