Phenolic ester groups

The solubility parameter of poly(ethylene terephthalate) is about 21.8 MPa but because it is a highly crystalline material only proton donors that are capable of interaction with the ester groups are effective. A mixture of phenol and tetrachloroethane is often used when measuring molecular weights, which are about 20 000 in the case of commercial polymers. 

The esters are prepared by first treating estradiol with the appropriate acid chloride. The resulting diester, 27, is then subjected to mild acid or basic hydrolysis in this way, the phenolic ester group is removed selectively. 

In UV spectra of secobisbenzylisoquinoline alkaloids possessing a phenolic hydroxy group para to the aldehyde function, a marked bathochromic shift is observed upon addition of base. In IR spectra absorption of the lactam group appears at 1645-1640 cm-1, that of the aldehyde function in the range between 1720 and 1680 cm-1, and that of the ester group at 1710 cm-1. 

The ability of esters to form hydrogen bonds with polar reactants is especially important for the reactions of peroxyl radicals with antioxidants such as phenols and amines. Amines form hydrogen bonds with ester groups. The hydrogen bonding lowers the activity of antioxidants as acceptors of peroxyl radicals (see Chapters 14 and 15). 

Partition coefficient ofun-ionised compound at acidic pH Octanol/water ca 631. Other drugs containing phenolic ester group metipranolol, vitamin E, benorylate, dipivefrin. 

Methylcoumarins bearing hydroxy and other electron-donating groups can be synthesized from the corresponding phenols by reaction with ethyl acetoacetate in the presence of sulfuric acid. Hydrolysis of the ester group in the product then allows the lactone ring of the coumarin to form (Scheme 5.6). 

Extrapolation of the above considerations to acetate esters less reactive than POAc, i.e., with leaving groups more basic than PO , leads to the prediction of lower catalytic efficiencies because the rate of acetylation of the catalyst is expected to decrease more rapidly than the rate of background methanolysis. In contrast, with esters of phenols more acidic than pNPOH, the catalytic reaction is predicted to be obscured by increased rates of background methanolysis. Thus, for one reason or... 

Fig. 21. Logarithmic plot of the second-order rate coefficients k2) for catalysis by imidazole of the hydrolysis of various esters, against the rate coefficients for alkaline hydrolysis. The most reactive compound is acetic anhydride the other open circles represent results for acetate esters of phenols, except for the two least reactive compounds, trifluorethyl acetate, and the acetate of acetone-oxime. The closed triangles represent data for ethyl esters with activated acyl groups, with the exception of the least reactive compound, which is ethyl acetate.

Polyphenolic phytochemicals are classified into three major groups phenolic acids, fla-vonoids, and tannins. Phenolic acids include hydroxybenzoic, hydroxyphenylacetic, and hydroxycinnamic acids (Figure 11.3.3). Hy-droxycinnamic acids are the most widely distributed of the phenolic acids in plant tissues. The important hydroxycinnamic acids are p-coumaric, caffeic, ferulic, and sinapic acids. Most hydroxycinnamic acids are rarely encountered in the free state in nature. They occur as glucose esters and, more frequently, as quinic acid esters (Herrmann, 1989). Phenolic acids are usually detected at wavelengths between 210 and 320 nm. In general, the polarity of phenolic acids is increased mainly by the hy-... 

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