Phenol, reaction with cyanates

Cyanatobenzene. This reagent can be prepared in a one-flask reaction by cyanation of phenol with cyanogen bromide prepared in situ. ... 

The reaction of proteins with cyanate has been exploited in the development of a method for the quantitative determination of NH2-terminal residues (Stark 1967a), as well as in a variety of interesting structure-function studies exemplified by those of Smyth (1967) on oxytocin, and Cerami and Manning (1971), as well as Lee and Manning (1973), on sickle cell hemoglobin. Whereas cyanate reacts with a-NH2, -NH2, thiol, imidazole, and phenolic OH groups of proteins, only the amino group derivatives are stable at alkaline pH. 

Cyanogen chloride reacts with sodium sulfide, Na2S, to form sodium thiocyanate, NaSCN. An extension of this involves the reaction of thiolate anions, RS, with CICN to form thiocyanates, RSCN. Similarly, the reaction of phenols produces aromatic cyanates (Kaupp et al., 1998). In such reactions, 3° amines are used to trap hydrogen chloride. 

Cyanate esters (CEs) are formed in excellent yields by the reaction of the corresponding phenols with cyanogen halide [34]. The reaction scheme is shown in Scheme la. The reaction is usually carried out in solution, in the presence of a tertiary amine as the acid scavenger at very low temperatures. Since the trimer-ization reactions of cyanate esters are highly prone to catalysis by spurious impurities, the most difficult aspect of cyanate ester synthesis is their scrupulous purification. Low molar mass esters are purified by distillation or recrystallization. Polymeric cyanates are purified by repeated precipitation in non-solvents such as water, isopropanol, etc. While distillation and recrystallization lead to pure materials, the precipitation method for polymeric cyanates is not always conducive to obtaining pure materials. A recent patent application claims a purification method for polymeric cyanates based on treatment with cation and anion exchangers [35]. 

Tris aryl cyannrate ( Tris aiyloxy s-triazine) Scheme 1. Synthesis of cyanate ester and its reaction with water and phenol... 

The model satisfactorily described the cure behavior for the entire range as experimentally monitored by FTIR, DSC, and torsional braid analysis (TBA). This model satisfactorily explained the cure behavior of both catalyzed and uncatalyzed systems over a wide range of temperature and throughout the curing process. The authors proposing the kinetic model considered the reaction to be triggered by the adventitious water and phenol impurities (whose reactions with the cyanate ester is considered as an equilibrium reaction). Catalysis by the added metal ions, which stabilizes the imino carbonate intermediates by complex-ing, is also considered. The model has considered all possible reaction paths and intermediates as detailed in Sect. 4 and depicted in Scheme 14. Considering the various reactions, expressions could be obtained for the individual apparent empirical rate constants of the second order auto catalytic model in terms of the actual rate constants and equilibrium constants. 

Despite their many attractive features, the search for further improvements in performance and reduction in cost of cyanate esters is never ending and a large number of studies have been devoted to matrix modification through blends, and co-curing of these systems. Reactions of cyanate esters with a variety of functional groups like amines [169], hydroxyl [34, 66], epoxy [170-172], phenols, etc., have been reported, among which the most studied are reactions with epoxy [173,174]. Epoxy-cyanate blends are common and found in many commercial and patented resin formulations. 

Cyanate esters may be modified by co-reaction with monomers or oligomers that contain active hydrogens (e.g., water, phenols, bisphenols, diamines, diepoxides, ethers, esters, etc) [2-6], The PCN modified with reactive monomers usually have a homogeneous single phase, with properties proportional to the ratio of the two components. 

Aryl cyanates585 can be prepared by reaction of phenols with cyanogen halides in the presence of a base ArO + C1CN — ArOCN + Cl. 586 This reaction has also been applied to certain alkyl cyanates.587... 

The cyanate and the epoxide network can be bound by the reaction of phenolic hydroxyls contained in the partially cyclotrimerized cyanate prepolymer with the epoxy groups. In the first stage, a prepolymer was obtained by heating a mixture of BPA monocyanate and dicyanate with Co naphthenate as a catalyst (Scheme 15). 

Although isocyanates have been known for some time, the isomeric cy-anates were unknown until 1964. The latter were first prepared almost simultaneously by two different methods (1) thermolysis of 5-aryl- or 5-alkyloxy-l,2,3,4-thiatriazoles67 and (2) by reaction of phenols or alcohols with cyanogen halides.8 Since their synthesis, cyanates have ac-... 

The classical Kolbe-Schmidt reaction treats alkali metal phenoxides and carbon dioxide at higher than atmospheric pressure, giving salicylic acid. Hirao and Kato developed several modifications for industrial production ". Recently, phenol phosphate was enzymatically carboxylated, giving p-hydroxybenzoic acid ". As for related reactions, Sartori and coworkers conducted o-carbamoylation of aluminum or boron phenoxides with alkyl isocyanate ", and Adachi and Sugasawa o-cyanated phenols using methyl thioisocyanate in the presence of BCI3 (equation 54). ... 

---