CycloRook
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Solvents ?
I have a very general question about solvents. I understand the idea behind polar and non polar solvents as well as some solvents reacting with other
chemicals as a reactant.
My question for example; if you had a synthesis that called for ether as a solvent could you use ethanol or methylene chloride in its place ?
I understand that one boils higher than the other and that this is all subjective but as a guide how would one determine substitution ?
I get that using hexane in a reaction containing something polar in place of methanol probably would work since one is polar and the other isn't
This is most likely a very complicated subject and I'm just looking for a starting point.
Thank you
[Edited on 4-1-2022 by cycloknight19]
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DraconicAcid
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It depends on what reaction you're doing. Some reactions require specific solvents, others require the absence of certain solvents.
Grignard reactions, for example, require the presence of an ether to form the organomagnesium halide. You can replace diethyl ether with THF or
glyme, but not toluene or dichloromethane. Once you've made the RMgX, you can have toluene or benzene in the solvent mixture, but not an ester,
ketone, or alcohol.
If you're extracting something organic from aqueous solution, dichloromethane will generally work just as well, but alcohol or acetone won't (because
it mixes with the water). Toluene might work, but then it's hard to boil off the solvent to get your extract out. Ethyl acetate would work, unless
the aqueous solution is acidic or basic enough to hydrolyze the ester.
Hydrocarbons are generally interchangeable, unless the boiling points are a problem (if the reaction calls for refluxing the reaction in toluene,
using pentane instead won't get you anywhere. If you want your solvent to boil off easily, decalin isn't a good choice). Photolysis with UV will
work in an alkane solvent, but aromatics are opaque to UV.
Light alkanes such as pentane and hexane are crappy solvents, and often good antisolvents, for most mildly polar solutes.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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MichaelBijanAfghani
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Solubility is different between hydrocarbons, too. For example, salicylic acid is soluble in aromatics such as toluene and benzene, but not in
aliphatics such as hexane. I guess because of favorable stacking interactions between the aromatic rings of solvent and salicylic acid, but I pulled
that out of my butt.
[Edited on 5-1-2022 by MichaelBijanAfghani]
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DraconicAcid
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Quote: Originally posted by MichaelBijanAfghani  | Solubility is different between hydrocarbons, too. For example, salicylic acid is soluble in aromatics such as toluene and benzene, but not in
aliphatics such as hexane. I guess because of favorable stacking interactions between the aromatic rings of solvent and salicylic acid, but I pulled
that out of my butt.
[Edited on 5-1-2022 by MichaelBijanAfghani] |
That's why I singled out the light alkanes as crappy solvents. Aromatics tend to be better solvents for many things (due to greater polarizability?),
but there's also some weird effects that make toluene a better solvent for big, complex molecules than benzene, and methylcyclohexane better than
cyclohexane.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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CycloRook
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| Quote: Originally posted by DraconicAcid | It depends on what reaction you're doing. Some reactions require specific solvents, others require the absence of certain solvents.
Grignard reactions, for example, require the presence of an ether to form the organomagnesium halide. You can replace diethyl ether with THF or
glyme, but not toluene or dichloromethane. Once you've made the RMgX, you can have toluene or benzene in the solvent mixture, but not an ester,
ketone, or alcohol.
If you're extracting something organic from aqueous solution, dichloromethane will generally work just as well, but alcohol or acetone won't (because
it mixes with the water). Toluene might work, but then it's hard to boil off the solvent to get your extract out. Ethyl acetate would work, unless
the aqueous solution is acidic or basic enough to hydrolyze the ester.
Hydrocarbons are generally interchangeable, unless the boiling points are a problem (if the reaction calls for refluxing the reaction in toluene,
using pentane instead won't get you anywhere. If you want your solvent to boil off easily, decalin isn't a good choice). Photolysis with UV will
work in an alkane solvent, but aromatics are opaque to UV.
Light alkanes such as pentane and hexane are crappy solvents, and often good antisolvents, for most mildly polar solutes.
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This is good. Definitely gave me more insight. Thanks
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CycloRook
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I hate ordering solvents and they are somewhat expensive. I have xylene toluene denatured alcohol isopropyl alcohol DCM readily available. Some of my
experiments call for Chloroform and Tetrahydrofuran. I find this to be annoying. Can any of the above be substituted ? Liquid-liquid extraction
Liquid-solid extraction. Nothing with hardcore acids
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CycloRook
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Bump
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Tsjerk
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You don't have to bump after three hours, your post will be visible in the last day list for 24 hours, and besides; many people look back further than
that.
You have to be more specific, you can't really generalise solvents as you do.
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Herr Haber
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Depends on what you are doing really, Tsjerk is right.
Draconic Acid gave a great clear and concise reply reply to your first question. Loved it.
As for your second question, without knowing more the answers will be vague. But yes, in some cases DCM and Chloroform can be substituted.
I dont see anything in your list that could replace THF in the reactions that I can think about. Diethyl ether could, maybe work.
Again, this is very dependent on what you are doing.
