A new fluorescent bis(acridino)-macrocycle containing two allyl groups was synthesized and photop... more A new fluorescent bis(acridino)-macrocycle containing two allyl groups was synthesized and photophysically studied. Studies were carried out on metal ion recognition and selectivity-influencing effects including the determination of the relevant thermodynamic constants as logK and pK a. The proposed sensor molecule is recommended for the development of Zn 2+-selective optochemical analyzers based on covalently immobilized ionophores as it has a unique pH-independent metal ion recognition ability, which is not influenced by anions and other potentially occurring metal ions in biological samples.
Periodica Polytechnica Chemical Engineering, May 23, 2023
Dry-column vacuum chromatographic technique is introduced for remediation of wastewater for the f... more Dry-column vacuum chromatographic technique is introduced for remediation of wastewater for the first time. A previously prepared chemically modified silica gel containing covalently immobilized Hg 2+-selective acridino-crown ether selector molecules was used as an adsorbent. Removal of Hg 2+ from highly contaminated river water was carried out to study practical applicability. Adsorption capacity, preconcentration factor, pH-sensitivity and selectivity in separation were determined. The adsorbent proved to be outstanding in selectivity, only Ag + and Cu 2+ interfered among 29 cations, was inert toward organic contaminants, exhibited regenerability and pH-independency between 3.0 ≤ pH ≤ 7.0. The proposed method showed a moderate efficiency in both adsorption (32 mg Hg 2+ / 1 g adsorbent) and preconcentration (preconcentration factor of 100). A maximum 10 L of wastewater / 1 g adsorbent ratio is recommended as an upper limit for applicability. The described method showed a unique robustness and simplicity compared to conventional ion-chromatographic methods and an improved selectivity over physical interaction-or simple functional group-based adsorptions.
In this work, anchoring of cinchona derivatives to trifunctional cores (hub approach) was demonst... more In this work, anchoring of cinchona derivatives to trifunctional cores (hub approach) was demonstrated to obtain sizeenlarged organocatalysts. By modifying the cinchona skeleton in different positions, we prepared four C3-symmetric size-enlarged cinchona derivatives (hub-cinchonas), which were tested as organocatalysts and their catalytic activities were compared with the parent cinchona (hydroquinine) catalyst. We showed that in the hydroxyalkylation reaction of indole, hydroquinine provides good enantioselectivities (up to 73% ee), while the four new size-enlarged derivatives gave significantly lower values (up to 29% ee) in this reaction. Anchoring cinchonas to trifunctional cores was found to facilitate nanofiltration-supported catalyst recovery using PolarClean alternative solvent. The C3-symmetric size-enlarged organocatalysts were completely rejected by all the applied membranes, whereas the separation of hydroquinine was found to be insufficient using organic solvent nanofiltration. Furthermore, the asymmetric catalysis was successfully demonstrated in the case of Michael reaction of 1,3-diketones and trans-β-nitrostyrene using Hub 3-cinchona (up to 96% ee) as a result of the positive effect of the C3-symmetric structure using a bulkier substrate. This means an increased selectivity of the catalyst in comparison to hydroquinine in the latter Michael reaction.
Journal of inclusion phenomena and macrocyclic chemistry, Dec 21, 2020
Studies on liquid-liquid extraction and bulk liquid membrane (BLM) technique-based metal ion sepa... more Studies on liquid-liquid extraction and bulk liquid membrane (BLM) technique-based metal ion separation by a previously published Pb 2+-selective acridono-18-crown-6 ether selector molecule were performed. The effects of the stirring speed, the quality of apolar organic membrane, the counterions of Pb 2+ , the pH of the aqueous phase, the concentration of the source phase, the concentration of the carrier in the BLM and the temperature on the Pb 2+-separation were investigated. Moreover, the effects of the competitive inhibition due to the presence of Ag + , Ca 2+ , Co 2+ , Cu 2+ , K + , Mg 2+ , Na + and Zn 2+ as competing ions in a multicomponent aqueous source phase of different ion-concentrations were also studied. After a proper dilution of the multicomponent aqueous source phase, excellent Pb 2+-selectivity was achieved without a significant reduction in the efficiency compared to the liquid membrane transport of single-component systems. Based on the BLM-cell studies the applied selector molecule proved to be suitable for the development of liquid membrane-based Pb 2+-selective separation methods, which can be greatly aided by the analysis of the effects on the separation and by the optimization of the parameters of the process discussed here.
