Base Promoted Intumescence of Phenols

Abstract

The intumescent process of sodium (substituted) phenolates has been studied. The generation of hydrogen radical via a homolytic cleavage of the Ar–H bond and the subsequent hydroarylation of phenolates to cyclohexadienes along with cyclization and elimination reactions of cyclohexadienes are critical steps in the base promoted intumescence of phenols. The substituents show great influence on the intumescence of phenolates. Phenolates substituted with a weak electron donating group enable intumescence while those with an electron withdrawing group or strong electron donating group suppresses intumescence. This distinction can be justified by both electronic and steric effects of substituents on the generation of hydrogen radical and the degree of hydroarylation.

A Probable Origin of Dibenzothiophenes in Coals and Oils

“…Since the formation of benzene requires hydrogenolysis, its early presence suggests the yield of hydrogen radical during the initial thermal degradation of thiophenolate. Therefore, thiophenolate follows the similar degradation chemistry as phenolate with the bond cleavage of Ar-H taking place first [26,27]. The thermal degradation of thiophenolate beginning with the homolysis of Ar-H has important consequences.…”

“…As a result, the FTIR spectra of off-gases The thermal degradation of thiophenolate beginning with the homolysis of Ar-H has important consequences. In the case of phenolate, the homolysis leads to hydroarylation which produces phenylphenolate or self-combination of aryl radicals to biphenolates [27]. Likewise, thiophenolate is expected to form phenylthiophenolate or bithiophenolate, the cyclization of which should yield DBT [34,35].…”

“…Further, benzonaphthothiophenes, which have been found in crude oils, coals, and sediment extracts [15], can also be readily elucidated. Referencing the formation of polyaromatic hydrocarbons during the thermal degradation of phenol [27], an exemplified pathway to benzonaphthothiophenes is shown in Scheme 3. In addition, the presence of benzonaphthothiophenes is consistent with MW = 235 + 76 n (n = 0, 1, 2) observed in the APCI positive mode.…”

An Extremely Efficient Silylated Benzensulfonate Flame Retardant for Polycarbonate

“…The reduction of CO yield can be justified by the action of potassium ion on the change of degradation pathway of phenols. It has been reported by one of us that the thermal degradation of sodium phenolates produces NaOH instead of CO [23,24]. Since PC mainly decomposes to bisphenol A, its interaction with potassium ion would certainly suppress the formation of CO.…”

“…The accumulation of potassium facilitated by the migration of trimethylsilyl group might be a key to the excellent flame retardancy of KTSS. Since alkali ions promote the char-formation of phenols [23,24], a high concentration of potassium in the surface of PC/KTSS suggests a strong acceleration of char formation of PC. From the results of UL94, KTSS is approximately 5 times more efficient than KSS on the basis of weight.…”