Search

The alcoholysis of acetyl chloride, propionyl chloride and butyryl chloride with some alcohols in acetone and toluene has been investigated by means of calorimetric measurements. Furthermore a comparison with benzoyl chloride has been made. In the case of i-propanol in acetone, a smaller rate constant has been found for the alcoholysis of propionyl chloride than for butyryl chloride. In contrast to this, almost equal rate constants have been determined for the reactions of these acyl chlorides with n-propanol and ethanol. In toluene, the rate constants for the reaction of acetyl chloride with all considered alcohols has the highest values under similar conditions but then decrease from acetyl chloride to butyryl chloride. The observed differences and the changes of rate constants are discussed and compared with literature data.

The alcoholysis of acetyl chloride under various reaction conditions has been investigated by isoperibolic calorimetry and HPLC-analysis. Non-linear kinetic evaluation has been realized by the program TA-kin 3.3 on the basis of temperature and concentration data. Depending on the excess of alcohol, different partial reaction orders are found. The reaction rate also depends on the basicity of the solvent. This could be caused by H-bonding with the alcohol increasing the activation energy. It was possible to distinguish between the kinetic parameters of the ethanolysis and the i -propanolysis of acetyl chloride in the evaluation of the alcoholysis of acetyl chloride by alcoholic mixtures at stoichiometric concentrations of the reagents. A partial order of n =0.5 for the alcohol, as determined in the evaluation of the single alcoholysis under these conditions, has been confirmed. The results show that heat accumulations are an important feature for the kinetic evaluation of reactions under the concentration conditions described.

The ethanolysis of acetyl chloride has been compared to the methanolysis and the hydrolysis, as well as to the reaction with n -propanol, n -butanol and n -pentanol in acetone and in toluene, to reveal chain-length effects. Pentanol, heptanol and nonanol have been included as well in the investigation, but at lower concentrations. Structural influences on the alcoholysis of acetyl chloride have been studied with the isomeric C 3 and C 4 -alcohols in acetone and in toluene. Furthermore, alcoholysis of acetyl chloride with some C 7 -alcohols and the reaction of benzoyl chloride with different types of alcohols have been investigated.

Part A of this series of papers (Parts B to E follow) presents the data and methods used, as well as the results obtained by participants in the ICTAC Kinetics Project. The isothermal and non-isothermal data sets provided were based on a hypothetical simulated process as well as on some actual experimental results for the thermal decompositions of ammonium perchlorate and calcium carbonate. The participants applied a variety of computational methods. Isoconversional and multi-heating rate methods were particularly successful in correctly describing the multi-step kinetics used in the simulated data. Reasonably consistent kinetic results were obtained for isothermal and non-isothermal data. There is, of course, no ‘true’ answer for the kinetic parameters of the real data, so the findings of the participants are compared. An attempt has been made to forecast the tendencies for the future development of solid state kinetics.

In 1994 the decomposition of calciumoxalate monohydrate as a three-step reaction has been investigated by 13 labs using the TG-method. The authors working group performed objective kinetic evaluations of 144 TG data sets obtained from the same charge of substance in different laboratories. A non-linear optimization procedure was applied for different reaction models to perform single and overall optimizations. The results were analyzed critically on the basis of real model concepts for the course of the dehydration, the CO-split off and of the CO2-split off, respectively. The results allow an optimistic assessment for the application of kinetic procedures to solid state reactions with well-known chemical course investigated by TG.

Investigations in chemical safety are necessary in case that the reaction course depends on changes of the reaction conditions sensitively. To break off a conversion in a hazardous situation, the precision calorimeter ACTRON 5 is equipped with two safety pumps. They empty and rinse the reactor with cold solvent. The pumps will be activated automatically. For testing the calorimeter the complex reaction of chloronitrobenzene with alkalined alcohol was used and break off at predefined conditions. The possibility of the kinetic estimation of these break-off files is shown.

Polyethers, which are produced by alcoholysis of oxiranes, are often used as solvents in chemical plants. The spectra of the products can be influenced by the choice of the catalyst (acid or base). The results of the base-catalyzed ethanolysis of 1,2-epoxybutane are displayed. The reaction was investigated calorimetrically by varying the molar ratio between ethanol and 1,2-epoxybutane, the starting temperature and the concentration of the catalyst sodium hydroxide. Additionally, the influence of the used alcohol will be shown in one example. To determine the activation parameters, the experiments were evaluated by the nonlinear software package TA-kin v3.3.