A D A 6 196li 1i omit ft. l4lt1 0-5e-' "-'~~~W *-a IWUt' "%Wq.e~q:' (13. off fMtleOaft. Iwm" 1010... more A D A 6 196li 1i omit ft. l4lt1 0-5e-' "-'~~~W *-a IWUt' "%Wq.e~q:' (13. off fMtleOaft. Iwm" 1010 %0" tfor oewe ~WuNK~t 01m' 0*11 % otd~UI t9~otdmI9 to *eAV-w~q .4*010110iv, Sowcee. 0O.'wttorsue 'roaamfg O0wonam atu Mee. 11 j 40W4 I2Aw4. a to Ow Ote" *4q9m4 • ap•g70e• U W U11 l tie OC zorn ,nk, 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED
Synthesis of acidic new crown ethers containing a diarylphosphinic acid unit has been accomplishe... more Synthesis of acidic new crown ethers containing a diarylphosphinic acid unit has been accomplished. The aromatic rings of the crown ethers were substituted with tertbutyl and nitro groups. Nitro substitution of the crown ethers was investigated. pKa determination of the new proton-ionizable crown ethers has been performed, showing the effect of the substituents of the aromatic rings on the acidity. An anomaly was discovered in the pKa values and an explanation was given based on quantum mechanical calculations and molecular dynamics simulations.
Chemical depolymerisation, or solvolysis, can be a sustainable plastic recycling method, as a cir... more Chemical depolymerisation, or solvolysis, can be a sustainable plastic recycling method, as a circular economy can be achieved by recovering the pure monomers. Polyethylene terephthalate (PET) is a ubiquitous plastic material with short-life application and slow biodegradation, so its waste management needs to be continuously improved. In this study, we tested three commercially available organocatalystmodified silica gels in the glycolysis of PET and developed another, functionalized with triazabicyclodecene (TBD), which was also tested. Organocatalysts are efficient in PET glycolysis, but their recyclability needs to be improved for industrial application. The applied heterogeneous modified silica gels can be recovered easily by filtration. Si-TEA catalyst was chosen for reaction optimisation because it has the highest thermal stability and good catalytic activity. The PET glycolysis process was optimised by fractional factorial experimental design and response surface methodology. Under optimal reaction conditions (PET (384 mg, 2 mmol), ethylene glycol (1.41 mL, 25.2 mmol), Si-TEA (15.5 mol%), 190°C, 1.7 h), 88.5% nonisolated bis(2-hydroxyethyl) terephthalate (BHET) monomer yield was obtained. Si-TEA and Si-TBD catalysts were recycled in five reaction cycles, and with both catalysts, high cumulative BHET yields (89 and 88%, respectively) were achieved. Additionally, environmental energy impacts were calculated for the two catalysts and were compared favourably with other organocatalysts in the literature. A process scale-up was also implemented. Finally, it has been verified that modified silica gels have much higher catalytic activities than native silica gel, as solvolytic reactions using the former catalysts took a significantly shorter time.
Three cinchona derivatives have shown remarkable activity to catalyze the aza-Markovnikov additio... more Three cinchona derivatives have shown remarkable activity to catalyze the aza-Markovnikov addition reaction of N-heterocycles to vinyl esters. The synthesis of aza-Markovnikov adducts possessing valuable biological activity was thoroughly optimized. By studying the ratio of the starting materials, bases and solvents, we achieved a new and efficient protocol, which could be performed under mild conditions with a small excess of vinyl ester affording products with excellent yields and high regioselectivity. This optimization reduced Sheldon's E-factor of the reaction by 42%. Furthermore, membrane separation for catalyst recycling was assessed to further improve the sustainability of the synthesis.
Magyar kémiai folyóirat, Kémiai közlemények (Online), 2018
A közlemény alapjául Németh Tamás "Synthesis and molecular recognition studies of acridono-and ac... more A közlemény alapjául Németh Tamás "Synthesis and molecular recognition studies of acridono-and acridino-crown ether-based sensor and selector molecules" címû doktori értekezése szolgált, mely a https://doktori.hu/index.php?menuid=193&lang=HU&vid=17939 oldalon érhetõ el.
