Melamine and Cyanuric Acid

Melamine is a triazine ring with three amino groups and a widely used compound in the manufecturing of plastics, adhesives, flame retardants, fertilizers, and glues. Cyanuric acid is a structural analog of melamine. It may be found as an impurity of melamine. Cyanuric acid is an FDA-accepted component of feed-grade biuret, a ruminant feed additive. It is also found in swimming pool water as the dissociation product of dichloroisocyanurates used for water disinfection. 

Due to the widespread use of melamine, also as a material in contact with food, low levels may be detected in food, not necessarily due to adulteration. Melamine is not metabolized and is rapidly eliminated in the urine. It is known to form bladder 

05 mL7min detection positive ESI-MS for melamine (SIM m/z 127), negative ESI-MS for cyanuric acid (SIM m/z 128) injection volume lOpL peaks (1) melamine and (2) cyanuric acid. 

3 Lunn, G. and Hellwig, L.G. (1998) Handbook ofDerivatization Reactions for HPLC, Wiley-Intersdence, New York. 

4 Wang, P.G. and He, W. (eds) (2011) Hydrophilic Interaction Liquid Chromatography (HRIC) and Advanced Applications, CRC Press, Boca Raton. 

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Co-ordination chemistry is not the only possible approach to the successful preparation of supramolecular dendrimers. Other examples include hydrogen-bonded dendrimers, which have been prepared using tetracar-boxylic acid moieties as the linking species, and others have been prepared where the hydrogen bonds were developed using melamine and cyanuric acid at the focal point (i.e. the point towards which convergent synthesis is directed). 

Above its melting point (360 0 about 90% of melamine cyanurate is converted to volatile products (360-450 0, 2nd step) in which free melamine and melamine cyanurate were recognised by IR. This indicates that a competition takes place between evaporation of the unalterated salt and its thermal dissociation to melamine and cyanuric acid. Melamine behaves then as described above while cyanuric acid which, heated alone in TG volatilises completely above 300 0, is known to decompose to cyanic acid (8). 

Exciting motives obtained by hydrogen bonding of calixarenes bearing 2-pyridone [32b], carbonyl and pyridyl [32c], urea [32d], melamine and cyanuric acid [32e] and other acceptor and donor groups have been recently reviewed by Bohmerand Shivanyuk [32a]. 

Hexagonal layer structure of the 1 1 complex of melamine and cyanuric acid. Three kinds of assembly in lower dimensions are possible (a) linear tape, (b) crinkled tape, and (c) rosette. 

Although less effective, intermolecular steric hindrance between substituents is another approach to achieving selection of the cyclic CA3M3 rosette in preference to competitive linear motifs in both the solid and solution states (Figure 3.2) [14]. Choosing the substituents on the melamine and cyanuric acid groups in such a... 

The complex between melamine and cyanuric acid (1 1) was reported in the literature in the late 1970s, but it was only in the early 1990s that the contributions from Whitesides and the concept of self-assembly popularized these systems [45]. Whitesides and co-workers reported the formation of tapes (Fig. 11.11), crinkled tapes and cyclic hexamers (rosettes) formed between barbituric acid and N,N -bis(p-substituted phenyl)melamine [46], In this they effectively blocked one face of melamine and, by manipulating substituents at the para position, different structures were obtained. Whiteside s putative suggestion that melamine/cyanuric acid formed an extended array (Fig. 11.12) was confirmed recently by Rao et al. with the crystal structure [47]. Hamilton and coworkers reported the crystal structure of a 5-substituted isophthalic acid derivative, which forms a cyclic aggregate held together with six pairs of hydrogen bonds, which in a way resembles the trimesic acid (Fig. 11.13) [48]. 

Figure 2 The structure of the hydrogen-bonded CA M lattice. Three classes of aggregates that we have observed in solution and the solid state are highlighted the rosette, crinkled tape, and linear tape motifs. The molecular strucmres of melamine and cyanuric acid and their abbreviated representation as dark and light disks are shown...

