Kinetics of Lisinopril degradation in solid phase

Summary The kinetics of degradation of lisinopril (LIS) in solid phase in presence of humidity at 343, 353, 358 and 363 K has been investigated. Changes of the LIS concentration were followed by an HPLC method with UV detection. The thermodynamic parameters at 293 K of degradation of LIS in solid phase E_a (kJ/mol) = 166 ± 47; H*(kJ/mol) = 163 ± 48; S*(J/(K × mol)) = 99 ± 135 for RH = 76.4% have been calculated. Identification of the product of LIS degradation in solid phase was carried out by HPLC-MS. Diketopiperazine derivative of LIS was the major product of its decomposition in the presence of humidity.     

Thermal degradation of pentaerythritol phosphate alcohol

Intumescent material, 2,6,7-trioxa-1-phosphabicyclo-[2,2,2]-octane-4-methanol phosphate (PEPA), is synthesized and characterized using FTIR, ¹HNMR and ¹³CNMR. The degradation properties of PEPA are studied by employing TG and TG?CMS technique. The activation energies for the degradation process of PEPA are calculated by using TG curves obtained from multiple heating rates (Friedman, Kissinger?CAkahira?CSunose and Flynn?CWall?COzawa methods). The degradation that is occurring in the temperature region 307?C366?°C has the highest activation energy. Eventhough the calculated activation energies for the degradation differ depending on the approximation method employed, the trend in variation of activation energy for degradation is similar. Single ion monitoring technique proved the evolution of H₂O, CO/C₂H₄, HCHO, C₂H₅OH/HCOOH and trace amounts of C₂H₇O₃P and C₄H₉O₄P from the degrading PEPA. The thermal conductivity and stability of the char formed during the TG analysis are also discussed.     

Kinetics of thermal degradation and thermal oxidative degradation of poly(p-dioxanone)

The kinetics of the thermal degradation and thermal oxidative degradation of poly(p-dioxanone) (PPDO) were investigated by thermogravimetric analysis. Kissinger method, Friedman method, Flynn-Wall-Ozawa method and Coats-Redfern method have been used to determine the activation energies of PPDO degradation. The results showed that the thermal stability of PPDO in pure nitrogen is higher than that in air atmosphere. The analyses of the solid-state processes mechanism of PPDO by Coats-Redfern method and Criado et al. method showed: the thermal degradation process of PPDO goes to a mechanism involving random nucleation with one nucleus on the individual particle (F₁ mechanism); otherwise, the thermal oxidative degradation process of PPDO is corresponding to a nucleation and growth mechanism (A₂ mechanism).     

Kinetics of polymerization of vinyl monomers initiated by lead tetraacetate

A systematic study of the thermal polymerization of α-chloroacrylic acid and α-bromoacrylic acid in aqueous nitric acid was carried out. The effect of variation of monomer concentration lead tetraacetate concentration, hydrogen ion concentration, ionic strength, and temperature on the rate of monomer disappearance was carried out. Based on the experimental observations, suitable reaction schemes were proposed for the polymerization of the above monomers. The rate constants and the thermodynamic parameters were evaluated.     

Kinetics study of thermal oxidative degradation of ABS containing flame retardant components

The thermal oxidative degradation kinetics of pure acrylonitrile–butadiene–styrene (ABS) and the flame-retarded ABS materials with intumescent flame retardant (IFR) were investigated using Kissinger, Flynn–Wall–Ozawa, and Horowitz–Metzger methods. The results showed that the degradation of all samples included two stages, the activation energy at the first stage decreased by the incorporation of these flame retardant components, while increased at the second stage. The activation energy order of the flame-retarded ABS samples at stage 2 illustrates the relationship between the composition of IFRs and their flame retardancy, FR materials with appropriate acid agent/char former ratio has higher activation energy and better flame retardancy.     

Kinetics of the formation of solid phase in electrolyte for electroless nickel deposition

The effect of 1-(3-methyl-4-phenylpyrazolyl)-3-phenylthiourea (PPTU) on the kinetics of formation of particles of the solid phase in the bulk of electrolyte for nickel plating is investigated by photocolorimetry and photon correlation spectroscopy. It is established that PPTU favors the formation of larger particles as compared to the solution containing no additive and, depending on the concentration, can accelerate or slow down the formation and growth of metal particles and affect the location of the process.     