This work presents the first successful applications of cinchona-thiosquaramides in asymmetric re... more This work presents the first successful applications of cinchona-thiosquaramides in asymmetric reactions. Binaphthyl-cinchona squaramides and thiosquaramides were synthesised, and then used as organocatalysts to promote the catalytic enantioselective Michael addition reaction of pentane-2,4dione to trans-b-nitrostyrene with excellent yields (up to 99%) and enantioselectivities (up to 99% ee) at as low as 0.2 mol% catalyst loadings. Thiosquaramides gave higher enantioselectivities (up to 92% ee) in conjugate addition reaction of lawsone to b,g-unsaturated a-keto ester than its oxo analogue, with high yields (up to 100%). Also, only thiosquaramide could catalyse the aza-Diels-Alder addition reaction of 2-siloxydiene to benzylideneacetone. Furthermore, quantum chemical computations showed that the geometrical structure of binaphthyl-cinchona thiosquaramide is similar to that of squaramide.
Although ion-selective membrane-based potentiometric sensors have already proved their analytical... more Although ion-selective membrane-based potentiometric sensors have already proved their analytical performance in several fields of life, their applicability is still limited in practice. Biodegradable, ionic additive-free, polylactic acid-based bulk electrode membrane matrix containing various environmentally friendly polyethylene glycol derivatives as plasticizer was developed for the first time to replace the conventional PVC-based ones. Moreover, the first introduction of 3D printing in potentiometric chemosensing was also reported. It was demonstrated that a thoroughly optimized and generalizable procedure for filament extrusion combined with 3D printing technology provides a unique tool for series production of the redesigned ion-selective bulk electrochemical membranes. Finally, the potentiometric detection of Hg 2+ in water was carried out as a proof-of-concept study on sensing. Results showed an unexpected improvement in electrochemical characteristics of the novel membranes compared to their conventional analogues. The present work expanded the practical applicability of conventional potentiometric cation-selective electrode membranes enabling their green, decentralized, and automated state-of-the-art manufacturing using a novel matrix composition.
The class of enantiopure α,α-disubstituted α-amino acids has gained considerable attention in the... more The class of enantiopure α,α-disubstituted α-amino acids has gained considerable attention in the past decades since some of them have interesting properties as antibiotics. The synthesis of such materials has been a challenging task to which enantioselective phase transfer catalysis offers an effective solution. In our work the synthesis starts from the easily available Meldrum's acid, that is converted into the key disubstituted malonate intermediates in an asymmetric alkylation step catalyzed by cinchona-crown ether derivatives. The aim was to obtain a new type of phase transfer catalystcinchona derivatives of aza-crown ethers-and compare the achieved enantiomeric excess values, while also optimizing the reaction conditions. The amino acids are gained by the selective hydrolysis of the key intermediates followed by a multistep reaction.
During my research work cinchona-, and proline-based chiral squaramide, and thiosquaramide organo... more During my research work cinchona-, and proline-based chiral squaramide, and thiosquaramide organocatalysts were synthesized. The promising new organocatalyst class, the thiosquaramides, were gained by the thionation of the appropriate squaramide with pyridine complex of phosphorus pentasulfide. In 2017, Rawal and his co-workers were the first ones who successfully managed to apply the double hydrogen-bond donor thiosquaramides in asymmetric reactions. They recognized the great potential of this new type of catalyst. If the carbonyl groups of squaramide are converted to thiocarbonyl groups, the acidity of the hydrogen-bond unit increases which can result in stronger hydrogen bond between the substrate(s) and the catalyst. Moreover, thiosquaramides are found to be more soluble in nonpolar organic solvent than their squaramide counterparts. The synthesized organocatalysts were applied in asymmetric CC coupling reactions, furthermore, the proline-based (thio)squaramide were proved to be excellent organocatalysts for the enamine catalysed Diels-Alder reaction.
The class of enantiopure α,α-disubstituted α-amino acids has gained considerable attention in the... more The class of enantiopure α,α-disubstituted α-amino acids has gained considerable attention in the past decades since some of them have interesting properties as antibiotics. The synthesis of such materials has been a challenging task to which enantioselective phase transfer catalysis offers an effective solution. In our work the synthesis starts from the easily available Meldrum's acid, that is converted into the key disubstituted malonate intermediates in an asymmetric alkylation step catalyzed by cinchona-crown ether derivatives. The aim was to obtain a new type of phase transfer catalystcinchona derivatives of aza-crown ethers-and compare the achieved enantiomeric excess values, while also optimizing the reaction conditions. The amino acids are gained by the selective hydrolysis of the key intermediates followed by a multistep reaction.
