Non-polymeric Applications of CNSL and its Component Phenols

The development of improved separational processes for obtaining pure (mixed) cardanol and cardol from technical CNSL has encouraged experimentation in chemical instead of polymer uses for these component phenols as well as for anacardic acid, by extraction from natural CNSL. Some of the earlier chemistry has been reviewed (ref. 2). Most of the more recent uses particularly for cardanol, but also cardol and anacardic add, stem from the conception of their semi-synthetic applications as readily available replenishable resources (refs. 278, 279). As with CNSL, the reactions considered in this section are concerned with the hydroxyl group of the side chain and substitution in the ring. 

Although it might be thought that its CIS side chain would make cardanol an ideal candidate for surface active agents comparatively few developments have materialised. The use of CNSL as a potential source of surfactants and additives has been briefly reviewed (ref. 280). The Mannich reaction of cardanol with dialkylamines and formaldehyde (ref. 281) and the formation of cationics such as 3-pentadecyl-6-dimethylaminomethyl methosulphate has been described (ref. 2). 

The synthesis of anionics is complicated in the case of unsaturated cardanol (ref. 282) by polymerisation reactions although the use of chlorosulphonic acid in chloroform at ambient temperature affords an unstable surface active product which probably contains side chain products and the phenol sulphate as well as the sulphonic add. 

Sodium anacardate is an excellent soap the water solubility of which has been used in a subsequent reaction (ref. 283). There has been, following work on the preparation of cardanol polyethoxylate (ref.284,285,286), by the reaction of cardanol with ethylene oxide at 180 C in the presence of a catalytic amount of potassium hydroxide, considerable interest in its ready biodegradability compared with that of ethoxylates derived from t-nonylphenol (ref.287). The individual ethoxy late oligomers were synthesised having values of n = 1 to 6 to identify the oligomers present in cardanol polyethoxylate and the ready biodegradation of cardanol and to a lesser extent that of of cardol polyethoxylates quantitatively established in comparison with that of t-nonylphenol polyethoxylate which remain comparatively undegraded. 

Drug analogues have previously been derived from saturated cardanol (ref. 2). In more recent work 3-pentadecylphenol and its 6-chloro derivative have been reacted with 2-chloropropionic acid and the derived methyl ester then converted to the hydrazide, reaction of which with cyanogen bromide afforded an aminooxadiazole while acetonylacetone gave a 2,5-dimethylpyrrole derivative (ref. 288). 

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