An FTIR Spectroscopic Study on the Effect of Molecular Structural Variations on the CO2 Absorption Characteristics of Heterocyclic Amines

Herein, the reaction between CO₂ and piperidine, as well as commercially available functionalised piperidine derivatives, for example, those with methyl‐, hydroxyl‐ and hydroxyalkyl substituents, has been investigated. The chemical reactions between CO₂ and the functionalised piperidines were followed in situ by using attenuated total reflectance (ATR) FTIR spectroscopy. The effect of structural variations on CO₂ absorption was assessed in relation to the ionic reaction products identifiable by IR spectroscopy, that is, carbamate versus bicarbonate absorbance, CO₂ absorption capacity and the mass‐transfer coefficient at zero loading. On absorption of CO₂, the formation of the carbamate derivatives of the 3‐ and 4‐hydroxyl‐, 3‐ and 4‐hydroxymethyl‐, and 4‐hydroxyethyl‐substituted piperidines were found to be kinetically less favourable than the carbamate derivatives of piperidine and the 3‐ and 4‐methyl‐substituted piperidines. As the CO₂ loading of piperidine and the 3‐ and 4‐methyl‐ and hydroxyalkyl‐substituted piperidines exceeded 0.5 moles of CO₂ per mole of amine, the hydrolysis of the carbamate derivative of these amines was observed in the IR spectra collected. From the subset of amines analysed, the 2‐alkyl‐ and 2‐hydroxyalkyl‐substituted piperidines were found to favour bicarbonate formation in the reaction with CO₂. Based on IR spectral data, the ability of these amines to form the carbamate derivatives was also established. Computational calculations at the B3LYP/6‐31+G** and MP2/6‐31+G** levels of theory were also performed to investigate the electronic/steric effects of the substituents on the reactivity (CO₂ capture performance) of different amines, as well as their carbamate structures. The theoretical results obtained for the 2‐alkyl‐ and 2‐hydroxyalkyl‐substituted piperidines suggest that a combination of both the electronic effect exerted by the substituent and a reduction in the exposed area of the nitrogen atom play a role in destabilising the carbamate derivative and increasing its susceptibility to hydrolysis. A theoretical investigation into the structure of the carbamate derivatives of these amines revealed shorter N? C bond lengths and a less‐delocalised electron distribution in the carboxylate moiety.     

Conformational analysis. Part 16 Conformational free energies in substituted piperidines and piperidinium salts

Summary The conformational free energies (-G^o) of a number of 4-substituted piperidines and piperidinium salts have been determined by the J-value method. For the 4-substituted piperidines (R=Me, Phenyl, CO₂Et, Br, OH, F) the relative conformer energies are almost identical to those of the analogous cyclohexanes.The methyl and phenyl compounds showed no change in the couplings on protonation, implying no change in the conformer energies. In constrast, in the remaining compounds with polar 4-substituents an almost constant stabilisation of the axial conformer of ca. 0.7–0.8 kcal mol^-1 was observed on protonation. In three cases (R=F, OH and Br) the conformational preferences is reversed on protonation and the axial form is favoured.The conformer energies of both the free bases and the piperidinium salts can be quantitatively predicted by molecular mechanics calculations using the COSMIC force-field, in which the electrostatic interactions are calculated by a simple Coulombic model with the partial atomic charges in the molecules given by the CHARGE2 routine, and an effective dielectric constant of five. The precise agreement obtained demonstrates conclusively that the electrostatic interactions between the substituents and the protonated nitrogen are the cause of the conformational changes on protonation, and that these can be modelled successfully using existing force-fields.For Part 15, see Ref. 1.     

