Preparation of Haloalkanes from Alcohols

This set of flashcards covers the various chemical reagents and mechanisms used to prepare haloalkanes from alcohols as outlined in the lecture notes.

Lucas Reagent

A combination of $\text{HCl}$ and $\text{anhy. } ZnCl_2$ used to convert alcohols ($R-OH$) into haloalkanes ($R-Cl$) through an $SN_1$ mechanism.

Reaction with $NaBr$ and $H_2SO_4$

A method to prepare alkyl bromides ($R-Br$) from alcohols according to the equation: $R-OH + NaBr + H_2SO_4 \rightarrow R-Br + NaHSO_4 + H_2O$.

Reaction with $PX_3$ ($X = Cl, Br$)

The reaction of three equivalents of alcohol with phosphorus trihalide ($3 R-OH + PX_3 \rightarrow 3 R-X + H_3PO_3$) which proceeds via an $SN_2$ mechanism.

Reaction with $PCl_5$

The conversion of an alcohol ($R-OH$) to an alkyl chloride ($R-Cl$) using phosphorus pentachloride, producing phosphorus oxychloride ($POCl_3$) and $HCl$ via an $SN_i$ mechanism.

Phosphorous oxychloride

The byproduct with the formula $POCl_3$ formed when an alcohol reacts with $PCl_5$.

Red hot $P/X_2$ method

A preparation method where an alcohol ($R-OH$) reacts with red hot phosphorus and a halogen ($X_2 = Br_2, I_2$) to form a haloalkane ($R-X$).

Thionyl chloride ($SOCl_2$)

A reagent used to convert alcohols to alkyl chlorides ($R-Cl$) which produces gaseous byproducts that are easily removed.

Darzens reaction

The reaction of an alcohol with thionyl chloride ($SOCl_2$) to produce an alkyl chloride, considered the best method of preparation because the byproducts ($SO_2$ and $HCl$) are escapable gases.

Mechanism of Darzens reaction

The specific reaction pathway for the Darzens reaction between an alcohol and thionyl chloride, identified as an $SN_i$ mechanism.