Preparation of ethanol Ethanol is manufactured by reacting

Preparation of ethanol • Ethanol is manufactured by reacting ethene with steam. The catalyst used is solid silicon dioxide coated with phosphoric(V) acid. The reaction is reversible. • • Only 5% of the ethene is converted into ethanol at each pass through the reactor. By removing the ethanol from the equilibrium mixture and recycling the ethene, it is possible to achieve an overall 95% conversion.

Making ethanol by fermentation This method only applies to ethanol. You can't make any other alcohol this way. • Yeast is killed by ethanol concentrations in excess of about 15%, and that limits the purity of the ethanol that can be produced. The ethanol is separated from the mixture by fractional distillation to give 96% pure ethanol. • For theoretical reasons, it is impossible to remove the last 4% of water by fractional distillation.

The manufacture of other alcohols from alkenes Take care of Markovnikov and anti Markovnikov additions

Reactions of Alcohols Acidic dehydration produces alkenes with the more substituted double bond (OH- is a bad leaving group, but H 2 O is a good leaving group, so the reaction starts by protonation of the OH group

Dehydration of tertiary butyl alcohol

Examples

Reaction of Alcohols with Hydrogen Halides The general reaction looks like this: A tertiary alcohol reacts if it is shaken with concentrated hydrochloric acid at room temperature. This reaction occurs by SN 1 mechanism, so the reaction rate is almost the same with HCl, HBr or HI, since the addition of the halide nucleophile occurs in the second fast step.

Mechanism of Substitution

SN 2 vs SN 1 Reactions SN 2 1 > 2 > 3 (due to Steric factor) Exception !!!!!!!

SN 1 3 > 2 > 1 (due to dispersal of charge) Very slow reaction

Rearrangement

Primary alcohol: The reaction is very slow with primary alcohols, and may occur by heating them with Zn. Cl 2 for several hours. Since this reaction occurs by SN 2 mechanism, the order of reactivity is: I > Br > Cl 1 - Reaction with phosphorus(III) chloride, PCl 3 Alcohols react with liquid phosphorus(III) chloride (also called phosphorus trichloride) to make chloroalkanes. 2 - Reacting alcohols with sulphur dichloride oxide (thionyl chloride) The reaction • • Sulphur dichloride oxide (thionyl chloride) has the formula SOCl 2. The two other products of the reaction (sulphur dioxide and HCl) are both gases. That means that they separate themselves from the reaction mixture

Oxidation of Alcohols Primary alcohols are oxidized to aldehydes using pyridinium chlorochromate (PCC). Oxidation by KMn. O 4, K 2 Cr 2 O 7 or Cr. O 3 dissolved in sulfuric acid (Jones’ reagent) gives the corresponding carboxylic acids).

Oxidation of secondary alcohols (gives ketones) Oxidation of tertiary alcohols (don’t occur)

Polyhydroxy compounds