Solvent effect in the chromatographic enantioseparation of 1,1′-bi-2-naphthol on a polysaccharide-based chiral stationary phase

Enantioseparation of 1,1′-bi-2-naphthol (BINOL) was performed on a polysaccharide-based chiral stationary phase, Chiralcel OD-H, under normal-phase mode. The effects of polar modifier in the mobile phase on the retention, enantioseparation and elution order were investigated in detail. Solvent-induced reversal of elution order for BINOL was observed. When linear alcohols were adopted, R-BINOL was always eluted first. S-BINOL was eluted first when 2-propanol was used as a polar modifier. Enantioseparation could not be obtained when sec-butyl alcohol or tert-butyl alcohol was used as a polar modifier. When isoamyl alcohol or cyclohexanol was used as a polar modifier, favorable enantioseparation was obtained as with 1-pentanol or 1-hexanol; also, R-BINOL was the first-eluted enantiomer. It is worth emphasizing that significantly better enantioseparation was obtained when higher alcohols were used as polar modifier of the mobile phase. A nonlinear characteristic for the ln α against 1/T plots was universally observed in this study though the ln k against 1/T plots exhibited a linear feature. Associated with the obtained thermodynamic parameters, some interesting inferences about chiral recognition mechanism were proposed.     

Development and validation of a chiral HPLC method for rapid screening of allylic alcohol asymmetric epoxidation processes

A simple and rapid HPLC method has been developed using a polysaccharide chiral stationary phase (Chiralpak AD-H) for the resolution of glycidyl tosylate enantiomers. These compounds were obtained by asymmetric epoxidation of allyl alcohol with chiral titanium-tartrate complexes as catalyst after in situ derivatization of the intermediate glycidols. Separations were achieved using two types of mobile phase: a normal-phase (n-hexane), and a polar-phase (methanol or acetonitrile). The influence of the type and concentration of organic modifier in the mobile phase (ethanol or 2-propanol), the flow rate and the column temperature was investigated. In normal-phase mode, the optimized conditions were: n-hexane/ethanol 70/30 (v/v) at a flow rate of 1.2 mL min⁻¹ and 40 °C. In polar-phase mode, the optimized conditions were: methanol at a flow rate of 0.8 mL min⁻¹ and 20 °C. In both cases, analysis time was ≤11 min and the chiral resolution was ≥2. Nevertheless, due to the better Rs obtained in normal-phase mode, only this method was validated to avoid peaks overlapping in real samples. This method was found to be linear in the 5-300 μg mL⁻¹ range (R² > 0.999) with an LOD of 1.5 μg mL⁻¹ for both glycidyl tosylate enantiomers. Repeatability and intermediate precision at three different concentrations levels were below 0.5 and 7.2% R.S.D. for retention time and area, respectively. This method was applied successfully for the determination of glycidyl tosylate enantiomers after in situ derivatization of glycidols obtained in allylic alcohol asymmetric epoxidation processes with chiral titanium-tartrate complexes as catalysts.     

High-performance liquid chromatographic enantioseparation of monoterpene-based 2-amino carboxylic acids on macrocyclic glycopeptide-based phases

The enantiomers of five monoterpene-based 2-amino carboxylic acids were directly separated on chiral stationary phases containing macrocyclic glycopeptide antibiotics such as teicoplanin (Astec Chirobiotic T and T2) and teicoplanin aglycone (Chirobiotic TAG) as chiral selectors. The effects of pH, the mobile phase composition, the structure of the analyte and temperature on the separations were investigated. Experiments were performed at constant mobile phase compositions in the temperature range 10–40 °C to study the effects of temperature and thermodynamic parameters on separations. Apparent thermodynamic parameters and T_iso values were calculated from plots of ln k or ln α versus 1/T. Some mechanistic aspects of the chiral recognition process are discussed with respect to the structures of the analytes. It was found that the enantioseparations were in most cases enthalpy driven. The sequence of elution of the enantiomers was determined in all cases.     

