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The Activation of Carbon−Chlorine Bonds in Per- and Polyfluoroalkyl Chlorides:  DMSO-Induced Hydroperfluoroalkylation of Alkenes and Alkynes with Sodium Dithionite

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journal contribution
posted on 09.06.1999, 00:00 by Zheng-Yu Long, Qing-Yun Chen
In DMSO, the addition reactions of perfluoroalkyl chlorides, RFCl, to alkenes or alkynes can occur smoothly in the presence of 1.5 equiv of Na2S2O4 and NaHCO3 at 75−80 °C for 4−10 h to give the corresponding adducts (RCH2CH2RF or RCHCHRF). Ethyl chlorofluoro- (1f), chlorodifluoro- (1g) acetates, even nonfluorinated compounds, such as ethyl dichloro- (1h), chloro- (1i) acetates, and chloroform (1j) can undergo the similar reaction. Treatment of ω-iodo (or chloro-) perfluoroalkyl chlorides [X(CF2)nCl, n = 2, 4, X= I or Cl] with >3 equiv of alkenes and Na2S2O4 gives directly the symmetrically disubstituted alkanes (RCH2CH2)2(CF2)n. The symmetrically and unsymmetrically disubstituted adducts RCH2CH2(CF2)nCH2CH2R‘ from ω- iodoperfluoroalkyl chlorides can be also obtained stepwise, i.e., through the further addition reactions of monoadducts, RCH2CH2(CF2)nCl to olefins. However, for α,ω-dichloroperfluoroalkanes, the similarly stepwise reactions with an alkene is not clean, both bis-adducts and the corresponding ω-hydrides, RCH2CH2(CF2)nH as byproducts are also formed. In the absence of alkenes or alkynes, per- and polyfluoroalkyl chlorides can be converted to their sulfinate salts and sulfonyl chlorides.