Membrane microreactors Knoevenagel condensation

The benefits of the use of micromembranes for the selective removal of one or more products during reaction have been demonstrated for equdibrium-limited reactions [289]. For example, the performance of hydrophilic ZSM-5 and NaA membranes over multichannel microreactors prepared from electro-discharge micromachining of commercial porous stainless steel plates was studied by Yeung et al. in the Knoevenagel condensation [290,291] and andine oxidation to azoxybenzene [292]. For such kind of reactions, the zeolite micromembrane role consists of the selective removal of water, which indeed yields higher conversions, better product purity, and a reduction in catalyst deactivation in comparison to the traditional packed bed reactor. 

Lai SM, Ng CP, Martin-Aranda R, and Yeung KL. Knoevenagel condensation reaction in zeohte membrane microreactor. Micropor Mesopor Mater 2003 66(2-3) 239-252. 

Lai SM, Martin-Aranda R, Yeung KL (2003) Knoevenagel condensation reaction in a membrane microreactor. Chem Commun 22 218-219... 

A microfluidic reaction system has also been used for the production of prodrugs. A multichannel membrane microreactor was fabricated and tested for Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate to produce a-cyanocinnamic acid ethyl ester, a known intermediate for the production of an antihypertensive drug [9]. Knoevenagel condensations of carbonylic coiiqtounds and malonic esters yield several important key products such as nitriles used in anionic polymerization, and the a,p-unsaturated ester intermediates employed in the synthesis of several therapeutic drugs that include niphendip-ine and nitrendipine. Unlike most condensation reactions. 

Knoevenagel condensation between carbonyl compounds and methylene malo-nic esters on a CsNaX zeolitic coating in a microreactor demonstrated an order of magnitude higher productivity as compared with a traditional packed-bed reactor while the selectivity remained the same in both reactors [107,108]. A nearly fourfold increase in reaction conversion was obtained for the microreactor when NH2 modified CsNaX zeolitic coatings were apphed [109]. The conversion was further improved when zeolitic coatings were grown onto a stainless steel membrane (0.2 pm pores) inserted in a microreactor [110]. 

Lai, S.M., Ng, C.R, Martin-Aranda, R. and Yeung, K.L. (2003) Knoevenagel condensation reaction in zeolite membrane microreactor. Microporous and Mesoporous Materials, 66,239-252. 

Lai S M, Ng C P, Martin-Aranda R and Yeung K L (2003), Knoevenagel condensation reaction in zeolite membrane microreactor , Micropor Mesopor Mat, 66, 239-252. 

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