Insight into a direct solid–solid transformation: a potential approach for the removal of residual solvents

Here we report two new crystal forms of adenosine 3′,5′-cyclic monophosphate sodium and the discovery of the direct solid–solid transformation process from its methanol trihydrate (solvate) to its pentahydrate form (hydrate) that is only mediated by humidity. These findings provide a potential approach for the removal of residual solvents in the manufacturing of pharmaceuticals and food additives.