Safety of chlorination reactions

Acetjiene has found use as a feedstock for production of chlorinated solvents by reaction with hydrogen chloride or chlorine (6). However, because of safety concerns and the lower price of other feedstock hydrocarbons, very Htfle acetylene is used to produce chlorinated hydrocarbons in the United States (see Acetylene-derived chemicals). 

A satisfactory way to accomplish the introduction of chlorine with minimal loss of the gas is to seal the reaction flask with a two-holed stopper equipped with a gas-inlet tube reaching just above the surface of the reaction mixture and an exit tube connected to a U-tube filled with mineral oil which is used as a gas-flow indicator. Chlorine is then introduced from the cylinder through a safety trap at such a rate as to maintain a small positive pressure in the reaction flask. 

Although active safety is provided by the control systems mentioned above, passive safety is an additional important feature of a distributed plant. Due to the low inventory, even a total release of the reaction volume or an explosion would create no significant impact on the environment [139]. To prevent such scenarios, a total containment of the plant is envisaged it needs to be sealed for life . Hydrogen cyanide synthesis and chlorine point-of-sale manufacture are two examples for safety-sensitive distributed syntheses. 

Safety precautions applicable to direct liquid phase fluorination of aromatic compounds are discussed [1]. Attention is drawn to the hazards attached to the use of many newer fluorinating agents [2], In a study of fluorination reactions of hafnium and zirconium oxides by the fluoroxidisers xenon difluoride, chlorine trifluoride and bromine trifluoride, reactivity decreased in the order given [3],... 

SAFETY PROFILE A human poison by ingestion and moderately toxic by inhalation. A poison by ingestion and inhalation experimentally. Corrosive. The action of bromine is essentially the same as that of chlorine, irritating the mucous membranes of the eyes and upper respiratory tract. Severe exposure may result in pulmonary edema. Usually, however, the irritant qualities of the chemical force the worker to leave the exposure area before serious poisoning can result. Chronic exposure is similar to the therapeutic ingestion of excessive bromides. See also BROMIDES. Regular physical examinations should be made of people who work with bromine or bromides. Flammable in the form of liquid or vapor by spontaneous chemical reaction with reducing materials. A... 

Electrolytic chlorine from a steel bottle contains small amounts of oxygen, chlorine oxides, nitrogen, carbon monoxide, carbon dioxide, hydrogen chloride, chlorinated hydrocarbons, and moisture. For complete purification, chlorine washed with concentrated sulfuric acid is condensed into a receiver (preferably calibrated) cooled in ether/carbon dioxide, and a regular stream of chlorine is produced by placing the receiver in a bath of ice and water. A safety flask should be placed between the reaction flask and the chlorine supply. Chlorine bombs cool very considerably if chlorine is removed in a rapid stream they should, if that happens, never be warmed above 30°C (vapor pressure of Cl2 at 0° 3.76 atm, at +10° 5.14, at +20° 6.86, at +30° 8.97, and +40° 11.52 atm). 

The toxicity of phosgene has spawned a lot of research into alternates for both MDI and TDI, as well as polycarbonates. In addition to safety, there are economic incentives for developing alternate routes. In the conventional MDI process, methylene diphenylmethane diamine (MDA) is formed by reacting aniline with formaldehyde. Separating excess aniline from crude MDA is an expensive operation. Also, by-product HCl formed in the conversion of MDA to MDI is an environmental issue. The final isocyanate product contains hydrolyzable chloride compounds that are difficult to separate and dispose of. The reactants must be kept bone dry to prevent corrosion, and the introduction of water can cause a runaway reaction. Similar concerns influence the search for nonphosgene routes for TDl. Conventional routes to polycarbonates also employ phosgene, which produces chlorine waste products, primarily sodium chloride, that present disposal problems. The elimination of chlorine from the polycarbonate process would constitute a major improvement. 

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