Abstract
During routine pharmaceutical development and scale-up work, severe corrosion of a Hastelloy Alloy C-22 (Alloy 22) filter dryer was observed after single, short (several hour) contact with the product slurry at room temperature. Initial investigations showed that the presence of both 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and HCl was sufficient in an acetonitrile solution to cause rapid corrosion of Alloy 22. More detailed mass loss studies showed initial corrosion rates exceeding 25 mm/y that then decreased over several hours to steady state rates of 3 mm/y to 5 mm/y. The corrosion was highly uniform. Electrochemical measurements demonstrated that although Alloy 22 is spontaneously passive in acetonitrile solution, the presence of HCl leads to the development of a transpassive region. DDQ is a sufficiently strong oxidizer, particularly in acidic solutions, to polarize the Alloy 22 well into the transpassive region, leading to the observed high-corrosion rates.
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