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Crystallization and Structural Linkages of COFs
Published in Atsushi Nagai, Covalent Organic Frameworks, 2019
Nowadays, Schiff base chemistry or dynamic imine chemistry is profusely utilized for the synthesis of COFs. Imine is a functional group or chemical compound containing a carbon-nitrogen double bond and is typically prepared by the condensation of primary amines and aldehydes and less commonly ketones (Eq. 2.5). In terms of mechanism, such reactions proceed via nucleophilic addition, giving a hemiaminal –C(OH)(NHR)– intermediate, followed by the elimination of water to give the imine (–N=C–) compound. The equilibrium in this reaction usually favors the carbonyl compound and amine, so azeotropic distillation or use of a dehydrating agent, such as molecular sieves or magnesium sulfate, is required to push the reaction in favor of imine formation. In recent years, several reagents, such as tris(2,2,2-trifluoroethyl)borate, pyrrolidine, acetic acid, and titanium ethoxide, have been shown to catalyze imine formation. Especially, according to synthesis of COFs, aqueous acetic acid as a catalyst is most useful.
The effect of urea-formaldehyde adhesive modification with propylamine on the properties of manufactured plywood
Published in The Journal of Adhesion, 2023
Jakub Kawalerczyk, Joanna Walkiewicz, Magdalena Woźniak, Dorota Dziurka, Radosław Mirski
Figure 1 presents FTIR spectra of both reference and modified variants. The course of each spectra revealed mostly peaks of UF resin by showing band at 3355 cm−1 which corresponds to O-H and N-H stretch vibrations.[39] Moreover, the symmetric and asymmetric stretching vibrations of C-H were observed at 2953 and 2882 cm−1.[39,40] Peak at 1645 cm−1 was assigned to C = O stretching.[41,42] After the addition of propylamine, the formation of bond linkages was confirmed. It was found that the spectra of PA-modified UF resin showed a weak peak at 1610 cm−1 which can be assigned to C = N bonding.[43] The imine bonds can be easily formed during the condensation reaction of amino and aldehyde groups.[44] At the first stage of reaction between formaldehyde and amine, a free electron pair of the amine nitrogen attacks the carbonyl carbon in formaldehyde. After the transfer of a proton from nitrogen to oxygen a hemiaminal is formed. In the next stage, protonation of hemiaminal and dehydration lead to formation of imine H2C = N-CH2-CH2-CH3.[22]
Removal of Th(IV) ion from wastewater using a proper Schiff base impregnated onto Amberlite XAD-4
Published in Particulate Science and Technology, 2020
The Schiff bases are considered a very important class of ligands, which form complexes with many metals. These complexes have wide applications in some biological aspects, analytical fields, organic catalysis, and oxygen carriers (Pui et al. 2011). A Schiff's base (or azomethine or imine), named after Hugo Schiff, is a functional group with the general formula of R1R2C = N–R3. These bases can be synthesized from an aromatic amine and a carbonyl compound (e.g., aldehydes, ketones) by nucleophilic addition, forming a hemiaminal, and followed by a dehydration to generate an imine. An imine (Schiff's base) particularly binds metal ions via the two donor atoms N and O (Ganjali et al. 2008).