Perchloric acid initiation

In 1968 Plesch and Westermann [131] published a report of 1,3-dioxo-lane polymerization in their adiabatic calorimeter under vacuum in CH2 CI2 with anhydrous perchloric acid as initiator. They confirmed that the polymerization can be an equilibrium involving only monomer and polymer without side reactions. For a one molar solution the ceiling temperature was found to be 1°C, - —18.6 1.2 cal deg mole  

Note that the propagating species here is a secondary oxonium ion. Transfer presumably involves the transfer of a proton from one cyclic species to another. Conductivity studies [129] of a HCIO4 initiated polymerization in a dilatometer indicate a polymerization with no induction period, but with an acceleration stage, and a first order stage. 

Shortly after Plesch and Westermann s work was published, Jaacks et al. [132] also reported a study of the polymerization of 1,3-dioxolane by HCIO4 in CH2CI2 at 20°C. Again the need for the most rigorous absence of water is emphasized [133]. They found a gradual but quantitative initiation reaction with no kinetic termination reaction. Eventually from further studies [134] they concluded that the slow initiation involves two reactions 

One involves protonation of the monomer and the other protonation of the polymer. They conclude that the second reaction must have a higher rate coefficient. Further, when initiation is fineilly complete, propagation occurs exclusively through tertiary oxonium ions. If monomer is added to such a system, they propose that the conversion—time curve is no longer S-shaped but linear, represented by the equation 

Jaacks et al. terminated the polymerizations by adding sodium alkoxide 

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Xenon Fluoro Perchlorate. (Xenon (II) fluoride perchlorate). FXea04 mw 249.75 colorl solid, red liq mp 16.5° (decompn) bp, detonates when heated rapidly above 20°. Sol in acetonitrile, Prepn is by reacting Xe difluoride with perchloric acid initially at —110°, then to reaction completion at —60°... 

In solution, the nature of the protonation agent affects the site of protonation of enamines267-269. The hard hydronium ion, such as is formed in 70% perchloric acid, initially leads at low temperature to the kinetically favoured N protonation, whereas the softer carboxylic acids, where the proton is situated on an uncharged oxygen, preferentially attack the softer base site, namely the /7-carbon atom, leading to C protonation and hence to the thermodynamically favoured product. 

Initially, Gandini and Plesch proposed that the perchloric acid-initiated low temperature polymerization of styrene is based on monomer insertion on the nonionic perchlorate chain ends, which was based on the observation that the polymerization mixture was not conductive [68, 69]. These nonionic polymerizations were referred to as pseudo-cationic polymerizations. However, more detailed investigations by stopped-flow UV-vis spectroscopy revealed the presence of short-lived carbocations indicating that these are the propagating species in the cationic polymerization of styrene [70, 71]. This was also confirmed for the polymerization of styrene with trifiic acid for which Matyjaszewski and Sigwalt showed that the covalent triflic ester adduct was unstable even at -78 °C leading to carbocationic propagating species [72]. 

In the temperature range from 0 to 30 °C, on the other hand, the perchloric acid-initiated polymerization of styrene follows a stationary-state kinetics, giving a linear first-order plot for monomer consumption Based on the absence of UV absorptions... 

X is an acidity function based on the first-order approximation, Eq. (8-92). Values of X have been assigned by an iterative procedure. The data consist of values of Cb/cbh+ as functions of Ch+ for a large number of indicators. For each indicator an initial estimate of pXbh+ and m is made and X is calculated with Eq. (8-94). This yields a large body of X values, which are fitted to a polynomial in acid concentration. From this fitted curve smoothed X values are obtained, and Eq. (8-94), a linear function in X. allows refined values of pXbh + and m to be obtained. This procedure continues until the parameters undergo no further change. Table 8-20 gives X values for sulfuric and perchloric acid solutions. ... 

