Carboxyclic Acids and Esters - K. A. Boudreaux, Angelo State University, Lecture notes of Chemistry

Download Carboxyclic Acids and Esters - K. A. Boudreaux, Angelo State University and more Lecture notes Chemistry in PDF only on Docsity! Chapter 5 Carboxylic Acids and Esters Chapter Objectives: • Learn to recognize the carboxylic acid, ester, and related functional groups. • Learn the IUPAC system for naming carboxylic acids and esters. • Learn the important physical properties of the carboxylic acids and esters. • Learn the major chemical reaction of carboxylic acids and esters, and learn how to predict the products of ester synthesis and hydrolysis reactions. • Learn some of the important properties of condensation polymers, especially the polyesters. Chapter 5 Carboxylic Acids and Esters 2 Carboxylic Acids • Carboxylic acids are weak organic acids which contain the carboxyl group (RCO2H): • The tart flavor of sour-tasting foods is often caused by the presence of carboxylic acids. R C OH a carboxylic acid O C O O H the carboxyl group C O H O RCOOH RCO2H condensed ways of writing the carboxyl group Mr. Kevin A. Boudreaux Angelo State University CHEM 2353 Fundamentals of Organic Chemistry Organic and Biochemistry for Today (Seager & Slabaugh) Chapter 5 Carboxylic Acids and Esters 3 Nomenclature of Carboxylic Acids 4 Nomenclature of Carboxylic Acids • Select the longest carbon chain containing the carboxyl group. The -e ending of the parent alkane name is replaced by the suffix -oic acid. • The carboxyl carbon is always numbered “1” but the number is not included in the name. • Name the substituents attached to the chain in the usual way. • Aromatic carboxylic acids (i.e., with a CO2H directly connected to a benzene ring) are named after the parent compound, benzoic acid. C OH O Benzoic acid Chapter 5 Carboxylic Acids and Esters 9 More Complicated Acids • For molecules with two carboxylic acid groups the carbon chain in between the two carboxyl groups (including the carboxyl carbons) is used as the longest chain; the suffix -dioic acid is used. • For molecules with more than two carboxylic acid groups, the carboxyl groups are named as carboxylic acid substituents. C O HO C O OH ethanedioic acid CCH2C O HO O OH propanedioic acid CHCH2 CH2 C O C O C O OH OHHO propane-1,2,3-tricarboxylic acid 10 Examples: Drawing Carboxylic Acids • Draw structural formulas for the following molecules: – 2-methylpropanoic acid – 2,2,5-trimethylhexanoic acid – 4,5-dimethyl-3-nitrooctanoic acid Chapter 5 Carboxylic Acids and Esters 11 Examples: Drawing Carboxylic Acids • Draw structural formulas for the following molecules: – para-bromobenzoic acid – 2,4,6-trinitrobenzoic acid – 4-ethylpentanedioic acid (what’s wrong with this name?) 12 Chapter 5 Carboxylic Acids and Esters 13 Physical Properties of Carboxylic Acids 14 Physical Properties of Carboxylic Acids • Carboxylic acids hydrogen bond to themselves to form a dimer: R C O O H RC OH O R C O O H H OH O H H • Carboxylic acids also form hydrogen bonds to water molecules: Chapter 5 Carboxylic Acids and Esters 19 Name Molecular weight Boiling point Solubility in water Pentane 72 g/mol 35°C Insoluble Diethyl ether 74 g/mol 35°C Insoluble Butanal 72 g/mol 76°C 7.1 g / 100 mL H2O 1-Butanol 74 g/mol 118°C 9.1 g / 100 mL H2O Propanoic acid 74 g/mol 141°C Infinite Boiling Point: Carboxylic acid Alcohols Aldehydes/Ketones Ethers Alkanes Water Solubility: Carboxylic acid Alcohols Aldehydes/Ketones Ethers Alkanes Comparing Physical Properties 20 Examples: Predicting Physical Properties • Arrange the following compounds in order of increasing boiling point. (All of the compounds have about the same molecular weight.) – 1-pentanol – hexane – butanoic acid – pentanal • Which member of each of the following pairs of compounds would you expect to have a higher solubility in water? – 2-butanone or propanoic acid – hexanoic acid or ethanoic acid Chapter 5 Carboxylic Acids and Esters 21 Some Important Carboxylic Acids 22 Important Carboxylic Acids C O Methanoic acid (Formic acid) (from Latin formica, ant) A component of the venom of ants and caterpillars; produced in the body when methanol is consumed