Trihaloisocyanuric acids/NaX: an environmentaly friendly system for vicinal dihalogenation of alkenes without using molecular halogen

Abstract

A reação de alquenos com ácidos trialo-isocianúricos / NaX em acetona aquosa produz os dialo-alcanos vicinais em rendimentos de moderados a excelentesThe reaction of alkenes with easily handled trihaloisocyanuric acids / NaX in aqueous acetone produces the corresponding vicinal dihaloalkanes in moderate to excellent yields. Keywords: dihaloalkanes, electrophilic addition, green chemistry, trihaloisocyanuric acid IntroductionThe great synthetic potential of organic halides puts them in a unique position within organic chemistry. They can be efficiently converted into other functionality by well-known methodologies, such as halogen-metal exchange, palladium-catalyed reaction for new C-C bond formation, conversion into radicals, nucleophilic substitution etc.1 Furthermore, several marine organic halides have been discovered in the last years with interesting biological activity. 2Although several reagents have been used to introduce halogen atoms in organic substrates, the typical route to prepare vicinal dihalo compounds is the electrophilic molecular halogen (X 2 ) addition to alkenes.3 Molecular chlorine (Cl 2 ) is a very toxic gas that presents a potential hazard and its quantitative utilization is generally problematical. Molecular bromine (Br 2 ) is a toxic and lowboiling lachrymatory liquid which causes severe burns on contact with skin. Moreover, both halogens are corrosive, difficult to handle and strong oxidants. 4 In addition, traditional halogenations of alkenes are performed in polychlorinated solvents, such as CHCl 3 or CCl 4 which are being considered "villains" from the green chemistry point of view.5 Furthermore, in chlorinated solvents, free radical reaction can compete to electrophilic process and some by products are usually obtained. 6 Based on the above considerations, the search for new methodologies that avoid the utilization of molecular halogen is of great interest and attractive. Unfortunately, some alternative reagents used for dihalogenation of alkenes are very hazardous, toxic, not readily available or need to be freshly prepared. 7 Trichloroisocyanuric acid (TCCA) is a stable and inexpensive solid frequently used for swimming-pool disinfection and easily available in pool supply and some hardware stores.8 Tribromoisocyanuric acid (TBCA), an analogue of TCCA, is easily and safely prepared from cyanuric acid, KBr and oxone. 9 We have shown that these trihaloisocyanuric acids are very interesting from Green Chemistry point of view, once they are easily handled stable solids and efficient source of electrophilic halenium ions (X + ) that can halogenate organic compounds without using X 2 . 10They also present a very good atom economy, once they can transfer most part of their mass to the substrate. For example, TBCA can transfer up to 65% of its mass to the substrate. Furthermore, in these reactions, cyanuric acid precipates as by-product, which can be recovered by filtration and reused to prepare more TBCA (Scheme 1).Herein we communicate our results on the utilization of trihaloisocyan...

Electrophilic Bromination of Alkenes: Environmental, Health and Safety Aspects of New Alternative Methods

“…[39] The latter was used to convert hydrobromic acid (entry 20), [40,41] which can also be oxidised by using Oxone (2 KHSO 5 ·KHSO 4 ·K 2 SO 4 , entry 21). [42] Oxone is applied directly during the synthesis to convert the alkene into the dibromide (entry 21, [42] entry 22 [43] ), but also to regenerate the reagent, which is a carrying agent (entry 10b), [29] an N-halo compound (entry 23), [44,45] or another N-halo compound, Nbromsuccinimide (NBS, entry 24). [46] Overviews of applications of the oxidants sodium perborate, [50][51][52] CAN, [53][54][55][56] Selectfluor [57,58] and other N-halo reagents, [59] sodium periodate, [60] DIB as a polyvalent iodine compound [61][62][63][64] and Oxone [65,66] can be found in the litera- ture.…”

“…[47] No. 19 [39] 9a [27] 20 [40] 9b [27] 21 [42] [g] 10a [28] 22 [43] [f] 10b [28] [h] 23a [44] 11a [29] 23b [45] 11b [29] 24 [46] [a] poly(vinylpyrrolidone)-bromine complex.…”

“…The latter was used to convert hydrobromic acid (entry 20),40, 41 which can also be oxidised by using Oxone® (2 KHSO 5 ⋅ KHSO 4 ⋅ K 2 SO 4 , entry 21) 42. Oxone® is applied directly during the synthesis to convert the alkene into the dibromide (entry 21,42 entry 2243), but also to regenerate the reagent, which is a carrying agent (entry 10b),29 an N ‐halo compound (entry 23),44, 45 or another N ‐halo compound, N ‐bromsuccinimide (NBS, entry 24) 46…”

Trichloroisocyanuric Acid: a Versatile and Efficient Chlorinating and Oxidizing Reagent

“…For this reason, the stoichiometry of reactions involving TCCA is frequently 3:1 (substrate: TCCA). The cyanuric acid by‐product obtained from TCCA can be recovered and re‐transformed to TCCA through a green methodology using NaCl and oxone TM …”

Ionic liquid immobilization on carbon nanofibers and zeolites: Catalyst design for the liquid-phase toluene chlorination

“…Considerable efforts have therefore been undertaken to achieve higher selectivity either by changing the solvent or the catalyst, acidity and solvent properties being key parameters. Recently, important advances were made by applying an environmentally friendly method for aromatics halogenation using trichloroisocyanuric acid (TCCA, C 3 N 3 O 3 Cl 3 ) as chlorination agent [7][8][9][10][11].…”