Simultaneous separation of five fluoroquinolone antibiotics by capillary zone electrophoresis

A chiral separation method for glycidol enantiomers determination by normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry was developed. Two chiral stationary phases, amylose tris-(3,5-dimethylphenylcarbamate) (Chiralpak AD-H) and (S)-indoline-2-carboxylic acid and (R)-1-(α-naphthyl) ethylamine (SUMICHIRAL OA-4900) have been investigated. The effects of the mobile phase composition, elution program and column temperature were also studied. Under the best conditions: Chiralpak AD-H column, mobile phase composition n-hexane:ethanol (70:30, v/v), flow rate of 0.8 mL/min and 40 °C column temperature, a good resolution (Rs = 1.6) for both enantiomers has been achieved with an analysis time of 16 min. The method was found to be linear in the range from 100 to 500 ppm for both glycidol enantiomers with a good determination coefficient (r² higher than 0.99) and good precision. Limits of detection of 31 and 50 ppm for (R)-(+)-glycidol and (S)-(−)-glycidol, respectively, were obtained. The method was applied to the determination of the enantiomeric excess and yield obtained in a asymmetric epoxidation process of allyl alcohol with a chiral titanium-tartrate complex as catalyst.     

Enantioseparation of paroxetine intermediate on an amylose-derived chiral stationary phase by supercritical fluid chromatography

The enantioseparation of trans-3-ethoxycarbonyl-4-(4′-fluorophenyl)-1-methyl piperidine-2,6-dione (3), which is one of the important racemic precursors of trans-(−)-paroxetine, has been investigated using supercritical fluid chromatography on a Daicel Chiralpak AD column. Supercritical CO₂ modified with methanol, ethanol and 2-propanol were used as mobile phase. The influence of type and concentration of alcohol modifier on retention factor, enantioselectivity and resolution were studied. Among methanol, ethanol and 2-propanol, 2-propanol was proved to be the most favorable modifier, and 9.5% (v/v) of 2-propanol was the preferred concentration at which racemate 3 could be separated with resolution of 15.86 and retention factor of 6.323. The effects of pressure and temperature were investigated at 9.5% (v/v) of 2-propanol in the pressure range of 12–24 MPa and temperature range of 303.15–318.15 K. It was found that the lower pressure and temperature were favorable to the enantioseparation. Using van’t Hoff plot, the isoenantioselective temperature was calculated to be 410 K. The enantioseparation process was “enthalpically driven” under experimental conditions. Finally, the retention factors were satisfactorily correlated by a simplified lattice–fluid model with average absolute relative deviation (AARD%) of both enantiomers smaller than 1.76%.     

Chiral Separation of Tenatoprazole and Several Related Benzimidazoles by Normal Phase LC Using Amylose-Based Stationary Phase

Simple and efficient analytical LC methods using amylose-based stationary phase Chiralpak AS-H were developed for direct enantioseparation of tenatoprazole and several related benzimidazoles. The chromatographic experiments were performed in the normal phase mode with n-hexane–ethanol–triethylamine (TEA) as mobile phase. The effects of the mobile phase additive, concentration of organic modifiers and column temperature were studied for the enantioseparation. The thermodynamic parameters were also calculated from the van’t Hoff plots. It was found that the enantioseparations were all enthalpy driven. The enantiomers of all compounds were resolved (R _s  > 3.3) within 14 min using n-hexane–ethanol–TEA (20:80:0.1%, v/v/v) as mobile phase with a flow rate of 0.4 mL min^?1 at 40 °C. The optimized method was validated for determination of the enantiomers of tenatoprazole in terms of linearity, precision and accuracy according to ICH guidelines and applied to the assay of tenantoprazole bulk drugs. The proposed method was shown to be accurate and suitable for the quantitative determination of tenatoprazole enantiomers.     

Enantioseparation of planar chiral ferrocenes on cellulose-based chiral stationary phases: Benzoate versus carbamate pendant groups

