- Kinetics and mechanism of gas-phase pyrolysis of ylides. Part 3. 1 Thermal reactivity of α-carbonyl- and thiocarbonyl-stabilized methylenetriphenylphosphoranes
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Fourteen ketone/thione-stabilized triphenylphosphonium methylides were subjected to conventional gas-phase and flash vacuum pyrolysis (FVP). The kinetics of the first-order thermal gas-phase reactions of all these compounds were investigated over 360-653K temperature range. The values of the Arrhenius logA and energy of activation of these ylides averaged 11.52±0.34s -1 and 133.20±3.14kJmol-1, respectively. The products of sealed-tube (static) and FVP were analyzed and compared. A mechanism is proposed to account for the products of reaction. The rate constants [k (s-1)] of the substrates at 500K were calculated and used to substantiate the proposed mechanism of pyrolysis, and to rationalize the thermal gas-phase reactivities of the ylides under study.
- Al-Bashir, Rasha F.,Al-Awadi, Nouria A.,El-Dusouqui, Osman M. E.
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experimental part
p. 311 - 319
(2012/04/17)
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- Solvent-free mechanochemical preparation of phosphonium salts, phosphorus ylides, and olefins
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The present invention provides a method of preparing a phosphonium salt of the formula [R1R2R3P—CR4R5R6]X, comprising ball-milling a phosphine of the formula R1R2R3P with a compound of the formula XCR4R5R6; a method of preparing a phosphorus ylide of the formula R1R2R3P═CR4R5, comprising ball-milling a phosphonium salt of the formula [R1R2R3P—HCR4R5]X in the presence of a base; and a method of preparing an olefin of the formula R4R5C═CR7H or R4R5C═CR7R8, comprising ball-milling a phosphorus ylide of the formula R1R2R3P═CR4R5 with a compound of the formula R7C(O)H or R7C(O)R8. The inventive method produces phosphonium salts and phosphorus ylides by mechanical processing solid reagents under solvent-free conditions. The advantages of the present invention over conventional solution methods, include: (1) extremely high selectivity; (2) high yields; (3) low processing temperatures; (4) simple and scalable reactions using commercially available equipment; and (5) the complete elimination of solvents from the reaction.
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- Mechanically induced solid-state generation of phosphorus ylides and the solvent-free wittig reaction
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We describe the nearly quantitative preparation of phosphorus ylides and the Wittig reaction occurring in the solid sate during high-energy mechanochemical processing. Initial insights into the details of the discovered chemical transformations indicate that high-energy mechanical processing supports the interaction of reacting centers by breaking crystallinity of the reactants and by providing mass transfer without a solvent. Copyright
- Balema, Viktor P.,Wiench, Jerzy W.,Pruski, Marek,Pecharsky, Vitalij K.
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p. 6244 - 6245
(2007/10/03)
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- Synthesis of C-glycosyl isoxazoles and branched-chain enuloses from 2,3-O-isopropylidene-D-glyceraldehyde
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The synthesis of 5-glycosyl isoxazoles with 3-alkyl-, 3-aryl, 3,4-dialkyl, 3-aryl-4-alkyl or 3-alkyl-4-bromo substituents is reported. Deoxyenuloses were obtained from reaction of 2,3-O-isopropylidene-D-glyceraldehyde and several phosphorus ylides, which contain a carbonyl group, by a Wittig reaction. C-glycosyl α,β-unsaturated ketones were obtained, with the polyhydroxylate chain lengthened by two or three carbon atoms. In the second phase the ketones were transformed into the corresponding C-glycosyl α,β-unsaturated ketoximes, leading to the C-glycosyl isoxazoles, which were converted into the title compounds via removal of the isopropylidene group of suitably protected carbohydrates. The solubility of the synthetized C-glycosyl isoxazoles were modified by free hydroxyl groups in such a way that their behaviour against certain viruses and their potential antiviral activity could be studied.
- Bá?ez Sanz,López Sastre,Pati?o Molina,Romero-ávila García
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p. 1331 - 1350
(2007/10/03)
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- CONVENIENT PREPARATION OF UNSYMMETRICALLY SUBSTITUTED BENZILS BY PERMANGANATE OXIDATION OF β-OXO PHOSPHORUS YLIDES
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Oxidative cleavage of a range of ylides 4 with R1 and/or R2 being aromatic groups, using KMnO4 in a two-phase system, affords unsymmetrical benzils and 1-arylpropane-1,2-diones 5 in moderate to good yield, and the ylide formation and oxidation can be combined in a convenient one-pot method.Key words: Phosphorus ylides, oxidation, 1,2-diketones, benzils, permanganate, oxoalkylidenetriphenylphosphoranes.
- Aitken, R. Alan,Cadogan, J. I. G.,Gosney, Ian
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p. 281 - 286
(2007/10/02)
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