Cashew phenols

The first synthesis modelled on biomimetic lines was directed to obtaining anacardic acids by way of polyketides [237] and later to a (17 l)-orsellinic acid [43]. A less complicated approach based on the Michael addition of ethyl acetoacetate and ethyl octadec-2-enoate, has led to a C15 orsellinic acid, Fig (4)-56, 2,4-dihydroxy-6n-pentadecylbenzoic, considered to be the biogenetic precursor of the cashew phenols [238], notably cardol, by decarboxylation. The use of bromine at the aromatisation stage in this synthesis precluded the extension of the method to components with unsaturated side-chains, although bromination with copper(ii)bromide and thermal debromination offers an alternative procedure. In a more recent approach, by the use of an oxazole intermediate and its addition to ethyl acetoacetate, (15 0) and (15 1) anacardic acid have been obtained [239] as shown in Scheme 5a, b. The 8(Z),1 l(Z)-diene and 8(Z),1 l(Z),14-triene have also been synthesised [240] by way of ethyl 6-(7-formylheptyl)-2-methoxybenzoate (C), prepared from acyclic sources, rather than, as in previous work, by semisynthesis from the ozonisation of urushiol. 

Cashew Phenols (Anacardiaceae) and Lacs (Rhus species) Anacardiaceae... 

The sap from Rhus vemicifera by extraction with light petroleum affords urushiol a mixture which is considerably more sensitive to oxidative deterioration and polymerisation than the cashew phenols since it is both a catechol and even more highly unsaturated. The composition of the sap is to some extent dependent on the source but typically it contains urushiol (55-65%), water (20-30%), glycoprotein (2-3%), polysaccharides (5-7%) and laccase (-c 1%) (ref. 196 ). 

CNSL used in polymerisation with formaldehyde as for example in friction dusts may not require elaborate analysis. Nevertheless interest in the industrial chemical uses of phenolic lipids has led to a study of quantitative methods of analysis by a variety of chromatographic methods. For cashew phenols these were first based on GLC. Thus the (15 3), (15 2), (15 1) and (15 0) constituents of methyl anacardate, cardol and cardanol have been separated by GLC on PEGA columns (ref.206), the free phenols (anacardic acid as methyl anacardate) by GLC on SE30 (ref207) and the hydrogenated anf fully methylated phenols on Dexsil and PEGA columns (ref.208). A further number of stationary phases have been investigated... 

GLC retention data proved useful in showing that Rhus vemicifera (from Japan) contains a small proportion of the 8,11,14-triene (ref. 89) in addition to the main 8,11,13- constituent. In Rhus toxicodendron the unsaturation is found at the 8 8,11 and 8, 11,14-positions as in the cashew phenols (ref. 228). 

Technical products such as medical and pharmaceutical rubber articles (3) and industrial vulcanizes (4) have been extracted with acetone. Natural cashew phenols Anacardiumoccidentak were extracted from the crushed shell by a variety of different solvents (5). In the determination of phenol additives in various edible oils by initial solvent extraction, the coextracted oil components were eliminated by the use of precoated silica plates (6). 

In the determination of carbamate insecticide residues, the parent phenols were coupled with diazotized p-nitroaniline and the azo dye isolated (29). In a combined TLCVGLC procedure for quantitative determination of the polyunsaturated constituents of the cashew phenols following an initial TLC separation, the eluted phenols, cardanol, 2-methylcardol, and a small proportion of anacardic acid each containing mono-, di-, and triene constituents were examined by GLC (30). 

Long-chain alkylphenols have been investigated extensively (33) by both adsorption and reversed-phase partition methods (34). The cashew phenols (from Anacardium occidentale) comprise cardanol (1), cardol (2), 2-methylcardol (3), and anacardic acid (4), each existing as a mixture of the saturated, 8 -monoene, 8 ,11 -diene, and 8 ,1 l ,14 -trieneconstituents. In ammoniated solvent [light petroleum-diethyl ether-ammonia (60 40 2)] the acidic compound anacardic acid remained practically on the baseline, whereas in an acidic solvent [light petroleum-diethyl ether-formic acid (70 30 1)] it migrated toward the solvent front as an intramolecularly bonded substance. In natural cashew nut shell liquid the phenols and their unsaturated constituents have the values 0.20 (cardol). 

The resins can be a novolak—hexa or a resole—novolak blend. In some appHcations Hquid resoles are used. Addition of alkylated phenol, oil, or cashew nutsheU Hquid (CNSL) reduces hardness and increases abrasion resistance. Modification by mbber improves the coefficient of friction and reduces brake fading. 

Other higher boiling phenolic bodies obtainable from coal tar distillates are sometimes used in the manufacture of oil-soluble resins. Mention may also be made of cashew nut shell liquid which contains phenolic bodies and which is used in certain specialised applications. 

During the past four decades phenolic resins have become of increased significance in rubber compounding. For example, the resin based on cashew nut shell liquid, which contains phenolic bodies such as anacardic acid (Figure 23.23), may, when blended with hexamine, be incorporated into nitrile rubber (butadiene-acrylonitrile rubber). 

Structural carbon shapes fabricated by heating coke with a mixture of tar and pitches are porous and are made impermeable by impregnation with a resin (usually a phenolic resin). Cashew nut shell liquid resin is used when resistance to alkalis and acids is required. 

Resol resins thermoset on heating and are used for adhesives. Novolacs require a further source of formaldehyde in the form of hexamethylenetetramine to produce molding powders. Phenolic moldings are resistant to heat, chemicals, and moisture with good electrical and heat insulation qualities. Complex phenols from, e.g., cashew-nut shell liquid, are used in making brake... 

This is one of the most widely distributed plants cultivated formally to obtain the well-known edible nut popularly known as a cashew nut. The phenolic lipid is only... 

CA 34, 1992 (1940) (Derivatives of a phenol obtained from cashew-nutshell)... 

Substituted phenols such as cresols, p-fcrf-butylphenol, / -phcnylphenol, resorcinol, and cardanol (derived from cashew nut shells) have also been used as precursors for phenolic resins. Alkylphenols with at least three carbons in the substituent lead to more hydrophobic phenolic resins that are compatible with many oils, natural resins, and rubbers.7 Such alkylphenolic resins are used as modifying and crosslinking agents for oil varnishes, as coatings and printing inks, and as antioxidants and stabilizers. Bisphenol-A (2,2-p-hydroxyphenylpropane),... 

Cardanol, a main component obtained by thermal treatment of cashew nut shell liquid (CNSL), is a phenol derivative having mainly the meta substituent of a C15 unsaturated hydrocarbon chain with one to three double bonds as the major. Since CNSL is nearly one-third of the total nut weight, a great amount of CNSL is obtained as byproducts from mechanical processes for the edible use of the cashew kernel. Only a small part of cardanol obtained in the production of cashew kernel is used in industrial fields, though it has various potential industrial utilizations such as resins, friction-lining materials, and surface coatings. Therefore, development of new applications for cardanol is very attractive. 

Talbiersky, J., Polaczek, J., Ramamoorty, R. and Shishlov, O. (2000) Phenols from cashew nut shell oil as a feedstock for making resins and chemicals. OIL GAS European Magazine, 35, 33-40. 

Cashew nut shell liquid (CNSL) is the exudate from the cashew nut shell. It is mainly phenolic in nature. Industrially used for making polymeric resins etc. A bath of the CNSL is traditionally used for heating the whole nuts with shells. 

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