Heterogeneous solid acids

Joseph JK, Jain SL, Sain B (2006) Ion exchange resins as recyclable and heterogeneous solid acid catalysts for the Biginelli condensation an improved protocol for the synthesis of 3,4-dihydropyrimidin-2-ones. J Mol Catal A Chem 247 99-102... 

Scheme 1 Sucrose is hydrolyzed into a mixture of glucose and fructose when exposed to an acid catalyst. Sulfuric acid has been used for this, but also heterogeneous solid acid catalysts have found use, especially acidic ion exchange resins.

Styrene. Styrene is the largest benzene derivative with annual consumption about 11.5 billion lb in the United States. It is produced mainly by catalytic dehydrogenation of high-purity ethylbenzene (EB) in the vapor phase. The manufacture process for EB is based on ethylene alkylation with excess benzene. This can be done in a homogeneous system with aluminum chloride catalyst or a heterogeneous solid acid catalyst in either gas or liquid-phase reaction. In the past decade, the liquid-phase alkylation with zeolite catalyst has won acceptance. Those processes have advantages of easier product separation, reducing waste stream, and less corrosion. In addition, it produces less xylene due to lower... 

Toshima, K, Kasumi, K, Matsumura, S, Novel stereocontrolled glycosidations of 2-deoxyglucopyranosyl fluoride using a heterogeneous solid acid, sulfated zirconia (SO4/Z1O2), Synlett, 813-815, 1999. 

Nagai, H, Kawahara, K, Matsumura, S, Toshima, K, Novel stereocontrolled a- and p-glycosidations of mannopyranosyl sulfoxides using environmentally benign heterogeneous solid acids. Tetrahedron Lett, 42, 4159-4162, 2001. 

Most of the units built prior to the 1990s employ a homogenous HF acid catalyst system and the units built post-1990 employ heterogenous solid acid catalyst systems. As such, detailed discussion in this entry will be focused on these two manufacturing routes with particular emphasis on the heterogenous catalyst system. 

Besides triflic acid, other acids may also be considered initially. Table 2. shows performances obtained with other acids (Bronsted and Lewis as well as heterogeneous solid acids) in arbitrary and non-optimized conditions. 

Heterogeneous solid-acid catalysis has the potential to make a major contribution towards improving the environmental acceptability of terpene rearrangement and isomerization processes. There are potential heterogeneously catalyzed replacement processes for the production of campholenic aldehyde, an important intermediate for many fragrance compounds. With continuing advances in the field of solid-acid catalysis it is likely that other industrially useful heterogeneous catalysts will be discovered. 

The application of ionic Hquids in catalysis has been reviewed by Hardacre and Parvulescu [127] hence, only selected examples are discussed herein. Molten salts have been used as an immobilization medium for homogeneous selox catalysis [128], for example, RuClj [129], Cu(C104)2 [130], or CuCl [131] (the latter in conjunction with molecular sieve 3A as a heterogeneous solid acid promoter). Van Doorslaer et al. [132] also reported the use of imidazolium ionic liquids for Pd(II)-acetate-catalyzed oxidation of alcohols to ketones, wherein, for... 

The disadvantages of using mineral acids such as concentrated HCl or H2SO4 to hydrolyse biomass is that they are toxic, corrosive, hazardous and difficult to recycle. The use of heterogeneous solid acids can ease product separation and provide better catalyst recyclability. For example, mesoporous transition metal oxides have been used in biomass transformations. " Polymer-based acids have been employed for the hydrolysis of various organic substrates. " In particular, carbon-based solid acids made by sulfonation of carbonized polymers, such as the solid acid shown in Figure 7.7, have shown promise. Sulfonated bio-char has been similarly used. ... 

ZSM-5, a heterogeneous solid acid catalyst with MFI cages connected by 10-ring micropores, has been widely used in the fields of oil refining and petrochemical industries [32]. 

Sabitha, G., Srinivas, C., Raghavendar, A., Yadav, J.S. 2010. Phosphomolyhdic acid (PMA)-S iOj as a heterogeneous solid acid catalyst for the one-pot synthesis of 2Ff-indazolo [ 1,2-fc] phthalazine-triones. Helvetica ChimicaActa 93(7) 1375-1380. 

Tungstate Sulfuric Acid as a New Heterogeneous Solid Acid Catalyst..69... 

TUNGSTATE SULFURIC ACID AS A NEW HETEROGENEOUS SOLID ACID CATALYST... 

To conclude, in this study, we presented a simple and clean method for the synthesis of several heterogeneous solid acid catalysts that are capable of efficiently catalyzing synthesis of various heterocyclic biological compounds. We believe that these eco-friendly, inexpensive, recyclable catalysts can be used for simple experimental procedures with solvent-free reaction conditions, low catalyst loading, short reaction... 

Such medium effects imply a dramatic difference between acid catalysis carried out over acidic surfaces in a gas-phase medium and that carried out in a polar solution phase medium in the absence of a heterogeneous solid acid surface. On a solid surface, the activation of an adsorbate occurs from a neutral state since the carbenium ion states are typically unstable and serve as transition states. On the other hand, protonation in a solution can occur from an ionized state, in which reactant molecules have already been protonated. This explains the much higher reactivity for protonation reactions which occur in polar media. 

Nagai H, Sasaki K, Matsumura S, Toshima K. Enviromnen-tally benign 3-stereoselective glycosidations of glycosyl phosphites using a reusable heterogeneous solid acid, mont-morillonite K-10. Carbohydr. Res. 2005 340 337-353. 

Toshima K, Nagai H, Kasumi K-1, Kawahara K, Matsumura S. Stereocontrolled glycosidations using a heterogeneous solid acid, sulfated zirconia, for the direct syntheses of a- and (3-manno- and 2-deoxyglucopyranosides. Tetrahedron 2004 60 5331-5339. 

Table 6.6 Recent heterogeneous solid acid catalysts for biodiesel production... 

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