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Heterogeneous Conditions (heterogeneous + condition)
Selected AbstractsPreparation of 2H -1,4-Benzoxazin-2-one Derivatives under Heterogeneous Conditions via Domino ProcessADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2009Roberto Ballini Abstract Carbonate on polymer is a valuable solid supported reagent (SSR) to promote, under eco-friendly conditions, the preparation of 2H -1,4-benzoxazin-2-one derivatives starting from ,-nitroacrylates and aminophenols via a domino process. [source] ChemInform Abstract: Metal-Free Oxidation of Urazole and 1,4-Dihydropyridine Derivatives under Mild and Heterogeneous Conditions by Nitro Urea, Derived from Urea Nitrate, and Silica Sulfuric Acid.CHEMINFORM, Issue 40 2010Arash Ghorbani-Choghamarani Abstract Advantages of the title procedure are the non-toxic and mild conditions and the easy and clean work-up of the products. [source] ChemInform Abstract: An Efficient and New Method on the Oxidative Coupling of Thiols under Mild and Heterogeneous Conditions.CHEMINFORM, Issue 45 2009Arash Ghorbani-Choghamarani Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Oxidation of Hantzsch 1,4-Dihydropyridines Using Supported Nitric Acid on Silica Gel and Poly Vinyl Pyrrolidone (PVP) under Mild and Heterogeneous Conditions.CHEMINFORM, Issue 37 2009Arash Ghorbani-Choghamarani Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Molybdatophosphoric Acid/NaNO2/Wet SiO2 as an Efficient System for the Aromatization of 1,2-Dihydroquinolines under Mild and Heterogeneous Conditions.CHEMINFORM, Issue 41 2007Khodabakhsh Niknam Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Molybdatophosphoric Acid/NaNO2/Wet SiO2 as an Efficient System for Oxidation of 1,4-Dihydropyridines under Mild and Heterogeneous Conditions.CHEMINFORM, Issue 30 2005Khodabakhsh Niknam Abstract For Abstract see ChemInform Abstract in Full Text. [source] Efficient and Selective Oxidation of Thiols to Disulfides by 1,4-Diazabicyclo[2.2.2]octane-di-N-oxide-diperhydrate under Neutral and Heterogeneous Conditions.CHEMINFORM, Issue 4 2005Peyman Salehi No abstract is available for this article. [source] Towards a Facile Synthesis of Triarylethanones: Palladium-Catalyzed Arylation of Ketone Enolates under Homogeneous and Heterogeneous Conditions.CHEMINFORM, Issue 28 2004Fatima Churruca Abstract For Abstract see ChemInform Abstract in Full Text. [source] Silica Sulfuric Acid: An Efficient Catalyst for the Direct Conversion of Primary and Secondary Trimethylsilyl Ethers to Their Corresponding Ethers under Mild and Heterogeneous Conditions.CHEMINFORM, Issue 6 2004Mohammad Ali Zolfigol Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Chemoselective N-Nitrosation of Secondary Amines under Mild and Heterogeneous Conditions.CHEMINFORM, Issue 31 2001Mohammad Ali Zolfigol Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Oxidation of Urazoles to Their Corresponding Triazolinediones under Mild and Heterogeneous ConditionsCHEMINFORM, Issue 3 2001Mohammad Ali Zolfigol Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Effects of search experience in a resource-heterogeneous environment on the oviposition decisions of the seed beetle, Callosobruchus maculatus (F.)ECOLOGICAL ENTOMOLOGY, Issue 4 2006ROU-LING YANG Abstract 1.,This study investigates how female seed beetles, Callosobruchus maculatus, distribute their eggs on various-sized seeds when the size of seed was varied during the egg-laying period. 2.,Beetles were allowed to lay eggs on one of three arrays of 64 adzuki beans (Vigna angularis). Each array contained four size classes of seed, ranging from small (5.0,5.5 mm diameter) to large (6.5,7.0 mm), but differed in how they were distributed within the environment. In the most heterogeneous condition (the 64-patch design), the four sizes were interspersed, while in the least heterogeneous condition (the four-patch design) they were grouped into four separate blocks. Thus, a beetle exploring the 64-patch design would frequently encounter all four seed sizes, whereas a beetle exploring the four-patch design would only rarely encounter a change in bean size. 3.,Beetles experiencing greater seed size heterogeneity were more likely to lay eggs on larger seeds, whereas those in the blocked condition were more likely to oviposit on small seeds. Beetle responses to seed size heterogeneity suggest that the degree of preference for large seeds depends on a female's recent experience. 