In
organosulfur chemistry, thiosulfinate is a
functional group consisting of the linkage R-S(O)-S-R (R are organic substituents). Thiolsulfinates are also named as alkanethiosulfinic (or arenethiosulfinic) acid esters.
They are the first of the series of functional groups containing an oxidized
disulfide bond. Other members of this family include
thiosulfonates (R-SO2-S-R), α-disulfoxides (R-S(O)-S(O)-R), sulfinyl sulfones (R-S(O)-SO2-R), and α-disulfones (R-SO2-SO2-R), of which all (except α‑disulfoxides[2]) are known. The thiosulfinate group can occur in cyclic as well as acyclic structures.[3][4][5]
Occurrence
A variety of acyclic and cyclic thiosulfinates are found in plants, or formed when the plants are cut or crushed.
Zeylanoxides are cyclic thiosulfinates containing the 1,2-
dithiolane-1-oxide ring, isolated from the tropical weed Sphenoclea zeylanica. These heterocyclic thiosulfinates are
chiral at carbon as well as at sulfur.[8]
Crushing the roots of Petiveria alliacea affords the thiosulfinates S-(2-hydroxyethyl) 2-hydroxyethane)thiosulfinate, S-(2-hydroxylethyl) phenylmethanethiosulfinate, S-benzyl 2-hydroxyethane)thiosulfinate and S-benzyl phenylmethanethiosulfinate (petivericin; PhCH2S(O)SCH2Ph).[9] Asparagusic acid S-oxide[10] and brugierol[11] are other natural 1,2-dithiolane-1-oxides occurring in Asparagus officinalis and Bruguiera conjugata, respectively.
Properties
Allicin, S-benzyl phenylmethanethiosulfinate, and related thiosulfinates show radical-trapping
antioxidant activity associated with easy formation of sulfenic acids[12] The acyclic thiosulfinates from Allium and Brassica species possess antimicrobial, antiparasitic, antitumor and cysteine protease inhibitory activity while the natural 1,2-dithiolane-1-oxides are growth inhibitors. The thiosulfinates from Petiveria also exhibit antimicrobial activity.[13]
Thiosulfinates feature a S(IV) center linked to a S(II) center, the former being
stereogenic. Conversion of simple disulfides to thiosulfinates results in a considerable weakening of the S–S bond from about 70 to 34.5 kcal mol−1 (16.7 to 8.25 kJ mol−1) for the S-S bond in PhS(O)SPh,[14] with the consequence that most thiosulfinates are both unstable and quite reactive. For this reason the mixtures of thiosulfinates from Allium plants can best be separated by
HPLC at room temperature rather than by
gas chromatography (GC), although GC has been used with some low molecular weight thiosulfinates. Thiosulfinates can be distinguished from
sulfoxides by
infrared spectroscopy since they have a characteristic S=O band at about 1078 cm−1 compared to 1030–1060 cm−1 in sulfoxides.[15]
Formation and reactions
Synthetic thiosulfinates were first reported in 1947 by Cavallito and coworkers by
oxidation of the corresponding disulfides.[16]
One example of a moderately stable thiosulfinate is the tert-
butyl derivative, (CH3)3CS(O)SC(CH3)3. This thiosulfinate can be obtained in optical purity by catalytic
asymmetric oxidation of di-tert-butyl disulfide with
hydrogen peroxide.[17] Upon heating, (CH3)3CS(O)SC(CH3)3 decomposes into tert-butanethiosulfoxylic acid (CH3)3CSSOH) as shown by trapping studies.[18]
In a similar manner racemic methyl methanethiosulfinate (CH3S(O)SCH3) can be obtained by
peracetic acid oxidation of
dimethyl disulfide.[19] Methyl methanethiosulfinate decomposes thermally giving methanesulfenic acid (CH3SOH), the simplest
sulfenic acid, as well as
thioformaldehyde (CH2=S). Methyl methanethiosulfinate can also disproportionate to a 1:1 mixture of dimethyl disulfide and methyl methanethiosulfonate (CH3SO2SCH3) and rearrange via a
Pummerer rearrangement to CH3S(O)CH2SSCH3.[20][21]
An unusual three-membered ring thiosulfinate (a dithiirane 1-oxide) has been prepared through rearrangement of a 1,3-
dithietane.[22] A related compound, 3-(9-triptycyl)dithiirane-1-oxide, was prepared by the reaction of (9-triptycyl)diazomethane and S8O. The
X-ray structure of the dithiirane-1-oxide reveals a significantly lengthened sulfur-sulfur bond (211.9(3)pm).[23]
Thiosulfinates have also been invoked as intermediates in the oxidation of
thiols to
sulfonic acids.
