Alkylated anthraquinone process

The alkylated anthraquinone process accounts for over 95% of the world production of H202, mainly because the it operates under mild conditions and direct contact of 02 and H2 is avoided. In this process, 2-alkylanthraquinone (the alkyl group is typically an ethyl, terf-butyl or amyl group) is dissolved in a mixture of a non-polar solvent (C9-Cn alkylbenzene) and a polar solvent [Trioctyl phosphate (TOP), or tetrabutyl urea (TBU) or diisobutyl carbinol (DIBC)] and then hydrogenated over a precious metal (Pd or Ni) catalyst in a three-phase reactor (trickle bed or slurry bubble column) under mild reaction conditions (<5bar, <80 °C) to generate 2-alkylanthrahydroquinone [1-3, 5], The latter is then auto-oxidized with air in a... 

The development of the autoxidation of alkyl anthraquinones led to a rapid iacrease ia the production of H2O2 but a sharp decline in the importance of the electrolytic process. In 1991 the total North American, Western European, and Japanese capacity for H2O2 production was more than 870,000 t (77). No H2O2 was produced by the electrolytic peroxydisulfate process. The last plant using this process closed in 1983. 

Alkyl anthrahydroquinone/alkyl anthraquinone in situ process, 24 173 Alkylanthrahydroquinones, 14 43, 44 oxidation of, 14 50... 

At present, its synthesis requires a sequential hydrogenation and subsequent oxidation of alkyl anthraquinone [248]. One of the main problems of this process is the high cost of the quinine solvent and the need for continuous anthraquinone replacement. The manufacturing process is also hindered by frequent storage and transport problems. In view of these obstacles, the development of a new synthetic method is of great interest from a commercial standpoint. 

The anthraquinone process involves a reduction/oxidation cycle with 2— alkyl-anthrahydroquinone where H202 is produced during the oxidation portion of the cycle. The alkyl group on the anthraquinone is usually ethyl, although /-butyl, /-amyl, and sec-amyl have been used [108]. 

Fig. 1 (a) Schematic representation of the "indirect" anthraquinone process for the production of hydrogen peroxide using 2-alkyl-anthraquinone (1) and 2-all lhydroan-thraquinone (2). (b) Schematic representation of the direct synthesis of hydrogen peroxide from H2 and O2 (route A). Other reactions that decrease the selectivity of direct synthesis reaction are decomposition of hydrogen peroxide (route B) to water and hydrogenation of hydrogen peroxide (route C) to water. 

Hydrogen peroxide, which is produced worldwide in quantities of 800,000 tpa is manufactured by wet-chemical processes based on barium peroxide, electrochemical processes and organic autoxidation processes. Hydrogen peroxide production by autoxidation was developed to industrial viability by BASF in the 1930 s, in the form of the hydrazobenzene process. The hydrazobenzene process, however, was characterized by the disadvantage that sodium amalgam had to be used to reduce azobenzene to hydrazobenzene. Georg Pfleiderer and Hans-Joachim Riedl then used alkylated anthraquinones in place of azobenzene. The first plant to use this process to produce H2O2 was started in Memphis, Tenn. by Du Pont in 1953. 

Hydrogen peroxide in combination with catalysts such as TS-1 acts as a good, "clean" epoxidation system. T e reactions that could be carried with this catalyst include ammoximation of cyclohexanone, epoxidation of propene and other small alkenes, and hydroxylation of aromatics and linear alkanes (Chapter 4). The system produces little waste, avoids the use of hazardous chemicals such as alkyl hydroperoxide, and reduces process complexity. However, the key parameter for industrial development is the cost of H2O2. H2O2 is produced by only a few companies, and very large capital expenditure is required, because H2O2 synthesis (by alkyl-anthraquinone route) is economical only when large quantities are produced. 

As mentioned earlier, the reductive power of an anion radical can be increased considerably by photoexcitation in the visible part of the spectrum. This type of reaction has been demonstrated in the case of the photo-assisted reductive cleavage of alkyl halides in presence of anthraquinone as mediator Further work is necessary to evaluate the scope of this potentially important process. 

Chen and coworkers published a formal [3 + 3]-type reaction to give highly substituted cyclohexenes 8. This domino process consists of an allylic-allylic alkylation of an a,a-dicyanoalkene derived from 1-indanone and Morita-Baylis-Hillman carbonates, following an intramolecular Michael addition, by employing dual orga-nocatalysis of commercially available modified cinchona alkaloid (DHQD)2AQN If (hydroquinidine (anthraquinone-l,4-diyl) diether) and (S)-BINOL. The cyclic adducts... 

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