Reactions of Alkyl Halides in Chemistry

Study Notes

Reactions of Alkyl Halides

Nucleophiles are species with a negative charge or available lone pairs (e.g., OH, RO⁻, CN, Br⁻, or :NH₃).
Alkyl halides undergo nucleophilic substitution reactions.
Different nucleophiles lead to different products.
- Hydroxide (NaOH) gives alcohol
- Alkoxide (R'ONa) gives ether
- Carboxylate (R'COONa) gives carboxylate
- Bisulfide (NaHS) gives thiol
- Sulfide (NaSR') gives sulfide
- Cyanide (NaCN) gives nitrile
- Bromide (NaBr) gives bromide
- Acetylinide (NaC≡C⁻R') gives acetylene
- Azide (NaN₃) gives azide
- Grignard reagent (Mg, ether) gives Grignard reagent

Amine preparation

SN₂ reactions are used to prepare amines from alkyl halides and ammonia or amines.
- Treating an alkyl halide (RX) with ammonia (NH₃) yields a primary amine (RNH₂).
- Treating an alkyl halide (RX) with a primary amine (R'NH₂) yields a secondary amine (R'NHR).
- Treating an alkyl halide (RX) with a secondary amine (R'₂NH) yields a tertiary amine (R'₂NR).
- Treating an alkyl halide (RX) with a tertiary amine (R'₃N) yields a quaternary ammonium salt (R'₃NR⁺).

Elimination Reactions

Zaitsev's rule: In elimination reactions of HX from alkyl halides, the more highly substituted alkene is the major product.
Elimination reactions produce alkenes, forming a double bond.
KOH (alcoholic) and other reagents generate alkenes.

Problems (various problems)

Various reactions and their products are described in the documents concerning alkyl halides, alcohols, ethers, and other compound transformations. The specific reactions and desired products should be referred to the details of each problem.

Reactions of Alcohols

Preparation of alkoxides: NaNH₂ or Na can convert alcohols (R-OH) into alkoxides (R-ONa).
Preparation of ethers: Williamson synthesis is a useful method for making ethers from alkyl halides and alkoxides.

Alkoxymercuration of Alkenes

Reaction of alkenes with water and mercuric acetate gives hydroxymercuration products.
NaBH₄ reduces the C-Hg bond (via a mercuric trifluoroacetate intermediate) to give an ether.

Problems (various problems - continued)

Various reactions and their products are referred to in the documents concerning alkyl halides, alcohols, ethers, and other compound transformations. The specific reactions and desired products should be referred to the details of each problem.

Conversion of Alcohols into Alkyl Halides

Tertiary alcohols react with HCl or HBr at 0°C through an SN1 mechanism (carbocation intermediate).
Primary and secondary alcohols react with SOCl₂ or PBr₃ through SN₂ mechanisms.

Lucas Test

Differentiates alcohol types (primary, secondary, and tertiary) based on reaction rate with conc. HCl and anhydrous ZnCl₂.
- Tertiary alcohols react immediately.
- Secondary alcohols react after 5 minutes.
- Primary alcohols show no reaction at room temperature.

Primary and Secondary Alcohols

Primary and secondary alcohols are best converted to alkyl halides using thionyl chloride or phosphorus tribromide.
These methods are often preferred over HX methods due to the lower risk of acid-catalyzed rearrangements.

Ester Formation

Ester formation involves an acid reacting with an alcohol.
Acid chlorides, anhydrides, and carboxylic acids can react to form esters.

Oxidation of Alcohols

Primary alcohols are oxidized to aldehydes and further to carboxylic acids.
Secondary alcohols are oxidized to ketones.
Tertiary alcohols do not undergo oxidation.

Oxidizing Agents

Strong oxidizing agents (e.g., KMnO₄, K₂Cr₂O₇/H₂SO₄) oxidize alcohols.
Moderate oxidizing agents (e.g., PCC) selectively oxidize primary alcohols to aldehydes.

Dehydration of Alcohols to Yield Alkenes

Acid-catalyzed dehydration of alcohols is an effective method for producing alkenes.
Zaitsev's rule typically applies, favoring the more stable alkene product where possible.

Additional Problems (various problem types)

Various reactions and their products for alkyl halides, alcohols, ethers, etc., are introduced throughout the documents. Specific detail requires referring to the problem context for specific reactants/products.