Chloroform [67-66-3] M 119.4, b 61.2o, d15 1.49845, d10 1.47060, n15 1.44858. It reacts slowly with oxygen, or oxidising agents, when exposed to air
and light, giving, mainly, phosgene, Cl2 and HCl. Commercial CHCl3 is usually stabilized with up to 1% EtOH or of dimethylaminoazobenzene. Simplest
purifications involve washing with water to remove the EtOH, drying with K2CO3 or CaCl2, refluxing with P2O5, CaCl2, CaSO4 or Na2SO4, and distilling.
It must not be dried with sodium. The distilled CHCl3 should be stored in the dark to avoid photochemical formation of phosgene. In an alternative
purification, CHCl3 (500mL) was shaken (mechanically) with several small portions of 12% H2SO4 for 1hour, washed thoroughly with water, saturated
NaHCO3, washed again with water, and dried over CaCl2 or K2CO3 (100g) for 1hour before filtering and distilling. After further drying for a short time
over P2O5, the CHCl3 was redistilled and stored over Drierite in the dark [Reynolds & Evans J Am Chem Soc 60 2559 1938].
EtOH can be removed from CHCl3 by passage through a column of activated alumina, or through a column of silica gel 4-ft long by 1.75-in diameter at a
flow rate of 3mL/minute. (The alumina column, which can hold about 8% of its weight of EtOH, is regenerated by air drying and then heating at 600o for
6hours. It is prepurified by washing with CHCl3, then EtOH, leaving in conc H2SO4 for about 8hours, washing with water until the washings are neutral,
then air drying, followed by activation at 600o for 6hours. Just before use it is reheated for 2hour at 154o.) [McLaughlin et al. Anal Chem 30 1517
1958.] Carbonyl-containing impurities can be removed from CHCl3 by percolation through a Celite column impregnated with 2,4-dinitrophenylhydrazine
(DHNP), phosphoric acid and water. (Prepared by dissolving 0.5g DHNP in 6mL of 85% H3PO4 by grinding together, then mixing with 4mL of distilled water
and 10g of Celite.) [Schwartz & Parks Anal Chem 33 1396 1961]. Chloroform can be dried by distillation from powdered type 4A Linde molecular
sieves. For use as a solvent in IR spectroscopy, chloroform is washed with water (to remove EtOH), then dried for several hours over anhydrous CaCl2
and fractionally distilled. This treatment removes material absorbing near 1600 cm-1. (Percolation through activated alumina increases this absorbing
impurity). [Goodspeed & Millson Chem Ind (London) 1594 1967, Beilstein 1 IV 42.]
Rapid purification: Pass through a column of basic alumina (Grade I, 10g/mL of CHCl3), and either dry by standing over 4A molecular sieves, or
alternatively, distil from P2O5 (3% w/v). Store away from light (to avoid formation of phosgene) and use as soon as possible. |
