Paraformaldehyde and formaldehyde - Which is the difference? (Feb/16/2008 )

Hello,

does anybody know the difference between formaldehyde and paraformaldehyde?

Thanks
Drosy

From a chemist point of view paraformaldehyde is a short chain polymere of formaldehyde.

An aqeous solution of formaldehyde will spontaneously polymerise forming insoluble paraformaldehyde. So to slow down this polymerisation, methanol is added to the aqeous solution.... making the typical (4%-15%) formaldehyde solution.

But sometimes a methanol free solution of formaldehyde is desired. And paraformaldehyde in solution will depolymerise to formaldehyde if strongly heated. The solution of formaldehyde thus obtain from depolymerisation of paraformaldehyde is incorrectly named 'paraformaldehyde'. A little confusing, I am sure.

In the past, and in labs like mine, this process of depolymerising paraformaldehyde was the way to prepare a contaminant free solution of formaldehyde. So you will still see alot of references in literature of 'paraformaldehyde' being used as a fixative, when they actually mean formaldehyde derived from depolymerisation of paraformaldehyde.