<sup>31</sup>P CIDNP in the free radical reactions of dialkyl phosphites

Levin, Ya. A.; Il'yasov, A. V.; Gol'dfarb, E. I.; Vorkunova, E. I.

doi:10.1002/mrc.1270051010

Cited by 14 publications

(8 citation statements)

References 12 publications

(1 reference statement)

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“…31 P NMR spectra of photolyzates also display numerous unidentified resonances. Products with known chemical shifts that could result from dimerization of phosphinoyl radical 6 were not evident: (MeO) 2 P(O)−(O)P(OMe) 2 , δ +8; (MeO) 2 P(O)−OP(OMe) 2 , δ 130 and −10. Photolyzate from irradiation of 8 in acetonitrile shows a very broad peak under the resonance for phosphonate 9 suggestive of polymer formation or a myriad of phosphonates in small quantities.…”

Section: Resultsmentioning

confidence: 99%

Photo-Arbuzov Rearrangements of Dimethyl Benzyl and Dimethyl p-Acetylbenzyl Phosphite

et al. 1999

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The direct ultraviolet irradiation of dimethyl benzyl phosphite (1) and dimethyl p-acetylbenzyl phosphite (8) was investigated in acetonitrile, cyclohexane, and benzene. Phosphite 1 gives predominantly the photo-Arbuzov product, dimethyl benzylphosphonate (2), in 67−81% accountability yields, based of phosphite consumed, along with minor amounts of bibenzyl (20) and dimethyl phosphite (10). The quantum yield for formation of 2 in cyclohexane, φP, is 0.43. By contrast, irradiation of phosphite 8 yields only 7−13% of photo-Arbuzov phosphonate (9) but relatively large amounts of radical diffusion products: dimethyl phosphite (10) the p-acetylbenzyl radical dimer (11); and p-acetyltoluene (12). Evidently 8, closely related to acetophenone, reacts predominantly via the triplet excited estate to generate long-lived, triplet, free-radical pairs (6 and 7a). In benzene, further products (15, 16, 17a and 17b) are identified that result from addition of the phosphinoyl radical (6) to benzene to give cyclohexadienyl radical 14, followed by combination and disproportionation reactions with radical 7a. (Total product quantum yields in benzene (Σφi) = 0.47.) In benzene, accountabilities of radical 6 from photolysis of 8 as high as 56% are encountered along with up to 92% accountabilities of p-acetylbenzyl (7a) radicals. Addition of radical scavengers PhSH, PhCH2Br, and TEMPO in the three solvents establishes the cage yield of 9 as 3 − 5%. The products of radical trapping provide further proof of the radical-pair nature of the photolysis of phosphite 8, including a 95% accountability of 6 with PhCH2Br in benzene. It is proposed that the CH2−O scission of triplet 8 must occur concertedly with partial phosphoryl (PO) bond formation. The trapping of radicals 6 and 7b from irradiation of phosphite 1 as the benzene adducts 22 and 23, analogous structurally to those (16 and 17) from phosphite 8, supports the postulation that photoisomerization of 1 to 2 proceeds via short-lived, presumably singlet, free-radical pairs.

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Section: Resultsmentioning

confidence: 99%

Photo-Arbuzov Rearrangements of Dimethyl Benzyl and Dimethyl p-Acetylbenzyl Phosphite

et al. 1999

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“…ESR experiments with the initiators investigated here indicate that the substitution of the benzoyl and phosphinoyl radicals does not lead to a significant deviation from this number. The hyperfine coupling constant, A P , is known to be positive 36a. Since the observed resonance shows enhanced absorption and is due to a cage recombination product, positive signs for Γ ne (Table ) and ε have to be used in eq 1.…”

Section: Resultsmentioning

confidence: 99%

“…The present work represents the first application of 31 P-NMR-CIDNP spectroscopy to investigate the formation and decay of phosphorus-centered radicals formed upon cleavage of photoinitiators. , Complementary experimental techniques were used to obtain additional information on the photoproducts.…”

