O- and p-Hydroxybenzyl alcohols

Acetylated products of the competitive reactions of equimolar proportions of o- and p-hydroxybenzyl alcohols with resorcinol were examined by 1H- and 13C-NMR in deuterochloroform. XH-NMR spectra were normalized using the relationship ... 

Table III. Methylol, Methylene, and Degree of Substitution per Mole of Resorcinol after Reaction with o- and p-Hydroxybenzyl Alcohols...

Figure 2. Percent of o- and p-hydroxybenzyl alcohol reacting with resorcinol as a function of time.

Resorcinol and phloroglucinol were reacted with either o- or p- hydroxybenzyl alcohol at pH 3.0 and pH 11.0. Condensation proceeded most rapidly at pH 3.0 with the p-hydroxybenzyl alcohol. Less than 65% of the o-hydroxybenzyl alcohol was condensed after 6 hours at 100 °C and pH 3.0, while less than 35% reacted under similar conditions at pH 11.0. In contrast, the p-isomer was almost 90% reacted after 6 hours at 100 °C and pH 11.0 and was completely consumed before 2 hours of reaction time at pH 3.0. 

Analytical studies of the tergal secretions of male B. germanica have identified a number of volatile compounds, none of which has so far been subjected to behavioral assays on females. Brossut et al. (1975) found p-hydroxybenzyl alcohol, o-hydroxybenzyl alcohol, di- and tri-methylnaphthalene, benzothiazole, two isomers of nonyl phenol, and myristic, palmitic, and oleic acids. The fatty acids constituted > 92% of the volatile fraction given their abundance in feces and frass, and their role as putative aggregation pheromones (Wileyto and Boush, 1983 Fuchs et al., 1985 Wendler and Vlatten, 1993 Scherkenbeck et al., 1999),... 

The O-protonated quinone methide corresponds to the p-hydroxybenzyl cation 24. Richard measured the rate constant ku for acid-catalyzed formation of this cation from p-hydroxybenzyl alcohol by monitoring formation of a thiol-trapped product by HPLC.157 Combining this rate constant with h2o yields pAR = -9.6 for the cation from the usual relationship KR = k]]2()/ku. This equilibrium constant may be combined with the pAa for the protonated quinone methide and an estimated pAa 9.9 for p-hydroxybenzyl alcohol to give pAR = 2.3 for the p O -substituted alcohol based on the cycle of Scheme 21. 

Reaction Conditions. Equimolar quantities of o-hydroxybenzyl alcohol, p-hydroxybenzyl alcohol and either resorcinol, phloroglucinol, or (-h)-catechin were dissolved in p-dioxane-water (1 2, v/v) and the solution pH adjusted to 3.0, 5.0, 7.0, 9.0, 10.0, or 11.0 by addition of acetic acid or 5.0M NaOH. An aliquot was freeze-dried immediately (0-Time), and the remainder was divided and added to a series of sealed vials, flushed with N2, and heated for time period of 1, 2, or 6 hours in a boiling water bath. After the appropriate reaction period, the samples were transferred to round-bottomed flasks and freeze-dried. In a similar manner, equimolar quantities of two competing phenols were reacted with one equivalent of either 0- or p-hydroxybenzyl alcohol. 

Generally, there is substantial selectivity in these condensation reactions for the p-hydroxybenzyl alcohol. Earlier work (5,6) had shown that the o-isomer reacted preferentially at the C-8 of (+)-catechin, whereas, there was little regios-electivity in reactions with the p-isomer. One might suspect that phloroglucinol and (-l-)-catechin would preferentially react with the p-isomer because of less steric hindrance. The results support that, but they also show that resorcinol exhibits this same preference for reaction with the p-isomer. Because of the dominance of the p-isomer in these reactions, there is little regioselectivity in... 

Among hydroxybenzaldehydes, the o- and p- hydroxy isomers are the most important for commercial applications in agricultural, flavor and fragance, pharmaceutical or polymer fields (ref. 1). The two main processes for the manufacture of hydroxybenzaldehydes are both based on phenol. The most widely used process is the saligenin process. Hydroxybenzyl alcohols (o- and p- isomers) are produced from base - catalyzed reaction of formaldehyde with phenol (ref. 2). Air oxidation of these alcohols over a suitable catalyst (based on palladium or preferentially on platinum) produces hydroxybenzaldehydes (ref. 3). The Reimer -Tiemann process allows the coproduction of o- and p- hydroxybenzaldehydes (ref. 4). Treatment of phenol with aqueous chloroform and sodium hydroxide leads to benzal chlorides which are rapidly hydrolyzed by alkaline medium to aldehydes. The previous processes need two chemical steps and produce salt effluents. 

