Home >
Community >
Does anyone know the best way to activate magnesium for the...
Upvote
31
Downvote
+ Synthetic organic chemistry
+ Organometallic synthesis
+ Organic synthesis
+ Organometallic chemistry
+ Organometallics
Posted by
Nahum Germanen Godfrey
Does anyone know the best way to activate magnesium for the...
some DOI's of interest for Reike magnesium: 10.1021/ja00775a066 10.1007/BFb0046185 10.1021/ar50116a005 Rieke is well known for his preparation of active metals using reduction of the metal halide with lithium/naphthalene or potassium. This an excerpt from 10.1021/bk-1987-0333.ch014: "A current method for producing Mg is based on the use of lithium as the reducing agent. This method is preferred for its inherent safeness. The reductions are carried out at room temperature, using naphthalene as an electron carrier to speed the reaction. 6-12 h are required for complete reduction. If naphthalene will interfere with additional reactions or product isolation, it may be removed by rinsing prior to further reaction. The reactivities are compared in Table I, along with some other methods of activation. It is clear that the magnesium prepared by reduction of MgC^ is the most reactive." My preferred method for activation of magnesium metal is the use of 5 mole % ethylene bromide and 5 mole% chlorotrimethylsilane, relative to the halide being converted. This method is also used for zinc and produces both zinc and magnesium almost as good as Rieke's method. This approach comes out of the Paul Knochel group over in Germany. Ethylene bromide has long been used to activate magnesium, but the use of concommitant ClSiMe3 is relatively new. In some cases one adds the ethylene bromide first and then the ClSiMe3. You have to check around on this; I can't find the protocol at the moment. Knochel also found that addition of one equivalent of DRY lithium chloride to the pot give large improvements in rate of formation of Grignard. He also invented the "turbo grignard reagent", ie isopropylmagnesium chloride-LiCl, which is the method of choice for preparation of aryl and heteroaryl grignards by from the corresponding bromide and some chlorides by metathesis with the turbo reagent. It's patented (US7387751, US7384580). This is an excellent review, and recent! : 10.1021/jo500297r (Journal of Organic Chemistry 79 (2014) 4253-4269) If you are unfamiliar with DOI's, go to http://dx.doi.org and enter the DOI in the line provided. You will be redirected to your article.
some DOI's of interest for Reike magnesium: 10.1021/ja00775a066 10.1007/BFb0046185 10.1021/ar50116a005 Rieke is well known for his preparation of active metals using reduction of the metal halide with lithium/naphthalene or potassium. This an excerpt from 10.1021/bk-1987-0333.ch014: "A current method for producing Mg is based on the use of lithium as the reducing agent. This method is preferred for its inherent safeness. The reductions are carried out at room temperature, using naphthalene as an electron carrier to speed the reaction. 6-12 h are required for complete reduction. If naphthalene will interfere with additional reactions or product isolation, it may be removed by rinsing prior to further reaction. The reactivities are compared in Table I, along with some other methods of activation. It is clear that the magnesium prepared by reduction of MgC^ is the most reactive." My preferred method for activation of magnesium metal is the use of 5 mole % ethylene bromide and 5 mole% chlorotrimethylsilane, relative to the halide being converted. This method is also used for zinc and produces both zinc and magnesium almost as good as Rieke's method. This approach comes out of the Paul Knochel group over in Germany. Ethylene bromide has long been used to activate magnesium, but the use of concommitant ClSiMe3 is relatively new. In some cases one adds the ethylene bromide first and then the ClSiMe3. You have to check around on this; I can't find the protocol at the moment. Knochel also found that addition of one equivalent of DRY lithium chloride to the pot give large improvements in rate of formation of Grignard. He also invented the "turbo grignard reagent", ie isopropylmagnesium chloride-LiCl, which is the method of choice for preparation of aryl and heteroaryl grignards by from the corresponding bromide and some chlorides by metathesis with the turbo reagent. It's patented (US7387751, US7384580). This is an excellent review, and recent! : 10.1021/jo500297r (Journal of Organic Chemistry 79 (2014) 4253-4269) If you are unfamiliar with DOI's, go to http://dx.doi.org and enter the DOI in the line provided. You will be redirected to your article.
