Weygand/Hilgetag Preparative Organic Chemistry

Cleavage of sulfur bonds 671
A simple method of preparing sulfinic esters consists of oxidative chlorination
of aliphatic thiols, thiophenols, or disulfides with chlorine in glacial acetic
acid, followed by alcoholysis of the resulting sulfinyl chlorides: 626
RSSR + 2CH3COOH + 3C12 • > 2RS(O)C1 + 2CH3COC1 -f 2HC1
RS(O)C1 + R'OH • RS(O)OR' + HC1
Chloro(dimethyl)sulfonium salts are readily formed in 92% yield by the
action of chlorine on the dimethyl sulfide-antimony chloride adduct 627 in
methylene dichloride solution:
(CH3)2S -+ SbCl5 + Cl2
• [(CH3)2SCl] + SbCl6-
The chlorine in this reaction may be equally well replaced by sulfuryl chloride
or by an excess of the antimony pentachloride:
Chloro(dimethyl)sulfonium hexachloroantimonate: 627 A solution of dimethyl sulfide (5 g,
80.5 mmoles) in methylene dichloride (20 ml) is dropped, with stirring, during 35 min into
a solution or suspension of antimony pentachloride (25 ml, 195 mmoles) in methylene dichloride
(40 ml) that is cooled in a mixture of methanol and Dry Ice. The mixture is stirred
in the cooling-bath for 24 h, then filtered, and the solid is washed with methylene dichloride
(200 ml). The product (30.6 g, 88%) has m.p. 185-186° (dec.).
Chloro(dimethyl)sulfonium salts are extremely reactive, usually losing the
chlorine as anion and thus able to transfer the dimethylsulfonium group readily
to nucleophilic compounds such as alcohols, compounds containing acidic
CH groups, organic sulfides, and disulfides. 627
III. Cleavage of sulfur bonds
1. Cleavage of the C-S bond 628
Fission of the C-S bond of thiols can occasionally be utilized for preparation
of sulfides:
2RSH • RSR + H2S
The reaction occurs merely on heating, for instance with 2-mercaptoanthraquinones,
629 but better in the presence of substances tha,t bind hydrogen
sulfide; a mixed catalyst composed of cadmium sulfide, zinc sulfide, and aluminum
oxide has been used. 630
Thiiranes can be cleaved by alcohols in the presence of boron trifluoride
and glacial acetic acid, yielding /S-alkoxy thiols; and using thiols affords
2-(alkylthio)ethanethiols. 631 The general procedure is as follows:
A mixture of the thiol (0.11 mole) and boron trifluoride-ether (2 drops) are stirred and
heated on a steam-bath while the sulfide (0.05 mole) is dropped in during about 45 min.
626 I. B. Douglass, /. Org. Chem., 30, 633 (1965).
627 H. Meerwein, K.-F. Zenner, and R. Gipp, Ann. Chem., 688, 67 (1965).
628 D. S. Tarbell and D. P. Harnish, Chem. Rev., 49, 1 (1951).
629 Ger. Pat. 254,561; Chem. Abstr., 7, 1618 (1913).
630 P. J. Wiezevich, L. B. Turner, and P. K. Frohlich, Ind. Eng. Chem., 25, 295 (1933).
631 H. R. Snyder, J. M. Stewart, and J. B. Ziegler, /. Amer. Chem. Soc, 69, 2675 (1947).