4.,Female beetles exhibited size discrimination throughout their egg-laying process; however, there was a trade-off between seed size and egg discrimination (i.e. avoiding those seeds already containing developing eggs) in response to the change in fitness gained from either laying on larger seeds or lower egg-load seeds during the egg-laying process. 5.,Our model provides the first evidence that evolving seed size discrimination ability is adaptive for the seed beetle with egg-discrimination ability. [source] A multicenter study on the prevalence and spectrum of mutations in the otoferlin gene (OTOF) in subjects with nonsyndromic hearing impairment and auditory neuropathy,HUMAN MUTATION, Issue 6 2008Montserrat Rodríguez-Ballesteros Abstract Autosomal recessive nonsyndromic hearing impairment (NSHI) is a heterogeneous condition, for which 53 genetic loci have been reported, and 29 genes have been identified to date. One of these, OTOF, encodes otoferlin, a membrane-anchored calcium-binding protein that plays a role in the exocytosis of synaptic vesicles at the auditory inner hair cell ribbon synapse. We have investigated the prevalence and spectrum of deafness-causing mutations in the OTOF gene. Cohorts of 708 Spanish, 83 Colombian, and 30 Argentinean unrelated subjects with autosomal recessive NSHI were screened for the common p.Gln829X mutation. In compound heterozygotes, the second mutant allele was identified by DNA sequencing. In total, 23 Spanish, two Colombian and two Argentinean subjects were shown to carry two mutant alleles of OTOF. Of these, one Colombian and 13 Spanish subjects presented with auditory neuropathy. In addition, a cohort of 20 unrelated subjects with a diagnosis of auditory neuropathy, from several countries, was screened for mutations in OTOF by DNA sequencing. A total of 11 of these subjects were shown to carry two mutant alleles of OTOF. In total, 18 pathogenic and four neutral novel alleles of the OTOF gene were identified. Haplotype analysis for markers close to OTOF suggests a common founder for the novel c.2905_2923delinsCTCCGAGCGCA mutation, frequently found in Argentina. Our results confirm that mutation of the OTOF gene correlates with a phenotype of prelingual, profound NSHI, and indicate that OTOF mutations are a major cause of inherited auditory neuropathy. Hum Mutat 29(6), 823,831, 2008. © 2008 Wiley-Liss, Inc. [source] Identification of Susceptibility Loci for Alcohol-Related Traits in the Irish Affected Sib Pair Study of Alcohol DependenceALCOHOLISM, Issue 11 2006Po-Hsiu Kuo Background: Alcoholism is a phenotypically and probably genetically heterogeneous condition. Thus, one strategy for finding genes influencing liability to alcoholism is to study the components of alcoholism, which may be more directly related to the underlying pathophysiology than is clinical diagnosis. The goal of this study was to identify genomic regions containing susceptibility loci for alcohol-related traits. Methods: A 4-cM dense whole-genome linkage study was conducted in the Irish Affected Sib Pair Study of Alcohol Dependence. Probands, affected siblings, and parents were evaluated by structured interview. Variance component linkage analysis was applied to data from 485 families for 5 measures: initial sensitivity and tolerance (based on scales from the self-report of the effects of ethanol; maximum drinks within 24 hours, an empirically derived factor score based on withdrawal symptoms, and age at onset of alcohol dependence. Results: Evidence for linkage (p<0.005) was found on 9 chromosomes. For age at onset, 2 regions were found on chromosome 9 (highest Lod=2.3, p=0.0005). For initial level of response to alcohol, suggestive regions were on chromosomes 1 and 11 (highest Lod=2.9, p=0.0001 on chromosome 11), while those for tolerance signals were on chromosomes 1, 6, and 22. Maximum drinking was associated with regions on chromosomes 12 and 18. For withdrawal symptoms, the highest peak was on chromosome 2 (Lod=2.2, p=0.0007). Conclusions: Using quantitative measures of components of alcohol dependence, we identified several regions of the genome that may contain susceptibility loci for specific alcohol-related traits and merit additional study. [source] Fibril protein fragmentation pattern in systemic AL-amyloidosisTHE JOURNAL OF PATHOLOGY, Issue 4 2009Stina Enqvist Abstract Immunoglobulin