Perchloric acid, decomposition

Solymosi, F. et al., Proc. 14th Combust. Symp., 1309-1316, 1973 The mixed oxide (copper chromite) was the most effective of several catalysts for the vapour-phase decomposition of perchloric acid, decomposition occurring above 120°C. 

Several common acid treatments for sample decomposition include the use of concentrated nitric acid, aqua regia, nitric—sulfuric acids, and nitric perchloric acids. Perchloric acid is an effective oxidant, but its use is ha2ardous and requkes great care. Addition of potassium chlorate with nitric acid also assists in dissolving any carbonaceous matter. 

Physical Properties. Aqueous chloric acid is a clear, colorless solution stable when cold up to ca 40 wt % (1). Upon heating, chlorine [7782-50-5] CI2, and chlorine dioxide [10049-04-4] CIO2, may evolve. Concentration of chloric acid by evaporation may be carried to >40% under reduced pressure. Decomposition at concentrations in excess of 40% is accompanied by evolution of chlorine and oxygen [7782-44-7] and the formation of perchloric acid [7601-90-3], HOCl, in proportions approximating those shown in equation 1. 

The decomposition of the carbonate may be effected with dilute hydrochloric acid, dilute perchloric acid, or phosphoric(V) acid. The last-named acid is perhaps the most convenient because of its comparative non-volatility and the fact that the reaction can be more easily controlled than with the other acids. If dilute hydrochloric acid is employed, a short, water-cooled condenser should be inserted between the decomposition flask and the absorption train (see below). 

A considerable amount of research has been conducted on the decomposition and deflagration of ammonium perchlorate with and without additives. The normal thermal decomposition of pure ammonium perchlorate involves, simultaneously, an endothermic dissociative sublimation of the mosaic crystals to gaseous perchloric acid and ammonia and an exothermic solid-phase decomposition of the intermosaic material. Although not much is presently known about the nature of the solid-phase reactions, investigations at subatmospheric and atmospheric pressures have provided some information on possible mechanisms. When ammonium perchlorate is heated, there are three competing reactions which can be defined (1) the low-temperature reaction, (2) the high-temperature reaction, and (3) sublimation (B9). 

Microscopic examination has shown [102,922] that the compact nuclei, comprised of residual material [211], grow in three dimensions and that the rate of interface advance with time is constant [922]. These observations are important in interpreting the geometric significance of the obedience to the Avrami—Erofe ev equation [eqn. (6)] [59,923]. The rate of the low temperature decomposition of AP is influenced by the particle ageing [924] and irradiation [45], the presence of gaseous products [924], ammonia [120], perchloric acid [120] and additives [59]. 

Several alkali chlorates and perchlorates undergo fusion during the onset of decomposition, the autocatalytic character of reaction then being attributable to the greater rate of reaction in the melt. Khorunzhii and II in [849], from work on the reactions of Na+ and K+ salts of chloric and perchloric acids, conclude that surface and grain boundary diffusion exert an essential role in decomposition rate control. 

V-chloro compounds have also been used for the preparation of sulphones from sulphoxides. /V-chlorosuccinimide(NCS) oxidizes sulphoxides in aqueous acetic acid and acetic acid-perchloric acid mixtures. In purely aqueous media, the reaction is very slow and marked decomposition of the NCS occurs with no oxidation being evident105. 

Although the oxidation of Cr(lII) by Ce(lV) is a rapid reaction in perchlorate solutions, the oxidation of Cr(III) by Co(III) in the same media occurs at a rate similar to or slower than that of the thermal decomposition of Co(lll) in perchloric acid (3 M). However, the Co(lII)- -Cr(III) reaction is subject to catalysis by Ag(I) ion and Kirwin et al have made a kinetic study of this system, viz. 

Although Ce(IV) oxidation of carboxylic acids is slow and incomplete under similar reaction conditions , the rate is greatly enhanced on addition of perchloric acid. No kinetics were obtained but product analysis of the oxidations of -butyric, isobutyric, pivalic and acetic acids indicates an identical oxidative decarboxylation to take place. Photochemical decomposition of Ce(IV) carbo-xylates is highly efficient unity) and Cu(ll) diverts the course of reaction in the same way as in the thermal oxidation by Co(IIl). Direct spectroscopic evidence for the intermediate formation of alkyl radicals was obtained by Greatorex and Kemp ° who photoirradiated several Ce(IV) carboxylates in a degassed perchloric acid glass at 77 °K in the cavity of an electron spin resonance spectro-... 

A lipid was extracted from a methanol/chloroform mixture, the solution obtained was then treated with 1.5 cm of 72% perchloric acid. This led to a violent detonation, which was explained by the decomposition of methyl perchlorate. 

Boron trifluoride in aqueous dioxan had been treated by three successive portions of nitric acid. After this treatment the medium was heated to eliminate boron trifluoride by vapourisation. Finally, perchloric acid was added, which caused detonation. It was explained by the decomposition of one of the two compounds below ... 

