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The Effect of 15-crown-5 ether on the reactivityof a Grignard reagent

Victoria Johnson

Dirt Poor Company

A division of San Jose State University

San Jose, CA 95192December 8, 2008



Overview of Presentation

• Review of the Grignard Reagent

• Discussion of current experiment

• Results• Conclusions

• Future Work



Review of the GrignardReagent

Discovered by Victor Grignard in 1900

Won the Nobel Prize in 1912

One of the most important organometallic

Reagents used Used in making new C--C bonds

Over 40,000 papers published usingGrignard Reagents



Synthesis of a GrignardReagent

RX + Mg(s) R-X Mg(s) R MgX(s)

R

RMgX (soln)

a b

c

d

e



Side ReactionIn Synthesis of Grignard Reagent

Wurtz Coupling

Addition of carbanionto organohalide

Bromobenzene givesrise to biphenyl

R + RX R 2



Schlenk Equilibrium

Grignard reagentsexist in two forms

Either form will react

Presence of dioxanepushes equilibrium tothe right

O ODioxane

2RMgX R 2Mg + MgX2

15-crown-5 etherO

O

O

O O



Reactions involving GrignardReagents

C

O

R R

C

O

R O

R

C

O

R Cl

1. R MgX

2. H+C

R

OH

R

R

R MgX

C

O

R R

1. R MgX

2. H+

C

R R

OH

R

R MgX

C

O

R R

1. R MgX

2. H+C

R R

OH

R

ROH



Current Experiment:Starting Point

In Presence of bis[2-(N,N-dimethylaminoethyl)] etherreaction stops at formation of ketone

No tertiary alcohol produced

Yields in range of 70 - 90%

Cl

O

R'MgX

THF

O

R'

N

O

N

RR



Reactivity of Grignard is decreased throughcomplexation with ligand

Tridentate ligands work best

No success with bidentate ligands

Mode of action

N

O

N

Mg

R X



Synthesis of Ketones

Acid Chlorides areinexpensive to make

Grignardsynthesis/reaction fastand easy

R

OH

R

O

R' R'

PCC

CH2Cl2

R

OH

R

O

R' R'

CrO3

H2SO4

CH3CCl

O

O

AlCl3

Heat

O

H3O+

HgSO4



Experimental Options

Make ligand and reactwith differentsubstrates

Try “stock” ligand(s)

and react with benzoylchloride, other

substrates

18-crown-6

15-crown-5

O

O

O

O

O

O

O

O

O

O O

18

18-crown-6

15-crown-5



Procedural Outline

Grignard reagentdivided into twoportions

Allowed to complex for15 minutes at 0 C

Added over 15 minuteperiod to substrate at -

60 C 1:1 ratio

MgBr

THF +15-crown-5at 0 C

THFat 0 C

O

Cl

O

Cl

-60 C



Results, Expt. 1

White precipitate formed duringcomplexation period

More seen with 15-crown-5 ether GC indicated no formation of product,

though presence of small amount of

biphenyl



Expt. 1:Analysis

Formation of precipitate: Grignard reagent cancome out of solution at cold temperatures

With 15-crown-5 ether, schlenk equilibriumprobably a factor

Biphenyl likely indicates successful synthesis ofgrigard reagent

Suspect purity of benzoyl choride



Experimental changes

Litmus test of benzoyl chloride gives acidicresults!

TLC gives two spots

Methyl benzoate chosen as new substrate Less reactive, but able to obtain brand new bottle



Plan B

Same prodedure asprevious expt.

GC indicates presence

of biphenyl GC aslo indicates very

small amount ofbenzophenone but not

able to confirm by GC-MS

MgBr

THF +15-crown-5at 0 C

THFat 0 C

-60 C

O

OCH3

O

OCH3



Plan B:analysis

Not making as much Grignard as assumed

Reaction temperature too low Overhandling of Grignard



Plan C:Final Attempt

No additional THF toGrignard

No pre-chilling of

Grignard reagent 2.3 : 1 ratio of

Grignard to substrate

One set at room temp,

one at 0 C

MgBr

THF +15-crown-5Room Temp

Grignard onlyRoom Temp

O

OCH3

O

OCH3

Grignard onlyRoom Temp

THF +

15-crown-5Room Temp

O

OCH3

O

OCH3

RoomTemp

0 C

RoomTemp

0 C



QuickTime™and aTIFF (Uncompressed) decompressor

are needed to see this picture.

GC-MS Results:

Grignard with 15-crown-5 etherat room temperature

Triphenylmethanol

QuickTime™ and aTIFF (Uncompressed) decompressor


Methyl Benzoate



Biphenyl

QuickTime™and aTIFF (Uncompressed) decompressor


O

Benzophenone

O

O

CH3

OH

Starting Material

desired productunwanted product



GC-MS Results:

Grignard without ligand at 0 C

QuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

O

O

CH3

Methyl BenzoateQuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

Biphenyl



QuickTime™ and aTIFF (Uncompres sed) decompressor


O

Benzophenone

OH

Triphenylmethanol

Starting Material

Starting material

Intermediate productExpected product



Results

Ratio of Benzophenone to Triphenylmethanol

With crown ether, 0 C - 10 : 0.86

With crown ether, RT - 10 : 1.16

No crown ether, 0 C - 1 : 5.00

No crown ether, - RT 1 : 5.73



Conclusions

Temperature appears to have effect on yield -more unreacted methyl benzoate at lowertemperatures

Grignard with 15-crown-5 reduces reactivity togive very low yields with methyl benzoate

Does not completely inhibit production of tertiaryalcohol



Future Work

Obtain fresh benzoyl chloride

Try 18-crown-6 ether

Try to synthesize bis[2-(N,N-dimethylaminoethyl)] ether and work withdifferent substrates



Thank You

My benchmates: Jamie, Monika, and Anne

Dr. Okuda Dr. Brook

And especially Dr. Straus

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