Silica polyphosphoric acid

The only 5//-1,3,6-triazonine system which has been reported and is fully supported by spectral data and elemental analysis is obtained by reaction of the imine 1 with chloroacetic acid and polyphosphoric acid.22 From a mixture of products, 2-chloro-6-(chloromethyl)-13-phenyl-dibenzo[e/, h [, 3,6]triazonine (2) was separated by silica-gel flash chromatography in poor yield. 

Another version of the reaction of 2-aminopyridines and /i-oxo esters is the isolation and cyclization of the intermediates of type 38 or 39. Compounds of type 38 were cyclized in concentrated sulfuric acid at ambient37 or elevated temperature,34,36 38,43,52,53 in polyphosphoric acid,41 or in toluene in the presence of p-toluenesulfonic acid.48 Cyclization of the acrylates (39) was carried out by heating without solvent47 or in solution in water,39-40 diethylbenzene,47 or toluene in the presence of p-toluenesulfonic acid.48 Cyclization also took place when 39 was chromatographed on a silica gel column.48... 

Phenanthrene and pyrene on treatment with diisopropylcarbodiimide, hydrogen peroxide, and acetic acid in ethyl acetate at room temperature give 1 and 4 in 28% and 27% yields, respectively.17 Similar reaction occurs with dicyclohexylcarbodiimide and cyclohexylbenzylcarbodiimide. The hydrogen peroxide can be either 98% or a 30% aqueous solution. Use of silica gel, Dowex 50W-X8, or diphenylphosphinic acid instead of acetic acid is also permissible. However, because of the sensitivity of arene oxides toward strong acids, hydrochloric, sulfuric, or polyphosphoric acids cannot be used. 

A mixture of dl-2-[4-(2 -carboxymethyl-4 -methylphenoxy)phenyl]propionic acid (15.3 g) and polyphosphoric acid (92 g) was heated with stirring at 110-120°C for 2 hours. To the reaction mixture was added water and the resulting mixture was extracted with chloroform. The organic layer was washed with water, dried over anhydrous sodium sulfate and concentrated. The residue was chromatographed on silica gel (75 g) using chloroform as an eluent to give a crude product, which was recrystallized from toluene to give the dl-2-(8-methyl-10,ll-dihydro-ll-oxodibenz[b,f]oxepin-2-yl)propionic acid (9.4 g, 65.3%), m.p. 128-129°C. 

Acetic anhydride (7 ml) was added to a solution of 6.16 g of crude 2-aminomethyl-7-chloro-2,3-dihydro-5-(2-fluorophenyl)-lH-1,4-benzodiazepine in 200 ml of methylene chloride. The solution was added to 200 ml of saturated aqueous sodium bicarbonate and the mixture was stirred for 20 minutes. The organic layer was separated, washed with sodium bicarbonate, dried over sodium sulfate and evaporated to leave resinous 2-acetylaminomethyl-7-chloro-2,3-dihydro-5-(2-fluorophenyl)-IH -1,4-benzodiazepine. This material was heated with 40 g of polyphosphoric acid at 150°C for 10 minutes. The cooled reaction mixture was dissolved in water, made alkaline with ammonia and ice and extracted with methylene chloride. The extracts were dried and evaporated and the residue was chromatographed over 120 g of silica gel using 20% methanol in methylene chloride. The clean fractions were combined and evaporated to yield resinous 8-chloro-3a,4-dihydro-6-(2-fluorophenyl)-l- methyl-4H-imidazo[l,5-a][l,4] -benzodiazepine. 

A solution of 6.7 g (25 mMol) of 2-n-propyl-benzimidazole-5-carboxylic acid-hemisulphate and 4.9 g (25 mMol) of 2-methylaminoaniline dihydrochloride in 200 g of polyphosphoric acid is stirred for 5 h at 150°C, then poured onto 600 ml of water and made alkaline with concentrated ammonia whilst cooling with ice. The resulting solution is extracted three times with 200 ml of ethyl acetate, the crude product thus obtained is purified by column chromatography (300 g of silica gel eluant methylene chloride/methanol = 15 1). Yield of 2-n-propyl-5-(l-methylbenzimidazol-2-yl)-benzimidazole 2.8 g of oil (39%). 

HSCH2CH2SH, polyphosphoric acid on silica gel, CH2CI2, 45-100% yield. Ketones react less efficiently than aldehydes. ... 

Silica-gel supported polyphosphoric acid (PPA/Si02) has been developed as a reusable catalyst-oxathio- and dithio- acetals were synthesized by using PPA/Si02. The recovered catalyst can be reused nine successive times, after drying each time at 100 °C for 2 h under reduced pressure [60],... 

Perchloric acid Phosphomolybdic acid Phosphorus oxychloride Phosphorus pentachloride Phosphorus trichloride y-Picoline Polyphosphoric acid Potassium silicate Rhodium Selenium Selenium dioxide Silica gel Silver oxide (ous) Sodium borohydride Sodium silicate Strontium carbonate Sulfur dioxide Tantalum Tellurium Tetraisopropyl di (dioctylphosphito) titanate Titanocene dichloride Trichloromethylphosphonic acid Tristriphenylphosphine rhodium carbonyl hydride Tungsten carbide Vermiculite Ytterbium oxide Zinc chloride Zinc dust Zinc 2-ethylhexanoate Zirconium potassium hexafluoride... 

Davoodnia and coworkers set up a simple and efficient procedure for the synthesis of 14-aryl-147f-dibenzo[fl, ]xanthenes using a one-pot condensation reaction of P-naphthol and aryl aldehydes catalyzed by silica gel-supported polyphosphoric acid (PPA/SiOj) (Khojastehnezhad et al, 2011). Xanthene derivatives occupy a prominent position in medicinal chemistry (Wang et al., 1997) and have been investigated for their agricultural bactericide activity (Handique and Baruah, 2002), antiinflammatory effect (Sirkecioglu et al, 1995), and antiviral activity. 

Aoyama, T., Takido, T., Kodomari, M. 2004. Silica gel-supported polyphosphoric acid (PPA/ Si02) as an efficient and reusable catalyst for conversion of carbonyl compounds into oxathioacetals and dithioacetals. Synlett 13 2307-2310. 

Khojastehnezhad, A., Davoodnia, A., Bakavoli, M., Tavakoli-Hoseini, N., Zeinali-Dastmalbaf, M. 2011. Silica gel-supported polyphosphoric acid (RRA/SiOj) An efficient and reusable heterogeneous catalyst for facile synthesis of 14-Aryl-14//-dibenzo[a/ xanthenes under solvent-free conditions. Chinese Journal of Chemistry 29 297-303. 

A. Davoodnia, S. AUameh, S. FazH, N. TavakoH-Hoseini, One-pot synthesis of 2-amino-3-cyano-4-arylsubstituted tetrahydrobenzo[b]pyrans catalysed by silica gel-supported polyphosphoric acid (PPA-Si02) as an efficient and reusable catalyst, Chem. Pap. Slovak Acad. Sci 65 (2011) 714-720. 

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