Silica perchloric acid

SCHEME 28 Synthesis of benzimidazole using silica perchloric acid. 

Atotalof 6.2gof 17 -acetoxyandrosta-4,6-dien-3-one-[2a,la-c]-A -pyrazoline is added portionwise to a solution consisting of 2.4 ml of perchloric acid (70%) in 240 ml acetone. The reaction mixture is then poured into ice water and extracted with methylene dichloride. The organic layer is washed to neutrality with water, dried over anhydrous sodium sulfate and taken to dryness. The residue is chromatographed on 300 g silica gel (deactivated with water 10% v/w) and eluted with methylene dichloride to yield 3.32 g (58%) of 17 -acetoxy-la,2cc-methyleneandrosta-4,6-dien-3-one mp 178-179° (from diisopropyl ether) [aj 188°(CHCl3) 281 mfi (e20,700). Further... 

The on-column synthesis approach was also explored, followed by in situ purification of the products for the glycosylation reactions using trichloroacetimidates. The authors primed the top of a standard silica chromatography column with perchloric acid immobilized on silica. After charging both reactants, dissolved in dry CH2C12, onto the... 

A. K. Chakraborti and R. Gulhane, Perchloric acid adsorbed on silica gel as a new, highly efficient, and versatile catalyst for acetylation of phenols, thiols, alcohols, and amines, Chem. Commun., 15 (2003) 1896-1897. 

B. Mukhopadhyay, D. A. Russell, andR. A. Field, One-pot acetalation-acetylation of sugar derivatives employing perchloric acid immobilised on silica, Carbohydr. Res., 340 (2005) 1075-1080. 

Open vessel digestion (HF HC104) for ceramics, glass, rocks, and soil These acids should completely dissolve most materials. HF removes the silica (as volatile SiF4), which reduces the total dissolved solid content and therefore reduces interferences, and C104 produces perchlorates, which are soluble (but explosive if dried out). The use of hydrofluoric and perchloric acids therefore has considerable safety risks and requires specialized fume hoods, handling equipment, and safety equipment. The hydrofluoric and perchloric acids are removed by a later evaporation stage unless the analytical instmment and safety considerations have been specially adapted. 

HPLC on a Cosmosil 5 Cis column, using a perchloric acid-acetonitrile eluent (pH 7.6), followed by CLD in the presence of hydrogen peroxide and bis(2,4,6-trichlorophenyl) oxalate (42), was applied to the determination of 1-aminopyrene (43a) and various diaminopyrenes (43b-d). Ascorbic acid was added to avoid oxidative degradation of the aminopyrenes in the presence of metals LOD in the sub-fmol range (SNR 3)147. A fast (less than 10 min) HPLC-ELCD method was proposed for determination of dopamine (19b) and its metabolites in microdialysates, using packed fused silica capillary columns LOD 0.05 Xg/L of dopamine in a 2 XL sample, RSD 3% (n = 10)148. 

This CSP is based on a chiral hydrophobic crown ether ((S)-2,3 4,5-Bis(l,2,3-phenylnaphtho)-l,6,9,12,15,18-hexaoxacycloeicosa-2,4-diene) that is physically adsorbed onto silica particles. Crownpak CR (-) is also available, but less used. Only a few alterations are allowed in the mobile phase for this CSP. Usually it consists of an aqueous perchloric acid solution with an amount of organic modifier. Varying pH or temperature afterwards can modify the obtained separation.Some examples of separations obtained on this CSP are given in Table 6. 

To a solution of 1.5 mmol of KDA, prepared from potassium lerl-butoxide, diisopropylamine and butyl-lithium, in 7 mL of diethyl ether is added dropwise, under an argon atmosphere, a solution of 0.293 g (1 mmol) of (/ )-2-methoxy-2-phenyl-l-[( )-3-phenyl-2-propenyloxy]propane in 2 mL of diethyl ether at — 100 °C (liquid nitrogen/methanol). After stirring for 5 h the resulting dark-red suspension is treated with a solution of 0.284 g (2 mmol) of iodomethane in 1 mL of diethyl ether. The mixture is stirred until the red color disappears (about 2 h). Then, the bath is removed and 5 mL of phosphate buffer (pH 7) are added, the mixture is extracted with ethyl acetate several times. The extracts are washed with aq NaCl, dried over MgS04, and concentrated. The residue is purified by TLC on silica gel to give (7 )-2-methoxy-2-phenyl-1-[(ii)-3-phenyl-l-butenyloxy]propane yield 0.232 g (75%). This is hydrolyzed to 3-phenylbutanal by treatment with aq perchloric acid (40 %)/diethyl ether. 

