In the preparation of ethynylmagnesium bromide by the transmetallation reaction of Eq. 14.24, ethylmagnesium bromide is added to a large excess of acetylene in THF solution. Two side reactions that can occur in this procedure are shown in Fig. P14.38,
Suggest a mechanism for reaction (2), and explain why an excess of acetylene is important for avoiding this reaction.

(1)

(2)

Transcribed Image Text:

H-C=C-MgBr + CH;CH2-MgBr CH;CH, + BrMg-C=C-MgBr