In an E1 reaction using cyclohexanol with phosphoric acid as a catlyst to produce Cyclohexene + water(also used potassium carbonate as drying agent)
My questions are what are the possible bases in this reaction? And which is the strongest that would be most likely to abstract the Beta Proton in the E1 reaction?
My hunch is that one of the bases is H3O, being the strongest, but what else could there be? Is the other one water?
I found this site showing a possible mechanism. I think it is unlikely that H^+ or H3O^+ is a base. I think it is more likely to be H2O and the carbocation loses a proton to water.
http://wwwchem.uwimona.edu.jm:1104/lab_manuals/c10expt8.html
My professor also said that its water, but he also asked my what else is in the reaction that could potentially act as a base. Is there anyway that phosphoric acid can turn into a base?
It is unlikely that H3PO4 can act as a base; however, since H3PO4 is a relatively weak acid (it has three Ka; k1,k2 and k3), the conjugate base of H3PO4 is H2PO4^- which can act both as an acid and a base. K1 for H3PO4 is approximately 10^-2 which makes H2PO4^- a weak base but a base anyway. It's a weaker base than OH^- for example.
In an E1 reaction, the reaction mechanism involves the formation of a carbocation intermediate. The abstracting base in this type of reaction is usually a weak base. In the given reaction using cyclohexanol with phosphoric acid as a catalyst, the possible bases can include:
1. Water (H2O): Water can act as a base by abstracting a proton from the β-carbon in the cyclohexanol molecule, forming the cyclohexene product and a hydronium ion (H3O+).
2. Hydrogen phosphate ion (HPO42-): Phosphoric acid can deprotonate to form hydrogen phosphate ion, which can also abstract a proton from the β-carbon to generate the alkene product.
In the E1 reaction, the strength of the base is not crucial because the rate-determining step involves the formation of the carbocation intermediate. However, the stronger the base, the more it will compete with the acid catalyst in abstracting the proton. Since water is a stronger base than hydrogen phosphate ion, it is more likely to abstract the β-proton in this scenario.
To summarize, the possible bases in the E1 reaction using cyclohexanol with phosphoric acid as a catalyst can include water (H2O) and hydrogen phosphate ion (HPO42-). Water is considered to be the stronger base of the two, making it more likely to abstract the β-proton in the E1 reaction.