Draw the structural formula of: 1.3,3-dimethylbutan-1-ol. 2.2-methyl-butan-2-ol. Review of data exercise: 1.Explain the trend of BP of staight chain primary alcohols. 2.Compare BP of alcohols with that of alkanes of similar molar mass, what’s the difference, why? 3.What’s the BP of water, why does it have a different BP.

Investigation: Oxidation of alcohols. Aim: To test different alcohols as reductants. Method: 1.Place 5 drops of each alcohol in separate test tubes, we have 4 alcohols. 2.Add 10 drops of dilute sulfuric acid to each test tube followed by 2 drops of potassium dichromate, shake. 3.If there is no change stand in warm water (60C) for 1 minute, smell the product and record your observation. 4.Repeat with potassium permanganate.

Reactions of alcohols

Oxidation of primary alcohols Oxidation by permanganate Methanol is a primary alcohol.

Acidify the methanol with dilute sulfuric acid.

Put it in a beaker of hot water.

Add a few drops of dilute potassium permanganate solution.

The purple colour of the MnO 4 – ion slowly fades. The final solution is colourless.

Methanol has reduced the MnO 4 – to Mn 2+ : MnO 4 – + 8H + + 5e – → Mn H 2 O Methanol is oxidised in this reaction. It is a two-step reaction: You only need to learn that methanol is oxidised to methanoic acid (HCOOH).

Oxidation by dichromate Pour a small amount of ethanol into a test tube and acidify with dilute sulfuric acid.

Place in a beaker of hot water and add a few drops of orange potassium dichromate solution.

Leave in the beaker until no further change takes place. The orange dichromate solution turns blue/green.

The dichromate, Cr 2 O 7 2–, has been reduced to Cr 3+ : Cr 2 O 7 2– + 14H + + 6e – → 2Cr H 2 O Ethanol is oxidised by this reaction. The final product of the oxidation reaction is ethanoic acid. CH 3 CH 2 OH + H 2 O → CH 3 COOH + 4H + + 4e – 3CH 3 CH 2 OH + 3H 2 O → 3CH 3 COOH + 12H e – 2Cr 2 O 7 2– + 28H e – → 4Cr H 2 O 3CH 3 CH 2 OH + 2Cr 2 O 7 2– + 16H + → 3CH 3 COOH + 4Cr H 2 O

In the days before electronic alcohol ‘sniffers’, New Zealand police used ‘breathalysers’ to measure breath alcohol. The subject blew through this tube to fill a bag. The crystals of potassium dichromate in the tube turned green if ethanol was present. If there was sufficient ethanol in the breath to turn crystals beyond the line green, then the person was over the legal limit for driving.

Elimination of alcohols: Elimination produces alkenes by the removal of water, this is done by heating with concentrated sulfuric acid, a dehydrating agent.

As with haloalkanes, this elimination will give more than one product if the original alcohol is not symmetric. The major product is the more highly substituted alkene. (Saytzeff’s rule, the poorer gets poorer.)

Substitution Alcohols undergo substitution reactions in which the – OH group is replaced with a halogen to form a haloalkane. For example chorination can happen when reacting alcohol with the following agents. The product chloroalkane is insoluble in water and separates out. Important chlorinating agents are: Phosphorus pentachloride, PCl 5 Phosphorus trichloride, PCl 3 Thionyl chloride, SOCl 2 Lucas reagent, HCl/ZnCl 2

All these reactions are fastest with tertiary alcohols.

Click on this movie to see what happens when solid PCl 5 is added to 2-methyl propan-2-ol (a tertiary alcohol).

Using Lucas reagent to distinguish alcohols Lucas reagent is used to distinguish between low mass primary, secondary and tertiary alcohols. Lucas reagent contains anhydrous zinc chloride dissolved in concentrated hydrochloric acid. It contains a very high concentration of chloride ions and the Zn 2+ ion acts as a catalyst. Take 1–2 mL of Lucas reagent in a dry test tube, add a few drops of the alcohol and shake. If there is no reaction, place the test tube in a beaker of boiling water for a few minutes.

Click on this movie to see 1°, then 2° and finally 3° alcohol added to Lucas reagent.

The primary and secondary alcohol test tubes you’ve just seen were placed in beaker of boiling water. Once heated, the secondary alcohol quickly turned cloudy. The primary alcohol tube is unchanged.

Tertiary alcohol turns cloudy immediately Secondary alcohol turns cloudy after gentle heating for a few minutes Primary alcohol does not react. Note: 1.Only add a few drops of alcohol. 2.Lucas reagent is very concentrated. Wash it off skin immediately. It’s also expensive, so use very small quantities.

Give the structural formula and the organic products for each of the following reactions, if there are two products, identify the major one.