Thiol/thiolate propanethiol

Reductive Thiolation. Treatment of aldehydes with triethylsilane, thiols, and boron trifluoride monohydrate 217 yields sulfides in a one-flask process. For example, this method gives a 97% yield of benzyl isopropyl sulfide from benzaldehyde and 2-propanethiol (Eq. 204).365... 

Thiols are more acidic than the corresponding alcohols and are converted into their salts using alkali metal hydroxides or alkoxides. The thiolate salts are powerful nucleophiles, a property which has been used in the cleavage of methyl esters and methyl ethers. The combination of a hard acid and a soft base such as lithium propanethiolate (Li SPr) may favour attack on the methyl group of an ester and lead to alkyl-oxygen fission of the ester, rather than the more common addition of a nucleophile to the carbonyl group and consequently acyl-oxygen fission. This is particularly useful in the hydrolysis of hindered esters. 

Several thiols occur naturally for example, skunk secretion contains 3-methyll-butanethiol and cut onions evolve 1-propanethiol, and the thiol group of the natural amino acid cysteine plays a vital role in the biochemistry of proteins and enzymes (see Introduction, p. 2). Primary and secondary thiols may be prepared from alkyl halides (RX) by reaction with excess sodium thiolate (SN2 nucleophilic substitution by HST) or via the Grignard reagent and reaction with sulfur. Tertiary thiols can be obtained in good yields by addition of hydrogen sulfide to a suitable alkene. Thiols can also be prepared by reduction of sulfonyl chlorides (Scheme l).la,2a... 

In the presence of a thiol such as propanethiol or thiophe-nol, this polymerization exhibits immortal character, that is, the number of polymer molecules exceeds that of the initiator molecules without affecting, however, the narrow MWD. This was attributed to an exchange of the thiol end groups of the polymer chains with the thiolate aaive species occurring at a rate that is much higher than the propagation rate. 

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