Submitted by Henry Gilman and W. E. Catlin.
Checked by C. S. Marvel and H. R. Snyder.
1. Procedure
In a dry
1-l. three-necked, round-bottomed flask fitted with a
mercury-sealed stirrer, a
500-cc. dropping funnel, and an
efficient reflux condenser to the upper end of which a
calcium chloride tube is attached, is placed
26.7 g. (1.1 atoms) of magnesium turnings. The reaction requires
450 cc. of ether and
118.5 g. (121 cc., 1 mole) of cyclohexyl chloride (Note
1). About
100 cc. of the ether,
15 cc. of the pure halide, and a crystal of
iodine are added to the
magnesium. Heat is applied, without stirring, for five to ten minutes after the
iodine color has disappeared. When reaction has set in, sufficient
ether is added to cover the
magnesium while it is stirred, and the remainder of the halide in
ether is added in one-half to three-quarters of an hour, the flask being cooled with ice water if necessary. When all the halide has been added, stirring and refluxing are continued fifteen to twenty minutes.
The
separatory funnel is now replaced by a
wide glass tube (about 12 mm. internal diameter) which reaches almost to, but not below, the surface of the liquid (Note
2). This tube connects directly with a
500-cc. round-bottomed flask containing
50 g. of paraformaldehyde which has been previously dried for two days in a
vacuum desiccator over
phosphorus pentoxide. This flask contains an
inlet tube for admitting dry
nitrogen. The stirrer is started (Note
3), and the flask containing the
paraformaldehyde is heated in an
oil bath to 180–200°. The
formaldehyde formed by depolymerization (Note
4) and (Note
5) is carried over into the Grignard reagent by a slow current of dry
nitrogen. At the end of about one and three-quarters hours the reaction is complete, as is indicated by a negative color test for Grignard reagent (Note
6).
The reaction mixture is then transferred to a
2-l. wide-necked, round-bottomed flask; 300 g. of cracked ice is added all at once; and the mixture is rapidly agitated until the decomposition is complete (Note
7). Twice the theoretical amount of
30 per cent sulfuric acid is added to dissolve the
magnesium hydroxide, and the mixture is then steam-distilled until no more oil is collected (Note
8). The distillate, which amounts to 1500–2500 cc., is saturated with
sodium chloride and the
ether-
alcohol layer separated. The aqueous layer is extracted with two
100-cc. portions of ether and the
ether extract added to the
ether-
alcohol layer. The
ether solution is dried over anhydrous
potassium carbonate, filtered, and heated carefully on a
steam cone until all the ether is distilled. The crude alcohol is warmed one-half hour with 5 g. of freshly dehydrated lime (Note
9). After filtering and washing the lime with a little ether, the ether is distilled, and then the residual alcohol distilled from a
Claisen flask (Note
10) under reduced pressure. The carbinol distils at 88–93°/18 mm. (practically all distilling at 91°). The yield is
72.5–78.5 g. (
64–69 per cent of the theoretical amount).
2. Notes
2. Since a considerable amount of
formaldehyde repolymerizes on the walls of the side tube, a wide tube is used to prevent clogging. Clogging by deposition of the reaction product is reduced by having the entry tube about 1 cm. above the surface of the solution.
3. Vigorous stirring is desirable as it materially affects the rate of absorption of the gaseous
formaldehyde.
4. The amount of
paraformaldehyde used is considerably in excess of 1 mole since it is difficult to tell when the reaction is complete because of repolymerization. For larger runs, the amount of
paraformaldehyde need not be increased in direct proportion, as the 20 g. excess used here is sufficient to insure complete reaction in a run of almost any size. An excess of
formaldehyde apparently does not decrease the yield provided that the product is steam-distilled from
sulfuric acid solution (Note
8) to hydrolyze the
acetal.
5. If
paraformaldehyde is used directly without depolymerization, the yield is only
40–50 per cent.
6. At the end of about one and one-quarter hours, tests are made at fifteen-minute intervals for the presence of Grignard reagent. The reaction need not be interrupted. About a

-cc. sample is pipetted out for each test. To this is added an equal volume of a
1 per cent solution of Michler's ketone in dry
benzene. The reaction product is then hydrolyzed by the slow addition of 1 cc. of water. The subsequent addition of several drops of a
0.2 per cent solution of iodine in glacial
acetic acid develops a characteristic greenish-blue color when Grignard reagent is present. The reaction is complete when no positive test is obtained for the Grignard reagent.
2
7. The ice must be added all at once so that the mixture stays cold at all times and local overheating does not occur. If this happens, the reaction becomes very vigorous, and the mixture is likely to foam out of the flask.
8. A high-boiling by-product, the
cyclohexylcarbinol acetal of
formaldehyde, is sometimes obtained, and in particularly large quantities if the steam distillation of the reaction mixture is omitted. The by-product can usually be minimized if twice the amount of
10 per cent sulfuric acid calculated to decompose the Grignard reagent is added to the reaction mixture before steam distillation is carried out. The
acetal which may be present is thus hydrolyzed.
9. The heating with freshly dehydrated lime not only removes traces of water, but also gives a product which is entirely free from halogen.
10. It is advisable to use a flask with fractionating side arm
(p. 130).
3. Discussion
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