Differential scanning calorimetry is well suited to record heat productions of chemical and physical processes as data for the following kinetic analysis. To obtain kinetic parameters of complex reactions, nonlinear optimization methods have to be used. Such complex reaction systems are polymerizations. We tried to evaluate measurements of the epoxy cure and the polymerization of s-propiolactame with simple and complex models. In both cases the simple models did not produce satisfactory results. But by using complex models a successful fitting of the measured data was possible. Our investigation shows that the combination of DSC and modern nonlinear evaluation methods presents a suitable tool for the kinetic investigation of polymerizations.

Acetylation of different hexanediols as a complex reaction has been investigated by calorimetry. The calorimetric curves demonstrate that the reaction rate depends on the molecular structure. In case of 1,6- and 2,5-hexanediols, the activation parameters have been obtained by nonlinear evaluation procedures with the program TA-kin v3.3. The kinetic results show, that the formation of the diester is characterized by higher activation energies than that of the monoester.

The kinetic control of exothermic reactions plays an important role in chemical safety technology. Predictions of thermal explosions by runaway, e.g. redox reactions, poly reactions, and decompositions, are required in case of simple as well as of complex reactions. Activation parameters of chemical reactions are often stressed by systematic errors which are caused by failures in accuracy of measurement and calibration. The influence of systematic errors for some selected reactions has been investigated by the software package TA-kin. The coupling between continuous data evaluation software and the precision calorimeter ACTRON 5.0, including a safety scenario equipment, was established to test the validity of calculated runaway predictions under practical conditions. Measured data are applied for kinetic evaluations by nonlinear optimization methods in real time. In this way, the experimental investigations of reaction systems become possible beyond the point of no return without any danger for the laboratory.

A computer program was developed for kinetic evaluations of calorimetric experiments to predict the further reaction run under adiabatic conditions. Kinetic modeling is based on elementary reaction steps whose rate laws form a set of differential equations. For the continuous parameter optimization time-temperature data and their derivatives are used. A special calorimeter of the ACTRON series with safety equipment was applied to investigate the kinetics of chemical reactions and to test kinetic on-line evaluations. In the paper, examples for the reaction of n-propanol with o-chlornitrobenzene and for the alcoholysis of phenyl isocyanate are given.

Different ACTRON calorimeters were used to investigate the alcoholysis of phenyl isocyanate and acetyl chloride, and the reaction of o-chloronitrobenzene with alkaline alcohol. An example for a scenario to break off a reaction in a hazardous situation is given. At least it will be shown, that it is possible to evaluate an interrupted reaction to get the kinetic activation parameters.

For the calculation of kinetic parameters from thermal data files numeric optimization has been well introduced. But suitable starting values near the global minimum of the sum of deviation squares are needed for a successfully parameter estimation. Namely the search for starting values requires a lot of time and diminishes the effectiveness of the total procedure. Therefore we have developed an algorithm of the automatic search of starting values for the optimization of activation energy end frequency factor of a chemical reaction. This search procedure uses the knowledge of the specific course of the corresponding SDS surface in the near of its global minimum. In this area the SDS describes two plateaus separated by a narrow valley. The search procedure avoids starting values at one of these plateaus. This PC program is part of the complex software package TA-kin v3.3 for kinetic evaluation of thermal measurements.

Objective: Tracheostomy is one of the most commonly performed surgical procedures in the critical care setting. The early use of tracheostomy as a method of primary airway management has been proposed as a means to decrease pulmonary morbidity and to shorten the number of ventilator, intensive care unit, and hospital days. We set out to (1) determine whether hypercarbia occurs during tracheostomy of the critically ill patient and (2) determine the extent to which the partial pressure of carbon dioxide in arterial blood (PaCO2) rises during percutaneous endoscopic, percutaneous Doppler, and standard surgical tracheostomy. Design: Prospective, open clinical trial. Setting: Surgical intensive care unit and operating room in teaching hospitals. Patients: During mechanical ventilation, patients underwent either percutaneous endoscopic (PET), percutaneous Doppler (PDT), or standard surgical tracheostomy (ST), based on surgeon preference. Arterial blood gas readings were obtained approximately every 4 min throughout each procedure. Measurements and results: All tracheostomies were successfully performed. No serious complications (including hypoxia) occurred during the study. Significant (p < 0.05 vs PDT and ST) hypercarbia (maximum Δ PaCO2 24 ± 3 mmHg) and acidosis (maximum Δ pH – 0.16 ± 0.02) developed during PET. The changes in PaCO2 and pH during PDT (maximum Δ PaCO2 8 ± 2 mmHg; maximum Δ pH – 0.07 ± 0.02) and ST (maximum Δ PaCO2 3 ± 1 mmHg; maximum ΔpH – 0.04 ± 0.01) were markedly less pronounced. Conclusions: Continuous bronchoscopy during percutaneous tracheostomy contributes significantly to early hypoventilation, hypercarbia, and respiratory acidosis during the procedure. Percutaneous tracheostomy, when performed using the Doppler ultrasound method to position the endotracheal tube, significantly reduces CO2 retention when compared to PET. Because of a possible rise in intracranial pressure, the potential for hypercarbia should be considered when choosing the method of tracheostomy in the critically ill and/or head-injured patient, where hypercarbia may be detrimental. If PET is to be performed, steps to minimize occult hypercarbia, such as using the smallest bronchoscope available, minimizing suctioning during bronchoscopy, and minimizing the length of time the bronchoscope is in the endotracheal tube, should be undertaken.