In this study, the enantioseparation of 14 planar chiral ferrocenes containing halogen atoms, and methyl, iodoethynyl, phenyl, and 2-naphthyl groups, as substituents, was explored with a cellulose tris(4-methylbenzoate) (CMB)-based chiral column under multimodal elution conditions. n-Hexane/2-propanol (2-PrOH) 95:5 v/v, pure methanol (MeOH), and MeOH/water 90:10 v/v were used as mobile phases (MPs). With CMB, baseline enantioseparations were achieved for nine analytes with separation factors (α) ranging from 1.24 to 1.77, whereas only three analytes could be enantioseparated with 1.14 ≤ α ≤ 1.51 on a cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC)-based column, used as a reference for comparison, under the same elution conditions. Pendant group–dependent reversal of the enantiomer elution order was observed in several cases by changing CMB to CDMPC. The impact of analyte and chiral stationary phase (CSP) structure, and MP polarity on the enantioseparation, was evaluated. The two cellulose-based CSPs featured by different pendant groups were also compared in terms of thermodynamics. For this purpose, enthalpy (ΔΔH°), entropy (ΔΔS°) and free energy (ΔΔG°) differences, isoenantioselective temperatures (T_iso), and enthalpy/entropy ratios (Q), associated with the enantioseparations, were derived from van ’t Hoff plots by using n-hexane/2-PrOH 95:5 v/v and methanol/water 90:10 v/v as MPs. With the aim to disclose the functions of the different substituents in mechanisms and noncovalent interactions underlying analyte–selector complex formation at molecular level, electrostatic potential (V) analysis and molecular dynamics simulations were used as computational techniques. On this basis, enantioseparations and related mechanisms were investigated by integrating theoretical and experimental data.     

Determination of Chiral Impurity of Naproxen in Different Pharmaceutical Formulations Using Polysaccharide-Based Stationary Phases in Reversed-Phased Mode

A novel, validated, reversed-phase (RP), chiral high performance liquid chromatography (HPLC) method was developed for the enantiopurity control analysis of naproxen, a frequently used non-steroidal anti-inflammatory agent using polysaccharide-type chiral stationary phase (CSP). In the screening phase of method development, seven columns were tested in polar organic (PO) mode using mobile phases consisting of 0.1% acetic acid in methanol, ethanol, 2-propanol, and acetonitrile. Enantiorecognition was observed only in five cases. The best enantioseparation was observed on a Lux Amylose-1 column with 0.1% (v/v) acetic acid in ethanol with a resolution (R_s) of 1.24. The enantiomer elution order was unfavorable, as the distomer eluted after the eutomer. When the ethanolic mobile phase was supplemented with water, enantiomer elution order reversal was observed, indicating a difference in the enantiorecognition mechanism upon switching from PO to RP mode. Furthermore, by changing ethanol to methanol, not only lower backpressure, but also higher resolution was obtained. Subsequent method optimization was performed using a face-centered central composite design (FCCD) to achieve higher chiral resolution in a shorter analysis time. Optimized parameters offering baseline separation were as follows: Lux Amylose-1 stationary phase, thermostated at 40 °C, and a mobile phase consisting of methanol:water:acetic acid 85:15:0.1 (v/v/v), delivered with 0.65 mL/min flow rate. Using these optimized parameters, a R_s = 3.21 ± 0.03 was achieved within seven minutes. The optimized method was validated according to the ICH guidelines and successfully applied for the analysis of different pharmaceutical preparations, such as film-coated tablets and gel, as well as fixed-dose combination tablets, containing both naproxen and esomeprazole.     

Enantiospecific resolution of rabeprazole by liquid chromatography on amylose-derived chiral stationary phase using photo diode array and polarimetric detectors in series

A simple and rapid liquid chromatographic method for enantioselective separation and determination of R-(+) and S-(−) enantiomers of rabeprazole in drugs and pharmaceuticals using photo diode array (PDA) and polarimetric detectors connected in series was developed. Chiralpak AD-H (250 mm × 4.6 mm) 5 μm column packed with amylose tris(3,5-dimethylphenyl carbamate) as a stationary phase and the mobile phase containing n-hexane:ethanol:2-propanol(75:15:10, v/v/v) in an isocratic mode has yielded baseline separation with resolution greater than 3.0 at 40 °C. Effects of ethanol, 2-propanol and temperature on separation were studied for optimum resolution. Lansoprazole sulphone was used as an internal standard (IS) for quantitative determination of individual enantiomers in bulk drugs as well as pharmaceutical formulations. The method was validated in terms of accuracy, precision and linearity according to ICH guidelines. The linearity of the method was studied in the range of 0.5-50 μg/ml and the r² was >0.9997. The inter- and intra-day precision of assay were determined (R.S.D. < 1%) and the recoveries were in the range of 99.63-100.22% with <1% R.S.D. The limits of detection (LOD) and quantification (LOQ) were 0.02 μg/ml and 0.07 μg/ml for both the enantiomers, respectively.     

