The alcohol molecule formed is much too large to be trapped by molecular sieves unfortunately. I think the amount water present is much to small to be removed by DS-trap at least if I use it the conventional way but I will try that. To ground the sieves is an interesting option, I have done that when doing Sharpless epoxidation with good result.
The alcohol molecule formed is much too large to be trapped by molecular sieves unfortunately. I think the amount water present is much to small to be removed by DS-trap at least if I use it the conventional way but I will try that. To ground the sieves is an interesting option, I have done that when doing Sharpless epoxidation with good result.
I have a ton of faith in sieves. How are you doing it with them? Are the fully activated? Fully activating them requires some fairly considerable asskicking conditions. 250°C+ for a few hours is preferable.
Are you leaving them in the solvent long enough? Different solvents have quite different drying kinetics with sieves. 3A is preferred over 4A. You should also load it at 10-20% m/v.
Agreed. It's been posted many times I'm sure, but for the effectiveness of sieves in solvent drying, see:
I have a ton of faith in sieves. How are you doing it with them? Are the fully activated? Fully activating them requires some fairly considerable asskicking conditions. 250°C+ for a few hours is preferable.
Are you leaving them in the solvent long enough? Different solvents have quite different drying kinetics with sieves. 3A is preferred over 4A. You should also load it at 10-20% m/v.
Agreed. It's been posted many times I'm sure, but for the effectiveness of sieves in solvent drying, see:
I mean water in the solvent and probably also to remove ROH that is formed in the reaction. It is a bit unclear but this is the theory I am exploring. Silylating agents work well and they do both. Calcium hydride would remove water forming CaOH2 and also ROH forming CaOR2 I suppose?
I mean water in the solvent and probably also to remove ROH that is formed in the reaction. It is a bit unclear but this is the theory I am exploring. Silylating agents work well and they do both. Calcium hydride would remove water forming CaOH2 and also ROH forming CaOR2 I suppose?
I use 4Å, they are activated at 250°C under vacuum. I use 3g sieves in 15ml DMF-reaction solution, the DMF is stored over 4Å sieves also. It would be nice to test water-content with Karl Fischer but I dont have that in the lab. The sieves get very hot on contact with water so they are activated. The reaction is runt at 124°C, I filter of the sieves before heating under N2. The sieves would not remove the ROH formed and for now that seems as a good explanation why they dont work.
I would increasing the amount of drying power by upping to something like ground 3Å MS 90% w/v. Did you try to use toluene and a dean stark trap? Can you obtain a molecular sieve with a larger radius like 5Å? One could put the dessicant in top of the DS trap to remove water and alcohols...
I use 4Å, they are activated at 250°C under vacuum. I use 3g sieves in 15ml DMF-reaction solution, the DMF is stored over 4Å sieves also. It would be nice to test water-content with Karl Fischer but I dont have that in the lab. The sieves get very hot on contact with water so they are activated. The reaction is runt at 124°C, I filter of the sieves before heating under N2. The sieves would not remove the ROH formed and for now that seems as a good explanation why they dont work.
I would increasing the amount of drying power by upping to something like ground 3Å MS 90% w/v. Did you try to use toluene and a dean stark trap? Can you obtain a molecular sieve with a larger radius like 5Å? One could put the dessicant in top of the DS trap to remove water and alcohols...
I use 4Å, they are activated at 250°C under vacuum. I use 3g sieves in 15ml DMF-reaction solution, the DMF is stored over 4Å sieves also. It would be nice to test water-content with Karl Fischer but I dont have that in the lab. The sieves get very hot on contact with water so they are activated. The reaction is runt at 124°C, I filter of the sieves before heating under N2. The sieves would not remove the ROH formed and for now that seems as a good explanation why they dont work.
I use 4Å, they are activated at 250°C under vacuum. I use 3g sieves in 15ml DMF-reaction solution, the DMF is stored over 4Å sieves also. It would be nice to test water-content with Karl Fischer but I dont have that in the lab. The sieves get very hot on contact with water so they are activated. The reaction is runt at 124°C, I filter of the sieves before heating under N2. The sieves would not remove the ROH formed and for now that seems as a good explanation why they dont work.
Do you mean water in the solvent, water that is produced in a reaction, or something else (atmospheric water, for example)? Burfield and Smithers saw about equal effectiveness for 3 angstrom versus 4 angstrom sieves in drying DMF, but had very good results with sequentially using 3 Å sieves. I am not sure that this is relevant to your application.
Do you mean water in the solvent, water that is produced in a reaction, or something else (atmospheric water, for example)? Burfield and Smithers saw about equal effectiveness for 3 angstrom versus 4 angstrom sieves in drying DMF, but had very good results with sequentially using 3 Å sieves. I am not sure that this is relevant to your application.
I have a ton of faith in sieves. How are you doing it with them? Are the fully activated? Fully activating them requires some fairly considerable asskicking conditions. 250°C+ under vacuum for a few hours is preferable.
Are you leaving them in the solvent long enough? Different solvents have quite different drying kinetics with sieves. 3A is preferred over 4A. You should also load it at 10-20% m/v.
I have a ton of faith in sieves. How are you doing it with them? Are the fully activated? Fully activating them requires some fairly considerable asskicking conditions. 250°C+ under vacuum for a few hours is preferable.
Are you leaving them in the solvent long enough? Different solvents have quite different drying kinetics with sieves. 3A is preferred over 4A. You should also load it at 10-20% m/v.
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I think the amount water present is much to small to be removed by DS-trap at least if I use it the conventional way but I will try that.
To ground the sieves is an interesting option, I have done that when doing Sharpless epoxidation with good result.
I think the amount water present is much to small to be removed by DS-trap at least if I use it the conventional way but I will try that.
To ground the sieves is an interesting option, I have done that when doing Sharpless epoxidation with good result.
More
VOTE
Agreed. It's been posted many times I'm sure, but for the effectiveness of sieves in solvent drying, see:
https://pubs.acs.org/doi/full/10.1021/jo101589h?src=recsys
Agreed. It's been posted many times I'm sure, but for the effectiveness of sieves in solvent drying, see:
https://pubs.acs.org/doi/full/10.1021/jo101589h?src=recsys
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Silylating agents work well and they do both. Calcium hydride would remove water forming CaOH2 and also ROH forming CaOR2 I suppose?
Silylating agents work well and they do both. Calcium hydride would remove water forming CaOH2 and also ROH forming CaOR2 I suppose?
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Are you leaving them in the solvent long enough? Different solvents have quite different drying kinetics with sieves. 3A is preferred over 4A. You should also load it at 10-20% m/v.
Are you leaving them in the solvent long enough? Different solvents have quite different drying kinetics with sieves. 3A is preferred over 4A. You should also load it at 10-20% m/v.
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VOTE