Zur gas-chromatographischen Analyse strahlenchemischer Reaktionsprodukte

Weeke, F.; Bastian, E.; Schomburg, G.

doi:10.1007/bf02270624

Cited by 38 publications

(23 citation statements)

References 2 publications

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“…Methane and CO 2 were scrubbed from the irradiated samples with argon as the carrier gas [12] and measured by GC on a 3.2 m Porapak-9 capillary column.…”

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confidence: 99%

The Importance of Mesomerism in the Termination ofα-Carboxymethyl Radicals from Aqueous Malonic and Acetic Acids

Wang¹,

Schuchmann²,

Schuchmann³

et al. 2001

Chem. Eur. J.

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In the dioxygen-free aqueous malonic and acetic acid systems. alpha-carboxymethyl radicals are produced through hydrogen abstraction from the parent compound by radiolytically generated OH radicals. H abstraction from the CO2-/CO2H group followed by decarboxylation is a process of small importance (< or = 5%). The alpha-carboxymethyl radicals terminate by recombination. Two types of recombination product are observed which are characterised by the formation of a C-C linkage or a C-O linkage. alpha-Carboxymethyl radicals are mesomeric systems. Their mesomeric state depends on the state of protonation and determines the proportion of the C-C- versus C-O-linked dehydrodimers they produce.

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“…Methane and CO 2 were scrubbed from the irradiated samples with argon as the carrier gas [12] and measured by GC on a 3.2 m Porapak-9 capillary column.…”

mentioning

confidence: 99%

The Importance of Mesomerism in the Termination ofα-Carboxymethyl Radicals from Aqueous Malonic and Acetic Acids

Wang¹,

Schuchmann²,

Schuchmann³

et al. 2001

Chem. Eur. J.

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“…ref. [65]). EPR spectra were recorded on a laboratory-built X-band spectrometer with 100 kHz modulation equipped with an interface (Stelar, Mede) and a PC.…”

Section: Methodsmentioning

confidence: 99%

Free-Radical-Induced Chain Breakage and Depolymerization of Poly(methacrylic acid): Equilibrium Polymerization in Aqueous Solution at Room Temperature

et al. 2000

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Hydroxyl radicals, generated by ionizing radiation in N2O saturated aqueous solutions, abstract H atoms from poly(methacrylic acid) at the methyl and methylene groups, and radicals 1 and 2 are formed, respectively. The reactions of the poly(methacrylic acid) radicals were investigated by pulse radiolysis (using optical and conductometric detection), EPR, product analysis, and kinetic simulations. The conductometric detection allowed us to measure the rate of chain scission and monomer release. Under conditions in which the polymer is largely deprotonated, the primary radical 1 abstracts a hydrogen (k= 3.5 x 10(2)s(-1)) from the methylene group, and this yields the more stable secondary radical 2. This radical undergoes chain scission by beta-fragmentation (k= 1.8 s(-1)), and the terminal (end-of-chain) radical 3 is formed. The polymer radicals terminate only slowly (2k= 80 dm3mol(-1)s(-1)). This allows effective depolymerization (depropagation) to take place (k=0.1 s(-1)). The yield of monomer release is higher than the original radical yield by up to two orders of magnitude. Once monomer is formed, it reacts with 3 (propagation, k= 15 dm3mol(-1)s(-1)), and a situation close to an equilibrium radical polymerization is approached. From these data, the equilibrium monomer concentration is calculated at 6.7 x 10(-3) mol dm(-3) at room temperature. The standard entropy of propagation is estimated at -185 to -150 J mol(-1)K(-1). Because the monomer reaches concentrations in the millimolar range, the *OH radicals increasingly react with monomers (results in oligomerization) rather than with the polymer. This effect is reflected by, for example, a lowering of chain-scission yields upon prolonged irradiation. In acid solutions, the decay of the polymer radicals becomes much faster (estimated at about 10(7)dm3mol(-1)s(-1) at pH3.5), and monomer release is no longer observed.

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“…17) were deaerated by purging with argon for 30 min and irradiated with the unfiltered light of a low-pressure mercury lamp at a dose rate. determined by means of the Farkas actinometer (2), of 4.0 x lo" quanta (185 nm) per min received by the sample.…”

Section: Methodsmentioning

confidence: 99%

“…Moreover, swift combination of the initial radical pair is favoured compared to the diffusion encounter pair case, since if the diradical is in the singlet state the ensuing radical pair would also be singlet, whereas an encounter pair would only have a 25% probability to be in this state. In fact, the product 3-methoxypropanol 11 might be most easily explained by a diradical mechanism ( [16], [17], [20] X = 0 ; see Scheme 2) where one must, however, assume that the radical pair is created by the hot alkyl oxyl diradical. Thermalized alkoxyl radicals are expected to react by hydrogen abstraction, in this and in similar systems, with a rate constant of between lo5 and lo6 M-' s-', cf.…”

Section: And References Therein)mentioning

confidence: 99%

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

Schuchmann¹,

Sonntag²

1985

Can. J. Chem.

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). 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.

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Zur gas-chromatographischen Analyse strahlenchemischer Reaktionsprodukte

Cited by 38 publications

References 2 publications

The Importance of Mesomerism in the Termination ofα-Carboxymethyl Radicals from Aqueous Malonic and Acetic Acids

The Importance of Mesomerism in the Termination ofα-Carboxymethyl Radicals from Aqueous Malonic and Acetic Acids

Free-Radical-Induced Chain Breakage and Depolymerization of Poly(methacrylic acid): Equilibrium Polymerization in Aqueous Solution at Room Temperature

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

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