Aromatic hydrogenation catalysts

The presence of benzo[6]thiophene in commercial naphthalene, its possible contamination with isomeric thienothiophenes 1 and 2, and their ability to poison aromatic hydrogenation catalysts led Maxted and Walker to develop detoxification by a preliminary short hydrogenation, in which thienothiophenes 1 and 2, and benzo[6]-thiophene are adsorbed on the catalyst. This is followed by their hydrogenation products that can easUy be oxidized with hydrogen peroxide or permolybdic acid to nontoxic sulfones subsequent hydrogenation of the aromatic hydrocarbons is then performed as usual. 

Uses Catalyst for olefin polymerization, aromatic hydrogenation catalyst component in linear oligomerization and cyclization of unsat. hydrocarbons rubber catalyst component intermediate in alkylation reactions... 

Uses Catalyst for olefin polymerization, aromatic hydrogenation catalyst in Friedel-Crafts alkylations and acylations Ziegler catalyst component (ethylene-propylene rubber prod.) In ethylation of metals and certain org. carbonyl compds. intermediate Manuf./Distrib. Akzo Nobel http //www.akzonobel.com, Albemarle http //www.albemarle.com, Aldrich http //www.sigma-aldrich.com, FIuka http //www.sigma-aldrich. com Ethylamine CAS 75-04-7... 

Aromatic compounds may be chlorinated with chlorine in the presence of a catalyst such as iron, ferric chloride, or other Lewis acids. The halogenation reaction involves electrophilic displacement of the aromatic hydrogen by halogen. Introduction of a second chlorine atom into the monochloro aromatic stmcture leads to ortho and para substitution. The presence of a Lewis acid favors polarization of the chlorine molecule, thereby increasing its electrophilic character. Because the polarization does not lead to complete ionization, the reaction should be represented as shown in equation 26. 

In some cases the effect of the nature of aromatic hydrogen substituent has been also observed (Table 48.2). These results contrast with those obtained using typical homogeneous Bronsted acid catalysts (e.g., sulphuric) for the acylation of the same substrate with acetic anhydride, under the same experimental conditions, where the yields (98%, 95%, 91% for R=N02, H, OMe, respectively) do not significantly depend on the nucleophile s substituent nature [23]. These data imderline the contribution of the heterogeneous catalyst. 

Results obtained in the acylation of aromatic sulfonamides with acetic acid, in the presence of SnOTf based catalysts are presented in Table 48.4. The rate of the sulfonamide acylation follows the seqnence benzenesnlfonamide > p-nitrobenzenesulfonamide > />-methoxybenzenesnlfonamide, and is very sensitive towards the nature of the aromatic hydrogen substituent (the selectivity in acylated />-methoxybenzenesnlfonamide did not exceed 7% irrespective of the catalyst nature this corresponds to an approximate relative yield... 

Friedel-Crafts Reactions on PPO and Properties of the Resulting Polymers. There are two hydrogens on the aromatic ring of PPO which can react through Friedel-Crafts reactions. The substitution of the first available position from the aromatic ring occurs easily by the treatment of the PPO with sulfonyl chloride or acid chlorides in the presence of a Friedel-Crafts catalyst. The remaining aromatic hydrogen could not be removed by a second abstraction reaction, and consequently only monosubstitution was achieved. 

Olefins and aromatic hydrogenation reaction are undesired in gasoline HDT unfortunately, they cannot be fully inhibited. The high requirement on hydrogenolysis, but low hydrogenation activity, makes CoMo the preferred catalysts. New catalysts are being offered by the manufactures for selective HDS. Speculatively, two concepts have been used to develop new selective catalyst (i) improve thiophene HDS, or (ii) passivate olefin hydrogenation. 

Other advances over the past few years have been the development of (a) homogeneous hydrogenation catalysts for substrates normally not readily reduced, e.g., aromatics, isonitriles, and nitro compounds, and (b) a number of catalyst systems with unusual selectivity properties, e.g., with the capability of reducing a,/3-unsaturated aldehydes to the corresponding a,/3-unsaturated alcohols (see Sections II,B,2 and VII). 

Furthermore, the qualitative influence of substituents on the symmetry and electronic structure of the substrate and its hydrogenation product on the efficiency of the transfer of polarization to the 13C-nuclei have been discussed, as well as the feasibility of a polarization transfer to other heteronuclei. Evidence in the form of a shift of the aromatic 13C resonances has been found for an initial attachment of hydrogenation products containing aromatic segments to the metal center of the cationic hydrogenation catalyst - probably in the form of a re-complex. 

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