CARBOXYLIC ACIDSCARBOXYLIC ACIDS

Functional group of carboxylic acid is called carboxyl group

Carboxylic acid can be aliphatic or aromatic

Nomenclature of carboxylic acid

1. Select the longest carbon chain containing carboxyl group.

2. Drop the final –e from the hydrocarbon name.

3. Add the suffix –oic acid.

4. Number the carbon of parent chain starting with the carboxylic group. Carboxylic group is always at the beginning of the carbon chain.

5. Name other groups attached to parent chain as usual.

Examples:

CH4 – methane; HCOOH – methanoic acid

CH3CH3 – ethane; CH3COOH – ethanoic acid

CH3CH2CH3 – propane; CH3CH2COOH – propanoic acid

CH3CH2CH2CH3 – butane; CH3CH2CH2COOH – butanoic acid

Name the following compounds:

CH3CH2CHCH2COOH

CH3

3-methypentanoic acid

CH3CH2CH CH2COOH

CH3

3-methyl-2-pentenoic acid

CH3CHCH2COOH

OH

3-hydroxybutanoic acid

CH2ClCH2CH2CHCH2COOH

CH2CH3

6-chloro-3-ethylhexanoic acid

CH2 CBrCH2CHCH2COOH

CH3

5-bromo-3-methyl-5-hexenoic acid

CH3C CClCOOH

OH

2-chloro-3-hydroxy-2-butenoic acid

Common names of carboxylic

acidsIUPAC method is not the most used method for naming carboxylic acids

Common names are used more oftenCarboxylic acids with even number of carbon atom (from 4 to 36 carbon atoms) – fatty acids

Nomenclature of carboxylic acids using Greek alphabetGreek letter , , , , …. are used to name certain derivatives of carboxylic acid.

The carbon atom adjacent to the carboxyl group is labeled , the next - …

Attention: when numbers are used (IUPAC system), the numbers begin with the carbon in the COOH group.

C

-hydroxybutiric acid2-hydroxybutanoic acid

-aminopropionic acid2-aminopropanoic acid

-chloropropionic acid3-chloropropanoic acid

Write formula for the following:

3-chloropentanoic acid

CH3CH2CHClCH2COOH

-hydroxybutyric acid

HO CH2CH2CH2COOH

phenylacetic acid

CH2COOH

2-methylpropanoic acid

CH3CHCOOH

CH3

-chlorocaproic acid

cyclohexanecarboxylic acid

CH3CH2CH2CHClCH2COOH

COOH

Physical properties of carboxylic acids Carboxylic acid – polar molecule (-COOH group and

hydrocarbon chain) formic, acetic, propionic and butyric acids are completely soluble 5-8 carbons carboxylic acids are partially soluble containing more than 8 carbons are insoluble

Carboxylic acids form hydrogen bonds (have high boiling point)

Saturated carboxylic acids having less than 10 carbon atoms are liquids, more than 10 – waxlike solids

In water carboxylic acids can dissociate (can cause acidosis)

Classification of carboxylic acids

1.Saturated (contain only single bonds)

2.Unsaturated (contain one or more carbon-carbon double bonds) -Monounsaturated -Polyunsaturated

Unsaturated carboxylic acids can undergo the reactions of unsaturated hydrocarbons (for example, addition reactions)

The more double bonds in carboxylic acids the more liquid this acid Plant oils contain unsaturated carboxylic acids

Polyunsaturated carboxylic

acid

Monounsaturated carboxylic

acid

Oleinic, linolic, linolenic and arachidonic unsaturated carboxylic acids are essential for living organisms

These acids are building blocks for biological membranesUnsaturated fatty acids can be in –cis and –trans forms

1. Aliphatic carboxylic acids (straight chain)

2. Aromatic carboxylic acids (contain benzene ring)

Classification of carboxylic acids

Carboxyl group –COOH is bonded directly to a carbon in aromatic ring

The parent compound is benzoic acid

Classification of carboxylic acids1.Monocarboxylic acids (one carboxylic group)

2.Dicarboxylic acids (two carboxylic groups)

3.Polycarboxylic acids (more than two carboxylic groups)

Selected dicarboxylic acids

The IUPAC names for dicarboxylic acids are formed by adding the suffix –dioic acid to the name of corresponding hydrocarbon.