Electrochemistry of 2-dimethylaminoethanethiol SAM on gold electrode: Interaction with SWCNT-poly(m-aminobenzene sulphonic acid), electric field-induced protonation–deprotonation,and surface pKa

Electrochemical behaviour of self-assembled monolayer of 2-dimethylaminoethanethiol (DMAET) on gold electrode, with and without integration with SWCNT-poly(m-aminobenzene sulphonic acid) (SWCNT-PABS) has been probed. It is proved that the so-called electric field induced protonation–deprotonation process, hitherto observed for the –COOH terminated SAMs, is also observed for the –N(H)⁺(CH₃)₂ terminated. The surface pK_a of DMAET was estimated as 7.6, smaller than its solution pK_a of 10.8. It is also shown that SWCNT-PABS is irreversibly attached to the DMAET SAM.     

Correlation of singlet energies of aromatic hydrocarbons with the rates of protonation of their anion radicals

Formation and protonation of aromatic anion radicals in 2-propanol were studied by kinetic spectrophotometric pulse radiolysis. All polycyclic hydrocarbons studied were found to react very rapidly with e^?_solv. Those with relatively high electron affinity were also reduced by (CH₃)₂CO^?. The anion radicals formed undergo protonation by direct reaction with the alcohol molecule. The rate constants for this protonation vary from ≈ 6 × 10⁵ s^?1 for cis-stilbene and naphthalene down to 20 s^?1 for perylene. The variations in rates are discussed in terms of changes in singlet energy separation (ΔE_{S1 ← S0}). The logarithm of the protonation rate constant for alternant hydrocarbons is linearly dependent on ΔE_{S1 ← S0}.     

The effect of benzyl amine on the efficiency of the base-catalyzed transamination of α-keto esters

This paper describes the effect of benzyl amine on the base-catalyzed transamination of α-keto esters. Among various benzyl amines examined, o-HOC₆H₄CH₂NH₂ was found to be highly effective for the reaction, affording a wide variety of α-amino esters in good yields. The o-OH group of the benzyl amine facilitates the transamination process likely via H-bond. Moderate enantiomeric excess was obtained for α-amino ester when a quinine derived catalyst was used.     

Characterization of the decomposition course of nickel acetate tetrahydrate in air

Thermogravimetry, differential thermal analysis, X-ray diffractometry and infrared spectroscopy showed that Ni(CH₃COO)₂·4H₂O decomposes completely at 500°C, giving rise to a mixture of Ni^o and NiO. The results revealed that the compound undergoes dehydration at 160°C and melts at 310°C. The water thus released hydrolyses surface acetate groups, acetic acid being evolved into the gas phase. At 330°C, the anhydrous acetate is converted into NiCO₃, releasing CH₃COCH₃ into the gas phase. The carbonate subsequently decomposes (at 365°C) to give NiO_(s), CO_2(g) and CO_(g). On further heating up to 373°C, a mixture of Ni^o and NiO is formed. Other gas-phase products were detected at 400°C, viz. CH₄ and (CH₃)₂CH=CH₂, which were formed in surface reactions involving initial gas-phase products. Non-isothermal kinetic parameters (A and ΔE) were calculated on the basis of temperature shifts experienced in the various decomposition processes as a function of heating rate (2–20 deg·min^?1).     

Photofragmentation of alpha-oxocarboxylic acids in aqueous solution. An EPR study. Formation of semidione radicals by decarboxylative substitution of alpha-oxocarboxylic acids by acyl radicals--II. Oxaloacetic acid (oxosuccinic acid).

