74492-30-1Relevant articles and documents
Facile synthesis of unsymmetrical 1,1-diaryl-2,2-difluoroethenes via stepwise coupling of 1,1-dibromo-2,2-difluoroethenes
Fujita, Takeshi,Suzuki, Naoto,Ichitsuka, Tomohiro,Ichikawa, Junji
, p. 97 - 101 (2013/10/01)
Unsymmetrical 1,1-diaryl-2,2-difluoroethenes were synthesized from 1,1-dibromo-2,2-difluoroethene, which is commercially available, via the Suzuki-Miyaura coupling in a stepwise fashion. Suitable ligands for each coupling process were used to achieve selective synthesis of these diaryldifluoroethenes.
Use of kinetic isotope effects in mechanism studies. Isotope effects and element effects associated with Hydron-Transfer steps during alkoxide-promoted dehydrohalogenations
Koch, Heinz F.,Lodder, Gerrit,Koch, Judith G.,Bogdan, David J.,Brown, Geoffrey H.,Carlson, Carrie A.,Dean, Amy B.,Hage, Ronald,Han, Patrick,Hopman, Johan C. P.,James, Lisa A.,Knape, Petra M.,Roos, Eric C.,Sardina, Melissa L.,Sawyer, Rachael A.,Scott, Barbara O.,Testa III, Charles A.,Wickham, Steven D.
, p. 9965 - 9974 (2007/10/03)
The Arrhenius behavior of the primary kinetic isotope effect, (k(H)/k(D))(Obs) and (k(H)/k(T))(Obs), associated with the methanolic sodium methoxide-promoted dehydrohalogenations of m-ClC6H4C(i)HClCH2Cl (I), m-CF3C6H4C(i)-HClCH2Cl (II) and p-CF3C6H4C(i)HClCH2F (III) has been used to calculate the internal-return parameters, a = k(-1)/K(Elim)(X), in a two-step mechanism featuring a hydrogen-bonded carbanion. This carbanion partitions between returning the hydron to carbon, k(-1), and the loss of halide, K(Elm)(X). Isotope effects at 25°C for I, (k(H)/k(D))(Obs) = 3.40 and (k(H)/ k(T))(Obs) = 6.20, and II, (k(H)/k(D))(Obs) = 3.49 and (k(H)/k(T))(Obs) = 6.55, result in similar values for a: a(H) = 0.59, a(D) = 0.13-0.14 and a(T) = 0.07. Smaller values of (k(H)/k(D))(Obs) = 2.19 and (k(H)/k(T))(Obs) = 3.56 for III are due to more internal return [a(H) = 1.9, a(D) = 0.50, and a(T) = 0.28] associated with the dehydrofluorination reaction. Calculation of k1 ( k(Obs) [a + 1]) results in similar isotope effects for hydron transfer in these reactions: k1(H)/k1(D) = 4.74 and k1(H)/K1(T) = 9.20; II, k1(H)/k1(D) = 4.91 and k1(H)/k1(T) = 9.75; III, k1(H)/k1(D) = 4.75 and k1(H)/k1(T) = 9.17. Reactions of m-ClC6H4C(i)HBrCH2Br and m-ClC6H4C(i)HClCH2Br have very small amounts of internal return, a(H) = 0.05 and a(D) = 0.01, and (k(H)/k(D))(Obs) = 4.95 results in k1(H)/k1(D) = 5.11 The measured isotope effects are therefore due to differences in the amount of internal return and not in the symmetry of transition state structures for the hydron transfer, and the element effect, (k(HBr)/ k(HCl)) = 29, for m-ClC6H4CHClCH2X is mainly due to the hydron-transfer step, k1(HBr)/k1(HCl) = 19, and not the breaking of the C-X bend. The kinetic solvent isotope effects, k(MeOD)/k(MeOH) ~ 2.5, are consistent with three methanols of solvation lost prior to the hydron-transfer step. The energetics associated with desolvation of methoxide ion are part of the measured reaction energetics of these systems.
Use of Kinetic Isotope Effects in Mechanism Studies. 4. Chlorine Isotope Effects Associated with Alkoxide-Promoted Dehydrochlorination Reactions
Koch, Heinz F.,McLennan, Duncan J.,Koch, Judith G.,Tumas, William,Dobson, Brian,Koch, Nanci H.
, p. 1930 - 1937 (2007/10/02)
The method of measuring k35/k37 for the alkoxide-promoted deprotiochlorination and dedeuteriochlorination reactions has been applied to C6H5CiH(CH3)CH2Cl (I-Cl), C6H5CiHClCH2Cl (V), and C6H5CiHClCF2Cl(III).For reactions occuring with ethanolic sodium ethoxide the following values for k35/k37 have been measured: I-Cl-h, 1.00590 + 0.00013, and I-Cl-d, 1.00507 +/- 0.00036 at 75 deg C; V-h, 1.00908 +/- 0.00008, and V-d, 1.00734 +/- 0.00012 at 24 deg C; III-h, 1.01229 +/- 0.00047, and III-d, 1.01003 +/- 0.00024 at 0 deg C.Methanolic sodium methoxide promoted eliminations gave similar results for V and III: V-h, 1.00978 +/- 0.00020, and V-d, 1.00776 +/- 0.00020 at 21 deg C; III-h, 1.01255 +/- 0.00048, and III-d, 1.01025 +/- 0.00043 at 20 deg C.The results for I-Cl are most consistent with an E2 mechanism, while the results for III and V suggest a multistep reaction sequence.The Arrhenius behavior of ethoxide-promoted dehydrochlorination of V-h gives a good linear correlation between -10 and 50 deg C, with an EaH = 21.26 +/- 0.05 kcal/mol and ln AH = 29.29 +/- 0.09.Rate constants measured for 55, 60, 65, and 70 deg C show increasing negative deviation from the slope.Similar behavior was not observed for V-d which resulted in EaD = 21.57 +/- 0.28 and ln AD = 28.37 +/- 0.28 when rate constants over a 50 deg C range (20 - 70 deg C) were used.The ΔEaD-H = 0.31 and AH/AD = 2.5 for an observed kH/kD = 4.24 at 25 deg C were similar for results obtained for III.The possibility that the high values of k35/k37 for both III and V could result from a chlorine isotope effect associated with the proton transfer step of an E1cB mechanism is discussed.
