during his studies with kolbe between 1862 and 1864, zaytsev discovered sulfoxides and trialkylsulfonium salts. in 1864, he moved to paris, where he worked for a year in the laboratories of wurtz before returning to marburg in 1865. at this time, kolbe accepted a call to leipzig, and zaytsev, now out of money, returned to russia. upon his return, zaytsev again joined butlerov as an unpaid assistant. during this time, he wrote a successful "kandidat" dissertation.