Kinetics of the oxidative degradation of d-xylose in the presence and absence of cationic and anionic surfactants

The oxidative degradation of d-xylose by cerium(IV) has been found to be slow in acidic aqueous solution with the evidence of autocatalysis. The reaction is accelerated in the cetyltrimethylammonium bromide (CTAB) micellar medium but sodium dodecyl sulfate (an anionic surfactant) has no effect. The pseudo first-order rate constants have been determined at different [reductant], [oxidant], [H₂SO₄], temperature, and [CTAB]. The reaction rate increased with increasing [d-xylose] and decreased with increase in [H₂SO₄]. The CTAB-micelle-catalyzed kinetic results can be interpreted by the pseudophase model. The kinetic parameters such as association constant (K _s), micellar medium rate constant (k _m), and activation parameters (E _a, ΔH ^# and ΔS ^#) are evaluated and the reaction mechanism is proposed. The reaction rate is inhibited by electrolytes and the results provide an evidence for the exclusion of the reactive species from the reaction site.     

Complex formation effects during the oxidation of cyclohexene with lead tetraacetate

The effect of complex formation between lead(IV) and trifluoroacetic or methanesulfonic acid and chloride ion in acetic acid and Freon 113 on the oxidation of cyclohexene by lead tetraacetate was investigated. As a result of the reaction the -chlorocyclohexyl esters of the corresponding acids are formed with high yields. The formation of the complexes Pb(OAc)_4–nL_n and Pb(OAc)_4–(n+1)L_nCl, where L = CF₃CO₂- or CH₃SO₃- with n=1 or 2, was demonstrated by potentiometric titration. A scheme is proposed for the oxidation of cyclohexene with the participation of unlike-ligand complexes of Pb(IV).Translated from Teoreticheskaya Eksperimental'naya Khimiya, Vol. 21, No. 5, pp. 567–572, September–October, 1985.     

Copper carboxylate formation in the thermal oxidative degradation of atactic polypropylene on copper oxide films

The thermal oxidation of atactic polypropylene on CuO_0.67 surfaces in air was studied using IR reflection-absorption spectroscopy. Degradative losses of primary, secondary, and tertiary alkyl hydrogens were observed. At 60 and 73°C, carboxylic acids are the primary degradation products, while at 85 and 100°C, copper carboxylate formation predominates and CuO_0.67 is decomposed. The distinct change in the oxidative mechanisms between 73 and 85°C apparently is related to an irreversible thermal transition in the atactic polypropylene films, which may favor carboxylate production by increasing the permeability of the films to oxygen and water vapor.     

High-pressure-induced phase transitions in pentaerythritol: X-ray and Raman studies

The high-pressure response of pentaerythritol crystals has been examined to 10 GPa in diamond-anvil cells using angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy. The results reveal two first-order phase transitions: one at 4.8 GPa from phase I, tetragonal I(), to phase II, orthorhombic Pnn2C2v10, with a small approximately 0.5% volume change, and the other at 7.2 GPa to phase III with an unknown crystal structure. We found that phase I exhibits a large crystallographic anisotropy which rapidly decreases with increasing pressure: the ratio of linear compressibilities between two primary crystal axes decreases from betao= 8.1 at 1 atm to betaP = 2.6 at 4 GPa. We suggest that this apparent decrease in crystal anisotropy is due to the disruption of hydrogen bonding in the (001) plane of phase I and eventually leads to an orthorhombic distortion from a quadrilateral network structure in phase I to a quasi one-dimensional structure in phase II. The crystal structure of phase III exhibits a disordered character, and it is likely a conformational variant of phase II.     

Kinetics of oxidative degradation of pantothenic acid by cerium(IV) in aqueous perchloric acid

The kinetics of oxidation of pantothenic acid (PA), Me₂C(CH₂OH)CH(OH)C(O)NHCH₂CH₂CO₂H, by cerium(IV) in aqueous HClO₄ medium at constant ionic strength, 2.0 mol dm^–3, has been studied spectrophotometrically. The reaction showed first-order kinetics in Ce^IV concentration, an apparent less than unit order dependence in [PA] and an inverse fractional order in [H⁺]. Initial addition of products had no significant effect on the rate of the reaction. A possible mechanism is proposed, and the reaction constants involved in the mechanism have been computed. There is good agreement between the observed and calculated rate constants under different experimental conditions. The activation parameters were calculated with respect to the slow step of the proposed mechanism.     

A redox-metric study of the formation of coloring substances in the synthesis of pentaerythritol

The redox potentials of the reaction mixtures in the course of pentaerythritol synthesis and of transformations of formaldehyde and glucose in a NaOH solution without catalyst and in the presence of copper prepared by reduction of CuO were measured.     

Synthesis of 6-hydroxycarvone derivatives and their oxidative decyclization with lead tetraacetate

6-Hydroxy derivatives of R-(−)-carvone and 7,8-epoxycarvone were synthesized and subjected to oxidative ring cleavage by the action of lead tetraacetate. These reactions followed different patterns, depending on the substrate structure.     