IUPAC naming of dicarboxylic acids

C CO

OH

O

OHC CH2 C

O

OH

O

OH

C CH2 CO

OH

O

OHCH2 C CH C

O

OH

O

OHCH

ethanedioic acid propanedioic acid

butenedioic acidbutanedioic acid

Significance of polycarboxylic acids

Oxalic acid: -is included into different vegetables and plants; -it is used in chemical industry (in the manufacturing of leather)

Malonic acid: -is used for the drug (barbiturates) production; -precursor for the synthesis of fatty acids

Succinic, fumaric and citric acids: -are metabolites of the citric acid cycle (Kreb’s cycle)

Citric acid: is widely distributed in plants (citrus fruits) and animal tissue

Hydroxy acidsContain functional groups of both a carboxylic acid and alcohol

Lactic acid – the end product of glycolysis in cells

Salicylic acid – precursor for many drugs (pain and inflammation relievers)

Amino acids

Amino acids – carboxylic acids containing amino group

Usually amino group is located on carbon atom

Amino acid is amphoteric compound because it has carboxyl group which can act as acid and amino group which can act as a base

Amino acids are building blocks of proteinsThere are 20 main amino acids including into the protein structure

Chemical properties of carboxylic acids

1. Substitution reactions Carboxyl group is involved in substitution reactions Group –OH can be replaced by another group or atom (halogens (-Cl, -Br); acyloxy group (-OOCR); an alkoxy group (-OR))

a) Acid chloride formation

Thionyl chloride (SOCl2) reacts with carboxylic acids to form acid chlorides. Chlorine atom replaces –OH group

b) Acid anhydride formation

Anhydride is formed by the elimination of a molecule of water from two molecules of carboxylic acids

Acetic anhydride is the most commonly used anhydride (can be prepared by the reaction of acetyl chloride with sodium acetate)

Acetic anhydride is very reactive and can be used for synthesis of esters and amides

c) Ester formation

Esters are formed by the reaction of an acid and an alcohol or a phenol. The molecule of water is eliminated.

Such type of reaction is called esterification

2. Acid-base reactions

Carboxyl group is acidic group (group –OH can donate protons)

As acids carboxyl acids can react with basis

Carboxylic acids:

1. Have sour taste

2. Change colors of different indicators

3. Form water solution with pH less than 7

4. Undergo neutralization reaction with bases to form water and a salt

ESTERSESTERS

General formula: RCOOR’R – alkyl group or aryl (aromatic) group or hydrogen R’ - alkyl group or aryl (aromatic) group R’ can not be hydrogen

Esters are alcohol derivatives of carboxylic acids

1. In ester recognize the portion that comes from the acid and the portion that comes from the alcohol

Nomenclature of esters

2. Replace the –ic ending of carboxylic acid by –ate (ethanoic acid - ethanoate or acetic acid - acetate)

4. The alcohol part is named first followed by the name of carboxylic acid (for example: methyl athanoate or methyl acetate)

3. Name the alcohol part R’ in R’O (for example: methyl, ethyl, propyl etc)

The ester formed from propanoic acid and methanol:

Esters of aromatic acids are named in the same way as those of aliphatic acid

isopropyl benzoate

methyl propanoate (methyl propionate)

Many esters have a specific fruity odor

isopentyl ethanoate (isopentyl acetate)

ethyl butanoate (ethyl butyrate)

isobutyl methanoate (isobutyl formate)

octyl ethanoate (octyl acetate)

2-hydroxymethyl-benzoate (methyl salicylate)

Name the following esters:

propyl methanoate

ethyl benzoate

diethyl malonate

C

O

O

phenyl benzoate

CH2 CHC

O

OCH3

methyl propenoate

methyl propanoate

phenyl ethanoate (phenyl acetate)

dimethyl succinate

methyl benzoate

methyl salicylate

Name the following esters:

Physical properties of esters

colorless nonpolar liquids or solids

don’t form hydrogen bonds to themselves (low boiling point)

up to 10 carbons - volatile liquids with specific odors (fruity)

high-molar-mass esters are solid (waxes)

nonpolar - good solvents for organic compounds

Using of esters

have odors - flavoring agents

good solvents for organic compounds - in paints, varnishes, and lacquers

high-molar-mass esters (16 or more carbons) are waxes - in furniture wax and automobile wax preparation

polyesters - in the textile industries

Polyestersare formed by ester linkages between carboxylic acids that have more than one carboxyl group and alcohols that have more than one hydroxyl groups

