Submitted by B. B. Corson, Ruth A. Dodge, S. A. Harris, and R. K. Hazen.
Checked by C. S. Marvel and F. E. Kendall.
1. Procedure
In a
12-l. earthenware crock equipped with an
efficient stirrer and a
strong motor are placed
375 g. (2.5 moles) of mandelic acid (p. 336) and 500 cc. of water. The stirrer is started, and a cool solution of
110 g. (2.8 moles) of sodium hydroxide (or 115 g. of technical sodium hydroxide) in 500 cc. of water is added. This is followed by the addition of 2000 g. of cracked ice and then after a few minutes by
275 g. (1.74 moles) of finely ground u.s.p. potassium permanganate in portions over a period of one-half hour. The mixture is stirred for one and one-half hours, the temperature being maintained at −2° to −4°. About 5 kg. of ice is necessary. At the end of one and one-half hours the mixture is tested for excess permanganate by placing a drop on a piece of
filter paper; a black or brown center of
manganese dioxide is formed, a greenish ring around this, and an outer ring which is colorless in the absence and pink in the presence of excess permanganate. Any excess is removed by adding
ethyl alcohol, generally about 200–300 cc.
When the permanganate has been destroyed, the stirrer is stopped and the
manganese dioxide allowed to coagulate for one hour. The mixture is filtered through two
20-cm. Büchner funnels; the filter cakes are washed with 1000 cc. of water (Note
1) and sucked dry again (Note
2). The filtrate is evaporated to 800–1000 cc. over a free flame. While the volume of solution is large, two
30-cm. evaporating dishes are used, but toward the end the two solutions are combined in one dish. The evaporation requires two to three hours. Sometimes a little
manganese dioxide will be coagulated during the evaporation; this should be removed by filtration.
The yellowish solution is transferred to a
3-l. round-bottomed, wide-necked flask and cooled with running water while
300 cc. of concentrated sulfuric acid is added slowly from a
separatory funnel. This acidification process requires thirty minutes, during which time the temperature should not rise much above 25°. The liquid froths and about
30 g. of benzoic acid separates but it is not filtered. Extraction of the reaction mixture with
200-cc. portions of ether until 1500 cc. of extract has been collected is now carried out in a separatory funnel. The
ether is distilled on a
steam bath from a
1-l. round-bottomed, wide-necked flask connected with a
water condenser, the extract being added from a separatory funnel as fast as the
ether distils. After most of the
ether has been removed, the heating is continued for an additional one-half hour.
The crude liquid acid (about 300 g.) is cooled with running water, and
15 cc. of concentrated sulfuric acid is added; the clear yellow oil becomes cloudy. The acid is esterified by passing the vapor of
ethyl alcohol into the hot solution as in the preparation of
ethyl fumarate in Org. Syn.
10, 48, or by the method described for
ethyl cyanoacetate in Org. Syn.
3, 54, with the following changes: all three flasks, the
alcohol flask, the
trap, and the
esterification flask are 1-l. round-bottomed, wide-necked flasks. The alcohol flask and the trap are set on adjacent steam baths. The esterification flask is placed in an
oil bath which is heated by a free flame. A
safety tube leads from the alcohol flask and dips under 7.5 cm. of mercury contained in a side-arm tube. This
mercury safety valve avoids all dangers which might result from the development of excess pressure within the system (Note
3). The temperature of the esterification mixture is kept at 105–110° and
ethyl alcohol vapor is passed through until 500 cc. of distillate has been collected. This requires about three hours. The distillate consists of alcohol, water, and a little
ether.
The crude ester is cooled, an equal volume of
benzene is added, then the free acid is neutralized by shaking with about
250 cc. of a 10 per cent solution of sodium carbonate (Note
4). The
benzene solution is poured into
1300 cc. of a saturated solution of sodium bisulfite (about 60 g. of technical sodium bisulfite per 100 cc.), contained in a
wide-necked bottle equipped with an efficient stirrer, and the mixture stirred for two and one-half hours. The mixture soon warms up a little and becomes semi-solid. It is filtered through a 20-cm. Büchner funnel and carefully washed, first with
200 cc. of a saturated solution of sodium bisulfite, finally with two
150-cc. portions of benzene (Note
5) and (Note
6). The white pearly flakes of the
sodium bisulfite addition product are transferred to a 3-l. round-bottomed, wide-necked flask equipped with a mechanical stirrer and containing 700 cc. of water,
175 cc. of concentrated sulfuric acid, and
500 cc. of benzene. The flask is heated on a steam bath under a
hood, the temperature being kept at 55°, and the mixture is stirred for thirty minutes (Note
7).
The solution is then poured into a separatory funnel, the
benzene separated, and the water layer extracted with a
200-cc. portion of benzene. The combined
benzene solution is shaken with excess of
10 per cent sodium carbonate solution to remove free acid and
sulfur dioxide (Note
8). The
benzene is washed with a little water and then dried over anhydrous
potassium carbonate (Note
9). The
benzene is distilled at ordinary pressure over a free flame from a
500-cc. Claisen flask, the solution being added from a separatory funnel as fast as the
benzene distils. It is advisable to distil the ester under reduced pressure although it can be done under ordinary pressure. The fraction distilling around
118°/5 mm.,
130°/10 mm.,
138°/15 mm.,
148°/25 mm.,
155°35 mm., or
254°/760 mm. is collected. The yield of
ethyl benzoylformate is
155–175 g. (
35–40 per cent of the theoretical amount) (Note
10) and (Note
11).
2. Notes
1. In order to wash the
manganese dioxide cake it must be removed from the funnel and stirred into a thin paste with water.
3. If it is necessary to generate the steam from a can or similar contrivance, the
steam generator should be connected with a safety tube dipping under 20–25 cm. of mercury.
6. If the stirring is not very efficient the
benzene layer should be stirred with the bisulfite solution a second time.
7. Longer contact with acid tends to hydrolyze the ester. The reaction should be performed under a hood since considerable
sulfur dioxide is generated. A
gas-absorption trap (Fig. 7 on p. 97) may be used.
9. The
potassium carbonate holds some ester which may be recovered by adding water and separating the ester layer.
10. The methyl ester is easily made by substituting
methyl for
ethyl alcohol. It boils at
250–255°/760 mm. The yield is about
175 g. (
43 per cent of the theoretical amount).
Since, at this stage, enough water is present to render the acid immiscible with
carbon disulfide, the liquid residue is dried by placing it in a
distilling flask with
70–90 cc. of toluene and distilling off the water and toluene (preferably under slightly reduced pressure). The dried liquid residue is taken up in an equal volume of
carbon disulfide; with adequate precautions to exclude moisture, the solution is cooled thoroughly in an ice-salt mixture. The yield of product melting at
58–61° is
190–250 g. (
50–67 per cent of the theoretical amount). (Charles D. Hurd and R. W. McNamee, private communication. Checked by Reynold C. Fuson and W. E. Ross.)
12. This work was done with the aid of a grant to the submitters from the Cyrus M. Warren fund of the American Academy of Arts and Sciences.
3. Discussion
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