- Generation of VBr? VBi? VO?? defect clusters for 1O2 production for molecular oxygen activation in photocatalysis
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Defect engineering on a semiconductor surface can provide coordinatively unsaturated sites for molecular oxygen activation in photocatalysis. In this work, we demonstrated that the vacancy type was key to modulate the molecular oxygen activation process on BiOBr nanosheets. By regulating the reaction time, an oxygen vacancy (VO??), a double atom defect cluster (VBi? VO??) and triple atom clusters (VBi? VO?? VBi? and VBr? VBi? VO??) were accordingly generated on the surface, subsurface and bulk of BiOBr. More importantly, the newly-discovered VBr? VBi? VO?? defect cluster was highly related to the singlet oxygen (1O2) production ability of BiOBr. Meanwhile, the excellent photocatalytic selective oxidation reactions were successfully realized over BiOBr with the VBr? VBi? VO?? defect cluster. In addition, time-dependent defect cluster generation and the associated molecular oxygen activation were discussed.
- Ding, Jie,Dai, Zan,Tian, Fan,Zhou, Bo,Zhao, Bin,Zhao, Huiping,Chen, Zhiquan,Liu, Yunling,Chen, Rong
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supporting information
p. 23453 - 23459
(2017/11/30)
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- Catalytic synthesis of dialkyl sulfides from dialkyl disulfides
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Dialkyl disulfides R2S2 where R = Me, Et, or Pr, both as individual compounds and as their mixtures, isolated from petroleum products can turn into alkanethiols and dialkyl sulfides under the action of catalysts having strong acid sites and medium-strength basic sites on their surface. In a helium atmosphere, the main conversion products are alkanethiols, while dialkyl sulfides form in low yield at a selectivity of no higher than 20%. A much higher dialkyl sulfide selectivity is attained in the reaction involving methanol. The most efficient catalyst for this reaction is alumina, with which the dialkyl sulfide selectivity is up to 99%.
- Mashkina,Khairulina
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p. 402 - 408
(2017/08/08)
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- GENERATION OF CHALCOGENIDE ANIONS IN HYDRAZINE HYDRATE MEDIUM
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Aromatic thiols and dichalcogenides in hydrazine hydrate are effective generators of chalcogenide ions that will react with organyl halides to form diorganyl chalcogenides.Alkanethiols and dialkyl dichalcogenides are less effective in reaction with organyl chalcogenides.
- Turchaninova, L. P.,Korchevin, N. A.,Deryagina, E. N.,Trofimov, B. A.,Voronkov, M. G.
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p. 125 - 126
(2007/10/02)
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- Elimination reactions: Experimental confirmation of the predicted elimination of (β-cyanoethyl)sulfonium ions through a concerted, E2 mechanism
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Extrapolation of the lifetimes of carbanion intermediates formed in the elimination reactions of a series of β-cyanoethyl thioethers with different leaving groups (J. Am. Chem. Soc. 1988, 110, 5087-5095) predicts that the carbanions will not have a significant lifetime for pKlg a 2SO/H2O, 25.0 °C). Values of βlg obtained from Br?nsted-type plots of log kB against the estimated pKa values of the leaving groups, decrease from 0.39 to 0.24 with increasing pKa of the base catalyst. The changes in β and βlg are described by the interaction coefficient pxy=d?βlg/?pK BH=?βlg/?KBH=0.026. The deuterium isotope effect for proton removal from Ph-S+(Me)-CH2CL2CN is kH/kD=4.4 and 4.9 for tris(hydroxymethyl)aminomethane and ethylamine buffers, respectively, and there is no detectable protium exchange into the deuterated substrate. The positive pxy coefficient provides evidence for coupling between proton abstraction and leaving group expulsion; it confirms the concerted AxhDHDN (E2) mechanism. The values of β and βlg indicate an imbalance in the transition state, in which proton transfer is ahead of leaving group expulsion. The change from a stepwise AxhDHH+DNN (ElcB) mechanism for thiophenoxide leaving groups to a concerted mechanism for sulfide leaving groups is consistent with the notion that the mechanism is determined solely by the lifetime of the carbanion; there is no evidence for the coexistence of stepwise and concerted mechanisms.
