Gas-Phase NMR Technique for Studying the Thermolysis of Materials: Thermal Decomposition of Ammonium Perfluorooctanoate

The kinetics of the thermal decomposition of ammonium perfluorooctanoate (APFO) has been studied by high-temperature gas-phase nuclear magnetic resonance spectroscopy over the temperature range 196−234 °C. We find that APFO cleanly decomposes by first-order kinetics to give the hydrofluorocarbon 1-H-perfluoroheptane and is completely decomposed (>99%) in a matter of minutes at the upper limit of this temperature range. Based on the temperature dependence of the measured rate constants, we find that the enthalpy and entropy of activation are ΔH⧧ = 150 ± 11 kJ mol-1 and ΔS⧧ = 3 ± 23 J mol-1 deg-1. These activation parameters may be used to calculate the rate of APFO decomposition at the elevated temperatures (350−400 °C) at which fluoropolymers are processed; for example, at 350 °C the half-life for APFO is estimated to be less than 0.2 s. Our studies provide the fundamental parameters involved in the decomposition of the ammonium salt of perfluorooctanoic acid and indicate the utility of gas-phase NMR for thermolysis studies of a variety of materials that release compounds that are volatile at the temperature of decomposition and that contain an NMR-active nucleus

Gas-Phase NMR Technique for Studying the Thermolysis of Materials: Thermal Decomposition of Ammonium Perfluorooctanoate

The kinetics of the thermal decomposition of ammonium perfluorooctanoate (APFO) has been studied by high-temperature gas-phase nuclear magnetic resonance spectroscopy over the temperature range 196−234 °C. We find that APFO cleanly decomposes by first-order kinetics to give the hydrofluorocarbon 1-H-perfluoroheptane and is completely decomposed (>99%) in a matter of minutes at the upper limit of this temperature range. Based on the temperature dependence of the measured rate constants, we find that the enthalpy and entropy of activation are ΔH⧧ = 150 ± 11 kJ mol-1 and ΔS⧧ = 3 ± 23 J mol-1 deg-1. These activation parameters may be used to calculate the rate of APFO decomposition at the elevated temperatures (350−400 °C) at which fluoropolymers are processed; for example, at 350 °C the half-life for APFO is estimated to be less than 0.2 s. Our studies provide the fundamental parameters involved in the decomposition of the ammonium salt of perfluorooctanoic acid and indicate the utility of gas-phase NMR for thermolysis studies of a variety of materials that release compounds that are volatile at the temperature of decomposition and that contain an NMR-active nucleus

Bimolecular Kinetic Studies with High-Temperature Gas-Phase ¹⁹F NMR: Cycloaddition Reactions of Fluoroolefins^†

A gas-phase NMR kinetic technique has been used for the first time to obtain accurate measurements of rate constants of some bimolecular, second-order cycloaddition reactions. As a test of the potential use of this technique for the study of second-order reactions, the rate constants and the activation parameters for the cyclodimerization reactions of chlorotrifluoroethylene (CTFE) and tetrafluoroethylene (TFE) were determined in the temperature range 240−340 °C, using a commercial high-temperature NMR probe. Obtaining excellent agreement of the results with published data, the technique was then applied to the reaction of 1,1-difluoroallene with 1,3-butadiene, the results of which indicate that the use of gas-phase NMR for reaction kinetics is particularly valuable when a reagent is available only in small amounts and in cases where there are several competing processes occurring simultaneously. The major processes observed in this reaction are regioselective [2+2] and [2+4] cycloadditions, whose rates and activation parameters were determined [k2 = 9.3 × 106 exp(−20.1 kcal mol-1/RT) L/mol-1 s-1 and k3 = 1.2 × 106 exp(−18.4 kcal mol-1/RT) L/mol-1 s-1, respectively] in the temperature range 130−210 °C

Reversible Oxygenation of a Diphenylmethyl Radical Rendered Supramolecularly Persistent

Reversible Oxygenation of a Diphenylmethyl Radical Rendered Supramolecularly Persisten

electronic supplementary material from Plants in the UK flower a month earlier under recent warming

figures S1-S

HornGrowthIncrements

Annually resolved and absolutely dated measurements of Alpine ibex (Capra ibex) horn growth increments from 8’355 males, harvested between 1978 and 2013, in the eastern Swiss Canton of Grisons

Climate—ring-width correlations.

Spearman rank correlation data points of single months and seasonal groupings (red dots) of chronologies from Mt. Etna (top panel) and Calabria (bottom panel) showing the correlation range of each monthly- or seasonal variable with the different group-chronologies; where T = temperature, P = precipitation and p = prior year. Boxplots show the median and lower and upper quartiles, and the whiskers display the minimum and maximum values.</p

Sample overview information.

Descriptive statistics of sample chronologies (Group 1–4) from Mt. Etna, and the chronologies from Calabria (Gambarie, Monte Pollino and Sierra da Crispo) displaying number of series (core-series), total length (years) of group chronologies, series intercorrelation (measure of common growth signal in the chronology), mean sample length (years), elevation (m a.s.l.) and species.</p

New Jersey defoliation damage in October-November 1991.

<p>The gray represents the extent of pine looper defoliation damage. The black dot is the location of the Brendan T. Byrne State Forest.</p

List of seed sources and relevant statistics.

<p>List of seed sources and relevant statistics.</p