2- ethylanthraquinone process

The above method has now been largely replaced by a newer process, in which the substance 2-ethylanthraquinone is reduced by hydrogen in presence of a catalyst to 2-ethylanthraquinol when this substance is oxidised by air, hydrogen peroxide is formed and the original anthraquinone is recovered ... 

Xi and coworkers [135-137] reported on the epoxidation of alkenes performed with (CP)3[P04(W03)4] catalyst. This insoluble catalyst formed soluble active species, (CP)3[P04 W02(02) 4], by the reaction with H202. When H202 was consumed completely, the catalyst became insoluble again. Therefore, the catalyst recovery was simple. When coupled with the 2-ethylanthraquinone/2-ethylanthrahydroquinone redox process for H202 production, 02 could be used as an oxidant for the epoxidation of propylene in 85% yield based on 2-ethylanthrahydro-quinone which was obtained without ary by-products (Figure 13.8). 

Figure 13.8 Proposed catalytic cycle for the epoxidation of alkenes by [jc-C5H5NC16H33]3[P04(WO)4] catalyst coupled with the 2-ethylanthraquinone/2-ethylanthrahydroquinone redox process. (From Xi, Z. et al., Science, 292, 1139, 2001.)...

A mixture of solvents is used 2-methylnaphthalene (22vol.%) to dissolve the alkylanthraquinone, a polar compound, preferably methylisobutylcarbynol (68vol.%) to dissolve the alkylanthrahydroquinone, and methanol (10 vol.%). Methanol is also a co-catalyst, since the rate of reaction is much accelerated in the presence of this solvent. The best yield to PO, based on starting ethylanthraquinone, was 78%, at 30 °C, with 3 atm propene, 2 atm air and 0.31 wt% TS-1 as the catalyst, in a 1.5 h reaction time. For this to happen, autoxidation and epoxidation must occur at the same temperature, that is to say, a moderate temperature, to prevent the degradation of anthraquinone. The disadvantage of the process is that the optimal conditions for the generation of H P are not the same as for the epoxidation reaction. 

Industrially, hydrogen peroxide is almost universally produced by the alternate hydrogenation and oxidation with air of an alkylanthraquinone [2], Although the process is efficient from a yield standpoint, it is quite complex and is carried out in two separate steps, using a stoichiometric amount of expensive high molecular weight quinones e.g. 2-ethylanthraquinone). 

In the autoxidation step of the AO process, the 2H /2e reduction of O2 to HjOj is coupled to the uncatalyzed oxidation of anthrahydroquinone to anthraquinone. A variety of 2-alkylanthraquinones have been reported, but 2-ethylanthraquinone... 

Based on the above, an initiating composition for cationic photopolymerization, with visible and long-wavelength UV light was described by Crivello et al. The structure of the monomers plays a key role in these photosensitization processes. Useful aromatic ketones are camphoquinone, benzyl, 2-isopropylthioxanthone, or 2-ethylanthraquinone. The monomer-bound radicals reduce diaryliodonium salts or dialkyl phenacylsulfonium salts rapidly to form monomer-centered cations. These cations then initiate the polymerization of epoxides, vinyl ethers, and heterocyclic compounds. Onium salts with high reduction potential, however, such as triarylsulfonium salts, do not undergo this reaction. 

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