Linear polyesters usually are obtained from dicarboxylic acid p-phthalic acid and 1,2-ethanediol (ethylene glycol)

Using: production of fibers or transparent films of great strength (synthetic textile, plastic bottles)

tricarboxylic acids + alcohols that have three hydroxyl groups = cross-linked polyesters

Such polyesters are thermostable

Example: glycerol can react with o-phthalic acid

The polymer formed - alkyd resin

Using: coating industry

Chemical properties of estersHydrolysis

Types of hydrolysis:

- acid - alkaline - enzymatic (in living systems)

Hydrolysis – splitting of molecule through the addition of water

Acid hydrolysis

Is catalyzed by strong acid (H2SO4, HCl)

Alkaline hydrolysis (saponification)

Saponification – hydrolysis of ester by a strong base (NaOH or KOH) to produce alcohol and salt

C

The carboxylic acid may be obtained by reacting the salt with a strong acid

C

Glycerol EstersEsters of glycerol and long chain tricarboxylic acids (fatty acids) are called fats or oils or triacylglycerols or triglycerides

Each molecule of triacylglycerols consist of one molecule of glycerol and three molecules of fatty acids

different length of fatty acid chain (4 to 20 carbons). The number of carbons in chain is usually even

fatty acid may be saturated, monounsaturated and polyunsaturated

may be the same fatty acids or different fatty acids

There can be different triacylglycerols:

The most abundant saturated fatty acids are palmitic and stearic fatty acids

The most abundant unsaturated fatty acids are 18 carbon chain acids - oleic, linolic and linolenic

Triacylglycerols are the main form of energy storage in the body

Oils contain greater amount of unsaturated fatty acids fats contain larger proportion of saturated fatty acids

Fats are obtained from animal sources; oils are obtained from plant sourcesFatty acid composition of fats and

oils

Hydrogenation of triacylglycerols

Hydrogenation – addition of hydrogen (addition reaction)

Unsaturated fatty acids contain double bonds therefore hydrogen can be added to such fatty acids

Using: production of solid fats from vegetable oils - hydrogen gas is bubbled through hot oil - catalyst - nickel - the double bonds are saturated and solid fats are formed

The products can be used for cooking and baking, for making margarine

Hydrogenation improves the keeping qualities of oils

Hydrogenolysis of triacylglycerolsHydrogenolysis – splitting by

hydrogen triacylglycerol react with hydrogen

a molecule of glycerol and three molecules of primary alcohols are yielded

catalyst - copper chromite

high temperature and high pressure are required

Hydrolysis of triacylglycerolsSplitting of triacylglycerols with participation of water Hydrolysis of triacylglycerols requires: - acids - alkalines and high temperature - enzymes in room temperature

Enzymatic hydrolysis: - in digestive tract and adipose tissue - enzyme – lipase

Fatty acids and glycerol are yielded

Acid or enzymatic hydrolysis

Saponification of triacylglycerols

Saponification – alkaline hydrolysis of triacylglycerols

Glycerol and sodium or potassium salts of fatty acids are formed

Such salts are called soaps

Soaps and synthetic detergentsDifference between soap and synthetic detergent -

chemical composition (functions or usage are the same)

Soaps - salts of long-chain fatty acids

How a soap works?-Sodium or potassium salts of fatty acids dissociates in water (Na+, K+ and anions RCOO- are formed) -RCOO- is amphiphilic molecule -The hydrophobic end, R-, is soluble in oils; hydrophilic, -COO-, is soluble in water -The hydrophobic end is dissolved in grease -Carboxylic groups are exposed on the grease surface -Carboxylic groups are attracted by water, small droplets are formed, and grease is lifted from soiled object

Hard water contains ions of calcium and magnesium Ca2+ and Mg2+ form insoluble salts with carboxylic acids

Soaps are ineffective in hard water

In acidic solution anions of fatty acids react with protons and water insoluble fatty acids are formed

Soaps are ineffective in acidic solutions

Synthetic detergentsAnionic detergents

Representatives of anionic detergents: -Sodium lauryl sulfate -Sodium p-dodecylbenzene sulfonate

Advantage over soaps: their calcium and magnesium salts are soluble in water (effective in hard water)

