A mild, expedient, solventless synthesis of bis(indolyl)alkanes using silica sulfuric acid as a reusable catalyst

Abstract

Silica sulfuric acid (SSA) was found to be a mild, efficient and reusable solid acid catalyst in electrophilic substitution reaction of indoles with carbonyl compounds to afford the corresponding bis(indolyl)alkanes in excellent yields under solvent-free conditions.

Bis- and Trisindolylmethanes (BIMs and TIMs)

“…Other factors that prompted new research include the price of catalysts, finding milder reaction conditions, reusability of catalysts, yield of products, reaction rates, simplicity of the workup, green chemistry, etc. Typical protic acids [124][125][126] used to catalyze the reaction include silica sulfuric acid (SSA), 127 oxalic acid, 128,129 zeolites HY 130,131 and ZnY, 132 amberlyst, [133][134][135] p-(ω-sulfonic-perfluoroalkylated)polystyrene (FPS) resins, 136 H 2 SO 4 , 101,137,138 HBr, 139,140 HCl, 68,[141][142][143][144][145][146] 168 PEGsupported sulfonic acid 169 and AcOH-MW, 170 Lewis acids, such as lanthanide resins, 171 zeolite (ZnY), 172 bentonitic clay/ IR, 173 montmorillonite clay K-10, 174,175 [231][232][233] Meldrum's acid/H 2 O/sonoirradiation, 234 SBA-15supported poly(4-styrenesulfonyl(perfluorobutylsulfonyl)imide), 235 carbohydrate-based tolylsulfonyl hydrazines, 236 triphenyl phosphonium perchlorate (TPP), 237 tetrakis[3,5bis(trifluoromethyl)phenyl]borate, 238 hexamethylenetetraaminebromine (HMTAB), 239,…”

“…Other factors that prompted new research include the price of catalysts, finding milder reaction conditions, reusability of catalysts, yield of products, reaction rates, simplicity of the workup, green chemistry, etc. Typical protic acids – used to catalyze the reaction include silica sulfuric acid (SSA), oxalic acid, , zeolites HY , and ZnY, amberlyst, – p -(ω-sulfonic-perfluoroalkylated)polystyrene (FPS) resins, H 2 SO 4 , ,, HBr, , HCl, ,– HCOOH, CH 3 COOH, – p -TsOH, NH 2 SO 3 H, – HBF 4 −SiO 2 , NaHSO 4 −SiO 2 , KHSO 4 , NaHSO 3 , 2KHSO 5 ·KHSO 4 ·K 2 SO 4 (oxone), H 4 SiMo 12 O 40 , H 3 PMo 12 O 40 , H 3 PW 12 O 40 , , H 3+ n PMo 12− n V n O 40 , H 3 PW 12 O 40 −ZrO 2 , H 3 PW 12 O 40 −SiO 2 , −TiO 2 , or −Al 2 O 3 , H 6 P 2 W 18 O 62 , H 14 [NaP 5 W 30 O 110 ])/SiO 2 /sonoirradiation, (NH 4 ) 2 HPO 4 , H 3 PO 4 −SiO 2 , PEG-supported sulfonic acid and AcOH−MW, Lewis acids, such as lanthanide resins, zeolite (ZnY), bentonitic clay/IR, montmorillonite clay K-10, , cerium ammonium nitrate (CAN), nanoceria (CeO 2 ) supported on vinyl pyridine polymer, CeCl 3 ·7H 2 O/glycerin, M(HSO 4 ) x , , KAl(SO 4 ) 2 ·12H 2 O, , AlPW 12 O 40 , AlMe 3 , ZrOCl 2 , ZrOCl 2 ·8H 2 O−SiO 2 , Cp 2 ZrCl 2 , ZrCl...…”

Synthesis of novel benzimidazole-diindolylmethane hybrid compounds within the green chemistry context

“…Its 13 C-NMR spectra showed 18 signals which corresponds to all magnetically inequivalent carbons. According to all of above, we think that our methodology to form compounds 3a-l has important green advantages over some previous mentioned synthetic methodologies for DIM derivatives, such as not use of solvent on reactions, compared with the use of dichloromethane 11,23,29,30,33,35 , chloroform 13,32 , acetonitrile 12,38 , ionic liquids 27,28,29 , not use of Broensted-Lowry and Lewis acid catalyst 11,12,13,23,25,26,30,32,33,34,37,39 , resins 31,35,36,38 , inert atmosphere 26 , and does not require long reaction times (7-10 h , with the use of microwave energy for the activation of reactions. In addition, to obtain benzimidazole compounds 4a-l we do not require any redox reagents, such as nitrobenzene 16 , sodium metabisulfite 17 , neither catalyst 16,18,22 or solvent.…”

“…21 A literature survey reveals examples of specific reactions, which do not occur under conventional heating, but could be possible by microwave irradiation. 22 The synthesis of some DIM derivatives using catalysts such as silica sulfuric acid 23 under thermal conditions involved reactions that took a long time and provided low to moderate yields. In some cases, many byproducts were formed when the reactions were carried out in aqueous medium and under controlled conditions at pH values of 1.0, 1.5, 2.5 and 7.2, respectively.…”

New Greener Alternative for Biocondensation of Aldehydes and Indoles Using Lemon Juice: Formation of Bis-, Tris-, and Tetraindoles

“…Synthetically, the reaction of indole with aldehyde or ketone produces azafulvenium salts that react further with a second indole molecule to form bis(3-indolyl)methanes [5]. Different protic acids [6,7] including silica sulfuric acid [8], silica supported NaHSO 4 and amberlyst-15 [9], silica supported KaHSO 4 [10] and Lewis acids [2,[11][12][13] are known to catalyze this reaction. The protic acids (e.g., HCl and H 2 SO 4 ) and Lewis acids (e.g., BBr 3 and BF 3 ) which are generally used are hazardous and difficult to handle and remove from the reaction mixture.…”