Monofunctional Amines Research Articles

Fluorinated Chiral Pyrans Obtained via Mechanochemical Organocatalytic Michael/oxa‐Michael Cascade

Fluorine‐containing compounds are important in medicine or crop‐protection. Herein, we show asymmetric organocatalytic Michael/oxa‐Michael cascade leading to chiral fluorinated pyrans under mechanochemical conditions. Formal oxa‐Diels‐Alder reaction between fluorine containing unsaturated keto esters and β,γ‐unsaturated ketones afforded a range of drug‐like pyran derivatives in short times and good to high yields. Ball‐milling convey the reaction in short times and high product yields, while keeping high enantiomeric purities of products. The reaction is diastereodivergent depending on the use of either monofunctional amine catalysts or bifunctional thiourea or squaramide.

Cyclopropenimine-Mediated CO2 Activation for the Synthesis of Polyurethanes and Small-Molecule Carbonates and Carbamates.

Carbon dioxide (CO2) is an abundant C1 feedstock with tremendous potential to produce versatile building blocks in synthetic applications. Given the adverse impact of CO2 on the atmosphere, it is of paramount importance to devise strategies for upcycling it into useful materials, such as polymers and fine chemicals. To activate such stable molecule, superbases offer viable modes of binding to CO2. In this study, a superbase cyclopropenimine derivative was found to exhibit exceptional proficiency in activating CO2 and mediating its polymerization at ambient temperature and pressure for the synthesis of polyurethanes. The versatility of this reaction can be extended to monofunctional amines and alcohols, yielding a variety of functional carbonates and carbamates.

Cyclopropenimine‐Mediated CO2 Activation for the Synthesis of Polyurethanes and Small‐Molecule Carbonates and Carbamates

AbstractCarbon dioxide (CO2) is an abundant C1 feedstock with tremendous potential to produce versatile building blocks in synthetic applications. Given the adverse impact of CO2 on the atmosphere, it is of paramount importance to devise strategies for upcycling it into useful materials, such as polymers and fine chemicals. To activate such stable molecule, superbases offer viable modes of binding to CO2. In this study, a superbase cyclopropenimine derivative was found to exhibit exceptional proficiency in activating CO2 and mediating its polymerization at ambient temperature and pressure for the synthesis of polyurethanes. The versatility of this reaction can be extended to monofunctional amines and alcohols, yielding a variety of functional carbonates and carbamates.

Synthesis of sustainable curcumin based photo-crosslinkable benzoxazines: Thermal, hydrophobic and anti-corrosion properties

Bifunctional polybenzoxazines have been developed using sustainable bio-phenol curcumin, paraformaldehyde with varying nature of monofunctional amines through Mannich condensation. The molecular structure of synthesized benzoxazines were confirmed by ATR-FTIR, 1HNMR and 13CNMR and high-resolution mass spectroscopic (HRMS) analyses. DSC thermograms were used to ascertain the curing behaviour of curcumin-based monomers. Thermal curing of Cu-api occurs at 192 °C and that of Cu-aa undergoes dual curing at 177 °C and 209 °C due to its inherent molecular structure. The thermal stability of synthesized polybenzoxazines was studied using TGA, Cu-a exhibits higher char yield of 63% due to higher aromatic content than that of other polybenzoxazines. The occurrence of dimerization (2π+2π cycloaddition) of curcumin based benzoxazines proceeds through conjugation present in the main chain of curcumin when exposed to UV irradiation, and was monitored through UV–visible spectroscopy. All the synthesized benzoxazine monomers were excited within the wavelength of UV range with occurrence of photoluminescence behaviour in visible region ranges between 448 nm and 530 nm. The value of band gap calculated for the curcumin-based monomers ranged from 3.55 to 3.77 eV. The explicit character of curcumin based benzoxazines can be exploited in the field of optical applications. The hydrophobic behaviour of polybenzoxazines was also studied and the highest water interface angle value of 146° was observed for poly(Cu-tfma) due to the presence of fluorine groups. Furthermore, the Cu-tfma coated cotton fabric was tested for its durability and the results indicated that these materials coated cotton fabrics are better suitable for sustainable high performance hydrophobic applications. The anti-corrosion studies indicated that the poly(Cu-api) coated on mild steel exhibits greater resistance towards corrosion amongst the other polybenzoxazines which can be potentially employed as coating in marine environments.

