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Self-ionisation

If we consider the effect of nitrous acid upon zeroth-order nitration in organic solvents we must bear in mind that in these circumstances dinitrogen tetroxide is not much ionised, so the measured concentration of nitrous acid gives to a close approximation the concentration of dinitrogen tetroxide. Further, the negligible self-ionisation of nitric acid ensures that the total concentration of nitrate ions is effectively that formed from dinitrogen tetroxide. Consequently as we can see from the equation for the ionisation of dinitrogen tetroxide ( 4.3.1),... [Pg.56]

Metals in practice are usually coated with an oxide film that affects the potential, and metals such as Sb, Bi, As, W and Te behave as reversible A//A/,Oy/OH electrodes whose potentials are pH dependent electrodes of this type may be used to determine the solution s pH in the same way as the reversible hydrogen electrode. According to Ives and Janz these electrodes may be regarded as a particular case of electrodes of the second kind, since the oxygen in the metal oxide participates in the self-ionisation of water. [Pg.1251]

In Section 4 there is an account of our exploration of the self-ionisation of the A1X3. Having established that phenomenon [35, 36], I could pursue with Grattan [37] the idea that it is the inorganic cation A1X2+ which initiates the polymerisations by cationating the monomer ... [Pg.27]

Suspecting that there may be an ionisation without complex formation, we then did a conductimetric study on TiCl4 in CH2C12 and EtCl [48]. This gave the useful result that there was no evidence for an ionisation yielding R+ and MtX"n+1, and it thus made solvent co-catalysis by the ionisation of the solvent very unlikely. A further useful outcome from these conductimetric studies was the realisation that the observed rectilinear dependence of the conductivity, K, on the concentration of TiCl4 could only be explained reasonably as due to the self-ionisation of TiCl4, for which reaction (11) seemed most likely ... [Pg.31]

Scheme 4 Energetics of the BIE for self-ionisation of a metal halide... Scheme 4 Energetics of the BIE for self-ionisation of a metal halide...
The situation presented above is, of course, a simplification. It is well documented that metal halides can take part in a self-ionisation reaction [34] involving only the metal halide. The Born-Haber cycle for such a BIE is given in Scheme 4. [Pg.201]

Supposition 1. The initiator solutions of aluminium chloride in alkyl chloride contain ions formed by self-ionisation of the aluminium chloride... [Pg.269]

Two of the suppositions on which the theory is based-self-ionisation of aluminium chloride, and complexing between aluminium chloride and isobutene-are made by analogy with the facts established for closely related systems. Unfortunately we have here a prime example of the well known fact that the less one knows about a situation, the more one needs to say about it. If reliable measurements on the conductivity of solutions of aluminium chloride in methyl chloride were available, and if we had direct evidence for... [Pg.270]

Supposition 1. In the paper in which we first described the self-ionisation of titanium tetrachloride in methylene dichloride or ethyl chloride, we also showed that the conductivity measurements on aluminium bromide solutions available at that time could be explained by a self-ionisation of the type... [Pg.271]

The self-ionisation of aluminium chloride and bromide in nitrobenzene has been studied in great detail [15], and the rates of the forward and back reactions have been determined so that all the relevant equilibrium constants are known. The whole body of evidence available shows that self-ionisation of the initiator, with or without other ionogenic reactions in the initiator solutions, can be regarded as well established for all aluminium halides and as highly probable for the alkyl aluminium halides. Moreover, the ionogenic reactions are relatively slow and - except under the dirtiest conditions - the concentration of ions in the initiator solution will be very much less than [A1X3]0. [Pg.272]

In the latest paper from Marek s group [29] they once again introduce the self-ionisation of titanium tetrachloride in order to explain their photo-initiation results. Unfortunately, their reaction scheme is very obscure, but evidently it does not involve addition of a metal-containing cation to the monomer. [Pg.277]

At the IUPAC Polymer Symposium in Helsinki in 1972, I put forward a new theory concerning the initiation of cationic polymerisations by metal halides [1]. This comprised three principal ideas (a) Initiating metal halides undergo self-ionisation in solution, (b) Metal halide cations formed in this way can be the principal initiators in certain circumstances, and act by combining additively with the monomer to give a metalated carbenium ion. (c) The metal halides form complexes with the monomers. [Pg.283]

Table 1 Experimental values of the equilibrium constants, K and 1C, for self-ionisation (Eq. (iii)) and of the rate-constant, kf, of ion formation, the left to right process of Eq. (iii) kf may be a composite quantity for some systems, especially at low temperatures ... Table 1 Experimental values of the equilibrium constants, K and 1C, for self-ionisation (Eq. (iii)) and of the rate-constant, kf, of ion formation, the left to right process of Eq. (iii) kf may be a composite quantity for some systems, especially at low temperatures ...
Having commented briefly on the first two parts of my new theory (the self-ionisation and the initiation by AlX+2), it is appropriate to consider the complex formation between monomer and metal halide, expressed by Equation (ii), which we have mentioned in the previous section. This complex formation actually provides an easy and plausible explanation for some of the hitherto rather obscure phenomenological differences which are observable when monomer and aluminium halide solutions are brought together in different ways we can distinguish three such techniques which give very different results. [Pg.288]

