Surfactant with Bronsted acid

After evacuation at 25°C (spectrum C), the physisorbed fraction of acetonitrile-d3 and also the H-bonding effects with the silica surface -OH have disappeared, while the Bronsted acidity is still present (2309 cm 1). Subsequent evacuation at 60°C does not change the intensity of the Bransted acidity (spectrum D). Even at 120°C and at 150°C Bransted acid sites are still detected (spectra E, F). Therefore, it can be concluded that the Al-PCH is characterized by an important Bransted surface acidity. This type of acidity is expected since the initial Na+ ions on saponite have been replaced by surfactant cations and then by protons upon destruction of the surfactant through calcination. Besides, by the grafting of Al-species onto the support, Si-(OH)-Al bonds have been created, giving rise to the band at 2309 cm 1 indicative of Bransted acidity [10]. 

The mesoporous materials discussed here comprise silicates and aluminosilicates that are formed from synthesis conditions comparable to zeolites. The main difference with the latter is the use of supra-molecular assemblies of surfactant molecules, e.g. alkyltrimethylammonium ions, as the structure directing agents. Due to the large dimensions of these spherical or cylindrical micelles, the framework of the silicates is not so well crystallized as in the case of zeolites. This causes lower framework stability as well as weaker Bronsted acidity. Upon calcination, large pores of uniform diameter (say 4-10 nm, depending on the surfactants used) become accessible. 

Several procedures for a one-pot Mannich-type reaction in water to give (3-amino carbonyl compounds catalyzed by either Lewis acid or Bronsted acid with or without addition of surfactants have been developed. The reactions are high yielding however, the diastereoselectivities are moderate. The HBF4-catalyzed reaction between aldimines and ketene silyl acetals in a water/SDS mixture provides high stereoselectivity with very good yields (Scheme 5.19). 

Synthesis of M41S mesoporous materials was attempted using MFI type zeolite as sources of silica and aluminum, that is, dissolution of MFI zeolite in an alkaline solution and successive precipitation of dissolved aluminosilicate species with a surfactant, cethyltrimethylammonium bromide (CTAB). Pure phase of M41S was obtained when the filtrate of alkali-treated slurry was mixed with CTAB and crystallized at 293K. The M41S materials obtained in this method showed a catalytic activity originated from Bronsted acid site of the parent MFI zeolite. This method enables us to obtain a new type of mesoporous materials, which have both characteristics of zeolitic and mesoporous materials a strong Bronsted acidity and mesopores with a uniform size. 

Boron has been shown to be an efficient catalyst. Various aldehydes and silyl enol ethers afforded the corresponding syn-substituted /3-hydroxyketones in high diastereoselectivities (80-94% de) when the reaction was performed in water with 10 mol% Ph2BOH, surfactant (SDS), and a Bronsted acid (Scheme 8.6). A mechanism involving a boron enolate intermediate generated by a silicon/metal exchange was proposed the improvement observed in the presence of benzoic acid could be due to an increase of the rate of the Si/B exchange. ... 

Surfactant-based synthesis of mesoporous metal oxides and metal sulfides emerged about four years after the initial report of MCM-41 [21-36]. High surface area and thermally robust mesoporous metal oxides and sulfides represent a new class of materials with diverse opportunities for the development of improved fuel and solar cells, batteries, membranes, chemical delivery vehicles, heavy metal sponges, sensors, magnetic devices and new catalysts. All of these applications could benefit from tailorable Bronsted and Lewis acidity and basicity, flexible oxidation states, and tunable electronic, optical and magnetic properties. 

Flux is sometimes thought of as a catalyst that lowers the surface tension between the molten solder and a metal surface [98]. In reality, the chemistry of flux interactions at oxide surfaces can be very complicated and involve acid-base, oxidation-reduction, and coordination-type and adsorption-type reactions discussed in later sections [102-104]. Spalik prefers to think of most fluxes used for electronic soldering as substances that react as Bronsted-Lowry acids with metallic oxides to form their respective salts and water, and that the salts serve as surfactants that promote solder wetting. 

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