Phloroglucinol, condensation

Jurd, L. Waiss, A.C. (1965). Anthocyanins and related compounds—VI Flavylium salt— phloroglucinol condensation products. Tetrahedron, 21, 1471-1483. 

The condensation on the fabric of 1-amino-3-iminoisoindo1enines or 2-amino-5-iminopyrro1enines with phloroglucinol, preferably in the presence of metal salts and solvents, yields fast dyeings in brown shades (158). Metallized azo dyes derived from phloroglucinol yield fast dyeings on leather (qv) or silk (qv) (159). 

There are also methods based on the detection of aldehydic substances, for the typical odor and flavor of rancidity seem to be associated with the liberation of aldehydic materials during the oxidative deterioration. The Kreis test (18), perhaps the best known of these methods, consists of treating the fat with concentrated hydrochloric acid and a solution of phloroglucinol. The red color formed is attributed to a condensation product of epihydrin aldehyde with phloroglucinol. Historically, the chief difficulty with this method has been that fats which are not rancid will often give a positive Kreis test. It has been shown that if this test is quantitatively correlated with the induction period... 

Jurd, L. and Lundin, R., Anthocyanidins and related compounds — XII. Tetramethylleucocyani-din-phloroglucinol and resorcinol condensation products. Tetrahedron 24, 2653, 1968. 

The condensation of a, 3-unsaturated carbonyl compounds with phenols is a well-established method for the preparation of 277-chromenes and is reviewed in the preceding volumes <1984CHEC, 1996CHEC-II>. Phenylboronic acid can effectively mediate this condensation <1998S279>. C(3)-Symmetrical 2/7-chromenes are synthesized using a phenylboronic acid-mediated triple condensation of phloroglucinol 53 with three equivalents of an a,(3-unsaturated carbonyl compound (Equation 28) <20050L467>. 

Phenols react with cinnamyl compounds via an intermolecular condensation/cyclization providing a reliable method for the construction of dihydrocoumarins. Montmorillonite K-10 clay can catalyze the condensation/cyclization reaction of phloroglucinol and cinnamoyl chlorides to provide a high-yielding route to dihydrocoumarins (Equation 416) <2001S2247>. 

The spectra of 0-Time samples generally contained only about 80% of the expected methylol protons, probably due to more hydration of the benzyl alcohols than the resorcinol or phloroglucinol. Also, some samples showed the presence of small amounts of methylene linkages due to some self-condensation of the hydroxybenzyl alcohols prior to their reaction with either resorcinol or phloroglucinol. Therefore, calculations of the number of methylols lost and... 

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. 

In all of the reactions, most of the condensation took place with phloroglucinol, yielding four to six times more of that condensation product. A somewhat higher ratio of phloroglucinol versus resorcinol condensation obtained with the p-hydroxybenzyl alcohol compared to the 0-isomer seems to indicate that steric factors do influence the product ratios, but not significantly. Although the overall reaction rates of resorcinol or phloroglucinol with the hydroxybenzyl alcohols... 

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... 

In addition to the effect pH has on the overall reaction rate, it is also important to note the effect of pH on rearrangement reactions of (+)-catechin. At alkaline pH, these secondary rearrangement reactions dominate. Epimerization of (+)-catechin to (-b)-epicatechin is a prominent reaction at pH 9.0. This is not serious in terms of adhesive formulation because it does not alter the reactivity of the aromatic nucleus toward condensation with benzyl alcohols. However, in reactions at pH 10.0 or 11.0, the intramolecular rearrangement to catechinic acid dominates and results in loss of the phloroglucinol functionality. 

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