Since the extent of self-ionisation of aluminium chloride and bromide in the alkyl halide solvent is very small (Table 1) ([AlX+2]/[AlX3] approximately 10"4) the isobutene whose concentration is always kept very low, reacts preferentially with the much more abundant A1X3 to form the complex, and if any isobutene does react with AlX+2, the resulting... [Pg.288]

If, however, these conditions are not fulfilled, for instance if the solution contains such a high level of basic impurities that they compete effectively with the monomer for the TiCI+3 then there will be no polymerisation until the concentration of impurities has been reduced sufficiently. It seems most likely now that it is these circumstances which produce the quiescent mixtures of monomer and initiator. In order to induce a polymerisation in such quiescent systems it is necessary to produce a sufficient quantity of reactive ions. This can happen either if one waits long enough for the self-ionisation to produce sufficient initiating TiCl+3 ions, or if one adds a co-initiator which reacts with the titanium tetrachloride to generate ions in a different manner and in greater numbers. [Pg.291]

In other words, if the conditions of the experiment are such that insufficient ions are formed by self-ionisation then a co-initiator is required to help generate the ions which are needed for the initiation of polymerisation. [Pg.291]

In order to account for the observations and the kinetics, it was suggested [3] that initiation was by the AlBr2+ ion, formed by the self-ionisation of the halide according to Equation (i) ... [Pg.297]

The BIE, are of course equally relevant to those systems in which a metal halide initiates by a cation which is formed in a self-ionisation BIE reaction, e.g., A1C13 (Grattan and Plesch, 1980) ... [Pg.529]

Acid/base reactions can be defined in non-protonic solvents. A popular solvent in this category is POCl3, which is believed - although there has been some controversy over this - to undergo self-ionisation ... [Pg.332]

It should be noted that self-ionisation is not an essential prerequisite for a satisfactory polar solvent. Liquids such as acetonitrile CH3CN or dimethylsulphoxide SO(CH3)2 appear not to ionise but they make very useful solvents for electrolytes as well as for polar molecular substances. As with H20, NH3, H2S04 etc., they owe their solvent powers to their polarity, leading to dipole-dipole interaction in the case of polar molecules as solutes and ion-dipole attraction in the case of electrolytes. There may in addition be considerable covalent bonding, via coordinate bond formation, in the case of cations. In solvents which do undergo appreciable self-ionisation, coordination often needs to be considered explicitly in discussing acid/base and other reactions and equilibria. [Pg.332]

The simple autoprotolysis reactions for the three fluoro-acids contrast markedly with the complexity of ionisation processes in H2S04 which include the self-ionisation equilibria in Eqns (2) and (3) ... [Pg.332]

Protonation by superacids of solutes such as these displaces the self-ionisation of the superacids causing enhancement of concentration of the base of the superacid system, F, S03F or CF3S03-. This may be a disadvantageous situation when acidity/basicity control is required for synthetic purposes. If controlled increase of basicity is required, the simplest procedure is by direct addition of the conjugate base of the parent acid, i.e. by addition of F, S03F- or CF3S03 as indicated in Sec. 11.2.3. [Pg.335]

The self-ionisation equilibrium (Eqn. (1)) is displaced, increasing the proton concentration effectively quantitatively in the case of relatively dilute solutions of SbF5. Weaker Lewis acids such as AsF5 and BF3, which will be described in Sec. 11.2.3.1, cause partial displacement of the equilibrium. [Pg.335]

Such perfection is aided by assuming, in equilibrium calculations, a pure water electrolyte. The small self-ionisation of pure water is sufficient at zero-current equilibrium. Practical features such as strong electrolytes can be added as perturbations. [Pg.57]

The above observations are obviously not intended as a rejection of this very useful technique. We shall have numerous opportunities to underline the important contributions made by its judicious exploitation. Perhaps the most interesting application of conductivity in cationic polymerisation relates to measurements in model systems such as the study of the self-ionisation of initiators, the interactions of Lewis acids with cocatalysts, and of course the extent of dissociation of stable carbenium salts. [Pg.37]

The third mechanism which can account for direct initiation involves the self-ionisation of the Lewis acid prior to the attack on the monomer ... [Pg.98]

The obvious explanation of the mechanian of initiation arisii from the self ionisation of Lewis acids, i.e., in the absence of a cwatalyst, is that ccHisisting of the attack... [Pg.117]

Biswas and Kabir rqjorted that benzoyl chloride is an initiator for the polymerisation of vinyl ethers and N-vinylcarbazole. Given the high nucler hilicity of these monomers the above observation is not surprising. The authors envisaged an initiation scheme involving the self-ionisation of the catalyst,... [Pg.215]


See other pages where Self-ionisation is mentioned: [Pg.33]    [Pg.33]    [Pg.222]    [Pg.264]    [Pg.268]    [Pg.283]    [Pg.312]    [Pg.317]    [Pg.323]    [Pg.563]    [Pg.213]    [Pg.2]    [Pg.328]    [Pg.341]    [Pg.131]    [Pg.206]    [Pg.71]    [Pg.251]   
See also in sourсe #XX -- [ Pg.69 ]




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Following Self-Ionisation

Ionisation

Ionised

Lewis acids self-ionisation

Self-ionisation of water

The self ionisation of water

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