Nowadays, the recovery of organocatalysts is a crucial issue considering both environmental and e... more Nowadays, the recovery of organocatalysts is a crucial issue considering both environmental and economic aspects. An effective and simple solution to meet this challenge is to change the solubility of the reaction components compared to each other. To reach this aim, lipophilic side chain can be incorporated into the organocatalyst. This causes a considerable difference in the polarity, which allows the catalyst and the other components of the reaction mixture to be separated from one another by filtration after changing the solvent or by an extraction step. Our aim was to develop a new synthetic method for the incorporation of a lipophilic moiety into the catalysts. At first, starting from methyl gallate, we prepared a carboxylic acid derivative containing three octadecyl groups. This lipophilic unit was then linked in an amide formation reaction to a cinchona squaramide organocatalyst (through an aminoethyl linker), which had previously led to excellent enantioselectivity in Michael reactions. In the amide formation, we examined the acyl chloride pathway and coupling agents as well. We plan to apply the gained lipophilic catalyst in various asymmetric conjugate addition reactions.
This short review summarizes the synthesis and molecular recognition studies of crown ether type ... more This short review summarizes the synthesis and molecular recognition studies of crown ether type macrocycles accomplished at the Institute for Organic Chemistry of Budapest University of Technology and Economics in the last few years. The research work reported here belongs to the areas of protonionizable crown ethers and chiral macrocycles. Proton-ionizable crown ethers at higher pH s than their pK a values are mostly ionized to ligand anions which increase the cation-ligand complex stability with enhancement of selectivity and avoid the need for a counter anion to accompany the cation transport or solvent extraction. The latter factor is not only advantageous from energetical point of view, but is also important when counter anions are not required to be transported. Enantiopure chiral macrocycles have also drawn the attention of many researchers, because owing to their enantioselective complexation they are excellent candidates for effective sensors and selectors of the enantiomers of biologically important chiral compounds such as protonated primary organic amines, amino acids and the derivatives of the latters. Keywords molecular recognition • enantiomeric recognition • protonionizable crown ethers • chiral crown ethers • chiral stationary phases
A new fluorescent bis(acridino)-macrocycle containing two allyl groups was synthesized and photop... more A new fluorescent bis(acridino)-macrocycle containing two allyl groups was synthesized and photophysically studied. Studies were carried out on metal ion recognition and selectivity-influencing effects including the determination of the relevant thermodynamic constants as logK and pK a. The proposed sensor molecule is recommended for the development of Zn 2+-selective optochemical analyzers based on covalently immobilized ionophores as it has a unique pH-independent metal ion recognition ability, which is not influenced by anions and other potentially occurring metal ions in biological samples.
Periodica Polytechnica Chemical Engineering, May 23, 2023
Dry-column vacuum chromatographic technique is introduced for remediation of wastewater for the f... more Dry-column vacuum chromatographic technique is introduced for remediation of wastewater for the first time. A previously prepared chemically modified silica gel containing covalently immobilized Hg 2+-selective acridino-crown ether selector molecules was used as an adsorbent. Removal of Hg 2+ from highly contaminated river water was carried out to study practical applicability. Adsorption capacity, preconcentration factor, pH-sensitivity and selectivity in separation were determined. The adsorbent proved to be outstanding in selectivity, only Ag + and Cu 2+ interfered among 29 cations, was inert toward organic contaminants, exhibited regenerability and pH-independency between 3.0 ≤ pH ≤ 7.0. The proposed method showed a moderate efficiency in both adsorption (32 mg Hg 2+ / 1 g adsorbent) and preconcentration (preconcentration factor of 100). A maximum 10 L of wastewater / 1 g adsorbent ratio is recommended as an upper limit for applicability. The described method showed a unique robustness and simplicity compared to conventional ion-chromatographic methods and an improved selectivity over physical interaction-or simple functional group-based adsorptions.