light chain (AL)-amyloidosis was one of the first types of amyloidosis discovered and still little is known about its pathogenic mechanisms. One major obstacle is the very heterogeneous condition; in fact, every patient could be considered to have their own disease since symptoms and outcome vary enormously. The reason for this is not known but intrinsic factors of the immunoglobulin light chain (LC) and the fact that every LC is unique seem to be important. Post-translational modifications such as glycosylation and proteolysis are most certainly involved. By using western blotting, we studied in detail the proteolytic pattern in six patients with AL-amyloidosis of kappa type with the aid of three peptide antisera against two domains in the constant segment and one conserved domain in framework 3 of the variable region. Materials from one to five organs were analysed. The result clearly demonstrates that the fragmentation pattern was similar in amyloid of different organs in one patient but differed greatly between patients. Full-length, N-, and C-terminal fragments were detected with the three antisera. The results strongly support the hypothesis that proteolytic cleavage occurs after fibril formation. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. [source] Goldenhar syndrome associated with prenatal maternal Fluoxetine ingestion: Cause or coincidence?BIRTH DEFECTS RESEARCH, Issue 7 2010Chantal Farra Abstract Goldenhar syndrome, also known as oculo-auriculo-vertebral spectrum, is a complex, heterogeneous condition characterized by abnormal prenatal development of facial structures. We present the occurrence of Goldenhar syndrome in an infant born to a woman with a history of prenatal Fluoxetine ingestion throughout her pregnancy. Because this is the first reported case associating maternal Fluoxetine intake with fetal craniofacial malformations, a potential mechanism of injury is discussed. The propositus, a male born from nonconsanguinous parents, had facial asymmetry with right microtia and mandibular hypoplasia; he also had bilateral hypoplastic macula, scoliotic deformity of the thoracic spine, and ventricular septal defect. The mother was under treatment with Fluoxetine 20 mg/day prior to conception and maintained the same dosage throughout her pregnancy. The drug is a selective serotonin re-uptake inhibitor, the most widely prescribed for the treatment of depression. The occurrence of developmental aberrations may be caused by a profound serotonin receptor suppressive state in utero leading to aberrant clinical manifestations of the first and second branchial arches. Despite the very many limitations of case reporting of teratogenic events, it remains an important source of information on which more advanced research is based. Birth Defects Research (Part A) 2010. © 2010 Wiley-Liss, Inc. [source] Developmental Coordination Disorder and Joint Hypermobility Syndrome , overlapping disorders?CHILD: CARE, HEALTH AND DEVELOPMENT, Issue 5 2007Implications for research, clinical practice Abstract Background, Joint Hypermobility Syndrome (JHS) and Developmental Coordination Disorder (DCD) are two childhood disorders usually identified separately. DCD is a heterogeneous condition with little known of the underlying aetiology of the disorder. This paper examines the potential overlap between DCD and JHS and examines children with DCD for symptoms which may be consistent with a diagnosis of JHS. Implications for research and clinical practice are considered. Methods, A questionnaire covering a range of symptoms consistent with a diagnosis of JHS and related autonomic nervous systemic symptoms was completed by parents from 27 children with DCD and compared with responses from parents of 27 typically developing children. Results, Children with DCD showed a significant difference from the group of typically developing children on questions regarding hypermobility, pain and autonomic nervous system symptoms, typifying JHS. Conclusions, This study has shown a similarity in symptoms seen in some DCD children to those with a diagnosis of JHS. In addition, children are also presenting with multi-system symptomatology including those involving the autonomic nervous system. This study reinforces other recent work showing the reverse pattern of JHS children showing similar functional similarities to DCD children. This has implications for future research in DCD in order