sulfur is mainly in the form of organic sulfur compounds like R-SH, where the sulfur is attached at the
end of an organic molecule. When the molecule is more complex, for instance when the sulfur is
surrounded or contained within the molecule then the sulfur compounds are more stable and less reactive,
like in R-S•S-R. Just a few years ago, disulfides (of which DBDS belongs) were once thought to be very
stable but it has been found that the disulfide linkage can be susceptible to cleavage resulting in the
production of mercaptans. Thiophenes are the most stable of all these sulfur compounds. Research at
Doble has shown that even thiophenes will break down given enough time and thermal stress. Whether
they form corrosive sulfur compounds or not is unknown. It is known that a large percentage of the
breakdown products will reform into smaller thiophene compounds. Crude selection and the refining
process are the two main factors that dictate the presence of any of the five sulfur groups in a finished
transformer oil.