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'Aromatic Photosubstitutions' in keywords
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1978 (1)
1Author    Claudia Bäk, Klaus PraefckeRequires cookie*
 Title    Photoreaktionen 2.2'-dihalogensubstituierter Benzoinether und Benzildimethylmonoketale in Lösung 1 Photoreactions of 2,2'-Dihalogen Substituted Benzoin Ether and Benzildimethylmonoketals in Solution  
 Abstract    The synthesis of a,a'-dihalogenated benzoin ether 6 and benzildimethylmonoketals 7 are discribed. Their reaction behavior under UV irradiation and electron impact conditions are discussed in comparison with those of arylesters 1 of seleno and thiobenzoic acid. The photoproducts of 6 and 7 are separated and identified with help of column or vaporphase chromatography. Photoinduced a-cleavages of 6 and 7 produce 2-halogenbenzoyl radicals 9 and a-monomethoxybenzyl radicals 10 or a,a-dimethoxybenzyl radicals 15 resp., which undergo four different stabilization reactions under formation of 1) 2-halogenbenzaldehydes 12 from 9 by hydrogenabstraction, 2) 2,2'-dihalogenbenzils 11 and l,2-di(2-chlorophenyl)-1,2-dimethoxyethan (13) via dimerization of 9 or 10 resp., 3) methylesters 16 of 2-halogen-benzoic acids by /^-elimination of methylradicals from 15, and 4) 2-halogenacetophenones 17 via combination of 9 with methylradicals from 15. In addition to these photoproducts 2-phenylbenzoic acidester 18, benzaldehyde (19), and acetophenone (20) are formed by photosubstitution of halogens in benzaldehydes 12 as well as in acetophenones 17 against hydrogen and in benzoic acid-esters 16 against phenyl resp. Independent photoexperi-ments prove 1) the formation of 2-phenylbenzoic acidester 18 by halogen-phenylreplace-ment in 16 and 2) that chlorine is easier than bromine, both in orZ/io-position to a carboxyl function, substituted by phenyl. No photoproducts {e.g. 8 or 14) are formed by substitution of halogen in the 2-halogenbenzoyl part of a-cleavage against neither a-monomethoxybenzyl nor a,a-dimethoxybenzylradicals resp. as expected like the photoinduced formation of selenoxanthones or thioxanthones 2 from selenol-or thiolesters 1. 
  Reference    (Z. Naturforsch. 33b, 106—112 [1978]; eingegangen am 5. Oktober 1977) 
  Published    1978 
  Keywords    Carbonyl Compounds, a-Cleavages, Free Radicals, Aromatic Photosubstitutions 
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 TEI-XML for    default:Reihe_B/33/ZNB-1978-33b-0106.pdf 
 Identifier    ZNB-1978-33b-0106 
 Volume    33