Browsing by Author "Robb, J. C."

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    Kinetics of Reaction of Metal Alkyls with Alkenes: Part 7.—n-Butyl Lithium and N : N : N' : N'-Tetramethyl Ethylene Diamine with Butadiene
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Hay, J. N.; McCabe, J. F.; Robb, J. C.
    The polymerization of butadiene, initiated by the complexes of n-butyl lithium and tetramethyl ethylene diamine, has been studied in the range 230-280 K by dilatometry. Initial rates of polymerization were second order in monomer, and first in both amine and butyl lithium concentrations. Maximum rates were observed at molar ratios of lithium alkyl/amine below' I /2. Rates of polymerization decreased with conversion, consistent with first-order dependence on unconverted monomer. Molecular weights of the polymers increased with conversion, and at ratios below' 1 /2 in alkyl/amine compared exactly with moles of monomer consumer per mole of butyl lithium initially present. The micro-structure of the polymers varied with polymerization temperatures between 70-90 % of 1,2 addition product. All the polymers had narrow molecular weight distributions independent of the final degree of conversion. It was concluded that the polymerization of butadiene occurred by a “ living” anionic addition mechanism, initiated by the 1 /2 amine complex. The nature of the active polymerizing species was confirmed by a molecular weight study of the complexes present at various molar ratios, and their concentration dependence.
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    Rational Definition of Rate of Reaction: General Method of Expressing Ratc Which Leads to No Anomalies in Systems of Changing Volume
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (2), 1973) Hutchison, J.; Lehrle, R. S.; Robb, J. C.; Suggate, J. R.
    The conventional way of expressing rate of reaction in terms of rate of change of concentration (e.g. –d[A]/dt) is shown to be inappropriate for systems in which any volume change accompanies the conversion. Thus for such liquid phase reactions, with or without inert solvent, it is demonstrated that the rate of decrease of reactant concentration is not equal to the rate of increase of product concentration, that the apparent external order of reaction depends on whether the rate is expressed in terms of reactant or product, and that the apparent internal order of reaction can not reflect the molecularity of the reaction process. A revised expression for rate of reaction is proposed; this defines the rate at any time as the product of the time derivative of the number of moles of a reaction component and the reciprocal volume of the system at that time, e.g.–(1/Vt)(dA/dt)t. The above anomalies do not arise when rates are expressed in this way; it is therefore recommended that this revised definition of rate be generally employed in all kinetic studies.