Perchlorates, dangers

Salts. In addition to the dangers of perchlorate salts, other salts such as nitrates, azides and diazo salts can be hazardous and due care should be taken when these are dried. Large quantities should never be prepared or stored for long periods. 

Barium perchlorate. Expensive. Used in desiccators (covered with a metal guard). Unsuitable for drying solvents or organic material where contact is necessary, because of the danger of EXPLOSION... 

Ferric perchlorate (9H2O) [13537-24-1] M 516.3, pK -2.4 to -3.1 (for HCIO4). Crystd twice from cone HCIO4, the first time in the presence of a small amount of H2O2 to ensure that the iron is fully oxidised [Sullivan J Am Chem SocS4 4256 7962]. Extreme care should be taken with this preparation because it is potentially DANGEROUS. 

Danger warning Mists of perchloric acid can condense in the exhausts of fume cupboards and lead to uncontrolled explosions So dipping is to be preferred. 

Warning of danger The perchloric acid-containing reagent should not be employed as a spray solution for reasons of safety. 

M.B. Powder (Modified Black Powder). Consisted of BkPdr in which part of the K nitrate was replaced by K perchlorate. The finely pulverized ingredients were preliminarily mixed, as in the prepn of BkPdr, and then incorporated together in a steam jacketed pan. The last operation was dangerous and some fires occurred, which were ascribed to friction in the hot, dry caked material. A similar expl was called Roslin Giant Powder Ref Marshall 1,385 (1917)... 

Use of perchloric acid gives the perchlorate. However, the perchlorate is so dangerously explosive that its use should be avoided.3... 

Perchloric acid, HC104, is prepared by the action of concentrated hydrochloric acid on sodium perchlorate, followed by distillation. It is a colorless liquid and the strongest of all common acids. Because chlorine has its highest oxidation number, +7, in these compounds, they are powerful oxidizing agents contact between perchloric acid and even a small amount of organic material can result in a dangerous explosion. 

The ketenides separate as insoluble, infusible solids. The perchlorate derivative II (Y = CIO4) is dangerously explosive. 

Sodium hypochlorite could also be dangerous when hot, and alkaline chlorites also in this case however it is not guaranteed that the acid character of this example is sufficient to form chlorine dioxide. Caution is still required when handling these mixtures to which chlorates and perchlorates can be added. 

Chlorine is one of the strongest oxidants whether it is in the elementary form or as oxidised anions, with oxidation states of +l (hypochlorites) to +VII (perchlorates). The chloride ion with an oxidation state of -I is very stable (octet electronic structure) only hydrochloric acid is dangerously reactive, linked to its strongly acidic character. This explains the nature of the dangerous reactions which have already been described and have caused a large number of accidents. The accidental aspect is aggravated by the fact that the derivatives mentioned in this paragraph are much used. 

Hypochlorites, chlorites, chlorates and perchlorates all represent the same dangers, which are linked to the fact that they are strong oxidants. The danger is not directly linked to the importance of the oxidation state of chlorine atom and this is partly for kinetic reasons. The main factors of the accidents described in the technical literature are not the intrinsic properties of each anion, but rather the frequency with which they are used. So chlorates and perchlorates are more often involved in accidents than hypochlorites and especially chlorites, which are hardly used. Thus the classification below does not provide positive indications about the dangerous properties of each substance mention. ... 

Their properties and many of their uses are very similar and their dangerous reactions are the same. Perchlorates seem more stable than chlorates. 

When hot, ammonia and compounds, which contain nitrogen-hydrogen bonds eg ammonium salts and cyanides react violently with chlorates and alkaline perchlorates. Diammonlum sulphate, ammonium chloride, hydroxyl-amine, hydrazine, sodamide, sodium cyanide and ammonium thiocyanate have been cited. So far as hydrazine is concerned, the danger comes from the formation of a complex with sodium or lithium perchlorate, which is explosive when ground. Many of these interactions are explosive but the factors which determine the seriousness of the accident are not known. 

Nickei powder gives rise to dangerous reactions, which has led to accidents with potassium perchlorate (ignition), with chlorine at 600°C (ignition) and with ammonium nitrate at about 200°C (detonation). It catalyses the explosive decomposition of hydrogen peroxide. 

