Precautions against explosions

Health and Safety Factors. Both pyromellitic acid and its dianhydride irritate skin, eyes, and mucous membranes, and they cause skin sensitization (156). When it comes in contact with moist tissue the dianhydride converts to the acid. Direct contact with should be avoided and protective clothing should be worn in areas where it is used. The LD q for intergastric administration in rats is 2.2—2.6 g/kg (157). In 6-mo experiments, the maximum nontoxic dose was 0.07 mg/kg/d, and it affected the fiver, kidney, and reproductive tract. Precautions against fire and dust explosions as explained in the terephthafic acid section should be foUowed. 

Ensure all precautions against fire or explosion are taken during carriage. 

HS(G)103 Safe handling of combustible dusts precautions against explosions... 

If oil is pressurized by compressed air, an explosive hazard exists. If high-pressure air encounters the oil, it may create a diesel effect, which may result in an explosion. A carefully followed preventive maintenance plan is the best precaution against explosions. 

Aryl and vinyl nitriles have been prepared very efficiently from the corresponding bromides by palladium-catalyzed reactions under microwaves. This energy source has been employed for the conversion of these nitriles into aryl and vinyl tetrazoles by cycloaddition reactions with sodium azide (Scheme 9.66). The direct transformation of aryl halides to the aryl tetrazoles in a one pot procedure could be accomplished both in solution and on a solid support [115], The reactions were complete in a few minutes, a reaction time considerably shorter than those previously reported for the thermal reactions. The cydoadditions were performed with sodium azide and ammonium chloride in DMF and, although no explosion occurred in the development of this work, the authors point out the necessity of taking adequate precautions against this eventuality. 

Caution. Opening of the Carius tube after completion of the heating must be carried out with suitable precaution against explosion, using heavy-duty safety gloves and protected by an explosion shield. The entire assembly should be placed in a well-ventilated hood. 

As a safety precaution against EXPLOSION (in case the purification has been insufficiently thorough) at least a quarter of the total volume of ether should remain in the distilling flask when the distillation is discontinued. To minimize peroxide formation, ethers should be stored in dark bottles and, if they are liquids, they should be left in contact with type 4A Linde molecular sieves, in a cold place, over sodium amalgam. The rate of formation of peroxides depends on storage conditions and is accelerated by heat, light, air and moisture. The formation of peroxides is inhibited in the presence of diphenylamine, di-tert-butylphenol, or other antioxidant as stabilizer. 

Trifluoromethyl hypofluorite is generally used at low temperatures with reactants dissolved in an inert solvent, but to increase the solubility of reactants a cosolvent (MeOH, acetone, THF) is often used however, it must be used with extra caution and appropriate safety precautions against explosions and fires, since trifluoromethyl hypofluorite is a powerful oxidizing agent. The toxicity of trifluoromethyl hypofluorite is expected to be high (as with fluorine). Fluori-nation reactions with trifluoromethyl hypofluorite have been discussed in the last twenty years in review papers6 11,65 and several monographs.12" 14... 

Caution Sodium hydride causes severe burns if brought into contact with the skin and, in the dry state, is pyrophoric. Since hydrogen is evolved during the course of the reaction, the necessary precautions against fire and explosion should be taken. 

During isolation of the di-A-oxide of 2,5-dimethylpyrazine [1] and of the mono-A-oxide of 2,2-bipyridyl [1], prepared by action of hydrogen peroxide in acetic acid on the heterocycles, violent explosions occurred on evaporation of the excess peroxy-acetic acid. In the preparation of 3-bromopyridine A-oxide, the necessity to take adequate precautions against the possibility of explosion while vacuum distilling off excess reagents from a water bath maintained at 50°C is stressed [3]. For a method not involving this considerable explosion risk,... 

Consequently, manufacturers handling such fine powders must take special precautions against fires and explosions. 

Precautions against explosions caused by dust or solvents are often a difficult task. Figure 153.1 describes three possible solutions. They include an inert gas closed loop (Figure 153.1(a)), design of the vessel to withstand the maximum (e.g. 7 bar) expected pressure (Figure 153.1(b)), or design of the vessel for increased pressure (e.g. 2 bar) and explosion vents (Figure 153.1c). 

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