About Us

Trichloroisocyanuric Acid (TCCA) as Atom-Economic Reagents

Trichloroisocyanuric acid (TCCA) is excellent reagents for direct halogenation of electron-rich aromatics under solventfree, ball-milling conditions, tribromoisocyanuric acid (TBCA) is also good. The results are remarkable in light of the fact that chlorination of aromatics without any acid catalyst is heretofore unknown. The procedure is operationally simple, and the reactions occur within a few hours, affording high yields of halogenated products. Similarly, crystalline β-keto dicarbonyl compounds are shown to undergo direct α,α-dihalogenation with TBCA and TCCA with ball milling. Whereas monoketones are found to be unreactive with TBCA/TCCA, addition of 25 mol-% of p-toluenesulfonic acid as a solid catalyst catalyzes the reaction, leading to the formation of α-chloro/bromo ketones in very good isolated yields. The fact that each of the reagents, in principle, serves as a source of three halogen atoms should render solvent-free halogenation of aromatics and carbonyl compounds with TBCA/TCCA an invaluable synthetic protocol.

Our attention was drawn toward trichloroisocyanuric acid (TCCA), which has been reported to be a versatile and innocuous oxidant with high stability. In the realm of synthetic organic chemistry, TCCA has been employed – due to its low price and ready availability, environmentally benign attributes, and ability to serve as a source of three chlorine atomsfor a variety of reactions that include oxidation of primary and secondary alcohols to their corresponding aldehydes and ketones, conversion of alcohols into alkyl chlorides, preparation of alkyl halides from alcohols, dihalogenation of olefins, halogenation of 1,3-dicarbonyl compounds, halofluorination of alkenes, aromatic halogenations, and N-halogenation. Juenge et al. were the first to report chlorination of aromatics by using TCCA in the presence of FeCl3 in 1970. 

The presence of three transferable chlorine atoms in trichloroisocyanuric acid (TCCA) render it highly advantageous and indispensable from the point of view of atom-economy when compared with other N-chlorinated reagents such as N-chlosaccharin, 1,3-dichloro-5,5-dimethylhydantoin, and N-chlorosuccinimide. In the same vein, its bromo analogue, namely, tribromoisocyanuric acid (TBCA), has also been found to be an effective source of bromonium ion for electrophilic bromination of arenes, 1,3-dicarbonyl compounds, and for the bromination of alkenes. Despite widespread use of both TCCA and TBCA for aromatic chlorination and bromination reactions, a conspicuous absence of their exploitation for solvent-free reactions spurred us to undertake the present investigation; notably, there are some reports of solventfree halogenations of aromatics and 1,3-diketones under ball-mill conditions using NaX/Oxone.