xidizing Alcohols SKILL FUS Predicting Performing and recording Analyzing and interpreting Acidified potassium permanganate solution, KMn 4(aq), acts as an oxidizing agent when it comes in contact with alcohols. In this investigation, you will discover how potassium permanganate reacts with a primary, a secondary, and a tertiary alcohol. Questions ow do primary, secondary, and tertiary alcohols react with an oxidizing agent? Prediction Predict which of the following alcohols will react with an oxidizing agent. Draw and name the product you expect for each reaction. 2-propanol 1-butanol 2-methyl-2-propanol Safety Precautions andle the sulfuric acid solution with care. It is corrosive. Wipe up any spills with copious amounts of water, and inform your teacher. Materials 2-propanol, 1-butanol, 2-methyl-2-propanol 0.01 mol/l KMn 4 solution 1 mol/l 2 S 4 distilled water 5 test tubes with stoppers dropper stopwatch or clock Procedure 1. Place 3 ml KMn 4, 3 ml water, and 2 ml acid in a test tube. This mixture should not oxidize quickly. You will use it as a standard to compare the colour of the other test tubes. 2. Prepare each of the following mixtures, one at a time. Test tube 1: 3 ml KMn 4, 3 ml 2-propanol, 2 ml acid Test tube 2: 3 ml KMn 4, 3 ml 1-butanol, 2 ml acid Test tube 3: 3 ml KMn 4, 3 ml 2-methyl-2-propanol, 2 ml acid 3. Place a stopper in each test tube, and shake the test tube gently to mix the contents. ecord the reaction time for each mixture. Use the change in the colour to determine if a reaction has taken place. 4. Dispose of your mixtures as directed by your teacher. Analysis 1. Draw the structure of each alcohol you used. Label each alcohol as primary, secondary, or tertiary. 2. Which alcohol(s) reacted with the potassium permanganate? ow did you know? Which alcohol(s) did not react with the potassium permanganate? Explain your observations. 3. Which alcohol(s) reacted the most quickly? Which reacted slowly? Make a general statement that summarizes your observations. 4. Write a chemical equation for each reaction. onclusions 5. Which alcohol reacted the fastest: primary, secondary, or tertiary? 6. Were there any sources of experimental error? What could you improve if you did this investigation again? 74 M Unit 1 rganic hemistry
eactions of Aldehydes and Ketones As you observed in the investigation, different alcohols react differently with an oxidizing agent. In the same way, aldehydes and ketones react differently with oxidizing and reducing agents, even though aldehydes and ketones have similar structures. xidation of Aldehydes In the presence of an oxidizing agent, an aldehyde is oxidized to produce a carboxylic acid. The hydrogen atom that is bonded to the carbon atom of the bond is replaced with an group. + [] aldehyde carboxylic acid Ketones do not usually undergo oxidation. Like tertiary alcohols, ketones do not have a hydrogen atom that is available to be removed. arbon-carbon bonds are too strong to be broken by an oxidizing agent. + [] no reaction ketone eduction of Aldehydes and Ketones You learned earlier that primary alcohols are oxidized to aldehydes, and secondary alcohols are oxidized to ketones. You can think of the reduction of aldehydes and ketones as the reverse of these reactions. Aldehydes can be reduced to produce primary alcohols. Ketones can be reduced to produce secondary alcohols. Explain why the transformation of an aldehyde into an alcohol is a reduction not an oxidation. + [] aldehyde primary alcohol + [] ketone secondary alcohol hapter 2 eactions of rganic ompounds M 75
eactions of arboxylic Acids Like other acids, a carboxylic acid reacts with a base to produce a salt and water. 3 2 2 2 + Na 3 2 2 2 pentanoic acid (acid) sodium hydroxide (base) sodium pentanoate (salt) Na + + 2 water As you learned earlier, a carboxylic acid reacts with an alcohol to produce an ester. Water is the second product of this reaction. A strong acid, such as 2 S 4, is used to catalyze (speed up) the reaction. The reverse reaction can also occur. (See eactions of Esters and Amides, below.) + 2 S 4 + 2 carboxylic acid alcohol ester water The reaction of a carboxylic acid with an alcohol to form an ester is called an esterification reaction. An esterification reaction is one type of condensation reaction. In a similar type of condensation reaction, an amide can be formed from a carboxylic acid and an amine, but this process is slightly longer and will not be discussed here. arboxylic acids can be reduced to form aldehydes and alcohols. eactions of Esters and Amides Both esters and amides undergo hydrolysis reactions. In a hydrolysis reaction, the ester or amide bond is cleaved, or split in two, to form two products. As mentioned earlier, the hydrolysis of an ester produces a carboxylic acid and an