Abstract— –On in situ photolysis (Λ= 250–400 nm) of aqueous oxaloacetic acid solutions, between pH 5 and 10, the radicals ^-O₂CCH₂C(O^->=C(O⁺)CH₂CO₂^- and ^-O₂CCH₂C(OH)CO₂ are identified. With acetone present, CH₂CO₂, CH₃C(OH)CO^-₂, CH₃C(O^-)=C(O)CH₂CO₂ and -O₂CCHCOCO₂ are also observed. CO₂ and CO are identified as reaction products. The experimental results are explained in terms of α-cleavage of the electronically excited keto-isomer dianion of oxaloacetic acid to yield O₂CCH₂CO and CO₂^-. ^-O₂CCH₂CO adds to the keto-isomer of oxaloacetic acid and to pyruvic acid, which is formed from oxaloacetic acid by thermal decarboxylation, to yield ^-O₂CCH₂C(O^-)= C(O^-)CH₂C0^- and CH₃C(O^-)=C(O)CH₂CO^-₂, respectively, via a decarboxylase substitution reaction. CH₂CO₂ is derived from ^-O₂CCH₂CO by decarbonylation. CO₂^- is scavenged by oxaloacetic acid and pyruvic acid to yield O₂CCH₂C(OH)CO₂ and CH₃C(OH)CO₂^-, respectively.     

Decarbonation curves and associated thermodynamic data for synthetic Cd-dolomites CdMg(CO3)2, CdMn(CO3)2 and CdZn(CO3)2

Decarbonation curve for the synthetic dolomite analogues; (Cd-dolomites) were determined for CdMg(CO₃)₂, CdMn(CO₃)₂ and CdZn(CO₃)₂ under CO₂ pressure of up to 2.5 kbar. All the three double carbonates were completely disordered at the decomposition temperatures and hence the thermodynamic data (Standard enthalpy; ΔH _f ^o, Standard free energy; ΔG _f ^o) retrieved from the univariant decarbonation curve corresponds to the disordered phases. They are: The mixing enthalpies and free energies for the formation of the disordered 1∶1 solid solution phases are: The thermodynamic data (ΔH _f ^o, ΔG _f ^o and ΔH _r ^o, ΔG _r ^o) showed a positive correlation with the decomposition temperatures. The mixing energies of the disordered double carbonates also show a direct correlation with the cationic size differences.     

Theoretical studies of the functionalized derivatives of fullerene C24H24 by attaching a variety of chemical groups

Based on the D_6d-symmetrical C₂₄H₂₄ fullerene, its derivatives, which have been exohedrally functionalized by replacing one of its H atoms with –CH₂OH, –CONH₂, –COOH, and –COH, have been firstly calculated using the hybrid DFT-B3LYP functional in conjunction with 6-31G(d) basis sets. Present calculations show that the C₂₄H₂₃(COOH) is the most stable under the values of ΔH and D_e. The calculated HOMO–LUMO energy gaps of the derivatives with –CH₂OH and –COOH groups are same as in the case of the not functionalized C₂₄H₂₄ cluster. In addition, the C₂₄H₂₃(CONH₂) displays the largest dipole moment (3.32 D), and the vertical electron affinities of the functionalized derivatives are all very higher. These can promote new development in the fields of the bio-medical applications.     

Effect of protonation exothermicity on the reaction of gaseous Brønsted acids with halobenzene derivatives

The protonation of haloaromatics by [N₂H]⁺ and [CO₂H]⁺ has been studied by chemical ionization mass spectrometry. In general, the fragmentation reactions following protonation by [CO₂H]⁺ are similar to those observed following protonation by [CH₅]⁺, while the fragmentation reactions induced by protonation by [N₂H]⁺ are intermediate between those observed on reaction with [CH₅]⁺ and with [H₃]⁺. These results are consistent with the conclusion that the fragmentation mode is determined by the protonation exothermicity since the proton affinity of CO₂ is the same as that of CH₄ while the proton affinity of N₂ is intermediate between that of CH₄ and H₂.     

Influence des effets de substituants sur la protonation de la pyridine

Standard thermodynamic values of proton ionisation of 3 substituted (Cl?, Br?, I?, C₂H₅? and CH₂CN?) pyridine derivatives are determined at 25°C, in an aqueous medium of ionic strength 0.5 M KNO₃.Free energies are deduced from equilibrium constants log K potentiometrically calculated. Enthalpies are obtained from calorimetric measurements.ΔG^o, ΔH^o and ΔS^o values are discussed in the context of the results of our earlier studies on this subject.The Hammett plot corresponding to the thirteen systems examined gives the proton ionisation constant of a substituted pyridine from the equation log K = 5,48 – 5,94Σσ.Besides, a linear relationship is found between ΔG^o and ΔH^o, which confirms the observation made previously in other series of pyridine derivatives.     

