Cashew nut shells, agro-waste generated from cashew nut factories, are rich in valuable bio-based green and renewable materials.

Cashew nut shells are agro-wastes produced from cashew nut processing factories and contain about 30-35 wt% oil called cashew nut shell liquid (CNSL). This liquid is a mixture of four potential compounds, namely anacardic acid, cardanol, cardol and 2-methyl cardol. Various reactions have been developed to convert the components of cashew nut shell liquid into industrially important chemicals, and these materials are herein described. Such reactions employed in the transformation include transfer hydrogenation reactions, isomerization reactions, metathesis reactions, carbonylation reactions, polymerization reactions, isomerizing metathesis reaction, and isomerizing carbonylation reactions. Through these descriptions, one realizes that cashew nut shells are not a waste, but they are rather a good source of a potential liquid, CNSL, which is a promising renewable resource for synthesizing various industrial chemicals.

A 1,2‐bis(di‐tert‐butylphosphinomethyl)benzene‐modified palladium catalyst has been used to synthesize bifunctional monomers of different chain lengths from cardanol. Short‐chain derivatives of cardanol, such as (E)‐3‐(dodec‐8‐enyl)phenol; HOPhC12‐ene, (E)‐3‐(undec‐8‐enyl)phenol; HOPhC11‐ene, (E)‐3‐(dec‐8‐enyl)phenol; HOPhC10‐ene, and 3‐(non‐8‐enyl)phenol; HOPhC9‐ene, were synthesized by the metathesis of cardanol with symmetrical internal alkenes. These derivatives were methoxycarbonylated to produce monomers with different chain lengths such as methyl‐16‐(3‐hydroxyphenyl)hexadecanoate; HOPhC15COOMe, methyl‐13‐(3‐hydroxyphenyl)tridecanoate; HOPhC12COOMe, methyl‐12‐(3‐hydroxyphenyl)dodecanoate; HOPhC11COOMe, methyl‐11‐(3‐hydroxyphenyl)undecanoate; HOPhC10COOMe, and methyl‐10‐(3‐hydroxyphenyl)decanoate; HOPhC9COOMe, respectively. Polymerization of the synthesized monomers produced oligomers that consist of up to seven monomer units as confirmed by MALDI‐TOF‐MS. Lactone formation was also observed in some cases under polymerization conditions.

Dedicated to Proifessor Frank Gunstone, an outstanding researcher of fats and oils and a great friend, on the occasion of his 90th birthday.Crystalline unsaturated lactone, 8-hydroxy-3-tridecyl-1H-isochromen-1-one (6) has been synthesized by isomerization of anacardic acid having heterogeneous alkyl side chains (a mixture of mono-, di-, and tri-unsaturated anacardic acid) (1). Hydrogenation of 8-hydroxy-3-tridecyl-1H-isochromen-1-one produced a saturated lactone, 8-hydroxy-3-tridecyl-3,4-dihydroisochromen-1-one (7). Isomerization of monoene anacardic acid resulted in a crystalline isoanacardic acid, (E)-2-hydroxy-6-(pentadec-1-enyl) benzoic acid (8) as a major product. This was then metathesized with 2-butene to give 3-prop-1enylphenol (10). Both isomerization reactions used a 1,2-bis(ditertiarybutylphosphinomethyl)benzene modified palladium catalyst. The two products, 8-hydroxy-3-tridecyl-1H-isochromen-1-one and (E)-2hydroxy-6-(pentadec-1-enyl)benzoic acid have been crystallographically characterized.Practical applications: Unsaturated lactones are structural elements often found in natural products, which have medicinal value. Benzolactones derived from anacardic acid reported in this work have some structural similarity with lactones such as massoia lactone having medicinal value. Therefore with this idea in mind, the unsaturated benzolactones reported in this work will be tested for their anti pathogenic activity. 3-Propylphenol is used in combination with racemic 1-octen-3-ol and p-cresol to prepare a kairomone for tsetse fly traps. Results from this work describe the suitability of anacardic acid for synthesizing 3-propylphenol. The fact that 3-propylphenol can be synthesized from anacardic acid, a component of cashew nut shell liquid is of particular interest since most of the areas affected with tsetse flies are suitable for growing cashew plants. This means the raw materials (CNSL) for synthesis of 3-propylphenol will be obtained from within the same region where the kairomone is to be applied, although we appreciate that specialized facilities would be required for the types of transformation described.

Preparation of useful materials using renewable resources, which are not in competition with food production is of particular importance in the current efforts to replace non-renewable resources. One example of a potential renewable resource, which is attracting the attention of researchers in the preparation of useful materials is cashew nut shell liquid (CNSL). CNSL which is a by-product of cashew processing factories, is a mixture of four potential compounds, namely anacardic acid, cardanol, cardol and 2-methyl cardol. Among other potential applications, cashew nut shell liquid is a good template source for preparation of mesoporous materials. Heterogeneous catalysts prepared using CNSL templates are more efficient than those prepared using the commercially available templates. The pore sizes of mesoporous materials prepared using CNSL templates are large (up to 25 nm) enough to immobilize enzymes. Another renewable resource; castor oil, has also been reported to be a good template source for preparation of mesoporous materials. This chapter therefore is aimed at describing in detail the preparation, characterization and applications of mesoporous materials templated by cashew nut shell liquid and castor oil.

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ABSTRACT. Cardanol extracted from cashew nut shell liquid (agro-waste) was used to synthesize a bifunctional monomer; methyl 16-(3-hydroxyphenyl)hexadecanoate using DTBPMB modified palladium catalyst. Hydrogenation of this monomer using a Ru(acac)3/triphos/MSA catalytic system in aqueous dioxane and ammonia solution gave 3-(16-hydroxyhexadecyl)phenol (75% yield) and 3-(16-aminohexadecyl)phenol (37% yield) respectively. Polymerization of 3-(16-aminohexadecyl)phenol and 3-(16-hydroxyhexadecyl)phenol with dimethyl nonadecanedioate (a di-ester obtained from methoxycarbonylation of methyl oleate) resulted into oligomers consisting of up to nine condensed monomer units (in the volatile fraction) as was revealed by MALDI-TOF MS.                 KEY WORDS: Cardanol, Bifunctional monomers, Catalytic hydrogenation, Polymerization   Bull. Chem. Soc. Ethiop. 2022, 36(1), 173-186.                                                             DOI: https://dx.doi.org/10.4314/bcse.v36i1.14