Difference between revisions of "Cyclic Voltammetry: Hints and Tips"
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Ethers (including tetrahydrofuran, diethyl ether, 1,4-dioxan, and 1,2-dimethoxyethane), as well as aromatic hydrocarbons (benzene, toluene, xylenes) can be first dried over sodium wire then distilled from freshly drawn sodium wire with a little benzophenone added to the distillation pot. A dark blue or purple color should develop and persist during reflux, for at least 10 minutes, which signals the presence of sodium benzophenone ketyl (a radical anion). The ketyl can only exist in the absence of water and oxygen. The anhydrous solvent can then be distilled. Excess sodium wire is destroyed by allowing the distillation pot to cool and cautiously adding absolute ethanol. | Ethers (including tetrahydrofuran, diethyl ether, 1,4-dioxan, and 1,2-dimethoxyethane), as well as aromatic hydrocarbons (benzene, toluene, xylenes) can be first dried over sodium wire then distilled from freshly drawn sodium wire with a little benzophenone added to the distillation pot. A dark blue or purple color should develop and persist during reflux, for at least 10 minutes, which signals the presence of sodium benzophenone ketyl (a radical anion). The ketyl can only exist in the absence of water and oxygen. The anhydrous solvent can then be distilled. Excess sodium wire is destroyed by allowing the distillation pot to cool and cautiously adding absolute ethanol. | ||
| − | Dichloromethane, 1,2-dichloroethane, cyclohexane, or hexane, can be dried by distillation from either P<sub>2</sub> | + | Dichloromethane, 1,2-dichloroethane, cyclohexane, or hexane, can be dried by distillation from either P<sub>2</sub>O<sub>5</sub>, or from CaH<sub>2</sub>. |
| − | Acetonitrile should be predried using a molecular sieve with a pore size of not greater than 4 Å. Distillation can take place after reflux with a small quantity of | + | Acetonitrile should be predried using a molecular sieve with a pore size of not greater than 4 Å. Distillation can take place after reflux with a small quantity of P<sub>2</sub>O<sub>5</sub> (about 0.5% w/v) to remove the residual water. Avoid using too much P<sub>2</sub>O<sub>5</sub> to prevent excessive formation of an orange polymeric material. |
Dimethyl sulfoxide or dimethylformamide should be predried using a molecular sieve with a pore size of not greater than 4 Å, followed by distillation at reduced pressure (10 – 20 mmHg). | Dimethyl sulfoxide or dimethylformamide should be predried using a molecular sieve with a pore size of not greater than 4 Å, followed by distillation at reduced pressure (10 – 20 mmHg). | ||
Revision as of 13:43, 22 March 2013
Safety
Purification and distillation of solvents should only be undertaken by an experienced chemist or laboratory technician. Incorrect procedures could lead to explosion or fire.
All organic solvents, to a lesser or greater degree, are toxic, and most are flammable. General safety procedures include working in a well ventilated area (a fume hood is usually necessary), with protective clothing including rubber gloves and safety glasses. Adequate ventilation must be ensured about the distillation apparatus to prevent the buildup of flammable and toxic solvent vapours.
Even if the solvent is relatively harmless, most organic solvents can penetrate the skin easily carrying potentially toxic solutes with them. Similarly most electrolytes used with organic solvents are toxic and/or skin irritants. Always familiarize yourself with the potential hazards by reading the MSDS (Materials Safety Data Sheets) available from the suppliers of solvents and electrolytes. Always assume that new compounds (for which no safety data may be available) are toxic and handle them with due care.
Only use the drying agent indicated for that particular solvent. Do NOT mix drying agents.
Solvents may be grossly wet and require predrying before drying with highly reactive drying agents such as sodium wire or phosphorous pentoxide. Appropriate care should be exercised in the handling and disposal of reactive drying agents such as metal hydrides, phosphorous pentoxide, and sodium wire
The constituent ions (both cations and anions) of electrolytes may be toxic and when dissolved in organic solvents they can be carried across the skin. In cases of accidental spillage, where a specific treatment is unknown, contaminated skin areas should be continuously flushed with water for at least several minutes.
Solvents
Ethers (including tetrahydrofuran, diethyl ether, 1,4-dioxan, and 1,2-dimethoxyethane), as well as aromatic hydrocarbons (benzene, toluene, xylenes) can be first dried over sodium wire then distilled from freshly drawn sodium wire with a little benzophenone added to the distillation pot. A dark blue or purple color should develop and persist during reflux, for at least 10 minutes, which signals the presence of sodium benzophenone ketyl (a radical anion). The ketyl can only exist in the absence of water and oxygen. The anhydrous solvent can then be distilled. Excess sodium wire is destroyed by allowing the distillation pot to cool and cautiously adding absolute ethanol.
Dichloromethane, 1,2-dichloroethane, cyclohexane, or hexane, can be dried by distillation from either P2O5, or from CaH2.
Acetonitrile should be predried using a molecular sieve with a pore size of not greater than 4 Å. Distillation can take place after reflux with a small quantity of P2O5 (about 0.5% w/v) to remove the residual water. Avoid using too much P2O5 to prevent excessive formation of an orange polymeric material.
Dimethyl sulfoxide or dimethylformamide should be predried using a molecular sieve with a pore size of not greater than 4 Å, followed by distillation at reduced pressure (10 – 20 mmHg).