Reversal of Elution Order between Enantiomers of Binaphthol on an Immobilized Polysaccharide-Based Chiral Stationary Phase

Enantioseparation of 1,1??-bi-2-naphthol (BINOL) was performed on an immobilized polysaccharide-based chiral stationary phase (CSP), Chiralpak IA, in the normal-phase mode. The effects of polar modifier in the mobile phase and column temperature on retention, enantioseparation, and elution order were investigated. An interesting reversal of elution order for BINOL was observed. When ethanol was used as a polar modifier, R-BINOL was eluted first with marginal enantioseparation. Excellent enantioseparation was obtained when ethanol was replaced by 1-propanol, and S-BINOL was eluted first, this effect being retained with 2-butanol, 1-butanol, 1-pentanol or 1-hexanol as the modifier. When isoamyl alcohol was used, reversal of elution order was again observed, i.e., R-BINOL eluted first with marginal enantioseparation, similar to the case of ethanol. When cyclohexanol and cyclopentanol were used, R-BINOL was still eluted first, but enantioseparation was as good as with 1-propanol as the modifier. This is the first report of large enantioseparation obtained in both elution orders for a given selector/selectant system. A retention model based on stoichiometric displacement theory for retention (SDT-R) was investigated to fit the chromatographic data. The reason for solvent-induced reversal of elution order was elucidated based on a derivation of the retention model. Reversal of elution order for BINOL induced by the content of isoamyl alcohol was also predicted based on the model and confirmed by experiment.     

Evaluation of triproline and tri-α-methylproline chiral stationary phases: Retention and enantioseparation associated with hydrogen bonding

In this study, to demonstrate preparation strategy and improve understanding of chiral recognition mechanisms, triproline chiral stationary phases (CSPs) were evaluated with a series of analytes classified as having none, one, two or three H-bond donors. The average retention factors and mobile phase strength generally followed none < one < two < three hydrogen bond donors. The average solvent volume ratio (H_r stands for average hexane volume ratio in the mobile phase, Hp_r for heptane, ACN_r for acetonitrile, or H₂O_r for water) normalized chromatographic parameters calculated for di-, tri-, tetra-, penta-, hexa-, and decaproline CSPs facilitated the characterization of properties associated to the H-bond donor categorization. The H_r of triproline CSP were 1.0, 0.96 and 0.88 for analyte of none, one and two hydrogen bond donors with hexane/2-propanol mobile phase, respectively. The number of hydrogen bond donors in an analyte was found to be a primary factor in influencing the retention and enantioseparation in the normal-phase and polar organic modes. Two H-bond acceptor solvents methyl tert-butyl ether and ethyl acetate increased chiral separation on oligoproline CSPs for some compounds. The role of carbon-donor hydrogen bonding at the H atom of proline asymmetric center was implied through testing a tri-α-methylproline stationary phase. On oligoproline CSPs, three factors including adjacent hydrogen bond acceptor and carbon-donor, and a rigid proline residue chain were recognized as important for contributing to the broad enantioselectivity. The α hydrogen atom on chiral center of stationary phase was found to play a crucial role in enantiomeric discrimination.     

Rapid chiral separation and impurity determination of levofloxacin by ligand-exchange chromatography

A sensitive, simple, and accurate method for determination of levofloxacin and its (R)-enantiomer was developed to determine the chiral impurity of levofloxacin in Cravit Tablets material by ligand-exchange high performance liquid chromatography. The effects of different kinds of ligands, concentration of ligands in mobile phase, organic modifier, pH of mobile phase, and temperature on enantioseparation were investigated and evaluated. Chiral separation was performed on a conventional C₁₈ column, where the mobile phase consisted of a methanol-water solution (containing10 mmol L⁻¹l-leucine and 5 mmol L⁻¹ copper sulfate) (88:12, v/v) and its flow-rate was set at 1.0 mL min⁻¹. The conventional C₁₈ column offers baseline separation of two enantiomers with a resolution of 2.4 in less than 20 min. Thermodynamic data (ΔΔH and ΔΔS) obtained by Van’t Hoff plots revealed the chiral separation is an enthalpy-controlled process. The standard curves showed excellent linearity over the concentration range from 0.5 to 400 mg L⁻¹ for levofloxacin and its (R)-enantiomer. The linear correlation equations are: y = 1.33 × 10⁵x + 6297 (r = 0.9991) and y = 1.34 × 10⁵x + 3565 (r = 0.9997), respectively. The relative standard deviation (RSD) of the method was below 2.3% (n = 3).     

