The
lithium is washed three times by transferring approximately
150-mL portions of anhydrous ethyl ether (Note
4) into the flask through the serum stopper by forced siphon through a
stainless-steel cannula, stirring the resulting suspension of
lithium briefly, allowing the
lithium to rise to the surface, and finally withdrawing the major part of the underlying ether by forced siphon through a cannula. Anhydrous
ethyl ether (500 mL) is added to the resultant oil-free
lithium.
Methyl chloride gas (bp
−24°C,
d−24°C 0.99 g/mL) from a compressed gas cylinder is passed through a flask containing Linde 4A molecular sieves and into a dry,
100-mL Pyrex graduated cylinder equipped with a
24/40 standard taper joint attached to a
Claisen adapter and
dry ice condenser, and cooled to −24°C with a bath of dry ice–
acetone (.htmFigure 1). When
52.7 mL (52.5 g, 1.04 mol) of liquid methyl chloride has been collected, the adapter and condenser are removed, several boiling chips are added to the cold (−24°C) graduated cylinder, and the cylinder is stoppered with a rubber septum through which is inserted a stainless-steel cannula. The other end of this cannula is inserted through the rubber septum of the flask so that its tip is just above the liquid surface of the reaction flask. Dry ice–
acetone is then added to the condenser attached to the reaction flask. Vigorous stirring of the ethereal
lithium dispersion is begun and the
methyl chloride is added over approximately a 1.5-hr period. The rate at which
methyl chlorideis distilled into the reaction vessel is controlled by slight cooling or warming of the graduated cylinder that contains the liquid
methyl chloride. During addition, the initial grey suspension changes to a brown to purple suspension; by the end of the addition, little, if any,
lithium metal should be seen floating on the surface of the ether solution when stirring is interrupted. After the addition of
methyl chloride is complete, the reaction mixture is stirred at 25°C for an additional 0.5–1 hr and then allowed to stand overnight or longer (Note
5) at 25°C under a static
argon atmosphere, whereupon the precipitated
lithium chloride settles to the bottom of the flask. The dry ice condenser and thermometer are removed from the flask and replaced with rubber septa. The supernatant
methyllithium solution is transferred by forced siphon using a
large-gauge cannula through a glass wool pad (Note
6) into a receiving flask previously flushed with an inert gas
(.htmFigure 2). The receiving flask, which contains the filtrate, a pale-yellow solution of
methyllithium, is removed (Note
7) and stored in a refrigerator for 12–24 hr during, which time an additional small quantity of
lithium chloride separates as fine crystals. The resulting supernatant solution is transferred with a stainless-steel cannula and a slight positive pressure of
argon or
nitrogen into one or more suitable
oven-dried, nitrogen-filled storage bottles capped with rubber septa. Two 1-mL aliquots of the solution are removed with a hypodermic syringe for a modified Gilman titration (Note
8) and a 5-mL aliquot is removed with a hypodermic syringe to determine the halide concentration (Note
9). The solution contains 1.40–1.77
M methyllithium accompanied by 0.07–0.09
M lithium chloride corresponding to a
70–89% yield of
methyllithium. If this solution is protected from
oxygen and moisture, it may be stored at 0–25°C for several months (and remain active).