Alkyl halides are synthesized from alcohols through a process known as nucleophilic substitution, utilizing a halogen acid.

To elaborate, the conversion of alcohols into alkyl halides involves a nucleophilic substitution reaction that occurs in two distinct steps. Initially, the alcohol acts as the nucleophile and reacts with a halogen acid, such as hydrochloric acid ($\text{HCl}$), hydrobromic acid ($\text{HBr}$), or hydroiodic acid ($\text{HI}$). This initial interaction produces an intermediate product, which subsequently undergoes a second reaction to yield the final alkyl halide.

In the first step, the oxygen atom of the alcohol donates a pair of electrons to the hydrogen atom of the halogen acid. This electron donation forms a bond between the oxygen and hydrogen atoms, resulting in the formation of a water molecule ($\text{H}_2\text{O}$) and leaving behind a positively charged alkyl group ($\text{R}^+$) along with a negatively charged halide ion ($\text{X}^-$).

During the second step, the positively charged alkyl group interacts with the negatively charged halide ion. The halide ion donates a pair of electrons to the alkyl group, establishing a bond between them and resulting in the formation of the final alkyl halide product.

It is crucial to recognize that the reaction conditions can significantly affect the results of this reaction. For instance, an acid catalyst is generally required to facilitate the reaction at a reasonable rate. Additionally, the specific choice of halogen acid can influence the outcome, as different halogen acids can lead to the production of various alkyl halides. Furthermore, the reaction is often conducted in the presence of a solvent, which can help regulate both the reaction rate and the formation of any by-products.

In summary, the preparation of alkyl halides from alcohols involves a nucleophilic substitution reaction with a halogen acid, proceeding through two steps to form an intermediate product before producing the final alkyl halide. The reaction conditions, including the selection of halogen acid and the presence of a solvent, play a significant role in determining the success and outcome of the reaction.