Solubility of glycine

[Mendelejev]

Could someone explain me why glycine isn't soluble in organic solvents. My prof said this today !! If you take some pure glycine in water it should be a zwitterion, so there would be positive and negative charges. That means it would be very soluble in water. Secondly, the R-group in glycine is -H, not very apolar ! But organic solvents can be polar (methanol, ethanol, ...) and apolar (heptane, ...) !! So, it would be soluble in methanol and ethanol, but not in heptane.

 

Then, why does he says it's NOT soluble at all in organic solvents, included methanol and ethanol ???

[akcapr]

The poor solubility of glycine in organic solvents such ahs hydrocarbons lik etahnol and heptane is because of the weak of attraction between the organic solvent molecules and the zwitterions, i think. Without strong attractions between solvent and amino acid, ther isnt enough energy released to pull the ionic connections apart ahnd thus dissolve the amino acid.

 

btw glycines also known as : 2-aminoethanoic acid

 

Edit: also i have a side question: in the formula ^ it says ethanoic. Does that mean an ether group? if it does the structural formula doesnt have an ether (ether is oxygen connected to 2 alkyls), so why is it called eathnoic. if im totally wrong, then what is the ehtanoic part, wats the formula?

[Mendelejev]

Yes, but ethanol, for example, could create strong intermolecular forces with glycine. even Hydrogen bonds. SO, i still don't understand

[jdurg]

Ethanoic means that it contains an ethyl group. Acetic acid is another name for ethanoic acid.

[akcapr]

but acetic acid doesnt contain a full ethyl group in its formula? why is it said that it contains one?

[jdurg]

Look at the formula for acetic acid. CH3-COOH. The CH3-C means that there is a two carbon chain in the structure which is what an ethyl group is; a two carbon chain. Methanoic acid is HCOOH. It's called methanoic because it has the one carbon (methyl) backbone to it. Propanoic acid is CH3-CH2-COOH, butanoic acid is CH3-CH2-CH2-COOH. The methyl, ethyl, propyl designations have to do with the size of the carbon backbone in the molecule. If it has a two carbon backbone, it's ethyl. Three carbon and it's propyl. Etc. etc.

[akcapr]

ohhh cool. i get it

[quratulain]

can i acylate glycine with ethylacetate

[Vdubovoy]

Glycine is the smallest, most polar amino acid due to -COOH and -NH2 groups on a molecule weighing 75g/mol. It's solubility in a given solvent is governed by the magnitude of the solvent-solute interaction. I'm sure you've heard of the term like dissolves like, meaning polar compounds are more soluble in polar solvents and vice versa. So the solubility of glycine will increase from ethanol to methanol to water as polarity increases.

 

Similarly you can think of solubility as the competition between lattice and hydration enthalpies. In lamens terms, how thermo dynamically favorable it is for glycine to be surrounded by solvent molecules as opposed to other glycine molecules. In the case of ethanol and methanol, it is less favorable for glycine ions to be surrounded by solvent so dissolution is not spontaneous.

[lessthannovice]

Hi, I'm here because I'm not a chemist, but a clueless layperson (just to be candid!)-- I'm curious to know whether glycine is soluble in glycerin, aka glycerol, I believe. I could just buy some of each and test it, but I was wondering if anyone could provide some insight.

Thank you for your help!!!!

[chenbeier]

In water its soluble 225 g/l, so it will be also soluble in Glycerin.  This thread is 9 years old , please open a new thread next time.

[TheVat]

His post is precisely on topic and the earlier posts are useful background in understanding glycine's low miscibility in organic solvents.  All about the zwitterions. 

[lessthannovice]

Thank you for the help. Sorry it didn't occur to me to start a new thread. I actually stumbled across this forum because this thread came up as a search result when I was using a search engine to try to find an answer to my question. I wasn't holding out much hope to get an answer, so thank you for the pleasant surprise. You proved my hunch that real people who have put in the time to study a subject are more reliable than a search engine.

By the way, is it true that as a rule, something that is soluble in water will usually be soluble in glycerin, too?

[chenbeier]

Glycerin has 3 OH group which support the solubility, because of Hydrogen bridge bonding.

[exchemist]

3 hours ago, lessthannovice said:

Thank you for the help. Sorry it didn't occur to me to start a new thread. I actually stumbled across this forum because this thread came up as a search result when I was using a search engine to try to find an answer to my question. I wasn't holding out much hope to get an answer, so thank you for the pleasant surprise. You proved my hunch that real people who have put in the time to study a subject are more reliable than a search engine.

By the way, is it true that as a rule, something that is soluble in water will usually be soluble in glycerin, too?

It's best not to think of solubility in black and white terms. There are degrees of it. I don't know for a fact, but my guess would be that glycine has appreciable solubility in glycerol, but less than in water. I would expect the same to be true of many other polar compounds.

When it comes to ionic compounds (inorganic salts) it may be a more complex picture, depending on the success that a big molecule like glycerol has in binding to a small, charged ion.  Others here may have more knowledge of this than I do.

But directionally yes, glycerol, being polar, should be able to dissolve polar species significantly. 

[lessthannovice]

8 hours ago, exchemist said:

It's best not to think of solubility in black and white terms. There are degrees of it.

That is very informative and helpful to someone like me who honestly probably isn't going to put in the time and effort to understand all the "why" behind it. (partly because of some limits on both time and my personal mental capacity!) Many thanks!!!!!