Hexamethylenetetramine Explained

Hexamethylenetetramine, also known as methenamine, hexamine, or its trade name Urotropin, 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 organic compounds, including plastics, pharmaceuticals, and rubber additives. It sublimes in vacuum at 280 °C.

Synthesis, structure, reactivity

Hexamethylenetetramine was discovered by Aleksandr Butlerov in 1859.[1] [2] It is prepared industrially by combining formaldehyde and ammonia:[3]

The reaction can be conducted in gas phase and in solution.

The molecule has a tetrahedral cage-like structure, similar to adamantane. Four vertices are occupied by nitrogen atoms, which are linked by methylene groups. 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 (e.g. alkylation with chloroallyl chloride gives quaternium-15).

Applications

The dominant use of hexamethylenetetramine is in the production of solid (powder) or liquid phenolic resins and phenolic resin moulding compounds, in which it is added as a hardening component. These products are used as binders, e.g., in brake and clutch linings, abrasives, non-woven textiles, formed parts produced by moulding processes, and fireproof materials.[3]

Medical uses

As the mandelic acid salt (methenamine mandelate) or the hippuric acid salt (methenamine hippurate),[4] it is used for the treatment of urinary tract infections. In an acidic environment, methenamine is believed to act as an antimicrobial by converting to formaldehyde.[4] [5] A systematic review of its use for this purpose in adult women found there was insufficient evidence of benefit and further research was needed.[6] A UK study showed that methenamine is as effective as daily low-dose antibiotics at preventing UTIs among women who experience recurrent UTIs. As methenamine is an antiseptic, it may avoid the issue of antibiotic resistance.[7] [8]

Methenamine acts as an over-the-counter antiperspirant due to the astringent property of formaldehyde.[9] Specifically, methenamine is used to minimize perspiration in the sockets of prosthetic devices.[10]

Histological stains

Methenamine silver stains are used for staining in histology, including the following types:

Solid fuel

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, although its fumes are toxic.

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.

Food additive

Hexamethylenetetramine 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,[11] where it is listed under E number E239, however it is not approved in the USA, Russia, Australia, or New Zealand.[12]

Reagent in organic chemistry

Hexamethylenetetramine is a versatile reagent in organic synthesis.[13] 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).

Explosives

Hexamethylenetetramine is the base component to produce RDX and, consequently, C-4[3] as well as octogen (a co-product with RDX), hexamine dinitrate, hexamine diperchlorate and HMTD.

Pyrotechnics

Hexamethylenetetramine is also used in pyrotechnics to reduce combustion temperatures and decrease the color intensity of various fireworks.[14] Because of its ash-free combustion, hexamethylenetetramine is also utilized in indoor fireworks alongside magnesium and lithium salts.[15] [16]

Historical uses

Hexamethylenetetramine was first introduced into the medical setting in 1895 as a urinary antiseptic.[17] It was officially approved by the FDA for medical use in the United States in 1967. However, it was only used in cases of acidic urine, whereas boric acid was used to treat urinary tract infections with alkaline urine.[18] Scientist De Eds found that there was a direct correlation between the acidity of hexamethylenetetramine's environment and the rate of its decomposition.[19] Therefore, its effectiveness as a drug depended greatly on the acidity of the urine rather than the amount of the drug administered. In an alkaline environment, hexamethylenetetramine was found to be almost completely inactive.

Hexamethylenetetramine was also used as a method of treatment for soldiers exposed to phosgene in World War I. Subsequent studies have shown that large doses of hexamethylenetetramine provide some protection if taken before phosgene exposure but none if taken afterwards.[20]

Producers

Since 1990 the number of European producers has been declining. The French SNPE factory closed in 1990; in 1993, the production of hexamethylenetetramine in Leuna, Germany ceased; in 1996, the Italian facility of Agrolinz closed down; in 2001, the UK producer Borden closed; in 2006, production at Chemko, Slovak Republic, was closed. Remaining producers include INEOS in Germany, Caldic in the Netherlands, and Hexion in Italy. In the US, Eli Lilly and Company stopped producing methenamine tablets in 2002.[21] In Australia, Hexamine Tablets for fuel are made by Thales Australia Ltd. In México, Hexamine is produced by Abiya. Many other countries who still produce this include Russia, Saudi Arabia, and China.