In this work, anchoring of cinchona derivatives to trifunctional cores (hub approach) was demonst... more In this work, anchoring of cinchona derivatives to trifunctional cores (hub approach) was demonstrated to obtain sizeenlarged organocatalysts. By modifying the cinchona skeleton in different positions, we prepared four C3-symmetric size-enlarged cinchona derivatives (hub-cinchonas), which were tested as organocatalysts and their catalytic activities were compared with the parent cinchona (hydroquinine) catalyst. We showed that in the hydroxyalkylation reaction of indole, hydroquinine provides good enantioselectivities (up to 73% ee), while the four new size-enlarged derivatives gave significantly lower values (up to 29% ee) in this reaction. Anchoring cinchonas to trifunctional cores was found to facilitate nanofiltration-supported catalyst recovery using PolarClean alternative solvent. The C3-symmetric size-enlarged organocatalysts were completely rejected by all the applied membranes, whereas the separation of hydroquinine was found to be insufficient using organic solvent nanofiltration. Furthermore, the asymmetric catalysis was successfully demonstrated in the case of Michael reaction of 1,3-diketones and trans-β-nitrostyrene using Hub 3-cinchona (up to 96% ee) as a result of the positive effect of the C3-symmetric structure using a bulkier substrate. This means an increased selectivity of the catalyst in comparison to hydroquinine in the latter Michael reaction.
Journal of inclusion phenomena and macrocyclic chemistry, Dec 21, 2020
Studies on liquid-liquid extraction and bulk liquid membrane (BLM) technique-based metal ion sepa... more Studies on liquid-liquid extraction and bulk liquid membrane (BLM) technique-based metal ion separation by a previously published Pb 2+-selective acridono-18-crown-6 ether selector molecule were performed. The effects of the stirring speed, the quality of apolar organic membrane, the counterions of Pb 2+ , the pH of the aqueous phase, the concentration of the source phase, the concentration of the carrier in the BLM and the temperature on the Pb 2+-separation were investigated. Moreover, the effects of the competitive inhibition due to the presence of Ag + , Ca 2+ , Co 2+ , Cu 2+ , K + , Mg 2+ , Na + and Zn 2+ as competing ions in a multicomponent aqueous source phase of different ion-concentrations were also studied. After a proper dilution of the multicomponent aqueous source phase, excellent Pb 2+-selectivity was achieved without a significant reduction in the efficiency compared to the liquid membrane transport of single-component systems. Based on the BLM-cell studies the applied selector molecule proved to be suitable for the development of liquid membrane-based Pb 2+-selective separation methods, which can be greatly aided by the analysis of the effects on the separation and by the optimization of the parameters of the process discussed here.
A D A 6 196li 1i omit ft. l4lt1 0-5e-' "-'~~~W *-a IWUt' "%Wq.e~q:' (13. off fMtleOaft. Iwm" 1010... more A D A 6 196li 1i omit ft. l4lt1 0-5e-' "-'~~~W *-a IWUt' "%Wq.e~q:' (13. off fMtleOaft. Iwm" 1010 %0" tfor oewe ~WuNK~t 01m' 0*11 % otd~UI t9~otdmI9 to *eAV-w~q .4*010110iv, Sowcee. 0O.'wttorsue 'roaamfg O0wonam atu Mee. 11 j 40W4 I2Aw4. a to Ow Ote" *4q9m4 • ap•g70e• U W U11 l tie OC zorn ,nk, 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED
Synthesis of acidic new crown ethers containing a diarylphosphinic acid unit has been accomplishe... more Synthesis of acidic new crown ethers containing a diarylphosphinic acid unit has been accomplished. The aromatic rings of the crown ethers were substituted with tertbutyl and nitro groups. Nitro substitution of the crown ethers was investigated. pKa determination of the new proton-ionizable crown ethers has been performed, showing the effect of the substituents of the aromatic rings on the acidity. An anomaly was discovered in the pKa values and an explanation was given based on quantum mechanical calculations and molecular dynamics simulations.
