Natural products extractions

Many solvent properties are related to density and vary with pressure in a SCF. These include the dielectric constant (er), the Hildebrand parameter (S) and n [5], The amount a parameter varies with pressure is different for each substance. So, for example, for scC02, which is very nonpolar, there is very little variation in the dielectric constant with pressure. However, the dielectric constants of both water and fluoroform vary considerably with pressure (Figure 6.3). This variation leads to the concept of tunable solvent parameters. If a property shows a strong pressure dependence, then it is possible to tune the parameter to that required for a particular process simply by altering the pressure [6], This may be useful in selectively extracting natural products or even in varying the chemical potential of reactants and catalysts in a reaction to alter the rate or product distributions of the reaction. 

Salt, sodium chloride classification compound. Stainless steel, mix of iron and carbon classification mixture. Tap water, dihydrogen oxide plus impurities classification mixture. Sugar, chemical name sucrose classification compound. Vanilla extract, natural product classification mixture. Butter, natural product classification mixture. Maple syrup, natural product classification mixture. Aluminum, metal classification in pure form—element (sold commercially as a mixture of mostly aluminum with trace metals, such as magnesium). Ice, dihydrogen oxide classification in pure form—compound when made from impure tap water—mixture. Milk, natural product classification mixture. Cherry-flavored cough drops, pharmaceutical classification mixture. 

We designate as natural all materials that are obtained from natural sources by the application of physical separation techniques such as distillation and extraction. Natural products have been used for many thousands of years as the raw materials of perfumery. Entire plants, flowers, fruits, seeds, leaves, as well as woods, roots, and the resins they exude, are all sources of fragrance materials. Similarly the scent glands of animals such as the civet cat and the musk deer have been used since early civilization to provide perfume for humans. 

At present, there are two main reasons why scientists extract natural products to find out what they are and/or to carry out further experimental work using the purified compound. In the future, it may be easy to determine structures of compounds in complex mixtures indeed, it is already possible to do this under some circumstances, but at present, most cases of structural determination of an unknown compoimd require that it be essentially pure. Similarly, to obtain valid biological or chemical data on a natural product usually requires that it be free fi om the other experimental variables present in the surrounding biological matrix. 

Soxhiet apparatus An apparatus for extracting components from a solid (e.g. extracting natural products from plant material). The material used is placed in a thimble made of thick filter paper and this is held in a specially designed reflex condenser with a suitable solvent. The chamber holding the thimble fills with warm solvent and this is led back to the source via a side arm. The apparatus can be operated for long periods, with components concentrating in the source vessel. It is named after Franz Soxhiet, who devised it in 1879. 

Solvent extraction is a valuable method for obtaining a desired substance from its natural source. A familiar example is the hot-water extraction of caffeine (19) and the various oils that constitute the flavors of freshly brewed coffee and tea from coffee beans and tea leaves. As contrasted to the liquid-liquid extractions described in Section 5.2, this process is an example of solid-liquid extraction. The theory underlying it is the same, however. Because most organic compounds we wish to isolate are insoluble in water, organic solvents such as diethyl ether, dichloromethane, ethanol, and acetone are used for extracting natural products, that is, compounds found in nature. 

As outlined above, several commercial processes for extracting natural products with near-critical solvents already exist. Although the use of the technique is not as yet widespread, it is slowly increasing. 

Industrial processes proposed for the extraction of natural products with near-critical solvents work in a pressure range between 50 bar and 500 bar, and in some exceptional cases up to LOOO bar. Therefore this type of extraction must be regarded as a high pressure process. The pressure vessels are very important, since it is in these that the initial extraction takes place and also in which the saturated solvent is separated from the product. The design and operation of the pressure vessels have a decisive influence on the successful performance of equipment for extracting natural products with near-critical solvents. While the calculation of the necessary wall thicknesses is based on well-established codes of practice for pressure vessels, the mechanical design and especially the operation itself are specific to the type of extraction process considered. 

The processes for extracting natural products with near-critical solvents which are of industrial interest at the present time can be divided into four basic types or groups (Table 8.1). 

The aim of this book is to present the current state of the art of extracting natural products with near-critical solvents and to view the possibilities of further extensions of the technique. Relevant background theory is given but does not dominate the book. Carbon dioxide is the near-critical solvent used in most recent applications and inevitably receives prominence. In addition to general descriptions and reviews, the book contains three chapters by industrial practitioners who describe in detail the operation of their processes and discuss the market for their products. Sections on the design of the pressure vessels and pumps required in these processes and on the acquisition of the data required for design are included. The costing of the processes is also discussed. 