the Grignard reaction is very difficult to starting Are many precaution to taking : very strong dired ether without any trace of water RX fresh Mg with aout oxyde in surface activig Mg in ether anhydre and put it in 80°C put Mg in few ether witn Iodine and few RX in glass and stiredd with your hand You must look a trouble solution and added ether and quite your RX in few ether ethylic Pr mahrouz mostafa UCA FSSM chemistry ERIDDECV/LICVEDDE Marrakech .
the Grignard reaction is very difficult to starting Are many precaution to taking : very strong dired ether without any trace of water RX fresh Mg with aout oxyde in surface activig Mg in ether anhydre and put it in 80°C put Mg in few ether witn Iodine and few RX in glass and stiredd with your hand You must look a trouble solution and added ether and quite your RX in few ether ethylic Pr mahrouz mostafa UCA FSSM chemistry ERIDDECV/LICVEDDE Marrakech .
I suggest that you use a minimum of ether or preferably THF (dried over calctum hydride) containing the magnesium and some of the halide that is to be converted to the Grignard agent. Then add a trace of mercuric chloride. The mercury that is formed by reduction, penetrates the oxide layer and gives a reactive amalgam with the magnesium. When the reaction begins (turbulence) additional solvent and the remaining halide may be added.
I suggest that you use a minimum of ether or preferably THF (dried over calctum hydride) containing the magnesium and some of the halide that is to be converted to the Grignard agent. Then add a trace of mercuric chloride. The mercury that is formed by reduction, penetrates the oxide layer and gives a reactive amalgam with the magnesium. When the reaction begins (turbulence) additional solvent and the remaining halide may be added.
Maybe you know this answer already: Normally the so called "entrainment method" is very satisfactory: a preliminary Grignard formation with a small amount of 1,2-dibromoethane, preferably in THF (room temperature) is forming first bromoethyl magnesium bromide. Subsequently, under spontaneous elimination of ethene, magnesium bromide solvated by THF is formed, thus leaving surface clean activated Mg for the final (intentional) Grignard reaction in an "oganic-traceless" manner .
Maybe you know this answer already: Normally the so called "entrainment method" is very satisfactory: a preliminary Grignard formation with a small amount of 1,2-dibromoethane, preferably in THF (room temperature) is forming first bromoethyl magnesium bromide. Subsequently, under spontaneous elimination of ethene, magnesium bromide solvated by THF is formed, thus leaving surface clean activated Mg for the final (intentional) Grignard reaction in an "oganic-traceless" manner .
this is the most recent: Krasovskiy, A.; Knochel, P. Synthesis 2006, 0890. (DOI 10.1055/s-2006-926345) A convenient and reliable procedure for the titration of various organometallic compounds, such as magnesium, zinc and lanthanoids by using 0.5 M THF solutions of LiCl as titration medium has been developed. Saturated Solution of LiCl in THF (0.5M) Anhyd LiCl (100 mmol) was placed in an argon-flushed flask and dried under high vacuum (1 × 10–2 mbar) for 4 h at 140 °C. After cooling to r.t., anhyd THF (200 mL) was added and the mixture was stirred for 24 h at r.t. until the LiCl was completely dissolved, resulting in the formation of a 0.5 M solution of LiCl. Titration Using I2 A 10-mL round-bottom flask equipped with a magnetic stirring bar and a septum was heated with a heat gun under reduced pressure and cooled to r.t. under an argon atmosphere. The dry flask was charged with accurately weighed I2 (254 mg, 1 mmol), fitted with a rubber septum, and flushed with argon. The sat. solution of LiCl in THF (3–5 mL) was added and stirring was started. After the iodine was completely dissolved, the resulting brown solution was cooled to 0 °C in an ice bath and the organometallic reagent was added dropwise via a 1.00-mL syringe (0.01-mL graduations) until the brown color disappeared. The amount consumed contains 1 equiv of the organometallic reagent relative to iodine in the case of monoorganometallic reagents and 0.5 equiv for diorganometallic reagents.
