Making mercury-photosensitized dehydrodimerization into an organic synthetic method: Vapor pressure selectivity and the behavior of functionalized substrates

Journal Article · Wed Apr 12 00:00:00 EDT 1989 · Journal of the American Chemical Society; (USA)

DOI:https://doi.org/10.1021/ja00190a031· OSTI ID:5208096

Brown, S H; Crabtree, R H ^[1]

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1. Yale Univ., New Haven, Connecticut (USA)

Mercury-photosensitized dehydrodimerization in the vapor phase can be make synthetically useful by taking advantage of a simple reflux apparatus, in which the products promptly condense and are protected from further conversion. This vapor pressure selectivity gives high chemical selectivity even at high conversion and on a multigram scale. Mercury absorbs 254-nm light to give the {sup 3}P{sub 1} excited state (Hg*), which homolyses a C-H bond of the substrate with a 3{degree} > 2{degree} > 1{degree} selectivity. Quantitative prediction of product mixtures in alkane dimerization and in alkane-alkane cross-dimerizations is discussed. Radical disproportionation gives alkene, but this intermediate is recycled back into the radical pool via H atom attack, which is beneficial both for yield and selectivity. The method is very efficient at constructing C-C bonds between highly substituted carbon atoms, yet the method fails if a dimer has four sets of obligatory 1,3-syn methyl-methyl steric repulsions, as in the unknown 2,3,4,4,5,6,7-octamethyloctane. We have extended the range of substrates susceptible to the reaction, for example to higher alcohols, ethers, silanes, partially fluorinated alcohols, and partially fluorinated ethers. We see selectivity for dimers involving C-H bond {alpha} to O or N and for S-H over C-H. An important advantage of our experimental conditions in the case of alcohols is that the aldehyde or ketone disproportionation product (which is not subject to H{sup {sm bullet}} attack) is swept out of the system by the stream of H{sub 2} also produced, so it does not remain and inhibit the rate and lower the selectivity. k{sub dis}/k{sub rec} is estimated for a number of radicals studied. The very hindered 3{degree} 1,4-dimethylcyclohex-1-yl radical is notable in having a k{sub dis}/k{sub rec} as high as 7.1.

• OSTI ID: 5208096
• Journal Information: Journal of the American Chemical Society; (USA), Journal Name: Journal of the American Chemical Society; (USA) Vol. 111:8; ISSN 0002-7863; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400500 -- Photochemistry
ALCOHOLS
ALKANES
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMICAL REACTORS
DATA
DESIGN
DIMERIZATION
DIMERS
EFFICIENCY
ELEMENTS
ETHERS
EXPERIMENTAL DATA
FLUIDS
GASES
HYDRIDES
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
INFORMATION
KINETICS
MERCURY
METALS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANIC SILICON COMPOUNDS
PHOTOSENSITIVITY
PHYSICAL PROPERTIES
POLYMERIZATION
QUANTUM EFFICIENCY
REACTION KINETICS
SENSITIVITY
SILANES
SILICON COMPOUNDS
SYNTHESIS
THERMODYNAMIC PROPERTIES
VAPOR PRESSURE
VAPORS