alcohol. The hydrolysis of an amide produces a carboxylic acid and an amine. There are two methods of hydrolysis: acidic hydrolysis and basic hydrolysis. Both methods are shown in Figure 2.9. ydrolysis usually requires heat. In acidic hydrolysis, the ester or amide reacts with water in the presence of an acid, such as 2 S 4. In basic hydrolysis, the ester or amide reacts with the ion, from Na or water, in the presence of a base. Soap is made by the basic hydrolysis of ester bonds in vegetable oils or animal fats. A 3 2 N-methylpropanamide (amide) 2 S 4 N 3 + 2 3 2 + 2 N 3 water propanoic acid (carboxylic acid) methanamine (amine) B 3 2 2 2 3 + Na 3 2 2 Na + + 3 2 ethyl butanoate sodium butanoate ethanol (ester) (salt of a carboxylic acid) (alcohol) Figure 2.9 (A) The acid hydrolysis of an amide produces a carboxylic acid and an amine. (B) The basic hydrolysis of an ester produces the salt of a carboxylic acid and an alcohol. 76 M Unit 1 rganic hemistry
Sample Problem Predicting the Products of More rganic eactions Problem Identify each type of reaction. Then predict and name the product(s). + [] + [] 3 3 3 + 3 2 Solution This reaction involves an aldehyde and an oxidizing agent. Thus, it is an oxidation. (If the reactant were a ketone, no reaction would occur.) The product of this reaction is a carboxylic acid called methanoic acid. + [] methanal This reaction involves a ketone and a reducing agent. Thus, it is a reduction. The product of this reaction is an alcohol called 2-propanol. + [] 3 3 3 3 propanone reducing agent 2-propanol This reaction occurs between a carboxylic acid and an alcohol. It is an esterification, or condensation, reaction. The product of this reaction is an ester called ethyl ethanoate. 3 + oxidizing agent 3 2 methanoic acid 3 2 3 ethanoic acid ethanol ethyl ethanoate hapter 2 eactions of rganic ompounds M 77
Practice Problems 14. Identify each type of reaction. (xidizing and reducing agents are not shown.) ( 3 ) 3 ( 3 ) 3 ( 3 ) 3 ( 3 ) 3 2-pentanone 2-pentanol (d) hexanoic acid + ethanol ethyl hexanoate + water 2 S 4 (e) butyl methanoate + water methanoic acid + 1-butanol 15. Name the reactants and products of the first two reactions in question 14. Draw the reactants and products of the last three reactions in question 14. 16. Name and draw the product(s) of each reaction. hexanal + [] octanal + [] propanoic acid + methanol (d) propyl ethanoate + water (e) 3-hexanone + [] (f) 2-propanol + 3-methylpentanoic acid 17. Name and draw the reactant(s) in each reaction.? + [] 3 2 ( 3 ) 2? + []? + [] 3 2 2 2? +? 2 S 4 oncept rganizer rganic eactions alkyl halide alkane addition of X or X 2 reduction alkene alkyne elimination substitution substitution elimination alcohol addition of 2 oxidation reduction aldehyde ketone oxidation carboxylic acid condensation hydrolysis ester 78 M Unit 1 rganic hemistry
Section Summary In this section, you learned about the reactions of alkenes, alkynes, aromatic compounds, alcohols, aldehydes, ketones, carboxylic acids, amides, and esters. You learned how to use Markovnikov s rule to predict the major product of an elimination reaction. You also learned how to predict the products of other types of reactions. In the next section, you will encounter a special branch of organic chemistry, which deals with much larger molecules. Section eview 1 K/U Identify each reaction as one of the following types of reactions: addition, substitution, elimination, oxidation, reduction, condensation, or hydrolysis. 2 2 3 2 S 4 2 3 + 2 3 3 l l 2 3 + l 2 2 3 3 + [] (d) 3 3 + 2 3 3 (e) l FeBr 3 + l 2 Br (f) 3 2 3 + 3 2 3 + Br 3 3 2 2 S 4 (g) 3 2 2 + 3 3 2 2 I Draw and name the product(s) of each addition or elimination reaction. 3 3 + Br 2 2 2 3 + l 3 + 2 3 2 2 2 2 2 3 Br 2 S 4 (d) 3 3 2 S 4 3 hapter 2 eactions of rganic ompounds M 79
3 I Draw and name the products of each substitution reaction. 4 5 FeBr 3 benzene + bromine 3 2 2 2 2 + Br I Draw and name the product of each oxidation or reduction. 2-pentanol + [] propanal + [] 2,3-dimethyl-1-butanol + [] (d) 2 2 + [] (e) 3-pentanone + [] (f) 3 2 + [] (i) + [] (ii) (g) 2-ethyl-3,4-dimethyloctanal + [] I Name and draw the reactant(s) in each reaction.? + 2 ( 3 ) 2 + 3 2? + []? +? 2-butyl methanoate (d)? + [] (e)? + 2 ethanamine + heptanoic acid 6 K/U State Markovnikov s rule. Under what circumstances is this rule important? K/U Which product of the following reaction is formed in the greater amount? 3 Br 3 Br 3 2 2 3 + Br 2 2 2 3 + 3 2 3 7 I At least one of the following reactions is not possible. Identify the impossible reaction(s), and explain your reasoning. 3 2 3 + [] 3 2 + [] 3 + l 2 l l (d) 3 2 3 + [] 8 3 opy the oncept rganizer into your notebook. Then make it more complete by giving an example of each type of reaction. 80 M Unit 1 rganic hemistry