Chromatographic Enantioseparation of Ten Amino Acid Amide Derivatives on Three Polysaccharide-Based Chiral Stationary Phases

Enantioseparation of ten kinds of amino acid amide derivatives bearing aniline moieties on three polysaccharide-based chiral stationary phases (CSPs) was first systematically investigated. The chromatographic experiments were performed in the normal phase mode, namely, with n-hexane and 2-propanol as mobile phase. The effects of chiral columns, concentration of 2-propanol and column temperature on the enantioseparation were studied in detail. These compounds can be well resolved on Chiralcel OD-H column with the resolution above 1.5. Enantioseparation mechanism of chiral analytes and the CSPs are proposed based on the thermodynamic analysis of the experimental data. Our study establishes a simple, fast and efficient analytical method for amino acid amide derivatives by chiral HPLC, and provides a reference for enantioseparation of chiral amino acid amide derivatives and similar chiral compounds.     

Ruthenium-catalyzed generation of hydrogen from iso-propanol

The dehydrogenation reaction of iso-propanol has been investigated in the absence of a hydrogen acceptor. Among different transition metals tested various ruthenium precursors in the presence of phosphine ligands proved to be active catalysts. Best results (turnover frequencies up to 155 h⁻¹ after 2 h) were achieved with RuCl₃·xH₂O and 2-di-tert-butyl-phosphinyl-1-phenyl-1H-pyrrole 4 at low temperature (90 °C).     

New group 4 half sandwich complexes containing triethanolamine ligand for polyethylene

(η⁵-C₅Me₅)M(TEA) (M = Ti, 1; Zr, 2; Hf, 3; TEA = triethanolateamine) was prepared by the reaction of (η⁵-C₅Me₅)MCl₃ with triethanolamine in the presence of NEt₃. The polyethylene catalytic efficiency in terms of activity decreases in the order 1/MAO > 2/MAO ? 3/MAO. In addition, the molecular weight (M_v) and melting temperature (T_m) of all the resulting polyethylene obtained by 2/MAO show the range of M_v = 91,200-356,200 and T_m = 137.0-141.9 °C, respectively; however, 1/MAO and 3/MAO gave polyethylenes with lower molecular weight (M_v = 6800-78,700) and lower melting temperature (T_m = 125.9-136.7 °C). Furthermore, 1/MAO showed significant decrease in the catalytic activity with increasing polymerization temperature though 2/MAO and 3/MAO have no dependence on the polymerization temperature.     

Kinetic and mechanistic study of the quasiliving cationic polymerization of styrene with the 2-phenyl-2-propanol/AlCl3 · OBu2 initiating system

The cationic polymerization of styrene with the 2-phenyl-2-propanol (CumOH)/AlCl₃ · OBu₂ initiating system at various dibutyl ether concentrations in a mixture of 1,2-dichloroethane and n-hexane (55:45 v/v) at −15 °C was investigated. The experimental results showed that an increase in dibutyl ether concentration leads to a noticeable decrease in the polymerization rate as well as to the more controlled polymerization in terms of molecular weight (M_n) and molecular weight distribution (MWD) evolutions. The kinetic investigation revealed that the polymerization proceeds in two stages. The first stage is characterized by high polymerization rate and slow initiation relative to propagation. During this stage molecular weight decreases or does not change and MWD increases with conversion. In the second stage considerably slower quasiliving polymerization of styrene occurs. The quasiliving nature of the styrene polymerization by the CumOH/AlCl₃ · OBu₂ system is proved and mechanistic scheme of the polymerization is proposed.     

Competition of phase dissolution and crystallization in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blend

