Application of Specific Deuterium Labeling and Nuclear Magnetic Resonance Spectroscopy to the Study of the Mechanism of Pyrolysis of tert -Butylarsine and tert -Butylarsine- d₂

The synthesis of tert-butylarsine-d₂ from tert-butylarsenic dichloride and LiAlD₄ is described. No resonances at 2.65 ppm (from AsH₂) are observed in the ¹H NMR spectrum, indicating the isotopic purity is greater than 95%. The pyrolyses of tert-butylarsine and tert-butylarsine-d₂ were studied by using a flow reactor operated between 425 and 550 °C at total pressures of 0.001, 5, and 700 Torr. At 5 and 700 Torr, nitrogen was used as the carrier gas. The volatile products of the reaction were trapped in a liquid nitrogen cooled trap, transferred under vacuum into an NMR tube, and quantitatively analyzed by using ¹H NMR spectroscopy. Three important results from the study are (1) the isobutane produced during the pyrolysis of tert-butylarsine-d₂ was Me₃CD, (2) C₂Me₆ was proven not to be a product of the reaction, (3) isobutane was found to be the major product at atmospheric pressure, while isobutene was predominant at low pressures in agreement with previous studies. These data allow us to evaluate the possible mechanisms for the pyrolysis and discard a mechanism involving radical non-chain reactions.