Org. Synth. 1965, 45, 12
DOI: 10.15227/orgsyn.045.0012
D,L-10-CAMPHORSULFONIC ACID (REYCHLER'S ACID)
Submitted by Paul D. Bartlett and L. H. Knox
1.
Checked by John D. Roberts and Dinshaw Patel.
1. Procedure
In a 3-l., three-necked, round-bottomed flask fitted with a powerful slow-speed stirrer having a Teflon® blade, a 500-ml. dropping funnel, and a thermometer arranged to dip into the liquid is placed 588 g. (366 ml., 6 moles) of concentrated sulfuric acid. The flask is surrounded by an ice-salt mixture, the stirrer started, and 1216 g. (1170 ml., 12 moles) of acetic anhydride (Note 1) is added at such a rate that the temperature does not rise above 20° (Note 2). The separatory funnel is removed and 912 g. (6 moles) of coarsely powdered D,L-camphor is added (Note 3). The flask is then closed with a stopper and stirring is continued until the camphor is dissolved. The stirrer is replaced by a stopper, the ice bath allowed to melt, and the mixture left to stand for 36 hours (Note 4). The camphorsulfonic acid is collected on a suction filter and washed with ether (Note 5). After being dried in a vacuum desiccator at room temperature, the nearly white crystalline product weighs 530–580 g. (38–42%). It melts at 202–203° with rapid decomposition and is relatively pure (Note 6).
2. Notes
1.
If the
acetic anhydride is of a good commercial grade, it need not be redistilled.
2.
When the temperature is allowed to rise above 20°, the acetic-sulfuric anhydride mixture acquires a yellow to orange color from which discolored crystals are subsequently deposited. The addition, which must be slow at first, requires 1–1.5 hours depending on the efficiency of the
cooling bath.
3.
The
camphor employed is of the synthetic variety supplied by Howe and French, Boston. If an optically active product is desired, active natural
camphor may be used.
4.
The yields vary with the length of the crystallization period. After 16 hours the yield is
470 g. (
34%). When the crystallization period is extended to 2 weeks, the yield is
615–655 g. (
44–47%).
5.
The checkers found the product to be very hygroscopic, in fact deliquescent, in a reasonably humid atmosphere. In such circumstances, it was preferable to decant the mother liquor from the crystals in the flask and to wash the solid by stirring it up with four
250-ml. portions of anhydrous ether, each washing being removed by decantation. The well-drained residual solid can then be transferred to a
crystallizing dish and the
ether removed by pumping under reduced pressure before the final drying in a
vacuum desiccator over
sulfuric acid.
6.
The product can be purified with some loss by recrystallization from
glacial acetic acid. About
60 g. of crude product dissolves in
90 ml. of acetic acid at 105° and gives a recovery of about
40 g. of purified material.
3. Discussion
The procedure described is that of Reychler.
24. Merits of the Preparation
D,L-10-Camphorsulfonic acid is used for the preparation of the corresponding chloride (
p. 196). The optically active acid has been used widely for the resolution of basic compounds into optical antipodes.
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
REYCHLER'S ACID
sulfuric acid (7664-93-9)
acetic acid (64-19-7)
ether (60-29-7)
acetic anhydride (108-24-7)
camphor (21368-68-3)
10-CAMPHORSULFONIC ACID,
camphorsulfonic acid,
D,L-10-CAMPHORSULFONIC ACID (5872-08-2)
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