Catalytic Performance of Immobilized Sulfuric Acid on Silica Gel for N-Formylation of Amines with Triethyl Orthoformate

In the search for convenient, green, and practical catalytic methods for the current interest in organic synthesis, a simple, green, and highly efficient protocol for N-formylation of various amines was carried out in the presence of immobilized sulfuric acid on silica gel (H₂SO₄–SiO₂). All reactions were performed in refluxing triethyl orthoformate (65 °C). The product formamides were obtained with high-to-excellent yields within 4 min to 2 h. The current approach is advantageous, due to its short reaction time and high yields. The catalyst is recyclable with no significant loss in catalytic efficiency.     

Morpholine Adsorbed on Silica Gel: A Novel and Mild Basic Catalyst for the Synthesis of α,β-Unsaturated Nitroalkenes

Summary.  Syntheses of α,β-unsaturated nitroalkenes have been carried out under mild condition using morpholine adsorbed on silica gel as a novel catalyst. Received February 14, 2000. Accepted March 28, 2000     

Morpholine Adsorbed on Silica Gel: A Novel and Mild Basic Catalyst for the Synthesis of α,β-Unsaturated Nitroalkenes

 Syntheses of α,β-unsaturated nitroalkenes have been carried out under mild condition using morpholine adsorbed on silica gel as a novel catalyst.     

Esterification in dry Media Using Ferric Perchlorate Adsorbed on Silica Gel

Adsorption of Fe(ClO₄)₃(H₂O)₆ onto chromatographic grade silica gel in the presence of alcohol (to be used for esterification) produces a supported reagent, Fe(ClO₄)₃(ROH)₆/SiO₂. This reagent, has been found effective for the rapid and high yield of esters, on grinding in the presence of carboxylic acids using pestle and mortar in the solid state.     

Synthesis of gem-Dihydroperoxides from Ketones and Aldehydes Using Silica Sulfuric Acid as Heterogeneous Reusable Catalyst

Silica sulfuric acid (SSA) was found to efficiently catalyze the conversion of aldehydes and ketones directly into the corresponding gem-dihydroperoxides (DHPs) on treatment with aqueous 30% H₂O₂ at room temperature. Mild reaction conditions, good to excellent yields, short reaction times, low environmental impact, and recyclability of the catalyst are the main advantages of this synthetic method.     

Correlation Between Specific Surface Area and Methyl Red Adsorbed on Silica Gel

Abstract

The amount of methyl red, adsorbed on bare silica gel, has been determined for 32 samples having a specific surface area ranging from 10 m²/g to 500 m²/g, as determined by a BET method. A linear relationship between amount of dye adsorbed and specific area exists up to about 300 m²/g. Beyond this value the amount of adsorbed dye does not increase correspondingly, which is believed to be due to the relative increase of micropores in the silica gel structure. It is proposed that the easily performed determination of the adsorbed methyl red can serve to estimate that part of the silica gel surface which is available for chromatographic interactions.     

Silica Sulfuric Acid: A Versatile and Reusable Catalyst for Synthesis of Coumarin-3-carboxylic Acids in a Solventless System

Synthesis of substituted coumarin-3-carboxylic acid via Knoevenagel condensation of meldrum's acid with ortho-hydroxyaryl aldehydes in solventless system is described.     

Iron (III) Perchlorate Adsorbed on Silica Gel: A Reagent for Organic Functional Group Transformations

Adsorption of Fe(ClO₄)₃(H₂O)₆ onto chromatographic‐grade silica gel in the presence of organic solvents (S=water, acetonitrile, or lower fatty acids) produces a supported reagent, Fe(ClO₄)₃(S)₆/SiO₂. This reagent has been found to be effective for the rapid organic functional group transformations such as dimerization of alkynes, aromatic hydrocarbons, selective oxidation of thiols to disulfides, and transannular reactions in 1,5‐cyclooctadienes on grinding using pestle and mortar in the solid state.     

硅胶负载钯: 一种新型有效而可循环的Heck反应的催化剂

本文报道了一种新型硅胶负载钯催化剂在Heck 反应中的应用。在硅胶负载钯催化剂,碳酸钾为碱,DMF为溶剂的反应条件下（无膦和无游离胺的存在）,碘代芳烃、溴代芳烃和活泼的氯代芳烃与烯烃发生偶联反应生成高产率相应的偶联产物。而且硅胶负载的钯催化剂经简单处理,可循环使用6次不降低活性。     

Trifluoroacetic Acid as a New Effective Catalyst for Preparing Monolithic Silica Gel by the Sol-Gel Process

Trifluoroacetic acid was proposed as a new effective catalyst for organic sol-gel synthesis. The influence of the solvent (polar or nonpolar, protic or aprotic) on the sol-gel process was studied.     

