Cyanuric acid esters

Cyanate/Cyanurate. When aryl cyanate esters are heated to 150 to 250°C, they cyclotrimerize to cyanuric acid esters (Fig. 3.62). They can be catalyzed by organo-metallic and active hydrogen compounds. When the monomer is a dicyanate such as bisphenol A dicyanate (Fig. 3.63), the result is a highly cross-linked heterocyclic polymer (Table 3.57). Using a novolac polycyanate has produced Tg and useful life over 300°C. 

FIGURE 3.62 Aryl cyanate ester cyclotrimerization to cyanuric acid ester. 

Residual monomers in the latex are avoided either by effectively reacting the monomers to polymer or by physical or chemical removal. The use of tert-huty peroxypivalate as a second initiator toward the end of the polymeri2ation or the use of mixed initiator systems of K2S20g and tert-huty peroxyben2oate (56) effectively increases final conversion and decreases residual monomer levels. Spray devolatili2ation of hot latex under reduced pressure has been claimed to be effective (56). Residual acrylonitrile also can be reduced by postreaction with a number of agents such as monoamines (57) and dialkylamines (58), ammonium—alkali metal sulfites (59), unsaturated fatty acids or their glycerides (60,61), their aldehydes, esters of olefinic alcohols, cyanuric acid (62,63), andmyrcene (64). 

Virtually all of the organo derivatives of CA are produced by reactions characteristic of a cycHc imide, wherein isocyanurate nitrogen (frequendy as the anion) nucleophilically attacks a positively polarized carbon of the second reactant. Cyanuric acid and ethylene oxide react neady quantitatively at 100°C to form tris(2-hydroxyethyl)isocyanurate [839-90-7] (THEIC) (48—52). Substitution of propylene oxide yields the hydroxypropyl analogue (48,49). At elevated temperatures (- 200° C). CA and alkylene oxides react in inert solvent to give A/-hydroxyalkyloxazohdones in approximately 70% yield (53). Alternatively, THEIC can be prepared by reaction of CA and 2-chloroethanol in aqueous caustic (52). THEIC can react further via its hydroxyl fiinctionahty to form esters, ethers, urethanes, phosphites, etc (54). Reaction of CA with epichlorohydrin in alkaline dioxane solution gives... 

A new polymer type which emerged as important materials for circuit hoards are polycyanurates. The simplest monomer is the dicyanate ester of hisphenol A. When polymerized, it forms three-dimensional, densly cross-linked structures through three-way cyanuric acid (2,4,6-triazinetriol) ... 

Its salts also exist in the form of a trimer, cyanuric acid (III), which is produced on heating the salts of isocyanic acid with acetic acid. Esters of cyanuric acid undergo isomerization when heated and are converted into esters of isocyanuric acid (IV) ... 

It many ways the alkyl cyanurates behave as typical esters. They are hydrolyzed to cyanuric acid and the appropriate alcohol, and readily undergo transesterification reactions. Cyanurates react with ammonia to form melamine under severe conditions <59HC(l3)l, p.i7). The reaction with amines usually gives mixed products, but triallyl cyanurates react to form the monosubstituted products in excellent yields (Scheme 35) (75S182.75S184). 

Squaric acid esters (Fig. 5a) sometimes are used to link glycans to proteins (52, 54—56). A-Acetyl-chito-oligosaccharides were linked to silk fibroin by reacting solubilized siUc fibroin with cyanuric chloride-activated oligosaccharides (Fig. 5b). 

Cyanuric Acid.—That iso-cyanic acid has the constitution given to it is established by the constitution of the alkyl derivatives which are not true esters (p. 73) and also by its relation to cyanuric acid. This latter acid is a polymer of iso-cyanic acid, viz., (HNCO)3. It is obtained by heating urea and the reactions will be considered presently when we study this compound. This source of the acid is the basis of the name cyan-uric acid. It is a solid crystallizing from water solution in prisms which contain two molecules of water of crystallization. Like iso-cyanic acid cyanuric acid yields alkyl derivatives of two isomeric forms, corresponding to polymers of cyanic and iso-cyanic acid derivatives. The ethyl derivatives have the following constitutions ... 

