Issue 0, 1975

Photochemistry of anhydrides. Part 3.—Primary processes in the photolyses of (CF3CO)2O and (C2F5CO)2O and the use of (CF3CO)2O and (C2F5CO)2O as gas phase actinometers

Abstract

The photolyses of the vapours of the anhydrides (CF3CO)2O and (C2F5CO)2O are quantitatively described by the overall equation (R = CF3 or C2F5), (RCO)2O +hv→ CO + CO2+ R2. The quantum yield of CO is independent of anhydride pressure in the range 0.5–16 Torr and increases slightly with temperature. For (CF3CO)2O, ϕCO(25°C)= 0.24 and ϕCO(200°C)= 0.29: for (C2F5CO)2O, ϕCO(25°C)= 0.26 and ϕCO(190°C)= 0.31. ϕCO is unaffected by the presence of mercury vapour and is virtually independent of whether photolysis is at 254 or 265 nm. Addition of CO2 or olefins indicates weak vibrational quenching. No evidence of involvement of excited triplet states was obtained, using the Cundall and biacetyl techniques. Weak emission of light was observed with ϕ(emission)⩽ 2 × 10–4 for (CF3CO)2O and ⩽ 2 × 10–3 for (C2F5CO)2O.

A proposed mechanism involves efficient internal conversion of excited singlet molecules of anhydride to the ground state, possibly via a valence isomerization. The anhydrides are recommended as useful vapour-phase actinometers at 254 and 265 nm.

Article information

Article type
Paper

J. Chem. Soc., Faraday Trans. 1, 1975,71, 1978-1990

Photochemistry of anhydrides. Part 3.—Primary processes in the photolyses of (CF3CO)2O and (C2F5CO)2O and the use of (CF3CO)2O and (C2F5CO)2O as gas phase actinometers

G. A. Chamberlain and E. Whittle, J. Chem. Soc., Faraday Trans. 1, 1975, 71, 1978 DOI: 10.1039/F19757101978

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