Derivatives—Building Blocks for Agrochemicals

The disinfectant, bactericidal and fungicidal properties of individual cresols and mixed cresol or cresylic acids had been well known for the last 60 years or so. So much so that within the recommended doses as prescribed by WHO cresols were used in the manufacture of carbolic soaps. Cresols were also used in place of phenol as disinfectant in domestic applications. They were also used as wood preservatives. As mentioned earlier para-chloro-meta-cresol is now one of the preferred preservatives for leather goods. 

However, it is not only the first generation derivatives of individual cresols but secondary and even tertiary derivatives that have proved to be very important plant growth regulators or agrochemicals apart from their uses as household insect and pest repellents. Synthetically made pyrethroids which are replacing more costly natural pyrethrum or pyrethrins are one such example. 

It may be recorded that the term agro-chemical would encompass in a broad sense acaricides, fungicides, herbicides, insecticides, rodenticides plant growth regulators, and others in the allied fields. 

Common names pyrethrins, firmotox, pyrethrins and pyrethroids, chrysanthemates, pyrethrum, etc. Chemically, the field pyrethroids consist of hydroxy and non-hydroxy fatty acids, alkanes, carotenoids sterols and triterphenols, flavonoids, etc. 

Functionally, pyrethroids are a group of insect growth regulators that act as neurotoxins resisting the development of insect larvae. They are especially effective against insects that are destructive in the adult stage. They are considered non-toxic to animals and humans. Pyrethrum consists of dried flower heads of chrysanthemum. The plant is a native of Dalmatia (Yugoslavia-Balkans) and is now widely cultivated in Kenya, East Central Africa, Japan, Brazil, Ecuador, and India. 

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Carbamic acid esters (methanes) and their derivatives are important precursors to agrochemicals (herbicides, fungicides, and pesticides) as well as to pharmaceuticals. Also, they can be transformed to isocyanates, which are major building blocks for polyurethanes, widely used in construction, transportation, and several other fields. Presently, the main technical process for the manufacture of isocyanates is phosgena-tion of the corresponding amines. Since the global consumption of polyurethane raw... 

Chiral alcohols are useful starting materials for the synthesis of various biologically active compounds. The need for enantiomerically pure drugs and agrochemicals has increased in recent years [13]. Derivatives of enantiopure 1-phenylethanol are important chiral building blocks, which can be used as synthetic intermediates for the production of pharmaceuticals, fine-chemicals agrochemicals, and natural products. In particular (R)-1-phenylethanol is in widespread use as an ophthalmic preservative, an inhibitor of cholesterol intestinal adsorption, a solvatochromic dye, a fragrance, and so on. 

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