Obtaining thin films of “reactive polymers” on metal surfaces by electrochemical polymerization: Part II. Alcohol substituted polyphenylene oxide films

The selective electrochemical oxidation of the phenol function in the case of hydroxymethyl phenol derivatives (o^?, m^?, p-hydroxybenzyl alcohol) leads to “reactive polymer” films of polyphenylene oxide substituted by CH₂OH groups. The transformation of the hydroxyl function into an ester function by acetyl chloride indicates the reactivity of the CH₂OH group. As for the family of carbonylated polyphenylene oxide films, reactivity is limited to the superficial layers of film. Average film thickness is between 50–100 nm; however with the ferrocene-ferricinium system acting as a redox catalyst, it can reach about 300 nm. This catalytic mechanism intervenes only when the oxidation potential of the ferrocene-ferricinium couple is very similar to that of the phenol derivative.     

The thermodynamic characteristics of complex formation between vanadium(V) and malonic acid

Coordination and protolytic equilibria in the system vanadium(V)-malonic acid were studied calorimetrically at 298.15 K and I = 1.0(NaClO₄). The heat effects of formation of the VO₂CH₂(COO) ₂ ^? complex and step protonation of the malonate ion were determined for the first time. The data obtained were used to calculate the thermodynamic characteristics (logK, ΔG, ΔH, and ΔS) of the equilibria studied.     

Amine catalysis in phosphoryl transfer from 2,4-dinitrophenyl phosphate in aprotic and protic solvents

Reactions of tetra-n-butylammonium 2,4-dinitrophenyl hydrogen phosphate, (ArPH)^?(R₄N)⁺, in aprotic and protic solvents, in the absence and in the presence of alcohols or water, ROH, are compared with analogous reactions of the salt in the presence of hindered and unhindered amines, e.g. diisopropylethyl amine and quinuclidine. Similar studies are performed with the acid, ArPH₂, in the presence of variable amounts of amines. The release of phenol and the fate of the phosphorus compounds are followed by ¹H and ³¹P NMR spectrometry. In the absence of free unhindered amine, reactions of the monoanion are relatively slow, sensitive to steric hindrance in the alcohol, and incapable of producing t-butyl phosphate from t-butanol; reactions of the dianion are relatively fast, insensitive to steric hindrance in the alcohol, and produce t-butyl phosphate. In the presence of free unhindered amine, reactions of the monoanion are relatively fast but still sensitive to steric hindrance in the alcohol, and hence do not produce t-butyl phosphate. The intermediate CH(CH₂CH₂)₃⁺NP(O)(OH)O^? is detected in the presence of quinuclidine. Reactions of the dianion in the presence of unhindered amines are analogous to those observed in the presence of hindered amines. The uncatalyzed and the nucleophilic amine-catalyzed reactions of the monoanion are assumed to proceed via oxyphosphorane, P(5), intermediates. The dianion reactions, which are not susceptible to nucleophilic catalysis, are assumed to proceed via the monomeric metaphosphate ion intermediate, PO₃^?. Significant effects related to solvent properties are observed in these reactions.     

