Method For Deoxygenation Research Articles

In-line deoxygenation for flow analysis with voltammetric detection

Voltammetric detection of metals in natural waters suffers from interference by dissolved oxygen. We describe here a deoxygenation method suitable for flow analysis with detection by cathodic stripping voltammetry (FIA-CSV). The apparatus is based on the permeation of oxygen through semi-permeable tubing (silicone, Poreflon and others) into an oxygen-free chamber. Two methods of oxygen removal are proposed: in the first oxygen is removed physically from the chamber by flushing with nitrogen at a rate of 50 ml min −1; in the second oxygen is removed chemically by filling the chamber with an aqueous solution of a reducing agent (Na 2SO 3 or other compounds). At a fixed sample flow rate of 1 ml min −1, the length of the tubing is the main parameter which affects the deoxygenation efficiency, as it determines the residence time of the sample. 98% oxygen removal is achieved using 3 m tubing (36 s residence time). A removal of 90% of oxygen (1 m tubing and 12 s residence time) is sufficient to obtain a background current similar to conventional (batch) voltammetric systems and reproducible metal (copper and cobalt) peak heights are obtained at low metal concentrations. This enables the determination of trace metals by flow analysis with voltammetric detection at concentration levels encountered in uncontaminated seawater.

Selective Deoxygenation of Heteroaromatic N-Oxides with Olefins Catalyzed by Ruthenium Porphyrin.

A new convenient method of deoxygenation of heteroaromatic N-oxides is described. Ruthenium prophyrin was used as a catalyst and this method expressed high yields for o-substituted pyridine N-oxides, quinoline N-oxide derivatives, acridine N-oxide, etc. under mild conditions. Moreover, nitro-, benzyloxy-, and ketone carbonyl groups, which can be affected by the usual deoxygenation methods such as catalytic hydrogenation or borane reduction, were retained.

Study of new facile deoxygenation methods in cyclodextrin induced room temperature phosphorescence

The traditional deoxygenation techniques in cyclodextrin induced room temperature phosphorescence (CD-RTP) include N 2(g) purging and Na 2SO 3 chemical deoxygenation. In this paper, we propose two new deoxygenation methods in which oxygen is eliminated by hydrogen gas and carbon dioxide produced by the reactions Zn(s)/HCl and Na 2CO 3/HCl in the measuring media. With 1-bromocyclohexane (BCH) as an external heavy atom perturber and phenanthrene as a model compound compared with traditional deoxygenation techniques, the two new methods: (1) are facile and do not need any complicated supplementary equipment; (2) are rapid, deoxygenation time needed is only 1–2 min; (3) have a wider acidic condition, which is a supplement of chemical deoxygenation by Na 2SO 3; (4) can maintain RTP signal without decay for 10 min; (5) have good analytical characteristics.

Cyclopentadienyl Titanium Derivatives in Organic Synthesis

<p> Among the numerous known compounds of titanium only relatively few have found wide applicability in organic synthesis. Prominent among these are some organotitanium compounds with one or two cyclopentadienyl substituents, which have found increasing use in recent years for a variety of synthetic transformations. Unlike many other transition metals, the use of titanium is not limited only to catalytic systems, but it is often used in stoichiometric quantities, due to the high abundance, low cost and low intrinsic toxicity of this element. </p> <p> This review focuses on the use of cyclopentadienyl titanium derivatives for the synthesis of titanium-free products. The reactions are classified according to the type of chemical transformation and illustrative examples are given for both stoichiometric and catalytic systems. Wherever applicable, asymmetric variants are also highlighted. </p> <p> After a general introduction on the most synthetically useful classes of cyclopentadienyl titanium compounds and their preparation, the review continues with the various types of reductions, including the hydrogenation, hydrosilylation and hydrometallation of unsaturated derivatives, and several methods for dehalogenation and deoxygenation. This is followed by a discussion of titanium-mediated oxidations, including alkene epoxidation and ketone hydroxylation. Several reactions in which the titanium compounds serve as Lewis acids are then discussed, including aldol reactions and cycloadditions. A number of methods involving the formation of C-C bonds, such as addition to carbonyls, nitriles and alkynes are then reviewed. This is followed by a discussion of methods involving the formation of C=C bonds from carbonyls, including pertinent synthetic applications. Several types of titanium-mediated cyclizations are then discussed with an emphasis on intramolecular reductive coupling reactions. Finally, an overview of several types of polymerization processes is given with an emphasis on Ziegler-Natta, ring-opening metathesis polymerizations, silane polymerizations and miscellaneous other polymerizations mediated by cyclopentadienyl titanium compounds. </p> <p> Overall, this review not only illustrates the high chemical diversity of titanium but it also demonstrates the unique reactivity exhibited by the cyclopentadienyl substituents.</p>

Chemistry of anti-o,o‘-Dibenzene

A new and efficient preparation of anti-o,o‘-dibenzene 1 has been achieved in three steps from cis-3,5-cyclohexadiene-1,2-diol 25. Utilizing a method for deoxygenation of 1,2-diols developed in our...

