Lecture 13: Carboxylic Acids, Esters, Amines and Amides

Book chapter: 14 Pages: 472-511

Carbon atom of a carbonyl group is attached to a hydroxyl group forming a carboxyl group As functional group – attached to an alkyl group or an aromatic group

IUPAC names Replace e of the alkene with oic acid If there are substituents – the carbon chain is numbered beginning with the carboxyl carbon

Common names of carboxylic acids Use prefixes: form, acet, propion, butyr Relate to the natural sources of the simple carboxylic acids

Properties of Carboxylic acids Most polar organic compounds – functional group consists of two polar groups (-OH) and (C=O) Solubility in water: Acids with 1-5 C atoms are soluble in water Length increases – the nonpolar portion reduces the solubility of acid in water More than 5C atoms – not very soluble in water

Acidity of Carboxylic Acids: Importnat property: ionization in water Hydrogen ion is transferred to a water molecule – forming of negatively charged cyrboxylate ion and hydronium ion Generally those acids are more acidic than most other organic compounds Weak acids; 1% of the acid molecules ionize in water

Neutralization of Carboxylic Acids: Completely neutralized by strong bases (NaOH or KOH) Products: carboxylate salt and water

Chemistry Link to Health: Carboxylic Acids in Metabolism Several are part of metabolic processes Example: glucose is broken down into two molecules of pyruvic acid or actually its carboxylate ion pyruvate (glycolysis) Pyruvic acid is reduced to give lactic acid (lactate ion)

Esters Carboxylic acid + alcohol -> ester + water -H of cyrboxylic acid is replaced by an alkyl group Esters contained in fats and oils (esters of glycerol and fatty acids)

Esterification Production of esters In the rpesence of an acid catalyst (H2SO4) and heat -OH group (carboxylic acid) and –H (alcohol) -> combined to form water

Naming esters Two words – derived from the names of the alcohol and the acid First word – indicates alkyl part from the alcohol Second word – name of the carboxylate from the carboxylic acid

Chemistry Link to Health: Salicylic acid from a Willow Tree In the past people were chewing the leaves or piece of bark of the willow tree Relief from pain Later (1800s)– salicin was discovered Has carboxyl and hydroxyl group - irritates the stomach lining 1899 – ester of salicylic acid and acetic acid – aspirin Less irritating, used as analgesic and anti-infammatory agent

Esters in plants Fragnances of perfumes and flowers or fruits – esters Small esters are volatile – smell and soluble in water; taste them

Hydrolysis of Esters Acid Hydrolysis Heating of esters with water in presence of a strong acid Water reacts with the ester to form a cyrboxylic acid and an alcohol Reverse of esterification reaction

Base Hydrolysis of Esters Esters undergo hydrolysis with a strong base Products: Carboxylate salt and corresponding alcohol Saponification

Amines Derivatives of ammonia (NH3) One or more hydrogen atoms are replaced with alkyl or aromatic groups

Naming and Classifying Amines Common names are often used when alkyl groups bonded to the nitrogen atom are not branched Groups are listed in alphabetical order Prefixes di and tri indicate substituents Classified – by counting the number of C atoms directly bonded to the nitrogen atom

Primary (1°) amine – nitrogen bonded to one alkyl group Secondary (2°) amine – 2 alkyl groups Tertiary (3°) amine – 3 alkyl groups

Aromatic amines Use the name aniline (approved by IUPAC) Alkyl groups attached to the nitrogen are named with the prefix N- followed by the alkyl name Aniline – used to make dyes (indigo) Give color to wool, cotton, silk fibers and blue jeans

Skeletal formula Similar like for other organic compounds We show the hydrogen atoms bonded to the N atom

Chemistry Link to Health: amines in Health and Medicine Histamine – in response to injury or allergy Causes blood vessels to dilate and increases the permeability of the cells Redness and swelling in the area Antihistamines – block the effect of histamine

In the body – biogenic amines (hormones) Carry messages between CNS and nerve cells Examples: epinephrine (adrenaline) and norepinephrine (noradrenaline) Released by adrenal medulla in “fight or flight” situations Raise the blood glucose level and move the blood to the muscles

Amphetamines – produced synthetically Stimulants of the CNS Also increase cardiovascular activity and depress the appetite Sometimes used to bring about weight loss; can cause chemical dependency

Solubility of amines in water Contain polar N-H bond – form hydrogen bonds with water Primary form more bonds with water than secondary Tertiary only with N atom in the amine

Amines react as bases in water: Ammonia acts as base because it accepts H+ from water Produces ammonium ion (NH4+) and hydroxide ion (OH-)

Ammonium salts: Example: lemon jiuce on the fish – revomes “fishy” odor by converting amines to their ammonium salts Neutralization reaction – amines (base) react with an acid to form ammonium salt Naming: using alkylammonium ion name followed by the name of the negative ion

Properties of Ammonium Salts: Ionic compounds Solids at room temperature, odorless and soluble in water and body fluids Amines used as drugs are usually in form of these salts If it reacts with a strong base – converted back to the amine

Heterocyclic amines Cyclic compound Contains one or more nitrogen atoms in the ring The heterocyclic amine ring consists of 5 or 6 stoms and one or more nitrogen atoms

Chemistry Link to Health: Alkaloids Active compounds produced by plants Contain heterocyclic amines Alkaloid - “alkali-like” or basic characteristics Some of them used in anesthetics, antidepressants and stimulants Examples: nicotine and caffeine

Several alkaloids – used in medicine Atropine – from nightshade; used to accelerate slow heart rates Codeine – poppy plant; painkiller Heroin – chemical modification of morphine; not used medically (strongly addictive)

Amides Derivatives of cyrboxylic acids Nitrogen replaces hydroxyl grouop

Preparation: Amidation reaction – carboxylic acid reacts with ammonia or primary/secondary amine

Naming: Dropping the oic acid or ic acid and adding the suffix amide If alkyl group is attached to the nitrogen atom – prefix N- or N,N- precedes the name of the amide

Solubility in water: Do not have properties of bases Amides with one to five C atoms are soluble in water (they can hydrogen bond with water molecules) More than five C atoms – effect of hydrogen bonding is diminished; longer carbon chain decreases the solubility

Chemistry Link to Health: Amides in Health and Medicine Simplest amide – urea (end product of protein metabolism) Removed by kidenys Malfunction of kidneys – urea is not removed; uremia Used also as fertilizer to increase nitrogen in the soil

Barbiturates – act as sedatives in small dosages or sleep inducers in larger dosages Aspirin substituetes contain phenacetin – used in Tylenol Reduces fever and pain, has little anti-inflammatory effect

Summary Carboxylic acids Properties of carboxylic acids Esters Acid/Base Hydrolysis of esters Amines Reaction of amines in water Ammonium salts Alkaloids Amides