By monitoring the intensity of the carbonyl absorption it was observed that oxidation of methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexopyrano-side with chromium trioxide-pyridine at room temperature gave initially the hexopyranosid-3-ulose (2) in low concentration, but attempts to increase this yield resulted in elimination of methanol to give compound 3. However, when methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexo-pyranoside is oxidized by ruthenium tetroxide in either carbon tetrachloride or methylene dichloride it affords compound 2 without concomitant elimination. When compound 2 was heated for 30 minutes in pyridine which was 0.1 M in either perchloric acid or hydrochloric acid it afforded compound 3, but in pyridine alone it was recoverable unchanged (2). Another example of this type of elimination, leading to the introduction of unsaturation into a glycopyranoid ring, was observed... 

Kinetics studies of acid-catalysed chlorination by hypochlorous acid in aqueous acetic acid have been carried out, and the mechanism of the reactions depends upon the strength of the acetic acid an<( the reactivity of the aromatic. Different groups of workers have also obtained different kinetic results. Stanley and Shorter207 studied the chlorination of anisic acid by hypochlorous acid in 70 % aqueous acetic acid at 20 °C, and found the reaction rate to be apparently independent of the hydrogen ion concentration because added perchloric acid and sodium perchlorate of similar molar concentration (below 0.05 M, however) both produced similar and small rate increases. The kinetics were complicated, initial rates being proportional to aromatic concentration up to 0.01 M, but less so thereafter, and described by... 

The variation in the second-order rate coefficients with time and with change in initial concentration of mercuric salt can also be explained on the basis of equilibria (213) and (214). At low acidities, conversion of mercuric acetate to acetoxymercury perchlorate is incomplete, and, therefore, decreasing the concentration of the acetate increases the concentration of free perchloric acid which thus increases the conversion of the acetate into the more reactive perchlorate, hence the second-order rate coefficients increase. Decreasing the concentration of mercuric perchlorate will, however, decrease the concentration of free perchloric acid and this effect will be particularly marked since solvation of the perchlorate produces two equivalents of perchloric acid the second-order rate coefficients will, therefore, decrease. In both cases, substitution changes the concentration... 

The rate of reduction of Tl(III) by Fe(II) was studied titrimetrically by John-son between 25 °C and 45 °C in aqueous perchloric acid (0.5 M to 2.0 M) at i = 3.00 M. At constant acidity the rate data in the initial stages of reaction conform to a second-order equation, the rate coefficient of which is not dependent on whether Tl(III) or Fe(II) is in excess. The second-order character of the reaction confirms early work on this system . A non-linearity in the second-order plots in the last 30 % of reaction was noted, and proved to be particularly significant. Ashurst and Higginson observed that Fe(III) retards the oxidation, thereby accounting for the curvature of the rate plots in the last stages of reaction. On the other hand, the addition of Tl(l) has no significant effect. On this basis, they proposed the scheme... 

The burning mechanism of composite propellants differs from that described above. There is no exothermic reaction which can lead to a self-sustaining fizz zone. Instead, the first process appears to be the softening and breakdown of the organic binder/fuel which surrounds the ammonium perchlorate particles. Particles of propellant become detached and enter the flame. The binder is pyrolysed and the ammonium perchlorate broken down, initially to ammonia and perchloric acid. The main chemical reaction is thus in the gas phase, between the initial dissociation products. 

Elliot, M. A. et al., Kept. Invest. No. 4169, Washington, US Bin. Mines, 1948 Tests of sensitivity to initiation by heat, impact, shock or ignition sources were made on mixtures of a variety of absorbent materials containing a stoicheiometric amount of 40-70% perchloric acid. Wood meal with 70% acid ignited at 155°C and a mixture of coal and 60% acid which did not ignite below 200° C ignited at 90° C when metallic iron was added. Many of the mixtures were more sensitive and dangerous than common explosives. 

Dining preparation of iron(II) perchlorate, a mixture of iron sulfate and perchloric acid was being strongly heated when a most violent explosion occurred. Heating should be gentle to avoid initiating this redox system. 

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