to understand the underlying aetiology of this complex disorder. In addition, it is important for clinicians to be aware of these findings in order to provide appropriate and tailored support and treatment for children presenting with differing patterns of co-ordination difficulties. Children with DCD and JHS may require appropriate podiatry as well as recognition of their symptoms of pain and how this may affect participation in physical activity. [source] Cytokine and anti-cytokine therapy in asthma: ready for the clinic?CLINICAL & EXPERIMENTAL IMMUNOLOGY, Issue 1 2009D. Desai Summary Asthma is a common disease with an increasing prevalence worldwide. Up to 10% of these patients have asthma that is refractory to current therapy. This group have a disproportionate use of health care resources attributed to asthma, have significant morbidity and mortality and therefore represent an unmet clinical need. Asthma is a complex heterogeneous condition that is characterized by typical symptoms and disordered airway physiology set against a background of airway inflammation and remodelling. The inflammatory process underlying asthma is co-ordinated by a cytokine network. Modulating this network with biological therapy presents a new paradigm for asthma treatment. Clinical trials undertaken to date have underscored the complexity of the inflammatory profile and its relationship to the clinical features of the disease and have raised the importance of safety considerations related to these novel therapies. T helper type 2 cytokine blockade remains the most promising strategy, with anti-interleukin-5 reducing asthma exacerbations. Although anti-cytokine therapy is not yet ready for the clinic, the long-awaited possibility of new treatments for severe asthma is moving ever closer. [source] Efficient Heterogeneous Asymmetric Catalysis of the Mukaiyama Aldol Reaction by Silica- and Ionic Liquid-Supported Lewis Acid Copper(II) Complexes of Bis(oxazolines)ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2 2008S. Doherty Abstract Lewis acid complexes based on copper(II) and an imidazolium-tagged bis(oxazoline) have been used to catalyse the asymmetric Mukaiyama aldol reaction between methyl pyruvate and 1-methoxy-1-trimethylsilyloxypropene under homogeneous and heterogeneous conditions. Although the ees obtained in ionic liquid were similar to those found in dichloromethane, there was a significant rate enhancement in the ionic liquid with reactions typically reaching completion within 2,min compared with only 55,% conversion after 60,min in dichloromethane. However, this rate enhancement was offset by lower chemoselectivity in ionic liquids due to the formation of 3-hydroxy-1,3-diphenylbutan-1-one as a by-product. Supporting the catalyst on silica or an imidazolium-modified silica using the ionic liquid or in an ionic liquid-diethyl ether system completely suppressed the formation of this by-product without reducing the enantioselectivity. Although the heterogeneous systems were characterised by a drop in catalytic activity the system could be recycled up to five times without any loss in conversion or ee. [source] Novel gel-entrapped base catalysts for the Claisen,Schmidt reactionJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2004Sachin S Chaphekar Abstract Novel gel-entrapped base catalysts (GEBCs) were prepared by entrapping aqueous solutions of bases in a gel matrix of agar agar. The bases used were NaOH, KOH, morpholine and piperidine. Ternary phase diagrams were constructed for the water,base,agar agar system to identify the various phases and especially the solid phase, useful as a solid base catalyst. The 10% NaOH solid gel was used to effect the Claisen,Schmidt reaction between benzaldehydes and acetophenones in ethanol under heterogeneous conditions to obtain 70,100% yield of the products. The solid GEBCs obtained using other bases were also used for the same reaction; however, the yields were lower. The catalyst needed no activation prior to use and could be recycled. Copyright © 2004 Society of Chemical Industry [source] Cyclohexene hydrogenation using Group VIII metal complexes as catalysts in heterogeneous and homogeneous conditionsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2001E Quiroga Abstract The stability and catalytic behaviour of a ruthenium complex with chloride and tridecylamine as ligands were studied. The hydrogenation of cyclohexene