Phenolic initiators

The initial phenol-formaldehyde reaction products may be of two types, novolaks and resols. 

Ratios [chloroformate]/[phenol] higher than 1 have been used in order to prepare modified polymers with a degree of substitution lower than 50 (runs 5-7, Table I). Under such conditions it can be noticed that the substitution reactions proceed quantitatively with respect to the initial phenol content. 

These methods utilize molecules of type B (p. 362) (=104) a. Synthesis of Benzofurans by Thermal Ring Closure and Cyclodehydrogenation (Thermal, Catalytic or Photochemical) of o-Substituted Phenols. The Hansch Reaction. o-Alkylhydroxy-compounds on heating with a suitable catalyst give either a benzofuran or a 2,3-dihydrobenzo-furan with the same number of carbon atoms.285-292 Side products are formed by decomposition of the starting material. The initial phenol can be o-alkylated and ring-closed in one stage. 

Figure 6 Phenol removal from a synthetic waste and a foundry waste as a function of HRP dose with and without the presence of 100 mg/L PEG. [Initial phenol] = 3.5 mM (330 mg/L as phenol), [initial peroxide] = 4.9 mM. (Adapted from Ref. 24.)... 

Fig. 10.8 Phenol concentration (closed triangle) and enzymatic activity (closed circle) in an enzymatic membrane reactor with HRT of 120 min. Initial phenol concentration 100 mg/L oxalic acid 1 mM Mn2+ 33 pM H202 addition rate 15 pmol/(L min) pH 4.5...

Fig. 1.10 Trend of the percentage of phenol converted to CO2 (open triangle) and to aromatic compounds (open square) during phenol electrolysis in 1M HCIO4 on BDD under (a) current limited control, initial phenol concentration 20mM, current density 5mA cm-2 (b) mass transport control, initial phenol concentration 5 mM, current density 60 mA cm 2...

Fig. 2.4 Influence of the initial phenol concentration on the EOI and EOD values obtained during electrochemical oxidation at platinum electrodes.

Fig. 2.8 Variation of the concentration of (1) phenol, (2) 1,4-benzoquinone, and TOC during electrochemical oxidation of phenol on a Ta/Pb02 anode at different temperatures. Initial phenol concentration 0.021 mol dm-3 i = 100 mA cm-2 (Tahar and Savall 1998)...

Figures 6 and 7 report the photoreactivity results obtained from representative runs carried out at different initial phenol concentrations (with the same amount of catalyst) and at different amounts of catalyst (with the same initial phenol concentration), respectively.

The oxidation of phenol on a platinum anode was studied by the same author [34]. At a current density of 50mA/cm, 70°C, and a pH of 3, the initial phenol concentration of 21 mmol/dm completely disappeared in 2 h. Apart from CO2, other organic intermediates such as hydroquinone, benzoquinone, maleic acid, fumaric acid, and oxalic acid were identified. An analysis of the reaction intermediates and a carbon balance showed that the destruction reaction occurred by two parallel pathways chemical oxidation with electrogenerated hydroxyl radicals, and direct oxidation of phenol and/or its aromatic intermediates to CO2. 

Sudoh et al. demonstrated the destruction of phenol via electrolytically generated Fenton s reagent in a ferrous sulfate/sodium sulfate electrolyte. These studies were performed in an H-type electrolyzer (Fig. 12) on a graphite plate cathode [52]. At an operating potential of -0.6 V vs. Ag/AgCl, a solution pH of 3, and a ferrous concentration of 2 mol/m, a phenol degradation current efficiency of 60% was reported for initial phenol values ranging from 260 to 2600 ppm. 

This copolymer forms liquid crystalline phases and self organize in thin films. The pyrolysis using continuous heating from 50 to 700° C generates initially phenol derivatives, then compounds resulting from the acrylic sequence, and further other fragments from the two comonomer units [61]. 

Glucuronide conjugates of pentachlorobenzene were observed following the initial phenol formation from hexachlorobenzene in rainbow trout (Oncorhynchus mykiss) fry following dietary exposure27. Other metabolites included traces of 2,5-dichloro-, 2,3,6-trichloro- and 2,4,5-trichloro-phenol. The biotransformation of pentachlorophenol... 

