Phenol formaldehyde precipitation

Naphthalene- and anthracene-derived phenols did, however, almost uniformly precipitate (Table VI). In natural materials (not grapes or wines) which contain them they would be included in the formaldehyde precipitable group. Several primary amines capable of SchifFs base formation reacted with formaldehyde to lose their F-C oxidizability, but only the resorcinol analog, 3-aminophenol, precipitated (Table VIII). Sulfite also reacted but did not precipitate with formaldehyde, and the F-C oxidizability was suppressed (Table IX). The resorcinol derivative, 2,4-dimethoxycinnamic acid, formed a precipitate with formaldehyde, but it did not react appreciably in the F-C assay. 

The characteristic reactions of formaldehyde with phenolic componnds and amines have also been adapted to the detection of the aldehyde in food-.stuffs. In such instances the material i generally steam-distilled and a qualitative analysis is then carried out on the distillate obtained. Cohn -shakes 2 ec of the distillate with an equal volume of 0.1 per cent resorcinol solution, then carefully adds 2 ce of concentrated sulfuric acid to produce a dense precipitate at the zone of contact between acid and solution with a dark violet-red zone immediate v below. Fomiic, ox alic, and tartaric acids are claimed not to interfere with this color reaction, which is sensitive to OjOO(K>5 mg foimaldehi de. Gallic acid reacts with like sensitivity to form an emerald green bandb The test devi.Sed by Pittarelli (page 247) is reported to be of value for the detection of formaldehyde in wine, milk. 

Certain alkyl-substituted phenol-formaldehyde resins can act as dispersants for asphalts and asphaltenes in crude oils [1681]. The dispersants help keep asphalt and asphaltenes in dispersion and inhibit fouling, precipitation, and buildup in the equipment. 

Table II. Molar Absorptivity in the Total Phenol Assay and Precipitability with Acidic Formaldehyde ...

The resorcinol and phloroglucinol derivatives (Table IV) all precipitated rather completely as expected except for 3,5- and 2,4-dihydroxy-benzoic acids. Their precipitation was enhanced if phloroglucinol was added this indicates that formaldehyde substitution occurred but the products were too soluble and too polar to precipitate until crosslinked with phloroglucinol. It had been shown previously that phenols which did not react with formaldehyde were not appreciably entrained in the precipitate formed with those which did (21) (see Table X). Hydro-quinone derivatives, except for one which is also a resorcinol derivative, did not precipitate with formaldehyde (Table V). 

Kramling and Singleton (41) developed an analysis that differentiated flavonoids from nonflavonoids in wine based on the ability of formaldehyde to precipitate the former but not the latter from solution under proper conditions. The total phenols (42) were determined colori-metrically before and after this precipitation. They (I, 41) also showed that the nonflavonoid content of all young wines was relatively low and constant. 

A third method relies on the precipitation of proanthocyanidins with formaldehyde. First, the total phenolic content is measured using the Folin-Ciocalteu reagent as described before. A 0.5 mole equivalent of phloroglucinol (1.3) is added for every gallic acid equivalent in the extract. To 2 mL of this plant extract and phloroglucinol is added 1 mL of a 2 5 HC1 /H20 solution and 1 mL of an aqueous solution of formaldehyde (13 mL of 37% formaldehyde diluted to 100 mL in water). After an overnight incubation at room temperature, the unprecipitated phenols are estimated in the supematent by the Folin-Ciocalteu method. The precipitate contains the proanthocyanidins and the known amount of phloroglucinol, which is always quantitatively precipitated. 

A substituted phenol (0.1 mol) was dissolved in 20 mL glacial acetic acid, and a cold solution of 20 g of cone. H2SO4 in 40 mL glacial acetic acid was then added. Over a period of 2.5 h, 4.2 mL 40% formaldehyde (0.055 mol) was added to the mixture at 0-5°C. The reaction mixture was stirred cold for an additional 3 h and was then stirred at room temperature for 24 h after the beginning of the reaction. The reaction mixture was poured into cold water, and the precipitate was filtered off and neutralized with sodium bicarbonate solution. The product was purified by crystallization. 

Colorimetric Indirect Method based on the typical reaction of polyphenols with formaldehyde, Singleton " proposed an assay for the quantification of phenolic material condensable with formaldehyde. He described a colorimetric procedure, instead of the gravimetric method, combining the Folin-Ciocalteu assay wifii the method of Stiasny (Fig 2). First, the total phenol content of the extract was measured before the precipitation reaction by the Folin-Ciocalteu method following the... 

To purify the genomic DNA fragments cross-linked into archaeal nucleosomes, the MN digestion is stopped as described above, and the lysate then treated with proteinase K (3(X) p-g/ml) for 3-4 hr at 37°. The formaldehyde cross-links are reversed by incubation at 65° for 6 and the nucleosomal DNA purified by phenol/chloroform extraction, chloroform extraction, and ethanol precipitation. Exposure to RNase A (40 p-g/ml) for 30 min at 37°C yields a solution containing only 60 bp nucleosomal DNA fragments. 

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