H OH C O Ethanoic acid (Acetic acid) (from Latin acetum, vinegar) Vinegar is a 5% solution of acetic acid dissolved in water; acetic acid is also responsible for the taste of sour wine (from the oxidation of ethanol) and sourdough bread CH3 OH C O Propanoic acid (Propionic acid) Found in Swiss cheese; salts of this acid are used as mold inhibitors CH3CH2 OH C O Butanoic acid (Butyric acid) (from Latin butyrum, butter) This acid has a foul, rancid odor; produced from the breakdown of soft triglycerides in butter CH3CH2CH2 OH C O Hexanoic acid (Caproic acid) Responsible for the odor of Limburger cheese. CH3CH2CH2CH2CH2 OH Chapter 5 Carboxylic Acids and Esters 23 para-Aminobenzoic aid (PABA) Used in sunscreens; absorbs short-wavelength UV light. It is also required by bacteria for the production of folic acid, needed to maintain the growth of healthy cell walls; sulfa drugs block the uptake of PABA by bacteria, causing them to be unable to manufacture folic acid, and thus preventing the bacteria from multiplying OH O H2N 2-hydroxy-1,2,3-propanetricarboxylic acid (Citric acid) Found in citrus fruits (lemons, grapefruit, oranges, etc.); commonly used in buffering solutions with sodium citrate OH OH O HO O OHO Oxalic acid Found in many leafy green plants such as rhubarb and spinach; combines with calcium ions in the body to produce insoluble salts, which form kidney stones HO O OH O Terephthalic acid A white, crystalline solid; used in the manufacture of some polyesters OH O HO O 24 Glycolic acid An alpha-hydroxy acid used in cosmetics and skin creams; alpha-hydroxy acids are thought to loosen the cells of the epidermis and accelerate the flaking off of dead skin; however these compounds can increase the skin's sensitivity to UV light O OH HO 2-hydroxypropanoic acid (Lactic acid) Produced from the fermentation of sugars under anaerobic conditions; found in sweat, sour milk, fermented pickles, sauerkraut, and yogurt; produced in muscles from glucose under anaerobic conditions (the buildup of lactic acid leads to a heavy, weak feeling, and muscle cramps); produced after death during the breakdown of sugars in the body by bacteria, inactivating the enzymes that allow the transport of calcium ions, causing rigor mortis OH O OH Malic acid Responsible for the sharp taste of apples (genus Malus) OH O OH HO O Chapter 5 Carboxylic Acids and Esters 29 Acids • An acid gives a proton (H+) to another species. Acids produce hydronium ions, H3O+, when they are dissolved in water: H—A + H2O  A– + H3O+ • A strong acid is one that completely dissociates in water (i.e., every molecule of the acid splits apart): H—Cl + H2O  Cl– + H3O+ • A weak acid is one in which only a small percentage of the molecules are dissociated at any one time (in other words, there is also a backwards reaction, where the acid molecule is regenerated): H—F + H2O h F– + H3O+ 30 The pH Scale • The acidity of a solution is measured using the pH scale. The pH of a solution is defined as pH = - log[H3O+] Acidic: pH < 7.00 [H3O+] > [OH-] Basic: pH > 7.00 [H3O+] < [OH-] Neutral: pH = 7.00 [H3O+] = [OH-] Chapter 5 Carboxylic Acids and Esters 31 The Acidity of Carboxylic Acids • Carboxylic acids are weak acids; in water, they dissociate to produce hydronium ions and carboxylate ions: • A 1.0 M solution of acetic acid is about 0.5% dissociated into hydronium and acetate ions: R C OH O carboxylic acid carboxylate ion + H2O R C O O + H3O CH3 C OH O acetic acid acetate ion + H2O CH3 C O O + H3O 32 The Acidity of Carboxylic Acids • The dissociation of a carboxylic acid is a reversible reaction, and the position of the equilibrium can be affected by the addition of acid (low pH) or by adding base (high pH): • At the physiological pH of 7.4 (the pH of most body fluids) the carboxylate form of most carboxylic acids is the predominate form. R C O O H + H2O + H3OR C O Obase (high pH) acid (low pH) carboxylic acid carboxylate ion Chapter 5 Carboxylic Acids and Esters 33 Carboxylate Salts Carboxylate Salts • Carboxylic acids react with strong bases such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) to produce carboxylate salts. • Carboxylate salts are named by naming the