this is the most recent: Krasovskiy, A.; Knochel, P. Synthesis 2006, 0890. (DOI 10.1055/s-2006-926345) A convenient and reliable procedure for the titration of various organometallic compounds, such as magnesium, zinc and lanthanoids by using 0.5 M THF solutions of LiCl as titration medium has been developed. Saturated Solution of LiCl in THF (0.5M) Anhyd LiCl (100 mmol) was placed in an argon-flushed flask and dried under high vacuum (1 × 10–2 mbar) for 4 h at 140 °C. After cooling to r.t., anhyd THF (200 mL) was added and the mixture was stirred for 24 h at r.t. until the LiCl was completely dissolved, resulting in the formation of a 0.5 M solution of LiCl. Titration Using I2 A 10-mL round-bottom flask equipped with a magnetic stirring bar and a septum was heated with a heat gun under reduced pressure and cooled to r.t. under an argon atmosphere. The dry flask was charged with accurately weighed I2 (254 mg, 1 mmol), fitted with a rubber septum, and flushed with argon. The sat. solution of LiCl in THF (3–5 mL) was added and stirring was started. After the iodine was completely dissolved, the resulting brown solution was cooled to 0 °C in an ice bath and the organometallic reagent was added dropwise via a 1.00-mL syringe (0.01-mL graduations) until the brown color disappeared. The amount consumed contains 1 equiv of the organometallic reagent relative to iodine in the case of monoorganometallic reagents and 0.5 equiv for diorganometallic reagents.
When I did the Grignard reaction, I will always wash the magnesium foil with dilute acid to remove the oxide formed around it, then keep this in a furnace about 300 degree for 12 hours and cooled and kept in desiccator. Use only freshly prepared ether /THF for the reaction. Use 2 to 3 balls of iodine to monitor the formation of grinard reagent . If colour not disappeared, that means Grignard reagent is not formed. In that case heat the reaction mixture with a hot air gun. At that time colour will disappear. then do the rest of the procedure as suggest above...
When I did the Grignard reaction, I will always wash the magnesium foil with dilute acid to remove the oxide formed around it, then keep this in a furnace about 300 degree for 12 hours and cooled and kept in desiccator. Use only freshly prepared ether /THF for the reaction. Use 2 to 3 balls of iodine to monitor the formation of grinard reagent . If colour not disappeared, that means Grignard reagent is not formed. In that case heat the reaction mixture with a hot air gun. At that time colour will disappear. then do the rest of the procedure as suggest above...
Hello all 'Grignardians,' alternatively You can reduce a Mg salt with pure cut (under inert solvent) K (Potassium) in situ under dry athmosphere in aprotic medium. In this way You get very fine pyrophore Magnesium, obviously with a huge surface area. But be really carefull, only small portions.
Hello all 'Grignardians,' alternatively You can reduce a Mg salt with pure cut (under inert solvent) K (Potassium) in situ under dry athmosphere in aprotic medium. In this way You get very fine pyrophore Magnesium, obviously with a huge surface area. But be really carefull, only small portions.
In addition to activation with iodine and dibromoethane if you are using turnings is push down on them with a glass stir rod until they break. This gives a fresh oxide free surface.
In addition to activation with iodine and dibromoethane if you are using turnings is push down on them with a glass stir rod until they break. This gives a fresh oxide free surface.
some DOI's of interest for Reike magnesium:
10.1021/ja00775a066
10.1007/BFb0046185
10.1021/ar50116a005
Rieke is well known for his preparation of active metals using reduction of the metal halide with lithium/naphthalene or potassium.
This an excerpt from 10.1021/bk-1987-0333.ch014:
"A current method for producing Mg is based on the use of lithium as the
reducing agent. This method is preferred for its inherent safeness. The
reductions are carried out at room temperature, using naphthalene as an
electron carrier to speed the reaction. 6-12 h are required for complete
reduction. If naphthalene will interfere with additional reactions or
product isolation, it may be removed by rinsing prior to further reaction.
The reactivities are compared in Table I, along with some other methods of
activation. It is clear that the magnesium prepared by reduction of MgC^
is the most reactive."
My preferred method for activation of magnesium metal is the use of 5 mole % ethylene bromide and 5 mole% chlorotrimethylsilane, relative to the halide being converted. This method is also used for zinc and produces both zinc and magnesium almost as good as Rieke's method. This approach comes out of the Paul Knochel group over in Germany. Ethylene bromide has long been used to activate magnesium, but the use of concommitant ClSiMe3 is relatively new. In some cases one adds the ethylene bromide first and then the ClSiMe3. You have to check around on this; I can't find the protocol at the moment.
