unit (9) carboxylic acids, esters, amines, and amides, Study notes of Chemistry

Download unit (9) carboxylic acids, esters, amines, and amides and more Study notes Chemistry in PDF only on Docsity! 9-1 UNIT (9) CARBOXYLIC ACIDS, ESTERS, AMINES, AND AMIDES 9.1 Carboxylic Acids The functional group in carboxylic acids is called the carboxyl group. A carboxyl group is a carbonyl group (C = O) with a hydroxyl group (-OH) attached to the carbonyl carbon atom. 9.2 Naming Carboxylic Acids The names of carboxylic acids end in “-oic acid,” indicating the presence of the carboxyl group, i.e.: propanoic acid, butanoic acid, pentanoic acid, etc. When naming carboxylic acids, the “–e” is dropped from the alkane containing the carboxyl group and replaced with “-oic acid”. The chain is numbered from the carboxylic acid group which is always located on the first carbon. The location of the functional group is not included in the name. Examples: Some members of this class are widely known by their common names. Common names of acids you should know: A solution of acetic acid and water is known as vinegar. 9-2 Worked Example 9-1 Give the IUPAC name for each of the following compounds: Solution a) 2,2-dimethylpropanoic acid b) 3-bromobutanoic acid c) 4-nitrobenzoic acid d) 3,4-dimethylhexanoic acid Practice 9-1 Name each of the following acids: Answer a) 3,3-difluoropentanoic acid b) 2-hydroxybutanoic acid c) 3,4-dihydroxybenzoic acid d) 3-methylbenzoic acid e) 2-aminopropanoic acid f) 2-ethylhexanoic acid 9-5 Worked Example 9-3 Complete the following esterification reaction: Solution Each ester has an “acid part” and an “alcohol part”. The acid part is the carboxylic acid minus the –OH group. The alcohol part is an alcohol molecule, minus the H atom of the –OH group. The –OH of the acid and the H of the alcohol form a H2O molecule. Worked Example 9-4 What carboxylic acid and alcohol are required to produce the following ester? Solution Separate the molecule by drawing a line down through the oxygen in the carbon chain. Add an –OH on both sides of your line to create the carboxylic acid on the carbonyl side and the alcohol on the alkyl side. 9-6 Practice 9-3 Complete the following esterification reaction: Answer OH O CH3 - CH2 -OH+ O- CH2 - CH3 O H2O+ [H + ] removal of OH and H produces the ester 9.5 Naming Esters Ester names consist of two words. Use the alkyl portion of the alcohol name first. The -ic acid ending of the name of the carboxylic acid is replaced with –ate and follows the first name. Examples: Worked Example 9-5 Name each of the following esters: Solution a) ethyl propanoate b) methyl benzoate c) cyclopentyl propanoate d) cyclobutyl benzoate 9-7 Practice 9-4 Write the name for each of the following esters. Answer a) methyl octanate b) isopropyl benzoate c) ethyl butanoate e) propyl propanoate 9.6 The Hydrolysis of Esters Hydrolysis is a reaction in which an organic molecule reacting with water splits into two parts, each of which has fewer carbons than the original organic molecule. Esters hydrolysis is a very slow reaction. The reaction is considerably more rapid under either acidic or basic conditions. Ester hydrolysis under acidic condition (acid hydrolysis) is the reverse of acid-catalyzed ester formation. Ester hydrolysis under basic condition (base hydrolysis) produces the metal carboxylate salt instead of the carboxylic acid. I) Acid Hydrolysis of Esters Acid hydrolysis of esters requires the presence of a strong acid catalyst such as sulfuric acid. This reaction requires heat. The generalized hydrolysis can be shown as: Ester Carboxylic Acid Alcohol (This hydrolysis is the reverse of esterification.) 9-10 Practice 9-5 Complete the following reactions: Answer CH3CH2-C-OCH2CH3 O + H2O H + CH3CH2-C-OCH2CH3 O + NaOH H2O CH3CH2-C-OH O + CH3CH2OH CH3CH2-C-O - Na + O + CH3CH2OH 9.7 Amines The three most common elements in organic compounds are carbon, hydrogen, and oxygen. Amines contain nitrogen and are commonly found in a wide variety of biomolecules and important pharmaceutical compounds. For this reason, nitrogen ranks fourth on the list of common elements found in organic compounds. Amines are considered organic derivatives of ammonia (NH3) in which one or more hydrogen atoms are replaced by an alkyl or aromatic group. Amines are classified as primary, secondary, or tertiary, depending on the number of organic groups directly attached to the nitrogen atom. Ammonia primary secondary tertiary amine amine amine 9-11 9.8 Naming Amines Common names are often used to name simple amines. If two or three alkyl groups are present, they are listed alphabetically along with the suffix –amine. The name is written as one word. Aromatic amines are usually named based on aniline. Examples: Worked Example 9-8 Name each of the following: Solution a) pentylamine (This amine has one alkyl group (pentyl) attached to the nitrogen atom.) b) dibutylamine (This amine has two identical alkyl groups (butyl) attached to the nitrogen atom.) c) isopropylmethylpropylamine (This amine has three alkyl groups (isopropyl, methyl, and propyl) attached to the nitrogen atom.) d) cyclohexyldimethylamine (This amine has three alkyl groups (a cyclohexyl and two methyl group) attached to the nitrogen atom.) 9-12 Practice 9-6 Name each of the following: Answer a) cyclopentylamine b) 3,4-dibromoaniline c) ethylhexylamine d) diethylmethylamine 9.9 Basicity of Amines Recall (unit 6) that ammonia is also a weak base and accepts H + from water to produce ammonium ion (NH4 + ) and hydroxide ion (OH - ): NH3 + H2O NH4 + + OH - ammonia ammonium ion Because the amines are derivatives of ammonia, they react in a similar ways. General reaction R-NH2 + H2O RNH3 + + OH - Specific reaction CH3 - NH2 + H2O CH3- NH3 + + OH - Methylamine methylammonium ion Just as amines accept H + from water, they can accept H + from acids and form salts. For example, when methylamine reacts with HCl, the acid-base reaction produces methylammonium chloride. CH3 – NH2 + HCl CH3 – NH3 + Cl - methylamine acid methylammonium chloride 9-15 9.12 Hydrolysis of Amides Amides are very stable in water. Hydrolysis requires the heating of the amide in the presence of strong acid or base. Acidic hydrolysis gives a carboxylic acid and an amine salt. In aqueous base, the products of hydrolysis are a carboxylic acid salt and ammonia or an amine. General Reactions: Example of Acid Hydrolysis of Amide: Example of Base Hydrolysis of Amide: 9-16 Worked Example 9-10 Draw the structures of the products in each of the following hydrolysis reactions. Answer 9-17 Practice 9-8 Draw the structures of the products in each of the following hydrolysis reactions. Answer + H2O + HCl heat + NaOH heat + NH4 + Cl - CH3 - CH2 - C - O - Na + O CH3 - CH2 - C - NH - CH3 O CH3-NH2+ O C NH2 O C OH