Acidification experimental methods

The experimental details already given for the detection and characterisation of aliphatic esters (determination of saponification equivalents h3 diolysis Section 111,106) apply equally to aromatic esters. A sfight modification in the procediu-e for isolating the products of hydrolysis is necessary for i)henolic (or phenyl) esters since the alkaline solution will contain hoth the alkali phenate and the alkali salt of the organic acid upon acidification, both the phenol and the acid will be hberated. Two methods may be used for separating the phenol and the acid ... 

The leadership position of NBO masks the difficulties of the method, such as its susceptibility to moderate experimental changes. As shown in Table 2.1, which reports on an interlaboratory comparative evaluation of lignin degradative analyses [20], the yield of monomeric products may differ to a very large extent, with a 20 to 30% standard deviation. This poor interlaboratory reproducibility may originate both from variations in reaction duration or temperature [21] and from analytical difficulties. After completion of the reaction, the classical procedure involves elimination of excess nitrobenzene and its reduction products from the alkaline reaction mixture this is followed by the acidification of the hydrolysate, the extraction of the benzoic aldehydes and acids and their HPLC or GC analysis [16]. The possibility of incomplete extraction [22,23], as well interference from residual nitrobenzene derivatives [23], is often overlooked. 

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