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Explore carboxylic acids, their nomenclature, and physical properties in organic chemistry. Learn about functional groups, IUPAC names, polarity, and boiling points.
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Announcements Chapter 17 Carboxylic acids
Next few chapterscompounds with OXYGEN Alcohols Ethers Aldehydes Ketones Carboxylic acids Esters 1 CH 14 2 Connections to O CH 17 More oxidized CH 18 3 CH 19 4
Chapter 18 Carboxylic Acids and Esters The functional group of carboxylic acids is the carboxyl group.
Concepts from chapter 1-10 needed for Chapter 18, 19 • The concept of Acids • The concept of ionic compounds • The concept of salts Then we can move on to: • Carboxylic acids and Esters
The Concept of Ionic Compounds • Ionic compounds are balanced with a full plus and minus charges • Positive charges are called cations • Negative charges are called anions The “t” looks like a plus “+” The “n” is the first letter of negative
The concept of Acids • An acid for us in 102 means that an H is loose and can come off as H+ (a cation) • leaving behind an anion (negative ion) if neutral • HCl Cl +H+ • Or leaves a neutral if started as positive • NH4+ NH3 + H+
The concepts of salts • Water is the basis for acids and bases H2O = HOH H+ + OH • Acid + base salt + water • HCl + NaOH NaCl + HOH acid base
An H+ is always associated with something • An H+ is a bare proton without electrons • It needs to find a pair of electrons to share with and will bounce from place to place • An H+ in water will associate with one or more waters and may be written as H+ + H2O H3O+ So you may see it as H+ or H+(aq) or H3O+
Strength of Acids Sulfuric acidhydrochloric acidH2SO4, HCl Phosphoric acid H3PO4 Carboxylic acids RCOOH CH3COOH • A strong acid will let loose its H greater than 90% of the time • A medium acid will let loose it H 30 to 90% of the time (ex 30% together 70% loose) • A weak acid will let loose 1% to 30% • NOTE: The H going and coming is reversible. Like a hot potato it exchanges freely.
A base in the last chapters • Inorganic bases are OH or NH3 • Organic bases will be 1 any nitrogen that has 3 bonds (not four) 2 or any oxygen that is negative • A base can take an H+ • A weak base takes and give up an H+ • A strong base take an H+ and holds on to it
H+ as a pet that wants to escape • Her name is H-plus or Proton and food or treats are lone pairs (empty spots) • She tries to escape from acids (the fence is low) or from strong acids (they don’t feed her) • Bases can be owners or strangers that feed her and are nice to her and she sticks around • The strongest the base becomes the new owner • “Proton” loves to play with the other pets in water • If you see an H but it is not loose it must have owners with very tall fences or strong leash (like in C-H or COH)
Carboxylic Acids • In this chapter, we study carboxylic acids, a class of organic compounds containing the carbonyl group. • The functional group of a carboxylic acid is a carboxyl group, which can be represented in any one of three ways.
Nomenclature • IUPAC names • For an acyclic carboxylic acid, take longest carbon chain that contains the carboxyl group as the parent alkane. • Drop the final -e from the name of the parent alkane and replace it by -oic acid. • Number the chain beginning with the carbon of the carboxyl group. • Because the carboxyl carbon is understood to be carbon 1, there is no need to give it a number.
Naming Carboxylic Acids Find the longest carbon chain that contains the –COOH group. (or –CO2H or Drop the –e from the end of the alkane name and substitute –oic acid. Number the longest chain. Carbon number 1 is the carboxyl carbon. Name and number other substituents.
Aromatic acid names are derived from the parent compound, benzoic acid. benzoic acid 3,4-dimethylbenzoic acid
Nomenclature • In these examples, the common name is given in parentheses. • An -OH substituent is indicated by the prefix hydroxy-; an -NH2 substituent by the prefix amino-.
Nomenclature • To name a dicarboxylic acid, add the suffix -dioic acid to the name of the parent alkane that contains both carboxyl groups; thus, -anebecomes -anedioic acid. • The numbers of the carboxyl carbons are not indicated because they can be only at the ends of the chain.
Nomenclature • For common names, use, the Greek letters alpha (a), beta (b), gamma (g), and so forth to locate substituents.
Physical Properties • The carboxyl group contains three polar covalent bonds; C=O, C-O, and O-H. • The polarity of these bonds determines the major physical properties of carboxylic acids.
Physical Properties • Carboxylic acids have significantly higher boiling points than other types of organic compounds of comparable molecular weight. • Their higher boiling points are a result of their polarity and the fact that hydrogen bonding between two carboxyl groups creates a dimer that behaves as a higher-molecular-weight compound.
Physical Properties of Carboxylic Acids Super H bonding: partially ionic, H-bonding, dipole, LDF The carboxylate group is very polar. Hydrogen bonding between carboxylates creates dimers (two identical molecules bonded together). This gives carboxylic acids high boiling points (greater than alcohols).
1. Two trends 1. with the same IMF as the molecules get larger (longer carbon chain: increase bp 2. With the same approx. weight the higher the IMF increase the bp 2. IMF=intermolecular force bp= boiling point Fig. 15-4, p.477
Physical Properties • Carboxylic acids are more soluble in water than are alcohols, ethers, aldehydes, and ketones of comparable molecular weight.
