Submitted by G. G. Urquhart, J. W. Gates, Jr., and Ralph Connor.
Checked by Lee Irvin Smith, R. T. Arnold, and Kenneth Stevenson.
1. Procedure
A mixture of
125 g. (0.5 mole) of n-dodecyl bromide (Note
1),
38 g. (0.5 mole) of thiourea, and
250 ml. of 95% ethanol is refluxed on a
steam cone for 3 hours (Note
2), (Note
3), and (Note
4). A solution of
30 g. (0.75 mole) of sodium hydroxide in 300 ml. of water is added, and the mixture is refluxed for 2 hours. During this period the mercaptan separates as a pink to red oil. The layers are separated, and the aqueous layer is acidified with dilute
sulfuric acid (7 ml. of concentrated acid to 50 ml. of water) and then extracted with one
75-ml. portion of benzene (Note
5). The extract is added to the crude mercaptan layer, and the whole is washed twice with 200-ml. portions of water and then dried over
20 g. of anhydrous sodium sulfate (Note
6). The solvent is removed and the residual oil distilled from a
modified Claisen flask. There is no appreciable fore-run (Note
6). The yield of
n-dodecyl mercaptan, b.p.
165–169°/39 mm., is
80–84 g. (
79–83%) (Note
7) and (Note
8).
2. Notes
2. The intermediate
laurylisothiourea hydrobromide may be obtained by cooling the
ethanol solution in ice and filtering the precipitate. It may be further purified by washing with
ether. An alternative method gives more satisfactory results. The
ethanol solution is diluted with 150 ml. of water and heated until the solution is homogeneous, and then, after cooling slightly,
200 ml. of concentrated hydrochloric acid is added; the
laurylisothiourea hydrochloride separates quantitatively as a waxy white solid.
3. The reflux period required for complete reaction varies considerably with the structure of the halide. Some alkyl bromides require more than 3 hours. Alkyl chlorides frequently require 16 hours and occasionally as much as 24 hours.
4. This procedure is useful for the preparation of other mercaptans. The yields are of the same order. The boiling points are as follows:
5. Although
benzene is the most satisfactory solvent for this extraction, emulsions are sometime produced when it is used for the extraction of other mercaptans. To obviate this difficulty the same amount of ether may be used, provided that the
ethanol is first removed by distillation on a
steam bath.
6. If the
ether extracts are not thoroughly dry, the mercaptan appears slightly cloudy on subsequent distillation. The checkers found that this cloudiness was frequently due to colloidal
sulfur. The
sulfur can be removed by shaking an
ether solution of the cloudy product with bone black, then filtering and distilling.
7. The odor of
lauryl mercaptan is not disagreeable, and no unusual precautions need be taken in working with it. With lower-molecular-weight mercaptans a
trap containing alkaline potassium permanganate solution will prevent the escape of unpleasant odors.
8. Other boiling points:
107–109°/2 mm.;
133–135°/7 mm.;
145–147°/15 mm.;
150–152°/20 mm.;
158–160°/28 mm.;
168–170°/38 mm.
3. Discussion
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