Knochel also found that addition of one equivalent of DRY lithium chloride to the pot give large improvements in rate of formation of Grignard. He also invented the "turbo grignard reagent", ie isopropylmagnesium chloride-LiCl, which is the method of choice for preparation of aryl and heteroaryl grignards by from the corresponding bromide and some chlorides by metathesis with the turbo reagent. It's patented (US7387751, US7384580).
This is an excellent review, and recent! :
10.1021/jo500297r (Journal of Organic Chemistry 79 (2014) 4253-4269)
If you are unfamiliar with DOI's, go to http://dx.doi.org and enter the DOI in the line provided. You will be redirected to your article.
some DOI's of interest for Reike magnesium:
10.1021/ja00775a066
10.1007/BFb0046185
10.1021/ar50116a005
Rieke is well known for his preparation of active metals using reduction of the metal halide with lithium/naphthalene or potassium.
This an excerpt from 10.1021/bk-1987-0333.ch014:
"A current method for producing Mg is based on the use of lithium as the
reducing agent. This method is preferred for its inherent safeness. The
reductions are carried out at room temperature, using naphthalene as an
electron carrier to speed the reaction. 6-12 h are required for complete
reduction. If naphthalene will interfere with additional reactions or
product isolation, it may be removed by rinsing prior to further reaction.
The reactivities are compared in Table I, along with some other methods of
activation. It is clear that the magnesium prepared by reduction of MgC^
is the most reactive."
My preferred method for activation of magnesium metal is the use of 5 mole % ethylene bromide and 5 mole% chlorotrimethylsilane, relative to the halide being converted. This method is also used for zinc and produces both zinc and magnesium almost as good as Rieke's method. This approach comes out of the Paul Knochel group over in Germany. Ethylene bromide has long been used to activate magnesium, but the use of concommitant ClSiMe3 is relatively new. In some cases one adds the ethylene bromide first and then the ClSiMe3. You have to check around on this; I can't find the protocol at the moment.
Knochel also found that addition of one equivalent of DRY lithium chloride to the pot give large improvements in rate of formation of Grignard. He also invented the "turbo grignard reagent", ie isopropylmagnesium chloride-LiCl, which is the method of choice for preparation of aryl and heteroaryl grignards by from the corresponding bromide and some chlorides by metathesis with the turbo reagent. It's patented (US7387751, US7384580).
This is an excellent review, and recent! :
10.1021/jo500297r (Journal of Organic Chemistry 79 (2014) 4253-4269)
If you are unfamiliar with DOI's, go to http://dx.doi.org and enter the DOI in the line provided. You will be redirected to your article.
More
VOTE
the Grignard reaction is very difficult to starting
Are many precaution to taking :
very strong dired
ether without any trace of water
RX fresh
Mg with aout oxyde in surface
activig Mg in ether anhydre and put it in 80°C
put Mg in few ether witn Iodine and few RX in glass and stiredd with your hand
You must look a trouble solution and added ether and quite your RX in few ether ethylic
Pr mahrouz mostafa
UCA FSSM chemistry
ERIDDECV/LICVEDDE
Marrakech
.
the Grignard reaction is very difficult to starting
Are many precaution to taking :
very strong dired
ether without any trace of water
RX fresh
Mg with aout oxyde in surface
activig Mg in ether anhydre and put it in 80°C
put Mg in few ether witn Iodine and few RX in glass and stiredd with your hand
You must look a trouble solution and added ether and quite your RX in few ether ethylic
Pr mahrouz mostafa
UCA FSSM chemistry
ERIDDECV/LICVEDDE
Marrakech
.
More
VOTE
I suggest that you use a minimum of ether or preferably THF (dried over calctum hydride) containing the magnesium and some of the halide that is to be converted to the Grignard agent. Then add a trace of mercuric chloride. The mercury that is formed by reduction, penetrates the oxide layer and gives a reactive amalgam with the magnesium. When the reaction begins (turbulence) additional solvent and the remaining halide may be added.
