Esters of gallic acids

Another way to keep the reactive components separate is encapsulation, in which either or both of the components are covered with a layer of low-melting material such as stearic acid or paraffin wax.227 Several tridentate azo dyes are reported as color-forming chelating agents as well as some esters of gallic acid. 

Except for ET reactions with strong oxidants, 02 is not very reactive (for a compilation of rate constants, see Bielski et al. 1985). For example, practically no reaction has been detected with amino acids (Bielski and Shiue 1979), and there is no reaction to speak of with the DNA constituents, that is, it is also practically unreactive towards DNA. However, where substantial reactivity has been recognized, its main route of reaction seems to be by addition. This has not only been proposed for its reaction with pyrogallol and the propyl ester of gallic acid [k = 3.4 x 10s and 2.6 x 10s dm3 mol1 s 1, respectively cf. reactions (67)-(71) Deeble et al. 1987, 1988], but it seems that an addition reaction triggers a number of chain reactions (von Sonntag et al. 1993, see below). 

Antioxidants are frequently added to unsaturated fats and oils in order to protect these against oxidative deterioration. For this reason, they are also added to a variety of food products containing unsaturated lipids. Antioxidants frequently applied are esters of gallic acid, butylated hydroxyanisole (BHA), butylated hydroxytoluene... 

ProgaUin . [NipaLabs] Esters of gallic acid antioxidants for cosmetics. 

Definition Ester of gallic acid Empirical C19H30O5... 

Polyphenols (syn vegetable tannins - proanthocya-nidins and esters of gallic acid, vide supra) constitute one of the most distinctive groups of higher plant secondary metabolites. Their uniqueness lies not only in their molecular size and polyphenolic character but also in their ability to complex strongly with proteins, carbohydrates, nucleic acids and alkaloids. Studies of these properties are not only of intrinsic scientific interest. a scientist who confesses to an interest in polyphenols is invariably asked one question - why do plants form them ... 

Table 7.2.1. Sources of complex esters of gallic acid and hexahydroxydiphenic acid of commercial importance...

Gallic acid is almost invariably found in plant tissues in ester form. Various simple esters of gallic acid have been described from plant sources (Table 7.2.2, Table 7.2.3) and these metabolites are in many ways analogous to the hydroxycinnamoyl esters occurring in plants. These esters are thus formed by association with sugars. 

The examination of plant extracts to determine the presence of esters of gallic acid is considerably facilitated by HPLC and by two-dimensional paper chroma-... 

Modern antioxidant technology is merely about 70 years old. Only four synthetic antioxidants are widely used in foods, namely the phenolic antioxidants BHA, BHT and diphenol TBHQ (which are antioxidants of low polarity), while more polar antioxidants are esters of gallic acid (gallates) and esters of ascorbic acid. Polar antioxidants are ascorbic and erythorbic acids and their salts. Ascorbic acid, its derivatives and its analogue erythorbic (isoascorbic) acid are described in Section 5.13.1. 

Propyl (PG, E 310), octyl (OG, E 311), and dodecyl (or lauryl) (DG, E 312) esters of gallic acid, usually named alkyl gallates, form a part of the synthetic phenolic antioxidants, mainly used as food additives, with PG being the most frequently used alkyl gallate. The molecular structure of these compounds is composed of a hydrophilic head (phenolic ring) and a hydrophobic alkyl chain (Figure 14.1). PG is slightly soluble in water but OG and DG are insoluble in water. The three compounds are soluble in ethanol, ethyl ether, and oils. 

Locatelli, C., F. B. Filippin-Monteiro, and T. B. Creczynski-Pasa. 2013. Alkyl esters of gallic acid as anticancer agents A review. Eur. J. Med. Chem. 60 233-239. 

---