Tailor-Made Bio-Based Non-Isocyanate Polyurethanes (NIPUs)

Non-isocyanate polyurethanes (NIPUs) based on biobased polyamines and polycarbonates are a sustainable alternative to conventional polyurethanes (PU). This article discloses a novel method to control the crosslinking density of fully biobased isocyanate-free polyurethanes, synthesized from triglycerides carbonated previously in scCO2 and different diamines, such as ethylenediamine (EDA), hexamethylenediamine (HMDA) and PriamineTM-1075 (derived from a dimerized fatty acid). As capping substances, water or bioalcohols are used in such a way that the crosslinking density can be adjusted to suit the requirements of the intended application. An optimization of the NIPU synthesis procedure is firstly carried out, establishing the polymerization kinetics and proposing optimal conditions set for the synthesis of the NIPUs. Then, the influence of the partial blocking of the active polymerization sites of the carbonated soybean oil (CSBO), using monofunctional amines, on the physical properties of the NIPUS is explored. Finally, the synthesis of fully biobased NIPUs with a targeted crosslinking density is achieved using hybrid NIPUs, employing partially carbonated oil and H2O or ethanol as blockers to achieve the desired physical properties in a very precise manner.

Catechol-Amine-Decorated Epoxy Resin as an Underwater Adhesive: A Coacervate Concept Using a Liquid Marble Strategy.

The attachment phenomena of various hierarchical architectures found in nature, especially underwater adhesion, have drawn extensive attention to the development of similar biomimicking adhesives. Marine organisms show spectacular adhesion characteristics because of their foot protein chemistry and the formation of an immiscible phase (coacervate) in water. Herein, we report a synthetic coacervate derived using a liquid marble route composed of catechol amine-modified diglycidyl ether of bisphenol A (EP) polymers wrapped by silica/PTFE powders. The adhesion promotion efficiency of catechol moieties is established by functionalizing EP with monofunctional amines (MFA) of 2-phenyl ethylamine and 3,4-dihydroxy phenylethylamine (DA). The curing activation of MFA-incorporated resin pointed toward a lower activation energy (50.1-52.1 kJ mol-1) compared with the neat system (56.7-58 kJ mol-1). The viscosity build-up and gelation are faster for the catechol-incorporated system, making it ideal for underwater bonding performance. The PTFE-based adhesive marble of the catechol-incorporated resin was stable and exhibited an adhesive strength of 7.5 MPa under underwater bonding conditions.

Synthesis and lithographic properties of positive-tone poly(benzoxazole)s by the effect of amine end-cappers

Positive-tone photosensitive poly(o-hydroxyamide) (PHA) precursors were synthesized from the polycondensation reaction of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (Bis-AP-AF), 4,4’-oxybisbenzoyl chloride (OBC) and three mono-functional amines as end-cappers. The synthesized PHA precursors were characterized and converted to polybenzoxazoles (PBOs) by thermal cyclization reaction. The photoresist formulations composed of the prepared PHA precursor and diazonaphthoquinone (DNQ) photoactive compound were prepared, and the photolithographic properties of the photoresist formulations were investigated by UV light irradiation, followed by a 2.38 wt.% tetramethylammonium hydroxide (TMAH) solution treatment in terms of the chemical structure of end-cappers. The dissolution rate at 2.38 wt.% TMAH solution by various UV light exposure doses and the shrinkage ratio by thermal cyclization of micro-patterns by UV light irradiation and developing process from the photoresist formulations are affected by the chemical structure of end-cappers.

