Monocyclic phenols

Monocyclic phenols and their methyl ethers react with benzene in HF—SbF5 medium to provide 4,4-disubstituted cyclohexenones 237 [Eq. (5.308)].3O1para-Methylanisole gives three products two cyclohexenone derivatives [see Eq. (5.112)] and an interesting tricyclic ketone 238. 

Aromatic amines, such as phenyl- -naphthylamine or condensation products of diphenylamine with acetone condensates, are excellent antioxidants and antiozonants but cause color development. From the sterically hindered phenols, monocyclic phenols, such as 2,6-di-teit-butyl-p-cresol, are less effective antioxidants but remain white and nontoxic during aging. They are, however, volatile and provide poor protection at elevated processing temperatures. Polycyclic phenols, such as 2,2 -methylene-bis (4-methyl-6-teit-butylphenol), are relatively nonvolatile, but become discolored by oxidation to a conjugated system. O Shea... 

Commercial antioxidants of monocyclic phenols have only one hydroxy group in the molecule. Pospisil, Taimr, and Kotulak determined the activity of monocyclic dihydrobenzenes. They prepared numerous... 

Cterically hindered phenols are used widely today as effective non- discoloring, nonstaining antioxidants for hydrocarbon systems, particularly rubbers and plastics. These compounds may be grouped in two broad classifications—monocyclic phenols represented by a compound such as 2,6-di-fer -butyl-4-methylphenol (I) and polycyclic phenols such as 2,2 -methylenebis(4-methyl-6-terf-butylphenol) (II). (Throughout this chapter, X represents tert-butyl). 

Monocyclic phenols generally afford excellent nondiscoloring properties and good activity against aging at ambient temperature. These compounds are volatile, however, and generally provide poor protection at elevated temperatures. 

Of all the compounds prepared in this work, these latter compounds, the ortho-linked compounds derived from dimercaptans, come the closest to realizing our objective of structures with the activity of a bisphenol and the nondiscoloring characteristics of a monocyclic phenol. For example, Table IV shows some results in cw-polybutadiene which demonstrate that a compound of the type XXVI is superior as a heat stabilizer to both 2,6-di-terf-butyl-4-methylphenol and 2,2 -methylenebis(4-methyl-6-ferf-butylphenol) in both activity and color. Screening results in cis-... 

Oxidative coupling of simple monocyclic phenolic units is not as efficient by this method. Phenol itself does not undergo the reaction. Compounds 89 and 91, however, lead to the desired ortho-ortho coupling products, 90 and 92, respectively, in moderate yields (the starting phenol or decomposition products are also present at the end of the reaction) (Scheme 21). 

Substituted monocyclic phenols have been widely studied on several stationary phases (alumina, silica gel, cellulose, polyamide, silanized silica gel) and also on chemically modified adsorbents (cyano- and amino-silica plates), ion-exchange layers, and impregnated plates. 

Layers of silica gel and alumina have been employed for the separation and identification of 126 monocyclic phenols eluted with 3 solvents of increasing polarity (benzene, diisopropylether, and ethanol) [2]. Alumina is more basic than silica gel and strongly retains phenolic compounds, particularly those with more acidic properties such as chlorophenols and nitrophenols, even when eluting with a medium-polarity solvent. 

Table 1 reports the retention data relative to some substituted monocyclic phenols examined on silica gel in benzene and diisopropylether. 

Consequently, it can be concluded that the tautomerism does not involve a mobile equilibrium in the series of monocyclic phenols containing one to four hydroxy groups. 

Molecular graphs 32 Molecular orbitals (MOs) 3 Molecular symmetry, study of 368 Molybdenum compounds, as allylation catalysts 677 as oxidants 1273, 1275 Monobenzylation 1395 Monocyclic phenols, keto-enol tautomerism in 715-719... 

Like other phenoloxidases, this enzyme has a low substrate specificity and is able to ortho-hydroxylate a whole range of para-substituted monocyclic phenols. The catechols produced belong to groups of fine chemicals and pharmaceuticals [66L Furthermore, also bi- and tri-cydic phenols were converted into catechols (Figurel6.3-12) [67] 2-Aminotetralines, on the basis of their dopaminergic properties, are compounds of pharmaceutical interest. 

Monocyclic phenols readily form dimers and oligomers involving both C-C and diaryl ether bonds (Scheme 10). In the dibenzodioxin M-677 probably two ether bonds are formed by oxidative coupling although it is unclear which ether oxygen is derived from which precursor. Oligomers can be exemplified by pentafuhalol, a homopentamer of pyrogallol (Scheme 11). 

A wide variety of stationary phases have been used to separate substituted monocyclic phenols and phenolic acid compounds and their derivates by thin-layer chromatography (TLC). In particular, the composition of phenolic acids and flavonoids in leaves, roots, and fruits of several plants and in natural products has been extensively studied by the two-dimensional TLC by using cellulose or silica gel plates in one direction and silanized silica gel in the second direction. Quantitative determinations of flavonoids components of plant extracts were widely performed. 

Table 1 Rf values of substituted monocyclic phenols in different chromatographic conditions.

In this section the thin-layer chromatographic properties of phenolic compounds as revealed by their / /Values are given. The first part covers essentially the substituted derivatives of monocyclic phenols, the second part is concerned with phenolic acids (with their derivatives), and the final one with more complex phenolic compounds such as phenolic glycosides, flavonoids, anthocyanins, lignan derivatives, phenolic steroids, cannabinoids, and other types. Some overlap between subsections is inevitable, but this feature serves incidentally to interrelate the thin-layer chromatographic properties of phenolic compounds as a whole. The material in the last section has been dealt with in other monographs (1), and more emphasis has been placed in this review on substituted phenols and phenolic acids and their simple derivatives. 

Khadem, S., and Rj., Maries. 2010. Monocyclic Phenolic Acids Hydroxy- and Polyhy-droxyhenzoic Acids Occurrence and Recent Bioactivity Studies . Molecules 15,7985-8005. 

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