Has a long hydrocarbon chain that is soluble in grease and a sulfate group that is attracted to water

Cationic detergents

Nonionic detergents

LIPIDSLIPIDS

Lipids - biomolecules that are insoluble in water and highly soluble in organic solvents such as chloroform, methanol, diethyl ether

Lipids do not have the common chemical structure

Distinctive characteristic - solubility behavior

Lipids - essential components of living organisms

The main elements – carbon and hydrogen

Can contain oxygen, phosphorous and nitrogen

Energetic role (fuel molecules)

Structural role (components of membranes)

Protective role (surround important organs)

Regulatory role (prostaglandins, precursors for steroids hormones)

Vitamins (vitamin A, D, E, K - derivatives of lipids)

Insulation against temperature extremes

Functions of lipids

The most of lipids are esters of fatty acids and different alcohols (glycerol, cholesterol etc)

Fatty acids

Fatty acids – biomolecules containing a carboxyl functional group (-COOH) connected to an unbranched aliphatic chain

Fatty acids - carboxylic acids with long carbon chain

CH3-(CH2)14-COOH (palmitic acid)

General formula - R-COOH (R - hydrocarbon chain)

Carboxyl groups are ionized at neutral pH - hydrophilic

Hydrocarbon chain – hydrophobic

The molecule of fatty acid -amphiphilic

Number of carbon atoms -from 4 to 36

Usually fatty acids contain an even number of carbon atoms (between 14 and 24)

Most common 16 and 18 carbon atoms (palmitic and stearic)

Hydrocarbon chain is unbranched

Fatty acids can contain one or more double bonds

If more then one double bond is present they are not conjugated, but are separated by methylene unit

•Fatty acids (FA) differ from one another in:

(1) Length of the hydrocarbon tails

(2) Degree of unsaturation (double bond)

(3) Position of the double bonds in the chain

•Saturated FA - no C-C double bonds

•Unsaturated FA - at least one C-C double bond

-Monounsaturated FA - only one C-C double bond

-Polyunsaturated FA - two or more C-C double bonds

Classification of fatty acids according to degree of

unsaturation

IUPAC nomenclature: carboxyl carbon is C-1

Common nomenclature: C-2 - C-3-

Carbon farthest from carboxyl group -

Nomenclature of fatty acids

• Unsaturated fatty acids may be either cis- or trans- isomers

• Trans- isomer is almost a linear

• Cis- configuration introduces the kink into the fatty acid structure

• In nature double bonds are usually cis-

• Kinked fatty acids can not stack together and hence do not solidify easily

Double bonds in fatty acids

Nomenclature of fatty acids

•Shorthand notation example: 18:39,12,15 - linoleate

(total # carbons : # double bonds, double bond positions)

Another method:

omega plus a number indicate the location of the first double bond, counting from the carbon (linoleate – 3)

• Unsaturated fatty acids have lower melting points than saturated of same length

• Shorter chains have lower melting points than longer chains

• Short chain length and unsaturation enhance the fluidity of fatty acids

Unsaturated fatty acids – linolic, linolenic and arachidonic – are essential for animal nutrition

Lack of these fatty acid in diet – dermatitis, retardation of growth, disorders of reproduction

Significance of unsaturated fatty acids

Eczema may be result from diet lacking essential

unsaturated fatty acids

•Arachidonic acid is a precursor of eicosanoids

•Eicosanoids have hormone-like activities

Subclasses:

- prostaglandins

- thromboxanes

- prostacyclins

- leukotrienes

Arachidonic acid

Prostaglandins (were first isolated from prostate gland)

distributed in all organs and tissues

take part in the generation of inflammation, fever and pain associated with injury and diseases

aspirin, ibuprofen, naproxon decrease pain, fever, and inflammation by inhibiting the synthesis of prostaglandins

stimulate platelet aggregation, blood clot formation

Leukotrienes (were first extracted from white blood cells leucocytes)

cause smooth-muscle contraction especially in bronchi

cause allergic reactions, asthmatic attacks

Thromboxanes (were first isolated from blood platelets)

Classification of lipids

LIPIDS

Simple lipids Compound (conjugated) lipids

Triacyl-glycerols (neutral

fats)

WaxesPhospholipids

Sphingo-lipids

Glycolipids

Miscellaneous lipids (fat soluble

vitamins, lipoproteins)

