Organic Syntheses, Coll. Vol. 7, p.124 (1990); Vol. 61, p.74 (1983).
Caution! This procedure should be carried out in an efficient hood to prevent exposure to alkane thiols.
A mixture of 46.5 g (0.26 mol) of cyclododecanone (Note 1)
, 24.1 g (21.5 mL, 0.26 mol) of 1,2-ethanedithiol (Note 1)
, and 0.75 g (0.004 mol) of p-toluenesulfonic acid monohydrate (Note 2)
, in 200 mL of toluene (Note 3)
is placed in a 500-mL, three-necked reaction flask
equipped for reflux under
a water separator
The mixture is heated at reflux for several hours until the theoretical amount of water (0.26 mol = 4.6 mL) has collected in the Dean-Stark trap
. The reaction mixture is cooled and transferred to a separatory funnel
. The mixture is washed with water, the toluene
is removed on a rotary evaporator
, and the residue is placed under reduced pressure (< 0.1 mm) for several hours to remove traces of solvent. Approximately 66 g
) of a white solid is recovered (0.26 mol, mp 84–86°C). The crude material is pure by GLC and TLC, and is used in the next step with no further purification.
B. Cyclododecyl mercaptan.
In a 1-L, three-necked, round-bottomed flask
equipped with a mechanical stirrer
and nitrogen inlet and outlet stopcocks
are placed 25.8 g (0.10 mol) of 1,4-dithiaspiro[4.11]hexadecane
and 300 mL of ether
, freshly distilled from sodium
. The mixture is purged with nitrogen
, cooled to 0°C with an ice bath
, and 125 mL (0.30 mol, 2.4 M in hexane) of butyllithium
is added by syringe (Note 4)
, (Note 5)
under a slow flow of nitrogen
. The light-yellow mixture is then allowed to warm to room temperature and stirred overnight with nitrogen stopcocks closed (Note 6)
. The reaction mixture is cooled to 0°C and 50 mL of water is added slowly and very carefully (Note 7)
. The resulting light brown solution is poured into 200 mL of water in a separatory funnel
and, after shaking, the organic layer is separated. The solution is dried over MgSO4
, concentrated (aspirator), and distilled through a 10-cm Vigreux column
at 103–108°C (1 mm) to give 17.2–17.9 g
) of pure cyclododecyl mercaptan (Note 8)
, (Note 9)
. A small forerun, bp < 95°C, (ca. 2 mL) is discarded.
The submitters used butyllithium from Alfa Products, Ventron Corporation
The reaction also occurs well with only 2 mol of butyllithium
, but traces of starting material remain.
The reaction is complete in about 6 hr.
The distilled cyclododecyl mercaptan
has the following spectral data: 1
H NMR (CCl4
) δ: 1.1 (d, 1 H, J
= 6, S-H
), 1.32 (broad s, 20 H), 1.64–1.82 (m, 2 H), 2.81 (m, 1 H, CH
SH); IR (neat, μ) 3.4, 6.82, 6.94. Anal. calcd. for C12
S: C, 71.93; H, 12.07; S, 16.00. Found: C, 71.83; H, 12.19; S, 16.03.
Mercaptans are generally prepared by displacement reactions.3
However, secondary or hindered mercaptans are more difficult to obtain. The dithiolane cleavage reaction4
is a convenient "in situ" generation of thioketones which are known to be reduced5
to secondary mercaptans by β-hydrogen transfer. Table I shows a number of mercaptans prepared from saturated
thioketals in 78–90% yields. The aryl example gives lower yields partly because of ring metalation.
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