Phenolic hydroxyl group analysis

Similar analysis of a lignin modified by hydroxypropylation in aqueous base yielded only products bearing single hydroxypropyl residues. This apparent lack of chain extension is of course consistent with the fact that the hydroxypropylation was carried out under conditions favoring reaction only on phenolic hydroxyl groups. 

The dansylation of estrogens which contain a phenolic hydroxyl group has been used for the sensitive analysis of these compounds in urine [105—107]. The derivatives are separated by TLC and are examined visually under UV light (excitation, 346 nm emission, 525 nm). The derivatives are quantitated by removing the spots followed by fluorescence measurements in solution, or by direct evaluation of the chromatoplates in situ. 

Tratnyek and Hoigne (1994) investigated 25 substituted phenoxide anions for QSARs that can be used to predict rate constants for the reaction of additional phenolic compounds oxidized by chlorine dioxide (OCIO). Correlating oxidation rates of phenols in aqueous solution is complicated by the dissociation of the phenolic hydroxyl group. The undissociated phenol and the phenoxide anion react as independent species and exhibit very different properties. The correlation analysis should be performed on the two sets of rate constants separately. 

The major drawback of the method is that only structures in lignin carrying free phenolic hydroxyl groups can be analyzed Therefore, the information obtained accounts for only a fraction of the total lignin structure However, in many cases, this information is sufficient to allow conclusions about the structure of a particular lignin Where such is not the case, alternative approaches are available to increase the number of free phenolic hydroxyl groups prior to analysis. 

For GC analysis, the salts of the lowest molecular weight acids present in ozonation products subjected to base-promoted hydrolysis have been converted to their benzyl esters by reaction with benzyl bromide (Bonnet et al. 1989). The salts of all acids produced have commonly been converted to the free acids, usually with the aid of a cation exchange resin. The acids have then been converted to methyl esters by reaction with diazomethane (Bonnet et al. 1989) or, more often, have been converted to trimethylsilyl (TMS) esters (Matsumoto et al. 1986, Taneda et al. 1989, Habu et al. 1990). Trimethylsilylation has the major advantage that alcoholic and phenolic hydroxyl groups are simultaneously converted to TMS ethers, thus greatly facilitating GC analysis. 

Chemical methods for analysis of phenolic hydroxyl groups include determination of the increase in methoxyl content resulting from diazomethane methylation (Bjorkman and Person 1957), the increase in phenolic acetyl group content after acetylation (Lenz 1968, Mansson 1983), and low-molecular weight compounds derived from the degradation of phenolic structures (Chap. 5.2). The phenolic acetyl group of acetylated lignin may also be determined by an NMR spectroscopic technique (Lenz 1968, Robert et al. 1986) or by a selective deacetylation in pyrrolidine (aminolysis) (Mansson 1983). 

Aminolysis is a laborious procedure, e.g., for wood samples, a 6-7-h reaction period may be required for the aminolysis step alone. The accuracy of this method is critically dependent upon both a quantitative acetylation of phenolic hydroxyl groups and a selective deacetylation of phenolic acetyl groups. Although these requirements may not represent a serious concern in the analysis of soluble or reagent-accessible lignin preparations, they could present a problem in the case of lignocellulosic materials. 

Analysis of the starting material indicates an acidic phenolic hydroxyl, a thioester susceptible to base-promoted hydrolysis, and an a,j8-doubly unsaturated ketone that could undergo 1,4-addition followed by subsequent reaction. From the structure of the product, it is clear that both the thioester and the a,/3-unsaturated ketone undergo reaction. Because hydroxide is the base, a proton will be removed readily from the phenolic hydroxyl group, forming 3-9-1. 

Rodiasine (mp 195°) was first isolated as the dimethiodide from Ocotea rodiei (57). The elemental analysis of this alkaloid did not distinguish between C38H44N2O6 and C36H40N2O6. The alkaloid was found to contain two methylimino groups, four methoxyl groups, and a phenolic hydroxyl group (55). 

Analysis of functional groups such as carboxyl, phenol, carbonyl, or meth-oxyl (Table 2) increases our understanding of the chemical structure of humic substances and can be used to explain the behavior of humic substances in various humification processes (Gjessing, 1976). Carboxyl and phenolic hydroxyl groups clearly predominate, although in some cases methoxyl groups are quantitatively important as well (Muenster, 1982). 

Tetrahydrocannabinol (marijuana) is rapidly metabolized in the body to the tetrahydrocannibinol carboxylic acid or THC (Fig. 8.5). It is the THC metabolite that is commonly monitored in urine for drug analysis of marijuana. Because the THC structure contains both a phenolic hydroxyl group and a car-... 

NIDA specifications call for the analysis of two opiates, codeine and morphine, whose structures are shown in Figure 8.9. Both compounds are amphoteric compounds because of the phenolic hydroxyl group and the amine group. Therefore, they are easily concentrated and purified by mixed-mode sorption. The compounds are present in urine as glycoside conjugates through the phenolic hydroxyl group. Thus, they must first be hydrolyzed in acid before isolation by SPE. 

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