Other Compounds with Potential Hydroxyl Groups

Other Compounds with Potential Hydroxyl Groups 

Infrared and ultraviolet spectral comparisons by Grob and Hofer show that the position of the equilibrium 86 87 predominantly favors 87. 

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I. Other Compounds with Potential Hydroxyl Groups... 

When dealing with the water solubility of ionized molecules, one also must consider the possibility of intramolecular ionic interactions. Compounds with ionizable functional groups that produce opposite charges have the potential to interact with each other rather than with water molecules. When this occurs, such compounds often become very insoluble in water. A classic example is the amino acid tyrosine (Fig. 2.11). Tyrosine contains three very polar functional groups, with two of these groups (the alkylamine and carboxylic acid) capable of being ionized, depending on the pH of the solution. The phenolic hydroxyl also is ionizable (pKg 9-10), but it... 

The activity of the 4-alkylpyrocatechols (la), 3-alkylpyro-catechols (lb), 3,5-dialkylpyrocatechols (Ic), 3,6-dialkylpyro-catechols (II), 4,5-dialkylpyrocatechols (III), 3,4,6-trialkyl-pyrocatechol (TV), and 4,5- and 4,6-dialkyl-2-alkoxyphenols (V and VI) was studied in isotactic polypropylene at 180 =t 0.1° C. The relative activities Ar were correlated with substituent constants and redox potentials. In the la series the activity of 4-n-alkyl derivatives exceeded that of 4-tert-alkyl derivatives. The length of the main alkyl chain in la and lb and the steric effects in the latter exerted a specific favorable influence. In agreement with these effects, 3-tert-alkyl-5-methyl derivatives are the most active compounds in Series Ic compounds with other combinations of alkyls are weaker antioxidants as are the isomeric substances II and III or compound IV. Etherification of one hydroxyl group exerts an unfavorable effect influences of substitution in 2-alkoxyphenols (V and VI) are generally the same as in the pyrocatechols Z-ZZZ. 

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