When S-cyclohexyl thioacetate is reduced by LiAlH₄ in ether, followed by protonolysis, cyclohexanethiol is formed. However, when a large excess of the Lewis acid BF₃ is added to the reaction mixture before the reduction, cyclohexyl ethyl sulfide is formed (Fig. P25.26). Account mechanistically for the effect of BF₃ in changing the outcome of the reaction.

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-S-C-CH3 + LiAlH₁ S-cyclohexyl thioacetate Figure P25.26 Et₂O BF3 Et₂O H₂O* H₂O* -SH+ HOCH₂CH3 cyclohexanethiol -S-CH₂CH3 cyclohexyl ethyl sulfide