Before any organic synthesis, a risk assessment is carried out. It depends on the difference between two words:A hazard is anything with the potential to cause harm, such as a substance that is flammable, toxic, corrosive, harmful, an irritant, an oxidising agent or carcinogenic.
A risk is the chance that harm will actually occur, and how serious it would be. It depends on how the substance is used: the amount, the concentration, the temperature and the precautions taken.A hazard cannot usually be changed, but the risk can be reduced with control measures:Flammable liquids (ether, ethanol, hydrocarbons): no naked flames; heat with a water bath, heating mantle or electric heater.
Toxic or volatile substances (bromine, halogenoalkanes, hydrogen cyanide): use a fume cupboard.
Corrosive substances (concentrated sulfuric acid, sodium hydroxide): wear gloves and eye protection, and use the lowest concentration that works.
Pressure: never heat a sealed system; leave a reflux condenser open at the top.Other general measures are to use smaller quantities, to replace a hazardous reagent or solvent with a less hazardous one that does the same job, and to know what to do in an accident.Some reactions need extra care. Potassium cyanide is very toxic and produces toxic hydrogen cyanide with acids, so it is used in a fume cupboard with gloves. Grignard reactions use dry ether, which is extremely flammable and forms explosive vapour with air.Worked example: in a nitration, concentrated nitric and sulfuric acids are corrosive (the hazard). The risk is reduced by wearing gloves and goggles, adding the acids slowly with cooling, and working in a fume cupboard.
A risk is the chance that harm will actually occur, and how serious it would be. It depends on how the substance is used: the amount, the concentration, the temperature and the precautions taken.A hazard cannot usually be changed, but the risk can be reduced with control measures:Flammable liquids (ether, ethanol, hydrocarbons): no naked flames; heat with a water bath, heating mantle or electric heater.
Toxic or volatile substances (bromine, halogenoalkanes, hydrogen cyanide): use a fume cupboard.
Corrosive substances (concentrated sulfuric acid, sodium hydroxide): wear gloves and eye protection, and use the lowest concentration that works.
Pressure: never heat a sealed system; leave a reflux condenser open at the top.Other general measures are to use smaller quantities, to replace a hazardous reagent or solvent with a less hazardous one that does the same job, and to know what to do in an accident.Some reactions need extra care. Potassium cyanide is very toxic and produces toxic hydrogen cyanide with acids, so it is used in a fume cupboard with gloves. Grignard reactions use dry ether, which is extremely flammable and forms explosive vapour with air.Worked example: in a nitration, concentrated nitric and sulfuric acids are corrosive (the hazard). The risk is reduced by wearing gloves and goggles, adding the acids slowly with cooling, and working in a fume cupboard.