I suggest that you use a minimum of ether or preferably THF (dried over calctum hydride) containing the magnesium and some of the halide that is to be converted to the Grignard agent. Then add a trace of mercuric chloride. The mercury that is formed by reduction, penetrates the oxide layer and gives a reactive amalgam with the magnesium. When the reaction begins (turbulence) additional solvent and the remaining halide may be added.
More
VOTE
I once (1986) made fresh Magnesium powder by reducing MgCl2 (magnesium chloride) with Potassium and using Potassium Iodide as catalyst under very dry conditions. The solvent was THF. This freshly made magnesium with a huge surface was superior to activated magnesium strips or chips. It is called "Rieke Magnesium".
https://books.google.dk/books?id=82CaxfY-uNkC&pg=PA66&lpg=PA66&dq=generation+of+magnesium+with+potassium+reduction&source=bl&ots=2LeLgS5K7N&sig=nQkbLkuTTE8ueB_DG4kLkMIEeO4&hl=en&sa=X&ved=0ahUKEwiE17fQ06HKAhUGWywKHTdlDyAQ6AEIIjAA#v=onepage&q=generation%20of%20magnesium%20with%20potassium%20reduction&f=false
I once (1986) made fresh Magnesium powder by reducing MgCl2 (magnesium chloride) with Potassium and using Potassium Iodide as catalyst under very dry conditions. The solvent was THF. This freshly made magnesium with a huge surface was superior to activated magnesium strips or chips. It is called "Rieke Magnesium".
https://books.google.dk/books?id=82CaxfY-uNkC&pg=PA66&lpg=PA66&dq=generation+of+magnesium+with+potassium+reduction&source=bl&ots=2LeLgS5K7N&sig=nQkbLkuTTE8ueB_DG4kLkMIEeO4&hl=en&sa=X&ved=0ahUKEwiE17fQ06HKAhUGWywKHTdlDyAQ6AEIIjAA#v=onepage&q=generation%20of%20magnesium%20with%20potassium%20reduction&f=false
More
VOTE
Maybe you know this answer already:
Normally the so called "entrainment method" is very satisfactory: a preliminary Grignard formation with a small amount of 1,2-dibromoethane, preferably in THF (room temperature) is forming first bromoethyl magnesium bromide. Subsequently, under spontaneous elimination of ethene, magnesium bromide solvated by THF is formed, thus leaving surface clean activated Mg for the final (intentional) Grignard reaction in an "oganic-traceless" manner .
Maybe you know this answer already:
Normally the so called "entrainment method" is very satisfactory: a preliminary Grignard formation with a small amount of 1,2-dibromoethane, preferably in THF (room temperature) is forming first bromoethyl magnesium bromide. Subsequently, under spontaneous elimination of ethene, magnesium bromide solvated by THF is formed, thus leaving surface clean activated Mg for the final (intentional) Grignard reaction in an "oganic-traceless" manner .
More
VOTE
could you please tell if anyone knows how to test grignard reagent before adding it to the compound
could you please tell if anyone knows how to test grignard reagent before adding it to the compound
More
VOTE
this is the most recent:
Krasovskiy, A.; Knochel, P. Synthesis 2006, 0890. (DOI 10.1055/s-2006-926345)
A convenient and reliable procedure for the titration of various organometallic compounds, such as magnesium, zinc and lanthanoids by using 0.5 M THF solutions of LiCl as titration medium has been developed.
Saturated Solution of LiCl in THF (0.5M)
Anhyd LiCl (100 mmol) was placed in an argon-flushed flask and dried under high vacuum (1 × 10–2 mbar) for 4 h at 140 °C. After cooling to r.t., anhyd THF (200 mL) was added and the mixture was stirred for 24 h at r.t. until the LiCl was completely dissolved, resulting in the formation of a 0.5 M solution of LiCl.