metal first, and changing the -ic acid ending of the carboxylic acid name to -ate. 34 R C OH R C O- Na+ ++ NaOH H2O O O carboxylic acid base metal carboxylate CH3CH2CH2CH2 C O- NH4 + O CH3 C O- Na+ sodium ethanoate (sodium acetate) O Chapter 5 Carboxylic Acids and Esters 39 Esters 40 Esters • An ester (“carboxylic ester” in the textbook) is a derivative of a carboxylic acid in which there is a carbon group connected to the single-bonded oxygen: R C O R' ester linkage carbon group O R C O C O Chapter 5 Carboxylic Acids and Esters 41 Nomenclature of Esters • Name the alkyl or aromatic portion contributed by the “alcohol part” first. • The “acid part” is named as a carboxylic acid, with the -ic acid suffix changed to -ate. R C O R' alcohol partacid part O CH3 C O CH3 O CH3CH2CH2 C O CH2CH3 O 42 Examples: Ester Nomenclature • Name the following compounds: H C O CH3 O CH C O CH3 CH3 CH3 O CH2CH2CHCH3COCH3CH2 O CH2CH3 Chapter 5 Carboxylic Acids and Esters 43 Examples: Ester Nomenclature • Name the following compounds: CH3CH2CH C O CHCH3 CH2CH3 CH3O C O CH2CH3 O 44 Examples: Ester Nomenclature • Name the following compounds: CH3CH2CH2 C O O C O CH3 O CH3 Chapter 5 Carboxylic Acids and Esters 49 OCH3 Methyl salicylate Also known as oil of wintergreen and betula oil; used as a flavoring and as an ingredient in deep heating rubs. It also fluoresces under ultraviolet light, producing visible blue light. This is most apparent in Wint-O-Green Lifesavers, which contain methyl salicylate as their flavoring. It is also used in some sunscreen lotions OH O Geranyl acetate geranium oil O O Spermaceti Also known as cetyl palmitate; found in the spermaceti organ or case above the skull of the sperm whale (Physeter macrocephalus). Its exact function is not known but it may be used as "cushioning," allowing the whale's head to be used as a battering ram in fights between males (see Moby Dick), as a regulator of the whale's buoyancy in water, or as an aid in echolocation in focusing sound waves. Spermaceti was highly sought by whalers in the 18th and 19th centuries, and was widely used commercially. O O(CH2)15CH3CH3(CH2)14 Coumarin Found in lavender oil, sweet clover and tonka beans O O Warfarin A potent rodenticide O O OH O 50 Polymers with Ester Groups Lauryl methacrylate Used to make the polymer poly(lauryl methacrylate); used as an additive in viscostatic engine oils, which keeps the oild viscous at high temperatures. O O C O O N Methyl cyanoacrylate Polymerizes on contact with surfaces containing trace amounts of water and alcohols to form Superglue; superglue is also used in surgery in place of sutures, and by morticians to seal the eyes and lips of their clients O O Methyl acrylate (vinyl acetate) Polymerizes to form polyvinyl acetate; used in acrylic paints in combination with pigments and a surfactant which causes the polymer to be suspended in an emulsion; also used in safety glass (a layer of PVA sandwiched between two layers of glass) and chewing gum O O Methyl methacrylate Polymerizes to form poly(methyl methacrylate); trade names are Lucite, Plexiglass, and Perspex; the bulky methyl and methyl ester groups cause the polymer to be oriented chaotically within the solid polymer, allowing light to pass through without scattering, rendering the plastic transparent Chapter 5 Carboxylic Acids and Esters 51 Reactions of Esters 52 Synthesis of Esters: Esterification Reactions • The simplest way to synthesize an ester is to heat a carboxylic acid with an alcohol or phenol (plus an acid catalyst); the oxygen of the alcohol adds to the carboxyl group, splitting out a molecule of water in the process (an esterification reaction). R C O O H R'OH R C O O R' HOH H+  a carboxylic acid an alcohol or a phenol an ester ++ Chapter 5 Carboxylic Acids and Esters 53 Synthesis of Esters: Esterification Reactions • Since this reaction is a reversible reaction, it often reaches an equilibrium with a large amount of unreacted starting material still present. • Better yields are obtained using either acid chlorides or acid anhydrides as starting materials. These reactions are nonreversible. R C Cl O acid chloride R C O O C R O acid anhydride 54 