Kinetics of propylene polymerization in the initial acceleration stage

The kinetics of propylene polymerization catalyzed over a superactive and stereospecific catalyst for the initial build-up period was investigated in slurry-phase. The catalyst was prepared from Mg(OEt)₂/benzoyl chloride/TiCl₄ co-activated with AlEt₃ in the absence or presence of external donor. Despite a very fast activation of the prepared catalyst the acceleration stage of polymerization could be identified by the precise estimation of polymerization kinetics for a very short period of time after the commencement of polymerization (ca. 2 min). The initial polymerization rate, (dR_p/dt)₀ extrapolated to the beginning of the polymerization was second order with respect to monomer concentration. The dependence of initial polymerization rate on the concentration of AlEt₃ could be represented by Langmuir adsorption mechanism. The initial rate was maximum at about Al/Ti ratio of 20. The activation energy for the initiation reaction was estimated to be 14.3 kcal/mol for a short-time polymerization. The addition of a small amount of p-ethoxy ethyl benzoate (PEEB) as an external donor increased the percentage of isotactic polymer, which was obtained after 120 s of polymerization, to 98% and the initial polymerization rate decreased sharply as [PEEB]/[AlEt₃] increased. © 1994 John Wiley & Sons, Inc.     

Co-microencapsulate of ammonium polyphosphate and pentaerythritol and kinetics of its thermal degradation

Co-microencapsulated ammonium polyphosphate (APP) and pentaerythritol (PER) (M (A&P)) is prepared using melamine-formaldehyde (MF) resin by in situ polymerization method, and characterized by Energy dispersive spectrometer (EDS) and Fourier transform infrared (FTIR) spectra. Thermal stability of M (A&P) has been analyzed and compared with APP/PER mixture. In air atmosphere, the mass loss of M (A&P) at different heating rates was investigated using TGA. The kinetics of thermal degradation and activation energy was described using Flynn-Wall-Ozawa and Kissinger methods. It showed that there were two degradation stages. Expanded carbon structure with honeycomb was formed in the first stage between 200 and 450 °C. The second stage was the oxidation of carbon with E_a as high as 151.7 kJ/mol, so the expanded carbon had a good thermal stability. The reaction order of thermal degradation was found to be 0.935, so the mechanism of M (A&P) thermal degradation was controlled by the process of random nuclear formation and growth.     

Kinetics of thermal oxidative degradation of a polyester resin and of its formulation with diethyldibenzylammonium bromide

The kinetics of thermal oxidative degradation of a polyester resin and of its formulation with diethyldibenzylammonium bromide was studied. The rate constants of the thermal decomposition were determined.     

Kinetics of the thermal degradation of polyimides

A number of temperature and kinetic parameters of thermal degradation of polyimides over the temperature range from 20 to 1000° have been determined on the basis of thermogravimetric investigations of a polyimide sample obtained from pyromellitic dianhydride and diaminodiphenyl ether. It was shown that such kinetic parameters as the reaction order and the activation energy of thermal degradation are directly dependent on the conditions under which the thermal analysis is carried out. It was found that when the static and dynamic conditions of the environment of a polymer sample are varied, the thermochemical processes occurring in a polyimide over the temperature range investigated are drastically changed.A critical analysis of the possibility of comparing the kinetic data on thermal degradation with the criteria generally used for the evaluation of the thermal stability of polyimides was carried out. The dynamic kinetic characteristics of the degradation of polyimide were correlated to prolonged thermal stability.

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Zusammenfassung Eine Anzahl von Temperatur- und kinetischen Parametern des thermischen Abbaus von Polyimiden wurde im Temperaturbereich von 20 bis 1000° aufgrund von an aus Pyromellitdianhydrid und Diaminodiphenyläther erhaltenen Polyimidproben durchgeführten Untersuchungen bestimmt. Es wurde gezeigt, daß kinetische Parameter wie die Reaktionsordnung und die Aktivierungsenergie der thermischen Zersetzung unmittelbar von den Bedingungen abhängig sind, unter welchen die Thermoanalyse durchgeführt wurde. Es wurde gefunden, daß im Falle der Änderung der statischen und dynamischen Bedingungen der Umgebung einer Polymerprobe, die in einem Polyimid in dem untersuchten Temperaturbereich stattfindenden thermochemischen Vorgänge drastisch geändert werden.Eine kritische Analyse der Möglichkeit des Vergleichs kinetischer Angaben bezüglich des thermischen Abbaus mit den zur Bewertung der Thermostabilität von Polyimiden allgemein gebräuchlichen Kriterien wurde durchgeführt. Die dynamischen kinetischen Charakteristika des Abbaus von Polyimiden wurden mit der verlängerten Thermostabilität korreliert.

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Kinetics of thermal oxidative degradation of a compound based on a polyester resin and dimethylethylphenylammonium iodide

The kinetics of thermal oxidative degradation of a compound based on a polyester resin and dimethylethylphenylammonium iodide was studied. The rate constants of thermal decomposition were determined. The degradation of the compound was studied by dynamic thermogravimetric analysis.