Preparation
the oxygen, creating a primary alcohol with formaldehyde, a secondary alcohol with an
aldehyde and a tertiary alcohol with a ketone.
With esters, the mechanism is slightly different. Two moles of Grignard are required for
each mole of the ester. Initially, the pi bond on the carbonyl oxygen attacks the magnesium
bromide ion. This opens up the carbon for attack from the R group of the Grignard. This
part of the reaction is slow because of the dual oxygens off of the carbon providing some
resonance stabilization. The oxygen’s pi bond then re-forms, expelling the O-R group of the
ester which then joins with the magnesium bromide, leaving R-O-MgBr and a ketone. The
R-O-MgBr is quickly protonated from the acidic solution and the ketone is then attacked
by Grignard reagent via the mechanism described earlier.
Synthesis from Formaldehyde
Figure 132 Synthesis of alcohol from formaldehyde and Grignard reagent
The image above shows the synthesis of an alcohol from formaldehyde reacted with a Grig-
nard reagent. When a formaldehyde is the target of the Grignard’s attack, the result is a
primary alcohol.
Synthesis from an Aldehyde
Figure 133 Synthesis of alcohol from an aldehyde and Grignard reagent
The image above shows the synthesis of an alcohol from an aldehyde reacted with a Grignard
reagent. When an aldehyde is the target of the Grignard’s attack, the result is a secondary
alcohol.
Synthesis from a Ketone
Figure 134 Synthesis of alcohol from an ketone and Grignard reagent
The image above shows the synthesis of an alcohol from a ketone reacted with a Grignard
reagent. When a ketone is the target of the Grignard’s attack, the result is a tertiary
alcohol.