Synthesis of β-hydroxywybutines, the most probable alternatives for the hypermodified base of rat liver phenylalanine transfer ribonucleic acid

Deoxygenation of the 1,2-glycol (±)- 5 was achieved at the position adjacent to the heterocycle through the cyclic carbonate (±)- 14, providing the monohydroxy compound 6. This new method of regioselective deoxygenation was employed for the first synthesis of β-hydroxywybutines [[R-(R ∗,S ∗)]- and [S-(R ∗,R ∗)]-2] : oxidation of the methyl butenoate 7 with osmium tetroxide, followed by deoxygenation through the cyclic carbonates ( 19 and 20), afforded the two diastereomers of 2.

Nucleophilic Substitution Versus Radical Reaction for Carbohydrates Deoxygenation: Application at c-4 of Methyl-α-D-Glucopyranoside Derivatives

Abstract Two methods for deoxygenation at C-4 of methyl 2,3-di-O-benzyl-α-d-glucopyranoside are reported. The first one involves nucleophilic displacement of a secondary methane sulfonate by lithium triethylborohydride to afford methyl 2,3-di-O-benzyl-4-deoxy-α-d-xylo-hexopyranoside (5). Compound 5 was also obtained in similar yield (=60%) by radical deoxygenation with tri-n-butyltin hydride of a thiocarbonylated derivative.

Synthetic and oxidative studies on 8-(arylamino)-2'-deoxyguanosine and -guanosine derivatives.

Facile aerial oxidation is a general feature of guanine ribo- and 2'-deoxyribonucleosides that are substituted at the 8-position by an aminoaryl group. In previous work, it had been suggested that two of the major oxidation products are a pair of diastereomers having a spiro structure. These were presumed to be related by a chiral difference at the spiro carbon atom. The pattern of the oxidative process involves a contraction of the pyrimidine ring. It was thought to be analogous to that suggested by other investigators for the oxidation of uric acid, but for which no really definitive evidence had been presented. We have been able now to isolate in a crystalline state one of the diastereomers produced by the aerial oxidation of 8-phenylaminoguanosine under alkaline conditions. Analysis by X-ray diffraction has now confirmed the type of spiro structure promulgated previously. These findings also imply that spiro compounds are likely to be produced during the aerial oxidation of any 8-arylaminoguanine nucleoside or 2'-deoxynucleoside. In addition, this work adds considerable weight to the results of Poje and Sokolic-Maravic who proposed that a spiro intermediate is produced during the aerial oxidation of uric acid (12,13). However, they found this compound to be unstable to base, in contrast to the arylaminoguanine oxidation products. In the course of the above work we showed that the 8-arylamino derivatives of guanosine can be converted by the Barton deoxygenation method to the corresponding 2'-deoxyribonucleosides. This makes available a number of the latter compounds, which are not easily prepared by other methods.

Electroreductive Deoxygenation of Methanesulfonates of α-Hydroxy Esters via a Catalytic Selenation–Deselenation Sequence

Abstract The methanesulfonates of α-hydroxy esters were converted to the corresponding deoxygenated esters in 70–88% yields by the indirect electrolysis with diphenyl diselenide as a recyclable reagent in a divided cell. This deoxygenation method may involve the formation of α-phenylselenoester by replacement of α-methylsulfonyloxyl group with phenylselenide anion followed by capture of the α-phenylseleno group with phenylselenide anion.

ChemInform Abstract: A New Method for Deoxygenation of Organoheteroatom Oxides Using Sodium Hydride‐Promoted by Organolanthanide Complexes.

AbstractDeoxygenation of the amine oxide (I), phosphine oxide (III), diphenyl sulfoxide (V), azoxybenzene (VII), or pyridine N‐oxide (IX) is achieved by treatment with sodium hydride or lithium alanate in the presence of tricyclopentadienylsamarium.

Environmental factors affecting micellar stabilized room-temperature phosphorescence lifetimes

Triplet lifetimes of organic compounds at low temperature are well established compared to the room-temperature phosphorescence (RTP) lifetimes. The environmental factors affecting micellar-stabilized TRP lifetimes are investigated. It was found that solution deoxygenation method, temperature, and heavy atoms are the major contributor to the variations of observed RTP lifetimes. A kinetic decay model of triplet molecules is proposed to describe the effects of triplet quenchers and external heavy atoms on phosphorescence lifetimes in micellar solution

Facile synthesis of 3'-O-methylthymidine and 3'-deoxythymidine and related deoxygenated thymidine derivative: a new method for selective deoxygenation of secondary hydroxy groups

