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Recent Developments in MOF-Polymer Composites
Published in Ram K. Gupta, Tahir Rasheed, Tuan Anh Nguyen, Muhammad Bilal, Metal-Organic Frameworks-Based Hybrid Materials for Environmental Sensing and Monitoring, 2022
Recently, MOF-polymer composites are highly valued as catalysts for several reactions such as the Knoevenagel condensation reaction. The Knoevenagel condensation reaction is a well-known organic reaction for the formation of carbon-carbon bonds that are essential for producing unsaturated acids, which in turn are used for fabricating a large number of products such as insecticides, pesticides, chemicals, cosmetics, and so forth. This reaction is catalyzed by organic and inorganic bases, which pose a significant threat to the environment. Hence to reduce the use of these bases, MOF-polymer composites are being fabricated and utilized. Zhao et al. [70] made use of the site isolation strategy to separate two different polymers with dissimilar properties in different porous regions in a MOF to fabricate a bifunctional catalyst. The acidic polymer, polystyrene sulfonate, and a basic polymer, polymethyl aminopyridine were formed by in-situ polymerization within the pores of Cr-MIL-101. These two types of MOF-polymer catalysts bearing isolated active sites were used to catalyze tandem reactions, namely decentralization by an acid catalyst and Knoevenagel condensation reaction of benzaldehyde glycol acetal. The simultaneous use of both acidic and basic MOF-polymer composites leads to faster catalytic conversions using mild reaction conditions. Cohen et al. [71] have fabricated layered MMM using MIL-101-NO2 and ZIF-8 to perform a two-step catalytic reaction. At first, the top layer of MIL-101-NO2 was used as an acid catalyst to convert a benzaldehyde dimethyl acetal into benzaldehyde and in the second reaction, a ZIF-8 MMM layer, which acts as a base catalyst, was used for the Knoevenagel condensation reaction of benzaldehyde with malononitrile. After passing through this layered MMM a conversion of 95% of the reactants to the final product was achieved.
Organic Synthesis
Published in Suresh C. Ameta, Rakshit Ameta, Garima Ameta, Sonochemistry, 2018
Chetna Ameta, Arpit Kumar Pathak, P. B. Punjabi
The Knoevenagel condensation reaction is an organic reaction named after Emil Knoevenagel. It is a modification of the aldol condensation (Knoevenagel, 1898). A Knoevenagel condensation is a nucleophilic addition of an active hydrogen compound to a carbonyl group followed by a dehydration reaction, where a molecule of water is eliminated. The product is often an a,P-unsaturated ketone (a conjugated enone).
Name Reactions
Published in Benny K.G. Theng, Clay Mineral Catalysis of Organic Reactions, 2018
The Knoevenagel condensation refers to the coupling of a carbonyl compound to an activated methylene compound followed by the elimination of water to yield an α,β-unsaturated ketone, and it is commonly catalyzed by amines.
Straightforward sustainable synthesis of novel non-endocrine disruptive bio-based organic UV-B filters with antimicrobial activity
Published in Green Chemistry Letters and Reviews, 2023
Matthieu M. Mention, Cédric Peyrot, Blandine Godon, Jimmy Alarcan, Fanny Brunissen, Marina Grimaldi, Patrick Balaguer, Albert Braeuning, Florent Allais
As described in previous studies, the steric hinderance on the β-position, in addition to an extended conjugation throughout the molecules, are necessary to confer good anti-UV properties to organic UV filters. However, beyond the level of absorbance and wavelength coverage, stability is also a critical parameter as molecules need to be active for a certain time in order to fully protect against harmful radiations. α,β-unsaturated esters can undergo a wide range of reactions on their C=C double bond, such as Michael reaction (25) or cycloaddition (26). A way to limit these reactions is to use bulky ester moieties in order to limit the access of potential reagents to the reactive double bond. However, Pallabi et al. (27) recently demonstrated than, even with high hindrance induced by the ester moiety, such molecules can easily undergo [2 + 2] cycloaddition under UV irradiation, reducing their conjugation and consequently, their level of UV protection through time. To avoid this, several new p-hydroxycinnamic derivatives were synthesized by introducing a second substituent on the β position (19), providing increased stability in result of the higher steric hinderance around the double bond. The Knoevenagel condensation, which consists in two key steps in the presence of a carbonyl group and an active hydrogen component, offers an easy access to such structures with a second substituents on the β position.
Novel DBU-based hydroxyl ionic liquid for efficient Knoevenagel reaction in water
Published in Green Chemistry Letters and Reviews, 2019
Sanhu Zhao, Dan Meng, Lingling Wei, Yongsheng Qiao, Fugui Xi
In summary, three ionic liquids based on DBU were prepared and the structure−property relationship of them was further explored. Due to the hydrogen bond effect and alkalinity, the ionic liquid [HyEtDBU]Br shows excellent catalytic effects on the Knoevenagel condensation and a recyclable protic-ionic-liquid solvent–catalyst system, [HyEtDBU]Br-H2O-DABCO, was developed and used in the Knoevenagel condensation reaction of aromatic aldehydes with ethyl 2-cyanoacetate. At room temperature, the Knoevenagel condensation preceded very well, short reaction time (1 min∼4.5 h) and high reaction yields (92%∼99%) were obtained. Furthermore, the solvent–catalyst system [HyEtDBU]Br-H2O can be recycled eight times without significant loss of catalytic activity. After completion of the reaction, the desired products can be obtained by simple filtration and recrystallization. This procedure offers some significant advantages including simple operation, excellent yield, short reaction time and recyclability of the solvent-catalyst system, which makes the present protocol practical for the preparation of multifunctional Knoevenagel condensation products.
Synthesis and application of layered double hydroxide-hosted 2-aminoterephthalate for the Knoevenagel condensation reaction
Published in Inorganic and Nano-Metal Chemistry, 2018
The Knoevenagel condensation reaction of an aldehyde or ketone with an activated methylene compound forming C-C bond formation have emerged as a powerful protocol in the preparation of substituted alkenes and bioactive compounds.[1,2] Conventionally, the reaction could carry out in the presence of alkali metal hydroxide or organic amine and its ammonium salts as well as Lewis bases/acids as catalyst.[3–6] However, the procedure has several drawbacks, such as the difficulty in recovering and recycling of the catalyst, and also generates the large quantities of toxic wastes, which makes the process ecologically unacceptable. Thus, various solid catalysts have been explored on the development of reusable and ecologically acceptable processes in recent years. Polystyrene-supported poly(amidoamine) dendrimers,[7] amine-functionalized MCM-41,[8] polystyrene immobilized DABCO,[9] Zeolitic imidazolate frameworks (ZIF-8, Fe3O4@ZIF-8 and ZIF-9),[10–12] DABCO-based ionic liquid,[13] ZIF-8/NaA,[14] chitosan,[15] diethylenetriamine-functionalized grapheme oxide with Fe3O4 nanoparticles,[16] NH2-modified MIL-53(Al)[17] and amine-functionalized sugarcane[18] have been studied.