Synthesis of Esters: Esterification Reactions R C Cl O R'HO R C O O R' ClH an alcohol or a phenol acid chloride an ester + + R C O O R'HO R C O O R'C R O R C O O H a carboxylic acid an alcohol or a phenol an esteracid anhydride + + Chapter 5 Carboxylic Acids and Esters 59 Pain, Pain, Go Away OH O OH Salicylic acid Found in the bark of the willow tree (Salix); a tea brewed from the bark reduces fever and relives pain and inflammation, but is very acidic, and causes irritation of the mucous membranes in the mouth, throat, and stomach, and can cause painful ulcers and stomach bleeding OH O O O CH3 Aspirin (acetylsalicylic acid) Produced by reacting salicylic acid with acetic anhydride, giving a compound which is less acidic, and does not cause as much irritation, but still retains all of the beneficial medical properties; aspirin seems to work by blocking the production of prostaglandins, hormones which may be responsible for producing pain, fever and inflammation; one of the most commonly used pharmaceutical drugs; over 40 million pounds are produced in the United States per year 60 More Pain Relievers HN CH3 O OH Acetominophen Does not cause stomach irritation, and has analgesic and antipyretic properties that are similar to aspirin, but no anti-inflammatory functions; available under the trade names Tylenol, Excedrin Aspirin Free, Panadol, and Anacin-3 Ibuprofen An analgesic, antipyretic, and anti-inflammatory drug; it is also not irritating to the stomach lining; available under the trade names Motrin, Advil, Ibuprin, Nuprin, and Mediprin OH O Naproxen An analgesic, anti-pyretic, and anti-inflammatory drug; active ingredient in Aleve O OH CH3O Chapter 5 Carboxylic Acids and Esters 61 Condensation Polymers: Polyesters • Condensation polymers are polymers which form with the loss of a small molecule (typically water or HCl). • Condensation polymers, such as polyesters and polyamides (Nylon, Ch. 6), form when each of the monomers contain two of the same functional group, so the reaction can take place at both ends. 62 Condensation Polymers: Polyesters C OH O C HO O Ethylene glycol Terephthalic acid HOCH2CH2OH Ethylene glycol HOCH2CH2OH C OCH2CH2OH O C HOCH2CH2O O C OCH2CH2O O C OCH2CH2O O C OH O C O C O C HO O C OCH2CH2O O C OCH2CH2O O C OCH2CH2OH O C O C O C HOCH2CH2O O C OCH2CH2O O C OCH2CH2O O C OCH2CH2O O C O C O C OCH2CH2O O C OH O C O C O C HO O etc. Chapter 5 Carboxylic Acids and Esters 63 Condensation Polymers: Polyesters Over 3 billion pounds of PET are made every year. It forms a very linear chain, and is very inert. It can be melted and pulled through spinnerettes to make fibers, threads, or yarn (Dacron, Fortrel, Terylene), where it can be used in automobile tire cord, permanent press clothing, sutures, replacements for damaged sections of blood vessels and the esophagus, etc. PET melts can also be forced through narrow slits to produce thin sheets or ribbons known as Mylar; this form is used as the support medium in audio and video tape. C C O O O O n H Polyethylene terephthalate (PET) A polyester CH2CH2 OH 64 Reactions of Esters: Ester Hydrolysis • Esters may be broken apart under acidic conditions by water (a hydrolysis reaction) to form a carboxylic acid and an alcohol. • This is essentially the reverse reaction of the synthesis of esters from carboxylic acids and alcohols. R C OR' R C OHH2O R'OH a carboxylic acid an alcoholan ester H+ O O + + Chapter 5 Carboxylic Acids and Esters 69 Some Saturated Fatty Acids OH O Stearic acid A saturated fatty acid found in lard, beef fat, butterfat, cottonseed oil; the sodium salt, produced by heating lard with sodium hydroxide, can be used as a soap OH O Lauric acid Found in coconut oil; commonly used in soaps OH O Myristic acid A fatty acid found in butterfat, coconut oil, and nutmeg oil OH O Arachidic acid A fatty acid found in peanut oil 70 Some Saturated Fatty Acids OH O Palmitic acid A fatty acid, found in lard, beef fat, butterfat, and cottonseed oil; the triglycerides in cocoa butter have oleic acid attached to the central oxygen, with stearic acid or palmitic acid on the other oxygens; this more regular composition gives cocoa butter a much sharper melting