This paper deals with convenient syntheses of 3'-O-methylthymidine and 3'-deoxythymidine (I) which involve Ag 2 O-promoted methylation and Barton-Robins reductive deoxygenation, respectively. New methods for the regioselective 3'- and 5'-deoxygenation of thymidine have also been developed. Namely, compound I was synthesized by the 3',5'-O-diacylation of thymidine with phenyl chlorothionoformate (PTCF) followed by the selective 3'-reduction with tributyltin hydride and successive alkaline hydrolysis. 5'-Deoxythymidine was obtained by the 5'-selective acylation of thymidine with PTCF followed by reduction with tributyltin hydride

A New Method for Deoxygenation of Organoheteroatom Oxides Using Sodium Hydride Promoted by Organolanthanide Complexes

A new method for deoxygenation of organoheteroatom oxides using organolanthanide complex-sodium hydride systems in tetrahydrofuran is described.

Oxygenation and deoxygenation methods for producing sharp 90 K and 60 K superconducting transitions in single crystal YBa2Cu3O6+x

Several oxygenation methods were developed for converting 90 K YBa2Cu3O6+x single crystals to 60 K single crystals. The temperature dependence of the dc magnetic susceptibility shows sharp superconducting transitions in the 90 K crystals and in 60 K crystals produced by the best method, with optimized parameters. Meissner fractions in the 60 K crystals are consistently lower, indicating, we believe, more flux pinning in them. Optical microscopy indicates that untwinned regions in the 90 K crystals remain generally untwinned upon conversion to 60 K crystals. Colors produced by crossed polarizers enable us to identify the a axis and b axis directions in the 90 K and the 60 K materials. Each untwinned region has the a axis oriented in the same direction on the opposite (001) faces of the crystal.

Reductive deoxygenation of .ALPHA.,.BETA.-unsaturated ketones via cyanophosphates by lithium in liquid ammonia.

A new method for deoxygenation of α, β-unsaturated ketones via cyanophosphates by lithium metal in liquid ammonia is described.

A Novel Method for the Deoxygenation of Acetylated Sugars

On fait reagir ici le triphenylsilane dans des conditions radicalaires sur divers furanoses et pyranoses

Deoxygenation reactions of c 19-diterpenoid alkaloids

Efficient methods for deoxygenation of secondary and tertiary alcohols of some C 19-diterpenoid alkaloids are presented. Delphisine ( 12) was converted to 1-deoxydelphisine ( 19) via either 1,2-pyrodelphisine ( 17) or phenyl thionocarbonate 20. The following alkaloids were deoxygenated via their thiocarbonylimidazolyl derivatives: 14-acetyldelcosine ( 13) to 14-acetyl-l-deoxydelcosine ( 22); alkaline hydrolysis of 22 gave 1-deoxydelcosine ( 23); aconitine ( 24) to 3-deoxyaconitine ( 27); yunaconitine ( 25) to crassicauline A ( 28). Deoxygenation of 14-acetyldictyocarpine ( 30) via the chloro-derivative 31 gave 14-acetyl-10-deoxydictyocarpine ( 34). Reduction of 31 with LiAlH 4 gave the unusual elimination product 32. An improved partial synthesis of hypaconitine ( 35) from aconitine ( 24) is also presented.

ChemInform Abstract: Deoxygenation, Deaeration and Degassing: A Survey and Evaluation of Methods

Techniques for the removal of dissolved gases from liquids are reviewed and classified according to their working principles. Consideration of these working principles reveals some inherent limitations of certain techniques and it may be concluded that the different methods complement each other in a number of aspects. Proton spin-lattice relaxation time measurements and polarographic analyses are used for evaluation of different deoxygenation methods. It is concluded that for most purposes the different methods yield satisfactory results if applied properly and within the inherent limitations of the techniques. When the presence of oxygen is very critical and its concentration must be reduced to very small amounts, a combination of methods appears advisable.

Deoxygenation, Deaeration and Degassing: A Survey and Evaluation of Methods

AbstractTechniques for the removal of dissolved gases from liquids are reviewed and classified according to their working principles. Consideration of these working principles reveals some inherent limitations of certain techniques and it may be concluded that the different methods complement each other in a number of aspects. Proton spin‐lattice relaxation time measurements and polarographic analyses are used for evaluation of different deoxygenation methods. It is concluded that for most purposes the different methods yield satisfactory results if applied properly and within the inherent limitations of the techniques. When the presence of oxygen is very critical and its concentration must be reduced to very small amounts, a combination of methods appears advisable.

Deoxygenation reactions of C 19-diterpenoid alkaloids

Efficient methods for deoxygenation of secondary and tertiary alcohols of some C 19-diterpenoid alkaloids are presented. Thus deltaline ( 1) was converted to delpheline ( 2) or to 10-deoxydeltaline ( 7); deltamine ( 8) to 6-deoxydetamine ( 10); and delpheline ( 2) to 6-deoxydelpheline ( 12). An unusual elimination product 4 was formed when chloro-derivative 3 was reduced with LiAlH 4.