Spectrophotometric and titrimetric studies on alkyl hypobromites

Roscher, Nina Matheny; Nguyen, Chinh K.

doi:10.1021/jo00205a040

Cited by 7 publications

(3 citation statements)

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“…Further analyses on the transient red photoproduct have not so far been attempted. However, its deep red color matches that reported for known alkyl hypobromites. − Acyl hypobromites, however, have been reported to have a strong green color, although, as with the alkyl hypobromites, this color results only from the long-wavelength tail of a broad absorption band that reaches its maximum in the UV. Nevertheless, in conjunction with the mass spectrometry, the color of the transient red species helps to rule out bromoformyl hypobromite ( I in Scheme ) as its structure.…”

Section: Resultssupporting

confidence: 74%

Bromine-Sensitized Solar Photolysis of CO₂

2012

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Direct photochemical reduction of CO(2) has generally been accomplished by using transition-metal compounds as electron transfer reagents. Here, we show that elemental bromine can function as an alternative photosensitizer. When sunlight is tightly focused on mixtures of CO(2) and Br(2), in the presence of a polar adsorbent such as silica gel, glass wool, alumina, or titania, a metastable red adduct is formed within seconds and concentrates at the point of illumination. Further illumination causes deposition of a stable black film on the polar adsorbent. Mass spectrometry of the cold-trapped red intermediate shows clusters of peaks corresponding to the expected distribution of isotopomers of C(2)O(4)Br(4)(+), as well as of C(2)O(4)Br(3)(+). DFT computations indicate that the lowest-energy species with the formula C(2)O(4)Br(4) is trans-2,4-dibromo-2,4-dihypobromo-1,3-dioxetane. Formation of this molecule from (2CO(2) + 2Br(2)) would require a minimum of 3 visible photons, two of which would hypothetically be used in formation of as-yet undetected CO(2)Br(2) and the third, in a subsequent photodimerization. By elemental analysis, the final amorphous solid product contains a C/Br atomic ratio >12, suggesting that Br(2) is acting photocatalytically. Even with a poorly optimized optical system, the reaction rate has reached as high as 1.6 mg reduced C with 40 s of solar collection using a 30 cm diameter paraboloid reflector. This rate is consistent with the storage of approximately 1% of incident solar energy.

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Section: Resultssupporting

confidence: 74%

Bromine-Sensitized Solar Photolysis of CO₂

2012

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“…By comparison, alkyl hypobromites are less stable, generally only at low temperatures in the dark. Most have been characterized solely by titrimetric and UV–visible spectrophotometric methods. , Ring-opening reactions of putative hypobromites have afforded products analogous to 2 or 8 …”

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confidence: 73%

“…Most have been characterized solely by titrimetric and UV−visible spectrophotometric methods. 17,18 Ring-opening reactions of putative hypobromites have afforded products analogous to 2 or 8. 19 In a hypobromite chain mechanism, a bromine atom would be abstracted from the hypobromite 10 by 7 to afford the product 8 and alkoxy radical 6.…”

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confidence: 99%

Energy Read-out as a Probe of Kinetically Hidden Transition States

Alvi

Singleton

2021

Org. Lett.

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The initial energy in a reactive intermediate is derived from the transition state before the intermediate but can affect selectivity after the intermediate. In this way an observable selectivity can report on a prior, kinetically hidden mechanistic step. This new type of mechanistic probe is demonstrated here for the oxidation of 1-methylcyclobutanol by phthaloyl peroxide/Bu4N+Br–, and it supports a hypobromite chain mechanism in place of the previously proposed hydrogen atom transfer mechanism.

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