A thermodynamic investigation of the nickel(II) chloride-acetonitrile system

Equilibrium vapor pressures were determined at temperatures between 294 K and 353 K for the NiCl₂-CH₃CN system.Compositions studied ranged from molar ratios of CH₃CN to NiCl₂ of 0.27 to 1.90. Three stoichiometric compounds were identified: NiCl₂(CH₃CN)₂, NiCl₂(CH₃CN), NiCl₂(CH₃CN)0.88. Per mole of gaseous CH₃CN the values of ΔH^o and ΔS^o were calculated to be 52.0 ±0.4 kJ mol^?1 and 149.0±1.3 J mol^?1 K^?1 for the decomposition of NiCl₂(CH₃CN)₂, and 25.9 ±0.8 kJ mol^?1 and 58.6± 2.1 J mol^?1 K^?1 for the decomposition of NiCl₂(CH₃CN). Below a composition of NiCl₂(CH₃CN)_0.88 the phase diagram is complex and could not be interpreted in terms of specific stoichiometric compounds.     

Dominant factors affecting the pressure dependence of melting temperatures in homologous series of aliphatic polyesters

The pressure dependence of the melting temperature of six aliphatic polyesters belonging to two different homologous series, poly(x-succinate) and poly(x-adipate) having even number of methylene groups (2,4,6) in the alkylene segment (x) was investigated by high pressure differential thermal analysis (HP-DTA) up to 500 MPa. The phase diagrams of these polyesters were newly determined except for poly(ethylene adipate). The dT_m/dp_o at atmospheric pressure was obtained from the quadratic equation and the trend of dT_m/dp_o with respect to the number of methylene groups in the monomer unit in each homologous series is discussed. Amorphous densities at 25 °C, expansion and compressibility coefficients in the melt of these polyesters are also reported. The entropy of fusion (ΔS_m), enthalpy of fusion (ΔH_m), volume change on melting (ΔV_m), conformational entropy (ΔS^or) and volume entropy (ΔS^v) were correlated with respect to the number of methylene groups in the alkylene segment. ΔV_m and ΔS^v displayed a similar trend as that of dT_m/dp_o while ΔS_m, ΔS^or and ΔH_m showed an increasing trend. The influence of these parameters on dT_m/dp_o is discussed in the context of the Clapeyron equation.     

New DTPA-derived bis-naphthalenophanes: fluorescence,protonation, and complexation with aromatic amines

Two fluorescent, water-soluble bis-naphthalenophane isomers with six carboxylate arms, abbreviated as (bis-dtpa14nap)H₆ and (bis-dtpa15nap)H₆, were synthesized, which consist of two 1,4- or 1,5-substituted naphthalene rings interlinked by two diethylenetriaminepentaacetic (DTPA) chains through amide-linkages. Both DTPA-based macrocycles exhibit intense excimer and monomer emission bands, which sensitively respond to pH in three protonation steps; more sensitive is the 1,4-naphthyl isomer. The full pH-emission profiles have confirmed that the mono-protonated anion (bis-dtpanap)H₅ ^? is the major protonation species at the physiological pH. Fluorometric titrations at pH 7.2 have proven that the 1,4-naphthalenophane anion forms 1:1-complexes with cationic phenethylamine (formation constant, 5700 M^?1) and histamine (3000 M^?1), excluding tryptamine cation, whereas the 1,5-isomer does not react with any of the three amines. The primary binding forces are electrostatic interactions between the CH₂CO₂ ^? arms of 1,4-naphthalenophane and the CH₂CH₂NH₃ ⁺ chain of an aromatic amine. The resulting ion-pair is stabilized by encapsulation of the guest molecule in 1,4-napthalenophane cavity, while the 1,5-isomer cannot encapsulate. NMR studies have demonstrated that 1,4-napthalenophane has a higher freedom in reorientation of naphthalene rings. Such geometrical properties controlled by selection of naphthalene units are the feature of the new naphthalenophanes, and are responsible for the pH?emission profiles and the complexation.     

