Dihydric phenol

The discoveries of the isomeric dihydric phenols were as old as that of phenol itself. Catechol,(1,2-benzenediol, 1,2-dihydroxybenzene, o-dihydroxybenzene) was first obtained in 1839 essentially from the dry distillation of tannin. Resorcinol (1,3-dihydroxybenzene), was isolated in 1864 from the alkaline fusion of galbanum, and of asafoetida, resins, repectively from Iranian species of Ferula and Narthex asafoetida. In 1820 hydroquinone was recovered from the dry distillation of quinic acid although it was not investigated structurally until 1844 by Wohler. 

Of the three isomers, catechol is the only member to occur naturally, namely in the leaves and branches of the oak and willow, in apples, onions, and crude sugar beet and in the tannin layer of mycorrhizas (ref.28). Its derivatives are widely distributed in higher plants. Hydroquinone occurs as the glucoside arbutin (4-hydroxyphenyl-D-glucopyranose) and resorcinol only in pyrolysis products in, for example, cigarette smoke. 

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In the case of low temperature tar, the aqueous Hquor that accompanies the cmde tar contains between 1 and 1.5% by weight of soluble tar acids, eg, phenol, cresols, and dihydroxybenzenes. Both for the sake of economics and effluent purification, it is necessary to recover these, usually by the Lurgi Phenosolvan process based on the selective extraction of the tar acids with butyl or isobutyl acetate. The recovered phenols are separated by fractional distillation into monohydroxybenzenes, mainly phenol and cresols, and dihydroxybenzenes, mainly (9-dihydroxybenzene (catechol), methyl (9-dihydtoxybenzene, (methyl catechol), and y -dihydroxybenzene (resorcinol). The monohydric phenol fraction is added to the cmde tar acids extracted from the tar for further refining, whereas the dihydric phenol fraction is incorporated in wood-preservation creosote or sold to adhesive manufacturers. Naphthalene Oils. Naphthalene is the principal component of coke-oven tats and the only component that can be concentrated to a reasonably high content on primary distillation. Naphthalene oils from coke-oven tars distilled in a modem pipe stiU generally contain 60—65% of naphthalene. They are further upgraded by a number of methods. 

Although resorcinol [108-46-3], C H O, a dihydric phenol, is a comparatively weak bactericide, a nuclear-substituted alkyl derivative, -hexylresorcinol [136-77-6], has a phenol coefficient of 45, and has had considerable use as a topical antiseptic. 

Since both phenol and acetone are available and the bis-phenol A is easy to manufacture, this intermediate is comparatively inexpensive. This is one of the reasons why it has been the preferred dihydric phenol employed in epoxide resins manufacture. Since most epoxide resins are of low molecular weight and because... 

Are long-chain linear polyesters of carbonic acid and dihydric phenols, such as bisf ... 

On the basis of these results they assigned formula (II) to ehelerythrine, and this was confirmed by the further observation that dihydrocheler -thrine, m.p. 166-7°, on treatment with phloroglucinol and sulphuric acid and subsequent methylation of the dihydric phenolic base so formed, yields tetramethoxy-A -methyldihydro-a-naphthaphenanthridine (VI), m.p. 182-3°, also obtainable from sanguinarine. ... 

Originally from China, Rhus vernicefera has been under cultivation in Japan since the sixth century AD. The latex is collected in the same way as the rubber plant Hevea brasiliensis. The product is known as urushiol, which consists mostly of dihydric phenols of structures (Fig. 6) and is used as lacquers. 

With a 5.6% concentration of poly (vinyl alcohol), the proportion of gelling agents should be approximately as given below, on the basis of the weight of the poly(vinyl alcohol) dihydric phenols 40%, trihydric phenols 30%, 1-naphthols 8%, and dihydroxynaphthalenes 3.5%. 

The other two dihydric phenols, benzene-1,2-diol (catechol) and benzene-1,4-diol (hydroquinone) are of little interest in this context since they reduce diazonium salts on attempted coupling, being themselves oxidised to the corresponding quinones. 

According to a general rule, not only dihydric phenols, but also those diamines of the p-series which still contain one hydrogen atom attached to each nitrogen, are dehydrogenated to quinone or quinonediimine with great ease. Hence in the oxidation solution emeraldine is also immediately converted into the doubly quinonoid chain... 

Chemically, conversion into a vat consists in a 1 6-addition of hydrogen and recalls exactly the conversion of quinone into quinol. Like quinol, indigo white , also a dihydric phenol , is a weak add, the alkali salts of which are coloured intensely yellow. 

Polycarbonates are polyesters of carbonic acid. The most important commercial polycarbonate is that based on 2,2 -bis(4-hydroxyphenyl)propane(bisphenol A) [Freitag et al., 1988 Sehanobish et al., 1996]. It has been synthesized by the reaction of the dihydric phenol with phosgene or by ester interchange with diphenyl carbonate ... 

S526, 81T1437). m-Substituted dihydric phenols give a mixture of the 5- and 7-hydroxy-chromans. 

An excellent survey of the various methods of synthesis is available53 this section includes some of the illustrative methods of synthesis of the simpler analogues. These methods may be considered under the following headings (a) the oxidation of hydrocarbons (b) the oxidation of phenols and the oxidative coupling of phenols (c) the oxidation of dihydric phenols and aminophenols and (d) the cyclisation of aroylbenzoic acids. 

At a pH less than 6, molecular ozone directly attacks the phenolic ring. Then, the ozone further oxidizes the dihydric phenol to either o- or p-quinone. Because ozone is a relatively less powerful oxidant, the selectivity can be clearly demonstrated, as in Figure 8.8. The Hammett plot was first reported by Hoigne (1982) and confirmed by Gurol and Nekoulnalni (1984) (Figure 8.9). At a pH greater than 6, however, ozone is decomposed as hydroxyl radicals, and substituted phenols are ionized to form phenolate anions, which are much stronger electrophilic species than the protonated forms at low pH. As a result, the measured rate constants for some substituted phe-nolates approach the diffusion-controlled limits. 

Example, 2.1.3.1) with relatively large positive standard potentials. Dihydric phenols such as hydroquinone and catechol are moderately reducing substances that can be oxidized to the corresponding quinones (Example 2.1.2.2). For the case of PCE and catechol, the combination of these reactions gives ... 

The method used by Yorkshire Water Authority [42] for determining phenols in potable waters has a criterion of detection of 3-70pg depending on the phenol. It is capable of determining phenols and cresols, xylenols, dihydric phenols, monochlorophenols, dichlorophenols and trichlorophenols. The phenols are extracted from the water sample with ethyl acetate using a liquid-liquid extractor. After drying, the extract is concentrated to a small volume then treated with... 

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