Diphenylmethanol, oxidation

Stance, oxidation of diphenylmethane with 0.1 mol % 5a and 10 equiv. of 30% H2O2 under ambient conditions afforded a 1 1 mixture of diphenylmethanol and benzophenone in 34% yield after 16 h. When heated to 80 °C for 5 h, the reaction is driven to the formation of benzoquinone in 87% yield. Cu(OAc)2 and Cu (salen) also afforded benzoquinone under identical conditions, but were found to be less effective than 5a. 

In a subsequent report, in 2005 [55], the same group described the preparation of imprinted polymer capable of oxidising alcohols and alkanes with 2,6-dichlor-opyridine /V-oxide (86) without mineral acid activation. The polymer was imprinted with a ruthenium porphyrin complex (87) using the diphenylmethana-mine (88) as pseudo-substrate template in order to achieve a shape of the cavity complementary to the substrates, diphenylmethane (89) and diphenylmethanol (84). The reaction, carried out with the imprinted polymer on the diphenylmethanol as substrate, showed a rate enhancement 2.5 higher than with the non-imprinted polymer. In the same conditions, but with diphenylmethane and... 

Further applications of the silane/acid (i. e. 720/trifluoroacetic acid) system include reductions of steroidal substrates95,96 Another notable variant is the use of methylpolysiloxane (757)88 97 especially in presence of bis(dibutylacetoxytin)-oxide (DIBATO)97 as hydrogenating agent via this method benzophenone (135) yields diphenylmethanol (138) (Scheme 16). Under hydrosilylation-like conditions... 

As an example, let us consider the stoichiometric oxidation of diphenylmethanol to benzophenone, one of the most commonly used photosensitizers in photochemistry (Figure 1.3). We will evaluate this reaction using the measures of product yield, product selectivity, E-factor, and atom economy. In this reaction, three equivalents of diphenylmethanol react with two equivalents of chromium trioxide and three equivalents of sulfuric acid, giving three equivalents of benzophenone. First, let us see how the reaction measures with respect to product yield and selectivity. Assume that this is an ideal chemical reaction which goes to completion, so one obtains 100% yield of the product, benzophenone. If no other (organic) by-product is obtained, the product selectivity is also 100%. This is all well and good, and indeed for many years this has been the way that chemical processes were evaluated, both in academia and in the (fine-) chemical industry. 

Figure 1.3 Oxidation of diphenylmethanol to benzophenone using chromium trioxide and sulfuric acid.

However, under somewhat different conditions (aqueous acetonitrile at 85°), no evidence for the free carbonium ion could be found (Bethell et al., 1965). Moreover, the invariance of the product proportions when water is replaced by deuterium oxide, coupled with the observation of a large tritium isotope effect on the formation of diphenylmethanol, is consistent only with the ylid mechanism (equation 21) (Bethell et al., 1969). For reaction of diarylmethylenes with alcohols, substantial hydrogen-isotope effects are observed, consistent with both equations 21 and 22. 

Amino acid 4-toluenesulfonate or 2-naphthalenesulfonate salts are esterified in high yield with diazodiphenylmethane in DMF (50 °C, 10min).P " l Diazodiphenylmethane is prepared by oxidation of benzophenone hydrazone, e.g. with yellow mercury(II) oxide in the presence of base, and can be stored in the dark.P P l In situ oxidation of the benzophenone hydrazone is performed with peracetic acid/l2 (trace) in the presence of the N-protected amino acids or peptides.P P l This method is not compatible with sulfur-containing amino acid residues. Alternatively, Dpm esters of protected amino acids and peptides are obtained using benzhydryl chloride or diphenylmethanol by standard esterification procedures. 

Benzyl alcohol is oxidized to benzaldehyde (74% yield), and diphenylmethanol gives benzophenone (87% yield).1... 

Ethanol, benzyl alcohol or 2-butanol coordinate to the proposed dinuclear copper complex (Fig. 16) to produce the active species I (Fig. 17, A). After H abstraction by one of the two phenoxyl groups, a radical is created which is oxidized to the corresponding carbonyl derivative by the second phenoxyl radical. In the case of 2-propanol and diphenylmethanol, two alcohol molecules coordinate to the dinuclear moiety resulting in species II (Fig. 17, B). The H abstractions by the two phenoxyl ligands generate two... 

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