carried out in mild conditions, both in homogeneous and heterogeneous conditions, was used as a test reaction. FTIR and XPS results show that the active species is the complex itself, which is stable under the reaction conditions. XPS determination shows that the ruthenium complex is tetra-coordinated, suggesting that its formula is [RuCl2(NH2(CH2)12CH3)2]. This ruthenium complex supported on ,-Al2O3 is more active and sulfur-resistant than the same complex unsupported and even more than a nickel complex with the above mentioned ligands. The Ru complex, supported or not, is also more active and sulfur-resistant than a conventional Ru/,-Al2O3 catalyst evaluated in the same operational conditions. © 2001 Society of Chemical Industry [source] A stereoselective three-component reaction: One-pot synthesis of cis -isoquinolonic acids catalyzed by silica sulfuric acid under mild and heterogeneous conditionsJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2006Javad Azizian A mild and stereoselective three-component one-step synthesis of cis -isoquinolonic acid using silica sulfuric acid as a heterogeneous catalyst from an aldehyde, amine and homophthalic anhydride in acetonitrile is described. This new method produces pure products in high yields (81-91%). [source] Selectivity of nitro versus fluoro substitution in arenes in their reactions with charged O - and S -nucleophilesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2007Irina A. Khalfina Abstract The relative mobility of nitro and fluoro substituents in 1,3-dinitro- and 1-fluoro-3-nitrobenzenes, 3,5-dinitro- and 3-fluoro-5-nitrobenzotrifluorides under the action of the nucleophiles (2ArYH)·K2CO3 and ArY,K+ in solution and the nucleophiles ArYH·K2CO3 (Y,=,O, S) under heterogeneous conditions was studied by a competitive method in DMF at 40,140,°C. The unique dependences of ,,H, on ,,S, and ,,H, on ,,G, were determined for all the substrates and nucleophiles. The dependence of the mechanistic pathway on the nucleophile is discussed. Two results are relevant to the reactions studied: (i) substituent effects in the nucleophiles (2ArYH)·K2CO3 and ArYH·K2CO3 on the activation entropies suggest that the entropy favours the displacement of nitro group; (ii) the negative signs of ,,H, and ,,S, for the reactions of the nucleophiles ArY,K+ indicate that the enthalpy determines the displacement of nitro group. It is concluded that the selectivity of the reactions with aryloxide and arylthioxide ions cannot be explained by the hard,soft acid,base principle only. Copyright © 2007 John Wiley & Sons, Ltd. [source] Cyclometalated 2-phenylpyridine complex [RuII(o -C6H4 -py)(MeCN)4]PF6 as a tunable catalyst for living radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2008F. Diaz Camacho Abstract The cyclometalated complex [RuII(o -C6H4 -py)(MeCN)4]PF6 (1) with a ,-RuC bond and four substitutionally labile acetonitrile ligands mediates radical polymerization of different vinyl monomers, viz. n -butyl acrylate, methyl methacrylate, and styrene, initiated by three alkyl bromides: ethyl 2-bromoisobutyrate, methyl 2-bromopropionate, and 1-phenylethyl bromide. The polymerization requires the presence of Al(OiPr)3 and occurs uncontrollably as a conventional radical process. The variation of the molar ratio of the components of the reaction mixture, such as initiator, Al(OiPr)3 and catalyst, affected the polymerization rates and the molecular weights but did not improve the control. A certain level of control has been achieved by adding 0.5 eq of SnCl2 as a reducing agent. Tin(II) chloride decreased the rate of polymerization and simultaneously the molecular weights became conversion-dependent and the polydispersities were also narrowed. Remarkably, the level of control was radically improved in the presence of excess of the poorly soluble catalyst (1), when the added amount of (1) was not soluble any more, i.e., under heterogeneous conditions, the system became adjustable and the living polymerization of all three monomers was finally achieved. Possible mechanisms of the (1)-catalyzed polymerization are discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4193,4204, 2008 [source] Two cases of subungual melanoma in situTHE JOURNAL OF DERMATOLOGY, Issue 11 2008Sumihisa IMAKADO ABSTRACT Melanonychia, which is characterized by brown or black pigmentation within the nail plate, includes heterogeneous conditions such as