Weak acids/strong bases

[rthmjohn]

I read in my text book that alcohols like methanol don't react with strong acids like sodium hyroxide. They will react, however, with organic acids. Why is this? Does this apply to all weak acids and strong bases?

[YT2095]

Sodium Hydroxide is a Base and not Acid.

they will react with Strong acids, Sulphuric acid will dehydrate Ethanol for instance and make Diethyl Ether.

[woelen]

Some alcohols also can react with HCl or HBr, forming the chloro-substituted compound. E.g., refluxing isopropyl alcohol (rubbing alcohol) with conc. hydrobromic acid gives CH3CHBrCH3 and H2O.

[budullewraagh]

alcohols may react with bases.

 

for example, NaH definitely will deprotonate an alcohol to form an alkoxide.

even NaOH will deprotonate some alcohols. consider what happens when you leave solid NaOH on paper- it collects moisture and the paper turns greenish yellow. while the MeO- anion is more basic than the OH- anion (which is why we don't see a reaction between MeOH and OH-) different types of alcohols may react. the reason we see a reaction between NaOH and paper is that the sugars in the paper are filled with vicinal hydroxyl groups, which makes each one of them more acidic. also, there's that carbonyl, which makes the adjacent OH groups more acidic.

 

but why do alcohols react with acids? the acids protonate the alcohols to form R-OH2+, which undergoes elimination via E1, then you have the conjugate base of the acid attack the resulting carbocation. (consider HCl+ROH reaction)

 

EDIT: merged two posts

 

also, i'd like to add to yt's post. when reacting ethanol with sulfuric acid, a number of products can be formed. true dehydration results in ethylene, though diethyl ether can be formed. it all depends on temperature.

[rthmjohn]

Allow me to rephrase my query; I was in an awful hurry when i first posted this thread and didn't bother to look at what I wrote. I know that sodium HYDROXIDE isn't and acid--hopefully I didn't sound too studpid there. What I meant to ask was why alcohols don't react with strong BASES and if this applies to all weak acids.

[budullewraagh]

alcohols may react with hydroxide, as mentioned above. however, something like ethanol really won't. the pKa of ethanol is approximately 16, whereas the pKa of water is about 15. ethoxide (EtO-) is therefore a stronger base than hydroxide, and so it holds onto its protons more strongly.

[rthmjohn]

thanks