Titanium silicalites alcohols

The reaction is carried out using a titanium silicalite-1 (TS-1) zeolite catalyst [30, 122]. This type of catalyst is known to accelerate the selective oxidation of alcohols, epoxidation of alkenes and hydroxylation of aromatics. These reactions have importance for fine-chemical production. 

Indeed, several interesting procedures based on three families of active catalysts organometallic complexes, phase-transfer compounds and titanium silicalite (TS-1), and peroxides have been settled and used also in industrial processes in the last decades of the 20th century. The most impressive breakthrough in this field was achieved by Katsuki and Sharpless, who obtained the enantioselective oxidation of prochiral allylic alcohols with alkyl hydroperoxides catalyzed by titanium tetra-alkoxides in the presence of chiral nonracemic tartrates. In fact Sharpless was awarded the Nobel Prize in 2001. 

In the field of heterogeneous catalysis using H2O2 as oxygen source, examples of the use of titanium-silicalite (TS-1) or Ti-beta in the oxidation of selected alcohols, with formation of a Ti-peroxo species, have been reported... 

The direct hydroxylation of benzene and aromatics with a mixture of 02 and H2 have been performed by simultaneously mixing benzene, oxygen and hydrogen in the liquid phase using a very complicated system containing a multi-component catalyst, a solvent and some additives. Besides the possibility of an explosive gas reaction, these hydroxylations gave only very low yields, 0.0014—0.69% of phenol and aromatic alcohols. For example, Pd-containing titanium silicalite zeolites catalyzed... 

The advantage of the above two methods are high yields of epoxides, and the titanium silicalite catalyst is not deactivated or poisoned by the contaminants in the crude oxidation mixture. Hence, the processes are commercially attractive. The in situ hydrogen peroxide generation based on the AO process from either the anthraquinone/anthrahydroquinone or ketone/alcohol redox couples has also been used for the following synthetic reactions ... 

Titanium silicalite (TS-1), an isomorphously substituted molecular sieve [215], is a truly heterogeneous catalyst for oxidations with 30% aq. H202, including the oxidation of alcohols [216]. 

The primary use for the titanium silicalites is as shape selective catalysts for hydrogen peroxide oxidations. " Propylene is converted to propylene oxide at greater than 98% selectivity and 99% peroxide conversion at 50°C over TS-1. 2,97 Butadiene is oxidized to the monoepoxide (Eqn. 10.26), also in high selectivity, and primary alcohols are oxidized to the aldehydes in all cases with selectivites greater than 80%.97... 

Improvements of already existing oxidation processes are continuously made (in MAA manufacture, with the riser reactor by DuPont, or in oxychlorination, by Montecatini Technologic and ICI). In addition, and still more clearly demonstrating the dynamism of industrial catal5rtic oxidation, completely new catalysts are discovered, especially with the titanium silicalite which permits the synthesis of hydroquinone from phenol, selective epoxidations, oxidations of alcohols to aldehydes, and the manufacture of cyclohexanoneoxime. 

Titanium siliealites TS-1 and TS-2 catalyze hydroxylation in the aromatic ring of the monoalkylbenzenes studied to corresponding alkylphenols, using hydrogen peroxide as oxidant. Para-isomers are mainly formed in methanol or ethanol as solvents. In the case of ethyl- and 1-propylbenzenes, the first carbon atom of the aliphatic chain is also oxidised both to alcohols and ketones. As expected, the terminal methyl groups in all hydrocarbons are not oxidised. The probable reasons for this behaviour of titanium silicalites are discussed. 

In the recent years a growing interest in the preparation, characterization and utilization of Titanium-silicalite has been observed. New interesting applications of TS-1, such as the low temperature oxidation of paraffins to alcohols and ketones, were reported. 

The interaction of different nitriles (acetonitrile, pivalonitrile and benzonitrile), of branched aliphatic compounds (2,2-dimethylbutane, reri-butyl-alcohol, methyl-rert-butylether, methyl and dimethylcyclohexanes) and of aromatics (benzene, toluene, ortho-, meta- and para-xylene, pyridine, picolines and lutidine) has been studied over four different ZSM5 zeolites, over silicalite-1 and titanium silicalite-1 and over boralite BOR-C. Internal, external and extraframework sites have been characterized and the access to the cavities discussed. 

Redox silicalites with elements other than titanium have found catalytic applications in various organic oxidations. V-ZSM-11 is reported to catalyze alkane oxidation and is found to oxidize even primary C-H bonds [98]. Detailed studies indicate that V silicalites are better than Ti silicalites for alkane oxidation, as it is found that molecular oxygen can act as the oxidant in the former case [99]. V-ZSM-5 shows selectivity toward alcohol oxidation in allyl and methallyl alcohols... 

---