Use of Other Oxidants

Eghbali et al. [185] have reported the details of a highly efficient method for converting alkenes and C02 into CCs directly in water, by using N-bromosuccin-imide (NBS) together with l,8-diazabicyclo[5.4.0]undecen-7-ene (DBU), or a catalytic quantity of bromide ion together with aqueous H202. 

The synthesis of cyclic carbonates, starting from olefins, can be also carried out via a multistep method based on two separate reactions. To this end, C02 and the carboxylation catalyst have been added to the same reactor in which a preliminary epoxidation process had been carried out. 

An example of the synthesis of CCs from olefins in a single reactor has been reported by Srivastava [187, 188], by using titanosilicalite as catalyst and hydroperoxide as oxidant in the form of H202 or TBHP. The reaction was carried out in two steps, in which the olefin was first epoxidated at 233 K using H202 or TBHP. The C02 was then added in presence of N,N-dimethylamionopyridine as cocatalyst, to afford a 33% yield of the CC at 293 K. 

Similarly, Ono et al. [189] have reported using a composed catalytic system, namely MTO/UHP/Zn[EMIm]2 Br4/[BMfm]BF4 (UHP, urea hydrogen peroxide and MTO, methyltrioxorhenium). With the multistep method described above, a 

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Both mechanisms require an acceptor of protons and electrons which, as shown by preliminary data, may be molecular oxygen. Attempts to distinguish between the two mechanisms were based on the use of other oxidizing agents and kinetic studies U3). In the case of mechanism (b), and in the presence of an excess of oxygen, the bi-molecular reaction of dimerization of free radicals competes with the oxidation reaction. Hence, with an increase in the initial concentration of dimer, one should observe... 

Aldehydes have been formed from alcohols by the use of other oxidizing agents. Dihydroxyacetone has been oxidized with excess cupric acetate to hydroxypyruvic aldehyde in 87% yield. p-Cyanobenzyl alcohol treated at 0° with a chloroform solution of nitrogen tetroxide gives practically pure p-cyanobenzaldehyde (90%). Aromatic alcohols containing nitro groups have been oxidized to the corresponding nitro aldehydes with concentrated nitric acid, e.g., o- and p-nitrobenzaldehydes (80-85%). m-Nitrobenzenesulfonic acid in basic media has been used for the oxidation of substituted benzyl alcohols, most satisfactorily for the water-soluble phenolic benzyl alcohols. Selenium dioxide, or less effectively tellurium dioxide, oxidizes benzyl alcohol slowly to benzaldehyde. ... 

The controlled oxidation using a peroxycarboxylic acid of trithiocarbonates (78) without a-hydrogens, and which therefore cannot form enethiols, yields the corresponding sulfines (79) (see p. 129). The use of other oxidants, e.g. concentrated nitric acid or an excess of the peroxycarboxylic acid, gives higher oxidation products like (80) and (81) (Scheme 42). 

The direct oxidation of methane to methanol or formaldehyde has been a dream reaction for a long time [537]. Attempts include gas-phase reaction, catalytic reactions, and use of other oxidants than air. Selectivities may be high, but at a lower conversion per pass resulting in yields being inferior for industrial use. 

Ozonolysis of olefins and the use of other oxidants such as permanganate, permanganate-periodate, dichromate-sulfuric acid, and hydrogen peroxide-lead tetraacetate are also useful in preparing ketones by cleaving the olefin into two fragments. 

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