Cyanuric acid-melamine

The 1,3,5-triazines are amongst the oldest known organic molecules. Originally they were called the symmetric triazines, usually abbreviated to s- or sym- triazines. The numbering follows the usual convention of beginning at the heteroatom as shown for the parent compound 1,3,5-triazine (1). Rather non-systematic nomenclature is prevalent even in the current literature, because some of the compounds have been known for at least 150 years. The non-systematic names of some of the more important 1,3,5-triazines are listed in Table 1. The terms melamine, cyanuric acid and cyan uric chloride will be used throughout this chapter, and the term triazine will refer to 1,3,5-triazines only. In addition to the above names, 2,4,6-trialkoxy-l,3,5-triazines (2) are called cyanurates. Similarly, 1,3,5-trialkyl-1,3,5-triazines (3) are called isocyanurates. 

Figure 10.51 Melamine-cyanuric acid derivatives arranged according to their relative stability as measured by the HBI(N — 1) parameter. (Reprinted with permission from Section Key Reference 1995 American Chemical Society).

We used our experience with reversible encapsulation to arrive at a rule regarding the proper filling of space, the 55% solution [87]. The filling of space probably drives other recognition phenomena, even in those synthetic receptors that do not completely surround their targets [88]. Some of the earliest, finite self-assemblies in solution based on melamine/cyanuric acid recognition [89] had no other function than to fill space. However unconventional, the departure from mainstream physical organic chemistry [90] is familiar to us and may offer rewards. 

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 11.12. Melamine/cyanuric acid crystal structure.

This approach mimics familiar biological self-assembly phenomena such as protein folding [ 192], protein aggregation [ 192] and nucleotide pairing [ 188]. It incorporates features described in each of the above strategies (i.e., I—III), to give specialized nanoscopic structures, that can be precisely designed, usually with excellent control over CMDPs. Recent examples include so called structure directed synthesis by Stoddart [3a] (see Chapter 1 of this book) to produce toroidal bis-bipyridinium cyclophanes that are reminiscent of a molecular abacus , melamine-cyanuric acid lattices by Whitesides [193] and unique helical structures based on coordination of bipyridyl units to copper (II) ions by Lehn [194],... 

Fig. 21 The hexagonal melamine-cyanuric acid hydrogen-bonded array [ 166]...

FIGURE 38.3. Melamine cyanuric acid poisoning, feline kidney tubules are lined by degenerate, necrotic and flattened epitbelium and contain crystalline material. Arrow shows crystalline material arranged in concentric pattern. H E stain x40. 

Similarly to melamine, cyanuric acid has two tautomeric forms [40] ... 

CAS 37640-57-6 EINECS/ELINCS 253-575-7 Synonyms Melamine-cyanuric acid compd. Melamine isocyanurate 2,4,6-Triamino-s-triazine compd. with s-triazinetriol s-Triazine, 2,4,6-triamino-, compd. with s-triazine-triol 1,3,5-Triazine-2,4,6-(1H,3H,5H)-trione, compd. with 1,3,5-triazine-2,4,6-triamine (1 1)... 

Melamine-cyanuric acid compd.. See Melamine cyanurate... 

Fig. 2.10 Chemical structures of melamine, cyanuric acid and uric acid. (Authors own work)...

Sanlu brand powdered milk was found to eontain significant amounts of melamine, with the highest coneentration being 2563 mg/kg of produet (0.2 %). The kidney stones in patients suffering from melamine were not melamine-cyanuric acid, but melamine and uric acid in 1 1.2-2.1 ratios (Fig. 2.11). Natural formation of uric acid kidney stones is not unknown, but they constitute only 5-10% of all kidney stones, especially in developing eountries. Babies excrete urie aeid in much... 

Examples of cocrystals containing chains, ribbons, and other infinite ID motifs (Scheme 8) include bipyridine dihydroxybenzene, melamine cyanuric acid, bipyridine (fluorinated)dibromobenzene, 2-aminopyridine dicar-boxylic acids, triaminopyrimidine barbituric acid, 2-aminopyrimidine dicarboxylic acid, " 1,2,3-trihydroxy-benzeneihexamethylenetetramine, diols diamines, bis-benzimidazole dicarboxylic acids, and 2-amino-5-nitro-pyrimidine 2-amino-3-nitropyridine." ... 

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. 

Secrecy surrounding the scandal has made it impossible to know for certain how many babies were poisoned—and how many died. The formation of the toxic melamine-cyanuric acid complex is the result of particularly strong attractive forces between the melamine and cyanuric acid molecules. Attractive forces between molecules (intermolecular forces) and within molecules (intramolecular forces) determine many of the physical properties of liquids and solids. 

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