Org. Synth. 1948, 28, 49
DOI: 10.15227/orgsyn.028.0049
2,4-DIMETHYLQUINOLINE
[Quinoline, 2,4-dimethyl-]
Submitted by W. R. Vaughan
1
Checked by Richard T. Arnold and Horace R. Davis, Jr..
1. Procedure
A. "Acetone-anil" (Note 1). A mixture of 279 g. (3 moles) of aniline and 9 g. of iodine is placed in a 1-l. three-necked round-bottomed flask. The flask is fitted with a dropping funnel (the delivery tube of which extends below the liquid surface), a mercury-sealed stirrer (Note 2), and an adapter carrying a thermometer which extends into the liquid and a condenser system such that most of the aniline will return and all the water produced (as well as excess acetone) will distil (Note 3). The flask is now heated in an oil bath (Note 4) and (Note 5), and the reaction mixture is maintained at 170–175° while acetone is passed in through the dropping funnel at such a rate that no more than 2 drops of liquid distils per second. During the addition the mixture is vigorously stirred. A total volume of 850 ml. (670 g., 11.6 moles) of acetone is added over a 4-hour period, and about 610 ml. of distillate is collected. At the end of this period the reaction mixture is cooled and distilled in vacuum, three fractions being collected (up to 136°/15 mm., 136–141°/15 mm., and 141–146°/15 mm.). The acetone-water distillate is now distilled through a simple column at atmospheric pressure until essentially all the acetone has come over. There remains a mixture of oil and water which is separated after being cooled. The oil is then used as the first fraction for a fractional distillation in vacuum of the reaction product, each of the previous fractions being added in succession. Three new fractions are collected: 78–82°/13 mm. (a little aniline); 82–133°/13 mm. (a small intermediate fraction); and 133–138°/13 mm. (acetone-anil). An appreciable quantity of tarry residue remains in the distillation flask. The yield based upon aniline actually consumed in the reaction is 61–68% (Note 5).
B. 2,4-Dimethylquinoline. A small quantity of copper powder (Note 6) is added to 4.6 g. (0.2 gram atom) of sodium metal (small pieces) and 56 g. (0.6 mole) of dry aniline (Note 7) contained in a 1-l. round-bottomed flask. The mixture is warmed carefully over a low flame until the evolution of hydrogen ceases, at which time the mixture is usually black. A few boiling chips and 346 g. (2 moles) of acetone-anil are then added. The resulting mixture is heated at the reflux temperature (220–230°) until the evolution of gas (methane) ceases (Note 8). At the end of the reaction the mixture is cooled and then distilled in vacuum. The fraction boiling at 135–140°/12 mm. weighs 252–283 g. (80–90%) (Note 9).
2. Notes
1.
The so-called
acetone-anil has been assigned the structure indicated in accordance with the work of Craig.
22.
A convenient
stirrer may be made from tantalum wire as described by Hershberg.
33.
A
Liebig condenser in reflux position is heated with steam and connected at the top to a water-cooled downward condenser.
4.
For a reaction temperature of 170–175° the oil is best maintained at about 200° during the addition of the
acetone.
5.
The reaction may be carried out at any temperature from 70° to 175°. At lower temperature it is much slower and is best carried out by refluxing the theoretical quantities of
acetone and
aniline with
iodine catalyst for an extended time. Regardless of the time or reaction temperature, if due allowance is made for
aniline reclaimed at the end of the reaction the yield falls between the limits indicated. At the higher temperature, equilibrium is attained more rapidly, as would be expected, and relatively little
aniline is recovered. (A typical run may yield
40 g. of
aniline and
297 g. of "anil," with 11 g. of middle fraction.)
6.
The exact amount of
copper powder used as a catalyst in the preparation of the
sodium salt of
aniline is not important. Approximately 0.2 g. has been found to be satisfactory in runs of the size described.
7.
Aniline which has been recently distilled is satisfactory. An excess of
aniline over the
sodium is used to minimize decomposition of the
2,4-dimethylquinoline.
28.
The time required for the decomposition of the
acetone-anil varies from 3 to 6 hours. The checkers, however, found that essentially all the
methane is eliminated after 2 hours.
9.
Fractionation of 245 g. of this product through a 14-plate Lecky-Ewell
4 column yielded
6 g. of
aniline, 3 g. of an intermediate fraction, and
218 g. (
89%) of
2,4-dimethylquinoline, b.p.
149–150°/20 mm. (controlled). If the material is to be nitrated, the crude product is quite satisfactory.
3. Discussion
The present procedure for the preparation of
acetone-anil is described by Reddelien.
5 A reaction at lower temperature is reported by Craig,
2 who also describes the alkaline decomposition of the anil to
2,4-dimethylquinoline and
methane and gives a method of purification of the final product. Other methods for the preparation of
2,4-dimethylquinoline involve the Beyer
6 synthesis from
aniline hydrochloride and
ethylidene acetone, a modification of this synthesis,
7 a synthesis using
2-chloro-2-pentenone-4,
8 and the Combes synthesis from
acetylacetone and
aniline.
9
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
acetone-anil
aniline (62-53-3)
hydrogen (1333-74-0)
aniline hydrochloride (142-04-1)
copper powder (7440-50-8)
iodine (7553-56-2)
acetone (67-64-1)
methane (7782-42-5)
sodium (13966-32-0)
Acetylacetone (123-54-6)
2,4-DIMETHYLQUINOLINE,
Quinoline, 2,4-dimethyl- (1198-37-4)
ethylidene acetone (625-33-2)
2-chloro-2-pentenone-4
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