Titration Using I2
A 10-mL round-bottom flask equipped with a magnetic stirring bar and a septum was heated with a heat gun under reduced pressure and cooled to r.t. under an argon atmosphere. The dry flask was charged with accurately weighed I2 (254 mg, 1 mmol), fitted with a rubber septum, and flushed with argon. The sat. solution of LiCl in THF (3–5 mL) was added and stirring was started. After the iodine was completely dissolved, the resulting brown solution was cooled to 0 °C in an ice bath and the organometallic reagent was added dropwise via a 1.00-mL syringe (0.01-mL graduations) until the brown color disappeared. The amount consumed contains 1 equiv of the organometallic reagent relative to iodine in the case of monoorganometallic reagents and 0.5 equiv for diorganometallic reagents.
this is the most recent:
Krasovskiy, A.; Knochel, P. Synthesis 2006, 0890. (DOI 10.1055/s-2006-926345)
A convenient and reliable procedure for the titration of various organometallic compounds, such as magnesium, zinc and lanthanoids by using 0.5 M THF solutions of LiCl as titration medium has been developed.
Saturated Solution of LiCl in THF (0.5M)
Anhyd LiCl (100 mmol) was placed in an argon-flushed flask and dried under high vacuum (1 × 10–2 mbar) for 4 h at 140 °C. After cooling to r.t., anhyd THF (200 mL) was added and the mixture was stirred for 24 h at r.t. until the LiCl was completely dissolved, resulting in the formation of a 0.5 M solution of LiCl.
Titration Using I2
A 10-mL round-bottom flask equipped with a magnetic stirring bar and a septum was heated with a heat gun under reduced pressure and cooled to r.t. under an argon atmosphere. The dry flask was charged with accurately weighed I2 (254 mg, 1 mmol), fitted with a rubber septum, and flushed with argon. The sat. solution of LiCl in THF (3–5 mL) was added and stirring was started. After the iodine was completely dissolved, the resulting brown solution was cooled to 0 °C in an ice bath and the organometallic reagent was added dropwise via a 1.00-mL syringe (0.01-mL graduations) until the brown color disappeared. The amount consumed contains 1 equiv of the organometallic reagent relative to iodine in the case of monoorganometallic reagents and 0.5 equiv for diorganometallic reagents.
More
VOTE
1 mol % of DIBAH (diisobutylaluminum hydride) per mol Mg at room temperature. This is used at plant scale by Scherring
Article Activation of Mg Metal for Safe Formation of Grignard Reagen...
1 mol % of DIBAH (diisobutylaluminum hydride) per mol Mg at room temperature. This is used at plant scale by Scherring
Article Activation of Mg Metal for Safe Formation of Grignard Reagen...
More
VOTE
When I did the Grignard reaction, I will always wash the magnesium foil with dilute acid to remove the oxide formed around it, then keep this in a furnace about 300 degree for 12 hours and cooled and kept in desiccator.
Use only freshly prepared ether /THF for the reaction.
Use 2 to 3 balls of iodine to monitor the formation of grinard reagent .
If colour not disappeared, that means Grignard reagent is not formed. In that case heat the reaction mixture with a hot air gun. At that time colour will disappear. then do the rest of the procedure as suggest above...
When I did the Grignard reaction, I will always wash the magnesium foil with dilute acid to remove the oxide formed around it, then keep this in a furnace about 300 degree for 12 hours and cooled and kept in desiccator.
Use only freshly prepared ether /THF for the reaction.
Use 2 to 3 balls of iodine to monitor the formation of grinard reagent .
If colour not disappeared, that means Grignard reagent is not formed. In that case heat the reaction mixture with a hot air gun. At that time colour will disappear. then do the rest of the procedure as suggest above...
More
VOTE
Hello all 'Grignardians,'
alternatively You can reduce a Mg salt with pure cut (under inert solvent) K (Potassium) in situ under dry athmosphere in aprotic medium. In this way You get very fine pyrophore Magnesium, obviously with a huge surface area. But be really carefull, only small portions.
Hello all 'Grignardians,'
alternatively You can reduce a Mg salt with pure cut (under inert solvent) K (Potassium) in situ under dry athmosphere in aprotic medium. In this way You get very fine pyrophore Magnesium, obviously with a huge surface area. But be really carefull, only small portions.
More
VOTE
In addition to activation with iodine and dibromoethane if you are using turnings is push down on them with a glass stir rod until they break. This gives a fresh oxide free surface.
In addition to activation with iodine and dibromoethane if you are using turnings is push down on them with a glass stir rod until they break. This gives a fresh oxide free surface.
More
VOTE