Reaction of Sterically Congested Phenols and Quinones with Organic Radicals

Abstract

In the course of radiation-induced free-radical transformations of hexane and ethanol, pyrocatechol and hydroquinone derivatives, as well as their respective quinones, are more effective than phenol and resorcinol derivatives in controlling reactions that involve alkyl and hydroxyalkyl radicals. The opposite result takes place in the inhibition by phenols of hexane oxidation in which the key role belongs to the peroxyl radicals generated from the starting compounds.Phenol, di-and polyphenol derivatives are widely known industrial [1] and natural [2] antioxidants, which brings interest in their properties. Considerable attention has been given to correlations between the structure of phenolic compounds and their antioxidant activity. It is commonly accepted that the ability of phenols to inhibit oxidation of organic compounds is determined by their high reactivity toward peroxyl (ROO . ) and other oxygen-centered radicals [1, 2].The main concept we develop in our studies is that processes involving ROO . and other reactive oxygen species are not the only ones responsible for damage of biosystems and industrial materials. Specifically, it was shown that fragmentation of carbon-centered radicals can cause destruction and modification of lipids [3,4], peptides [5], carbohydrates [6], and other biologically important molecules. Peroxide oxidation of synthetic and natural objects, too, begins with generation of carbon-centered radicals from the starting materials. Reactions of carbon-centered radicals with phenolic compounds have scarcely been studied [1,7]. In this connection we have performed a comparative assessment of the reactivity of phenol, di-, and polyphenol derivatives toward oxygen-and carbon-centered radicals [8,9].In the present work we studied the effect of sterically congested phenolic compounds on radiochemical transformations of hexane and ethanol. The resulting data allow us to judge about the reactivity of the compounds studied toward oxygen-and carboncentered organic radicals.It is known that radiolysis of hexane involve reactions leading to hexyl radicals [10] whose recombination gives dodecanes [schemes (1)3(6)].

Synthesis and Biological Evaluation of Novel Coumarins withtert‐Butyl and Terpene Substituents

“…The starting 2-isobornyl-1,4-dihydroxybenzene (9), [40] 4-tert-butyl-1,3-dihydroxybenzene (1), [41] 4,6-di-tertbutyl-1,3-dihydroxybenzene (2) and 2,5-di-tert-butyl-1,4-dihydroxybenzene (4) [42] was synthesized according to known procedures and used after crystallization. (6).…”

Intramolecular and intermolecular hydrogen bonds in aminophenols

“…Derivatives of phenols and aromatic amines are effective antioxidants and, therefore, are used widely as stabilizers of industrial organic materials and food preservatives [1,2]. Certain derivatives of diphenols [3,4] and aminophenols (AP) [5, 6] turned out to be effective regulators of radiation-induced reactions involving various types of organic radicals. It was found that the antioxidant properties of AP derivatives are diminished upon forming intramolecular hydrogen bonds (IHB) in solution and are enhanced when the hydroxyls in the molecules occur in the free state [7].…”

Intramolecular hydrogen bonds and antioxidant activity of aminophenols

“…Today, derivatives of aminophenols are widely used as antiviral drugs for treatment of herpes infection [5][6][7]. Furthermore, some derivatives of diphenols [8,9] and aminophenols [10,11] have proven to be effective regulators of radiationinduced reactions involving participation of different types of organic radicals. One factor affecting the radical-inhibition activity of aminophenols may be the ability of the phenol hydroxyl to engage in intramolecular hydrogen bonds [12,13].…”