CARBOXYLIC ACIDS

CARBOXYLIC ACIDS

Functional group of carboxylic acid is called carboxyl group Carboxylic acid can be aliphatic or aromatic

Nomenclature of carboxylic acid • Select the longest carbon chain containing carboxyl group. • Drop the final –e from the hydrocarbon name. • Add the suffix –oic acid. • Number the carbon of parent chain starting with the carboxylic group. Carboxylic group is always at the beginning of the carbon chain. • 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

CH3CH2CHCH2COOH CH3CHCH2COOH OH CH3 Name the following compounds: CH2ClCH2CH2CHCH2COOH CH2CH3 6-chloro-3-ethylhexanoic acid 3-methypentanoic acid CH2 CBrCH2CHCH2COOH CH3CH2CH CH2COOH CH3 CH3 3-methyl-2-pentenoic acid 5-bromo-3-methyl-5-hexenoic acid CH3C CClCOOH OH 2-chloro-3-hydroxy-2-butenoic acid 3-hydroxybutanoic acid

Common names of carboxylic acids IUPAC method is not the most used method for naming carboxylic acids Common names are used more often Carboxylic acids with even number of carbon atom (from 4 to 36 carbon atoms) – fatty acids

C Nomenclature of carboxylic acids using Greek alphabet Greek 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. -hydroxybutiric acid 2-hydroxybutanoic acid -aminopropionic acid 2-aminopropanoic acid -chloropropionic acid 3-chloropropanoic acid

CH3CHCOOH CH3 HO CH2CH2CH2COOH COOH CH2COOH Write formula for the following: 3-chloropentanoic acid 2-methylpropanoic acid CH3CH2CHClCH2COOH -chlorocaproic acid -hydroxybutyric acid CH3CH2CH2CHClCH2COOH cyclohexanecarboxylic acid phenylacetic acid

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 • Saturated (contain only single bonds) • 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

Oleinic, linolic, linolenic and arachidonic unsaturated carboxylic acids are essential for living organisms These acids are building blocks for biological membranes Monounsaturated carboxylic acid Polyunsaturated carboxylic acid Unsaturated fatty acids can be in –cis and –trans forms

Classification of carboxylic acids 1. Aliphatic carboxylic acids(straight chain) 2. Aromatic carboxylic acids(contain benzene ring) The parent compound is benzoic acid Carboxyl group –COOH is bonded directly to a carbon in aromatic ring

Classification of carboxylic acids • Monocarboxylic acids(onecarboxylic group) • Dicarboxylic acids(twocarboxylic groups) • Polycarboxylic acids(more than two carboxylic groups) Selected dicarboxylic acids

IUPAC naming of dicarboxylic acids The IUPAC names for dicarboxylic acids are formed by adding the suffix –dioic acid to the name of corresponding hydrocarbon. propanedioic acid ethanedioic acid butanedioic acid butenedioic 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 acids Contain 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 proteins There 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 anhydrideis 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: • Have sour taste • Change colors of different indicators • Form water solution with pH less than 7 • Undergo neutralization reaction with bases to form water and a salt

ESTERS

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

Nomenclature of esters 1. In ester recognize the portion that comes from the acid and the portion that comes from the alcohol 2. Replace the –ic ending of carboxylic acid by –ate (ethanoic acid - ethanoate or acetic acid - acetate) 3. Name the alcohol part R’ in R’O (for example: methyl, ethyl, propyl etc) 4. The alcohol part is named first followed by the name of carboxylic acid (for example: methyl athanoate or methyl acetate)

The ester formed from propanoic acid and methanol: methyl propanoate (methyl propionate) Esters of aromatic acids are named in the same way as those of aliphatic acid isopropyl benzoate

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 methyl propenoate phenyl benzoate

Name the following esters: methyl propanoate dimethyl succinate methyl benzoate phenyl ethanoate (phenyl acetate) methyl salicylate

Physical properties of esters • colorlessnonpolar 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

Polyesters are 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 esters Hydrolysis Hydrolysis – splitting of molecule through the addition of water Types of hydrolysis: - acid - alkaline - enzymatic (in living systems) Acid hydrolysis Is catalyzed by strong acid (H2SO4, HCl)

C C Alkaline hydrolysis (saponification) Saponification – hydrolysis of ester by a strong base (NaOH or KOH) to produce alcohol and salt The carboxylic acid may be obtained by reacting the salt with a strong acid

Glycerol Esters Esters 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

There can be different triacylglycerols: • 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 • The most abundantsaturated 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 • Fatsare obtained fromanimal sources; • oilsare obtained fromplant sources Fatty 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 triacylglycerols Hydrogenolysis– 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 triacylglycerols Splitting 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 Acid or enzymatic hydrolysis Fatty acids and glycerol are yielded

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 detergents Difference 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 detergents Anionic detergents Representatives of anionic detergents: -Sodium lauryl sulfate -Sodiump-dodecylbenzene sulfonate Has a long hydrocarbon chain that is soluble in grease and a sulfate group that is attracted to water Advantage over soaps: their calcium and magnesium salts are soluble in water (effective in hard water)

Cationic detergents Nonionic detergents

LIPIDS

Lipids do not have the common chemical structure Distinctive characteristic - solubility behavior Lipids - biomolecules that are insoluble in water and highly soluble in organic solvents such as chloroform, methanol, diethyl ether The main elements – carbon and hydrogen Can contain oxygen, phosphorous and nitrogen Lipids - essential components of living organisms

Functions of lipids • 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

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

CARBOXYLIC ACIDS