Ion chemistry at high temperatures. 1. Thermochemistry of the ammonium ion from variable-temperature equilibrium measurements. Proton transfer, association, and decomposition reactions in ammonia, isobutene, and tert-butylamine
- National Institute of Standards and Technology, Gaithersburg, MD (USA)
At 580-680 K, the proton-transfer reaction t-C{sub 4}H{sub 9}{sup +} + NH{sub 3} {leftrightarrow} NH{sub 4}{sup +} + i-C{sub 4}H{sub 8} is in equilibrium in mixtures containing ammonia and isobutene. In the same mixtures, t-C{sub 4}H{sub 9}NH{sub 3}{sup +} is also formed reversibly, and kinetic experiments identify the addition/thermal decomposition equilibrium NH{sub 4}{sup +} + i-C{sub 4}H{sub 8} + M {leftrightarrow} t-C{sub 4}H{sub 9}NH{sub 3}{sup +} + M. The decomposition of t-C{sub 4}H{sub 9}NH{sub 3}{sup +} is at the low-pressure limit, with rate constants of (1-14) {times} 10{sup {minus}14} cm{sup 3}/s, and E{sub a} = 29.1 kcal/mol. The thermally activated addition of NH{sub 4}{sup +} to i-C{sub 4}H{sub 8} shows third-order kinetics with k = (2-6) {times} 10{sup {minus}29} cm{sup 6}/s and a negative temperature coefficient of k = AT{sup {minus}10.8}. Equilibrium studies of the proton-transfer reaction yield {Delta}H{degree} = {minus}12.5 kcal/mol and {Delta}S{degree} = {minus}6.1 cal/(mol K). Referred to PA(i-C{sub 4}H{sub 8}) = 195.9 kcal/mol, these results yield PA(NH{sub 3}) = 208.4 kcal/mol, at the high end of published values ranging from 202 to 210 kcal/mol (PA = proton affinity).
- OSTI ID:
- 6422375
- Journal Information:
- Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 94:19; ISSN 0022-3654; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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& High-Temperature Chemistry
AMMONIA
AMMONIUM COMPLEXES
BARYONS
CALIBRATION STANDARDS
CHARGED PARTICLES
CHEMICAL REACTIONS
COMPLEXES
DECOMPOSITION
ELEMENTARY PARTICLES
FERMIONS
HADRONS
HIGH TEMPERATURE
HYDRIDES
HYDROGEN COMPOUNDS
IONS
KINETICS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NUCLEONS
PROTONS
REACTION KINETICS
STANDARDS
THERMOCHEMICAL PROCESSES