Applications benzoxazoles

Many engineering thermoplastics (e.g., polysulfone, polycarbonate, etc.) have limited utility in applications that require exposure to chemical environments. Environmental stress cracking [13] occurs when a stressed polymer is exposed to solvents. Poly(aryl ether phenylquin-oxalines) [27] and poly(aryl ether benzoxazoles) [60] show poor resistance to environmental stress cracking in the presence of acetone, chloroform, etc. This is expected because these structures are amorphous, and there is no crystallinity or liquid crystalline type structure to give solvent resistance. Thus, these materials may have limited utility in processes or applications that require multiple solvent coatings or exposures, whereas acetylene terminated polyaryl ethers [13] exhibit excellent processability, high adhesive properties, and good resistance to hydraulic fluid. 

Many other compounds have been marketed as polyester brighteners for application by exhaustion or in the pad-thermosol process. No account would be complete without mention of the important class of coumarin disperse FBAs, of which structure 11.39 is a typical example. Many commercial brighteners for polyester contain one or two benzoxazole groups, including compounds 11.31, 11.35, 11.36, 11.40 and 11.41. 

Most of the compounds in this group are used for the brightening of synthetic fibres, especially polyester. Application to polyester is either by exhaustion at 125-30 °C, with or without carriers, or by continuous pad bake methods at 160-200 °C with FBAs of a larger molecular size. The benzoxazole group is an important feature of this class, other examples being (3.59) and the bis(benzoxa-zolyl)stilbene (3.60), which is used to produce pre-brightened polyester by adding to the melt prior to extrusion of the fibre. 

Benzoxazoles.1 Benzoxazoles (2) are obtained in generally good yield by Beckmann rearrangement of the oxime of 2 -hydroxyacetophenones (1) using POCl3-DMA in CH3CN at 30° (equation I). The method is applicable to synthesis of hydroxy-substituted benzoxazoles, which are usually difficult to prepare. 

Thienyl-substituted benzoxazoles have been studied for their potential application for fluorescent sensors of metals. They showed absorption bands near 315 nm and emission at 393-394 nm (Of = 0.66-0.80) (07MI2096). Thienyl-substituted imidazopyridines show absorption bands in the range 309-340 nm and emit in the range 474-533 nm (09T5062). Bithienyl-imidazo-anthraquinone derivatives were studied showing an absorption band at 444 nm (070L3201). 

The photodehalogenation of 2-(4-halophenyl)benzoxazoles has been investigated394,395, particularly because derivatives of these compounds have therapeutic applications which... 

A large body of information on the methods of synthesis, application, structure, and properties of all known five-membered nitroazoles - pyrazoles, imidazoles, triazoles, tetrazoles, oxazoles, isoxazoles, oxadiazoles, thiazoles, isothiazoles, thiadiazoles, selenazoles, selenadiazoles, and their benzo analogs - indazoles, benzimidazoles, benzoxazoles, benzisoxazoles, benzoxadiazoles, benzothiazoles, benzoisothiazoles, benzothiadiazoles, benzotriazoles, benzoselenazoles, and ben-zoselenadiazoles has been systematized, summarized, and critically discussed in this monograph. 

In, this mini book we have focused our attention to the application of micro-wave irradiation in synthesis of various important heterocyclic organic compounds viz. pyrazoles, imidazoles, oxazoles, thiazoles, oxadiazoles, oxazolines, triazoles, triazines, benzimidazoles, benzoxazoles and benzthiazoles. The selected heterocyclic moieties are synthetically important due to their interesting pharmacological properties (anti-HIV, anti-parasitic, anti-histaminic, anti-cancer, anti-malarial etc.). 

Comparisons have been made among benzimidazole, benzoxazole and benzoselenazole using MO calculations and PE spectra. The theoretical calculations agree with the observed relative band intensities for the He(I) and He(II) spectra (78MI40600). Application to imidazoles of He(I) PE spectroscopy demonstrates that the lone pair levels are heavily localized on nitrogen, while the other MOs of the valency shell are strongly delocalized (73T2173). 

Triplet states of xanthone depend upon the composition of the solvent the presence of water enhances the yield of 2 un state Dual phosphorescence from 2-(2 -hydroxyphenyl) benzoxazole is due to keto-enol tautomerism and the kinetics multi-exponential decay is due to differences of environment . Triplet state properties and triplet state-oxygen interactions of the biologically interesting linear and angular furocoumarins are useful in view of possible clinical application . 

