Unsubstituted Phenol

For phenols unsubstituted in the 4-position decomposition of the hydroper-oxycyclohexadienone to the corresponding benzoquinone and phenoxy radical C-C coupling products can occur. It has also been proposed [104,105] that, in the case of particularly electron rich phenols, chemical reaction takes place via formation of an endoperoxide (Eq. (41)) which opens to the hydroperoxycyclohexadienone. 

Pyridoxal, pyridoxamine and pyridoxine all show the typical reactions of an aromatic phenol unsubstituted fara to the phenolic group. In sufficient concentration they thus show reddish colors on addition of ferric chloride, couple with diazotized sulfanilic acid to yield orange to red-colored products, and with 2,6-dichloroquinone chlorimide to yield blue indophenols. The latter two reactions have been used for the quantitative estimation of vitamin Be imfortunately, other phenols occur in many products and the three forms of the vitamin do not, in general, yield equal color values. 

A typical resin has an initial molecular weight of 150 to perhaps 1500. For systems of unsubstituted phenols, the final cross-link density is 150—300 atomic mass units (amu) per cross-link. In other words, 25—75% of the ring-joining reactions occur during the cure phase. 

Aqueous dispersions are alternatives to solutions of Hquid and soHd resins. They are usuaUy offered in 50% soHds and may contain thickeners and cosolvents as stabilizers and to promote coalescence. Both heat-reactive (resole) and nonheat-reactive (novolak) systems exist that contain unsubstituted or substituted phenols or mixtures. A related technology produces large, stable particles that can be isolated as discrete particles (44). In aqueous dispersion, the resin stmcture is designed to produce a hydrophobic polymer, which is stabilized in water by an interfacial agent. 

The aromatic ring of alkylphenols imparts an acidic character to the hydroxyl group the piC of unhindered alkylphenols is 10—11 (2). Alkylphenols unsubstituted in the ortho position dissolve in aqueous caustic. As the carbon number of the alkyl chain increases, the solubihty of the alkah phenolate salt in water decreases, but aqueous caustic extractions of alkylphenols from an organic solution can be accomphshed at elevated temperatures. Bulky ortho substituents reduce the solubihty of the alkah phenolate in water. The term cryptophenol has been used to describe this phenomenon. A 35% solution of potassium hydroxide in methanol (Qaisen s alkah) dissolves such hindered phenols (3). 

As tannins contain many phenolic -type subunits (Fig. 3), one may be tempted to think that they will exhibit a similar reactive potential to that of phenol, and that therefore procedures used in standard PF production can be transferred to those containing tannin. This, however, is not the case. The real situation is that tannin is far more reactive than unsubstituted phenol due to the resorcinol and catchecol rings present in the tannin. This increase in hydroxyl substitution on the two aromatic rings affords an increase in reactivity to formaldehyde by 10 to 50... 

The influence of an ort/io-imidazole substituent on the bond dissociation energy of the O—H bond in phenol was studied by DFT calculations [00IJQ714]. The imidazole ring is twisted with respect to the phenol ring by 59° and causes a decrease of the bond dissociation energy by about -1 kcal/mol with respect to the unsubstituted molecule only. 

Reaction of the potassium salt of salicylaldehyde with chlo-roacetone affords first the corresponding phenolic ether aldol cyclization of the aldehyde with the ketonic side chain affords the benzofuran (1). Reduction of the carbonyl group by means of the Wolf-Kischner reaction affords 2-ethyl-benzofuran. Friedel-Crafts acylation with anisoyl chloride proceeds on the remaining unsubstituted position on the furan ring (2). The methyl ether is then cleaved by means of pyridine hydrochloride (3). lodina-tion of the phenol is accomplished by means of an alkaline solution of iodine and potassium iodide. There is thus obtained benziodarone (4)... 

Phenols (ArOH) are relatively acidic, and the presence of a substituent group on the aromatic ring has a large effect. The pKa of unsubstituted phenol, for example, is 9.89, while that of p-nitrophenol is 7.15, Draw resonance structures of the corresponding phenoxide anions and explain the data. 

Would you expect p-methylphenol to be more acidic or less acidic than unsubstituted phenol Explain. (See Problem 16.74.)... 

The method can be applied to most phenols substituted in the ortho or meta position and to phenols substituted in the para position by OH or OCH3 groups most other substituents in the para position inhibit the reaction. Aromatic primary amines unsubstituted in the para position interfere and must be removed if possible before commencing the determination by extraction with acid. 

The molecular ions of the unsubstituted phenols are present, but are smaller than the underivatized aminophenols. The M - 42 is characteristic of acetates. Prominent ions are m/z 109,151, and 193. 

Degrees of polymerization can be calculated from quantitative 13C NMR data by considering the number of substituted (reacted) relative to unsubstituted (not yet reacted) ortho and para phenolic carbons where [5] is the sum of substituted ortho and para carbons and [5] + [f/ is the total ortho and para carbons. The fraction of reacted ortho and para sites is denoted by fs [Eq. (7.2)]. Thus, the number-average number of phenol units per chain Or) can be calculated using Eq. (7.3). This leads to a simple calculation of Mn = x x 106 — 14 ... 

Because steric factors strongly influence the rate of silylations, primary alcohols are normally silylated much more rapidly than secondary alcohols whereas tertiary alcohols are silylated much more slowly. The same is true for phenols - ortho-substituted phenols such as o-cresol are silylated much more slowly than unsubstituted phenols. Obviously, the same applies to cleavage of silylated alcohols or phenols on transsilylation, e.g. with excess boiling methanol (Section 2.3). 

In the presence of acid, unsubstituted BIPS assumes a thermally stable protonated colored form, and shows reversed photochromism, in which the phenolate form changes to a phenol.20 22 In this case, the absorption band remarkably shifts to the short wavelength. For example, in the presence of acid the absorption band of 6-nitro-BIPS occurs at 405 nm in acetone. 

Patents of Dow Chemicals first described 9,9-diaryl-substituted PF homopolymers 204 and 205 by Yamamoto polymerization of the corresponding 2,7-dibromo monomers [272], although the methods for monomer preparation were not described. For unsubstituted fluorenone, a convenient method for its conversion into 9,9-(4-hydroxyphenyl)-[307-309] and 9,9-(4-alkoxyphenyl)fluorenes [310] was reported previously, which included condensation of fluorenone with phenol or its ethers in acidic conditions (dry HC1 [308,309] or H2SO4 [307,311]) in the presence of (3-mcrcaptopropionic or mercaptoacetic acids. Both polymers 204 and 205 showed similar Mn 21,000 with PDI of 1.48 and 1.75, respectively, and spectral data typical for PF (205 Aabs = 389 (r 50,000 //(mol cm) APL = 417, 439, and 473 mn (THF)) (Chart 2.48). 

OH resonance shift of substituted phenol, 1n ppm, OH resonance shift of unsubstituted phenol, reaction constant, substituent constant,... 

In unsubstituted phenyl ethers, the enolisation is faster than the Cope reaction. This is why the product is predominantly ortho isomer. When both the ortho positions are substituted, the allyl group undergoes a second migration via a concerted sigmatropic mechanism giving a para substituted phenol. This is called para Claisen condensation. 

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