melamine
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| Surname | melamine | |||||||||||||||
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| Molecular formula | C 3 H 6 N 6 | |||||||||||||||
| Brief description |
colorless and odorless monoclinic prisms |
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| Molar mass | 126.12 g mol −1 | |||||||||||||||
| Physical state |
firmly |
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| density |
1.57 g cm −3 (20 ° C) |
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| Melting point |
> 280 ° C ( decomposition ) |
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| Vapor pressure |
<0.1 Pa (20 ° C) |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | ||||||||||||||||
Melamine (2,4,6-triamino- s -triazine ), a colorless substance, is a heterocyclic aromatic compound with nitrogen . Melamine is the starting material for the production of melamine resins , which are used as glues and adhesives or converted into thermosetting plastics .
Extraction and presentation
Justus von Liebig presented melamine from potassium thiocyanate and ammonium chloride for the first time in 1834. The first commercial production took place in 1930, whereupon the importance and quantity of melamine produced annually rose sharply. The trimerization of dicyandiamide (cyanoguanidine) and cyanamide used to play a role.
Melamine is currently carried trimerization of urea won. There are high pressure (> 8 MPa ) and low pressure processes (approx. 1 MPa).
It is one of the chemical substances that are produced in large quantities (" High Production Volume Chemical ", HPVC) and for which the Organization for Economic Cooperation and Development (OECD) collects data on possible hazards (" Screening Information Dataset ", SIDS ) was made. Important manufacturers include BASF , Borealis Agrolinz Melamine , the world's largest producer Orascom Construction Industries ( OCI Melamine division , formerly DSM Melamine ) and Zakłady Azotowe Puławy (ZAP). For the European market, imports from Asia , especially from the People's Republic of China , are also becoming increasingly important.
Plants for the production of melamine are mostly connected directly to those for the production of urea .
In addition to polycyclic compounds such as melam and melem , compounds with hydroxyl groups (-OH) instead of amino groups (-NH 2 ) are produced as by-products. These are ammeline with one, ammelide with two and cyanuric acid with three OH groups. The hydroxy compounds usually only occur in concentrations of less than 0.1% in the finished technical product.
properties
Physical Properties
Melamine begins to decompose when it melts (from around 350 ° C). It is not very soluble in cold water and readily soluble in hot water. The flash point is> 280 ° C, the ignition temperature > 600 ° C.
Chemical properties
The three reactive amine groups enable a large number of chemical reactions, of which the reaction with formaldehyde to form so-called methylol melamines is the most economically important (see figure).
The reaction conditions and the molar ratio of melamine to formaldehyde can influence the equilibrium of melamine via mono-, di-, tri-, tetra-, penta- and even hexamethylolmelamine.
During the production of the impregnating resin (as well as other so-called MF resins ) the reaction product is condensed further, resulting in higher molecular weight compounds.
In addition, melamine forms water-soluble salts with many mineral and organic acids .
Analytics
The qualitative and quantitative determination of melamine or melamine metabolites in complex matrices such as B. Food is reliably carried out with high specificity and sensitivity using the methods of HPLC and the coupling of HPLC with mass spectrometry . Furthermore, Romer Labs developed a screening method based on the ELISA principle. The test method is approved for animal feed, wheat gluten, milk and milk powder according to the criteria of the Grain Inspection, Packers and Stockyards Administration (GIPSA).
use
Industry
The majority of melamine is to aminoplast - resin under the name of melamine resin processed:
- Wood-based glue : For standard products ( e.g. chipboard in furniture construction), pure urea resins are used for cost reasons ; For applications that have increased requirements in terms of moisture resistance, melamine is used as a component in high-quality resin adhesive systems (such as melamine-urea-formaldehyde resins = MUF, with "U" for urea ).
- Impregnating resin: As an MF impregnating resin, melamine resin is used to bond decorative papers to carrier boards (e.g. chipboard). Printed or colored paper is often impregnated with melamine resin, dried and later bonded to the carrier material under pressure and elevated temperature. The resulting surface is characterized by good durability and scratch resistance.
- Melamine resins are often used in camping and children's dishes due to their break resistance. However, when heated to over 70 ° C, this can release harmful amounts of melamine and formaldehyde , which is why it should not be used in microwave ovens . Melamine resin is also found in normal kitchen utensils or as a component in bamboo dishes. There is also the risk that these dishes will be used for cooking and that harmful amounts of melamine and formaldehyde will be released into the prepared food. For the same reasons, dishes containing melamine are unsuitable for storing acidic foods.
