Difference between revisions of "Hexamine"

Revision as of 07:28, 17 October 2015

Recrystallised hexamine and an example of it in tablet form.

Hexamine (or methenamine) is a solid, flammable organic compound that finds a use as a starting point for a few energetic materials.

Properties

Chemical

Hexamine burns slowly, without producing smoke or melting. It is an effective reducing agent in energetic mixtures.

It is able to form salts, but at low pH the molecule breaks down into ammonia and formaldehyde. 

Reactions with hydrogen peroxide form a very unstable organic peroxide explosive, similar to acetone peroxide, called HMTD.

Mild nitration forms hexamine dinitrate while complete nitration forms the powerful military explosive RDX. 

Hexamine can also be reacted with perchloric acid to form the moderately powerful explosive hexamine diperchlorate.

Tablets of hexamine set on fire can be used as heat sources in a home lab. It is included in some chemistry sets for this purpose. You can also buy them, and a simple apparatus for burning them, in a camping or survival store.

Physical

Hexamine is soluble in water. The solid and solutions have a mild smell akin to fish, or cat food. Some people find this quite unpleasant. 

It is similar to the superbase DABCO, mainly in structure and physical properties. 

Availability

Hexamine is widely used in camping fuel tablets, either pure or mixed with 1,3,5-trioxane. In both cases, a wax binding covers the small tablets, requiring the hexamine to be dissolved in water and the binders filtered off before use.  

Preparation

Combinations of ammonia and formaldehyde create very pure hexamine, and the solution can be boiled to expel excess ammonia or fomaldehyde and to crystallize out the soluble hexamine. Hexamine can be further purified by sublimating it at high heat and depositing it on a cool surface. This can be accomplished with a bucket, a lid, and a heating source. 

Projects

• RDX synthesis
• HMTD synthesis
• Lithium perchlorate-hexamine rocket fuel

Handling

Safety

Hexamine is not terribly toxic, so its major hazard comes from its high flammability. Also, because it does not melt or produce smoke while burning, it can be difficult to tell that samples are actually on fire, leading to accidental burns. 

Storage

Hexamine should be stored in closed bottles, at room temperature or lower.

Disposal

Hexamine can be safely burned.

References

Relevant Sciencemadness threads