Reactive spreading

Xia Y and Whitesides G M 1994 Use of controiied reactive spreading of iiquid aikanethioi on the surface of goid to modify the size of features produced by microcontact printing J. Am. Chem. Soc. 117 3274-5... 

Sites of reactivity spread thro ugh large volume... 

Modelling of non-reactive spreading has been performed mainly for the configuration of a small droplet spreading on a horizontal and perfectly smooth solid substrate so that gravitational forces are negligible. The effect of gravity will be briefly described at the end of this Section. 

It has also been found that highly active catalysts can be prepared in situ by reducing a platinum, palladium, or rhodium salt with sodium borohydride in the presence of a carbon support. Similar reductions of nickel salts produce colloidal nickel-boron, which is highly selective toward olefins of different structural types. The normal order of reactivity—i.e., terminal > disubstituted > trisubstituted—is observed, but the reactivity spread is sufficiently large that selective hydrogenation of polyenes is possible, as illustrated by a step in a synthesis of the natural product... 

Braun, R.J. Murray, B.T. Boettinger, W.J. McFadden, G.B. Lubrication theory for reactive spreading of a thin drop. Phys. Fluids 1995, 7 (8), 1797-1810. 

Generally the determination of the reactivity of a particular compound depends upon comparison of its rate of nitration with that of benzene at the same acidity and temperature. Because of the spread of rates this may not be practically possible and, in any case, is usually not necessary because of the parallelism existing among rate profiles (fig. 2.4). Reactivities in aqueous sulphuric acid are, in fact, very nearly independent of acidity, and stepwise comparison of data for a compound with those of benzene determined at different acidities is possible. 

Bromine reacts with alkanes by a free radical chain mechanism analogous to that of chlorine There is an important difference between chlorination and brommation how ever Brommation is highly selective for substitution of tertiary hydrogens The spread m reactivity among pnmary secondary and tertiary hydrogens is greater than 10 ... 

At 100—300°C sodium readily wets and spreads over many dry soHds, eg, sodium chloride or aluminum oxide. In this form the metal is highly reactive (7), but it does not easily wet stainless or carbon steels. Wetting of stmctural metals is influenced by the cleanliness of the surface, the purity of the sodium, temperature, and the time of exposure. Wetting occurs more readily at >300°C and, once attained, persists at lower temperatures (5). 

Results for the neutral pyrazole molecule show a considerable spread. The tt-electron and total (Tr-l-cr) densities predict electrophilic substitution at the 4-position as found. Results for thiazole also agree with experimentally determined electrophilic and nucleophilic reactivity. 

Modified liquid epoxy resins liquid epoxy resins with added reactive diluents or solvents mild to moderate irritants moderate to strong sensitizers low volatility, exposure unlikely unless heated, sprayed, or spread over large unventilated surfaces low toxicity... 

Despite the relative simplicity of the kinetics of molecular chlorination, there has so far been only one measurement of the rate coefficient with a heterocyclic compound and the need for more work in this area is indicated. Marino265 found that chlorination of thiophene by chlorine in acetic acid at 25 °C gave the second-order rate coefficient of 10.0 1.5, so that thiophene is 1.7 x 109 times as reactive as benzene in this reaction and this large rate spread is clearly consistent with the neutral and hence relatively unreactive electrophile. 

Relative rates and partial rate factors have been determined for the chlorination of some aromatics by chlorine acetate in 76 % aqueous acetic acid at 25 °C209 these are given in Table 65. The spread of rates is, therefore, smaller than is found with molecular chlorine and this is entirely consistent with the lower reactivity of the latter reagent. 

Robertson et al.261 measured rates of bromination of some aromatic hydrocarbons in acetic acid containing sodium acetate (to eliminate protonation of the aromatic by liberated hydrogen bromide) and lithium bromide (to reduce the rate to a measurable velocity ) at 25 °C, the second-order rate coefficients for 3-nitro-N,N-dimethylaniline and anisole being 14.2 and 0.016 respectively the former compound was thus stated to be about 1012 times as reactive as benzene (though no measurement of the latter rate coefficient, inferred to be 1.33 xlO-11, could be found in the literature) and this large rate spread gives one further indication of the unreactive nature of the electrophile. Other rates relative to benzene were ... 

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