Thermally reprocessable bio-based polymethacrylate vitrimers and nanocomposites

Vitrimers are covalently cross-linked polymeric materials that can be processed upon heating wherein triggerable polymer networks shuffle chemical bonds through exchange reactions without losing their network integrity. In this work, we apply vitrimers to develop recyclable thermosets derived from materials with relatively high bio-source content. We explore the reaction between β-ketoesters derived from commercially available (2-acetoacetoxy) ethyl methacrylate (AAEMA) incorporated within isobornyl methacrylate (IBOMA, from pine sap), and a bi-functional amine (Priamine, derived from vegetable oils) to synthesize catalyst-free vitrimers. Controlled radical miniemulsion polymerization was also used to synthesize the water-borne copolymer analogs. Vitrimer nanocomposites were obtained by the incorporation of amine‐functionalized polyhedral oligomeric silsesquioxane (POSS–NH2) at different loadings (0, 5, 10 and 20 wt%). Incorporation of 20 wt% POSS-NH2 improved tensile modulus (from 96 to 176 MPa), tensile strength (from 2.5 to 5 MPa) and decomposition temperature (225–255 °C), and slowed down the relaxation rate and increased apparent activation energy of stress relaxation compared to the neat vitrimer. We further show that the vitrimers studied here and the nanocomposites containing vinylogous urethane cross-linking networks can be un-cross-linked by dissolving in excess mono-functional amine at 65 °C or recycled by grinding and remolding at 125 °C without compromising the mechanical properties.

Impact of amine additives on the mechanical properties of hydrogen bonding π-conjugated polymers

Reversibly interacting π-conjugated polymers of lower modulus are needed to generate intrinsically healable materials for bioelectronics applications. However, strong interchain interactions between π-conjugated polymers increases modulus and reduces flexibility of networks as well as self-healing capability. Herein, to understand the impact of amine additives on the thin film moduli of hydrogen bonding π-conjugated polymer, poly[3-(6-carboxyhexyl)thiophene-2,5-diyl] (PTCOOH) was complexed with a lean (Di-2oMe) and bulky (Di-2onBu) 1,6-difunctional secondary amines. The amines interact with the PTCOOH via weak ionic interactions and/or hydrogen bonding interactions. Amine complexed PTCOOH polymer samples and PTCOOH are characterized using DSC and PXRD to correlate the assembly structure with the observed modulus. The amines acted as plasticizers and reduced the modulus of PTCOOH. Moreover, the polymer modulus decreased with increasing amine group size, indicating the importance of the amine group size. Also, the difunctional amines acted as a better plasticizer than the monofunctional amines. PXRD analysis indicates that the interchain hydrogen bonding interactions between the polymer chains play a key role in determining the moduli of thin films.

Rational design of nucleophilic amine sites via computational probing of steric and electronic effects

Accessibility of the nucleophilic site in organocatalysts is essential to ensure adequate catalytic activity. Gas-phase trimethylborane (TMB) Lewis basicity and Brønsted proton basicity of several amine based organocatalysts have been calculated using the CBS-QB3 model chemistry. This TMB basicity scale can, as opposed to the proton basicity scale, account for steric effects encountered in the initial nucleophilic attack of the nitrogen free electron pair on a substrate. Since such a step is the first one in several amine catalyzed reactions, severe steric hindrance of the nucleophilic center would render the catalyst ineffective. Comparing the TMB basicity and proton basicity with the experimentally observed catalytic activity of both homogeneous and heterogeneously supported amine sites found in literature for the aldol reaction of acetone with 4-nitrobenzaldehyde showed that, due to the inclusion of these steric effects, the TMB basicity scale is a much better predictor of catalytic activity than the proton basicity. According to this computational Lewis basicity scale, potential steric hindrance in alternative nitrogen containing active sites was probed. This resulted in 3-propylpyrrolidine being proposed among the most promising monofunctional amine groups and 1-(methylamino)propan-2-ol among the most promising bifunctional amine-hydroxyl groups for heterogeneous aldol reaction catalysts.

Thermoplastic Aluminoborophosphate-Aniline Polycomplexes

Products are obtained from interaction between oligomeric aluminoborophosphate (ABP) and aniline, both complexes based on hydrogen bonds, as confirmed with IR spectroscopy and quantum chemical calculations. Nitrogen and hydrogen atoms of an amino group in aniline form hydrogen bonds with hydrogen and oxygen atoms of a phosphate group in ABP, respectively, with a total energy of 14.2 kcal/mol. Aniline, when added to ABP surrounded with a shell of water molecules, displaces two water molecules from the surface of the chain. The energy gain is 9.1 kcal/mol. IR spectroscopy data show that there are strong donor-acceptor interactions between water molecules and aluminum and phosphorus atoms of ABP in the solid-state polycomplex sample. The thermoplastic oligomeric complexes leads to an increase in the softening temperature and fluidity with an increase in an amount of aniline. This means that polyoxide inorganic polymer (metal phosphate) is possible to be modified with a monofunctional amine under “mild” conditions. We showed that the water resistance of the polycomplex is greater than that of ABP.