Other, quantitatively less important applications:
- Melamine resin foam (trade name Basotect (BASF)) is used as a non-combustible upholstery material in aircraft and cinema seats and as an acoustic absorber. Melamine resin foam panels on walls and / or ceilings absorb sound waves in cinemas, recording studios (e.g. anechoic rooms), classrooms and kindergartens. This improves the acoustics (e.g. better speech intelligibility, less reverberation / shorter reverberation time , acoustically "warmer" atmosphere). Basotect is also used for thermal and acoustic insulation (e.g. soundproofing in discos ).
- Open-pored foam made of melamine resin is also used as a "dirt eraser", such as the trademarks of "Meister Proper", "Meiko" or "Oetex" and "Nanoform". The cleaning effect is based on the abrasive resin particles that are created when rubbing. The particles are picked up by the sponge together with the dirt particles. The sponge is thus used up when cleaning.
- The salt of melamine with cyanuric acid, melamine cyanurate and melamine polyphosphate, are used as flame retardants . Melamine cyanurate is stable up to about 320 ° C, melamine polyphosphate up to 350 ° C.
safety instructions
Ingestion of large amounts leads to the formation of crystals in the urine and urinary bladder stones in various animal species. When high doses in the lethal range were administered to mice and rats, the symptoms were tearing, breathing disorders, tremors, circulatory disorders and paralysis of the forelegs. The lethal oral dose LD 50 is 3161 mg / kg for rats and 3296 mg / kg for mice. An increased incidence of bladder tumors was observed in male rats . Long-term high-dose intake can result in death from kidney failure. The observed crystallization in the urinary tract is not based on melamine, but on its salts, e.g. B. with glycolic acid. Accumulation in the food chain is considered highly unlikely.
The IARC classified melamine as a possible carcinogen in 2017.
Limit values
At the beginning of July 2010, the World Health Organization set a maximum limit of 2.5 milligrams of melamine in one kilogram of food and pet food in the Codex Alimentarius . A limit value of 1 milligram melamine per kilogram has been determined for infant food such as milk powder.
Current studies by the Federal Institute for Risk Assessment have shown that cookware and cooking utensils made of melamine must not be heated to 100 ° C, as otherwise relevant amounts of melamine and formaldehyde could be released. Up to a temperature of 70 ° C there are no health concerns. In 2019, a study by the institute showed that melamine-formaldehyde resin (MFR) dishes in general, and in particular from “bamboo ware” dishes, can release harmful amounts of formaldehyde and melamine when mixed with hot liquids such as coffee, tea or infant formula is filled. The MFH tableware advertised as “bamboo goods” contains bamboo fibers as filler, but is not biodegradable despite the addition of natural fillers. From the “bamboo ware” objects, on average, even significantly higher amounts of formaldehyde and melamine were released than from “conventional” MFR dishes. For melamine the release was on average more than twice as high. While the measured melamine values do not pose a health risk for adults according to the BfR, small children who very often consume hot food from MFH dishes and especially from "bamboo products" could ingest up to three times the tolerated daily dose .
Abuse in animal feed and food
In China in 2006, melamine was used to stretch a shipment of wheat gluten - a component of pet food - destined for the US , to simulate a higher protein content . The feeding resulted in pet deaths from kidney failure, and a nationwide feed recall was initiated in 2007. A comprehensive scientific study has now been presented on the pathophysiology of melamine in domestic cats .
In order to cover up the illegal stretching of milk powder and other dairy products by hitherto unknown substances, but also water , melamine was added to milk powder by Chinese dairies and baby food manufacturers. The resulting increased nitrogen content simulates a higher protein content , since the determination of the nitrogen content according to Kjeldahl is used in food analysis as a simple but unspecific method for determining the protein content. The toxic effects of melamine on the kidneys led to the death of six infants in China in 2008 and the disease of around 294,000 children due to the formation of kidney stones . Melamine has also been found in ready-to-use milk products and common liquid milk.
According to Merck Sequant, who are involved in the production of corresponding test procedures, melamine is not particularly toxic per se. Only when combined with cyanuric acid , a breakdown product of melamine, are kidney stones formed to a considerable extent. It is therefore assumed that in the specific case milk powder was stretched with inferior, impure melamine, but that the mess with melamine itself has been going on unnoticed for years.
On September 25, 2008, the European Union Commission banned the importation of all products for infants and young children from China that contain milk. Nevertheless, at the beginning of October 2008, milk beverages contaminated with melamine had to be withdrawn from circulation in both Austria and Slovakia. At the end of 2008, the Baden-Württemberg Ministry of Consumption found traces of melamine in deer horn salt from China. The authorities started a recall campaign for the product concerned, which does not comply with the purity requirement under food law.
