Oxidation solvent dependence

Oxidation can also occur at the central metal atom of the phthalocyanine system (2). Mn phthalocyanine, for example, can be produced ia these different oxidation states, depending on the solvent (2,31,32). The carbon atom of the ring system and the central metal atom can be reduced (33), some reversibly, eg, ia vattiag (34—41). Phthalocyanine compounds exhibit favorable catalytic properties which makes them interesting for appHcations ia dehydrogenation, oxidation, electrocatalysis, gas-phase reactions, and fuel cells (qv) (1,2,42—49). 

The cyclization product is thermally unstable relative to Z-stilbene and reverts to starting material unless trapped by an oxidizing agent. The extent of eyclization is solvent-dependent, with nonpolar solvents favoring cyclization more than polar ones. ° Whereas the quantum yield for Z-E isomerization is nearly constant at about 35%, the cyclization... 

A general solvent dependence of the a y ratio similar to that noted above is also probable for piperidino-dehalogenation of A-oxides. 4-Bromoquinoline and its A-oxide show a strong and nearly identical dependence on the nature of the solvent, the rate increases on going from benzene to 95% ethanol, being in the order of 10 at 120°. 

The reaction of lead tetraacetate (LTA) with monohydric alcohols produces functionalization at a remote site yielding derivatives of tetrahydrofuran (THF) 12). An example is the reaction of 1-pentanol with LTA in nonpolar solvents which produces 30% THF. The reaction, which is believed to proceed through free-radical intermediates, gives a variable distribution of oxidation products depending on solvent polarity, temperature, reaction time, reagent ratios, and potential angle strain in the product. 

Modified alkyds Air drying and/or stoving Oxidative and/or A wide range of solvents depending on Fair Fair Usually good Fair/ Usually good very good ... 

Irradiation of phenanthridine 5-oxides gives complex mixtures containing dibenzoxazepines. The reaction is solvent dependent. In benzene, for example, 6-phenylphenanthridine 5-oxide affords the dibenzoxazepine 4a (26%), 6-phenylphenanthridine (12%), 5-phenylphenanthrid-6(5//)-one (19%) and (V-benzoyl-2-(2-hydroxyphenyl)aniline (7%).27... 

The single-electron reduction and oxidation of Co(salen) is solvent dependent as a result of the available coordination sites perpendicular to the CoN202 plane.1220 Furthermore, substituents on the phenyl rings modulate the observed redox potentials and subsequently the 02 binding constants. Hammett correlations are obtained.1221 Potentiometric titrations were performed to determine the 02 binding constants and species distribution as a function of pH for a variety of Schiff base Co complexes.1222... 

The structure of [Ir2dcbmi(CO)4] (424) is reported.680 The binuclear compounds were all oxidized around +0.1 V vs. SCE, with the oxidation potential dependent on the solvent.681 Oxidation of [NBu4][Ir2(dcbmi)(CO)4] results in growth of a conducting film on the surface. The partially oxidized material [NBu4]0.5[Ir2(dcbmi)(CO)4] has been characterized by X-ray photoelectron spectroscopy. 

Hydrophosphorylation has recently been extended to rhodium catalysts as a route to anti-Markovnikoff products.198 Thus, 3mol.% Rh(PPh3)3Cl affords the ( )-alkenylphosphonates (R = H, Ph, -Cr,I I ]3, CH2CH2CN, SiMe3, or cyclohexenyl) in high yields (>80%) at room temperature when 4,4,5,5-tetramethyl-l,3,2-dioxaphospholane-2-oxide (74) is used as the PH source (Equation (19)).199 The rate of reaction is highly solvent dependent... 

The reactivity of phenols depends on several structural factors, as well as on the conditions of oxidation (solvent, temperature). Let us discuss the main factors that determine phenol reactivity. This analysis will be performed within the scope of IPM (see Chapter 6). 

Table 21. Solvent dependence of coupling constants in styrene oxide, styrene sulfide and 2,2-dichlorocyclopropylbenzene...

A polar solvent like DMF is known to accelerate the oxidative addition of a C — I bond by low-valent metals, which is thought to be the preceding step for the formation of 2-iodovinylidene intermediates 77. Scheme 6.27 illustrates one application of this solvent-dependent chemoselectivity, that l-iodo-naphthen-2-ols 79 and 6-iodo-7-oxa-benzocydoheptenes 80 can be selectively produced in DMF and benzene using the same substrate. 

Early studies have shown that tryptophan, tyrosine, histidine, methionine and cysteine, either as free amino acids or as components of peptides, are excellent substrates for O2 oxidation reactions. Usually, reaction of O2 with amino acids is mostly described in terms of chemical quenching with the exception of tryptophan, for which collisional deactivation as the result of physical quenching is not neghgible. The rate constants of O2 toward the main reactive amino acids that show a strong solvent dependence are reported in Table 2 for neutral aqueous solutions with values within the range 0.8-3.7... 

As part of an extensive study of the 1,3-dipolar cycloadditions of cyclic nitrones, Ali et al. (392-397) found that the reaction of the 1,4-oxazine 349 with various dipolarophiles afforded the expected isoxazolidinyloxazine adducts (Scheme 1.78) (398). In line with earlier results (399,400), oxidation of styrene-derived adduct 350 with m-CPBA facilitated N—O cleavage and further oxidation as above to afford a mixture of three compounds, an inseparable mixture of ketonitrone 351 and bicyclic hydroxylamine 352, along with aldonitrone 353 with a solvent-dependent ratio (401). These workers have prepared the analogous nitrones based on the 1,3-oxazine ring by oxidative cleavage of isoxazolidines to afford the hydroxylamine followed by a second oxidation with benzoquinone or Hg(ll) oxide (402-404). These dipoles, along with a more recently reported pyrazine nitrone (405), were aU used in successful cycloaddition reactions with alkenes. Elsewhere, the synthesis and cycloaddition reactions of related pyrazine-3-one nitrone 354 (406,407) or a benzoxazine-3-one dipolarophile 355 (408) have been reported. These workers have also reported the use of isoxazoles with an exocychc alkene in the preparation of spiro[isoxazolidine-5,4 -isoxazolines] (409). 

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