Cashew nut shell liquid, a potentially important commercial source of biological active natural phenols, is a mixture of alkenyl salicylic acid, and alkenylresorcinols. This mixture undergoes thermal degradation in the industrial cashew kernel shelling process to give a mixture of alkenylphenols (cardanols) and alkenylresorcinols.
Using the Kamlet-Taft classification of solvents as an heuristic guide, a solvent system allowing selective extraction of alkenyl salicylic acid, alkenylphenols and alkenylresorcinols has been found, allowing a cheap, large scale separation of cashew nut shell liquid constituents. Others approaches tested (complexes with divalent metals, alkaline extraction, or chromatographic techniques) were not so successful.
Vacuum pyrolysis of cardanols on copper has been found to be a useful technique to synthesize 3-vinylphenol, a synthon for the production of a variety of pharmaceutical drugs. In comparison with others materials, copper inhibited coke deposition, increasing yields so that the commercial value of the reaction products is higher than that of the starting material. Pyrolysis of cardanols follows the same characteristic pattern as the pyrolysis of alkylaromatics, i.e. giving as the main products vinylphenol and ethylphenol in place of styrene/toluene. Yields of minor compounds are a function of operational conditions. Pyrolysis of cardanol (15:0) in the same apparatus and conditions to the ones used for mixed cardanols, gave a smaller conversion. This is consistent with the possibility that the reaction is initiated by homolytic scission of a carbon-carbon bond which is simultaneously a to a double bond and 3 to another one in the alkyl chain. 3-Pentadecylsalicylic acid provided in 3 steps 8-pentadecyl-l-oxa-spiro-[5,7]-dien-4- one, which undergoes a rearrangement to 4-pentadecyl-benzo[l,3]dioxole, under a variety of conditions. The oxaspirodienone was unreactive in a range of Diels Alder reactions.
Synthons for the synthesis of diaromatic compounds with HIV integrase inhibition properties were provided by a selective cleavage of double bonds in the carbon chain of CNSL constituents.