Alkyl Halides & Alcohols Reactions PDF

Reactions of Alkyl Halides 1) Nucleophilic substitution reactions Nucliophiles are species that carry negative charge or available lone pair e.g. OH-, RO-, CN-, Br- or :NH3 Problem: Write the reaction of propyl chloride with all reagents in this slide. Amine preparation 2) Elimination Rea...

Reactions of Alkyl Halides 1) Nucleophilic substitution reactions Nucliophiles are species that carry negative charge or available lone pair e.g. OH-, RO-, CN-, Br- or :NH3 Problem: Write the reaction of propyl chloride with all reagents in this slide. Amine preparation 2) Elimination Reactions Zaitsev’s rule  Reactions of Alcohols 1- Preparation of alkoxides:  2- Preparation of ethers: Williamson synthesis Works well with 1o alkyl halides However, with 2o or 3o alkyl halides elimination (E1 or E2 respectively) takes place according to Zajtsev rule (elimination occurs on the more substituted carbon atom). Solution: Which route you choose to prepare ethyl i-propyl ether? What is the product of the second route? Substitution vs Elimination Of Alkyl Halides Alkoxymercuration of Alkenes We saw that alkenes react with water in the presence of mercuric acetate to yield a hydroxymercuration product. Subsequent treatment with NaBH4 breaks the C- Hg bond and yields the alcohol. A similar alkoxymercuration reaction occurs when an alkene is treated with an alcohol in the presence of mercuric acetate or, even better, mercuric trifluoroacetate, (CF3CO2)2Hg. Demercuration by reaction with NaBH4 then yields an ether. The net result is Markovnikov addition of the alcohol to the alkene. Problems How would you prepare the following ethers? Primary alkyl halide C4​H9​Br (a) reacted with alcoholic KOH to give compound (b). Compound (b) is reacted with HBr to give (c) which is an isomer of (a). How can you prepare (a) from (b). When (a) is reacted with sodium metal it gives compound (d), C8​H18​ which is different from the compound formed when n-butyl bromide is reacted with sodium. Give the structural formula of (a) and write the equations for all the reactions.  3- Conversion of Alcohols into Alkyl Halides Tertiary alcohols react with either HCl or HBr at 0 °C by an SN1 mechanism through a carbocation intermediate. Primary and secondary alcohols are much more resistant to acid, however, and are best converted into halides by treatment with either SOCl2 or PBr3 through an SN2 mechanism.  Primary and secondary alcohols Primary and secondary alcohols are best converted into alkyl halides by treatment with either thionyl chloride (SOCl2) or phosphorus tribromide (PBr3). These reactions, which normally take place readily under mild conditions, are less acidic and less likely to cause acid-catalyzed rearrangements than the HX method. Thionyl Chloride  4- Dehydration of Alcohols to Yield Alkenes An important reaction of alcohols, both in the laboratory and in biological pathways, is their dehydration to give alkenes. One method that works particularly well for tertiary alcohols is the acid-catalyzed reaction. The reaction is an E1 process. Acid- catalyzed dehydrations usually follow Zaitsev’s rule and yield the more stable alkene as the major product. Teriary alc E1 Alcohol dehydrations carried out in basic condition with POCl3 in pyridine take place by an E2 mechanism. pri and sec alc E2 5- Ester formation: Problems: Draw and name the esters formed from the following reactions: * Propionic acid + methanol * Benzoic acid + propanol * Pentanoic acid + isopropanol * Ac2O + Hexanol * Propionyl chloride + butanol 6- Oxidation of alcohols:  Oxidizing agents Strong oxidizing agents Moderate oxidizing agents Problems: 1) Show the difference between the reaction of 2-chloropentane with either aqueous or alcoholic KOH. 2) How do you prepare ethyl magnesium chloride (Grignard reagent) from ethanol? 3) Show how you perform the following transformations: 4- Complete the following reactions: