Preparation and Isolation of Active Catalyst

Upon completion of the reaction, the catalyst is released from solution in three steps. First, the reaction medium is heated under vacuum to partially remove acetic acid (75% of the initial amount used). At 100 mbar pressure, the pot temperature remains below 60 °C throughout the distillation, minimizing the potential for thermal degradation of the catalyst. The vacuum is then released to nitrogen and the reaction medium is cooled to room temperature. Next, methanol is back added to the reactor in an amount equivalent to the volume of acetic acid removed. Finally, water, used as a non-solvent, is added continuously drop wise to precipitate the catalyst. Seeding the mixture with catalyst crystals during water ad- 

Owing to the large crystal size, the subsequent filtration, washing, and cake drying steps are facilitated, and the catalyst stability is enhanced. The isolated yield of product is typically in the range of 95-97% of theory, an improvement over that for the Co(II) complex. Ironically, oxidation of the Co(II) complex to the Co(III)OAc catalyst is problematic during isolation of the Co(II) species and results in non-trivial losses. Fig. 3 shows an enlarged view of representative catalyst crystals prepared via this new method. 

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