Phenols thymol

Essential oils are known to have detrimental effects on plants. The inhibitory components have not been identified, but both alde-hydic (benzol-, citrol-, cinnamal-aldehyde) and phenolic (thymol, carvacol, apiol, safrol) constituents are suspected. Muller et al. (104) demonstrated that volatile toxic materials localized in the leaves of Salvia leucophylla, Salvia apiana, and Arthemisia californica inhibited the root growth of cucumber and oat seedlings. They speculated that in the field, toxic substances from the leaves of these plants might be deposited in dew droplets on adjacent annual plants. In a subsequent paper, Muller and Muller (105) reported that the leaves of S. leucophylla contained several volatile terpenes, and growth inhibition was attributed to camphor and cineole. 

Figure 3.6 Phenols. Thymol (C10H140). Courtesy Spiring Enterprises Ltd.

The GC analysis (Fig. 7.7) shows a commercial white thyme with a high percentage of the phenols thymol (55.8%) and carvacrol (2.07%). This contrasts with that of sweet thyme (Fig. 7.8) with no phenolic compounds present and alcohols terpineol-4 (13%), a-terpineol (12.37%) and bomeol (5.95%) making up a total of 31.34% for this particular sample. 

Aromatic versions of cyclohexane monoterpenes (benzenoid menthanes or cymenes) are also found in nature and are constituents of some plants frequently used as spices. The hydrocarbon p-cymene (E19) has been found to occur in the oils of cinnamon (Cinnamonum zeylanicum), cypress, eucalyptus, thyme, and turpentine, whereas m-cymene (E20) is a constituent of the oil of blackcurrant Rites nigrum, Saxifragaceae). The corresponding phenols, thymol (p-cymen-3-ol) (E21) and carvacrol... 

Gum arabic is incompatible with several phenolic compounds (phenol, thymol, cresols, eugenol) and under suitable conditions forms coacervates (see section 8.6.3) with gelatin and positively charged polyelectrolytes. 

The absorption of light by the strong acid forms of phenol-, thymol- and cresolsulfonephthaleins runs parallel with the absorption by the alkaline forms. 

While present in only a relatively few aromatic herbs, phenolic volatile oils are among the most potent and potentially irritant compounds found in essential oils. Phenols are represented in both major classes of aromatic compounds—the monoterpenes and phenylpropanoids. The major monoterpene phenols, thymol and carvacrol, are found in thyme. Thymus spp., and oregano. Origanum vulgare (Lamiaceae). 

Thyme oil consists entirely of terpenes, the most dominant being a mixture of the phenols thymol and carvacrol. Other compounds present are the alcohols linalool, geraniol and a-terpineol (Stahl-Biskup 1991). Thymol is an expectorant, antimicrobial, anthelminthic and antispasmodic. It is a dermal and mucous membrane irritant and caution is required in its use. The tincture is a safer means of administration than the oil itself. 

In addition to tibLe phenols, thymol or carvacrol, these oils contain cymene, thymene aixid. pinene. 

Simple phenols (thymol, carvacrol) and their dimers (diterpenes)... 

Other toxic preservatives commonly used by museum personnel include formaldehyde phenol, thymol, o-phenyl, and copper and zinc naphthanates. 

Dehydration is carried out with sulfuric acid, hydrochloric acid, or phosphoric acid. Among phenols, phenol, thymol, guaiacol, resorcinol, orcinol, catechol, phloroglucinol, a-naphthol, and naphthoresorcinol have been proposed. Among amines, aniline, p-anisidine, benzidine, 3,3 -di-methoxybenzidine, diphenylamine, indole and its derivatives, carbazole, N-ethylcarbazole, a,a-dinaphthylamine, and 1,2,7,8-dibenzocarbazole have been found valuable. In its classical form (Molisch reaction) the test for saccharides is carried out With 1-naphthol and cone, sulfuric acid (70). It is supposed that under the conditions of the reaction corresponding triphenylmethane dyes are formed, although the course of the reaction might be more complicated (71). 

Monoterpenes (Cio) are the simplest members of the terpene series. They result from the condensation of two isoprene units and may be acyclic, monocyclic, bicyclic or tricyclic. The monoterpenes can have another functional moiety like alcohol (geraniol, linalool, menthol, bomeol), aldehyde (geranial, cihonellal), ketone (menthone, carvone, thujone), ester (bomyl acetate, linalyl acetate), ether (1,8-cineol) and phenol (thymol, carvacol). In the case of optically active molecules, the proportions of the enantiomers vary largely from one species to another. 

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