Aromatic Hydroxy Compounds

Labelling studies have shown27 that the unusual base-catalysed rearrangement of the P-O-4 lignin model (25) to (27) containing an a-O-4 linkage, proceeds by way of intermediate (26). Acylation of hydroxy aromatic compounds with 2-bromo-2-... 

It is well known that the acidity of many hydroxy-aromatic compounds is strongly affected by electronic excitation and that these molecules become significantly more acidic in the excited states than in the ground state. For example, phenol and 1-naphthol... 

The domain of oxidations with silver oxide includes the conversion of aldehydes into acids [63, 206, 362, 365, 366, 367 and of hydroxy aromatic compounds into quinones [171, 368, 369]. Less frequently, silver oxide is used for the oxidation of aldehyde and ketone hydrazones to diazo compounds [370, 371], of hydrazo compounds to azo compounds [372], and of hydroxylamines to nitroso compounds [373] or nitroxyls [374] and for the dehydrogenation of CH-NH bonds to -C=N- [375]. Similar results with silver carbonate are obtained in oxidations of alcohols to ketones [376] or acids [377] and of hydroxylamines to nitroso compounds [378]. 

A process has now been discovered from the conversion -d ai omatic compounds to hydroxy aromatic compounds which does not isolate an intermediate haloaromatic compound and which permits... 

Alkylation of the hydroxy aromatic compound to the corresponding alkoxy aromatic compound may be performed in accordance with known alkylation procedures in which the hydroxy aromatic compound is reacted with an alkyl sulfate, alkyl halide or alkyl sulfonate in a suitable solvent, usually water, containing a base such as sodium hydroxide. Such reactions are shown at various places in the literature, as for ex. in Organic Synthesis, Col. Vol. II, page 619, 1943, in which veratraldehyde is prepared from vanillin. The iodide salt may, if desired, be recaptured subsequent to the alkylation reaction. 

Weidner, J. J., Peet, N. P. Direct conversion of hydroxy aromatic compounds to heteroaryiamines via a one-pot Smiies rearrangement procedure. J. Heterocyd. Chem. 1997, 34, 1857-1860. 

In their first electronic singlet state, hydroxy aromatic compounds are much stronger acids than in their ground state (Weller, 1961 Gutman et al., 1981 Schullman, 1977). The pK shift ApK = pK — pKo can be... 

Figure 9. The dependence of the proton transfer rate on water activity for various excited hydroxy aromatic compounds. (O) 2-naphthol-3,6-disulfonate (A) 2-naphthol-6,8-disulfonate (A) 8-hydroxypyrene-1,3,6-trisulfonate ( ) 2-naphthol-6-sulfonate (O) 2-naphthol ( ) Bromo Cresol Green (ground state). Note the discontinuity of the ordinate.

Fatty Acids. The above process is an old and direct method by which to make soap but if fatty acids are wanted, and their use is increasing, the addition of alkali must be avoided unless subsequent treatment with acid at additional expense iis to be incurred. For making these fatty acids several processes may be used, the autoclave and the traditional Twitched method, which are batch operations, and the more modem continuous-countercurrent procedures developed by Colgate-Palmolive-Peet and by The Procter Gamble Company. Darkening of the resulting products from this type of operation is retarded by the use of hydroxy aromatic compounds as stabilizers. ... 

Ion pairs are produced when aqueous solutions of certain hydroxy aromatic compounds are irradiated by light. The excited hydrated molecules dissociate in their first excited singlet state according to Scheme l.(l 3). 

Historically, phenol-formaldehyde resins (phenolic resins, phenoplasts) are the oldest synthetic thermoset materials as early as in 1910 the first ones ( bakelite to their inventor Baekeland) were introduced. Who does not remember the black telephones and light switches that were popular in the 1930s and 1940s Phenolic resins are based on hydroxy-aromatic compounds (phenol and phenol derivatives) and aldehydes [2]. Furfural is occasionally used as aldehyde but by far the most widely used aldehyde is formaldehyde. Formaldehyde can be administered as an aqueous solution (formalin), polymeric solid (paraformaldehyde) or solid adduct with ammonia (hexamethylenetetramine, HMTA). The resins are formed by a step-growth mechanism in aqueous solution. 

The reactive group involved on the hydroxy-aromatic compound is not the hydroxy group itself but the carbon atoms on the ortho (2,6) and para (4) positions relative to the hydroxy group (attached to carbon atom 1). Unsubstituted phenol can therefore react with formaldehyde from three different positions independently, so should be regarded as a three-functional monomer. If the phenol derivatives have substituents on the ortho and/or para positions, their functionality is decreased accordingly. For example (see Scheme 16.1), cresol (methylphenol) is two-functional when the methyl group is in the 2 or 4 position relative to OH (o-cresol and p-cresol, respectively) but three-fimctional when in the 3 position (m-cresol). Further, commonly used two-functional substituted phenol derivatives are p-tert-butylphenol and p-tert-nonylphenol. The aliphatic groups on these monomers decrease the solubility of the resins in water but increase the solubility (compatibility) of these resins with more hydrophobic solvents (hydrocarbons) and resins. 

Table 1.8 Formylation of hydroxy aromatic compounds using the HF/BF3/CO system. ...

AUen, N. S., Photostabihzing action of ortho-hydroxy aromatic compounds a critical review, Polym. Photochem., 3,167,1983. 

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