Section: Introductionmentioning

confidence: 99%

Reaction Mechanism of Monoacyl- and Bisacylphosphine Oxide Photoinitiators Studied by ³¹P-, ¹³C-, and ¹H-CIDNP and ESR

et al. 1996

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31P-NMR-CIDNP (CIDNP = chemically induced dynamic nuclear polarization) spectroscopy was applied for the first time to investigate the formation and reaction of phosphorus-centered radicals obtained from phosphorus-containing photoinitiators. 13C-NMR- and 1H-NMR-CIDNP and ESR spectroscopies were used as complementary experimental techniques for the elucidation of the photochemistry of these compounds. The large hyperfine coupling constants of the 31P-nucleus results in a violation of Kaptein's rules, which is the only observation of this kind in 13C-NMR-CIDNP spectra reported so far. Interpretation of the CIDNP spectra, using a modification of Kaptein's rules for the 13C-NMR- and 1H-NMR-CIDNP, consistently shows that all compounds investigated undergo a photoinduced cleavage of the carbonyl−phosphinoyl bond from a triplet state. The fate of the primary radicals is discussed, and it is unambiguously shown by trapping experiments that the novel bisacylphosphine oxide photoinitiators give four radicals in a stepwise process.

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“…[10] For that reason, the peroxy carbonates 6a-c were investigated by DFT calculations. The fact that diperoxycarbonates of this type are known to be free radical precursors [11] indicates that simple homolytic O-O cleavage also needs to be considered here. In addition to the M05-2X calculations, CCSD(T)/cc-pVTZ single point energy calculations based on B3LYP/cc-pVTZ geometries were performed for peroxy carbonate 6a.…”

Section: (E)-bis(acetaldoxime) Carbonate (4)mentioning

confidence: 99%

Ester Pyrolysis of Carbonates: Bis(benzene hydrate) Carbonate as Potential Precursor for Monomeric Carbonic Acid

Bucher

2010

Eur J Org Chem

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The twofold ester pyrolysis of carbonates, yielding monomeric carbonic acid, was investigated by computational methods. By comparison with CCSD(T)/cc-pVTZ//B3LYP/ccpVTZ benchmark calculations, the M05-2X method was found to give the most accurate reaction enthalpies among the DFT methods employed. While the first ester pyrolysis of diethyl carbonate, (E)-bis(acetaldoxime) carbonate or di-N,N-dimethylhydroxylamine carbonate will yield the corresponding monocarbonates, these highly labile compounds

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³¹P CIDNP in the free radical reactions of dialkyl phosphites

Abstract: Abstract-The polarisation of phosphorus nuclei (31P CIDNP) takes place during the homolytic reactions of dialkyl phosphites. The mechanisms of CIDNP and the corresponding chemical reactions are discussed.

Cited by 14 publications

References 12 publications

Photo-Arbuzov Rearrangements of Dimethyl Benzyl and Dimethyl p-Acetylbenzyl Phosphite

Photo-Arbuzov Rearrangements of Dimethyl Benzyl and Dimethyl p-Acetylbenzyl Phosphite

Reaction Mechanism of Monoacyl- and Bisacylphosphine Oxide Photoinitiators Studied by ³¹P-, ¹³C-, and ¹H-CIDNP and ESR

Ester Pyrolysis of Carbonates: Bis(benzene hydrate) Carbonate as Potential Precursor for Monomeric Carbonic Acid

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31P CIDNP in the free radical reactions of dialkyl phosphites

Abstract: Abstract-The polarisation of phosphorus nuclei (31P CIDNP) takes place during the homolytic reactions of dialkyl phosphites. The mechanisms of CIDNP and the corresponding chemical reactions are discussed.

Cited by 14 publications

References 12 publications

Photo-Arbuzov Rearrangements of Dimethyl Benzyl and Dimethyl p-Acetylbenzyl Phosphite

Photo-Arbuzov Rearrangements of Dimethyl Benzyl and Dimethyl p-Acetylbenzyl Phosphite

Reaction Mechanism of Monoacyl- and Bisacylphosphine Oxide Photoinitiators Studied by 31P-, 13C-, and 1H-CIDNP and ESR

Ester Pyrolysis of Carbonates: Bis(benzene hydrate) Carbonate as Potential Precursor for Monomeric Carbonic Acid

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³¹P CIDNP in the free radical reactions of dialkyl phosphites

Reaction Mechanism of Monoacyl- and Bisacylphosphine Oxide Photoinitiators Studied by ³¹P-, ¹³C-, and ¹H-CIDNP and ESR