Lab 9: CARBOXYLIC ACIDS, ESTERS, AND AMINES
This is an online lab activity: you will not use your Lab Kit for Lab 9
Learning Outcomes for this Lab Experiment:
口
Demonstrate how to prepare a carboxylate salt from a carboxylic acid
Demonstrate how to prepare an ester
Demonstrate how to prepare an ammonium salt from an amine
Introduction and Background
Properties of Carboxylic Acids
Carboxylic acids are structurally similar to aldehydes and ketones in that they all contain a carbonyl group. The important difference, however, is that carboxylic acids contain a hydroxyl group attached to the carbony group. This combination is called a carboxylic acid:
Carboxylic acids are weak acids because the carboxylic acid group ionizes only slightly in water (to give a carboxylate ion and a proton). Typically, carboxylic acids ionize to the extent of only 1% or less in water. Acids with 1-4 carbon atoms are soluble in water; larger carboxylic acids are water-insoluble.
Reactions of Carboxylic Acids with a Strong Base to Form Carboxylate Salts
An important feature of carboxylic acids is their neutralization by bases such as NaOH to form carboxylate salts and water. These salts are generally soluble in water. For this reason, carboxylic acids used in medications are usually provided in their soluble salt form instead of as the acid itself.
Na
+ NaOH
+ H20
Benzoic Acid
Insoluble
Sodium Benzoate
Soluble
Reactions of Carboxylic Acids with Alcohols to Form Esters
The combination of a carboxylic acid and an alcohol produces an ester; water is the other product in this condensation reaction. Ester formation is an equilibrium process:
H*/heat
Сз -С-ОН + HO-CH2—СНз
+ H20
Properties of Esters
Esters are structurally similar to aldehydes and ketones in that they all contain a carbony! group. The important difference, however, is that carboxylic acids contain an -OR group attached to the carbonyl group. This combination is called a ester:
OR
The most notable feature of esters is that many lower-molecular weight esters have very characteristic, pleasant odors. Esters are responsible for many sweet and fruity smells you are familiar with (wintergreen, sour apple, mango, pineapple, butterscotch).
A distinctive difference between carboxylic acids and their esters is their characteristic odors.
Carboxylic acids are noted for their sour odors, while esters typically have a sweet, fruity odor.
Properties of Amines
Amines can be considered derivatives of ammonia in which one or more hydrogen atoms are replaced with alkyl or aromatic groups. Amines are often found as part of compounds that are physiologically active or used in medications. The number of alkyl groups attached to the nitrogen atom determines the classification of the amine as primary (1°), secondary (2°), or tertiary (3°).
CH3-N-CH2-CH 3
NH3
Ammonia
CH, -CH, – NH, CH;-CH, -NH-CH;
Ethylamine
Ethylmethylamine
(Primary, 1°)
(Secondary, 2°)
Ethyldimethylamine
(Tertiary, 3)
Ammonia and amines act as weak bases because the unshared electron pair on the nitrogen attracts protons. Smaller amines are generally soluble in water; larger amines are usually water-insoluble.
Reactions of Amines with a Strong Acid to Form Ammonium Salts
An important feature of amines is their neutralization by acids such as HCl to form ammonium salts and water. Ammonium salts are soluble in water, while the parent amine may or may not be soluble in water. For this reason, amines used in medications are usually provided as their soluble salt form instead of the amine itself.
CH NH + HCI → CHaNH + CI-
CH3
СН з
Procedure
Because you will be completing Lab 9 as an online lab activity, you will not carry out the steps of this procedure. Even so, you should read through the procedure to familiarize yourself with the different lab tests used in studying reactions of carboxylic acids, esters, and amines. After you have read through the procedure, everything you need to complete this lab can be found on D2L.
A. Carboxylic Acids And Their Salts
You will measure the solubility of 2 carboxylic acids in water, then you will prepare the corresponding carboxylate salts and measure their water solubility.
1. Place 2-3 mL deionized water in each of 2 test tubes.
2. Add ~5 drops glacial acetic acid to the 1st tube
3. Add a small amount (enough to cover the tip of a small spatula) benzoic acid to the 2nd test tube.
4. Mix the contents of each tube by swirling gently. Note the solubility and record.
5. Now add ~10 drops of 10% NaOH to each tube. Note the solubility and record the results.
B. Formation of Carboxylic Esters
You will attempt to make two esters whose odors are easily recognizable: n-pentyl acetate and methyl salicylate.
The reactants for making the first ester (n-pentyl acetate) are shown here:
•:
СНз
+ HO-CHCHCH2CHCH3 →
Acetic Acid
1-pentanol
B1. Formation of pentyl acetate: (1-pentanol + acetic acid → pentyl acetate + H20)
1. Place 3 mL of 1-pentanol in a large dry test tube
2. Add 1 mL of glacial acetic acid
3. Cautiously add 10 drops of concentrated H2S04
4. Mix thoroughly, then place in a hot (near boiling) water bath for 5-10 minutes.
5. Predict the odor using the provided chart.
The reactants for making the second ester (methy/ salicylate) are shown here:
ОН
COOH
+ НО-СНз ~
Salicylic Acid
Methanol
B2. Formation of methyl salicylate (methanol + salicylic acid → methyl salicylate + H20)
1. Place 3 mL of methanol in a large dry test tube
2. Add about 0.5g of solid salicylic acid (this is a pea-sized amount).
3. Stir to dissolve all the acid.
4. Cautiously add 10 drops of concentrated H2SO4
5. Mix thoroughly, then place in a hot (near boiling) water bath for 5-10 minutes
6. Predict the odor using the provided chart.
Amines and Their Salts
You will measure the water solubility of 3 amines in water, then you will prepare the corresponding ammonium salts and measure their water solubility.
***YOU SHOULD DO ALL OF PART C IN THE FUME HOOD.***
also,
***IT IS RECOMMENDED THAT YOU WEAR GLOVES WHILE DOING PART C***
1. Start with 3 clean, dry large test tubes.
2. Add 5 drops of aniline to the 1st test tube.
3. Add 5 drops dimethylaniline to the 2nd test tube.
4. Add 5 drops triethylamine to the 3rd test tube.
5. Cautiously note the odor of each amine.
6. Add ~2 mL of deionized water to each test tube and swirl gently to mix.
7. Record the solubility of each amine on your data sheet.
8. Add 6 M HCl dropwise to each of the 3 test tubes until the amine dissolves.
9. Record any changes in the solubility of each amine. Record any changes in odor.
Safety Notes:
1. Follow all rules and procedures in your Chemistry Lab Safety Agreement.
2. SPECIAL NOTE!! You will be working with concentrated H2SO4 in this experiment.
Concentrated H2SO can cause serious skin burns!! Use extra caution when working with H2SO4:
• DO NOT REMOVE THE H¿SO CONTAINER FROM THE FUME HOOD
• WASH YOUR HANDS AFTER WORKING WITH H2SO4
• NOTIFY YOUR INSTRUCTOR IMMEDIATELY IF THERE IS A SPILL
3. SPECIAL NOTE!! You will be working with amines in this experiment. Amines can cause skin irritation and their odor is unpleasant. For these reasons:
• DO NOT REMOVE THE AMINES FROM THE FUME HOOD
• COMPLETE THE ENTIRE PART C IN THE FUME HOOD
• WEAR GLOVES FOR PART C
4. SPECIAL NOTE!!! Many of the compounds you will be making have strong odors. For