Glycols and their ethers undergo violent decomposition in contact with 70% perchloric acid. This seems likely to involve formation of the glycol perchlorate esters (after scission of ethers) which are explosive, those of ethylene glycol... 

In view of the ready commercial availability and apparent stability of the hexahy-drate, it is probable that the earlier report of explosion on impact, and deflagration on rapid heating [1] referred to the material produced by partial dehydration at 100°C, rather than the hexahydrate [2], The caked crystalline hydrated salt, prepared from aqueous perchloric acid and excess cobalt carbonate with subsequent heated evaporation, exploded violently when placed in a mortar and tapped gently to break up the crystalline mass, when a nearby dish of the salt also exploded [3]. Subsequent investigation revealed the probable cause as heating the solid stable hexahydrate to a temperature ( 150°C) at which partial loss of water produced a lower and endothermic hydrate (possibly a trihydrate) capable of explosive decomposition. This hazard may also exist for other hydrated metal perchlorates, and general caution is urged [4,5],... 

The use of the perchlorate as desiccant in a drybag where contamination with organic compounds is possible is considered dangerous [1], Magnesium perchlorate ( Anhydrone ) was inadvertently used instead of calcium sulfate (anhydrite) to dry an unstated reaction product before vacuum distillation. The error was realised and all solid was filtered off. Towards the end of the distillation, decomposition and an explosion occurred, possibly owing to the presence of dissolved magnesium perchlorate, or more probably to perchloric acid present as impurity in the salt [2]. 

Studies of the decomposition of this substance have been carried out in order to further understanding of the mechanism of the deflagration of ammonium perchlorate440 and of the reactions occurring in perchloric acid fuel flames441. 

Some wet dissolution/decomposition reagents such as hydrofluoric or hydrochloric acid may have strong completing action. Very often, the complex formed may prevent the determination proper from being performed, because it is kinetically or thermodynamically very stable. In many cases the dissolution/decomposition reagents are used to destroy an organic substrate. For example, the use of nitric-perchloric or nitric-sulphuric-perchloric acid mixtures is well known. 

The impact which was made by the writer s revival of the old ester mechanism in the context of polymerisations is attested by the number of polymer chemists who set about examining the validity of the theory experimentally. For example, Bywater in Canada confirmed that during the progress of a polymerisation of styrene by perchloric acid the acid could not be distilled out of the reaction mixture, but after exhaustion of the monomer it could be. This regeneration of the initiating acid after the consumption of the monomer is an often attested characteristic of pseudocationic polymerisations with many different protonic acids it is most simply explained by the decomposition of the ester to an alkene and the acid, i.e., a reversal of the initiation, when the monomer has been consumed. Enikolopian in the USSR found that the effect of pressure on the rate of polymerisation in the same system was not compatible with the propagation step involving an ion, and... 

Methylene dichloride [6] and perchloric acid [7] were purified and dosed as described. Silver perchlorate (BDH) was treated in vacuo for a few hours before use. 1-Phenylethyl bromide (Eastman-Kodak) was fractionally distilled under high vacuum and the middle fraction was collected into breakable phials since this compound undergoes a slow decomposition, yielding hydrogen bromide and styrene, when kept in bulk, solutions of it in methylene dichloride were prepared from the original phials by the tipping technique [7]. Styrene was purified [8], dried, and stored [9] as described. Shortly before use it was vacuum-distilled into breakable phials from a microburette. 

Methyl, ethyl and propyl perchlorates, readily formed from the alcohol and anhydrous perchloric acid, are highly explosive oils, sensitive to shock, heat and friction [1], Many of the explosions which have occurred on contact of hydrox-ylic compounds with cone, perchloric acid or anhydrous metal perchlorates are attributable to the formation and decomposition of perchlorate esters [2,3,4], Safe procedures for preparation of solutions of 14 sec-alkyl perchlorates are described. Heated evaporation of solvent caused explosions in all cases [5], l-Chloro-2-propyl, iram-2-chlorocyclohexyl, l-chloro-2-propyl, 1,6-hexanediyl, hexyl, and 2-propyl perchlorates, prepared by a new method, are all explosive oils [6],... 

Two arguments can he put forward in favour of wet chemical decomposition methods in open vessels, firstly, price, and, secondly, sample throughput. A wet decomposition can, if necessary, be performed with a beaker and a heating plate, whereas apparatus for modem high performance decompositions can cost as much as 25 000. With respect to sample throughput, the automatic wet digestion device can be used for up to 1 SO samples per hour for some materials. Such throughput cannot be realized by any other method. Some special cases exist that necessitate decomposition in open vessels (for instance, when the sample needs to be treated with perchloric acid). 

Wet chemical decomposition in a closed system, with nitric acid or mixed acids consisting of nitric acid, hydrochloric acid, perchloric acid, hydrogen peroxide and hydrofluoric acid. The following devices are available ... 

---