Experimental and theoretical evidence suggests carbamate intermediates play a key role in CO2 sequestration catalysed by sterically hindered amines

The chemisorption of CO₂ by aqueous-hindered amines has been investigated experimentally and theoretically. Negative-ion ESI–MS analysis of solutions containing a sterically hindered amine and a source of ¹³CO₂ reveals peaks corresponding to [M–H + 45]^?. These ions readily lose 45 Da when subjected to collisional activation, and together with other key fragments confirms the generation of the ¹³C-labelled carbamate derivatives. The thermochemistry of the two key capture reactions: $$2.{\text{amine }} + {\text{ CO}}_{ 2} { \leftrightarrows }{\text{amine}} - {\text{CO}}_{ 2}^{ - } + {\text{ amine}} - {\text{H}}^{ + } {\kern 1pt} \quad 1:{\text{carbam}}$$ $${\text{amine }} + {\text{ CO}}_{ 2} + {\text{ H}}_{ 2} {\text{O}}{ \leftrightarrows }{\text{HCO}}_{ 3}^{ - } + {\text{ amine}} - {\text{H}}^{ + } \quad 2:{\text{ bicarb}}$$ at 298 K was modelled using composite chemistry methods, CCSD(T), DFT, and SM8 free energies of solvation. The aqueous reaction free energies (ΔG ₂₉₈) for reaction 1 are predicted to be more negative than ΔG ₂₉₈ for reaction 2 when amine = ammonia, 2-aminoethanol (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-hydroxymethyl-propane-1,3-diol (tris), and 2-piperidinemethanol (2-PM). For AMP, tris, and 2-PM, activation free energies ΔG ₂₉₈ ^? for reaction 1 (SM8 + CCSD(T)/6-311 ++G(d,p)//M08-HX/MG3S: 38–67 kJ mol^?1) are smaller than the corresponding values for 2 (109–113 kJ mol^?1). For 2-PM, the computed carbamate ΔG ₂₉₈ ^? (38 kJ mol^?1) is comparable to the MEA value (45 kJ mol^?1), whereas the primary amines with tertiary alpha carbons have slightly larger values (60–70 kJ mol^?1). The organic amine values are much lower than the value for ammonia (93 kJ mol^?1). The results indicate CO₂ chemisorption proceeds via a carbamate intermediate for all aqueous primary and secondary amines. Hindered carbamates are susceptible to further chemical transformations following their formation.     

Synthesis and structural characterization of diorganotin(IV) esters with pyruvic acid isonicotinyl hydrazone and pyruvic acid salicylhydrazone Schiff bases

Eight diorganotin esters of Schiff base ligands formulated as [R₂SnLY]₂, where L₁ is 4-NC₅H₄CON₂C(CH₃) CO₂ with Y = H₂O, R = Ph (1), PhCH₂ (2), m-ClC₆H₄CH₂ (3), and L₂ is 2-HOC₆H₄CON₂C(CH₃) CO₂ with Y = CH₃OH, R = PhCH₂ (4), o-ClC₆H₄CH₂ (5), m-ClC₆H₄CH₂ (6), o-FC₆H₄CH₂ (7), p-FC₆H₄CH₂ (8) have been prepared and characterized by elemental analysis, IR, ¹H and ¹¹⁹Sn NMR spectra. The crystal structures of compounds 1, 2 and 4 have been determined by X-ray single crystal diffraction. Their structures show that the tin atoms of three compounds are all rendered seven-coordinated in distorted pentagonal bipyramid geometries with a planar SnO₄N unit and two apical aryl carbon atoms. A comparison of the IR spectra of the ligands with those of the corresponding compounds, reveals that the disappearance of the bands assigned to carbonyl unambiguously conforms that the ligands coordinate with tin in the enol form.     

Platinum-promoted cyclization reactions of amino-olefins : I. The cyclization of 4-aminopentene and related compounds

Olefinic amines of the ytpe CH₂CH(CH₂)_nNHR undergo cyclization in acidic aqueous solution at 60°C in the presence of PtCl₄^2?. The PtCl₄^2? is regenerated at the end of the cyclization so that the reaction may be considered as catalytic. Both pyrrolidines and piperidines may be formed although the former are favored.