Epoxidized Lignin Derivatives as Bio-based Cross-linkers Used in the Preparation of Epoxy Resins

Lignin, which is the most abundant aromatic polymer in nature, was used as a green substitute for the toxic bisphenol A. In particular, the ability of epoxidized lignin to simultaneously serve as a cross-linker and rigid segment was investigated. The epoxidized lignin was preferably reacted with a monofunctional amine, which acted as a chain extender, to evaluate its performance as a cross-linker, and in the presence of poly(ethylene glycol) diglycidyl ether as a soft segment to adjust the resin properties. Different poly(ethylene glycol) diglycidyl ether/lignin stoichiometric ratios were tested, whereas the amine/epoxy equivalent ratio was fixed at 1:2. Some of the remarkable resin samples were subjected to differential scanning calorimetry analysis and compared with blank samples that did not include lignin in the composition. Moreover, the evolution over time of the molecular weight distribution of the selected compositions was analyzed by gel permeation chromatography until the solubility in tetrahydrofuran was appreciable.

Monofunctional amines substituted fluorenylidene bridged cyclotriphosphazenes: ‘Turn-off’ fluorescence chemosensors for Cu2+ and Fe3+ ions

In the present work, the reaction of 2,2,4,4-tetra(anilino)-6,6-dichlorocyclotriphosphazene (4) and 2,2,4,4-tetra(2-naphthylamino)-6,6-dichlorocyclotriphosphazene (5) with 4,4′-(9-fluorenylidene)diphenol, FDP, (6) and 4,4′-(9-fluorenylidene)dianiline FDA (7) were studied in THF and new aniline (8 and 9) and 2-naphthylamine (10 and 11) substituted FDP-bridged cyclotriphosphazenes and aniline (12) and 2-naphthylamine (13) substituted FDA-bridged cyclotriphosphazene derivatives were obtained. All newly synthesized monofunctional amines substituted fluorenylidene bridged cyclotriphosphazenes (8–13) were fully characterized by elemental analysis, 1H and 31P NMR spectroscopies, MALDI-TOF mass spectrometry and UV–Vis electronic absorption spectra. The florescence properties of the synthesized new compounds were studied. The chemosensory behavior of the compounds against to metal ions was also investigated. The obtained fluorenylidene bridged 2-naphthylamine substituted cyclotriphosphazenes (10, 11 and 13) showed fluorescence chemosensor behavior with high selectivity for Fe3+ and Cu2+ ions in the solution.

Silicone boronates reversibly crosslink using Lewis acid-Lewis base amine complexes.

Silicone elastomers are normally thermosets, which are not readily recycled or repurposed. The few examples of thermoplastic silicone elastomers depend on reversible covalent and non-covalent molecular interactions. It is demonstrated that amine-boronate complex formation provides a simple and flexible route to reversible crosslinked silicones. A variety of network structures were prepared by use of terminal and pendantly functionalised silicone boronates and amines. The crosslink density was quantified using a combination of Shore-hardness measurements, swelling, and rheological analyses. Stress induced by compressive force could be relieved through dynamic B-N bond reformation at 60 °C. Materials could be fully disassembled through introduction of n-butylamine and successfully reformed upon removal of the monofunctional amine by evaporation.

Multifunctional Macrocyclic Receptors as Templates for Aromatic Amino Acids: A Rare Example of a Highly Selective Multi-Input Multi-Output Chemo-"Logic Gate".

