Structure of phenols

Structure of phenolic resin-poly(dimethyl siloxane) copolymers. 

Phenol red immobilized PVA membrane for an optical pH sensor is developed based on the same approach, since the molecular structure of phenol red is similar to that of phenolphthalein. Phenol red was first reacted with the formaldehyde to produce hydroxymethyl groups, and then it was attached to PVA membrane via the hydroxymethyl groups. The changes of spectra characteristics after immobilization, the ionic strength effects, response time, reproducibility and long-term stability of the sensor membrane are discussed by Z. Liu et al. [170],... 

Stager, H., W. Siegfried, and R. Sanger Chemical constitution and structure of phenolic resins. II. Mechanical properties in relation to structure. Schweiz. Arch, angew. Wiss. Tech. 7, 129, 153 (1941). 

Figure 4. Structures of phenol and various mono- and dihydroxybiphenyls showing steric relationships that permit intramolecular hydrogen bonding. Values of pK are for aqueous solutions at 20°C (31).

B Bartolome, ML Bengoechea, MC Galvez, FJ Perez-Ilzarbe, T Hernandez, I Estrella, C Gomez-Cordoves. Photodiode array detection for elucidation of the structure of phenolic compounds. J Chromatogr 655 119-125, 1993. 

Figure 2.2 Chemical structure of phenolic acids. Phenolic acids commonly found with two substitutions on the (a) phenyl ring on the 3- and 4-positions and (b) some less commonly found with triple substitutions on the 3-, 4-, and 5-positions.

Figure 18.1 Chemical structures of phenolic compounds with neuroprotective activity.

Phenols are organic compounds containing an -OH group attached to an aromatic ring. The structure of phenol, the prototype compound of this class, is... 

W. Siebrand, M. Z. Zgierski, J. K. Smedarchina, M. Vener and J. Kaneti, The structure of phenol-ammonia clusters before and after proton transfer. A theoretical investigation, Chem. Phys. Lett., 266 (1997) 47-52. 

In the case of highly cross-linked material, water is not released until above 400°C, and decomposition starts above 500°C as confirmed using differential thermal analysis (DTA).55 The amount of char depends on the structure of phenol, initial cross-links, and tendency to cross-link during decomposition. The main decomposition products may include methane, acetone, CO, propanol, and propane. 

Oxidative nucleophilic substitution is, however, a more versatile technique and a much better choice for target-oriented synthesis (Sections 15.1.1 and 15.1.2.2). In 1950, Wessely and co-workers examined the use of lead tetraacetate (LTA) in acetic acid to determine the structure of phenols and, in doing so, they developed their oxidative acetoxylation reaction, referred to herein as Wessely oxidation (Figure 13) [68-76]. If both an ortho- and a para-position are available to accommodate the entry of the acetoxy nucleophile, ortho products often predominate even when the ortho position is already occupied by a resident alkyl (e.g. 40 —> 41a/b) or allcoxy group (Figure 13) [69, 74]. 

We believe the coupling may be a potential method of enabling the specific and efficient modification of the aglycone structures of phenolic glycosides, without protection and de-protection steps. 

Carboxylation. The introduction of carboxyl groups into the structures of phenols and naph-thols produces some important dye intermediates, including salicylic acid and (3-oxynaphthoic acid (BON acid). This process is conducted under pressure at elevated temperatures using the sodium salts of phenols/naphthols and in the case of (3-naphthol, the carboxyl group enters... 

It has been known that cyclohexanones are formed as intermediates in the hydrogenation of phenols.83,88,123 124 However, the amounts of the ketone intermediates accumulated during the hydrogenation depend greatly on the nature of catalysts and reaction conditions, as well as on the structure of phenols. 

Recent work using the atmospheric dioxane extraction of cork has proved extremely difficult, yielding only small amounts of a lignin- enriched material (7). This was explained by the presence of suberin, a complex structure of phenolic and aliphatic domains and the interaction with lignin. Further work using a saponified cork stressed these arguments (8). 

PHBH is the protype of the flavoprotein aromatic hydroxylases. Each subunit of this dimeric enzyme contains two active sites which, during catalysis, are alternately visited by the isoalloxazine ring of the FAD cofactor (31). Catalysis is iiutiated by reduction of the flavin in the exterior active site. The reduced flavin then moves to the interior active site where the reactions with oxygen occur. A similar conformational flexibility of the FAD cofactor has been observed in the crystal structures of phenol hydroxylase (EC 1.14.13.7) and 3-hydroxybenzoate 4-hydroxylase (EC 1.14.13.23). PHBH obeys the following kinetic mechanism ... 

Enroth C, Neujahr H, Schneider G, Lindqvist Y. The crystal structure of phenol hydroxylase in complex with EAD and phenol provides evidence for a concerted conformational change in the enzyme and its cofactor during catalysis. Structure 1998 6 605-617. 

Figure 14.7 Representative structures of phenol-formaldehyde resins (a) novolac (formed under acidic conditions), and (b) resole (formed under basic conditions).

In all photographs obtained by a scanning electron microscope Lowe and coworkers have observed interstices between macrocells, the cross section of which is 1.5-2 fim. A large number of interstices of approximately the same size have also been ob rved in the structure of phenolic foams Lowe et al. deduced the... 

Hence, the formation of microcells in the structure of phenolic foams is due to the fact that, at a certain str e of foaming (region III), thermodyramic conditions are created for the liberation of gas from the oversaturated mixture (formation of a new portion of bubbles). These bubbles expand according to the same laws as bubbles formed at point A, but they do not attain the same sizes as the macrobubbles. This is ascribed to the fact that at point C the viscosity of the foam system has in-aeased to mch an extent that the ps pressure in ail bubbles (both macro- and microbubbles) is insufficient to cause a further expansion and the foam does not rise further. 

Figure 2. Illustration of the cross-linked structure of phenol-formaldehyde resin.

Potassium permanganate Potassium permanganate is mainly used to destroy phenolic componnds in indnstrial wastewater. It reacts by cleaving the aromatic ring structure of phenol to produce a straight chain aliphatic molecule. The aliphatic is then further oxidized to carbon dioxide and water. The initial reaction takes place almost immediately, and almost 90% of the phenol is oxidized in the first 10 min. A retention time from one to three hours is sufficient to insure complete oxidation of the phenol. The process is affected by pH the higher the pH (up to 9.5), the faster is the reaction time. 

Figure 5. Structure of phenol derivatives isolated from Aconitum naviculare (DalFAcqua et al., 2008)...

II. MOLECULAR STRUCTURE AND BONDING OF PHENOL A. The Equilibrium Structure of Phenol In the Ground Electronic State... 

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