There is a relatively easy way to do this. You can determine the Gutmann Acceptor number. To do this you mix the Lewis acid with triethylphosphine oxide and monitoring the 31P shift in the NMR. I have attached a paper where people have used the technique to determine the Lewis acidity of some novel trialkoxy boranes. Another method was developed using crotonaldehyde and monitoring the proton shift of the vinyl peak at the beta-position. Its not perfect but may be handy for comparative purposes.
There is a relatively easy way to do this. You can determine the Gutmann Acceptor number. To do this you mix the Lewis acid with triethylphosphine oxide and monitoring the 31P shift in the NMR. I have attached a paper where people have used the technique to determine the Lewis acidity of some novel trialkoxy boranes. Another method was developed using crotonaldehyde and monitoring the proton shift of the vinyl peak at the beta-position. Its not perfect but may be handy for comparative purposes.
Bhardwage, To find the answer to your question I recommend that you read the attached file and the reference cited therein. You may also search google book Good luck
Bhardwage, To find the answer to your question I recommend that you read the attached file and the reference cited therein. You may also search google book Good luck
The article recommended by Adel covers a large range of Lewis acids and is certainly a good basis for a kinetic and reactivity classification. Another extensive Lewis-acid classification by Olah and coworkers was based on Friedel-Crafts reaction: Aromatic Substitution. XXX. Friedel-Crafts Benzylation of Benzene and Toluene with Benzyl and Substituted Benzyl Halides, Olah et al. JACS 1972, 94, 7448-7461. It seems that SbCl3 is rather inactive, as compared to the very active AlCl3. From the thermodynamic point of view, the enthalpy or Gibbs energy of adduct formation with a standard base would be helpful but I did not find such data in a rapid literature search. From the data at hand (enthalpies) and from my experience, I’d say that the Lewis acidity strength order is AlCl3 > BF3 (almost certain) and BF3 > SbCl3 (estimate). So I guess that AlCl3 >> SbCl3. Remember anyway that there is no universal Lewis acidity(basicity) scales, because the order may depend on the choice of the reference Lewis base (acid).
The article recommended by Adel covers a large range of Lewis acids and is certainly a good basis for a kinetic and reactivity classification. Another extensive Lewis-acid classification by Olah and coworkers was based on Friedel-Crafts reaction: Aromatic Substitution. XXX. Friedel-Crafts Benzylation of Benzene and Toluene with Benzyl and Substituted Benzyl Halides, Olah et al. JACS 1972, 94, 7448-7461. It seems that SbCl3 is rather inactive, as compared to the very active AlCl3. From the thermodynamic point of view, the enthalpy or Gibbs energy of adduct formation with a standard base would be helpful but I did not find such data in a rapid literature search. From the data at hand (enthalpies) and from my experience, I’d say that the Lewis acidity strength order is AlCl3 > BF3 (almost certain) and BF3 > SbCl3 (estimate). So I guess that AlCl3 >> SbCl3. Remember anyway that there is no universal Lewis acidity(basicity) scales, because the order may depend on the choice of the reference Lewis base (acid).
I agree that the suggestion by Luke may give easily useful data, but remember that NMR is also sensitive to effects other than “pure” electronic effects or bond strength. The AN scale was initially devised as a solvent acidity scale. It was shown that AN for solvents contains a contribution from hydrogen bond donor strength, but AN contains also a significant polarity (dipole/dipole interaction) component. My experience with calorimetric measurements with Lewis acid/base interactions suggests that these NMR scales may not represent solely the bond strength. I just cite the Britovsek paper as a caution: “From our results, we suggest that (such) a linear correlation [between Gutmann’s method and Child’s method] does not strictly apply to all Lewis acids, but that different bases can give different trends.” This is evident for decades of works, i.e. HSAB and Drago covalent/electrostatic models. The question of the nature of the bases(s) to be reacted with SbCl3 (and AlCl3?) is certainly of importance.
I agree that the suggestion by Luke may give easily useful data, but remember that NMR is also sensitive to effects other than “pure” electronic effects or bond strength. The AN scale was initially devised as a solvent acidity scale. It was shown that AN for solvents contains a contribution from hydrogen bond donor strength, but AN contains also a significant polarity (dipole/dipole interaction) component. My experience with calorimetric measurements with Lewis acid/base interactions suggests that these NMR scales may not represent solely the bond strength. I just cite the Britovsek paper as a caution: “From our results, we suggest that (such) a linear correlation [between Gutmann’s method and Child’s method] does not strictly apply to all Lewis acids, but that different bases can give different trends.” This is evident for decades of works, i.e. HSAB and Drago covalent/electrostatic models. The question of the nature of the bases(s) to be reacted with SbCl3 (and AlCl3?) is certainly of importance.
i found these suggestions very helpful in solving my problem related to lewis acidity.
i found these suggestions very helpful in solving my problem related to lewis acidity.