Chemical depolymerisation, or solvolysis, can be a sustainable plastic recycling method, as a cir... more Chemical depolymerisation, or solvolysis, can be a sustainable plastic recycling method, as a circular economy can be achieved by recovering the pure monomers. Polyethylene terephthalate (PET) is a ubiquitous plastic material with short-life application and slow biodegradation, so its waste management needs to be continuously improved. In this study, we tested three commercially available organocatalystmodified silica gels in the glycolysis of PET and developed another, functionalized with triazabicyclodecene (TBD), which was also tested. Organocatalysts are efficient in PET glycolysis, but their recyclability needs to be improved for industrial application. The applied heterogeneous modified silica gels can be recovered easily by filtration. Si-TEA catalyst was chosen for reaction optimisation because it has the highest thermal stability and good catalytic activity. The PET glycolysis process was optimised by fractional factorial experimental design and response surface methodology. Under optimal reaction conditions (PET (384 mg, 2 mmol), ethylene glycol (1.41 mL, 25.2 mmol), Si-TEA (15.5 mol%), 190°C, 1.7 h), 88.5% nonisolated bis(2-hydroxyethyl) terephthalate (BHET) monomer yield was obtained. Si-TEA and Si-TBD catalysts were recycled in five reaction cycles, and with both catalysts, high cumulative BHET yields (89 and 88%, respectively) were achieved. Additionally, environmental energy impacts were calculated for the two catalysts and were compared favourably with other organocatalysts in the literature. A process scale-up was also implemented. Finally, it has been verified that modified silica gels have much higher catalytic activities than native silica gel, as solvolytic reactions using the former catalysts took a significantly shorter time.
Three cinchona derivatives have shown remarkable activity to catalyze the aza-Markovnikov additio... more Three cinchona derivatives have shown remarkable activity to catalyze the aza-Markovnikov addition reaction of N-heterocycles to vinyl esters. The synthesis of aza-Markovnikov adducts possessing valuable biological activity was thoroughly optimized. By studying the ratio of the starting materials, bases and solvents, we achieved a new and efficient protocol, which could be performed under mild conditions with a small excess of vinyl ester affording products with excellent yields and high regioselectivity. This optimization reduced Sheldon's E-factor of the reaction by 42%. Furthermore, membrane separation for catalyst recycling was assessed to further improve the sustainability of the synthesis.
Magyar kémiai folyóirat, Kémiai közlemények (Online), 2018
A közlemény alapjául Németh Tamás "Synthesis and molecular recognition studies of acridono-and ac... more A közlemény alapjául Németh Tamás "Synthesis and molecular recognition studies of acridono-and acridino-crown ether-based sensor and selector molecules" címû doktori értekezése szolgált, mely a https://doktori.hu/index.php?menuid=193&lang=HU&vid=17939 oldalon érhetõ el.
This work presents the first successful applications of cinchona-thiosquaramides in asymmetric re... more This work presents the first successful applications of cinchona-thiosquaramides in asymmetric reactions. Binaphthyl-cinchona squaramides and thiosquaramides were synthesised, and then used as organocatalysts to promote the catalytic enantioselective Michael addition reaction of pentane-2,4dione to trans-b-nitrostyrene with excellent yields (up to 99%) and enantioselectivities (up to 99% ee) at as low as 0.2 mol% catalyst loadings. Thiosquaramides gave higher enantioselectivities (up to 92% ee) in conjugate addition reaction of lawsone to b,g-unsaturated a-keto ester than its oxo analogue, with high yields (up to 100%). Also, only thiosquaramide could catalyse the aza-Diels-Alder addition reaction of 2-siloxydiene to benzylideneacetone. Furthermore, quantum chemical computations showed that the geometrical structure of binaphthyl-cinchona thiosquaramide is similar to that of squaramide.
Although ion-selective membrane-based potentiometric sensors have already proved their analytical... more Although ion-selective membrane-based potentiometric sensors have already proved their analytical performance in several fields of life, their applicability is still limited in practice. Biodegradable, ionic additive-free, polylactic acid-based bulk electrode membrane matrix containing various environmentally friendly polyethylene glycol derivatives as plasticizer was developed for the first time to replace the conventional PVC-based ones. Moreover, the first introduction of 3D printing in potentiometric chemosensing was also reported. It was demonstrated that a thoroughly optimized and generalizable procedure for filament extrusion combined with 3D printing technology provides a unique tool for series production of the redesigned ion-selective bulk electrochemical membranes. Finally, the potentiometric detection of Hg 2+ in water was carried out as a proof-of-concept study on sensing. Results showed an unexpected improvement in electrochemical characteristics of the novel membranes compared to their conventional analogues. The present work expanded the practical applicability of conventional potentiometric cation-selective electrode membranes enabling their green, decentralized, and automated state-of-the-art manufacturing using a novel matrix composition.
