Photochemical, Radical, and Deoxygenation Reactions

There has been the very interesting report that dialkyl(hydroxymethyl)phosphines rearrange to dialkylmethylphosphine oxides on irradiation with u.v. light.4 No mechanistic details are available. 

Irradiation of the phosphine (1) causes a molecular rearrangement, and it was proposed that the primary chemical reaction is C—P bond cleavage.5 

Irradiation of dianisyl alkyl phosphates gives alkyl phosphates and 4,4 -dimethoxy-biphenyl in yields exceeding 90%.6 As stated by the authors, this type of reaction appears to have promise for the synthesis of nucleotides. 

The phosphonium compounds (2) normally give the phosphonates (3) quite readily on heating. However, when R = Ph the salts are thermally stable but will rearrange under the influence of u.v. radiation.7 

Addition of tristearyl phosphite to polyethylene containing ferric acetylacetonate has been shown to decrease the stability of the polymer towards photo-oxidation.8 

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The Chapter on Photochemical, Radical, and Deoxygenation Reactions does not appear this year because of illness of the Reporter at a critical time. 

The photocatalytic system is shown in Scheme 5, where BNAH is oxidized by the ZnP + moiety in the radical ion pair ZaP -Ceo (ki) produced upon photoirradiation of ZnP-Ceo, whereas HV " is reduced to HV by the Ceo" moiety of ZnP +-C6o ki). These individual electron-transfer processes compete, however, with the BET in the radical ion pair (/cbet)- This pathway was experimentally confirmed by photolysis of the ZnP-Ceo/BNAH/HV and ZnP-H2P-C6o/BNAH/HV + systems with visible light (433 nm) in deoxyge-nated PhCN [70], For instance. Fig. 4 depicts the steady-state photolysis in deoxy-genated PhCN, in which the HV absorption band (X ax = 402 and 615 nm) increases progressively with irradiation time. By contrast, no reaction occurs in the dark or in the absence of the photocatalyst (i.e., ZnP-Ceo or ZnP-H2P-C6o) under photoirradiation [70]. Once HV+ is generated in the photochemical reaction, it was found to be stable in deoxygenated PhCN. The stoichiometry of the reaction is established as given by Eq. (3), where BNAH acts as a two-electron donor to reduce two equivalents of HV [70] ... 

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