Baumann-Fromm disulfides

The dissociation of 28 by path A is exemplified by the reactions of the l,2-dithiol-3-ones (30a) ( Baumann-Fromm disulfides 48) and of the trithiones (30b) with halogens. 

This nucleophilic substitution in the trithione ring calls to mind Boberg s report10 85 that halogen substituents in the 5-position of Baumann-Fromm disulfides are also susceptible to displacement by nucleophilic reagents such as amines. 

No reactions of either 1,2-dithiolium salts or trithionium salts with hydroxylamine have been described in the literature. The explanation in the case of the trithionium salts is probably the fact that the expected condensation products, i.e., the oximes of the Baumann-Fromm disulfides, can be obtained via the trithiones themselves2 this is one of the few examples in which trithiones react with carbonyl reagents without undergoing cleavage of the 1,2-dithiole ring. 

According to NMR measurements, the dissolution of Baumann-Fromm disulfides in strong acids (e.g., trifluoroacetic acid) is accompanied by protonation of the exocyclic oxygen atom (Section II,A,2,c). Water is sufficiently basic to liberate the bases from these strongly acidic 3-hydroxy-1,2-dithiolium salts. 52,53 The salts 164 and 167 are also vinylogous acids of the Baumann-Fromm disulfides with indicator properties. In neutral and alkaline media they are capable of splitting off one and two protons, respectively, with formation of the (sometimes unstable) quinoid compounds 165, 166, and 168.58 59... 

The literature at present contains very few NMR data for 1,2-dithiolium salts. The results of systematic NMR studies on a number of 1,2-dithiolium salts and on many Baumann-Fromm disulfides and trithiones are presented in a Dissertation by Dr. E. Futterer (Freiburg-im-Breisgau, 1964). Most of the data in the following tables were taken from this dissertation. 

Both the Baumann-Fromm disulfides (197) and the trithiones (200) are readily protonated in trifluoroacetic acid (Section II,A,2,c). The chemical shifts of the ring protons of some of these compounds in both carbon disulfide and trifluoroacetic acid are given in Table XII. 

The paramagnetic shift of the H-4 signal on passing from carbon disulfide into trifluoroacetic acid is more pronounced for the trithiones than for the similarly substituted Baumann-Fromm disulfides. This has been tentatively accepted as evidence that the importance of the resonance structure 202 in relation to 201 is rather greater than that of 199 in relation to 198, in agreement with the repeated observation that a carbonium center is much more effectively stabilized by an adjacent oxygen than by sulfur. 

Chemical Shifts of Baumann-Fromm Disulfides (X = 0) and of Tbithiones (X=S)... 

No alkoxy-l,3-dithiolium salts (250) are formed by the action of alkyl halides, dimethyl sulfate, or trialkyloxonium fluoroborates on isodithiones, which, like the Baumann-Fromm disulfides (Section II, A, 2,c), are stable towards these reagents. ... 

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