Notes and References

  1. Ueber einige Derivate des Jodmethylens . Butlerow A . . 1859 . 111 . 2 . 242–252 . de . 10.1002/jlac.18591110219 . On some derivatives of methylene iodide. In this article, Butlerov discovered formaldehyde, which he called "dioxymethylen" (methylene dioxide) [page 247] because his empirical formula for it was incorrect (C4H4O4). On pages 249–250, he describes treating formaldehyde with ammonia gas, creating hexamine.
  2. Ueber ein neues Methylenderivat . Butlerow A . Ann. Chem. Pharm. . 1860 . 115 . 3 . 322–327 . 10.1002/jlac.18601150325 . On a new methylene derivative . de.
  3. Encyclopedia: Amines, Aliphatic . Ullmann's Encyclopedia of Industrial Chemistry . Wiley-VCH Verlag GmbH . 2000 . 9783527306732 . 10.1002/14356007.a02_001 . Eller K, Henkes E, Rossbacher R, Höke H .
  4. Lo TS, Hammer KD, Zegarra M, Cho WC . Methenamine: a forgotten drug for preventing recurrent urinary tract infection in a multidrug resistance era . Expert Review of Anti-Infective Therapy . 12 . 5 . 549–554 . May 2014 . 24689705 . 10.1586/14787210.2014.904202 . 207199202 .
  5. Chwa A, Kavanagh K, Linnebur SA, Fixen DR . Evaluation of methenamine for urinary tract infection prevention in older adults: a review of the evidence . Therapeutic Advances in Drug Safety . 10 . 2042098619876749 . 2019 . 31579504 . 6759703 . 10.1177/2042098619876749 .
  6. Bakhit M, Krzyzaniak N, Hilder J, Clark J, Scott AM, Mar CD . Use of methenamine hippurate to prevent urinary tract infections in community adult women: a systematic review and meta-analysis . The British Journal of General Practice . 71 . 708 . e528–e537 . July 2021 . 34001538 . 8136580 . 10.3399/BJGP.2020.0833 . Systematic review .
  7. 2022-12-20 . Methenamine is as good as antibiotics at preventing urinary tract infections . NIHR Evidence . en . 10.3310/nihrevidence_55378. 254965605 .
  8. Harding C, Mossop H, Homer T, Chadwick T, King W, Carnell S, Lecouturier J, Abouhajar A, Vale L, Watson G, Forbes R, Currer S, Pickard R, Eardley I, Pearce I, Thiruchelvam N, Guerrero K, Walton K, Hussain Z, Lazarowicz H, Ali A . 6 . Alternative to prophylactic antibiotics for the treatment of recurrent urinary tract infections in women: multicentre, open label, randomised, non-inferiority trial . BMJ . 376 . e068229 . March 2022 . 35264408 . 8905684 . 10.1136/bmj-2021-0068229 .
  9. Susak Z, Minkov R, Isakov E . The use of Methenamine as an antiperspirant for amputees . Prosthetics and Orthotics International . 20 . 3 . 172–175 . December 1996 . 8985996 . 10.3109/03093649609164439 . 24088433 . free .
  10. Susak . Z. . Minkov . R. . Isakov . E. . December 1996 . The use of Methenamine as an antiperspirant for amputees . Prosthetics & Orthotics International . en . 20 . 3 . 172–175 . 10.3109/03093649609164439 . 8985996 . 24088433 . 0309-3646. free .
  11. UK Food Standards Agency: Web site: Current EU approved additives and their E Numbers . 2011-10-27.
  12. Australia New Zealand Food Standards CodeWeb site: Standard 1.2.4 - Labelling of ingredients . 8 September 2011 . 2011-10-27.
  13. Hexamethylenetetramine, A Versatile Reagent in Organic Synthesis . Blažzević N, Kolbah D, Belin B, Šunjić V, Kajfež F . . 1979 . 1979 . 3 . 161–176 . 10.1055/s-1979-28602 . 97756228 .
  14. DE. 3402546. Pyrotechnischer Satz zur Erzeugung von Lichtblitzen. patent. 1985-08-01. Lohmann. Erwin.
  15. US. 6214139. Low-smoke pyrotechnic compositions. patent. 2001-04-10. Hiskey. Chavez. Naud. Michael A.. David E.. Darren L.. The Regents of the University of California. Los Alamos National Laboratory.
  16. GB. 2502460. Pyrotechnic composition with spark producing material. patent. 2013-11-27. Wraige. John Douglas Michael.
  17. 10.1001/jama.1913.04350190019006. An Experimental Study of the Antiseptic Value in the Urine of the Internal Use of Hexamethylenamin. 1913. Hinman F . JAMA: The Journal of the American Medical Association. 61. 18. 1601.
  18. On Urinary Antiseptics. Elliot. 1913. British Medical Journal. 98. 685–686.
  19. Heathcote RS . Hexamine as an Urinary Antiseptic: I. Its Rate of Hydrolysis at Different Hydrogen Ion Concentrations. II. Its Antiseptic Power Against Various Bacteria in Urine. British Journal of Urology. 7. 1. 1935. 9–32. 0007-1331. 10.1111/j.1464-410X.1935.tb11265.x.
  20. Diller WF . The methenamine misunderstanding in the therapy of phosgene poisoning . Archives of Toxicology . 46 . 3–4 . 199–206 . December 1980 . 7016075 . 10.1007/BF00310435 . 2423812 .
  21. Web site: Re: Equialence of methenamine Tablets Standard for Flammability of Carpets and Rugs . July 29, 2004 . Alan H. Schoen . https://web.archive.org/web/20081005165422/https://www.cpsc.gov/businfo/methtabs.pdf . 2008-10-05.