Reaktionswege in der photokatalytischen Umsetzung tertiärer Alkohole auf Rutil‐TiO₂(110)

Abstract

Laut Lehrbüchern sind tertiäre Alkohole inert gegenüber Oxidationen. Die Photokatalyse tertiärer Alkohole auf einem Titandioxideinkristall unter definierten Vakuumbedingungen offenbart unerwartete und neue Reaktionen, die Disproportionierung in ein Alkan und das entsprechende Keton. Im Gegensatz zu primären und sekundären Alkoholen führt die Abwesenheit eines a-H zu einem C À C-Bindungsbruch statt der üblichen Wasserstoffabspaltung.D ie Bindung zu einer Methylgruppe wird nichtg espalten, wenn sich im Alkohol eine hçhere Alkankette in a-Stellung zur Hydroxylgruppe befindet. Eine Platinbeladung erhçht nicht nur die Reaktionsrate,sondern ermçglicht einen neuen Reaktionsweg: die Bildung molekularen Wasserstoffs und eines langkettigen Alkans,d as sich durch Rekombination zweier Alkylspezies bildet. Diese Arbeit zeigt, dass neue synthetische Routen durch Einführungen photokatalytischer Reaktionsschritte mçglich gemacht werden, in denen der Cokatalysator eine entscheidende Rolle spielt.

Influences of Quinoid Structures on Stability and Photovoltaic Performance of Nonfullerene Acceptors

“…Moreover, due to the oxidation rearrangement of the tertiary alcohol, Int1 is then degraded to the radical species Int2 through a C(sp 2 )—C(sp 3 ) bond cleavage. [ 65 ] Quenched by oxygen, the oxidation product Int3 would be rapidly converted to the monoaldehyde product SP1. Meanwhile, through bimolecular coupling of Int2, the coupling product Int4 is generated and then converts to SP2, which is also found on the mass spectrum at an m/z ratio of 2533.9 [M SP2 ] + (Figure S9, Supporting Information).…”

Metal-Loaded Semiconductor-Photocatalysis of Alcohols for Selective Organic Synthesis: A Personal Account

“…To step forward, we are now interested in another reaction channel of alcohols on the TiO 2 photocatalytic surface: 3° alcohols undergo β-scission after being adsorbed on the TiO 2 surface, giving carbon-centered radicals and ketones, both of which would also be adsorbed and stabilized on the surface (Figure 11 and Figure 12 ). 59…”

“…Although this adsorptive interaction was experimentally confirmed by detecting a carbon-centered radical itself or products/intermediates derived from the carbon-centered radical, together with ketone detection by mass-spectrometric analysis, 59 60 it has not been extended to useful organic synthesis. We consider that this photoinduced β-scission is attractive from the following three aspects: (i) It would expand the synthetic utility of 3° alcohols as limiting reagents in organic synthesis; (ii) Judicious choice of symmetrical/non-symmetrical 3° alcohols would enable the selective formation of targeted carbon-centered radicals (Figure 13 ); and (iii) Organometallic reagents (R–Ms), which have been used as conventional two-electron nucleophiles, would be available as precursors of carbon-centered radicals (Figure 14 ).…”

“…44 62 The authors also reported the exclusive formation of ethyl and propyl radicals against methyl radical from a non-symmetrical 3° alcohol, 3-methyl-3-hexanol ( 28 , Figure 13B). 59…”

“…The selectivity as to which alkyl radical (carbon-centered radical) would be favorably generated is affected by both thermodynamic and kinetic parameters: by the degree of stabilization of the alkyl radical and the ketone by-product on the surface; and also by how small the activation energy of the transition state where the carbon chain to be released from the 3° alcohol pre-interacts with the surface. 59 Deep consideration of the thermodynamics and kinetics may enable the selective formation of the targeted carbon-centered radical.…”