Oxidation of TMP

Chemical precedent for the nonenzymic elimination of base and inorganic pyrophosphate may be found in the attempted synthesis of 3 -ketothymidine by oxidation of TMP (54), which led instead to the formation of Pj, thymine, and unidentified sugars. Furthermore, Hershfield reported that 2 -deoxyadenosine inactivated S-adenosylhomocysteine hydrolase and that this inactivation was accompanied by adenine release (55). 

A mechanism involving charge-transfer complexes formed by HAS, polymer, O2, and ROO, i.e. [HAS - -02], [polymer - - -O2], [HAS - -ROO ], has been proposed [111]. It is considered to contribute in the early stages of the hindered amine stabilization mechanism [87]. The oxidation of TMP derivatives as illustrated in Scheme 9.15 commences when the polymer is processed. It continues later, when the polymer is exposed to light. 

Alkylphenols can be converted to p-BQ using dioxygen and HPA- ( =2-6) [121]. Oxidation of TMP in AcOH-HjO (95/5) produced TMBQ with a selectivity of 86% at complete TMP conversion [121a]. The main reaction by-product was 2,2, 3,3, 5,5 -hexamethyl-4,4 -biphenol. Based on kinetic and spectroscopic studies, a stepwise mechanism that involves dissociation of HPA-w in the acidic medium generating the active species VOj, oxidation of TMP by VOj to produce phenoxyl radical and VCP+ followed by reoxidation of V(fV) to V( V) with in the coordination... 

Oxidation with Hydrogen Peroxide Shimizu et al. have developed a method for the production of TMBQ and ubiquinone 0 based on the oxidation of TMP and 3,4,5-trimethoxytoluene (TMT), respectively, with in the presence of HPAs H PMuO and H,SiMj,0, (M=W,Mo)[123]. 

Chinese manufactures produce TMQ on an industrial scale by the oxidation of TMP using stoichiometric amounts of inorganic salts as oxidants, and thus generating stoichiometric amounts of inorganic waste. For example 2,3,6-TMP (3) is... 

Homogeneous catalyst systems include transition metals, e.g. the cobalt Schiff base complex salcomine." "" " However, the quite expensive Schiff base cannot be recovered and recycled, which is a drawback of this method. Copper salts, e.g. CuCl2 and CuBr2, are widely used for the oxidation of TMP with molecular oxygen at larger scales." In addition, applications of the halides of Cr, Mn, Fe, Ni and Zn as catalysts have been described. Copper halides have been combined with earth metal halides, e.g. magnesium chloride." ... 

Electrochemistry and spectroscopy of the tt cation radical of meso-tetraalkylchlorin (tetra-methyl) and various porphyrins (tetramethyl, tetraethyl, and tetra-ra-propyl) indicate that these do not convert to Nim at low temperatures.280 Optical evidence reveals, however, that oxidation of the tt cation radical of [Ni(pEt2N)(TPP)] leads to a Ni111 cation radical which can be further oxidized to a Ni111 porphyrin dication. Similar studies have been carried out for various other derivatives of me.so-tetraarylporphyrins such as /V-oxides of TPP and 5,10,15,20-tetramesitylpro-phyrin (TMP). Addition of trifluoroacetic acid (TFA) to the /V-oxide of [NinTMP] at —25 °C in CH2C12 results in [Nim(TMP)]+ with a rhombic EPR spectrum, g = 2.40, 2.12, and 2.04.281... 

Dioxo-ruthenium porphyrin (19) undergoes epoxidation.69 Alternatively, the complex (19) serves as the catalyst for epoxidation in the presence of pyridine A-oxide derivatives.61 It has been proposed that, under these conditions, a nms-A-oxide-coordinated (TMP)Ru(O) intermediate (20) is generated, and it rapidly epoxidizes olefins prior to its conversion to (19) (Scheme 8).61 In accordance with this proposal, the enantioselectivity of chiral dioxo ruthenium-catalyzed epoxidation is dependent on the oxidant used.55,61 In the iron porphyrin-catalyzed oxidation, an iron porphyrin-iodosylbenzene adduct has also been suggested as the active species.70... 

Figure 5.13 Yields in the Montanari-Anelli oxidation of 1-nonanol to give nonanal in the presence of silica-supported TEMPO (SG-TMP-O, front row), and in the presence of sol gel ORMOSIL doped with TEMPO [SG-TEMPO-1 is 25% and SG-TEMPO-2 is 100% methylated (middle and back row, respectively)]. (Reproduced from ref. 25, with permission.)...