A more detailed study of the reactions of phenol and formaldehyde was carried out by O. Manasse [33], and independently by L. Lederer [34]. A basic catalyst was employed. The initial product was analyzed and found to be saligenin (o-hydroxybenzyl alcohol). Further work also isolated p-hydroxybenzyl alcohol. When saligenin was reacted in the presence of acid, it oligomerized into saliretin, a mixture of many substances. 

A widely used industrial process for the production of salicylaldehyde is the Saligenin process that produces hydroxybenzyl alcohols (o- and p-isomers) from the base-catalyzed reaction of formaldehyde with phenol, followed by oxidation using a palladium or platinum catalyst to produce the hydroxybenzaldehyde (Eq 1 44) 129,130.131... 

Sahcyl alcohol [90-01-7] (saligenin, o-hydroxybenzyl alcohol) crystallizes from water in the form of needles or white rhombic crystals. It occurs in nature as the bitter glycoside, saUcin [138-52-3] which is isolated from the bark of Salix helix S. pentandra S. praecos some other species of willow trees, and the bark of a number of species of poplar trees such as Folpulus balsamifera P. candicans and P. nigra. 

To a solution of 24.4 g. (0.20 mole) of salicylaldehyde in 100 ml, of 95% ethanol are added 0.5 ml. of 2 If aqueous ferrous chloride solution and 0.1725 g. of platinum oxide catalyst [Org. Syntheses Coll. Vol. 1, 463 (1941)]. The mixture is shaken under a pressure of 3 atm, of hydrogen in a low-pressure hydrogenation apparatus [Org. Syntheses Coll. Vol. 1, 61 (1941)]. The absorption of hydrogen is complete in 1 hour. To the mixture is added 0.4 ml. of 1 iV aqueous sodium hydroxide solution, and the catalyst is recovered by filtration of the mixture. The solvent is removed from the filtrate by evaporation under vacuum, and the solid residue is recrystallized from 150 ml. of hot benzene. There is obtained a 92% yield of o-hydroxybenzyl alcohol as white crystals, m.p. 84.5-85°. 

The formation of the isomers of the quinonemethide (131) by irradiation of the corresponding o-hydroxybenzyl alcohol has been described. A further study on the formation and reactivity of quinone methides has reported the flash photolysis of the phenol derivative (132) in perchloric acid solution. This affords the p-quinone methide (133). Irradiation of the benzene derivative (134) results in the formation of the quinodimethane (135). A two-colour laser method... 

Reaction or the procyanidins with formaldehyde proceeds so rapidly that these products are usually not useful as wood adhesives. Herrick and Bock (153) advocate crosslinking these compounds with methylol-phenols rather than aldehydes. To gain further information about these reactions, both catechin and tetra-O-methyl catechin have been reacted with p- and o-hydroxybenzyl alcohol (142, 247). Reactions of catechin with /7-hydroxybenzyl alcohol gave the C-6, C-8, and C-6 + C-8 disubstituted products in approximately equal mole ratios. With o-hydroxybenzyl alcohol, substitution at C-8 was favored, with approximate yield ratios of 1 2.5 1.7, respectively. Foo and Hemingway (105) have also examined the regioselectivity of reactions of catechin with furfuryl alcohol and have obtained 2-furyl-(6-catechinyl)-methane and 2-furyl-(8-catechinyl)-methane in approximate relative yields of 1 2.7. 

Wan, P. and Hennig, D., Photocondensation of o-hydroxybenzyl alcohols in an alkaline medium synthesis of phenol-formaldehyde resins, /. Chem. Soc., Chem. Commun., 939, 1987. 

Oxidation of / -cresol to -hydroxybenzyl alcohol, />-hydroxy-benzaldehyde, p-hydroxybenzoic acid, and protocatechuic acid by Pseudomonas sp. (Eq, 16) (Dagley and Patel, 1957). o- or wi-Hydroxy or methyl substitution did not alter the oxidation specificity. 

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