盐酸三甲胺三氧化铬／硅胶载体试剂的制备及其对苯偶姻体系的氧化

报道了盐酸三甲胺三氧化锆／硅胶载体试剂的制备方法及其对苯偶姻的氧化反应。该试剂制备简单，用于地苯偶姻的氧化，高收率地得到相应的苯偶酰在化合物，并且反应条件温和，产物易分离。     

Amperometric Biosensor for Lactate Based on Meldola's Blue Adsorbed on Silica Gel Modified with Niobium Oxide

A reagentless amperometric biosensor sensitive to lactate was developed. This sensor comprises a carbon paste electrode modified with lactate dehydrogenase (LDH), nicotinamide adenine dinucleotide (NAD⁺) cofactor and Meldola's blue (MB) adsorbed on silica gel coated with niobium oxide. The amperometric response was based on the electrocatalytic properties of MB to oxidize NADH, which was generated in the enzymatic reaction of lactate with NAD⁺ under catalysis of LDH. The dependence on the biosensor response was investigated in terms of pH, supporting electrolyte, ionic strength, LDH and NAD⁺ amounts and applied potential. The biosensor showed an excellent operational stability (95% of the activity was maintained after 250 determinations) and storage stability (allowing measurements for over than 2.5 months, when stored in a refrigerator). The proposed biosensor also presented good sensitivity allowing lactate quantification at levels down to 6.5×10^?6 mol L^?1. Moreover, the biosensor showed a wide linear response range (from 0.1 to 14 mmol L^?1 for lactate). These favorable characteristics allowed its application for direct measurements of lactate in biological samples such as blood. The precision of the data obtained by the proposed biosensor show reliable results for real complex matrices.     

Potassium Vanadates of Mixed Valence as Sulfuric Acid Catalyst Precursors

The kinetics of hydrolytic precipitation of potassium vanadates K_xV₁₂O_31-δ ·nH₂O(0 < x ≤ 2.25; 0 <δ ≤ 1.15) from a KVO₃ solution at pH = 1.7 and 80°C in the presence of K₂SO₄ and VOSO₄ is controlled by second and third order reactions respectively occurring on the precipitate surface. This difference is due to the effect of VO²⁺ ions on the polymer anion [V₁₂ O_31-δ]ⁿ formation. Potassium vanadates K_xV₁₂O_31-δ ·nH₂O and K_xV₃O_8-δ·nH₂O (1.02 ≤ x ≤ 1.91; 0 ≤ δ ≤ 0.22) can be used as vanadium-containing precursors for sulfuric acid catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

硅胶硫酸:一种在温和及无溶剂条件下一锅法合成1,4-二氢吡啶的高效多相催化剂(英文)

A series of 1,4-dihydropyridines have been prepared by a one-pot condensation of aldehydes,ethyl acetoacetate,and ammonium acetate in the presence of a heterogeneous catalyst silica sulfuric acid at room temperature under solvent-free condition. This new protocol has the advantage of short reaction time and excellent yields,and is an environmentally benign route to the synthesis of 1,4-dihydropyridines.     

Nitric Acid on Silica Gel: A Useful Nitrating Reagent for Activated Aromatic Compounds

Phenols and arylmethyl ethers are rapidly mononitrated by nitric acid adsorbed in silica gel at room temperature in high yields.     

Interaction of Formic Acid with the Silica Gel Network

Silica gels can be made by direct reaction of formic acid with tetraethyl orthosilicate. We have characterized wet gels of this type using a beam-bending technique that yields the elastic modulus, Poisson’s ratio, viscoelastic relaxation function, and permeability. When the experiment is performed in ethyl formate, the silica network behaves in an elastic fashion; the permeability is low (<1 nm²), indicating a pore radius of <4.3 nm. The capillary pressure generated in such small pores is estimated to be sufficient to cause collapse of the pores during drying, which would account for the observed ultramicropores in this type of gel. When the pore liquid contains formic acid, viscoelastic relaxation is relatively rapid. Studies of cyclosiloxane compounds indicate that formic acid can attack only the strained siloxane bonds of the network, which would account for the relaxation behavior. Aging in formic acid causes rapid initial shrinkage, because formic acid accelerates condensation of silanols, which drives syneresis; the modulus increases and the permeability decreases monotonically, so there is no indication of coarsening during aging in formic acid, even at 70°C.