Steroids

•Triacylglycerols are esters of glycerol and fatty acids

Triacylglycerols (fats and

oils)

The “R” can be either long-chain saturated or unsaturated hydrocarbon groups

One fatty

acid is unsaturated

(kink is formed)

All fatty acids are saturated

Fats may be considered to be triesters formed from the glycerol and three molecules of fatty acids

The three R groups are usually different

TGs are the storage of energy in organism

Oxidative metabolism of fats gives twice as much energy per gram as for carbohydrates or proteins

TGs are very hydrophobic, and are stored in cells in an anhydrous form (e.g. in fat droplets)

TGs isolated from animals are called neutral fats are solid in room temperature contain predominantly saturated fatty acids

TGs from plant seeds are called oils

are liquids in room temperature contain mainly unsaturated fatty acids

Waxes

•Waxes - nonpolar esters of long-chain fatty acids and long chain monohydroxylic alcohols

• Waxes are very water insoluble and high melting

• They are widely distributed in nature as protective waterproof coatings on leaves, fruits, animal skin, fur, feathers and exoskeletons

Myricyl palmitate, a wax

The “shine” on these leaves is due to a thick,

protective wax coating

Compound Lipids: Phospholipids

Glycerophospholipids (contain alcohol glycerol) – the most common phospholipids

Class of lipids containing the residue of phosphoric acids Phospholipids also contain one or more fatty acids, alcohol and usually nitrogenous base.

H2C O

HC O

H2C O

fatty acid

fatty acid

phosphate + nitrogen base

hydrophilic

hydrophobic

The foundation molecule for glycerophospholipids is phosphatidic acid

Fatty acids with 16 and 18 carbon atoms are most prevalent

Saturated fatty acid is usually attached to C1, unsaturated – to C2

Phosphatidic acid is a key intermediate in the biosynthesis of triacylglycerols and phospholipids

Nitrogenous bases:

amino alcohols ethanolamine, choline, or amino acid serine

Free hydroxyl group of phosphoric acid is esterified with hydroxyl group of nitrogenous base

Phosphatidyl choline (lecithin)

glycerol ester of fatty acids, phosphoric acid and choline

the most important membrane component (amphipathic molecule)

digestible emulsifying agent (in food industry – chocolate and margarine production)

Phosphatidyl ethanolamine (cephalin)

glycerol ester of fatty acids, phosphoric acid and ethanolamine

membrane component

Compound Lipids: Sphingolipids

compound lipids containing the alcohol sphingosine

Sphingosine - amino alcohol that contains a long un-saturated hydrocarbon chain

Sphingomyelin

amino group of sphingosine backbone is linked to a fatty acid by an amide bond the primary OH group of sphingosine is esterified to phosphorylcholine

Sphingomyelinis found in cell membranes especially in myelin membranes

Compound Lipids: Glycolipids

The most important glycolipids are cerebrosides and gangliosides

Cerebrosides contain a single sugar residue (glucose or galactose attached)

Gangliosides contain oligosaccharidesFunction: abundant in the membranes of the brain and nervous system

compound lipids containing carbohydrate group

Steroids

Steroids – compounds containing the characteristic four fused ring systems: 3-six carbon rings and a 5-carbon ring (17 carbon atoms)

Cholesterol is the best known steroid has hydroxyl group and long hydrocarbon tail and double bond

Functions: component of the cell membranes

precursor of the steroid hormones (sex hormones and adrenal cortex hormones), bile salts, vitamin D

Structures of several steroids

ATHEROSCLEROSISmetabolic disease that leads to

deposits of cholesterol and other lipids on the inner walls of the arteries plaque accumulates, the arterial passages become progressively narrower

artery thrombosis (heart attack, stroke)

The surface of lipoproteins contains a layer of phospholipids and proteins, while the core contains hydrophobic triacylglycerols and cholesterol

The causes atherosclerosis: high level and improper transport of cholesterol through the blood

Cholesterol and other lipids are insoluble in water and must be packaged for transport in spherical particles called lipoproteins

There are different kinds of lipoproteins.

Low-density lipoproteins (LDL) deliver cholesterol to peripheral tissues

People with high-plasma LDL concentrations are prone to atherosclerosis

High-density lipoprotein (HDL) acts as a cholesterol scavenger by collecting cholesterol and returning it to the liver – prevents the development of atherosclerosis