دانلود رایگان مقاله لاتین کانیزارو بر روی هیدروتالکیت منیزیم از سایت الزویر
عنوان فارسی مقاله:
وقوع واکنش کانیزارو بر روی هیدروتالکیت های منیزیم و آلومنیوم
عنوان انگلیسی مقاله:
The occurrence of Cannizzaro reaction over Mg-Al hydrotalcites
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
In recent years hydrotalcites (HTCs) have found numerous applications as adsorbents or ion exchangers, catalyst precursors or supports, etc. [1–4]. These materials represent a class of hydrated double hydroxides with a general formula [M2+nM3+m(OH)2(n+m)]m+ (Ax−)m/x·yH2O. Themost commonlyused Mg-Al HTCs consist of a brucite-like [Mg(OH)2] network wherein isomorphous substitution of Mg2+ ion by a trivalent Al3+ occurs and the excess positive charge of the framework is compensated by gallery anions which are located in the interlayer along with water molecules [4–6]. As-prepared HTCs typically contain carbonates as compensating anions whichmakes thesematerials inactive inbasecatalyzed reactions [7]. Thermaltreatment of Mg–Al HTCs results in decomposition of carbonate groups accompanied by the release of CO2 and the formation of a well-dispersed mixture of magnesium and aluminum oxides (MgAlO). The calcined mixed oxides act as weak Lewis acid/strong base catalysts and find various applicationsas effective catalysts in transesterification [8,9], alcohol elimination [10] and condensation [11,12] reactions. A distinctive feature of MgAlO materials is their ability to reconstruct the lamellar HTC structure (so-called memory effect) when contacted with water vapor or liquid water in absence of carbon dioxide. This leads to meixnerite (magnesiumaluminiumhydroxidehydrate),thatis HTC intercalated with OH− as compensating anions in the interlayer [11,12]. In addition, the treatment of MgAlO with aqueous reaction mixture (in situ rehydration) leading to reconstructed HTCs is also known [12–14]. These rehydrated materials have been applied to a number of base-catalyzed reactions which require Brønsted basic character, including different self- and cross-condensations [12–15] Michael additions [16], etc. Condensation reactions attract much attention because they allow obtaining more complex compounds with more carbon atoms starting from relatively simple molecules. The interest in these reactions stems from the fact that many of the initial molecules for the syntheses can be obtained by biomass processing. For example, furfural can be obtained by acid hydrolysis of sugar cane bagasse, a residue from sugar cane processing, followed by extraction [17]. The needed acetone may be obtained by ketonization of acetic acid [18] that is an important productof biomass pyrolysis. Aldol condensation of these relatively simple molecules allows increasing chain length to 8+ carbon atoms. This route has attracted significant interest, because hydrogenation/hydrodeoxygenation of these aldol condensation products leads to various hydrocarbons suitable for blending in conventional diesel fuel and kerosene [19]. A comprehensive study of aldol condensation over solid catalysts is thus necessary for designing the pathway to components of motor fuels from renewable natural resources. Aldol condensation of furfural (F) and acetone (Ac) in the presence of a basic catalyst begins with the initial abstraction of the -proton from acetone, forming a carbanion that consecutively attacks the carbonyl groupofthenearby adsorbedfurfuralmolecule [20,21]. Additionally, acetone can be transformed on basic (or acidic as well) sites by its own reaction pathway which is acetone self-condensation resulting to the formation of diacetone alcohol, mesityl oxide, etc [11,13]. Both aldol condensation of furfural with acetone and acetone self-condensation can proceed simultaneously; in this case the rate-determining step should be shared by both reaction pathways and involve basic sites with similar strength [20]. Much less attention is paid to the transformation of furfural on basic sites of a solid catalyst in absence of acetone, or generally in absence of carbonyl compounds having no -hydrogen atoms. Nevertheless, furfural can hardly be considered as an inert component when contacted with basic sites and a specific parallel reaction route has to be considered. Cannizzaro reaction (CR) is a well-known base-induced redox reaction of an aldehyde lacking a hydrogen atom in the alpha position. It represents the disproportionation of an aldehyde into a carboxylic acid and an alcohol catalyzed by a strong aqueous base, i.e. it takes two aldehydes to produce one acid and one alcohol. In case of furfural, two furfural molecules would produce