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Rates of nitrosation are reported for benzene, toluene, diphenyl ether, anisole, and phenol in 1 0 . 4 ~-H C J 0 , a t 52.9 "C, for benzene in 1 ~. ~M -H , S O , , and for [aH6]benzene in 1 2M-D2S0,. The effective reagent under these conditions is NO+ and substitution occurs predominantly a t the para-position of monosubstituted substrates. Benzene reacts about 50 times more rapidly in HzS04 than in HCIO, of the same Ho acidity, and about 8.5 times more rapidly than [2H6]benzene in D2S04, which shows that H+-loss from the Wheland intermediate is ratelimiting. Rates of nitrosation are moderately increased by electron-donating substituents and log (partial rate factors) for the para-position correlate with Q+ parameters to give p = -6.9. This relatively low p value is consistent with the rate-limiting step suggested. The reactivity of NO+ is discussed and it is shown to be at least 1 014 times less reactive than NOz+. The significance of the findings to recent explanations of aromatic reactivity in nitrations is also discussed.London S.W.7 THE reaction of nitrous acid with aromatic substrates is usually difficult in the absence of powerfully activating substituents such as OH, OR, and NR,. Often the nitroso-product formed initially undergoes further transformation and nitrous acid is unstable in moderately acidic solutions at high temperature^.^ This combination of adverse factors has discouraged detailed investigation of these reactions and relatively little is

relative rates of subsequent steps on the reaction path.( I 1 limiting step for reactivity controlled reactions is determined by the of the k-a and kb steps.

Sorption and diffusion of ethanol, 1,1,1-trichloroethane (TCA), and trichloroethylene (TCE) were investigated in polydimethylsiloxane (PDMS) membranes using a gravimetric technique. The thermodynamic equilibrium and kinetic properties were evaluated at temperatures of 25, 100, and 150ЊC. The sorption isotherms for TCA and TCE can be correlated well using the Flory-Huggins model. However, a three parameter Koningsveld-Kleinjtens variation to the Flory-Huggins equation is required for correlation of the ethanol isotherm. The solubility coefficients of TCA and TCE increase with activity, but it remains almost constant for ethanol. The calculated sorption energies reveal high positive heat of mixing for ethanol. TCA and TCE sorption in PDMS decreases strongly with temperature as opposed to ethanol. Clustering function analysis is used to explain the anomalous ethanol sorption and diffusion behavior in PDMS. TCA and TCE diffusivities do not exhibit large variations with volatile organic compound activity. However, ethanol demonstrates a maxima in its diffusivity at activities where it has minimum clustering tendencies.

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