Phenol thermal degradation

Keywords Antioxidants, dehydrating agents, PBT, PET, phosphate stabilizers, phosphite antioxidants, stabilizers, sterically hindered carbodi-imides, sterically hindered phenols, thermal degradation, thermo-oxidative degradation, thermo-oxidative stability. 

Methylene chloride is one of the more stable of the chlorinated hydrocarbon solvents. Its initial thermal degradation temperature is 120°C in dry air (1). This temperature decreases as the moisture content increases. The reaction produces mainly HCl with trace amounts of phosgene. Decomposition under these conditions can be inhibited by the addition of small quantities (0.0001—1.0%) of phenoHc compounds, eg, phenol, hydroquinone, -cresol, resorcinol, thymol, and 1-naphthol (2). Stabilization may also be effected by the addition of small amounts of amines (3) or a mixture of nitromethane and 1,4-dioxane. The latter diminishes attack on aluminum and inhibits kon-catalyzed reactions of methylene chloride (4). The addition of small amounts of epoxides can also inhibit aluminum reactions catalyzed by iron (5). On prolonged contact with water, methylene chloride hydrolyzes very slowly, forming HCl as the primary product. On prolonged heating with water in a sealed vessel at 140—170°C, methylene chloride yields formaldehyde and hydrochloric acid as shown by the following equation (6). 

When cured with room temperature curing system these resins have similar thermal stability to ordinary bis-phenol A type epoxides. However, when they are cured with high-temperature hardeners such as methyl nadic anhydride both thermal degradation stability and heat deflection temperatures are considerably improved. Chemical resistance is also markedly improved. Perhaps the most serious limitation of these materials is their high viscosity. 

Thermal degradation below 300°C in inert atmospheres produces only small amounts of gaseous products. These are mostly unreacted monomers or water, which are by-products eliminated from condensation reactions between hydroxymethyl groups and reactive ortho or para positions on phenolic rings. A small... 

Recently, several reports of the flame-retardant properties of boron-containing bisphenol-A resins have appeared from Gao and Liu.89 The synthesis of a boron-containing bisphenol-A formaldehyde resin (64 and 65) (Fig. 42) from a mixture of bisphenol-A, formaldehyde, and boric acid, in the mole ratio 1 2.4 0.5, has been reported.893 The kinetics of the thermal degradation and thermal stability of the resins were determined by thermal analysis. The analysis revealed that the resin had higher heat resistance and oxidative resistance than most common phenol-formaldehyde resins. 

Photochemistry of Model Compounds. Preliminary photochemical studies have been carried out on l,3-diphenoxy-2-propanol (3)8 as a model compound for bisphenol A-epichloro-hydrin condensates 1. The utilization of 3 as a model compound for thermal degradation of 1 has been reported. Irradiation (254 nm) of 3 in acetonitrile (N2 purge) provides two major volatile products, which have been identified as phenol and phenoxyacetone (4), by comparison of retention times (gas chromatography) with known samples. A possible mechanism for... 

Enthalpy barriers for the decarbonylation and dethiocarboxylation of y-thiobutyrolactone (364) have been calculated as 378 and 404 kJ moP respectively, which accords with the experimental results which saw CO as the major and COS as the minor thermal degradation products.Phenyl and 4-nitrophenyl chlorothionoformates (365 X = H, NO2) reacted with phenolates in aqueous dioxane with /3 uc = 0.55 and 0.47, respectively, from which it was concluded that a concerted mechanism prevailed. 

Lee, L-H. "Mechanism of Thermal Degradation of Phenolic Condensation Polymers" in Proceedings of Battelle Sym., on Thermal Stability of Polymers" Dec. 5,6, 1963. 

Crosslinking has no specific direct effect on thermal degradation crosslinks can be either weak points (e.g., tertiary carbons in polyester or anhydride-cured epoxies) or thermostable structural units (e.g., trisubstituted aromatic rings in phenolics, certain epoxies, or certain thermostable polymers). Indirect effects can be observed essentially above Tg crosslinking reduces free volume and thus decreases 02 diffusivity. It also prevents melting, which can be favorable in burning contexts. 

More than 700 constituents have been identified in aroma extracts of roasted coffee. Heterocyclic aroma components represent the greatest amount of the steam volatile aroma complex (80 - 85 %) which amounts to 700 -900 ppm in medium roasted Arabica coffees. The concentration of individual components varies depending on coffee varieties and roasting conditions. Typical components are formed by thermal degradation of free and bound amino acid and chlorogenic acid precursors. Compared to other roasted foodstuffs, sulfur containing constituents and phenols are formed in high amounts and contribute to desirable coffee flavor or off-flavor. 

Phenolic compounds. Thermal degradation of various types of phenolic compounds has been shown to produce undesirable off-flavor compounds. Tatum et al. (4) identified 4-vinyl guaiacol as the most detrimental off-flavor compound in aged orange juice. When added to freshly expressed orange juice at a level of 0.075 ppm, it imparted an old fruit or rotten flavor. Substantial amounts of 4-vinyl guaiacol, from 0.6 to 1.6 ppm, were found in orange juice stored for 12 weeks at 35°C by Tatum et al. (6). 

These polymers may be compared with the more detailed discussion of thermal degradation pathways for phenol-formaldehyde resins described in Section 2.3.3 earlier, which explains the... 

Phenolic resins have a low flammability by themselves due to the high aromatic content which leads to a high char formation on thermal degradation. However, end-capped brominated epoxy resins are used when necessary. Decabromodiphenyl ether in combination with antimony oxide is also used. 

Figure 3 (Top) Structures of drug A and the known thermal degradation product, referred to as phenol in this report (bottom) ultraviolet/visible absorption spectrum of 0.064 mM drug A in water (dashed line) compared to the combined spectral outputs of the International Conference on Harmonization ultraviolet and visible lamps (solid line).

The structures of the lignins are amenable to conversion to several classes of substituted phenols by thermochemical and thermal degradation methods. The displacement of pyroligneous tars by coal tars eliminated much of the demand that existed for the lignin-based products. Creosote oil or cresylic acid, a mixture of o-, m-, and p-cresols, is now manufactured mainly from coal tars, while only small amounts of cresols are made from wood tars. The use of wood tars and other biomass-derived tars as substitutes for a major portion of the phenol and formaldehyde in phenol-formaldehyde resins could reverse this trend (Himmelblau, 1995). The key to this process seems to be that the... 

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