Perchloric acid

Perchloric acid can be produced by electrolysis or by a ion exchange mechanism using a resin.
See: Trans. Electrochem. Soc. 75, 271 - 78 (1939) for electrolysis method.
US Patent No. 2,392,861 describes the industrial production of Perchloric acid using NaClO4 and HCl.
Also US Patent No. 1271633 describes making Perchloric acid from HCl by electrolysis.
There is a discussion regarding Perchloric acid manufacture at: http://www.sciencemadness.org/talk/viewthread.php?tid=12&page=1

The acid is extremely corrosive and is very damaging to tissue. It will form explosive mixtures with anything combustible and these mixtures may ignite or detonate without warning. The usual strength of the acid is 72%wt where it forms a constant boiling point azetope. The 70% acid is fairly stable, the anhydrous acid (100%) will explode of its own accord if stored for a period of time. It can only be stored indefinitely at liquid air temperatures.

Preparation

The following is from JACS 15 page 15 (1910)
The Perchlorate must be free from Chlorate.
A saturated solution of Sodium Perchlorate was poured into two and one half times its volume of pure HCl (density 1.20). After thorough agitation the Sodium Chloride was allowed to settle, the the clear liquid was siphoned off, and the Sodium Chloride drained in a funnel by suction, and washed with a little more acid. The solution containing HCl and Perchloric acid, with a little salt of Na was evaporate until dense white fumes of Perchloric acid began to appear. The liquid was found to be completely free from HCl. At this point the concentration of the Perchloric acid is approx. the density of the dihydrate, about 70%.
The acid above may contain small amounts of NaClO4 which may ppt out of solution. The acid can be distilled (use a Kieldahl bulb) if necessary.
It is not advisable to store Perchloric Acid, make and use as required.

See THE PREPARATION OF PERCHLORIC ACID. by H. H. WILLARD in 'Further Reading' section.

Uses of Perchloric acid

Perchlorates are the salts of Perchloric acid. Most of the Perchlorates can be produced by Perchloric acid and the Chloride or Nitrate of the metal and heating to drive off the HCl or HNO3 formed.
All of the Perchlorates can be formed by reacting the appropriate Hydroxide or Carbonate with the acid. This method of production is not used because of the expense of Perchloric acid compared to Sodium Perchlorate, but it gives very pure Perchlorates.

Further reading

A A Zinov'ev, "PERCHLORIC ACID", RUSS CHEM REV, 1963, 32 (5), 268-282 here (1.9M pdf).

Dangers

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A violent explosion took place in an exhaust duct from a laboratory hood in which
perchloric acid solution was being fumed over a gas plate. It blew out windows,
bulged the exterior walls, lifted the roof, and extensively damaged equipment and
supplies. Some time prior to the explosion, the hood had been used for the
analysis of miscellaneous materials. The explosion apparently originated in
deposits of perchloric acid and organic material in the hood and duct.

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An employee dropped a 7-lb bottle of perchloric acid solution on a concrete floor.
The liquid was taken up with sawdust and placed in a covered, metal waste can.
Four hours later, a light explosion blew open the hinged cover of the can.

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A stone table of a fume hood was patched with a glycerin cement and several
years latter, when the hood was being removed, the table exploded when a
workman struck the stone with a chisel.

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During routine maintenance involving partial dismantling of the exhaust blower on
a perchloric acid ventilating system, a detonation followed a light blow with a
hammer on a chisel held against the fan at or near the seal between the rear
cover plate and the fan casing. The intensity of the explosion was such that is
was heard four miles away and of the three employees in the vicinity, one
sustained face laceration and slight eye injury; the second suffered loss of four
fingers on one hand and possible loss of sight in one eye; the third was fatally
injured with the 6 in. chisel entering below his left nostril and embedded in the
brain. 

[K. Everett and F.A. Graf Jr. Handling Perchloric Acid and Perchlorates. In: N.V.
Steere, ed. Handbook of Laboratory Safety. Second Edition - 1971.]



--
donald j haarmann - eminence grise

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