Solid-liquid Conditions Research Articles

Hydrotalcites as base catalysts. Kinetics of Claisen-Schmidt condensation, intramolecular condensation of acetonylacetone and synthesis of chalcone

The activity of hydrotalcites has been investigated by means of several reactions able to evidence their basic properties and the mechanism involved, and also to show their interest in the synthesis of fine chemicals of great practical interest for pharmaceutical applications. With this aim, the Claisen-Schmidt condensation of benzaldehyde with excess acetone has been performed in solid-liquid conditions. The kinetic study suggests a Langmuir-Hinshelwood mechanism, in which the rate-determining step would be the condensation of benzaldehyde and acetone, in agreement with former results of Hammett correlations. The reaction rate goes through a maximum as a function of calcination temperature of the catalyst, or the water content of the solvent, suggesting that the active sites are basic hydroxyls. These results are obtained by the intramolecular condensation of acetonylacetone as test reaction giving selectively 3-methyl-2-cyclopentanone, and showing, indeed, the presence of mainly basic sites on the hydrotalcite. Taking these results into account, the synthesis of chalcone has been performed over a suitably activated hydrotalcite.

Catalytic activity of cyclophosphazenic polypodands in phase-transfer reactions. Comparison with open-chain analogues.

The catalytic activity of cyclophosphazenic polypodands 1a-c was evaluated in typical reactions performed under solid-liquid (SL) and liquid-liquid (LL) phase-transfer catalysis (PTC) conditions. Such activity is largely determined by the complexation extent of 1a-c which is in turn related to the number of binding sites of the ligand ( 1a<1b⩽1c) and to the nature of the inorganic salt M +Y − (Na +>K +2>Rb + and SCN −∼I −> Br −). Also the presence of water was found to play an important role. Comparison with open-chainanalogues PEG 2 and TRIDENT 3 showed that polypodands 1a-c due to their excellent stability simplicity of preparation and high complexing ability can be considered promising phase transfer catalysts especially under SL-PTC conditions. Cyclophosphazenic polypodands are efficient catalysts in anion promoted reactions (e.g. nucleophilic substitution, alkylation, reduction, oxidation reactions) under SL and LL-PTC conditions. Catalytic activity is mainly related to their complexation capability.

ChemInform Abstract: New Cs2CO3 Catalyst for the Wittig‐Horner Synthesis of Acrylates in Interfacial Solid Liquid Conditions.

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Epoxide synthesis under interfacial solid-liquid conditions

In this paper an analysis of the factors responsible for discrimination among differing structures of organic reagents by the microcrystalline structure of solids is presented. As a vehicle for this study, the epoxide synthesis using three sulfur ylide precursors (sulfonium and sulfoxonium salts) and four microcrystalline solids was investigated. Neither the surface area nor the number of active sites at the solid surface control the epoxide yield. It appears that the cell lattice of the solid determines the ylide structure, its nucleophilicity, and thus the reaction yield

AlPO4 as catalyst in organic reactions. IV. Transesterification of methyl methacrylate

The transesterification of methyl methacrylate with n-BuOH has been studied in solid-liquid and gas solid conditions. The reaction takes place with better selectivity in solid-liquid than in solid-gas conditions. The influence of temperature, ester/alcohol ratio, etc., on the transesterification process are discussed.

ChemInform Abstract: Catalyzed Synthesis of Chalcones Under Interfacial Solid‐Liquid Conditions with Ultrasound.

Abstract The sonochemical synthesis of chalcones, catalyzed by an activated barium hydroxide catalyst under interfacial solid-liquid conditions, is carried out with very good yields. The sonochemical process takes place at room temperature and with a lower catalyst weight and reaction time than the thermal process.

ChemInform Abstract: Wittig‐Horner Reaction Catalyzed by Activated Barium Hydroxide in the Presence of Ultrasound.

Abstract The sonochemical Wittig-Horner reaction, catalyzed by an activated barium hydroxide catalyst in interfacial solid-liquid conditions leads to E-acrylates with very good yields. The sonochemical process takes place at room temperature and with lower catalyst weight and reaction time than the thermal process.

