Sulfoxides fragmentation

Diphenylthiirene 1-oxide and several thiirene 1,1-dioxides show very weak molecular ions by electron impact mass spectrometry, but the molecular ions are much more abundant in chemical ionization mass spectrometry (75JHC21). The major fragmentation pathway is loss of sulfur monoxide or sulfur dioxide to give the alkynic ion. High resolution mass measurements identified minor fragment ions from 2,3-diphenylthiirene 1-oxide at mje 105 and 121 as PhCO" and PhCS, which are probably derived via rearrangement of the thiirene sulfoxide to monothiobenzil (Scheme 2). 

Conceptually closely related, cefroxadi ne (40) can be prepared by several routes, including one in which the enol (33) is imethylated with diazomethane as a key step. A rather more involved route starts with comparatively readily available phenoxymethylpenicillin sulfoxide benzhydryl ester (36). This undergoes fragmentation when treated with benzothiazole-2-thiol to give Ozonolysis (reductive work-up) cleaves the... 

The loss of an oxygen atom from the molecular ions of 10 occurs also to some extent and is most pronounced when R = CH3 (route I in equation 2). The predominant fragmentation route of methyl and ethyl 2-hydroxyphenyl sulfoxides is II (equation 2) which, however, is not important when R > Et. Ethyl 2-hydroxyphenyl sulfoxide undergoes also fragmentation via route III, which is the main path of fragmentation when R > Et10. 

The main primary fragment ions of diaryl sulfoxides 13 and 14 have the structures 16a or 16b(C8H7S02 + m/z 167) and the ion m/z 152 (17) can be obtained from both by the loss of CH3 (equation 5)13. Ions 16a and 16b are formed from the sulfenate ester structure of the molecular ions of 13 and 14 through a cyclization process and a simultaneous loss of the other O Ar part. A similar ortho effect is not possible in 15 and hence its most intense ion is M+ (23% of the total ionization in comparison with 2.7 and 0.6% for 13 and 14, respectively) and its primary fragments are typical for a normal diaryl sulfoxide. 

Phenanthro[4,5-b, c, d]thiophene 4-oxide (19) and 4,4-dioxide (20)15 undergo first the well-known sulfenate (22) or sulfinate ester (23) rearrangements1 4,6, respectively (equation 6). The sulfoxide loses an oxygen atom and enters the fragmentation pathway of 18 or loses HCO (more likely in two steps) from 22. Both sulfenate and sulfinate ions can fragment further via 21 after losing a sulfur atom or eliminating SO5, respectively. 

Acyclic sulfoxides fragment into olefins and sulfenic acids on thermolysis97. Cyclic sulfoxides exhibit essentially the same ready mode of fragmentation106. 

The main result of the thermolysis of the three-membered ring sulfoxides and sulfones is the extrusion of the sulfur monoxide and the sulfur dioxide moieties (Section III.C. I)99 10 5. Only in the presence of a suitably disposed /J-hydrogen does the ordinary sulfoxide-sulfenic acid fragmentation take place in the thiirane oxide series (equation 9). 

The formation of adduct is followed by fragmentation and subsequent H-atom abstraction reaction from the sulfinic acid produced. Strong acid solutions of aromatic sulfoxides like thianthrene 5-oxide (7) or phenothiazine 5-oxide (8) gives rise to ESR signals, which... 

Potzinger and coworkers determined ionisation and appearance energies for the molecular and major fragment ions of several dialkylsulfoxides, R SOR (R =Me R = Me, Et, i-Pr, and i-pentyland R = R = Et or i-Pr). In addition to the evaluation of dissociation energies in the ions and their enthalpies of formation, a value of 280 + 30kJmol" for the C—S dissociation energy in neutral dialkyl sulfoxides was derived. 

The other fragmentation pathways are typical for diaryl sulfoxides "" . A corresponding ortho effect was found in chlorodiphenyl ethers and sulfides but not in sulfones (12) were the sulfinate ester rearrangements " and the consequent formation of the m/z 125 and m/z 159 ions suppress the other possible fragmentations of the molecular ions (equation 4). It is also noteworthy that the ratio [m/z 125] [m/z 159] increases with increasing distance between the chlorine and the sulfur (equation 4). 

Pedersen and coworkers investigated the El mass spectra of several 2-hydroxyphenyl alkyl sulfones (39) and sulfoxides (Section II.B). The methyl derivative seemed to fragment only via sulfinate ester formation giving the primary product ions m/z 157 and 109 (equation 14). Obviously hydrogen bonding between the ortho hydroxyl and the sulfone sulfur makes the loss of CH3SO2 difficult in contrast to the situation in methyl phenyl sulfone. The sulfinate ester rearrangement is not important when R>Et in 39. 

Klemm and coworkers studied the spectra of several thienopyridine sulfones (72-78) and found that it is possible to distinguish by mass spectrometry between a sulfone function and a combination of two sulfoxide or JV-oxide functions in the same molecule . For instance, compound 77 forms 78 losing the 7V-oxygen atom, since except for the molecular ion their mass spectra are very similar. Compound 78 rearranges prior to fragmentation to the two possible cyclic sulfinates (80 and 81), which then fragment further by losing SO and CNO, respectively. 

RSO and RSOH" (1-8%) were unique to the sulfoxides. In the case of 145 most of the fragments arise, however, from the precursor ion 150. 

In the presence of a suitably disposed /i-hydrogen—as in alkyl-substituted thiirane oxides such as 16c—an alternative, more facile pathway for thermal fragmentation is available . In such cases the thiirene oxides are thermally rearranged to the allylic sulfenic acid, 37, similarly to the thermolysis of larger cyclic and acyclic sulfoxides (see equation 9). In sharp contrast to this type of thiirane oxide, mono- and cis-disubstituted ones have no available hydrogen for abstraction and afford on thermolysis only olefins and sulfur monoxide . However, rapid thermolysis of thiirane oxides of type 16c at high temperatures (200-340 °C), rather than at room temperature or lower, afforded mixtures of cis- and trans-olefins with the concomitant extrusion of sulfur monoxide . The rationale proposed for all these observations is that thiirane oxides may thermally... 

Mass spectrometry was applied in conjunction with thermolysis studies leading mainly to sulfines and rearranged products with four-membered sulfoxides and to a loss of sulfur dioxide with sulfones The fragmentation pattern of thietes under electron impact can be explained by the sequential loss of the elements of sulfur monoxide and oxygen from an intervening cyclic sulfmate intermediate . ... 

The sulfoxide substituent was also used to introduce the C(10)-C(13) fragment and was reduced to a vinyl sulfide in Step B-l. In Step C-l, the vinyl sulfide was hydrolyzed to an aldehyde, which was elaborated by addition of isobutylmagnesium bromide. 

Fragment search in the Cambridge Crystallographic Data Base reveals 127 hits out of 42381 entries (state May 1985) having dimethyl sulfoxide as the search query and allowing for the presence of metal atoms. In absence of such elements, the number of hits is reduced to 27. 

The products of the reactions of picryl chloride with isomeric 4- and 5-aminobenzofurazans in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were studied by means of nonaqueous potentiometric titration. The effect of the position of the furazan fragment in 4- and 5-picrylaminobenzofurazans on the NH acidity is considered. The electron-acceptor properties of the furazan fragment were evaluated via inclusion of the resulting data into the pK -cr correlation for 2,4,6-trinitrodiphenylamines <2005RJC933>. 

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