Figure 36 Supramolecular assemblies of finite size (a) rosettes from melamine and cyanuric acid [272,405]. (b) Cyclic hexamers from isophthalic acid bearing bulky substituents in 5-position, (c) 3 x 3 grid from metal-complexed biphenyl phenanthrolines [407]. With permission of Wiley-VCH...

Pet Food-Related Toxicity by Melamine and Cyanuric Acid... 

N. Kimizuka, T. Kawasaki, K. Hirata, T. Kunitake, Supramolecular Membranes. Spontaneous Assembly of Aqueous BUayer Membrane via Formation of Hydrogen Bonded Pairs of Melamine and Cyanuric Acid Derivatives ,]. Am. Chem. Soc., 120,4094 (1998)... 

One of the most highly studied hydrogen bond systems is that based on the triple hydrogen bond interaction between melamine and cyanuric acid. Melamine possesses three DAD faces, whereas cyanuric acid possesses three complementary ADA faces (Fig. 3a). The two molecules cocrystallize to form hexagonal two-dimensional sheets in which all hydrogen bond donors and acceptors are satisfied, a fact that despite earlier predictions was only... 

Fig. 3 (a) The structures of melamine and cyanuric acid and the hydrogen-bonded sheet formed by a 1 1 combination of them, (b) The... 

World Health Organization (2008) Melamine and cyanuric acid toxicity, preliminary risk assessment and guidance on levels in food. 25 September 2008—Updated 30 October 2008. http // www.who.int/foodsafety/fs management/Melamine.pdf (last access February 25, 2014). 

I n 2007, dogs and cats in North America suddenly began to die from kidney failure. The illness was traced to animal food from China. Melamine, used to make plastics, had been deliberately added to food in a bid to meet the contractual demand for the amount of protein in the products. Cyanuric acid, used to disinfect swimming pools, was also found in the food. Melamine alone does not cause kidney failure, but the combination of melamine and cyanuric acid makes a crystalline product that does cause kidney failure. 

In response to these events, a spectrophotometric method was developed to distinguish protein from melamine. Also, mass spectrometric and chromatographic methods were developed to measure melamine and cyanuric acid in foods. 

Melamine Cyanurate [37640-57-6]. This 1 1 adduct (salt) of melamine and cyanuric acid, decomposition temperature 413°C, is a leading flame retardant for unfilled polyamide 6, where it is typically used at 5-10% by weight, but it does not work very well in most glass-filled polyamide 6. It is also less efficient in polyamide 6,6. It is available from Ciba and several other producers. The mode of action has been studied (141-143). 

Figure 14 Aggregates in solution (a) 1 3 complex of hub B with melamines and cyanuric acid A and (b) dendritic hexamer.

Figure 7.29 Effect of mobile-phase pH in the LC-MS analysis of melamine and cyanuric acid on Acclaim Mixed-Mode WAX-1. Column dimensions 150mmx2.1 mm i.d., Spm column temperature 30 °C eluent 90 10 (v/v) MeCN/...

Wang, L Henday, S.M., Liu, X., Tracy, M and Schnute, W.C. (2007) Simultaneous determination of melamine and cyanuric acid using LC-MS with the Acclaim Mixed-Mode WAX-1 column and mass spectrometric detection. Presentation at the 24th Montreux Symposium on LC/MS and Related Techniques, Hilton Head Island, SC, USA. 

Figure 10.257 HILIC separation of melamine and cyanuric acid with MS detection. Separator column Accucore HILIC, 2.6 pm column dimensions 1S0mmx4.6mm i.d. eluent MeCN/50mmol/L NH OAc, pH 5 (90 10 v/v) ...

Figure 2. Schematic representations of preorganization of three melamine by covalent attachment to a center hub (left) and the formation of a rosette structure due to large groups (depicted here as spheres) by peripheral crowding (right). Melamines and cyanuric acid are represented as disks.

There is some evidence demonstrating the advantages of altering/controlling the solid form by co-crystal formation. However, co-crystallization of otherwise non-toxic molecules can sometimes also prove to be fatal. One such case, involving the unexpected co-crystallization of melamine and cyanuric acid has acted as an eye-opener in this field. It further underlines the importance of detailed studies of the solid state characteristics of not only the individual components in a formulation but also their different combinations. 

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