Oxidation by Chemical Manganese Dioxide. Part 2.1 Simple and High-yielding Synthesis of Symmetrical Disulfides via the Oxidative Coupling of Thiols†

Abstract

Aromatic, aliphatic, and alicyclic thiols readily underwent oxidative coupling with chemical manganese dioxide in hexane to afford the corresponding disulfides in essentially quantitative yields under relatively mild conditions.

On benzo[b][1,4]diazepinium-olates, -thiolates and -carboxylates as anti-Hückel mesomeric betaines

“…Catalytical hydrogenation of 13 in the presence of Raney-nickel immediately yielded the symmetric disulfide 14 via the monomeric form on exposure to air in 54% yield (Scheme 5). This dimerization with atmospheric air in alkaline media has also been observed with other aromatic thiols 24 and can be monitored by the spontaneous formation of a nonpolar spot on the TLC. Correspondingly, the molecular peak is found at m/z = 279.1 amu (M ϩ H ϩ ) in ESI mass spectrometry.…”

“…The bond distances between C(2) and C (3), and between C(3) and C(4) were determined to be 1.384(3) and 1.394(3) Å, respectively, and are longer than corresponding bond lengths in reported molecules. 24,25 As the bond distances between the vinamidinium chromophore and the benzene ring are very large [N(1)-C(11) 1.419(2) Å; N(5)-C(6) 1.426(2) Å] for C(sp 2 )-N-bonds, there obviously is no considerable electronic interaction between these two parts of the molecule. This result strongly confirms, that the 4n π-mesomeric betaines described here contains isolated cationic and anionic segments as in VI (Scheme 2), and that the charges are exclusively restricted to separate parts of the conjugated system.…”

“…The resulting solid was purified by recrystallization from water to give 8 as pale brown needles (0.225 g, 74%); mp 198-200 ЊC (Found: C, 55.0; H, 5. (24), 119 (10) and 80 (11).…”

“…The mixture was then poured into water (400 cm 3 ) and extracted with ethyl acetate (2 × 100 cm 3 ). The combined organic extracts were washed with brine, dried over magnesium sulfate, and evaporated to give 13 as a red solid (2.08 g, 68%); mp 99-100 ЊC (Found: C, 42.2; H, 3.5; N, 16 (24), 119 (10) and 80 (11).…”

Selective and Simple Phase Transfer Catalyzed Synthesis of Disulfides from Thiols

“…1 The main type of these reactions is the oxidation of thiols in the presence of molecular oxygen, 2À4 DMSO, 5Y6 metal oxide, 7 metal ions, 8 nitric oxide, 9 sodium perborate, 10 thallium(III) acetate, 11 bromine, 12 iodine, 13 borohydride exchange resin, 14 calcium hypochlorite and silica gel, 15 DMSO/alumina, 16 and NaIO 3 /alumina, 17 MnO 2 . 18 We have developed two novel and simple phase transfer catalytic (PTC) methods for the synthesis of aliphatic, aromatic and heterocyclic disul¢des (2a^g) from the corresponding thiols (1a^g) (see Experimental). Both methods included oxidation of thiols (1a^f) by CBr 4 /solid u P gy Q /18-crown-6/benzene (method A, Scheme 1) or by sodium thiolates (1d,g) by CBr 4 /18-crown-6/toluene (method B) (Table 1).…”