Phenolic acids and aldehydes

Hydroxy-benzoic acids are characterized by the presence of a carboxyl group substituted on a phenol. Examples include /7-hydroxybenzoic acid (1.4), gallic acid (1.5), protocathechuic acid (1.6), salicylic acid (1.7) and vanillic acid (1.8). Related are hydroxybenzoic aldehydes, such as vanillin (1.9), which have an aldehyde group in stead of a carboxyl group. 

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Key words xylose-rich pectic polysaccharide, pectin, wheat straw, extraction, sugars, lignin, FT-IR, phenolic acids and aldehydes. 

Phenolic acids and aldehydes released from graminaceous cell walls by treatment with alkali are shown in Figure 1. Examples of the amounts released from various cell walls are listed in Table I. 

The toxicity of monomeric phenolic acids and aldehydes of graminaceous cell walls to microflora in the rumen has been examined by several workers (3,27-32). In general, frans-p-coumaric acid was found to be the most toxic of the phenolic acids and decreased the rate of digestion of the cell walls. An important effect of the acid is that it limits the attachment of wall-degrading bacteria (32). The toxicity of p-hydroxybenzaldehyde was similar to p-coumaric acid but only very small amounts of the aldehyde... 

Gioacchin, A.M. Roda, A. Galletti, G.C. Bocchini, P. Manetta, A.C. Baraldini, M. 1996. High-performance liquid chromatographic-electrospray mass spectrometric analysis of phenolic acids and aldehydes. J. Chromatogr. A. 730 31-37. 

Wender, S.H. and C.H. Yang Free phenolic acids and aldehydes in cigarette smoke and in tobacco 145th Natl. 

GLC for the determination of phenolic acids and aldehydes, and does not require the preparation of derivatives before separation. A further important advantage is that while extracts from soils often contain compounds which interfere with GLC separations, such problems rarely occur in HPLC. 

HARTLEY R.D. and BUCHAN H. 1979. High-performance liquid chromatography of phenolic acids and aldehydes derived from plants or from the decomposition of organic matter in soil. Journal of Chromatography 180, 139-143. 

Plant canopy LMM aliphatic acids, phenolic acids and aldehydes, polymeric phenols (flavanoids)... 

Somewhat different type 2-amino-4H-chromene synthesis is represented by the interaction of CH-acidic nitriles 27 with salicylic aldehyde 157 where the phenolic OH and aldehyde groups are present in the same molecule. A conventional mechanistic scheme is represented (Scheme 58), where in the presence of a base nitrile 27 condenses with the aldehyde to give Knoevenagel intermediate 158. Then nucleophilic addition of the OH group leads to iminochromene 159, which then adds a nucleophile (as a rule, the second equivalent of nitrile 27) at position 4 to form 2-amino-4H-chromene 160. 

Table I. Amounts of Phenolic Acids and Phenolic Aldehydes Released from Graminaceous Cell Walls by Treatment with Sodium Hydroxide...

Polyvinylpyrrolidone (PVP) is suited for the preparation of samples that contain humic acids, lignins, tannins, and azo dyes. In addition, PVP exhibits a high selectivity for phenolic compounds as well as for aromatic carboxylic acids and aldehydes. PVP is stable to all common HPLC solvents and is stable in the pH range between 1 and 10. 

Spectroscopic studies of the interaction between ozone and organic molecules on catafyst sur ces have been very rare. Mariey et aL [S] rq>orted a Fourier transform infrared (FTIR) study of ozone interaction with phenol adsorbed on rilica and ceiia. Ozone was found to be reactive toward phenol and carboxylic acids and aldehydes were detected as posable intermediates. However, the study was carried out from 77 to 220 K, which is far from... 

Von Ebner (61, 187) long ago observed that certain phenols, phenolic acids and higher aldehydes exert a profound effect on collagen double refraction, reversing its sign. Kuntzel (130) demonstrated that the same effect is accomplished by treatment with several pyrogallic tanning... 

There are several ways in which phenols have been categorized. Harbome and Simmonds categorized polyphenols based on the number of carbon atoms, which includes simple phenols (Ce) phenolic acids and related compounds (Ce—Ci) acetophenones and phenyl acetic acids (Cg—C2) cinnamic acids, cinamyl aldehydes, and alcohols (Cg—C3) coumarins, isocoumarins, and chromones (Cg—C3) flavonoids (C15) biflavonyls (C30) stilbenes (Cg—C2—Cg) benzophenones and xanthones (Cg—C2—Cg) quinones (Cg, Cio, Cm) betacyanins (Cjg) and lignans, lignins, tannins, and phlobaphenes (which are dimmers, oligomers, or polymers) [19]. Polyphenols have also been categorized by some researchers based on their... 

Fig. 3.8. Derivation of some classes of natural products from the final metabolites of the shikimate pathway. In the cases of cinnamic acid and aldehyde derivatives X = H or X = OR. In the case of the cinnamyl alcohol derivatives, reduction occurs only if X = OR. The two phenolic units represent triketide precursors...

Two reaction parameters are of specific importance pH and molar ratio. When phenol and formaldehyde are dissolved together in water, a pH of about 3-4 is reached (phenol is slightly acidic). After prolonged heating, hardly any reaction is noticeable. The reaction requires a catalyst, either an acid or a base, to reach a sufficient speed. Depending on the ratio between phenolic monomers and aldehyde, the phenolic resins are classified as either resol or novolac types. 

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