Pressurized liquid extraction phenolic acids

Mukhopadhyay, S. Luthria, D. Robbins, R. 2006. Optimization of extraction process for phenolic acids from black cohosh (Cimicifuga racemosa) by pressurized liquid extraction. J. Sci. Food Agric. 86 156-162. 

Supercritical fluid extraction has been applied to extract phenolic acids from a variety of plant samples. It uses high-pressure to force carbon dioxide to be a mixture of liquid and gas phases, which is called a supercritical fluid. The liquid and gas phase mixture of carbon dioxide can more readily permeate the sample matrix than only the gas phase of carbon dioxide. The compounds solublized in the liquid phase of carbon dioxide are extracted from the sample matrix and collected after they elute from the outlet of the system. The biggest advantage of supercritical fluid extraction is that there is no, or less, organic solvent involved in the extraction, due to the use of carbon dioxide supercritical fluid as the major solvent.. The carbon dioxide readily evaporates as gas phase at the system outlet. Thus, unlike other solvent extraction methods, there is no evaporation step for the extraction, making this an environmentally friendly method. However, the system is much more expensive and delicate than the other novel technology extraction... 

Most of the extraction techniques of phenolic compounds from vegetables are based on ultrasound-assisted extraction (UAE) [27,44,45], In addition, other techniques have been successfully applied to the pretreatment of phenolic compounds in fruits and vegetables, including pressurized liquid extraction (PLE) [46], solid-phase extraction (SPE) [47], supercritical fluid extraction (SFE) [48], microwave-assisted extraction (MAE) [49], rotary shaker-assisted extraction (RAE), [50] and QuEChERS (acronym of quick, easy, cheap, effective, rugged and safe) [51], as can be observed in Tables 16.3 and 16.4. In some cases, an acid treatment [52] was applied to hydrolyze the glycosides in order to determine the content of free and conjugated flavonoids as aglycons. 

Luthria, D.L. 2012. Optimization of extraction of phenolic acids from a vegetable waste product using a pressurized liquid extractor. J. Funct Foods 4 842-850. 

Because phenols are weak acids, they can be freed from neutral impurities by dissolution in aqueous N sodium hydroxide and extraction with a solvent such as diethyl ether, or by steam distillation to remove the non-acidic material. The phenol is recovered by acidification of the aqueous phase with 2N sulfuric acid, and either extracted with ether or steam distilled. In the second case the phenol is extracted from the steam distillate after saturating it with sodium chloride (salting out). A solvent is necessary when large quantities of liquid phenols are purified. The phenol is fractionated by distillation under reduced pressure, preferably in an atmosphere of nitrogen to minimise oxidation. Solid phenols can be crystallised from toluene, petroleum ether or a mixture of these solvents, and can be sublimed under vacuum. Purification can also be effected by fractional crystallisation or zone refining. For further purification of phenols via their acetyl or benzoyl derivatives (vide supra). 

Furfural is a colourless liquid which darkens in air and has a boiling point of 161.7°C at atmospheric pressure. Its principal uses are as a selective solvent used in such operations as the purification of wood resin and in the extraction of butadiene from other refinery gases. It is also used in the manufacture of phenol-furfural resins and as a raw material for the nylons. The material will resinify in the presence of acids but the product has little commercial value. 

Under the protection of nitrogen, the substrate 2-bromo-6-methyl phenol (30.0 g, 160 mmol) and diisopropyl ethyl amine (82.9 mL, 480 mmol) were added to 0 °C dichloromethane (600 mL). Under the stirring condition, MOMCl (18.1 g, 240 mmol) was added, heated to room temperature, and reacted for 3 h. TLC showed that the reaction was completed. 1 N diluted hydrochloric acid (200 mL) was slowly added drop wise at 0 °C to adjust pH = 7. Dichloromethane (200 mL) was added to the system. The aqueous phase was extracted with dichloromethane (3 X 200 mL). The organic phases were combined, washed with saturated brine (200 mL), dried over anhydrous sodium sulfate, and hltered. The hltrate was concentrated under reduced pressure. The resulting crude product was separated and purihed by hash column chromatography (PE/EA = 100 1) to give 32 g colorless liquid Rf— 0.80, PE/EA = 10 1), 89 % yield. 

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