Adiabatic calorimetry is a suitable method for investigations of reactions because the generated heat remains completely in the reactor. For the investigation of organic reactions, the adiabatic precision calorimeter ACTRON 5 is used. The alcoholyses of phenyl isocyanate and 1,2-butyleneoxide were investigated. The temperature-time course was estimated by means of the nonlinear program TA-kin. Inclusion of the concentration-time course in the estimation procedure led to an increase in the reliability of the parameters. Probes were taken during isoperibolic measurements and were analysed by means of HPLC.

Safety production in chemical plants is a high-priority task, especially as concerns reactions which can change mechanism suddenly under defined conditions, e.g. from a simple well-defined to an undesired autocatalytic reaction. An example of this kind, the reaction of chloronitrobenzene with alkaline alcohol, was investigated with the new adiabatic precision calorimeter ACTRON 5, designed with a safety concept. It is shown that the reaction can be interrupted safely under predicted conditions.

All temperature sensors have a finitely time constant. The influence of the sensor time constant gts on the results of kinetic evaluation is demonstrated at four reaction types. The ignorance of the sensor indolence gives incorrect activation parameters. Therefore the determination of Τs is necessary.

The method of computer-experiments can be applied successfully on the radical depolymerization under inclusion of initiation, depropagation and termination. The comfortable PC-program ‘TA-kin’ for the non-linear estimation of parameters for TG- or DSC-experiments was applied to the determination of activation parameters of depropagation and termination. Therefore the overall-evaluation of three or more data sets is a prerequisite. The determination of kinetic parameters runs satisfactory if the measured curves are strongly different, e.g. by varying the heating rate, including acceptable experimental errors. Several recommendations for laboratory experts are given. A great support for a very sufficient estimation is the inclusion of simultaneous analysis of the radical concentration.

Four computer programs as well as one demo-version for non-linear evaluation of kinetic data in thermal analysis and calorimetry, were presented. The multi-task program TA-kin meets all mathematical requirements for solving the numerical assignments. It is shown that the so-called compensation effect is due to the mathematical structure of the Arrhenius equation. Several applications of TA-kin to a lot of DSC- and TG-measurements and isoperibolic batch experiments as well as adiabatic semi batch experiments realized by precision calorimetry have been discussed.

Because there is risk of autocatalytic reduction, the conversion of chloronitrobenzene with alkaline alcohol is important in safety management. The influence of several parameters on the reaction will be described. The experiments were realized in a non commercial calorimeter, equipped with for the precision calorimeter ACTRON developed hard- and software. For the non-linear kinetic evaluation of the experiments the program TA-kin was used.

The investigation of the hazardous potential of reaction courses is very important for the chemical industry. Compared with the isoperibolic the adiabatic calorimetry has essential advantages for kinetic evaluations, because corrections of heat flux are not necessary. With the adiabatic precision calorimeter ACTRON 5 is the investigation of reaction courses in small volumes possible. The possibilities of the nonlinear investigation program TA-kin are shown with examples of Semi-Batch-Measurements. With this program the change in heat capacities whilst encoring the second component is included.

Reactions with large negative enthalpy changes are often encountered in the chemical industry. Sometimes they give rise to technical dangers and hazards, including explosions. This investigation concentrates on examination of adiabatic temperature-time-curves and gives non-linear optimization procedures for obtaining kinetic parameters of simple decompositions,e.g. o-nitrobezaldehyde, two types of autocatalysis, consecutive reactions and competitive consecutive reactions. The advantage of this computing method is that only differential kinetic equations are needed.

