# Determining the mechanism followed when alcohols undergo a reaction with sodium bromide and sulphuric acid

$$\ce{R-OH + NaBr + H2SO4 -> R-Br + NaHSO4 + H2O}$$

Due to sulphuric acid, the $$\ce{-OH}$$ group will get protonated and convert into $$\ce{-H2O+}$$ which is a great leaving group in comparison to the hydroxyl group. Therefore I assumed it would readily form a carbocation and then $$\ce{Br-}$$ could attack to form the alkyl bromide.

That is, it would follow the SN1 pathway (since the reaction is happening in 2 steps, first the formation of carbocation and then the attack of $$\ce{Br-}$$) but I also read somewhere that we might need to have a look on the substrate, if it is primary then it would follow SN2.

I am a bit confused after so many conditions and situations being introduced so I was hoping if someone could give me a brief and crisp explanation about this, and is there any particular factor that needs to be focused on before judging this mechanism?

• Both reaction happen but the extent of each reaction depends on what the R is and to some extent on the solvent. May 6 at 13:21
• Alright, so is it safe to assume that it would majorly follow SN2 if it is a primary alcohol and SN1 for a tertiary alcohol? Also, what should be our approach for a secondary one? Do we simply conclude that SN2 and SN1 both happen in a considerable amount? I'm not sure about the solvent part because my book didn't mention anything else but the reaction that I mentioned. May 6 at 14:45