ChemInform Abstract: Synthesis of 2′‐Hydroxychalcones and Related Compounds in Interfacial Solid‐Liquid Conditions.

Abstractα‐Hydroxyacetophenone (I) is coupled with the aldehydes (II) in the presence of a Ba(OH)2‐catalyst, yielding the 2‐hydroxyphenyl ethenyl ketones (III).

Ba(OH)2 as the catalyst in organic reactions. Part XIV. Mechanism of Claisen–Schmidt condensation in solid–liquid conditions

The mechanism of the Claisen–Schmidt condensation, catalyzed by a series of activated barium hydroxide catalysts, is discussed. Two kinds of ketones are studied: R—CO—CH3 (R = Me, Et, Pri, But) and acetophenone (R = Ph). The influence of the chemical and textural properties of the catalysts, as well as the nature of the solvent, are studied. The process is an interfacial solid–liquid reaction between the adsorbed carbanion and the benzaldehyde. The different structures of the adsorbed carbanion produced from Ph—CO—CH3 and R—CO—CH3 are analyzed by infrared spectroscopy, and could explain the different reactivities observed in the process. The kinetic runs are discussed.

An efficient and stereoselective Wittig–Horner synthesis of acyclic α-enones with barium hydroxide as solid catalyst

Wittig–Horner reactions under interfacial solid–liquid conditions using activated barium hydroxide catalyst C-200 produce acyclic α-enones with high yields and selectivities.

Wittig-Horner reaction catalyzed by activated barium hydroxide in the presence of ultrasound

The sonochemical Wittig-Horner reaction, catalyzed by an activated barium hydroxide catalyst in interfacial solid-liquid conditions leads to E-acrylates with very good yields. The sonochemical process takes place at room temperature and with lower catalyst weight and reaction time than the thermal process.

Synthesis of 2′-hydroxychalcones and related compounds in interfacial solid-liquid conditions

A general synthetic method of 2′-hydroxychalcones and 2′-hydroxyphenyl-(2-alkylvynyl) ketones in interfacial solid-liquid conditions, is described. No secondary reactions were observed. The interfacial mechanism is discussed by means of the structure of active sites of solid.

Ba(OH) 2 as catalyst in organic reactions : Part XVI-Contribution to the study of the michael addition mechanism to chalcone in interfacial solid-liquid conditions

The Michael addition of several active methylene compounds to chal-cone, catalyzed in interfacial solid-liquid conditions is described.The mecha -nism of the process is analyzed using the Michael addition of diethyl malonate to chalcone as the reaction test. Several microcrystalline barium hydroxide ca-talysts are tested.The nature of the solid catalyst active sites taking part in the process is discussed. The presence of the adsorbed carbanion from the malo-nate-on the strong basic site of the solid-is shown by IR spectroscopy. A Me-rifield resin is used to prove that the process takes place on the solid sur-face.

Catalyzed synthesis of chalcones under interfacial solid-liquid conditions with ultrasound

The sonochemical synthesis of chalcones, catalyzed by an activated barium hydroxide catalyst under interfacial solid-liquid conditions, is carried out with very good yields. The sonochemical process takes place at room temperature and with a lower catalyst weight and reaction time than the thermal process.

Selectivite de la reduction de cyclohexen-2 ones par NBu 4BH 4 dans divers solvants et par NaBH 4 dans des conditions de transfert de phase

The 2-cyclohexenone 1 and isophorone 2 reductions with NBu 4BH 4 in aprotic solvents lead to a highly preferential 1–4 attack; i.e. 85% with 1 and 96% with 2 in THF. These regioselectivities are nearly the same as those observed with LiBH 4 in the presence of[2.1.1) cryptand confirming thus the cation influence. This method which is inexpensive and easy to work up, seems to constitute a general way to reduction of α-enones to saturate alcohols while other reagents such as K(sec Bu) 3BH are not able to reduce the carbon-carbon double bond of isophoron. Phase transfer catalysis conditions are not useful for selective reduction: large amounts of allylic alcohols are formed in liquid-liquid phase transfer conditions (60% in toluene-water); a good regioselectivity is only obtained when a cryptand is used as a transfer agent in solid-liquid conditions.