2- Ethylanthraquinone

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.)...

Others 1,4-dioxane, 1,3,5-trioxane, terahydrofuran, 2-butyl tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, epsilon-caprolactam, benzothiazole, biphenyl, pyrazine, 2-butanone oxime, l-methyl-2-pyrrolidone, N,N-dimethyl-aniline, N,N-dimethyl-p-toluidine, l-methyl-7-isopropyl phenanthrene, dibenzyl-amine, hexamethylenetetramine, squalene, 2-ethylanthraquinone... 

A very interesting new method [was developed by I. G. Farben in Germany during the World War II. In this method 2-ethylanthrahydroquinone is oxidized by gaseous oxygen whereby 2-ethylanthraquinone and hydrogen peroxide are formed. Hydrogen peroxide is extracted from the resultant liquor with water... 

The first production stage is effected in a series of closed enamelled iron kettles filled with a mixture of equivalent amounts of 2-ethylanthraquinone and 2-ethylanthrahydroquinone dissolved in benzene and methylcyclohexanol oxygen is injected into the liquid through a porous filter while the temperature is maintained at 30 and 37 °C. The reaction may be symbolized as follows ... 

Retention and Efficiency of 2-Ethylanthraquinone using a Micellar Sodium Dodecylsulfate Mobile Phase and a C-18 Reversed Phase Column... 

The effect of change in column temperature on the retention of anthraquinone, methyl- and ethylanthraquinones between 25°C and 55°C was a decrease of 75, 76 and 77 respectively. 

When the H2O2 reaches about 5.5 g/1., the solution is extracted with water to give an 18% aqueous solution which is concentrated as described above. The 2-ethylanthraquinone is reduced to the original compound with hydrogen in the presence of palladium on an inert support, the catalyst being suspended in the liquid by the stream of gas. 

The elution strength of hybrid micellar mobile phases was measured for a number of organic additives (alcohols, alkane diols, alkanes, alkylnitriles, and dipolar aprotic solvents, such as dimethyl sulfoxide and dioxane) added to micellar SDS, CTAC, and Brij-SS. Benzene and 2-ethylanthraquinone were used as probe compounds. The presence of alcohols, alkane diols, alkylnitriles, and dipolar aprotic solvents produced a diminution of the retention times, reaching remarkable levels for the most hydro-phobic compound (2-ethylanthraquinone). The observed elution strength order roughly paralleled the octanol-water partition coefficients of the additives, Rq/w (Fig- 2), or their ability to bind to micelles, am- In contrast, alkanes (pentane, hexane, and cyclohexane) had relatively little effect on the retention. 

Fig. 2 Correlation between octanol-water partition coefficients of the organic solvents (log Po/w). and the retention factors of (a) benzene and (b) 2-ethylanthraquinone in hybrid SDS micellar mobile phases. The concentration of surfactant and organic solvent was 0.285 M and 5% (v/v), respectively. (From Ref [11].)...

Plots of Po/w or vs. plate counts for benzene and 2-ethylanthraquinone eluted with micellar SDS, in the presence of several alkanols and alkane diols, show an initial steep increase in efficiency, after which an approximately constant value is reached (Fig. 3). Among the alcohols, maximal efficiency for benzene and 2-ethylanthraquinone is obtained with the butanols and the pen-tanols, with enhancement factors of 2.5 and 25 (compared to pure SDS), respectively. However, final efficiencies for the latter compound are much lower compared to that for benzene. Dipolar aprotic modifiers (acetonitrile or dimethylsulfoxide) appear to be somewhat more effective in enhancing efficiencies than alcohols with comparable Pq/w- Some recent work has shown the advantage of using acetonitrile as additive in MLC for the analysis of sulfonamides, tetracyclines, and the most polar steroids. 

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. 

The compound was used as a catalyst for the hydrogenation of olefins. No rhodium was lost. This type of polymer shows inverse temperature solubility. When the temperature was raised, the polymeric catalyst separated from solution for easy recovery and reuse. This type of smart catalyst will separate from solution if the reaction is too exothermic. The catalytic activity ceases until the reaction cools down and the catalyst redissolves. Poly (A i sop ropy lacrylamide) also shows inverse temperature solubility in water. By varying the polymers and copolymers used, the temperature of phase separation could be varied (e.g., from 25 to 80°C).214 A terpolymer of 2-isopropenylan-thraquinone, A-isopropylacrylamide, and acrylamide has been used in the preparation of hydrogen peroxide instead of 2-ethylanthraquinone.215 The polymer separates from solution when the temperature exceeds 33 C to allow re-... 

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... 

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