A computer-aided calorimeter for the region of −15° to 180°C and with a resolution 2·10−5 K is described. The reactive volume may be varied from 10 to 100 ml.

For kinetic evaluation by TG and DSC of simple and complex reactions we used a direct fit on the basis of TG differential equations and DSC non-linear equations. The advantages of an overall evaluation, i.e. the simultaneous inclusion of all data sets at different heating rates, are described. TG and DSC measurements of the dehydration of calcium oxalate monohydrate and the decomposition of calcium oxalate are used as examples.

Telomerization of isoprene is characterized by intense thermal effects. The reaction system di-μ-chlorobis(η3-allyl)-dipalladium(II): tri-n-butylphosphine: sodium methylate: isoprene=1∶2∶3∶200 in a solvent-mixture of methanol∶benzene=1∶3 is used as a model. It is concluded that reaction of the catalyst combined with reduction of Pd(II) is followed by the telomerization reaction. There is a marked influence of Pd and phosphine concentration in the catalyst as well as concentration of isoprene. Results are available to optimize technical applications.

Although significant progress has been made in the treatment of patients with acute lung failure in the critical care setting, the mortality rate from acute lung injury and ARDS is unacceptably high, given the numbers of patients treated for these syndromes each year. The improved understanding of the pathophysiology of respiratory failure from basic science and clinical research is reflected in improved survival rates over the years. Advances in the mechanical ventilator (through microprocessor technology); biosurface technology; liquid ventilation; and, in some cases, returning to so-called "antiquated" practices of patient care (e.g., prone positioning) seem to have had an impact nonetheless. As refinement continues to occur in these areas, morbidity and mortality from lung failure will have a lesser impact on patients as physicians treat the consequences of organ failure in the ICU.

Acute or adult respiratory distress syndrome (ARDS) contributes to mortality and morbidity in the intensive care environment. Appropriate application of microprocessor-controlled mechanical ventilatory support, pathophysiology of the disease, and new pharmacologic modalities are currently being investigated. Mechanical ventilation is usually begun when respiratory failure is caused by alveolar hypoventilation or hypoxia. Primary choices for this therapy are control-mode ventilation, assist-control ventilation, pressure-control ventilation, intermittent mandatory ventilation, and synchronized intermittent mandatory ventilation with the addition of positive end-expiratory pressure. Patients who deteriorate despite these interventions may require alternative modes of ventilation. Pharmacologic agents in ARDS is important due to the multifactorial pathophysiologic and pharmacodynamic processes that are part of the disease. Clinical studies will continue to determine advantageous agents. Unfortunately, no convincing data exist that any pharmacologic or nonpharmacologic strategy is superior for the support of these patients or results in a better outcome than others.

Bronchoscopy has been incorporated as a useful adjunct to increase the safety and effectiveness of percutaneous endoscopic tracheostomy (PET). Insertion of the bronchoscope, along with the intraluminal dilators of the PET set, into the airway potentially leads to hypoventilation and hypercarbia during the procedure. Using continuous in-line arterial blood gas monitoring, we documented profound hypercarbia in two patients undergoing PET in the surgical ICU. In a third patient, the rise in PaCO2 was accompanied by a marked rise in intracranial pressure (ICP), and a corresponding fall in cerebral perfusion pressure. While transient hypercarbia seems well tolerated by most patients, this phenomenon and its effect on cerebral blood flow should be strongly considered before performing PET on the critically ill patient with evidence of elevated ICP.

This study was based on an analysis of essays written by 47 teacher education students in response to the question, "If you could live your high school days over again, what, if anything, would you change?" The responses were organized into 20 different categories and tabulated according to students' age and sex. In retrospect, 38% of these students would have improved their attitude toward high school. Thirty-six percent indicated that high school was a positive experience, though this attitude was often unrelated to academic achievement. The responses strongly suggest that for many high school students, general attitude toward school affects achievement more than do attitudes toward specific school characteristics.

Percutaneous dilatational tracheotomy is a safe, efficient procedure for elective tracheostomy placement. It is not a technique for emergency tracheotomy. It should be performed only by surgeons experienced in conventional tracheotomy. The advantages of placement at the bedside, speed, and relative inexpense make it attractive in the care of critically ill patients.

