Chapter 9 Alcohol Reactions Reactions of Alcohols with Acids and Bases Preparations of Alkoxides To deprotonate an alcohol, Base more basic than RO- Alkali Metal Reductions give Alkoxides 2 H2O + Na (Li, K, Cs) 2 Na+OH- + H2 (Violent!) 2 ROH + Na 2 Na+OR- + H2 Reactivity: MeOH > primary > secondary > tertiary

3) Uses of Alkoxides Strong base for E2 reactions Ether synthesis by SN2 reactions (stay tuned!) Protonation of Alcohols form a better Leaving Group X- + ROH RX + OH- (OH- is a poor leaving group) Strong acid converts OH- leaving group to H2O (good leaving group) Synthesis of Haloalkanes from Alcohols Only I- and Br- are nucleophilic enough to work Works best for primary alcohols

4) Reaction of Secondary and Tertiary ROH with H+ a) Secondary and Tertiary alcohols easily lose water to from carbocations If the acid contains a good nucleophile, you get SN1 substitution If there is no nucleophile or have high Temperature, you get E1 Dehydration = loss of an H2O molecule Use non-nucleophilic acid = H2SO4, H3PO4 As usual, Tertiary ROH only does SN1, E1 while Secondary ROH can do SN2, SN1, or E1 in a strong acid Catalytic

Carbocation Rearrangement Hydride Shift Sometimes we get mixtures of products from 2o and 3o ROH reactions How does the rearrangement occur? Carbocation intermediate rearranges Hydrogen and both electrons move = hydride shift Mechanism H:- and + trade places Very fast (faster than SN1/E1) if new C+ more stable

Orbital Picture of the Hydride Shift Mechanism Primary ROH/RX won’t form carbocations, so don’t do Hydride Shift Secondary and Tertiary ROH give mixture of products with nucleophile

Mixture of E1 Products are also observed at high Temp., no nucleophile B. Alkyl Shifts If the carbocation doesn’t have a H- positioned to shift, an alkyl group can move = Alkyl Shift

Ester Formation from Alcohols Hydride and Alkyl Shifts occur at about the same rate Very fast if rearranged carbocation is more stable Formation of tertiary carbocation is faster than secondary Concerted Hydride and Alkyl Shifts in Primary Alcohols Primary alcohol will not form a carbocation, but sometimes rearranged products are observed anyway Only observed with much heat and much time Concerted mechanism explains how Ester Formation from Alcohols Esters are derivatives of organic and inorganic acids

Synthesis of Organic Esters Subject of chapters 19 and 20 Synthesis of Haloalkanes from Alcohols involves Inorganic Esters R—OH + HBr R+ multiple products Use Inorganic Reagent to make the water leaving group 1o or 2o ROH + PBr3 1o or 2o RBr + H3PO3 Mechanism Reaction also works to make iodoalkanes with PI3 Chlorination of an alcohol requires thionyl chloride = SOCl2

Mechanism Amine works as a base to remove H+ from reaction Alkyl Sulfonates in Substitution Reactions Preparation of Alkyl Sulfonates (good leaving groups) Substitution reactions take advantage of the good sulfonate leaving group