Vacuum–ultraviolet photolysis (185 nm) of liquid 1,3-dioxan

Abstract

). 1.3-Dioxan photolytic destruction at 185 nm occurs with a quantum yield of about 0.3 in the liquid phase. Of the 22 products determined, the major ones are n-propylformate ( 4 = 0. lo), formaldehyde (0.075), 1,3-diox-4-en (0.06), hydrogen (0.05), ethylene (0.04), and 3-methoxypropionaldehyde (0.04). A number of the minor products are of the general type B, some of which bear a hydroxyl function at the end of the side chain. NZO interacts with excited 1,3-dioxan, leading to the production of NZ.Some experiments have been carried out in the vapour phase, the results of which indicate that considerable fragmentation of hot primary intermediates and products into low-molecular-weight products occurs. The nature of these products cannot be linked directly to the primary photolytic processes inferred from the liquid-phase studies.Certain contrasts in the photolytic behaviour of 1,3-dioxan and 1,4-dioxan are discussed. 1833 (1985). La destruction du dioxanne-1,3 lors de sa photolyse a 185 nm se produit avec un rendement quantique prks de 0,3 dans la phase liquide. Parmi les 22 produits mesurCs, le formiate de propyl ( 4 = 0,16), le formaldehyde (0.075), le diox-1,3-he-4 (0,06), I'hydrogkne (0,05), I'Cthylkne (0,04) et le methoxy-3-propionaldthyde (0,04) sont les majeurs. Divers produits, mineurs, dont quelques-uns portent une fonction hydroxyl au bout de la chaine IatCrale, rcvetent la structure gCnCrale B.Le N,O interagit avec le dioxanne-1,3 excitt, ce qui mene i la production de N,.Quelques exptriences ont CtC faites en phase vapeur, dont les rtsultats indiquent une fragmentation considCrable des intermtdiaires et produits primaires, chauds. La nature des produits finaux ainsi form& ne peut pas &tre associee directement aux processus photolytiques primaires que I'on saurait reconnaitre moyennant les Ctudes faites en phase liquide.Certaines diffkrences entre le dioxanne-1,3 et le dioxanne-1,4, en ce qui concerne leur comportement photolytique, sont discuttes. IntroductionSandorfy (1) has shown that the first absorption band of saturated alcohols and ethers is due to an essentially 3 s + n transition. Its band maximum is around 185 nm where the low-pressure Hg arc has a strong emission llne. Studies on the liquid-phase 185 nm photolysis of open-chain ethers have shown that the predominant process is the scission of a C-0 linkage, a reaction the quantum yield of which can approach unity (2, 3). In cyclic ethers the same process also occurs, but the quantum yields are often considerably lower due to reclosure of the intermediate (singlet) diradical. A similar situation prevails in the series of open-chain acetals (4-6) and cyclic acetals (7,8). Another member of this group is 1,3-dioxan, whose photochemistry was of special interest to us because it is an isomer of 1,4-dioxan whose photochemistry (9-13) and photophysics (1 3-15) have so far been receiving more attention.

Catalytic Oxidative Ring Opening of THF Promoted by a Carboxylate-Bridged Diiron Complex, Triarylphosphines, and Dioxygen

“…Radical 18 is an intermediate in oxidations of 1,3-dioxane, a known source of formate 3 . − Reaction of 18 with O 2 provides radical 19 , which is reduced by a second equivalent of phosphine and abstracts a hydrogen atom from THF, propagating the cycle (Scheme 4). The resulting symmetric compound, 14 , is unstable and will cleave at either of the two orthoformate C−O bonds to give formate 3 , accounting for the result of the 18 O labeling study.…”

A Green Method to Determine VUV (185 nm) Fluence Rate Based on Hydrogen Peroxide Production in Aqueous Solution

“…Several liquid-phase chemical actinometers for VUV fluence rate determination have been reported so far (7)(8)(9)(10). Schuchmann and Sonntag (7) determined the VUV fluence rate by analyzing the H 2 production rate in the process of ethanol photolysis under 185 nm VUV irradiation (Farkas actinometer).…”

“…Several liquid-phase chemical actinometers for VUV fluence rate determination have been reported so far (7)(8)(9)(10). Schuchmann and Sonntag (7) determined the VUV fluence rate by analyzing the H 2 production rate in the process of ethanol photolysis under 185 nm VUV irradiation (Farkas actinometer). Schuchmann et al (8) also used the photoisomerization reaction between cis-cyclooctene and trans-cyclooctene to determine the VUV fluence rates at both 172 nm (Xe-excimer lamp) and 185 nm (low-pressure mercury lamp) with different quantum yields.…”