In the first trial of the poisoned baby food, a court in Hebei Province sentenced three defendants to death in January 2009, and two of them were executed on November 24, 2009. You have been convicted of being involved in the manufacture of contaminated milk powder. The court also imposed terms of between five and 15 years in prison for other defendants.
Review articles
- Anthony Kai-ching Hau, Tze Hoi Kwan, Philip Kam-tao Li: Melamine toxicity and the kidney . In: Journal of the American Society of Nephrology . 20, No. 2, February 2009, ISSN 1533-3450 , pp. 245-250. doi : 10.1681 / ASN.2008101065 . PMID 19193777 .
Web links
- Questions and answers on dishes and kitchen utensils made of melamine-formaldehyde resin , FAQ of the BfR of 25 November 2019
Individual evidence
- ↑ a b c Entry on melamine. In: Römpp Online . Georg Thieme Verlag, accessed on November 3, 2014.
- ↑ a b c d e f g Entry on melamine in the GESTIS substance database of the IFA , accessed on December 20, 2019 (JavaScript required)
- ↑ a b c Toxicology and Applied Pharmacology . Vol. 72, Pg. 292, 1984.
- ↑ Paul Giger: On the reaction mechanism of the formation of melamine from urea , dissertation, Zurich, 1958.
- ↑ OECD : Screening Information Dataset (SIDS) Initial Assessment Report (SIAR) for melamines , accessed on October 3, 2014.
- ↑ Orascom: OCI Nitrogen. ( Memento of the original from July 5, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Romer Labs - AgraQuant® Melamine ELISA Test Kit ( Memento from September 24, 2008 in the Internet Archive ).
- ↑ Do not put melamine resin dishes in the microwave , Welt Online, May 13, 2011.
- ↑ Materials with melamine. Retrieved November 21, 2019 .
- ↑ basotect.de .
- ^ Stiftung Warentest : Melamine in dairy products: Don't panic , report from October 1st, 2008.
- ↑ Flame Retardants Center: Melamine Compounds ( Memento of the original from September 22, 2008 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. .
- ↑ Melamin Salts ( Memento of the original from December 8, 2008 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , Department of Macromolecular Chemistry at the Vienna University of Technology
- ↑ Interim Melamine and Analogues Safety / Risk Assessment, US Food and Drug Administration, May 25, 2007.
- ↑ Yann Grosse, Dana Loomis, Kathryn Z Guyton, Fatiha El Ghissassi, Véronique Bouvard, Lamia Benbrahim-Tallaa, Heidi Mattock, Kurt Straif: Some chemicals that cause tumors of the urinary tract in rodents. In: The Lancet Oncology . 18, 2017, pp. 1003-1004, doi : 10.1016 / S1470-2045 (17) 30505-3 .
- ↑ WHO : International experts limit melamine levels in food. Communication dated July 6, 2010.
- ↑ Release of melamine and formaldehyde from dishes and kitchen utensils. (PDF; 64 kB) BfR Opinion No. 012/2011 of March 9, 2011.
- ↑ Federal Institute for Risk Assessment (BfR): Vessels made of melamine-formaldehyde resin such as “coffee to go” cups made of “bamboo goods” can release substances that are harmful to health in hot food. Federal Institute for Risk Assessment (BfR), November 25, 2019, accessed on December 3, 2019 .
- ↑ MSNBC: Human, pet food makers checked for melamine May 3, 2007
- ^ Science Daily: Pet Food Recall: How Melamine Impairs Kidney Function .
- ↑ Cianciolo et al .: Clinicopathologic, histologic, and toxicologic findings in 70 cats inadvertently exposed to pet food contaminated with melamine and cyanuric acid. J Am Vet Med Assoc. 2008 Sep 1; 233 (5): 729-737, PMID 18764706 .
- ↑ "Covered up and concealed: the melamine scandal is spreading" ( Memento of the original from January 29, 2009 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (Zeit Online from December 2, 2008).
- ↑ "Melamine discovered in dairy products in China and Hong Kong" ( Memento from September 18, 2008 in the Internet Archive ) (AFP news from September 18, 2008).
- ↑ a b c The life-threatening fraud with melamine May 11, 2009 magazin.merck.de.
- ↑ Melamine milk also discovered in Slovakia on www.heute.de ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. , October 4, 2008.
- ↑ RP Online: Melamine scandal is widening: chemical also in Christmas cookies? ( Memento of the original from December 5, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , December 2, 2008.
- ↑ FOCUS Online: Two executions in China , November 14, 2009.
- ^ Court imposes death sentences in the milk powder scandal Spiegel Online, January 22, 2009.