Blend of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile was studied. The PCL/SAN blend having LCST (lower critical solution temperature) phase boundary above the melting point T_m of PCL offered an excellent opportunity to investigate the competition of liquid-solid phase transition (crystallization) and liquid-liquid phase transition (phase dissolution). A blend with the critical composition (80/20 PCL/SAN) underwent a temperature-jump above LCST to proceed spinodal decomposition, yielding a regularly phase-separated structure (SD structure). Then, it was quenched to the temperatures below T_m at which both the crystallization and the phase dissolution could occur. By transmission electron microscopy it was found that during isothermal annealing after quenching to high temperatures close to T_m (e.g. 51 °C), the SD structure gradually disappeared, and then the crystallization started from a single-phase mixture to yield normal crystalline structure similar to that of a neat crystalline polymer. At lower temperatures (e.g. 40 °C), crystallization quickly occurred and the SD structure was preserved, implying that the crystallization prevailed over the dissolution yielding a bi-continuous structure consisting of amorphous (SAN-rich) and crystalline (PCL-rich) regions. At intermediate temperatures (e.g. 45 °C), the phase dissolution competed with the crystallization, resulting in a bi-continuous structure with longer periodic distance and a broad boundary having a gradient in composition of amorphous region between PCL crystal lamellae. Light-scattering analysis quantitatively revealed a competition of the crystallization and the phase dissolution in terms of the crystallization rate (from H_v scattering) and the apparent diffusion coefficient for dissolution (from V_v scattering).     

Separation of C1-C5 aliphatic carboxylic acids on a highly sulfonated styrene-divinylbenzene copolymer resin column with a C6 aliphatic carboxylic acid solution as the mobile phase

Simultaneous separation of C₁-C₅ aliphatic carboxylic acids (formic, acetic, propionic, iso-butyric, butyric, iso-valeric and valeric acids) on a highly sulfonated styrene-divinylbenzene copolymer resin column (TSKgel SCX,  mm i.d.) was performed with C₆ aliphatic carboxylic acids (3-methyl-n-valeric, iso-caproic and caproic acids) solutions as the mobile phases. Using 0.05 mM sulfuric acid at pH 4.0 as the mobile phase, although good separation of these C₁-C₅ acids was achieved, peaks of the C₅ acids (iso-valeric and valeric acids) with large hydrophobicity tailed strongly. In contrast, using 1 mM C₆ acids at pH ca. 4.0 as the mobile phases, although vacant peaks corresponding to the C₆ acids in the mobile phase appeared, the peak shapes of the C₅ acids were improved greatly. Excellent simultaneous separation, symmetrical peaks and relatively high-sensitivity conductimetric detection for these C₁-C₅ acids were achieved on the TSKgel SCX column in 15 min with 1 mM iso-caproic acid at pH 4.0 as the mobile phase.     

Calorimetric study of sodium-rich zirconium phosphate

The heat capacity investigation of crystalline pentasodium zirconium tris(phosphate) was carried out in a vacuum adiabatic calorimeter between 7 and 340 K and in a differential scanning calorimeter of the heat bridge type between 330 and 620 K. Between 389 and 424 K, an isostructural solid-to-solid phase transition of Na₅Zr(PO₄)₃, has been found, the nature of which is connected with a centering of off-centered zirconium atoms in octahedral sites and an occupation transfer between sodium sites in the structure. The results were used to calculate the characteristics of the phase transition and the thermodynamic functions of Na₅Zr(PO₄)₃: the transition temperature T°_trs, enthalpy of transition Δ_trsH°, entropy of transition Δ_trsS°; enthalpy H°(T)−H°(0), entropy S°(T) and Gibbs function G°(T)−H°(0) over the range from 0 to 620 K. From hydrofluoric acid solution microcalorimetry, the enthalpy of solution of Na₅Zr(PO₄)₃ at 298.15 K has been determined and the standard enthalpy of formation has been derived. By combining the data obtained by the two techniques, the Gibbs function of formation of Na₅Zr(PO₄)₃ at 298.15 K has been calculated.     

Thermodynamics of 2D polymerized tetragonal phase of fullerene C60 in the range from T→0 to 650 K at standard pressure

By dynamic calorimetry the temperature dependence of heat capacity for two-dimensional (2D) polymerized tetragonal phase of C₆₀ has been determined over the 300-650 K range at standard pressure mainly with an uncertainty ±1.5%. In the range 490-550 K, an irreversible endothermic transition of the phase, caused by the depolymerization of the polymer, has been found and characterized. Based on the experimental data obtained and literature information, the thermodynamic functions of 2D polymerized tetragonal phase of C₆₀, namely, the heat capacity C°_p(T), enthalpy H°(T)−H°(0), entropy S°(T), and Gibbs function G°(T)−H°(0), have been calculated over the range from T→0 to 490 K. From 150 to 330 K in an adiabatic vacuum calorimeter and between 330 and 650 K in a dynamic calorimeter the thermodynamic properties of the depolymerization products have been examined and compared with the corresponding data for the monomeric phase C₆₀.