Supercritical fluid extraction (SEE) of the volatile oil from Thymus vulgaris L. aerial flowering parts was performed under different conditions of pressure, temperature, mean particle size and CO2 flow rate and the correspondent yield and composition were compared with those of the essential oil isolated by hydrodistillation (HD). Both the oils were analyzed by GC and GC-MS and 52 components were identified. The main volatile components obtained were p-cymene (10.0-42.6% for SFE and 28.9-34.8% for HD), gamma-terpinene (0.8-6.9% for SFE and 5.1-7.0% for HD), linalool (2.3-5.3% for SFE and 2.8-3.1% for HD), thymol (19.5-40.8% for SFE and 35.4-41.6% for HD), and carvacrol (1.4-3.1% for SFE and 2.6-3.1% for HD). The main difference was found to be the relative percentage of thymoquinone (not found in the essential oil) and carvacryl methyl ether (1.0-1.2% for HD versus t-0.4 for SFE) which can explain the higher antioxidant activity, assessed by Rancimat test, of the SFE volatiles when compared with HD. Thymoquinone is considered a strong antioxidant compound.
Ostwald solubility coefficients, L, have been determined for 37 gases and vapours in methylene iodide at 298 K, and have been correlated through equation (i). where the solute explanatory log L = -0.74 + 0.32R2 + 1.34~: + 0.83@ + 1.1 9 B + 0.87 log L"variables are R, an excess molar refraction, . n: the solute dipolarity/polarisability, a: and fl the solute hydrogen-bond acidity and basicity, and log L16 where L" is the solute Ostwald solubility coefficient on hexadecane at 298 K. Similar equations have been constructed for solvation of solutes in tetrachloromethane, trichloromethane and 1.2-dichloroethane using literature data. It is shown that polarisability effects favour solvation in methylene iodide, through the R, term, but that such effects enhance the solubility of polarisable solutes only moderately: thus the R, term contributes 0.4 log units more in methylene iodide than in trichloromethane for the solute benzene.
We have studied the ability of a novel molecule (diphenyl
bis(octadecylamino) phosphonium bromide)
to form both Langmuir films and Langmuir−Blodgett films under
different experimental conditions. It
has been found that this substance is capable of forming stable
monolayers at the air−water interface and
building up highly ordered LB films yielding Z-type LB films of high
quality (transfer ratio of 1) which
were characterized by UV−vis and IR spectra, electron microscopy, and
X-ray diffraction.
An overview of the studies carried out in our laboratories on supercritical fluid extraction (SFE) of volatile oils from seven aromatic plants: pennyroyal (Mentha pulegium L.), fennel seeds (Foeniculum vulgare Mill.), coriander (Coriandrum sativum L.), savory (Satureja fruticosa Béguinot), winter savory (Satureja montana L.), cotton lavender (Santolina chamaecyparisus) and thyme (Thymus vulgaris), is presented. A flow apparatus with a 1 L extractor and two 0.27 L separators was built to perform studies at temperatures ranging from 298 to 353 K and pressures up to 30.0 MPa. The best compromise between yield and composition compared with hydrodistillation (HD) was achieved selecting the optimum experimental conditions of extraction and fractionation. The major differences between HD and SFE oils is the presence of a small percentage of cuticular waxes and the relative amount of thymoquinone, an oxygenated monoterpene with important biological properties, which is present in the oils from thyme and winter savory. On the other hand, the modeling of our data on supercritical extraction of volatile oil from pennyroyal is discussed using Sovová’s models. These models have been applied successfully to the other volatile oil extractions. Furthermore, other experimental studies involving supercritical CO2 carried out in our laboratories are also mentioned.
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