Proton-bound [M⋅H⋅G]+ diastereomeric complexes between some chiral aromatic amino acids or dipeptides (G) and a chiral multifunctional macrocyclic receptor (M=Chirabite-A) undergo, in the gas phase, highly selective substitution and addition reactions by amines, such as 2-aminobutane and piperidine. All the [M⋅H⋅G]+ complexes follow time-dependent monoexponential decays. In some cases, the kinetic curves exhibit a plateau revealing the presence of unreactive [M⋅H⋅G]+ structures. In them, the amino acid is accommodated in the macrocycle cavity in the zwitterionic form by sharing its acidic hydrogen atoms with the pyridine nitrogen atoms of the host. The same interactions are structurally inaccessible to G=dipeptides or monofunctional amines, which then can be readily released from [M⋅H⋅G]+ . When the amino acid interacts with the amidocarbonyl oxygen atoms pointing outside the macrocycle cavity, it saves the canonical structure and can be readily displaced by the amine. The Chirabite-A may act as an efficient template for aromatic amino acids by releasing them or not depending upon the amino acid configuration and the basicity of the amine. These unique properties confer to the gas-phase diastereomeric [M⋅H⋅G]+ complexes the features of multi-input multi-output chemo-"logic gates".

Kinetic study of 2-butanol O-acylation and sec-butylamine N-acylation catalyzed by Candida antarctica lipase B

The aim of this work was to study the differential behavior shown by Candida antarctica lipase B during the O-acylation and N-acylation of monofunctional alcohols and monofunctional amines. To achieve this, 2-butanol and sec-butylamine were used as model molecules. Yields, kinetics and enantioselectivity were studied for both reactions. Although a steady-state ordered ternary complex bi–bi mechanism was obtained for the O-acylation of 2-butanol, a ping–pong bi–bi mechanism was obtained for the N-acylation in case of low sec-butylamine concentrations. The values of apparent kinetic parameters were calculated: the enantiomeric ratios (E) were evaluated and confirmed the preference of C. antarctica lipase B for the (R)-enantiomer, which was consistent with the literature. The enantioselectivity was calculated for the alcohol (E ≈ 3.17) and for the amine (E ≈ 1.34). Concerning the O-acylation, the yields were found to be very similar for both enantiomers R and S. However, both initial rates and yields of the (R)-enantiomer N-acylation were higher than those of the (S)-enantiomer. In the last part of our study, the chemoselectivity of C. antarctica lipase B was evaluated, showing that C. antarctica lipase B was a chemoselective enzyme that preferentially catalyzed the O-acylation to the detriment of the N-acylation (C ≈ 92, for the selective acylation of (R)-enantiomers). These results provide new insights for the synthesis of products issued from the selective acylation of multifunctional substrates such as amino-alcohols.

Selective Chain-End Postpolymerization Reactions and Property Tuning of a Highly Conjugated and All-Thiophene Polyazomethine

A highly conjugated polyazomethine (3) consisting uniquely of thiophenes was investigated for sustaining postpolymerization property tuning. This was courtesy of the ever-present and reactive amino and aldehyde chain ends. Subjecting the polymer to polymerization conditions in the absence of monomers resulted in a DPn increase from 15 to 70. The aldehyde chain end was selectively reacted with an aliphatic amine by undergoing reductive amination with sodium triacetoxyborohydride (NaBH(OAc)3) while the imines along the conjugated polymer framework remained intact. This illustrates the robustness of the azomethine bond. Reductive amination of 3 with a monofunctional amine resulted in selective chain-end capping and prevented repolymerization. 3 was resistant to dynamic component exchange and monomer shuffling as a result of its high degree of conjugation. Conversely, chain extension was possible both by reductive amination with an α−ω-diamine and by reheating the polymer. Covalent attachment of two separate segments of 3 was possible by reductive amination with a 2:1 polymer/α−ω-diamine stoichiometry. This resulted in molecular weight doubling and serves to illustrate the possibility of multiblock tethering via the ever-active chain ends. Meanwhile, a 1:1 polymer/α−ω-diamine stoichiometry gave rise to a polymer with an aliphatic and aromatic amine functionalized at either chain end. As a result of the noncomplementary of the two chain ends, the polymer could not be repolymerized. However, it exhibited consistent molecular weight under various repolymerization reaction conditions indicating the robustness of the heteroconjugated bonds and their tolerance toward dynamic component exchange. The color of 3 was also changed from its inherent blue color to green via the covalent attachment of a yellow dansyl derivative by reductive amination at the aldehyde chain end. The collective property modification including repolymerization, coblock tethering, color modification, and increased degree of polymerization presenting unequivocal evidence that polyazomethines are capable of undergoing postpolymerization property tailoring.