DCM and THF are great to repair / glue plastics.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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Monoamine
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I really don't understand why people seem to use chlorinated solvents for performing AlCl3-catalysed Friedel-Crafts alkylations (or
acylations). Why doesn't the substrate get alkylated by the chlorinated solvents themselves too??
Come to think of it... What would a good solvent be? Ether? Hexane?
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MaeBorowski
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Ether looks like a bad solvent for Friedel-Crafts because of the nucleophilic oxygen. Hexane, as well as carbon disulfide, petroleum ether and
nitrobenzene are classic choise. Also, you can use an excess of your substrate e. g. benzene, toluene or something else.
please leave comments about my English in PM
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CycloRook
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| Quote: Originally posted by Tsjerk | You don't have to bump after three hours, your post will be visible in the last day list for 24 hours, and besides; many people look back further than
that.
You have to be more specific, you can't really generalise solvents as you do. |
anthranillic acid to methyl
anthranilate. Extraction calls for water and diethyl ether liquid liquid extraction.
Can I use DCM ?
If so why what's the difference with diethyl ether?
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Tsjerk
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| Quote: Originally posted by cycloknight19 | anthranillic acid to methyl anthranilate. Extraction calls for water and diethyl ether liquid liquid extraction.
Can I use DCM ?
If so why what's the difference with diethyl ether? |
That should work, I assume it is only for workup right? In that case you just need an apolar solvent in which methyl anthranilate is soluble. Too
apolar would make you need more solvent, but ether and DCM are in the same ballpark.
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DraconicAcid
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| Quote: Originally posted by Monoamine | I really don't understand why people seem to use chlorinated solvents for performing AlCl3-catalysed Friedel-Crafts alkylations (or
acylations). Why doesn't the substrate get alkylated by the chlorinated solvents themselves too??
Come to think of it... What would a good solvent be? Ether? Hexane? |
Dichloromethane is far less reactive towards FC alkylations than singly-chlorinated alkanes (especially tertiary ones). It's an excellent solvent
with the milder FeCl3 catalyst.
I'm not sure hexanes would work- they're pretty lousy for the formation of the intermediate carbocations. Ethers and alcohols are right out because
they coordinate the metal catalyst. Nitromethane and nitrobenzene work, but are nasty to work with.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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CycloRook
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| Quote: Originally posted by Tsjerk | | Quote: Originally posted by cycloknight19 | anthranillic acid to methyl anthranilate. Extraction calls for water and diethyl ether liquid liquid extraction.
Can I use DCM ?
If so why what's the difference with diethyl ether? |
That should work, I assume it is only for workup right? In that case you just need an apolar solvent in which methyl anthranilate is soluble. Too
apolar would make you need more solvent, but ether and DCM are in the same ballpark. |
Yes just for workup.
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CycloRook
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There are a few bromination reactions I'm interested in. One of them calls for chloroform to be used. Is there a reason I can't use DCM ?
I read that ethanol or DEG can be used. I assume the reason it asks for chloroform is because it's less prone to be brominated. The reactions us
bromosuccinimide.
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CycloRook
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| Quote: Originally posted by cycloknight19 | There are a few bromination reactions I'm interested in. One of them calls for chloroform to be used. Is there a reason I can't use DCM ?
I read that ethanol or DEG can be used. I assume the reason it asks for chloroform is because it's less prone to be brominated. The reactions us
bromosuccinimide. |
Wohl–Ziegler bromination
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stinkypower96
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| Quote: Originally posted by cycloknight19 | There are a few bromination reactions I'm interested in. One of them calls for chloroform to be used. Is there a reason I can't use DCM ?
I read that ethanol or DEG can be used. I assume the reason it asks for chloroform is because it's less prone to be brominated. The reactions us
bromosuccinimide. |
As you said the reason is because chloroform is less prone to further halogenation. In fact the ideal solvent for this reaction would be carbon
tetrachloride, although since it's always more difficult to get some CCl4, chloroform is the best second choice that I can think of.
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CycloRook
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| Quote: Originally posted by stinkypower96 | | Quote: Originally posted by cycloknight19 | There are a few bromination reactions I'm interested in. One of them calls for chloroform to be used. Is there a reason I can't use DCM ?
I read that ethanol or DEG can be used. I assume the reason it asks for chloroform is because it's less prone to be brominated. The reactions us
bromosuccinimide. |
As you said the reason is because chloroform is less prone to further halogenation. In fact the ideal solvent for this reaction would be carbon
tetrachloride, although since it's always more difficult to get some CCl4, chloroform is the best second choice that I can think of.
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I would imagine that this is the case bit I found this page that says otherwise. https://www.researchgate.net/post/What_are_the_other_solvent...
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CycloRook
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Does anyone know?
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CycloRook
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Can 2-Methyltetrahydrofuran replace Tetrahydrofuran completely for grignard reactions ?
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CycloRook
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Can someone please answer this question if they know so I don't have to post another topic about 2-Methyltetrahydrofuran
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