pigmented nevus, subungual melanoma and lentigo. We treated two cases of subungual melanoma in situ. One case was a 58-year-old woman who suffered from a malignant melanoma in situ of the left third fingernail, who had also suffered from melanonychia of the fingers for more than 30 years. She had a past history of carcinoma of the uterine cervix. The other patient was a 42-year-old man, who suffered from a malignant melanoma in situ of the right fifth fingernail. He had a past history of carcinoma of the stomach for which he had undergone surgery 2 years earlier. Both cases were accompanied by Hutchinson's sign on the fingertip skin, and the presence of this sign led to the correct diagnosis of subungual melanoma in situ. Judging from previously reported cases, it is unlikely that patients with malignant melanoma have an increased risk of carcinoma of the uterine cervix or of the stomach. [source] 2242: Update on ophthalmic molecular geneticsACTA OPHTHALMOLOGICA, Issue 2010E DE BAERE Purpose To provide an overview of the recent technological advances in human molecular genetics that can be applied in ophthalmic genetics. Methods Since the finalization of the Human Genome Project many novel genomic technologies emerged that led to significant advances in gene identification and genetic testing of hereditary eye disorders: (1) genomewide copy number screening (array CGH); (2) genomewide SNP genotyping; (3) next-generation sequencing. Results (1) Microarray comparative genomic hybridisation or array CGH allows genomewide discovery of submicroscopic deletions and duplications in a single experiment. This technique is applied in routine molecular cytogenetic testing. Using array CGH a causal genomic defect can be found in at least 10% of all cases with mental retardation and/or multiple congenital anomalies. In ophthalmic genetics array CGH is mainly useful in the context of developmental eye disorders, with chorioretinal coloboma and anterior segment dysgenesis as an example. (2) Genomewide chip-based SNP genotyping can be used for homozygosity mapping in inbred and outbred pedigrees. Recent successes in gene identification using this approach are illustrated. (3) Next-generation sequencing or NGS. The application of this technology in gene identification and genetic testing of genetically heterogeneous conditions (with LCA as a paradigm) is discussed. Conclusion The rapid progress of genomic technologies such as array CGH, SNP chip analysis and next-generation sequencing lead to a boost in gene identification and genetic testing of both developmental and retinal eye disease. [source] Use of ,,,-Unsaturated ,-Ketocarbonyls for a Totally Regioselective Oxidative Multicomponent Synthesis of Polyfunctionalized PyridinesCHEMISTRY - A EUROPEAN JOURNAL, Issue 47 2009Christophe Allais Versatile partners: ,-Ketocarbonyls have been shown for the first time to be versatile partners in a Michael addition promoted oxidative domino three-component reaction under heterogeneous conditions. This multicomponent reaction sequence led to the development of a general synthesis of highly functionalized pyridines (see scheme), allowing selective and simultaneous incorporation of a substituent at the 4-position and a synthetically useful functionality at the strategic 2-position. [source] Heterogeneous Gold Catalysts for Efficient Access to Functionalized LactonesCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2008Florentina Nea Abstract A novel class of heterogeneous gold catalysts supported on zeolite beta-NH4+ was prepared by the deposition,precipitation method. This new class of catalyst showed interesting catalytic activities for the intramolecular cycloisomerization of ,-acetylenic carboxylic acids leading to functionalized ,-alkylidene ,-butyrolactones. Analysis of the supported gold species with in situ X-ray photoelectron spectroscopy (in situ XPS) suggests that cationic Au (possibly AuIII) can play an important role in such reactions. The high discrepancy in catalyst stability in favor of the Au supported on the zeolite system over bulk Au2O3 is explained by 1),the size of the particles and 2),the reversibility of the redox deactivating process (AuIII,AuI) in the presence of oxygen for the supported system. The efficiency of this system allowed reaction under mild heterogeneous conditions. The potential for catalyst recycling was also highlighted. [source] | |||||||||||||||||||