Take an H-bond Can give 1 H-bond Can take4 H-bonds(One each lone pair) Physical Properties, cont. Carboxylate groups can hydrogen bond with water. If the hydrophobic –R group is not too large, carboxylic acids are very water soluble. Give an H-bond Water can give 2 H-bonds can take 2 H-bonds
Fatty acids and Soaps • We will cover these in the lipid chapter (21) • All we need to know about them here is that • long chain carboxylic acids are called fatty acids • The longer the chain the higher the boiling point • Short chain fatty acids are more soluble in water than alcohols or aldehydes
We will cover “fatty acids” in more detail in the lipid chapter ( ch 21) (fatty acids are long chain acids) Fatty acids Table 15-2, p.476
-oate -oic acid Happy owner Good owner Acidity of Carboxylic Acids Carboxylic acids behave as weak acids (low dissociation), forming carboxylate ions in water.
Note the 3 in H3O+ Examples: benzoic acid benzoate ion
Acidity of RCOOH • Carboxylic acids are weak acids: • Values of Ka for most unsubstituted aliphatic and aromatic carboxylic acids fall within the range 10-4 to 10-5 (pKa 4.0 - 5.0).
Acidity of RCOOH • When a carboxylic acid is dissolved in aqueous solution, the form of the carboxylic acid present depends on the pH of the solution in which it is dissolved. Mainly this form (99%) Small amount this form (1%) Plain water Buffered solutions (Like blood)
Has the coolest treats for “Proty” Salts of Carboxylic Acids Carboxylic acids react readily with strong bases (NaOH, KOH) to form salts. Has the cool treats for Proty Note: a base is a molecule that can accept an H+ Hydroxide (OH) is a strong base and will accept an H+ to become water (HOH)
Reaction With Bases • All carboxylic acids, whether soluble or insoluble in water, react with NaOH, KOH, and other strong bases to form water-soluble salts. • They also form water-soluble salts with ammonia and amines.
Reaction With Bases • Like inorganic acids, carboxylic acids react with sodium bicarbonate and sodium carbonate to form water-soluble sodium salts and carbonic acid. • Carbonic acid then decomposes to give water and carbon dioxide, which evolves as a gas.
ethanoic acid sodium ethanoate Examples:
Salts, cont. To name a carboxylic acid salt, name the metal ion first and change the –ic ending of the acid to –ate. Example: Know Na = Sodium K = Potassium Ca = Calcium 1+ 1+ 2+
Useful Carboxylic Acid Salts Na and K salts of long-chain acids are used as soaps (sodium stearate). Calcium and sodium propanoate are used as preservatives in bakery products. Sodium benzoate is a food preservative used in ketchup and soda pop. Zinc 10-undecylenate is used to treat athelete’s foot.
Butyric Acid • It is notably found in rancid butter, parmesan cheese, vomit, and the smell of foul, stale, unwashed, rancid human bare feet, and has an unpleasant odor and acrid taste, with a sweetish aftertaste (similar to ether). Butyric acid can be detected by mammals with good scent detection abilities (e.g., dogs) at 10 ppb, while humans can detect it in concentrations above 10 ppm. • Its name was made from Greek boutros = butter. • Butyric acid is a fatty acid occurring in the form of esters in animal fats and plant oils. The glyceride of butyric acid makes up 3% to 4% of butter. When butter goes rancid, butyric acid is liberated from the glyceride by hydrolysis leading to the unpleasant odor. • Normal butyric acid or fermentation butyric acid is also found as a hexyl ester in the oil of Heracleum giganteum (cow parsnip) and as an octyl ester in parsnip (Pastinaca sativa); it has also been noticed in the fluids of the flesh and in perspiration. • It is ordinarily prepared by the fermentation of sugar or starch, brought about by the addition of putrefying cheese, with calcium carbonate added to neutralize the acids formed in the process. The butyric fermentation of starch is aided by the direct addition of Bacillus subtilis. • Butryic acid is used in the preparation of various butyrate esters. Low-molecular-weight esters of butyric acid, such as methyl butyrate, have mostly pleasant aromas or tastes. As a consequence, they find use as food and perfume additives.
2-hydroxy propanoic acid Alpha hydroxy acid p.478a
Tartaric Acid Found in grapes and grape peels - by-product in wine making It is also called Cream of Tartar and is the acid used in baking powders to acidify baking soda (NaHCO3) to make CO2 bubbles H+ + HCO3 H2CO3 H2O + CO2 (gas) Acid + bicarbonate carbonic acid water + carbon dioxide
REACTIONS(other than acid-base) Esters, Phosphate Ester, and Amides
Aldehyde Reactions of Carboxylic acids excess O2 CO2 + H2O Carboxylic acid [O] Combustion [H] amine Amide + H20 + another RCOOH Alcohol ROH Ammonia (NH3) Ester + H20 Anhydride ( losing H20 ) 1º amine 2º amine
Introduction • In this chapter, we study three classes of compounds derived from carboxylic acids; anhydrides, esters, and amides • Each is related to a carboxyl group by loss of H2O. Acid + Acid Acid + Alcohol Acid + Amine
Fischer Esterification • Fischer esterification is one of the most commonly used preparations of esters. • In Fischer esterification, a carboxylic acid is reacted with an alcohol in the presence of an acid catalyst, most commonly concentrated sulfuric acid. • Fischer esterification is reversible. • It is possible to drive it in either direction by the choice of experimental conditions (Le Chatelier’s principle).
Fischer Esterification • In Fischer esterification, the alcohol adds to the carbonyl group of the carboxylic acid to form a tetrahedral carbonyl addition intermediate. • The intermediate then loses H2O to give an ester.
Phosphoric Esters • Phosphoric acid forms mono-, di-, and triphosphoric esters. • In more complex phosphoric esters, it is common to name the organic molecule and then indicate the presence of the phosphoric ester by either the word "phosphate" or the prefix phospho-. • Dihydroxyacetone phosphate and pyridoxal phosphate are shown as they are ionized at pH 7.4, the pH of blood plasma.