point than is usually observed in fats, and chocolate remains brittle almost up to its melting point of 34°C (just below body temperature); the sudden melting of chocolate in the mouth gives it a pleasant feeling of coolness Chapter 5 Carboxylic Acids and Esters 71 Some Unsaturated Fatty Acids OH O Oleic acid An unsaturated fatty acid; the chain is much less flexible than that of stearic acid because of the double bond, and cannot pack as tightly, so the triglycerides it forms are oils and not fats; found in olive oil, cocoa butter and chocolate, beef fat, lard, and peanut oil OH O Linolenic acid A omega-6 polyunsaturated fatty acid found in linseed oil and corn oil Arachidonic acid An omega-6 polyunsaturated fatty acid found in corn oil, linseed oil, animal tissues OH O 72 Some Unsaturated Fatty Acids OH O Eicosapentaenoic acid A omega-3 polyunsaturated fatty acid found in fish oil and seafoods; omega-3 fatty acids may, according to some studies, help to lower the risk of heart disease OH O Palmitoleic acid An unsaturated fatty acid found in butterfat and cod liver oil Docosahexaenoic acid An omega-3 polyunsaturated fatty acid found in fish oil and seafoods OH O Chapter 5 Carboxylic Acids and Esters 73 Triglycerides (Fats and Oils) O O O R O R O R O O O O O R O R R O Triglycerides fats and oils (lipids) Tristearin One of the principle compounds in beef fat and cocoa butter; triglycerides such as this lubricate meat fibers, and make the meat more tender when cooked; the yellow color of beef fat comes from carotene dissolved in tristearin. O O O C(CH2)16CH3 O C(CH2)16CH3 O C(CH2)16CH3 O Trimyristin Found in nutmeg, a spice obtained from the seed of the nutmeg tree, found in Indonesia and the West Indies, and other tropical areas O O O C(CH2)12CH3 O C(CH2)12CH3 O C(CH2)12CH3 O 74 O O O O O O O O O OO O O O O O O O O Olestra A substitute for dietary fats developed by Procter & Gamble after 30 years and $200 million dollars worth of research; it is a combination of sucrose and fatty acids obtained from soybean oil and cottonseed oil; it is too hindered for digestive enzymes to react with; can carry small amounts of fat-soluble vitamins out of intestinal tract Chapter 5 Carboxylic Acids and Esters 79 Esters of Inorganic Acids 80 Esters of Inorganic Acids R O H P O HO OH OH P O RO OH OH R OH P O RO OH OR R OH P O RO OR OR a phosphate ester (monoester) phosphoric acid a phosphate diestera phosphate triester H+ an alcohol Chapter 5 Carboxylic Acids and Esters 81 Some Important Phosphate Esters O HO OH OH OH CH2O P O O- O- glucose-6-phosphate P O RO O- P O O O- P O O O- O- a phosphate triester P O O- P O O O- P O O-O O- CH2 OH OH O O N N N N NH2 Adenosine TriPhosphate (ATP) Adenine Ribose 82 P O O- -O CH2 O O N N N N NH2 P O O -O CH2 O O N NO NH2 P O O -O CH2 O O HN N N N O H2N P O O -O CH2 O O HN NO O OH CH3 thymine guanine cytosine adenine Deoxyribonucleic Acid (DNA) deoxyribose Chapter 5 Carboxylic Acids and Esters 83 R C O O H R C O- O carboxylate ioncarboxylic acid 1. Reaction of a carboxylic acid with water to form a carboxylate ion. + H2O + H3O+ 2. Reaction of a carboxylic acid with a base to form a carboxylate salt and water. R C O O H R C O- Na+ O carboxylate saltcarboxylic acid + NaOH + H2O R C O O H R'OH R C O O R' HOH H+  carboxylic acid alcohol or phenol ester 3. Reaction of a carboxylic acid with an alcohol to produce an ester and water. + + 4. Reaction of an acid chloride with an alcohol to produce an ester and HCl. R C Cl O R'OH R C O O R' ClH acid chloride alcohol or phenol ester + + Reactions of Carboxylic Acids 84 R C O O C R O R C O O H carboxylic acidacid anhydride 5. Reaction of an acid anhydride with an alcohol to produce an ester and a carboxylic acid. R'OH R C O O R' alcohol or phenol ester + + 6. Hydrolysis of an ester to produce a carboxylic acid and an alcohol. R C O O R' ester + H2O H+  R C O O H carboxylic acid R'OH alcohol + 7. Saponification of an ester to produce a carboxylate salt and an alcohol. R C O O R' ester + NaOH R C O- Na+ O carboxylate salt R'OH alcohol + R O HP O HO OH OH P O RO OH OH phosphate monoesterphosphoric acid alcohol 8. Formation of a phosphate monoester. + H+ + H2O