Introduction of mesityl groups at the porphyrin ring can prevent the formation of the dimeric products and the reaction with dioxygen now leads to ruthenium(VI)-dioxo complexes of TMP (tetramesitylporphyrin) [35], The tram-Ru(VI)02-TM P species can catalyse the epoxidation of alkenes as well as whole range of other oxidation reactions. After transfer of one oxygen atom to an organic substrate Ru(IV)0-TMP is formed, which disproportionates to an equilibrium of Ru02 and llu ). 

The authors ascribed the ds-stilbene preference to steric interference between the phenyl groups of tranx-stilbene and the phenyl groups on the [Fe -0(TPP+ )]+ intermediate. The Groves research group also gathered the first spectroscopic indications of a synthetic, compound I analog. The [Fe =0(TMP+ )]+ complex (TMP equals the dianion of mexo-tetramesityl-phenylporphyrin) was prepared by the m-CPBA (3-chloroperoxybenzoic acid) oxidation of [Fe -0(TMP)C1]. (See Figure 7.21.)... 

Some successful attempts to immobilize catalysts for the oxidation of alcohols to carbonyl compounds involve the attachment of TEMPO-derivatives to a solid phase. Bolm et al. were the first to immobilize l-hydroxy-2,2,6,6-tetramethylpiperi-dine to modified silica gel (SG-TMP-OH) (11) and applied in the oxidation of multifunctional alcohols [68]. Other groups further investigated the use of polymer-supported TEMPO [69]. This system allowed the oxidation of alcohols to aldehydes and ketones, respectively, using bleach to regenerate the immobilized ni-troxyl radical (Scheme 4.6). 

Wet oxidation is a process where organic contaminants in liquids or soils are extracted into an aqueous phase and reacted with an oxidant at high temperature (220-290°C) and pressures (100-250 bar) to promote rapid destruction. Laari et al. [67] evaluated the efficiency of wet oxidation for the treatment of TMP processing waters. The major objective of this research was to reduce the concentration of lipophilic wood extractives (LWE) and to treat concentrated residues from evaporation and membrane filtration by low-pressure catalytic wet oxidation. 

Ru (0)2(por " )] (for por = TMP and OEP) have been generated by oxidation of [Ru (0)2-(por)] with phenoxathiin hexachloroantimonate. The products show a broad Q band and a less intense and blue-shifted Soret band, consistent with the formation of the porphyrin cation radical. 

Epoxidation of propene and oct-l-ene was effected with tran5-Ru(0)j(TMP)/ O ll atm)/water-CH2Cl2. After some 40 turnovers in a day, the deactivated form of the complex, Ru(C0)(TMP).H20 was detected (vide infra). Use of (l-( C)-oct-l-ene suggest that, in part at least, the carbon atom of the Ru(CO)(TMP) formed derives from the first C atom of the octene [591]. For styrene epoxidation by trans-Ru(0)2(TMP)/(LN0)/CgH (LNO=N-oxides of 2,3,5,6-tetramethylpyrazine, acridine, 2-methylquinoline and 3,6-dichloropyridazine) the mono- and bis-A-oxides of tetramethylpyrazine were the most effective co-oxidants [586]. 

Kinetics and mechanisms of oxidation of amines by Ru porphyrin complexes (particularly TMP species) have been reviewed [42]. rranx-Ru(0)2(TMP)/02/ CgHg/50°C/24h oxidised primary and secondary amines in the oxidation of ben-zylamine frani-Ru(NHj)jCHjPh)2(TMP) was isolated and characterised crystallo-graphically. A mechanism involving a two-electron oxidation of benzylamine to A-benzylideneamine by tra i-Ru(0)2(TMP) was proposed with concomitant reduction of the latter to Ru (0)(TMP). This disproportionates to tranx-Ru "(0)2(TMP) and Ru"(TMP) the latter regenerates Ru" (0)(TMP) with O, while the second two-electron oxidation of the imine to the aldehyde is effected by tranx-Ru(0)2(TMP) [597], (Table 5.1) [598]. 

Fig. 1.27 Reaction scheme for oxidation of sulfides to sulfoxides catalysed by Ru(TMP) complexes [603]...

RuCl/TMP), as RuCl2(TMP)/(Cl2pyNO)/CDCl3, oxidised alkenes RCHj=CH to the aldehydes RCH CHO. Oxidation of 1,3-dienes gave the unsaturated aldehyde -thus 1-phenyl-l,3-butadiene gave the p, y-unsaturated aldehyde 4-phenylbut-3-enal (styrylacetaldehyde) RuClj(TDCPP) also effected these reactions [584],... 

Trimethylphenol (TMP) can not undergo C-0 polymerization (vide infra. Sect. 4.7). The selective oxidation of the para-methyl group by molecular oxygen to yield 3,5-dimethyl-4-hydroxybenzaldehyde (HDB) has been... 

---