Synthesis of highly symmetric mesomeric triazaphenalene betaines

Kafka, Stanislav; Larissegger‐Schnell, Barbara; Kappe, Thomas

doi:10.1002/jhet.5570410511

Cited by 12 publications

(7 citation statements)

References 49 publications

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“…As discussed before, the dissolution mechanism of TBD-EG/NMP should be similar to the mechanism by TBD-EG, as NMP did not participate in dissolution directly. As shown in Scheme , TBD would first react with ester via nucleophilic attack of both disubstituted nitrogen at the carbonyl groups to form betaine-like intermediate (step 1) . The protonated nitrogen allows an easy proton transfer that affords the intermediate product of TBD amide and liberates the alcohol (step 2).…”

Section: Resultsmentioning

confidence: 99%

“…As shown in Scheme 2, TBD would first react with ester via nucleophilic attack of both disubstituted nitrogen at the carbonyl groups to form betaine-like intermediate (step 1). 42 The protonated nitrogen allows an easy proton transfer that affords the intermediate product of TBD amide and liberates the alcohol (step 2). In the case of a TBD-NMP solution, only these two steps proceed and TBD molecules would gradually be consumed to cleave the ester linkages.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Recycling of Epoxy Thermoset and Composites via Good Solvent Assisted and Small Molecules Participated Exchange Reactions

Xiao

Zhou

Shi

et al. 2018

ACS Sustainable Chem. Eng.

169

136

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Thermosetting polymers and composites are a class of high-performance materials with significant industrial applications. However, recycling of thermosets and their filling matters are significantly challenging. Here, we propose a method to recycle epoxy thermosetting polymer and composites efficiently by a synergistic effect of a solvent mixture using a highly efficient organic catalyst at an ordinary pressure and mild temperatures. The anhydrideepoxy network depolymerization enabled by selective ester bond cleavage process is substantially enhanced by a good solvent assisted and alcohol participated transesterification reaction. The epoxy thermoset can be dissolved in 28 min with 50% mass loss, and 70 min with 95% mass loss at 170 °C under ambient pressure. We demonstrate that this method can be used to reclaim carbon fibers from industrial reinforced epoxy composite products and embedded metal parts from commercial electronic products with undiminished properties at a mild temperature (∼170 °C) under an ordinary pressure in a short time (1.5 h). Moreover, the decomposed epoxy oligomer can be reused as a reactive ingredient for the preparation of new epoxy materials with high strength and modulus. This work provides a new insight into the thermosets dissolution and recycling.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Recycling of Epoxy Thermoset and Composites via Good Solvent Assisted and Small Molecules Participated Exchange Reactions

Xiao

Zhou

Shi

et al. 2018

ACS Sustainable Chem. Eng.

169

136

View full text Add to dashboard Cite

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“…TBD first reacts with ester via nucleophilic attack of both disubstituted nitrogens at the carbonyl groups forming betaine-like intermediate. 38 Then the proton transfer on the protonated nitrogen leads to the intermediate product of TBD amide and liberating the alcohol. With the incorporation of another alcohol, new ester can be rapidly formed by regenerating TBD.…”

Section: Resultsmentioning

confidence: 99%

Dissolution of epoxy thermosets via mild alcoholysis: the mechanism and kinetics study

et al. 2018

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“…Moreover, TBD was shown to react with malonate esters via nucleophilic attack of both disubstituted nitrogens at the carbonyl groups to form betaine-like structures. 20 In this communication, we describe a facile route to structurally diverse acyclic guanidines together with their viability as catalysts for the ROP of lactide. The activity and mechanism of these new catalysts are compared to the cyclic guanidines previously reported.…”

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confidence: 99%

Acyclic Guanidines as Organic Catalysts for Living Polymerization of Lactide

et al. 2010

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We describe a facile route to structurally diverse guanidinium organic catalysts by reaction of carbodiimides with secondary amines. The efficacy of these catalysts for the living ring-opening polymerization (ROP) of lactide was demonstrated including predictable molecular weights and end-group fidelity.Theoretical studies indicate that the acyclic guanidines are less basic than 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), but as for the more active TBD, they catalyze ring opening by activation of the alcohol and by stabilizing the resultant tetrahedral intermediates through hydrogen bonding. These results demonstrate that weak secondary interactions are an important concept for controlled polymerization.Ring-opening polymerization (ROP) of cyclic esters, such as lactide and lactones, is a powerful method for generating polyesters with controlled molecular weight and end-group functionality; several reviews of the elegant organometallic catalytic routes to such materials have appeared. 1 In addition to polymerization techniques that give predictable molecular weights, narrow molecular weight distributions, and end-group fidelity, many advanced applications require the removal of undesired contaminants such as heavy metal ions from catalysts. Toward this goal, new methods based on organocatalytic ring-opening polymerization have been developed. 2-9 Examples of successful organocatalysts for the ROP of cyclic esters, carbonates, and siloxanes include 4-dimethylaminopyridine, 3 phosphines, 4 N-heterocyclic carbenes (NHC), 5 acids, 6 bifunctional aminothioureas, 7 phosphazene bases, 8 amidines, and guanidines. 9,10 The bicyclic guanidine moiety is a substructure common to many biologically active natural products and the catalytic role in natural products has received considerable attention. 11 Guanidines and chiral guanidines have been used in several asymmetric transformations, 12 but the synthesis of the catalysts, particularly the chiral bicyclic guanidine's is very demanding. 13,14 Along these lines, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBDH þ , pK a = 26 in acetonitrile) 15 drew our attention as a ROP catalyst for cyclic esters since it is commercially available and easily handled with reported use as a transesterification catalyst. 16 For example, in a ROP of lactide in the presence of TBD in a 1000:1:10 monomer/catalyst/initiator monomer conversion was complete in 2 min, rivaling the NHC catalysts in turnover frequency. 17 As TBD is a strong base, our initial hypothesis was that it deprotonates the alcohol and propagates by an anionic mechanism. However, solvent effects on the polymerization with TBD were inconsistent with a purely anionic mechanism. For the TBD-catalyzed ROP of lactide, the reaction was fastest in CH 2 Cl 2 (>90% conversion in 2 min), slightly slower in THF (60% conversion in 2 min), and much slower in DMF (0% conversion in 2 min), the opposite of what would be expected for a conventional anionic polymerization.These observations and the fact that the much faster rate of TBD relative to oth...

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Synthesis of highly symmetric mesomeric triazaphenalene betaines

Cited by 12 publications

References 49 publications

Recycling of Epoxy Thermoset and Composites via Good Solvent Assisted and Small Molecules Participated Exchange Reactions

Recycling of Epoxy Thermoset and Composites via Good Solvent Assisted and Small Molecules Participated Exchange Reactions

Dissolution of epoxy thermosets via mild alcoholysis: the mechanism and kinetics study

Acyclic Guanidines as Organic Catalysts for Living Polymerization of Lactide

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