Checked by C. F. H. Allen and C. V. Wilson.
1. Procedure
A.
Methyl hydrogen succinate. A mixture of
400 g. (4 moles) of succinic anhydride (Note
1) and
194 ml. (4.8 moles) of methanol (Note
2) in a
1-l. round-bottomed flask is refluxed on a
steam bath. After about 35 minutes the mixture is swirled frequently until it becomes homogeneous (this requires 15–30 minutes); the flask is then half immersed in the
steam bath for an additional 30–25 minutes (Note
3).
The excess
methanol is removed by distillation under reduced pressure (
water pump) from a steam bath, and the residual liquid is poured into an
18- to 25-cm. evaporating dish which is cooled in a shallow pan of cold water. As the half ester crystallizes, it is stirred and scraped off the dish in order to prevent formation of a solid cake. After being dried to constant weight in a
vacuum desiccator (5–8 days), the product weighs
502–507 g. (
95–96%) and melts at
57–58° (Note
4) and (Note
5).
2. Notes
2. Synthetic
methanol was used. Since this anhydrous alcohol is hygroscopic, partly filled bottles that have been opened intermittently in the laboratory should be rejected.
3. Thirty minutes is allowed if solution resulted after 15 minutes of swirling; 25 minutes if 30 minutes was needed for homogeneity.
The time factor is very important. In one run in which the mixture was heated for a total of 55 minutes, a product was obtained which was shown by titration to contain about 6% of anhydride. Longer heating than that specified increases the yield of diester. Any change in quantity of materials used may necessitate a new set of conditions in order to obtain the maximum yield.
4. The checkers prefer the following procedure, which can be carried through in one day. A suspension of approximately one-half of the crude product in
750 ml. of carbon disulfide is warmed on a steam bath; two layers form, in which some solid remains in suspension. This is dissolved by the addition of
350 ml. of ether. The whole is chilled to 0°, and the solid is filtered by suction. The other half of the crude product is now dissolved in this filtrate, the solution is again chilled to 0°, and the solid is filtered. The combined yield of acid ester, m.p.
57–58°, is
438–449 g. (
83–85%). A further
32–37 g. (6–7%) of less pure material (m.p.
56–57°) can be obtained by concentrating the filtrate to half its volume and chilling to 0°.
5. The product, which is sufficiently pure for the next step, contains at least 98%
methyl hydrogen succinate as shown by titration or distillation through an
18-in. Podbielniak-type column.
6. Equipment with ground-glass joints is used throughout.
7. Eastman's
thionyl chloride (b.p.
75–76°) was used. The checkers obtained equivalent yields of the chloride by using only 20% excess of
thionyl chloride. The mixture was heated for 1 hour at 40°, allowed to stand overnight, and heated again for 2 hours at 40°.
8. Since
hydrogen chloride is evolved, it is advisable to work in a
hood or employ a
gas trap.
9. An electric heating mantle is convenient.
10. Other boiling points are
85.5–87°/13 mm. and
89–90°/15 mm. The use of as low a pressure as possible is advisable, since the substance tends to lose
methyl chloride and form
succinic anhydride.
11. The submitter obtained the same yield when
phosphorus pentachloride was used instead of
thionyl chloride. Consistent results were obtained with the former reagent only when the acid chloride was distilled at pressures below 3 mm. (b.p.
58–59°/2.5 mm.).
3. Discussion
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