Deperoxidation

Table 3.8 Comparison of group 4 metals in cyclohexyl hydroperoxide (chhp) deperoxidation.

Figure 3.29 Si-0-Ta(0Me)4 catalyst recycling in the cyclohexyl hydroperoxide deperoxidation reaction.

Titanium Alkoxides Silica-supported titanium(IV) alkoxides and Ti-silicalite are industrial epoxidation catalysts [53-56] and have been applied in deperoxidation reactions [57]. Computational and EXAFS data [53, 54] as well as spectroscopic investigations on the surface species [58] have indicated that the dominant active surface species is a four-coordinate trisUoxy complex [(=SiO)3TiOH] [59] whose coordination shell expands to six-coordinate during catalysis [60]. 

D, R, Burfield, J, Org, Chem. 47, 3821 (1982) Deperoxidation of ethers with self-indicating molecular sieves 0,4 nm. 

Detection and removal of peroxides from solvents Organic Solvents Physical Properties and Methods of Purification, 4th ed., ed. J. A. Riddick et al. (Chichester Wiley, 1986). Deperoxidation of ethers with molecular sieves Burfield, D. R., J. Org. Chem., Al, 3821-3824, 1982. 

It is strongly recommended that the THF first be checked for the amount of peroxide or hydroperoxide before any further purification is attempted. If more than 0.1 % is found, the peroxide must be decomposed. This can be done by agitating with flake caustic soda. It has also been suggested to effect the deperoxidation by means of self-indicating molecular sieves [95], but inasmuch as this must result in a peroxide enrichment in the molecular sieve, this procedure is viewed as a source of danger which has not been sufficiently investigated so far. 

Einally the effect of UV on deozonation, dechlorination, dechloramination, and deperoxidation must be considered in the AOP engineering design when ozone, chlorine, chloramine, and peroxide, respectively, is to be used (43,44). 

Cyclohexane is obtained either by the hydrogenation of benzene, or from the naphtha fraction in small amounts. Its oxidation to the KA Oil dates back to 1893 and was first industrialized by DuPont in the early 1940s. Oxidation is catalyzed by Co or Mn organic salts (e.g., naphthenate), at between 150 and 180 °C and 10-20 atm. Indeed, this reaction is a two-step process (an oxidation and a deperoxidation step), and two variants are currently in use [2,3]. The oxidation step can be performed with or without a catalyst. The deperoxidation step always uses a catalyst (Co(II) or NaOH). The overall performance of both variants is almost identical, although the selectivity in the individual steps may be different. For example, in a first reactor, cyclohexane is oxidized to cyclohexylhydroperoxide the concentration of the latter is optimised by carrying out the oxidation in passivated reactors and in the absence of transition metal complexes, in order to avoid the decomposition of the hydroperoxide. In fact, the synthesis of the hydroperoxide is the rate-limiting step of the process, and, on the other hand, alcohol and ketone are more reactive than cyclohexane. The decomposition of the hydroperoxide is then carried out in a second reactor, in which the catalyst amount and reaction conditions are optimised, thus allowing the Ol/One ratio to be controlled. 

Cyclohexane oxidations by [Fe2(HPTP)(0H)(N03)2](C104)2 complexes are perfomed at low substrate conversions around 2-5 %. The use of MeCN as a solvent results in an increase of the reaction rate and the selectivity for cyclohexylhydroperoxide (CHHP). In the /BHP oxidation the formation of CHHP and cyclohexyl-fbutylperoxide (CHBP) points to a radical proces. In the presence of organic peroxides triphenylfosfine oxidation occurs as well. Decomposition products such as triphenylphosphine-oxide and cyclohexanol from CHHP confirm the radical nature of the reaction. In the H2O2 oxidation CHHP is again formed. As the [Fe2(HPTP)(0H)(N03)2](C104)2 complexes catalyse fast decomposition of CHHP a rather complete deperoxidation occurs. 

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