Antimony (III) salts are thought to give rise to dangerous reactions with perchloric acid. There is no detail regarding the nature of the dangers. 

All other dangerous reactions consist of oxidations of bismuth by strong oxidants. Thus, chloric and perchloric acids lead to highly sensitive explosives (probably bismuth chlorate and perchlorate). Fuming nitric acid causes the incandescence of bismuth at ambient temperature whereas a detonation occurs when molten bismuth is mixed with concentrated nitric acid. Rnally, a bismuth/molten ammonium nitrate mixture causes a very violent or even an explosive reaction. 

Benzene and toluene form complexes with some salts these complexes are often very unstable. With silver perchlorate, benzene gives rise to a complex that leads to very dangerous benzenic solutions. Besides, it detonates when it is ground up. its enthalpy of formation corresponds to -3.4 kJ/g, which makes it dangerous according to the CHETAH criterion (see para 2.3.2). 

Except with nitric acid, most dangerous reactions are those of alcohols with perchloric acid or its salts (that can form acid). All accidents reported are caused by the formation of highly unstable organic perchlorates. 

Similar accidents have happened when barium perchlorate is added to to C3 alcohols as well as 1 -octanol. The latter alcohol demonstrates the nature of this danger and is a counter-example of the typical observation of stabilisation of unstable species, when the number of carbon atoms increases (whereas it is the case for peroxides and peracids). 

With perchloric acid, the following dangerous reactions have been reported ... 

With DMSO and aliphatic sulphoxides, dry perchloric acid also forms very unstable salts. If the acid concentration is 70% or more, when it comes into contact with DMSO, this gives rise to an immediate explosion. Aromatic sulphoxides give rise to far less dangerous interactions. 

Before nitrates and particularly ammonium nitrate were readily available commercially, explosives were developed based on chlorates and perchlorates. These also are still used in some countries. In general perchlorates are considered less dangerous than chlorates and therefore preferred. They are easily sensitised, so that in addition to explosives of this type based on nitroglycerine, others have been based on various organic liquids, particularly nitrobodies. History shows that chlorates and perchlorates must be regarded as temperamental substances, liable in bulk to lead to inexplicable accidents. Particularly when mixtures of chlorates and oxidising materials are allowed to become wet and then dry out, conditions can arise in which there is an appreciable sensitiveness to friction and impact. Explosives of this type have an unfortunate record of accidents. They are used, therefore, to a limited extent only, now that safer compositions are available. 

Silver perchlorate forms solid complexes with aniline, pyridine, toluene, benzene and many other aromatic hydrocarbons [1], A sample of the benzene complex exploded violently on crushing in a mortar. The ethanol complex also exploded similarly, and unspecified perchlorates dissolved in organic solvents were observed to explode [2], Solutions of the perchlorate in benzene are said to be dangerously explosive [3], but this may be in error for the solid benzene complex. The energy released on decomposition of the benzene complex has been calculated as 3.4 kJ/g, some 75% of that for TNT [4],... 

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. 

The improved preparation of 1,4-octadecanolactone [1] involves heating oleic acid (or other Ci8 acids) with 70% perchloric acid to 115°C. This is considered to be a potentially dangerous method [2],... 

The crystalline salt obtained by action of phosphine on 68% perchloric acid at —20°C is dangerously explosive, sensitive to moist air, increase in temperature, or friction [1] and cannot be dried [2],... 

As the anhydride of nitrous and perchloric acids, it is a very powerful oxidant. Pinene explodes sharply acetone and ethanol ignite, then explode ether evolves gas, then explodes after a few s delay. Small amounts of primary aromatic amines-aniline, toluidines, xylidines, mesidine-ignite on contact, while larger amounts exploded dangerously, probably owing to rapid formation of diazonium perchlorates. Urea ignites on stirring with the perchlorate, (probably for a similar reason). 

Reaction with epoxides gives the dangerously unstable and explosive mixed nitrate-perchlorate diesters, such as 1,2-ethanediyl nitrate perchlorate from ethylene oxide. 

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