Protease Catalyzed In Situ C-Terminal Modification of Oligoglutamate

One-pot biotransformations gave oligo(γ-L-Et-Glu) decorated with selected amine-functio- nalized end-groups at C-termini. Motivations for this work were to (i) control the end group structure of peptidessynthesizedbyprotease-catalyzed peptidesynthesisand(ii)incorporate end-groupsthatcanbeused directly or after further modification as polymerizable entities. Papain, bromelain, R-chymotrypsin, Multi- fect P-3000, and Purafect prime 4000 L were used as catalysts for oligomerization of γ-L-(Et)2-Glu in the presence of monofunctional amines. The series of amine nucleophiles (NH2-R, acyl acceptors) studied mimic phenylalanine in that they possess aromatic rings linked to amine groups by one or more methylenes. Generally,additionofincreasedquantitiesofNH2-Rfrom0to30,50,and70mol%withrespectto γ-L-(Et)2- Glu results in decreased % yield, but increased mol % of NH2-R end-capped oligo(γ-L-Et-Glu)-NH-R (determinedbyNMR).Irrespectiveoftheproteaseused,2-thiophenemethylamine(TPMA)gavethehighest fraction of oligo(γ-L-Et-Glu)-NH-R chains. For example, using Multifect P-3000 and a feed ratio of TPMA- to γ-L-(Et)2-Glu of 7:3, >90 mol % of oligopeptides formed had TPMA C-terminal groups. With all five proteases studied herein, L-phenylalanine and L-histidine did not produce end-capped oligo(γ-L-Et-Glu). In contrast, L-phenylalanine analogs benzylamine (BzA) and L-phenylalaninol (F-OH), both of which lack the R-carboxyl group, gave substantial quantities of oligo(γ-L-Et-Glu)-F-OH or -BzA chains. Hence, the results of this study prove that the promiscuity of proteases used herein can be exploited to create a diverse family of desired end-functionalized oligopeptides. MALDI-TOF spectra recorded of oligo(γ-L-Et-Glu) with amine nucleophiles showed molecular ions that affirmed the formation of corresponding NH2-R functionalized oligo(γ-L-Et-Glu).

Facile Preparation of Nanoparticles by Intramolecular Cross-Linking of Isocyanate Functionalized Copolymers

A new synthetic approach to the preparation of intramolecularly collapsed nanoparticles under mild, room temperature conditions has been developed from commercially available vinyl monomers. Reaction of isocyanate functionalized linear copolymers with a diamine in dilute solution leads to the efficient formation of nanoparticles where the diameter of the nanoparticle can be varied by controlling both the molecular weight and mole percentage of isocyanate repeat units. Physical properties for the intramolecularly collapsed nanoparticles were fully consistent with a three-dimensional structure and analysis of the collapse reaction revealed that approximately 75% of the isocyanate groups along the backbone underwent crosslinking with 25% being available for further reaction with mono-functional amines. This stepwise consumption of the isocyanates allows the chemical and physical properties of the nanoparticles to be further tuned and significantly opens up the range of nanoparticles that can be prepared using this mild and highly efficient chemistry.

Analysis of modified polyamide 6.6 using coupled liquid chromatography and MALDI–TOF–mass spectrometry

A new approach of analysis of polyamide 6.6 using the principle of coupling polymer liquid chromatography to matrix assisted laser desorption ionization–time of flight–mass spectrometry (MALDI–TOF–MS) is presented. In contrast to the known technique of two-dimensional chromatography, MALDI–TOF–MS was applied in the 2nd chromatographic dimension. According to the synthesis of polyamide 6.6 various species with different end groups are expected. Due to the capping of the end groups during the synthesis, either performed by the addition of mono-functional amines or acids, additional structures are formed and found. Although the resolution of chromatography applied for separation was poor in comparison to the broad variety of expected species, a complete identification of those components was achieved applying the MALDI–TOF–MS technique. The results were presented in a two-dimensional plot, which can be used as a fingerprint method for the analysis of polyamide 6.6.