Home > Community > Is iso-butanol more soluble in water than 1-butanol?
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+ Solubility
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Neal Pepper

Is iso-butanol more soluble in water than 1-butanol?

Barry Gehm  Follow

First, understand that the solubility of alcohols decreases with the increasing number of carbon atoms.

If I may ask, look at iso-butanol and count the number of C atoms?

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Castle Richard  Follow

Butanol.
It's an alcohol i.e. it has an O-H group which is polar. Now because of this, it can form H Bond with water, which is also polar H-O-H.
Butane on the other hand, is a non polar molecule and thus isn't likely to dissolve in a polar solvent.

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Choo Laik Tan  Follow

Methanol, ethanol, propanol…these are all -OH groups saturated with an extra hydrocarbon link (CH3OH, CH3CH2OH, CH3CH2CH2OH…etc). The -OH group at the end is the polar bit that allows the otherwise non-poloar CH groups to be soluble in water, however, the more and more you add to the non-polar end, the more difficult it is to dissolve in a polar solvent like H2O (HOH).

It’s interesting to note that pork fat and olive oil (try dousing a layer of water with either) are nowhere near miscible (dissolvable) in water…yet there is an, OH group at the end of each…ENORMOUS chain of non-polar carbohydrates (CH2s). It’s this chain if non-polar carbons and hydrogens that begins -s after enough repetition - to render the molecules to which they’re attached unable to dissolve in a polar solvent like water (whose molecules are very small and VERY polar)

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Brittany Roma  Follow

Butanol is much better. It contains about 30 percent more energy per gallon than ethanol, is easier to handle and more of it can be blended into each gallon of gasoline. ... Catalysts speed up chemical reactions by lowering the amount of energy needed need to jumpstart reactions.

Butanol has about 1.5 times more volumetric energy content than ethanol. Another advantage over ethanol is that butanol has decreased water solubility; therefore, butanol can be both an additive to fuel and a standalone fuel source.

Butanol has about 1.5 times more volumetric energy content than ethanol. Another advantage over ethanol is that butanol has decreased water solubility; therefore, butanol can be both an additive to fuel and a standalone fuel source.

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Daniel Lynge  Follow

The answer is yes. Generally, the more substituted isomer is more water soluble. In this case the difference is quite remarkable. The water solubility of 1-butanol is 70–80 g / L of H2O, likewise for iso-butanol (2-methyl-propan -1-ol) (various sites give this range of solubilities so, empirically, can’t say and have to stay with the prediction.

Edit: Thanks to Claudio Gemini for letting me know my answer was wrong. It has been corrected.

Edit 2: Geez, sometimes it is best to quit while you are ahead. I meant to write Claudio Giomini, not Claudio Gemini but auto correct changed Giomini to Gemini and I did not note.

From Claudio’s 2nd comment, indeed the source I used said 87 ml/L. I thought this was the oddest way I had ever seen a water solubility written and that perhaps it was in error and should really be 87 g/L. On googling a bit and finding multiple water solubilities for it, all I can say is that it has a water solubility of 70–80 g/L of water. Unfortunately, the same is true for 1-butanol so, from the reported values, it is hard to give an empirical based answer.

However, alkyl chains are the hydrophobic component of these compounds. The 1-butanol has the least water solubility due to the larger surface area of the hydrophobic component. The t-butyl alcohol has the greatest water solubility because the hydrophobic component has a lower surface area due to the more spherical nature of the alkyl chain. isobutanol resides in between so the prediction is isobutanol will be more water soluble than 1-butanol.

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Connor Becz  Follow

mu.

Solubility is not applicable when describing the interactions between identical compounds. Talking about the solubility of water in water is equally nonsensical as talking about the speed of red, or the color of a tone of 1000 Hz, or the temperature of a perfect vacuum.

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Anil Saraf  Follow

Because it is better at hydrogen bonding.

The OH on the alcohol can hydrogen bond as a hydrogen acceptor and donor. Water can hydrogen bond. Like dissolves like. So, when you have a molecule that can act as a donor and acceptor you end up with a much better interaction with water and end up with something that is more miscible. Ethers are only acceptors since they do not have a hydrogen attached to the oxygen. So, they can only accept a proton from water.

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Attraction & Success  Follow

There are four butanols, as in the list at the end of this answer. The first two are linear-chain alcohols; the third and fourth are branched-chain ones. As you can see, the solubilities in water of 1-butanol and iso-butanol are not very different, although iso-butanol is somewhat more soluble. The reason could be that both are primary alcohols and, in both cases, the C atom holding the -OH group is attached to only one hydrophobic carbon chain of the same size (three carbon atoms), irrespective of being linear or branched. Yet, in iso-butanol, the surface area of the hydrophobic chain C3H7 should be somewhat smaller than in 1-butanol, which should account for the larger solubility of the former. As for the other two isomers, for secondary alcohol 2-butanol, the C atom holding the -OH group is at the junction of two carbon chains of two and one carbon atoms, whose sizes are smaller than those of 1-butanol and iso-butanol. Last, for tert-butanol, which is a tertiary alcohol, the C atom holding the -OH group is at the junction of three extremely short carbon “chains” of just one carbon atom. Small-size hydrophobic chains, despite their larger number, seem to improve water solubility. As a conclusion, for these isomeric alcohols, the rule seems to be that the more substituted is the OH-holding carbon, the more soluble is the alcohol. When equally substituted, as for iso-butanol and 1-butanol, the smaller the surface area of the hydrophobic chain, the larger the solubility.

Finally, I would thank prof. P. Gannett for suggesting that a previously reported solubility datum of mine about iso-butanol was questionable.

  1. —- 1-butanol 73 g/L
  2. —- 2-butanol 290 g/L
  3. —- 2-methylpropan-1-ol (aka isobutanol) about 87 g/L
  4. —- 2-methylpropan-2-ol (aka tert-butanol) completely miscible.

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Brad Walter  Follow

It has to do with the concept of chemical polarity. The chemical polarity refers to the separation of electrical charge with respect to the actual molecule itself. It is solely dependent on the atom species constituting the molecule and there electronegativity. The electronegativity describes the tendency of an atom to attract electrons towards itself. As a consequence, we speak about non-polar and polar molecules. The polar molecules have intra molecular charge separation whereas the non-polar has not. The concept of electronegativity was first introduced by the Swedish chemist Jöns Jacob Berzelius in 1811.

The two major solvents in organic chemistry are commonly referred to as water solution and organic solution. The prior (water) is very polar, due to the oxygen atom with high electronegativity, and the other (organic phase) is normally very non-polar due to the structure and symmetry of organic molecules that normally has long hydrocarbon chains with low intra molecular charge separation.

Coming back to your question. Methanol is a very small molecule consisting of only one carbon atom, a few hydrogen atoms and one hydroxyl group (-OH). The buthanol molecule comprises of a longer hydrocarbon chain (four carbons) and one -OH. Due to the longer hydrocarbon chain of buthanol, it is less polar and consequently less soluble in water compared to methanol.

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Brian Tucker  Follow

Yes , solubility of alcohols in water decreases with increase in molecular mass. In case of methanol, alkyl group present in smaller,and hence it forms strong hydrogen bonding with water.

On other hand,in case of propanol ,size of Alkyl group is large,hence hydrophobic part is dominant. Thus propanol is less soluble than methanol.

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