- Banait, Narinder S.,Jencks, William P.
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p. 6950 - 6958
(2007/10/02)
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- New Oxyfunctionalization Capabilities for ω-Hydroxylases: Asymmetric Aliphatic Sulfoxidation and Branched Ether Demethylation
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Due to inherent difficulties in the chemical generation of aliphatic synthons, the stereo- and regioselective oxyfunctionalization of simple aliphatic substrates represents an area where chemical applications of biocatalysis would be particularly useful.The hydrocarbon monooxygenase from Pseudomonas oleovorans is a prototypical "ω-hydroxylase" known to carry out hydroxylation at the terminal methyl of alkanes as well as epoxidation of terminal olefins.It is now demonstrated that this enzyme system catalyzes stereoselective sulfoxidation of methyl thioether substrates, representing the first clear example of oxygenase-produced chiral aliphatic sulfoxides yet reported.In addition, it is shown that this enzyme system catalyzes oxygenative O-demethylation of branched alkyl methyl and branched vinyl methyl ethers to secondary alcohols and ketones, respectively.These findings establish new oxyfunctionalization capabilities, and thus a significantly expanded biotechnological potential, for the hydrocarbon monooxygenases.
- Katopodis, Andreas G.,Smith, Homer A.,May, Sheldon W.
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p. 897 - 899
(2007/10/02)
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- ORGANOBORANES FOR SYNTHESIS. 1. PROTONOLYSIS OF TRIALKYLBORANES. A CONVENIENT NON-CATALYTIC CONVERSION OF ALKENES INTO SATURATED COMPOUNDS via HYDROBORATION-PROTONOLYSIS
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The protonolysis of trialkylboranes with carboxylic acids proceeds very rapidly for the first group, somewhat slower for the second, but requires elevated temperatures for removal of the third.A close examination of the protonolysis of representative symmetrical, as well as mixed trialkylboranes, reveals that the steric requirements of the alkyl groups attached to boron play an important role in the rate.Secondary alkyl groups protonolyze less readily than primary alkyl groups.More hindered alkyl groups are still more resistant.Since the hydroboration-protonolysis sequence involves relatively mild conditions, this procedure can be applied for hydrogenating olefinic derivatives containing labile groups, such as active sulfur, halogen and nitrogen functionalities.The stereochemistry of protonolysis has been established via deuteroboration of norbornene and deuterolysis of the product.It is evident that protonolysis proceeds with retention of configuration at the migrating carbon.Partially alkylated boranes can be used for hydroboration-protonolysis with improved regioselectivity.Subsequent protonolysis of the resulting mixed trialkylboranes provides the desired alkanes in good yields.Products sensitive to the action of hot acetic acid offer difficulties.For example, when this procedure was applied to the preparation of 1-menthene from d-limonene, the product was racemic.
- Brown, Herbert C.,Murray, Kenneth J.
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p. 5497 - 5504
(2007/10/02)
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- EXCRETION OF S- AND O-METHYL ESTERS AND OTHER VOLATILE COMPOUNDS BY OCHROMONAS DANICA
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The formation of volatile excretion was studied in axenic cultures of Ochromonas danica.Under microaerobic conditions in the light, an accumulation of O- and S-methyl esters, alcohols, dimethyldisulphide was observed in the medium.Most of the compounds are structurally derived from the amino acids methionine, valine , leucine and isoleucine.The excreted volatile compounds, particularly the methyl thioesters, were rapidly metabolized in the dark.Key Word Index - Ochromonas danica; metabolism; volatile excretion products; O-esters; S-esters; microaerobiosis.
- Juettner, Friedrich,Wiedemann, Evi,Wurster, Karl
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p. 2185 - 2188
(2007/10/02)
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