84507-56-2Relevant academic research and scientific papers
Mechanism of Thermal Eliminations. Part 30. Pyrolysis of 2-Trimethylsilylethanol and 1-Aryl Derivatives
Taylor, Roger
, p. 1703 - 1706 (2007/10/02)
The Arrhenius parameters (Eact = 45.57 kcal mol-1, log A/s-1 = 12.865) and rate coefficient at 600 K (1.84 * 10-4 s-1) for the cis β-thermal elimination of trimethylsilanol from 2-trimethylsilylethanol are identical (within experimental error) with those reported in the literature for elimination of methyl trimethylsilyl ether from 1-methoxy-2-(trimethylsilyl)ethane.This indicates that the driving force for the reaction, formation of the Si-O bond, is such that alteration of the nucleophilicity of oxygen has little effect on the reaction rate.A series of 1-aryl-2-trimethylsilylethanols have been prepared and their rates of elimination determined.The activating effect of the 1-aryl substituent (5.2-fold) is much less than the corresponding effect in the pyrolysis of ethyl acetates (63-fold) and 2-trimethylsilylethyl acetates (87-fold).Breaking of the α-C-O bond is thus kinetically less important than in the other reactions, and this conclusion is confirmed by a correlation of the rate data with the Yukawa-Tsuno equation which gives ρ = -0.4, r = 0.3.Si-O bond formation in the reaction is thereby shown to be of over-riding kinetic importance.For the 4-methylphenyl- and 4-methoxyphenyl compounds a minor competing reaction was the elimination of water to give the corresponding 1-aryl-2-trimethylsilylethene, and this has a higher activation energy than for the elimination of trimethylsilanol.NMR spectra for the 1-aryl-2-trimethylsilylethanols show that interaction between the OH and SiMe3 groups inhibits free rotation about the C(1)-C(2) bond.Preparation of 1-aryl-2-trimethylsilylethanols gave 1,3-diaryl-4-trimethylsilylbutyl trimethylsilyl ethers as byproducts arising from elimination of water from two molecules of the alcohols in a process believed to be two-step.
Silicon Effects. II. Structure and Stability of 1-Phenyl-2-(trimethylsilyl)ethyl Cation in Solution
Shimizu, Nobujiro,Watanabe, Shin-ichiro,Tsuno, Yuho
, p. 2249 - 2254 (2007/10/02)
Solvolysis rates have been measured in various solvents at 25 deg C for 1-(substituted phenyl)-2-(trimethylsilyl)ethyl trifluoroacetates (1a - 1g; R=H, 4-Me, 4-Cl, 4-Br, 3-Cl, 3,4-Cl2, and 3,5-Cl2, respectively) and structurally related compounds, 1-phenylethyl-, 3,3-dimethyl-1-phenylbutyl-, and 1-(4-methylphenyl)ethyl trifluoroacetates (3a, 4, and 5).In dioxane/water mixtures 1g solvolyzes with the same sensitivity to the change in solvent ionizing power as that for a kc substrate 5.The solvolyses of 1e and 5 exhibit almost identical α-deuterium kinetic isotope effects (kH/KD) of 1.18 - 1.19 in aq dioxane.Substituent effect on the solvolysis of 1 in 90 percent aq dioxane is expressed by an LArSR equation: log kX/kH = -3.05 (?0 + 1.05 Δ?(mean)+R) (R = 0.9997).These findings are consistent with kc mechanism for the solvolysis of 1.Relative rates for the solvolysis of 1a, 3a, and 4 in 30 percent aq dioxane are 2.99x105:2.84:1.0 indicating solvolytic generation of α-(trimethylsilylmethyl)benzyl cation to be about 7 kcal mol-1 energetically more favorable than that of the corresponding α-alkylbenzyl cations.