References
^See
sulfoxide for discussion and references regarding the bonding in divalent monooxosulfur structures.
^Block, S. S.; Weidner, J. P. (1966) [1 Sept 1964]. "Vibrational behavior and structure of disulfide dioxides (thiolsulfonates)". Applied Spectroscopy. 20 (2).
doi:
10.1366/000370266774386272.
^Kice JL (1980). "Mechanisms and reactivity in reactions of organic oxyacids of sulfur and their anhydrides". Advances in Physical Organic Chemistry. 17: 65–181.
doi:
10.1016/S0065-3160(08)60128-8.
ISBN9780120335176.
^Takata, T; Endo, T (1990). "Thiosulphinic acids and esters". The Chemistry of Sulphinic Acids, Esters and Their Derivatives, S. Patai, Ed. (John Wiley, NY): 527–575.
doi:
10.1002/9780470772270.ch18.
ISBN9780470772270.
^Braverman, S; Cherkinsky, M.; Levinger, S. (2007). "Alkanethiosulfinic Acid Esters". Sci. Synth. 39: 229–235.
^Kubec, R; Cody, RB; Dane, AJ; Musah, RA; Schraml, J; Vattekkatte, A; Block, E (2010). "Applications of DART Mass Spectrometry in Allium Chemistry. (Z)-Butanethial S-Oxide and 1-Butenyl Thiosulfinates and their S-(E)-1-Butenylcysteine S-Oxide Precursor from Allium siculum". J. Agric. Food Chem. 58 (2): 1121–1128.
doi:
10.1021/jf903733e.
PMID20047275.
^Block, E; Dane, AJ; Thomas, S; Cody, RB (2010). "Applications of Direct Analysis in Real Time–Mass Spectrometry (DART-MS) in Allium Chemistry. 2-Propenesulfenic and 2-Propenesulfinic Acids, Diallyl Trisulfane S-Oxide and Other Reactive Sulfur Compounds from Crushed Garlic and Other Alliums". J. Agric. Food Chem. 58 (8): 4617–4625.
doi:
10.1021/jf1000106.
PMID20225897.
^Block, E (1972). "The Chemistry of Alkyl Thiosulfinate Esters. III. tert-Butanethiosulfoxylic Acid". J. Am. Chem. Soc. 94 (2): 644–645.
doi:
10.1021/ja00757a060.
^Moore, TL; O'Connor, DE (1966). "The Reaction of Methanesulfenyl Chloride with Alkoxides and Alcohols. Preparation of Aliphatic Sulfenate and Sulfinate Esters". J. Org. Chem. 31 (11): 3587–3592.
doi:
10.1021/jo01349a027.
^Block, E; O'Connor, J (1974). "The Chemistry of Alkyl Thiosulfinate Esters. VI. Preparation and Spectral Studies". J. Am. Chem. Soc. 96 (12): 3921–3929.
doi:
10.1021/ja00819a033.
^Block, E; O'Connor, J (1974). "The Chemistry of Alkyl Thiosulfinate Esters. VII. Mechanistic Studies and Synthetic Applications". J. Am. Chem. Soc. 96 (12): 3929–3944.
doi:
10.1021/ja00819a034.
^Ishii, A; Akazawa, T; Ding, MX; Honjo, T; Nakayama, J; Hoshino, M; Shiro, M (1993). "First isolable dithiiranes: 3-(1,1,3,3-tetramethyl-4-oxo-4-phenylbutyl)-3-phenyldithiirane 1-oxides". J. Am. Chem. Soc. 115 (11): 4914–4915.
doi:
10.1021/ja00064a072.
^Ishii, A; Kawai, T; Noji, M; Nakayama, J (2005). "Synthesis and reactions of a monosubstituted dithiirane 1-oxide, 3-(9-triptycyl)dithiirane 1-oxide". Tetrahedron. 61 (28): 6693–6699.
doi:
10.1016/j.tet.2005.05.017.