Perchloric acid fume cupboards

Perchloric Acid Fume Cupboards Use of concentrated perchloric acid gives rise to special hazards and these special fume cupboards should be for perchloric acid use only. Contact of hot perchloric acid with organic materials and certain metals (especially copper) can lead to the formation of perchlorates which,... 

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. 

Note. Evaporation with perchloric acid or perchlorates should be carried out in a fume cupboard which is kept clean and free from combustible materials. In the presence of carbon and easily oxidisable organic compounds a violent explosion may occur on heating. The determination is not suitable for the beginner and should only be carried out by an experienced analyst. 

Thomas, R. N., Univ. Safety Assoc. Safety News, 1981, 15, 16-17 Failure of the product (0.5 g) to crystallise out from the aqueous DMF reaction liquor led to vacuum evaporation of the solution at 60-70°C. Dining evaporation the mixture exploded violently, shattering the fume cupboard sash of toughened glass. The product may well be thermally unstable, but reaction of DMF with excess warm perchloric acid, possibly in near-absence of water, may also have been involved. 

Fume cupboards or their vent lines which have frequently been used with perchloric acid have often spontaneously deflagrated or exploded because of spillage or absorbed vapour. 

Perchloric acid. This can react violently with organic material such as cork, cloth, rubber or wood. In addition the fumes which are readily evolved from the liquid acid are easily absorbed by these substances which are thus rendered violently flammable or explosive. For this reason, perchloric acid should not be stored in a wood-framed fume cupboard or near to any organic material. 

Contact of the hot concentrated acid or the cold anhydrous acid with cellulose (as paper, wood fibre or sawdust, etc.) is very dangerous and may cause a violent explosion. Many fires have been caused by long-term contact of diluted acid with wood (especially in fume cupboards) with subsequent evaporation and ignition [1,2]. Contact of cellulose acetate with 1200 1 of uncooled anhydrous acid in acetic anhydride led to a particularly disastrous explosion [1], and interaction of benzyl cellulose with boiling 72% acid was also explosive [3], Perchlorate esters of cellulose may have been involved in all these incidents. 

Chemistry does not limit itself to spaces called reactors. Considerable quantities of dust, mist, and vapours may be transferred to vent lines and fumehood ducts, possibly accumulating and reacting there for years. In consequence fires and explosions can start, or blockages form. Vent lines would be better for occasional scrubbing down. See Perchloric acid Fume cupboards See Silver nitrate Sodium dithionite... 

Acid digestion must be conducted in a fume cupboard with efficient scrubbers installed. The evaporation of perchloric acid should be performed only in an appropriate stainless steel, stoneware, or PP hood, with washing facilities to eliminate any perchlorate deposit. 

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