Extracorporeal membrane oxygenation is now standard treatment of severe respiratory failure in newborn infants in our center (200 cases) and worldwide (over 2500 cases), but there are few reports of such trials in older children. We reviewed our experience with extracorporeal membrane oxygenation in 33 children aged 1 week to 18 years between 1971 and 1989. The modality was used when all other treatment failed. Extracorporeal membrane oxygenation provided excellent cardiopulmonary support for 1 to 25 days (average 7 1/2 days). The survival rate was 25% for cardiac support patients and 47% for respiratory failure patients (36% overall survival). Mechanical complications included membrane lung failure, tubing rupture, and pump failure, all managed without mortality. Physiologic complications included bleeding, pneumothorax, cardiac arrest, renal failure, hepatic failure, and brain injury. The major cause of death was irreversible injury to lung, heart, or brain. Extracorporeal life support is a reasonable approach for children with serious but reversible cardiopulmonary failure.

The alcoholysis of triethylaluminium can be investigated by DTA in the liquid phase. The reaction enthalpy of the alcoholysis with primary alcohols is from −150 to −170 kJ mole−1 in tetrahydrofuran/toluene as solvent. The reaction rate in pure hydrocarbons is higher than in the presence of Lewis bases. The reaction mechanism is probably ofSE2 type and the reactivity decreases in the sequence primary, secondary, tertiary alcohol. In the second step of substitution the diethylaluminium alkoxides are less reactive than triethylaluminium because of the stronger association of the alkoxides. For the turnover of two moles of alcohol with one mole of triehylaluminium two DTA peaks appear in accordance with consecutive reactions.

The properties of the transverse momenta and angular distributions of hadrons produced in muon-proton scattering with first-order quantum-chromodynamics calculations. The quantum-chromodynamics prediction for the Q/sup 2/ dependence of the average hadron transverse momentum squared agrees with the data provided a constant term is added in quadrature to the prediction. This additive term is attributed to the intrinsic transverse momentum of the quarks in the nucleon and to the transverse momentum inherent in quark fragmentation.

Thermal Investigation of the Formation of the Catalyst System Cobalt Acetylacetonate – Aluminium Triethyl The formation of the Ziegler catalyst system cobalt-tris- and cobalt-bis-acetylacetonate with triethylaluminium was investigated by means of quantitative differential thermal analysis and calorimetry in solution. From DTA and heat flow curves qualitative and quantitative relations were determined between Al/Co-ratio and thermal reaction power. For both systems in both systems in the first step second order reactions are postulated and kinetic and thermodynamic parameters are evaluated, whereas the course and order of the following steps differ distinctively. For the complete reduction of one mole Co(III) or Co(II), respectively, every alkyl group of AlEt3 is suitable.

Das Problem der rationellen Losung des Zeitintegrals stand bei der kinetischen Auswertung nichtisothermer Prozesse haufig zur Diskussion. Nun werden fur lineare und nichtlineare Aufheizung gemas dT/dt=Q·Tb mitb von 4 bis −2 Auswerteverfahren vorgestellt, die in jedem Fall eine vollstandige Korrektur derjenigen kinetischen Parameter gestatteten, die durch linearisierte Auswertung erhalten worden sind. Diese Methode der vollstandigen Exponentialintegrale zeigt, das eine klare Abstufung nach dem Typ der Aufheizung besteht. Die notwendigen Korrekturen furb=1, 2 und 3 sind kleiner als furb=0 d.h. fur lineare Aufheizung. Die vier Korrekturtabellen sind fur Verfahren der kinetischen Analyse anwendbar, denen ein Aktivierungsansatz nach Arrhenius bzw. Eyring zugrunde liegt. Die Realisierung nichtlinearer Aufheizprogramme wird empfohlen.

An exact kinetic evaluation is practicable in homogeneous systems if no gradients of concentration or temperature appear. With permanent stirring, the measurement of the real difference temperature and absolute temperature at a suitable heating rate allows the application of liquid-phase DTA in the range between 170 and 380 K. For the examination of air — and moisture-sensitive substance too, equipment has been developed, that operates under inert conditions.

Results on the protron structure function, ${F}_{2}$, are presented for $0.3l{q}^{2}l80.0$ Ge${\mathrm{V}}^{2}$ and $10l\ensuremath{\nu}l200$ GeV. The results support the conclusions of earlier work at 97 and 147 GeV that scaling is violated. A new value for $R=\frac{{\ensuremath{\sigma}}_{S}}{{\ensuremath{\sigma}}_{T}}=0.44\ifmmode\pm\else\textpm\fi{}0.25$ has been obtained using all the Fermilab proton measurements.