Hexamethylenetetramine (methenamine) is a heterocyclic organic compound with the formula (CH2)6N4. This white crystalline compound is highly soluble in water and polar organic solvents. It has a cage-like structure similar to adamantane. It is useful in the synthesis of other chemical compounds, e.g., plastics, pharmaceuticals, rubber additives. It sublimes in vacuum at 280 °C.
Synthesis, structure and reactivity of methenamine
Hexamethylenetetramine is prepared industrially by combining formaldehyde and ammonia.The reaction can be conducted in gas phase and in solution.
The molecule has a symmetric tetrahedral cage-like structure, similar to adamantane, whose four "corners" are nitrogen atoms and "edges" are methylene bridges. Although the molecular shape defines a cage, no void space is available at the interior for binding other atoms or molecules, unlike crown ethers or larger cryptand structures.
The molecule behaves like an amine base, undergoing protonation and N-alkylation.
Applications of methenamine
The dominant application of hexamethylenetetramine is in the production of powdery or liquid preparations of phenolic resins and phenolic resin moulding compounds, where it is added as a hardening component. These products are always used as binders, e.g. in brake and clutch linings, abrasive products, non-woven textiles, formed parts produced by moulding processes, and fireproof materials.
It has been proposed that hexamethylenetetramine could work as a molecular building block for self-assembled molecular crystals.
As the mandelic acid salt (generic methenamine mandelate, USP) it is used for the treatment of urinary tract infection. It decomposes at an acidic pH to form formaldehyde and ammonia, and the formaldehyde is bactericidal; the mandelic acid adds to this effect. Urinary acidity is typically ensured by co-administering vitamin C (ascorbic acid) or ammonium chloride. Its use had temporarily been reduced in the late 1990s, due to adverse effects, particularly chemically-induced hemorrhagic cystitis in overdose, but the use has now been re-approved because of the prevalence of antibiotic resistance to more commonly used drugs. This drug is particularly suitable for long-term prophylactic treatment of urinary tract infection, because bacteria do not develop resistance to formaldehyde. It should not be used in the presence of renal insufficiency. Methenamine in the form of cream and spray is successfully used for treatment of excessive sweating and related to it odour.
Methenamine silver stains can be used for staining in histology, including the following types:
Grocott's methenamine silver stain is used widely as a screen for fungal organisms.
Jones' stain, a methenamine silver-Periodic acid-Schiff that stains for basement membrane, availing to view the "spiked" Glomerular basement membrane associated with membranous glomerulonephritis.
Together with 1,3,5-trioxane, hexamethylenetetramine is a component of hexamine fuel tablets used by campers, hobbyists, the military and relief organizations for heating camping food or military rations. It burns smokelessly, has a high energy density of 30.0 megajoules per kilogram (MJ/kg), does not liquify while burning, and leaves no ashes.
Standardized 0.149 g tablets of methenamine (hexamine) are used by fire-protection laboratories as a clean and reproducible fire source to test the flammability of carpets and rugs.
Hexamethylene tetramine or hexamine is also used as a food additive as a preservative (INS number 239). It is approved for usage for this purpose in the EU, where it is listed under E number E239, however it is not approved in the USA, Russia, Australia, or New Zealand.
Reagent in organic chemistry
Hexamethylenetetramine is a versatile reagent in organic synthesis. It is used in the Duff reaction (formylation of arenes), the Sommelet reaction (converting benzyl halides to aldehydes), and in the Delepine reaction (synthesis of amines from alkyl halides).
Hexamethylenetetramine is the base component to produce RDX and, consequently, C-4 as well as Octogen, hexamine dinitrate and HMTD.