[Ram012593]

Why is anhydrous sodium hypochlorite less stable than its calcium counterpart? Thanks much in advanced!

[TheodorCurtius]

My guess would be because calcium hypochlorite forms an anhydrous salt, preventing the formation of hypochlorous acid in storage, which readily disproportionates into chloric acid (HClO3) and hydrochloric acid. Solutions of calcium hypochlorite similarly disproportionate upon heating or during storage, while anhydrous calcium hypochlorite mainly decomposes by the much slower oxygen evolution pathway according to: 2 ClO^- ---> O₂ + 2 Cl^-.

For sodium hypochlorite, only a relatively stable pentahydrate is used commercially, but it needs to be stored in the cold to be somewhat stable.

Kirihara, Masayuki, et al. "Sodium hypochlorite pentahydrate crystals (NaOCl· 5H2O): a convenient and environmentally benign oxidant for organic synthesis." Organic Process Research & Development 21.12 (2017): 1925-1937.

[Edit}, just noticed you referred to anhydrous sodium hypochlorite, in that case, it might relate to the crystal structure of anhydrous sodium hypochlorite, which is unknown to date. https://www.chemistryworld.com/news/first-crystal-structure-of-bleach-in-its-200-year-history/4014173.article

This turned out to be a long story with no real answer...apologies.  Most calcium hypochlorite is sold with a reduced hypochlorite content of 65-70%, not even sure if 100% pure calcium hypochlorite is more stable.