The imidazole, benzoxazole, and benzthiazole derivatives in Table 7-3 are rather moisture-sensitive.92 On the whole, however, the heteroarylstannanes show the same reactions that characterise the homoarylstannanes. With a palladium catalyst, they undergo coupling112 and cross-coupling reactions68 and indeed much of the recent interest in the heteroarylstannanes stems from their applications in the Stille reaction (see Section 22.2). One aspect of this is the synthesis of oligomers and polymers or copolymers, for example by the cross-coupling of 2,5-distannylthiophene with a 1,4-diiodo-arene.113,114... 

Another group of thermally stable polymeric materials for electronic application includes poly(ether-imide-benzoxazolejs. Mercer and McKenzie [228] prepared the polymer by polycondensation of 2,2 -bis[2-(4-aminophenoxy)benzoxazole-6-yl] hexafluoropropane with pyromellitic, biphenyl, benzophenone etc., followed by thermal imidization of polyamic acid films. The polymers showed an onset temperature for polymer degradation in the range of 424°-456°C and glass transition temperatures in the range of 299 -337°C. 

Kim HJ, Cho EA, Jang JH, Choi DK, Yoon CW, Nam SW et al. Poly(benzimidazole-co-benzoxazole) and method for preparing the same. US patent application 20130216935, assigned to Korea Institute of Science and Technology, Seoul, KR 2013. 

Pla-Dalmau, A. 2-(2 -Hydroxyphenyl)benzothiazoles, -benzoxazoles, and -benzimidazoles for plastic scintillation applications. J. Org. Chem. 1995, 60, 5468-5473. 

As it was previously mentioned polyesters and copolyesters containing 1,4-CHDM are prone to photodegradation. Then, in applications were the polymer o copolymer is exposed to ambient atmosphere, photostabilizers, as benzoxazole (119) or benzophenone derivatives must be added (Figure 6.24). 

Stabilizers UVA 2-(2H-benzotriazol-2-yl)-p-cresol phenol, 2-(5-chloro-2H-benzotriazole-2-yl)-6-(1,1 -dimethylethyl)-4-methyl- 2-(2H-benzotriazol-2-yl)-4,6-bis(1 -methyl-1 -phenylethyl)phenol isopropenyl ethinyl trimethyl piperidol (cellulose diacetate), biphenyl cellulose (UV absorber fro paper), phenylbenzimid-azole (reactive stabilizer for application in cellulosic textiles) Optical brighteners 2,2 -(2,5-thiophenediyl)bis(5-tert-butyl-benzoxazole) Mixtures an ortho-hydroxy tris-aryl-s-triazine compound+hindered hydroxybenzoate compound+hindered amine compound containing a 2,2,6,6-tetraalkylpiperidine or 2,2,6,6-tetraalkylpiperazinone radical ... 

The recent developments on the metallation chemistry of oxazoles and benzoxazoles, isoxazoles and benzisoxazoles, pyrazoles and indazoles, thiazoles and benzo-thiazoles, and isothiazoles, benzo[c]isothiazoles, and benzoMisothiazoles have been reviewed. The two-decade history of catalytic carbon-carbon bond formation via direct borylation of alkane C-H bonds catalysed by transition metal complexes has been reported. The alkane functionalization via electrophilic activation has been underlined. " Recent advances of transition-metal-catalysed addition reactions of C-H bonds to polar C-X (X=N, O) multiple bonds have been highlighted and their mechanisms have been discussed. The development and applications of the transition metal-catalysed coupling reactions have been also reviewed. - ... 

A simple and efficient method has also been developed for the synthesis of benzoxazoles from 2-aminophenol and substituted aldehydes in the presence of a cataljdic amount of zinc triflate (Equation (8.34)) [68]. Benzoxazoles are an important class of heterocyclic compounds that have many applications in medicinal chemistry, amyloidogenesis inhibitors, kinase inhibitors, and antitumor agents. 

Soon after, Xue s group also demonstrated a visible-light photocatalytic transformation of chloroamines to nitrogen-centered radicals. This strategy was utilized for the direct C-H amination of benzoxazoles in a one-pot, two-step process (Eq. (13.27)) [76]. This one-pot process circumvents the needs for purification of the chloroamines, showing the potential of this amination for synthetic applications. 

High performance polymer films and coating materials are increasing being required by the electronics industry for use as interlayer dielectrics and as passivation layers. Aromatic polyimides are general the polymers of choice for these applications because of their unique combination of chemical, physical, and mechanical properties (i). Another class of polymers which have been investigated for these applications are the po arylene ether)s that can be prepared by the nucleophilic displacement of activated aromatic dihalides alkali metal bisphenoxides. Heterocycles such as benzoxazoles (2), imidazoles (5), phenylquinoxalines (.4), and 1,2,4-triazoles (5) have been incorporated within poly(arylene ethers) utilizing this thetic procedure. 

---