Nitrobenzene safety

Health nd Safety Factors. The mononitrochlorobenzenes are toxic substances which may be absorbed through the skin and lungs giving rise to methemoglobin. Their toxicity is about the same as or greater than that of nitrobenzene. The para isomer is less toxic than the ortho isomer, and the maximum allowable concentration that has been adopted for -nitrochlorobenzene is 1 mg/m (0.1 ppm) (6). The mononitrochlorobenzenes are moderate fire hazards when exposed to heat or flame. They ate classified by the ICC as Class-B poisons. The same handling precautions should be used for these compounds as are used for nitrobenzene. 

Health and Safety Factors. The toxic effects of the mononitrotoluenes are similar to but less pronounced than those described for nitrobenzene. The maximum allowable concentration for the mononitrotoluenes is 2 ppm (11 mg/m ) (6). Mononitrotoluenes are low grade methemoglobin formers (4) and may be absorbed through the skin and respiratory tract. The toxicity of alkyl nitrobenzenes decreases with an increasing... 

Though safer than the decomposition of pure, solid diazonium tetrafluoroborates, dediazoni-ation of these compounds mixed with inert solid salts cannot be scaled up to a large extent since heat exchange through large quantities of powdered solids rapidly becomes difficult. Thus, dediazoniation of arenediazonium tetrafluoroborates suspended in inert fluids is an alternative proposition.13105 141 175-219 220 In addition to the safety improvement, lower quantities of tar are formed using this technique. The inert fluid can be ligroin,143 petroleum ether,147 Decalin,3 or simple aromatic compounds,1-3,5,131-221 such as toluene, xylene, biphenyl, nitrobenzene,177 or quinoline. Simple esters have also been used as solvents in the dediazoniation... 

Catalytic reduction of aromatic nitro compounds to the amines is highly exothermic (AH = —548 12 kJ/mol) and has high potential for hazard in the event of cooling- or other process-failure. The total reaction proceeds via nitroso and hydroxylamino intermediates, both of which are reactive and may undergo undesired condensation or disproportionation reactions, and the thermochemistry of all these possibilities was investigated. The reduction or disproportionation of the hydroxylamino intermediate (which is of low thermal stability) is identified as the fastest and most exothermic step (despite which it can frequently be concentrated or trapped) implications for process safety are considered in detail and verified by experiment with typical compounds and intermediates [1]. A calorimetric study of the hazards inherent in hydrogenation of nitroaromatics was made, using nitrobenzene as model compound [2]. Individual incidents of this type are ... 

At present the nitration of benzene is one of the simplest processes in the organic chemical industry. Nevertheless, the safety factor should not be neglected. The explosion in Rummelsburg of the plant for the nitration of benzene to nitrobenzene, described earlier (p. 152), was the result of defective operation of the nitrator. 

ACGIH TLV TWA 2 mg(Al)/m3 DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE Moderately toxic by ingestion. Experimental teratogenic and reproductive effects. Mutation data reported. The dust is an irritant by ingestion, inhalation, and skin contact. Highly exothermic polymerization reactions with alkenes. Incompatible with nitrobenzenes or nitrobenzene + phenol. Highly exothermic reaction with water or steam produces toxic ftimes of HCl. See also ALUMINUM COMPOUNDS, CHLORIDES, and HYDROCHLORIC ACID. 

DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE Poison by inhalation. Moderately toxic by ingestion. A severe eye, skin, and mucous membrane irritant. Corrosive to body tissues. Flammable by chemical reaction. Explosive reaction with chlorine dioxide + chlorine, sodium, urea + heat. Reacts to form explosive products with carbamates, 3 -methyl-2-nitroben2anilide (product explodes on contact with air). Ignites on contact with fluorine. Reacts violently with moisture, CIO3, hydroxyl-amine, magnesium oxide, nitrobenzene, phosphorus(III) oxide, K. To fight fire, use CO2, dry chemical. Incompatible with aluminum, chlorine dioxide, chlorine. 

The feed consists of 3 to 7% HNO3, 59 to 67%H2S04, and 28 to 37% water. Sulfuric acid is necessary to adsorb the water and energy generated by the heat of reaction. The plant, which produces 15,000 lb nitrobenzeneUi, requires one or two operators per shift together with a plant supervisor and part-time foreman. This exothermic reaction is carried out essentially adiabatically, so that the temperature of the feed stream rises from 90°C to 135°C at the exit. One observes that the nitrobenzene stream from the separator is used to heat the benzene feed. However, care must be taken so that the temperature never exceeds 190°C, where secondary reactions could result in an explosion. One of the safety precautions is the installation of rehef valves that will rupture before the temperature approaches 190°C, thereby allowing a boil-off of water and benzene, which would drop the reactor temperature. 

Infrared photometers designed to monitor the concentration of air pollutants, such as carbon monoxide, nitrobenzene, vinyl chloride, hydrogen cyanide, and pyridine, are often used to ensure compliance with regulations established by the Occupational Safety and Health Administration (OSHA). Interference filters, each designed for the determination of a specific pollutant, are available. These transmit narrow bands of radiation in the range of 3 to 14 p,m. 

Matheson D. 1972. Nitrobenzene. In Encyclopaedia of occupational health and safety. Vol. 2. New York, NY McGraw-Hill Book Company, 1448-1449. 

NIOSH. 1977. Nitrobenzene-method S217. In NIOSH manual of analytical methods. Vol 3. Cincinnati, OH National Institute for Occupational Safety and Health, S217-1-S217-9. 

For safety, mixtures of nitrobenzene with aluminum chloride or alkali hydroxide should not be heated above 100°. 

The synthesis had a series of disadvantages, like a poor regioselectivity in the Friedel-Crafts acylation, in which the 1-isomer is also produced, accompanied by educts and by-products with safety-critical properties (nitrobenzene, sodium hydride, methyl iodide, sulfide salts) and an undesirable waste disposal problem, demanding a different synthetic path for the larger production scale. 

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