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Solid‐State Decomposition Kinetics of Phenyl Phosphorodiamidate
Author(s) -
Gautney J.,
Barnard A. R.,
Penney D. B.,
Kim Y. K.
Publication year - 1986
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1986.03615995005000030045x
Subject(s) - chemistry , urea , kinetics , decomposition , reaction rate constant , activation energy , thermal decomposition , ammonium chloride , analytical chemistry (journal) , inorganic chemistry , organic chemistry , physics , quantum mechanics
Kinetic studies were conducted to determine the effect of temperature, phenyl phosphorodiamidate (PPDA) production impurities, and relative humidity on the solid‐state decomposition of the urease inhibitor, PPDA, alone and in urea‐PPDA mixtures (960 g kg −1 of urea and 40 g kg −1 of PPDA). In general, the solid‐state decomposition of pure PPDA obeys first‐order reaction kinetics, whereas the decomposition of the urea‐PPDA mixtures obeys zero‐order kinetics. Rate constants (d −1 ) for pure PPDA ranged from 0.05 at 70°C to 4.78 at 100°C. Rate constants (decomposition d −1 ) for urea‐PPDA mixtures ranged from 7.26% at 50°C to 1200% at 90°C. The activation energy (kJ mol −1 ) is 164 for pure PPDA and 127 for urea‐PPDA mixtures. The presence of production impurities, ammonium chloride (NH 4 Cl) and diphenyl phosphoramidate (C 6 H 5 O) 2 ·PO·NH 2 , increased the decomposition rate for pure PPDA, but did not significantly affect the decomposition of the urea‐PPDA mixtures. Increasing relative humidity dramatically increased the decomposition rate for PPDA. These results suggest that researchers should minimize the time between preparation and testing of urea‐PPDA mixtures, because at room temperature over half of the PPDA can be lost in 1 yr.