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There is a relatively easy way to do this. You can determine the Gutmann Acceptor number. To do this you mix the Lewis acid with triethylphosphine oxide and monitoring the 31P shift in the NMR. I have attached a paper where people have used the technique to determine the Lewis acidity of some novel trialkoxy boranes.
Another method was developed using crotonaldehyde and monitoring the proton shift of the vinyl peak at the beta-position.
Its not perfect but may be handy for comparative purposes.
There is a relatively easy way to do this. You can determine the Gutmann Acceptor number. To do this you mix the Lewis acid with triethylphosphine oxide and monitoring the 31P shift in the NMR. I have attached a paper where people have used the technique to determine the Lewis acidity of some novel trialkoxy boranes.
Another method was developed using crotonaldehyde and monitoring the proton shift of the vinyl peak at the beta-position.
Its not perfect but may be handy for comparative purposes.
More
VOTE
Bhardwage,
To find the answer to your question I recommend that you read the attached file and the reference cited therein. You may also search google book
Good luck
Bhardwage,
To find the answer to your question I recommend that you read the attached file and the reference cited therein. You may also search google book
Good luck
More
VOTE
Please feel free to ask if you have a specific question (interaction with a substrate...)
J-F
Please feel free to ask if you have a specific question (interaction with a substrate...)
J-F
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VOTE
The article recommended by Adel covers a large range of Lewis acids and is certainly a good basis for a kinetic and reactivity classification. Another extensive Lewis-acid classification by Olah and coworkers was based on Friedel-Crafts reaction:
Aromatic Substitution. XXX. Friedel-Crafts Benzylation of Benzene and Toluene with Benzyl and Substituted Benzyl Halides, Olah et al. JACS 1972, 94, 7448-7461.
It seems that SbCl3 is rather inactive, as compared to the very active AlCl3.
From the thermodynamic point of view, the enthalpy or Gibbs energy of adduct formation with a standard base would be helpful but I did not find such data in a rapid literature search. From the data at hand (enthalpies) and from my experience, I’d say that the Lewis acidity strength order is AlCl3 > BF3 (almost certain) and BF3 > SbCl3 (estimate). So I guess that AlCl3 >> SbCl3. Remember anyway that there is no universal Lewis acidity(basicity) scales, because the order may depend on the choice of the reference Lewis base (acid).
The article recommended by Adel covers a large range of Lewis acids and is certainly a good basis for a kinetic and reactivity classification. Another extensive Lewis-acid classification by Olah and coworkers was based on Friedel-Crafts reaction:
Aromatic Substitution. XXX. Friedel-Crafts Benzylation of Benzene and Toluene with Benzyl and Substituted Benzyl Halides, Olah et al. JACS 1972, 94, 7448-7461.
It seems that SbCl3 is rather inactive, as compared to the very active AlCl3.
From the thermodynamic point of view, the enthalpy or Gibbs energy of adduct formation with a standard base would be helpful but I did not find such data in a rapid literature search. From the data at hand (enthalpies) and from my experience, I’d say that the Lewis acidity strength order is AlCl3 > BF3 (almost certain) and BF3 > SbCl3 (estimate). So I guess that AlCl3 >> SbCl3. Remember anyway that there is no universal Lewis acidity(basicity) scales, because the order may depend on the choice of the reference Lewis base (acid).
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Thank you so much sir.... i find the attachment very informative...
Thank you so much sir.... i find the attachment very informative...
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I agree that the suggestion by Luke may give easily useful data, but remember that NMR is also sensitive to effects other than “pure” electronic effects or bond strength. The AN scale was initially devised as a solvent acidity scale. It was shown that AN for solvents contains a contribution from hydrogen bond donor strength, but AN contains also a significant polarity (dipole/dipole interaction) component. My experience with calorimetric measurements with Lewis acid/base interactions suggests that these NMR scales may not represent solely the bond strength. I just cite the Britovsek paper as a caution: “From our results, we suggest that (such) a linear correlation [between Gutmann’s method and Child’s method] does not strictly apply to all Lewis acids, but that different bases can give different trends.” This is evident for decades of works, i.e. HSAB and Drago covalent/electrostatic models.
The question of the nature of the bases(s) to be reacted with SbCl3 (and AlCl3?) is certainly of importance.
I agree that the suggestion by Luke may give easily useful data, but remember that NMR is also sensitive to effects other than “pure” electronic effects or bond strength. The AN scale was initially devised as a solvent acidity scale. It was shown that AN for solvents contains a contribution from hydrogen bond donor strength, but AN contains also a significant polarity (dipole/dipole interaction) component. My experience with calorimetric measurements with Lewis acid/base interactions suggests that these NMR scales may not represent solely the bond strength. I just cite the Britovsek paper as a caution: “From our results, we suggest that (such) a linear correlation [between Gutmann’s method and Child’s method] does not strictly apply to all Lewis acids, but that different bases can give different trends.” This is evident for decades of works, i.e. HSAB and Drago covalent/electrostatic models.
The question of the nature of the bases(s) to be reacted with SbCl3 (and AlCl3?) is certainly of importance.
More
VOTE