Metal hydroxides with phenols

Alkali metal alkoxides and phenoxides may be obtained by reacting the metal hydroxide with either alcohol or phenol. With alcohols the generated water must be removed, typically as an azeotrope, as with sodium hydroxide dissolved in ethanol-benzene followed by reflux.69 With the more acidic phenols the phenoxides of Li, Na, K, Rb and Cs are more readily formed by simply heating MOH in absolute ethanol with phenol followed by recrystallization.70"72... 

Preparation of phlorogluciaol or its monomethyl ether by reaction of a halogenated phenol with an alkaU metal hydroxide in an inert organic medium by means of a benzyne intermediate has been patented (142). For example, 4-chlororesorcinol reacts with excess potassium hydroxide under nitrogen in refluxing pseudocumene (1,2,4-trimethylbenzene) with the consequent formation of pure phlorogluciaol in 68% yield. In a version of this process, the solvent is omitted but a small amount of water is employed (143). 

Scheme 1. Phenol activation by base. Phenol is treated with a metal hydroxide or other strong base to form the activated salt.

One would think that thermal destruction of polyethylene should be inhibited by hydroxides of alkali metals according to the following scheme, as with phenols ... 

Metal hydroxides of first- and second-group elements can enhance ortho substitution, the degree of which depends on the strength of metal-chelating effects linking the phenolic oxygen with the formaldehyde as it approaches the ortho position. Transition metal ions of elements such as Fe, Cu, Cr, Ni, Co, Mn, and Zn as well as boric acid also direct ortho substitutions via chelating effects (Fig. 7.9). 

The type of catalyst influences the rate and reaction mechanism. Reactions catalyzed with both monovalent and divalent metal hydroxides, KOH, NaOH, LiOH and Ba(OH)2, Ca(OH)2, and Mg(OH)2, showed that both valence and ionic radius of hydrated cations affect the formation rate and final concentrations of various reaction intermediates and products.61 For the same valence, a linear relationship was observed between the formaldehyde disappearance rate and ionic radius of hydrated cations where larger cation radii gave rise to higher rate constants. In addition, irrespective of the ionic radii, divalent cations lead to faster formaldehyde disappearance rates titan monovalent cations. For the proposed mechanism where an intermediate chelate participates in the reaction (Fig. 7.30), an increase in positive charge density in smaller cations was suggested to improve the stability of the chelate complex and, therefore, decrease the rate of the reaction. The radii and valence also affect the formation and disappearance of various hydrox-ymethylated phenolic compounds which dictate the composition of final products. 

Other reported syntheses include the Reimer-Tiemann reaction, in which carbon tetrachloride is condensed with phenol in the presence of potassium hydroxide. A mixture of the ortho- and para-isomers is obtained the para-isomer predominates. -Hydroxybenzoic acid can be synthesized from phenol, carbon monoxide, and an alkali carbonate (52). It can also be obtained by heating alkali salts of -cresol at high temperatures (260—270°C) over metallic oxides, eg, lead dioxide, manganese dioxide, iron oxide, or copper oxide, or with mixed alkali and a copper catalyst (53). Heating potassium salicylate at 240°C for 1—1.5 h results in a 70—80% yield of -hydroxybenzoic acid (54). When the dipotassium salt of salicylic acid is heated in an atmosphere of carbon dioxide, an almost complete conversion to -hydroxybenzoic acid results. They>-aminobenzoic acid can be converted to the diazo acid with nitrous acid followed by hydrolysis. Finally, the sulfo- and halogenobenzoic acids can be fused with alkali. 

By Reactions of Metal Hydroxides and Oxides with Alcohols and Phenols 338... 

Evidence for intramolecular hydrolysis of the methyl ester (62) by metal hydroxide has been provided.329 Molecular models of the metal complex (63) indicate that when complexation with the imidazole nitrogen and the phenolic hydroxyl group occurs, it is not possible for coordination of the ester carbonyl group to occur. This point, taken in conjunction with the observed pH rate profile which shows that ionization of the M—OH2 group is associated with catalysis, eliminates metal ion activation of the carbonyl bond to intermolecular attack by OH- as a contributing factor. For base hydrolysis of (62) kOH = 2.7 x 10-2 M-1 s-1 at 25 °C. The specific rate constants for intramolecular hydrolysis by the M—OH species are 0.245 s-1 and 2 x 10-2 s-1 for the Co11 and Ni11 complexes respectively. 

Irritant dermatitis does not involve an immune response and is typically caused by contact with corrosive substances that exhibit extremes of pH, oxidizing capability, dehydrating action, or tendency to dissolve skin lipids. In extreme cases of exposure, skin cells are destroyed and a permanent scar results. This condition is known as a chemical burn. Exposure to concentrated sulfuric acid, which exhibits extreme acidity, or to concentrated nitric acid, which denatures skin protein, can cause bad chemical bums. The strong oxidant action of 30% hydrogen peroxide likewise causes a chemical bum. Other chemicals causing chemical bums include ammonia, quicklime (CaO), chlorine, ethylene oxide, hydrogen halides, methyl bromide, nitrogen oxides, elemental white phosporous, phenol, alkali metal hydroxides (NaOH, KOH), and toluene diisocyanate. 

On neutralization with a series of alkali metal hydroxides or tetramethylammonium hydroxide in ethanol, weak acid 5 gave a colored solution with an absorption maximum at 615 nm independent of the cation species. This fact suggests that the phenolate anion from 5 interacts with the solvated cations or form solvent-separated ion pairs in the protic solvent, in marked contrast to those of azophenol crowns 4 with alkali metal salts. 

Carbomers are discolored by resorcinol and are incompatible with phenol, cationic polymers, strong acids, and high levels of electrolytes. Certain antimicrobial adjuvants should also be avoided or used at low levels, see Section 11. Trace levels of iron and other transition metals can catalytically degrade carbomer dispersions. Intense heat may be generated if a carbomer is in contact with a strong basic material such as ammonia, potassium or sodium hydroxide, or strongly basic amines. 

The alkali metal dithiocarbonates (xanthates) are prepared by reacting carbon disulfide with alcohols or phenols in the presence of an alkali metal hydroxide (usually KOH) using as solvent an excess of alcohol reagent,176 a hydrocarbon, or acetone.177... 

It is convenient to discuss the Reimer-Tiemann reaction in terms of its normal and abnormal versions. The normal reaction, discovered in 1876 by Reimer, consists of the treatment of a phenol or naphthol with chloroform in the presence of an alkali metal hydroxide solution (see equations 1 and 2), and results... 

---