The class of enantiopure α,α-disubstituted α-amino acids has gained considerable attention in the... more The class of enantiopure α,α-disubstituted α-amino acids has gained considerable attention in the past decades since some of them have interesting properties as antibiotics. The synthesis of such materials has been a challenging task to which enantioselective phase transfer catalysis offers an effective solution. In our work the synthesis starts from the easily available Meldrum's acid, that is converted into the key disubstituted malonate intermediates in an asymmetric alkylation step catalyzed by cinchona-crown ether derivatives. The aim was to obtain a new type of phase transfer catalystcinchona derivatives of aza-crown ethers-and compare the achieved enantiomeric excess values, while also optimizing the reaction conditions. The amino acids are gained by the selective hydrolysis of the key intermediates followed by a multistep reaction.
During my research work cinchona-, and proline-based chiral squaramide, and thiosquaramide organo... more During my research work cinchona-, and proline-based chiral squaramide, and thiosquaramide organocatalysts were synthesized. The promising new organocatalyst class, the thiosquaramides, were gained by the thionation of the appropriate squaramide with pyridine complex of phosphorus pentasulfide. In 2017, Rawal and his co-workers were the first ones who successfully managed to apply the double hydrogen-bond donor thiosquaramides in asymmetric reactions. They recognized the great potential of this new type of catalyst. If the carbonyl groups of squaramide are converted to thiocarbonyl groups, the acidity of the hydrogen-bond unit increases which can result in stronger hydrogen bond between the substrate(s) and the catalyst. Moreover, thiosquaramides are found to be more soluble in nonpolar organic solvent than their squaramide counterparts. The synthesized organocatalysts were applied in asymmetric CC coupling reactions, furthermore, the proline-based (thio)squaramide were proved to be excellent organocatalysts for the enamine catalysed Diels-Alder reaction.
The class of enantiopure α,α-disubstituted α-amino acids has gained considerable attention in the... more The class of enantiopure α,α-disubstituted α-amino acids has gained considerable attention in the past decades since some of them have interesting properties as antibiotics. The synthesis of such materials has been a challenging task to which enantioselective phase transfer catalysis offers an effective solution. In our work the synthesis starts from the easily available Meldrum's acid, that is converted into the key disubstituted malonate intermediates in an asymmetric alkylation step catalyzed by cinchona-crown ether derivatives. The aim was to obtain a new type of phase transfer catalystcinchona derivatives of aza-crown ethers-and compare the achieved enantiomeric excess values, while also optimizing the reaction conditions. The amino acids are gained by the selective hydrolysis of the key intermediates followed by a multistep reaction.
Nowadays, the recovery of organocatalysts is a crucial issue considering both environmental and e... more Nowadays, the recovery of organocatalysts is a crucial issue considering both environmental and economic aspects. An effective and simple solution to meet this challenge is to change the solubility of the reaction components compared to each other. To reach this aim, lipophilic side chain can be incorporated into the organocatalyst. This causes a considerable difference in the polarity, which allows the catalyst and the other components of the reaction mixture to be separated from one another by filtration after changing the solvent or by an extraction step. Our aim was to develop a new synthetic method for the incorporation of a lipophilic moiety into the catalysts. At first, starting from methyl gallate, we prepared a carboxylic acid derivative containing three octadecyl groups. This lipophilic unit was then linked in an amide formation reaction to a cinchona squaramide organocatalyst (through an aminoethyl linker), which had previously led to excellent enantioselectivity in Michael reactions. In the amide formation, we examined the acyl chloride pathway and coupling agents as well. We plan to apply the gained lipophilic catalyst in various asymmetric conjugate addition reactions.
This short review summarizes the synthesis and molecular recognition studies of crown ether type ... more This short review summarizes the synthesis and molecular recognition studies of crown ether type macrocycles accomplished at the Institute for Organic Chemistry of Budapest University of Technology and Economics in the last few years. The research work reported here belongs to the areas of protonionizable crown ethers and chiral macrocycles. Proton-ionizable crown ethers at higher pH s than their pK a values are mostly ionized to ligand anions which increase the cation-ligand complex stability with enhancement of selectivity and avoid the need for a counter anion to accompany the cation transport or solvent extraction. The latter factor is not only advantageous from energetical point of view, but is also important when counter anions are not required to be transported. Enantiopure chiral macrocycles have also drawn the attention of many researchers, because owing to their enantioselective complexation they are excellent candidates for effective sensors and selectors of the enantiomers of biologically important chiral compounds such as protonated primary organic amines, amino acids and the derivatives of the latters. Keywords molecular recognition • enantiomeric recognition • protonionizable crown ethers • chiral crown ethers • chiral stationary phases
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