furfuryl alcohol (F-OH) and furoic acid (F-OOH) according to the reaction scheme below (Scheme 1). The mechanism of the CR is well postulated. The reaction begins with the attack of hydroxide from basic NaOH on the carbonyl carbon followed by deprotonation to give a dianion. This unstable intermediate releases a hydride anion which attacks another molecule of aldehyde. In this process the dianion converts to a carboxylate anion and the aldehyde to an alkoxide. The alkoxide then picks up a proton from water to provide the alcohol final product, while the caboxylate is converted to the carboxylic acid product after acid work-up [22]. It should be mentioned that in aqueous basic solution carboxylic acid produced by CR can hardly be detected in pure form as it immediately reacts with the base to form a corresponding salt. Taking into account the scheme of furfural transformation by CR the occurrence of this reaction on a basic solid can also be assumed provided that the catalyst possesses hydroxides of suffi- cient strength as active sites and the reaction proceeds in aqueous medium. Indeed, this reaction was proposed among others when considering all possible reactions occurring during aqueous furfural aldol condensation with acetone using base solid catalysts [23]. Additionally, it was mentioned that MgO in aqueous media could catalyze the formation of the intermediate species for the Cannizzaro reaction (furfuryl alcohol and furoic acid) resulting in the formation of esterification product, 2-furancarboxylic 2- furanmethyl ester (furoyl furoate, FF)[24]. Nevertheless,there is no information available on the effect of CR on the physico-chemical properties of a solid basic catalyst as well as on its impact on the behavior of the catalyst in aldol condensation. The scope ofthe present work is thus to understand the behavior of calcined Mg-Al mixed oxide as a catalyst for converting aqueous furfural mixture and to provide information on the extent of CR and its impact on the catalyst performance in aldol condensation.
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کلمات کلیدی:
Cannizzaro reaction - Wikipedia https://en.wikipedia.org/wiki/Cannizzaro_reaction The Cannizzaro reaction, named after its discoverer Stanislao Cannizzaro, is a chemical reaction that involves the base-induced disproportionation of an ... Mechanism · Scope · Variations · See also Cannizzaro Reaction - Organic Chemistry Portal www.organic-chemistry.org › Reactions › Name Reactions Cannizzaro Reaction. This redox disproportionation of non-enolizable aldehydes to carboxylic acids and alcohols is conducted in concentrated base. STUDIES PERTAINING TO THE MECHAKISM OF THE HETEROGE ... pubs.acs.org/doi/pdf/10.1021/jo01157a015 by MS KHARASCH - 1949 - Cited by 9 - Related articles Benzyl benzoate has been isolated from benzaldehyde Cannizzaro reaction ... reactions occurring simultaneously in the two phases, the non-aqueous phase .... effect the average rate of reaction over the first 7.5% of conversion may fairly. Why can enolizable aldehydes undergo Cannizzaro reactions? https://chemistry.stackexchange.com/.../why-can-enolizable-aldehydes-undergo-canni... Dec 24, 2016 - Why does 2-methylpropanal undergo a Cannizzaro reaction even ... in the case of 2-methyl-propanal the canizzaro reaction gets favoured over ... Microwave Assisted Organic Synthesis https://books.google.com/books?isbn=1405168447 Jason Tierney, Pelle Lidström - 2009 - Science Pourjavadi, A., Soleimanzadeh, B. and Malandi, G.B., Microwave-induced Cannizzaro reaction over neutral gamma-alumina as a polymeric catalyst, React. Objective Chemistry For Iit Entrance - Page 17 - Google Books Result https://books.google.com/books?isbn=812241365X Alok Mittal - 2002 Aldol condensation of acetaldehyde involves the formation of which of the following ... Ethanol vapour is passed over heated copper at 300' C and product is ... type (b) The addition reaction occurring across C=0 bond are nucleophilic type (c) ... The Importance of Cannizzaro-Type Reactions during Electrocatalytic ... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5330657/ by YY Birdja - 2017 Jan 18, 2017 - The Cannizzaro reaction is a base-catalyzed disproportionation .... aldol reaction is suppressed or the Cannizzaro reaction is preferred over the ... Searches related to occurrence of Cannizzaro reaction over cannizzaro reaction definition cannizzaro reaction lab report intramolecular cannizzaro reaction cannizzaro reaction class 12 cross cannizzaro mechanism cannizzaro reaction of 4-chlorobenzaldehyde cannizzaro reaction ppt cannizzaro reaction of 4-chlorobenzaldehyde lab