Alcoholysis of amides is possible, although it is usually difficult. It has been most common with the imidazolide type of amides (e.g., 100). For other amides, an activating agent is usually necessary before the alcohol will replace the NR2 unit. Dimethylformamide, however, reacted with primary alcohols in the presence of 2,4,6-trichloro-l,3,5-pyrazine (cyanuric acid) to give the corresponding formate ester. Treatment of an amide with triflic anhydride (CF3SO2OSO2CF3) in the... 

Another general approach to acid anhydrides from carboxylic acids was developed with esters of cyanuric acid as reagents (equation 37). If the reactions are carried out in solvents like carbon tetrachloride or benzene, the resulting aryl esters of carbaminic acid are insoluble and can be removed by filtration. 

Ketene S/v -acetals are usually attacked by electrophilic reagents at the -carbon, yielding iminium salts, thus ketene 5,lV-acetals have been alkylated and acylated. Similar reactions are described with chlo-roformic acid esters, cyanuric chloride, m-nitrophenylsulfenyl chloride, 2,4-dinitrochlorobenzene, 3-chloro-2-cyanoacrylonitriles and 2-chlorovinyl phenyl ketone. Usually it is not the initially formed iminium compounds but the substituted ketene Sfl-acetals which are isolated, e.g. (120) and (121 Scheme 12). ... 

Polycyanurates take their name from the propagation of their three-dimensional, densely crosslinked structures through three-way cyanuric acid (2,4,6-triazinetriol) linkages. In actual production, they are formed by trimerization of cyanate ester monomers (Table 3.29) of the form Ar-O-CN, where Ar is an aromatic group (Figure 3.40). 

Beilstein Handbook Reference) Activator OC Ai3-26448 BRN 0235560 Cyanuric acid, tri-2-propenyi ester Cyanuric acid triallyl ester EINECS 202-936-7 NSC 4804 Perkalink 300 Perkalink 300-50D Rhenofit TAC TAG Triallyl cyanurate Tripropargyl cyanurate 2,4,6-Tri(allyloxy)-s-triazine 2,4,6-Triallyloxy-1,3,5-triazine 1,3,5-Triazine, 2,4,6-tris(2-propenyloxy)- s-Triazine, 2,4,6-tris(allyloxy)- 2,4,6-Triprop-2-ynyloxy-s-triazine ... 

Reaction of cyanuric chloride with amines to give reactive dyes 2. Sulfonation and nitration of naphthalene at low temperatures 3. Reaction between terephthalic acid and ethylene oxide in a solvent in the presence of dissolved catalysts 4. Manufacture of diisocyanate by reaction between phosgene and hydrochlorides of amines 5. Alkaline hydrolysis of solid esters such as di-/3-chloroelhyl oxalate and nitrobenzoic acid esters Venkatraman (1972) Groggins (1958) Hydrocarbon Proc. Petrol. Refiner (1971) Bhatia et al. (1976) Sharma and Sharma (1969, I970a,b)... 

The Aicello Chemical Co. of Aichi, Japan has disclosed a flame retardant for polyolefins (US 5852082) consisting of melamine cyanurate, fine silica and a phosphoric acid ester. The material emits no hazardous gases on combustion or incineration, needs no extra costs for treating ash, and exhibits excellent flame resistance and strength. 

A variety of non-cyanoacrylate-based modifiers have also been proposed over the last two decades. Some of the earliest of these were the dialkenyl phthalates. Addition of 1-25% concentrations of the phthalate ester to the cyanoacrylate was claimed to improve wet heat resistance. A similar type of heat durability promoter consists of acrylate or methacrylate esters of phosphonates, polyols, or cyanuric acid. Here too, the improvement in heat resistance depends upon curing at elevated temperature, presumably to form a network of the additive, which may also coreact radically with the cyanoacrylate. The use of such additives results in improved heat resistance at 1-20% concentrations. 

The resulting polymers of intermediate molecular weight can be recovered as liquids solids or solutions which can be further reacted to a fully thermoset matrix linked by s-triazine ring structures. This network can be more accurately classified as a polycyanurate comprising the esters of bisphenol A with cyanuric acid. 

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