Grignard.doc - Grignard Reaction Chem 355 Jasperse Grignard...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Grignard Reaction 81 Chem 355 Jasperse Grignard Synthesis of Triphenylmethanol 2 PhBr 1. 2 Mg, ether 2. 1 PhCO 2 CH 3 3. H Ph Ph OH Ph Summary I. Background In 1912 Victor Grignard received the Nobel prize in chemistry for his work on the reaction that bears his name, a carbon-carbon bond-forming reaction by which almost any alcohol may be formed from appropriate alkyl halides and carbonyl compounds. The Grignard reagent RMgBr is easily formed by redox reaction of an alkyl halide with magnesium metal in anhydrous diethyl ether solvent. R-Br + Mg RMgBr RMgBr = R + Mg 2+ + Br The Grignard reagent can be viewed as an ionic species consisting of carbanion R - , with a Mg 2+ counterion and an additional Br - counterion. The carbanion R - is very reactive, and functions both as an extremely strong base and an extremely strong nucleophile . Some of its reactions are shown below . It reacts as a strong base with water or alcohols . o Conversion from less stable R - to more stable HO - or RO - is favorable. It reacts as a strong nucleophile with carbonyl groups aldehydes, ketones, and esters. o Conversion from less stable R - to more stable RO - is favorable, followed by protonation to give alcohols ROH. 1. 2. H R H OH R R H O R H H O H + H O Water Aldehyde R 1. 2. H R R OH R R R O R H R O H + R O Alcohol Ketone R 1. 2. H R R OH R R OR O Ester R
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Grignard Reaction 82 II. Overview of Our Experiment Our experiment is shown below. During week one we will generate the Grignard reagent (step one) and react it with the ester (step two). During the second week we will neutralize the alkoxide (step three), isolate the alcohol, purify the alcohol by recrystallization, and do product analysis. Br 2 Bromobenzene mw 157 g/mol d: 1.49 g/mL + 2 Mg 24.3 g/mol anhydrous ether MgBr 2 OCH 3 O 1 Methyl Benzoate mw = 136 g/mol d: 1.094 g/mL O H OH Triphenylmethanol mw=260.3 g/mol melting range: 158-160 2 PhBr 1. 2 Mg, ether 2. 1 PhCO 2 CH 3 3. H Ph Ph OH Ph Summary 1 1 1
Background image of page 2
Grignard Reaction 83 Ph Br + Mg Ph• + Br - + Mg Ph: - + Br - + Mg +2 Ph• H 2 O Ph-H + HO Two Principle Side Products Note: No Water Allowed! Need water-free solvent and glassware! Ph OCH 3 O Ph OCH 3 O Ph Ph Ph O + CH 3 O Ph: Ph Ph O Ph Unstable, Eliminates Very Rapidly H + Ph Ph OH Ph Week Two Stable, Sits Around Until Proton Provided Step One: Addition Step Two: Elimination Step Three: Addition Step Four: Protonation Once Ph is made, Four Steps: Addition Elimination Addition Protonation. Ph-Ph The overall mechanism is illustrated above. The carbanion is generated by electron transfer from magnesium metal. The reactive carbanion then attacks electrophilic carbonyl to give an anionic intermediate (step one). This unstable intermediate rapidly eliminates a methoxide anion (step two). The resulting ketone is attacked again (step three). The resulting anion waits patiently until next laboratory period, at which time acid will be added to protonate the anion (step four). Byproducts and Potential Problems
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/14/2010 for the course CHEM CHEM266L taught by Professor Christine during the Fall '10 term at Waterloo.

Page1 / 10

Grignard.doc - Grignard Reaction Chem 355 Jasperse Grignard...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online