Preparation of Coal and Fly Ash for Isotope Dilution Analysis. Separate aliquots of coal and fly ash are weighed out and spiked with 204Pb and 233U, respectively. The chemical treatment and extraction of lead and uranium from coal and fly ash are identical, except coal is ashed at 450 °C before chemical treatment. The samples are dissolved with a mixture of hydrofluoric, nitric, and perchloric acids in Teflon beakers. The lead is separated by dithizone extraction, evaporated to dryness, redissolved in dilute nitric acid, and 10 ng are loaded on filaments with silica gel for mass analysis. 

Hull and Conant in 1927 showed that weak organic bases (ketones and aldehydes) will form salts with perchloric acid in nonaqueous solvents. This results from the ability of perchlonc aad in nonaqueous systems to protonate these weak bases. These early investigators called such a system a superacid. Some authorities believe that any protic acid that is stronger than sulfunc aad (100%) should be typed as a superaad. Based upon this criterion, fluorosulfuric arid and trifluoro-methanesulfonic acid, among others, are so classified. Acidic oxides (silica and silica-aluminai have been used as solid acid catalysts for many years. Within the last few years, solid acid systems of considerably greater strength have been developed and can he classified as solid superacids. 

The 1,3-dioxolane and 1,3-dioxane systems are stable to an extremely wide range of reaction procedures provided that an acidic medium is avoided. Deprotection is effected under a wide variety of mild acid conditions such as, for example, aqueous tartaric acid,134 perchloric acid,135 or moist silica gel either alone or in the presence of oxalic or sulphuric acids.136 The mild oxidative cleavage reaction with triphenylmethyl tetrafluoroborate in dichloromethane is... 

The plant sample is digested with 60% mlm perchloric acid 70% m/m nitric acid, 1 4 v/v. The acids are then removed by volatilisation and any silica present is dehydrated to render it insoluble. The concentration of molybdenum in this solution is then determined spectrophotometrically at 470 nm on a diisopropyl ether extract. 

Quantitation of Napelline.—The pharmacological activity of napelline (35)38 has prompted the development of a method for the quantitation of this alkaloid in raw plant materials.39 This method consists of the extraction of the total alkaloids, chromatographic separation, and a micro-scale acid-base titration of the napelline eluate in a non-aqueous medium. The total alkaloids were exhaustively extracted from a sodium carbonate suspension with chloroform. This extract was concentrated, dissolved in acetone, and chromatographed on silica-gel plates, with a standard reference of napelline as a marker. The appropriate bands were quantitatively removed and extracted, and the extracts were concentrated to dryness. These residues were dissolved in glacial acetic acid and titrated with 0.01N perchloric acid. The standard deviation of this method was 3.39 x 10 3. No limits of detection are reported. 

Silica and silicates (Si032- and SiO,1 ) react with hydrochloric or perchloric acid to form silicic acid, H2Si03. Evaporation of the solution precipitates dehydrated silica. Upon ignition, dehydration is completed. The reaction steps are summarized below ... 

Richter, E., Detection of sterols with naphthoquinone-perchloric acid on silica gel layers, J. Chromatogr., 18, 164, 1965 Chem. Abs., 63, 7653a, 1965. 

Tablets HPLC Extract powder with Silica, Spherisorb 5W, 2 ml/min. C-18 Sj = MeOH-perchloric acid (IL IOOmI) S4 = MeOH, H.O, TFA (997 2 1) Water-acetonitrile...

The chloride [Ir(NH3)6Cl]Cl2 (3 g.) is dissolved in a solution of sodium hydroxide (100 ml. of a 1 M solution) and refluxed for 8 hours. The red-brown solution is filtered in order to remove impurities. To the filtrate 10-12 ml. of 60% perchloric acid is carefully added white crystals form. The product is collected on a filter washed with 1 M HC104 and with alcohol. For purification the crystals are dissolved in about 40 ml. of warm (40°C.) water. After filtration from some gelatinous residue, the product is recovered by precipitation with 2 ml. of 60% HCIO4. The white crystals are washed by dilute HCIO4 and alcohol and dried in a desiccator over silica gel. Yield is 3.2-3.4 g. (69-73%). Anal. Calcd. for [Ir(NH3)6-(H20)](C104)3 Ir, 32.4 N, 11.8 H, 2.89 Cl, 17.91. Found Ir, 32.23 N, 11.9 H, 3.02 Cl, 18.13. 

Effecting deposition-precipitation by decreasing the pH level is interesting with metal ions present in the stable state in aqueous solution as anions [35]. With silica no interaction is observed, which has led to the development of the electrochemical reduction procedure. To apply metal ions, such as, molybdenum or vanadium, on alumina, a homogeneous decrease in pH level is interesting. The pH level has been decreased by injection of nitric acid or perchloric acid and electro-chemically. However, the rate of crystallization of the hydrated oxides of vanadium(V) and molybdenum(VI) was observed to be fairly low. To prevent dissolution of the alumina supports the pH cannot be decreased to levels below about 3, at which the crystallization of the hydrated metal oxides does not proceed rapidly. 

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