The most prominent player in the field of cresols from coal tar had been SASOL of South Africa that has been operating coal chemical plants using pressure gasification of bituminous coals based on Lurgi process. In these plants, initially phenol and ortho-cresol are separated from the cresylic acid mixture using fractionation, and a mixture rich in cresols (upto 94%) containing some xylenols is produced and the product is marketed as mixed cresols (primarily para cresol, meta cresol, and small percentage of mixed xylenols and a very little quantity of unrecovered phenol). It has been reported that for select customers, SASOL can supply upto 99% pure cresols (metal + para cresols). 

Danishefsky has exploited his widely utilized silyloxydiene chemistry to complete a formal total synthesis of 90 (Scheme 1.20). By employing the appropriate oxidation levels for both the diene and dienophile, a resorcinyl ester possessing the required differentiation of the phenolic groups was obtained without further oxidative manipulation. To this end, the dianion of propiolic acid was alkylated with l-bromo-7-octene to give acid 98 in 68% yield. Further alkylation with methyl iodide then gave the ester 99. A Diels-Alder reaction with diene 100, a derivative of methyl acetoacetate, and alkyne 99 then furnished an initial phenolic intermediate which was protected as the benzyl ether to afford... 

The maximum percentage of phenol removal was indirectly proportional to the initial phenol concentration in the feed phase. This statement is supported by the removal of 100% of phenol at the initial concentration of 100 mg dm after 6 h and only 25% of phenol at the initial concentrations... 

Similar observations were made with all catalysts used. Hydroxylation occurred with high selectivities and yields to phenol. Except phenol only benzoquinone was produced in higher yields. Formation of CO2 was not observed below 400 C. Initial phenol yields were about 25% but deactivation by coke formation quickly led to a decreasing activity. 

Fig. 15.2,23. Structures of polyacenic films. Initial phenol-formaldehyde film (top), partially cured (middle), fully cured (bottom).

The recovered cyanamide-peroxide lignin had greatly increased carboxylic acid content and had undergone more demethoxylation than the lignin obtained from the traditional alkaline peroxide treatment. Both the cyanamide-peroxide and the alkaline-peroxide preparations had lost about 30% of their initial phenolic hydroxyl groups. Vanillic acid was the compound isolated in the highest yield but 4-hydroxy... 

The goal of initial phenolic resin efforts was the development of a cheap thermoplastic resin replacement for shellac. The result was the phenol/formaldehyde, nonheat-reactive resins that Baekeland referred to as novolaks. These products did not have the toughness of shellac and, therefore, never became successful substitutes. 

The Friedel-Crafts alkylation of phenol and p-cresol with tert-butanol, isopropanol and n-propanol was investigated [50, 51] (Scheme 14.6). At 275 °C, concentrations of H3O+ and OH reached a maximum, this is therefore the temperature applied for this acid-catalyzed reactions. The fastest alkylation of phenol was the reaction of tert-butanol with phenol. After a short reaction time, up to 17 % 2-tert-butyl-phenol was found. This yield decreases to the equihbrium value of aroimd 10 % (yields relative to initial phenol content). The yield of 4-tert-butylphenol reaches 20 % and the residual phenol content was around 70 % after attaining equilibrium. 

Scheme 2. Reaction scheme for precursor catalyst The system includes initiator, phenol, and alkyl iodide (shown as polymer-1 in this scheme).

Sterically hindered phenoxyls having an alkyl on a-hydrogen atoms in the para position disproportionate readily to the initial phenol and quinone methide L48 58, 59. This disproportionation is an irreversible process. 

Figure 1. Evolution of the ICE (from the oxygen flowr rate method) during the electrochemical oxidation of phenol, i = 57 mA cm-2, T = 70 °C, pH 12,5 (constant). Initial phenol concentration 23 mmol dm 3...

Figure 13. Influence of the anode material on EOI values for the electrochemical treatment of phenol for a given degree of oxidation (x = 0,71 ) i = 50 mA/cm2, T = 70° C, pH s= 12,5. Initial phenol concentration 10,6 mM...

Fig. 7-29. Threshold odor from chlorination of phenol, (a) Initial chlorine 0.2 ppm, initial phenol 50 ppb (b) initial chlorine 1.0 ppm, initial phenol 50 ppb and (c) initial chlorine 0.2 ppm, initial phenol 5.0 ppb. All were 25 C. From G. F. Lee, chapter in Principles and Applications oi Water Chemistry, S. D. Faust and J. V. Hunter, eds., John Wiley, 1967. Reprinted by permission oi John Wiley, Sons, Inc. 

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