One possible alternative production method is through chemical synthesis. Examples of the total chemical synthesis of many natural, plant-derived anticancer drugs have been reported in the literature [3-6]. However, in terms of commercial production, the total chemical synthesis is still not economical and sustainable, mainly because it involves many reaction steps, uses harsh solvents, and usually ends up with a low yield of the target product that is often mixed with various structurally similar byproducts. Instead, semi-chemical synthesis procedures are favored for generating derivatives that present better pharmaceutical properties from either extracted natural products or metabolic intermediates [7]. 

The ease with which amines are extracted into aqueous acid combined with their regeneration on treatment with base makes it a simple matter to separate amines from other plant materials and ni trogen containing natural products were among the earliest organic compounds to be studied Their basic... 

Materials for flavoring may be divided into several groups. The most common groupings are either natural or artificial flavorings. Natural materials include spices and herbs essential oils and thek extracts, concentrates, and isolates fmit, fmit juices, and fmit essence animal and vegetable materials and thek extracts and aromatic chemicals isolated by physical means from natural products, eg, citral from lemongrass and linalool from hois de rose. 

One class of flavorings, known as tme fmit, is composed of fmit juices, their concentrates, and their essences. A second group, fmit flavor with other natural flavors (WONF), contains fmit concentrates or extracts that may be fortified with natural essential oils or extractives (isolates), or other naturally occurring plants (64,65). This class of flavor is employed when the manufacturer is compelled by regulation to use only natural products, as in wines and cordials in the United States. 

Contraction in the number of EPA-allowed biocides has heightened efforts to develop naturally derived preservatives and microorganisms capable of countering microbial degradation. Neem oil A. dirachta indica seed extract) has been featured as an exceptional natural candidate for the preservation of cosmetic products. Naturally derived chemicals with antimicrobial properties have been used since antiquity as preservatives. However, displacement of successhil synthetic products by natural products in preservatives of any category remains to be witnessed. 

NAPRALERT (Natural Products ALERT) University of Illinois at Chicago STN information on the pharmacology, biological activity, taxonomic distribution, medicine and chemistry of plant, microbial, and animal (including marine) extracts... 

Natural Products. Various methods have been and continue to be employed to obtain useful materials from various parts of plants. Essences from plants are obtained by distillation (often with steam), direct expression (pressing), collection of exudates, enfleurage (extraction with fats or oils), and solvent extraction. Solvents used include typical chemical solvents such as alcohols and hydrocarbons. Liquid (supercritical) carbon dioxide has come into commercial use in the 1990s as an extractant to produce perfume materials. The principal forms of natural perfume ingredients are defined as follows the methods used to prepare them are described in somewhat general terms because they vary for each product and suppHer. This is a part of the industry that is governed as much by art as by science. 

Natural products Vegetable oils waxes, mineral oils plus their sulfated derivatives (including those of animal oils and fats) Sugar extraction glue manufacture cutting oils... 

Adsorption and Desorption Adsorbents may be used to recover solutes from supercritical fluid extracts for example, activated carbon and polymeric sorbents may be used to recover caffeine from CO9. This approach may be used to improve the selectivity of a supercritical fluid extraction process. SCF extraction may be used to regenerate adsorbents such as activated carbon and to remove contaminants from soil. In many cases the chemisorption is sufficiently strong that regeneration with CO9 is limited, even if the pure solute is quite soluble in CO9. In some cases a cosolvent can be added to the SCF to displace the sorbate from the sorbent. Another approach is to use water at elevated or even supercritical temperatures to facilitate desorption. Many of the principles for desorption are also relevant to extraction of substances from other substrates such as natural products and polymers. 

Application of rotating coiled columns has become attractive for preparative-scale separations of various substances from different samples (natural products, food and environmental samples) due to advantages over traditional liquid-liquid extraction methods and other chromatographic techniques. The studies mainly made during the last fifteen years have shown that using rotating coiled columns is also promising for analytical chemistry, particularly for the extraction, separation and pre-concentration of substances to be determined (analytes) before their on-line or off-line analysis by different determination techniques. 

Supercritical fluid extraction (SFE) has been widely used to the extraction processes in pharmaceutical industries. Besides application of SFE in phannaceuticals, it has been applied on a wide spectmm of natural products and food industries such as natural pesticides, antioxidants, vegetable oil, flavors, perfumes and etc [1-2]. 

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