Réaction de Mannich

Résumé

La réaction de Mannich est une méthode classique pour la préparation de bêta-aminocétones et aldéhyde (base de Mannich). C'est une étape clé dans la synthèse de nombreux produits pharmaceutiques et naturels. La réaction de Mannich fait intervenir un aldéhyde ou une cétone énolisable, une amine secondaire, du formaldéhyde, en solution aqueuse d’acide chlorhydrique comme catalyseur. Le produit obtenu est une aminocétone formée par addition sur la cétones d'une molécule de formaldéhyde et d'une molécule d'amine. Mécanisme de la réaction Le mécanisme de la réaction de Mannich est détaillé ci-dessous : 600px 500px 600px Conditions de réaction On utilise un solvant protique tel que l'éthanol, le formaldéhyde, ou le paraformaldéhyde car cela favorise l'équilibre de la réaction. La base obtenue est un solide blanc. Mannich

Source officielle

https://fr.wikipedia.org/wiki/R%C3%A9action_de_Mannich

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Water-soluble ruthenium m-triphenylphosphinetrisulfonate (TPPTS) complexes are excellent catalysts for formic acid dehydrogenation. Interestingly, the choice of metal catalyst precursor has a direct influence on initial activities. The reaction with hexaaquaruthenium(II) tosylate directly yields bisphosphine complexes in the presence of TPPTS and formic acid, whereas trisphosphine adducts are involved if the reaction starts with ruthenium(III) chloride. We present the results of a series of manometric and spectroscopic experiments that reveal the true nature of these highly active species, and subsequently propose a rational "fast" cycle mechanism explaining this peculiar activity profile.

Wiley-V C H Verlag Gmbh2014

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Amine functionalized activated carbon fibers as effective structured adsorbents for formaldehyde removal

Guillaume Bastien Baur, Lioubov Kiwi, Jonathan Spring

Activated carbon fibers (ACFs) with surface modified by a diethylene triamine (DETA) are synthesized for the abatement of formaldehyde in gas phase at low concentration. Adsorbents with several DETA loadings were tested and characterized. The amount of DETA deposited on the ACFs surface is shown to diminish the porosity. The influence of the DETA on the adsorption capacity towards formaldehyde is studied via dynamic adsorption experiments. The deposition of 20 wt.% DETA allowed100-fold increase of adsorption capacity as compared to original ACFs. A Schiff base reaction between the amine groups of DETA and formaldehyde was suggested as the adsorption mechanism. Adsorbent surface chemistry was shown to be more important than its microporous structure for efficient formaldehyde removal. [GRAPHICS] .

2018

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The kinetics and mechanism of the title heterogeneous halogen exchange reactions of potential atmospheric importance have been studied under molecular flow conditions in a FEP Teflon-coated Knudsen flow reactor on HX (X = Cl, Br, I) - doped ice condensed from the vapor phase under conditions of several formal monolayers of HX coverage at approximately 200 K. In addition, the halogen exchange reactions involving the expected primary reaction products BrCl, ICl and IBr of the above mixed anhydrides with HX-doped ice have been studied at 200 K as well. The uptake coefficient γ for the heterogeneous reaction ClONO2 + HBr on ice is 0.56±0.11 and Cl2 and Br2 are formed in yields of 100% and 66 to 80%, respectively, in the range 180 to 200 K. The γ value for the reaction ClONO2 + HI on ice is 0.30±0.02 at 200 K with Cl2 being the main product appearing after an induction time. The primary product ICl is formed at the same time as Cl2 whereas HOCl appears at a later time under conditions of waning HI supply. The γ value for the reaction BrONO2 + HI on ice is 0.40±0.02 at 200 K with Br2 being the main product observed after a short delay. The primary product IBr is observed without delay, whereas HOBr is observed at a later time once HBr has reacted. The mechanism of the reactions of the interhalogens BrCl, ICl and IBr with HX on ice at 200 K involves the formation of trihalide ions at the ice interface which is consistent with the observed significant negative temperature dependence for the reaction ICl + HBr on ice in the range 180 to 205 K as well as for the reaction BrCl + HBr between 190 and 200 K. The uptake coefficient γ for each of the interhalogens increases from ice to HI-doped ice in the order of increasing molecular weight of HX with the exception of ICl, whose g attains a limiting value of γ = 0.32±0.05. A halogen exchange reaction on ice has been observed in cases where the most stable hydrohalic acid could be formed: HCl > HBr > HI. A propensity for the formation of the homonuclear halogen molecule in the reactions of halogen nitrates with HX-doped ice has been explained by the occurrence of fast secondary reactions of the primary interhalogen product at the HX/ice interface.

2000

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2000