Molybdenum catalyzed ethylene carbonylation. II. Spectroscopic investigation of the reactions and equilibria of molybdenum hexacarbonyl and molybdenum halocarbonyls under reaction conditions

A surprisingly efficient carbonylation of ethylene to yield propionic anhyd ride and propionic acid using halide promoted Mo(CO)(6) catalysts has been recently reported in the literature. Although the earlier report included d etailed kinetics and a unique mechanistic interpretation involving a metall oradical process, the spectroscopic examination, which played an important role in clarifying the reaction mechanism, was only described qualitatively . This report describes the in situ infrared spectroscopic investigation of the chemistry of the molybdenum carbonyl catalysts in greater detail. Emph asis will be on the spectroscopic examinations of the equilibria of Mo(CO)( 6) and the molybdenum halocarbonyls, the oxidation of Mo(0) with alkyl hali des, and in situ regeneration of the active catalyst under reaction conditi ons. As part of this investigation, a general method for the determination of equilibrium constants for reactions involving infrared active species us ing attenuated total reflectance technique, ATR, is described wherein neith er the extinction coefficient nor the effective pathlength are known with c ertainty. The method is demonstrated using the equilibrium between Mo(CO)(6 ) and Mo(CO)(5)I- as an example. (C) 1999 Elsevier Science B.V. All rights reserved.