Introduction to Organic and Biochemistry (CHE 124) Reading Assignment General, Organic, and Biological Chemistry: An Integrated Approach 3 rd. Ed. Ramond Chapter 8 Carboxylic Acids, Phenols, and Amines Gasses, Solutions, Colloids, and Suspensions Work Problems 8. 3,4,5,6,8,12,14,32,42,90

Functional Groups Carboxylic Acids –Found in fatty acids and amino acids Phenols Esters Amines –Found in amino acids

Characteristic of Carboxylic Acids High b.p. –Form H-bonds with water and other carboxylic acids. See p –See Table 8.1 p Water soluble –Water solubility ↓ as # of carbons ↑ Odor –Carboxylic acids with 3 – 10 carbons STINK E.g. Butyric acid –Carboxylic acid with 10 + carbons have a low vapor pressure, therefore, little or no odor. Weak Acid (discussed in a few slides) –Acid is a compound that losses (donates) a proton.

Naming Carboxylic Acids 1. Select longest chain (parent compound) containing the carboxylic acid and name as alkane –Number carbon containing acid group as #1. 2. Drop e from name of alkane and add –oic acid. 3. Name / number side chains. # of C IUPAC NAME COMMON NAME B.P. (C °) 1Methanoic AcidFormic Acid100 2Ethanoic AcidAcetic Acid118 3Propanoic Acid-141 4Butyric Acid-161

Characteristics of Phenols High b.p. for size –H-bonding Water soluble –Due to H-bonding with water Weak Acid

Naming Phenols Substituted Phenols –1. Number carbon containing hydroxyl group as #1. –2. Number side chains so they have the lowest possible number. Disubstituted phenols –Ortho o1,2 di-substituted benzenes –Meta m1,3 di-substituted benzenes –Para p1,4 di-substituted benzenes –Show the following examples 4-ethylphenol(p-ethylphenol) 2-chlorophenol(o chlorophenol) 2,4-dinitrophenol (Trisubstituted)

Carboxylic acids and Phenols are Weak acids Acid – compound that losses (donates) a proton. –Draw acid (-oic acid) and carboxylate (-ate ion) forms of acetic acid (ethanoic acid) and phenol.

Acid Equilibrium Constant or Acid Dissociation Constant (K a ) CH 3 COOH + H 2 0 ↔ CH 3 COO - + H 3 O + Acetic acid + water ↔ acetate + hydronium ion K a = products = [CH 3 COO - ] [H 3 O] = 1.8 x reactants [CH 3 COOH] pKa = -log Ka **remember do not include water, pure liquids or solids in this equation. Only include species whose concentration can change.

Acid Dissociation Constant (K a ) Cont’ Most carboxylic acids have pKa values around 5. This means at a pH of 7, the predominant species in solution is the carboxylate ion. This is important for the solubility of fatty acids. At physiologic pH, fatty acids are amphipathic. Amphipathic – has both hydrophobic and hydrophilic properties. –Hydrophobic – water fearing –Hydrophilic – water loving

Reactions of Carboxylic Acids 1. Decarboxylation Rxn. – lose of carbon dioxide from a carboxylic acid. –This occurs to carboxylic acids with alpha (α) or beta (β) keto group (carbon double bonded to an oxygen). These compounds are called α or β keto acids. Draw α or β keto acids. –Alpha is carbon attached to carbon with carboxylic acid –Beta carbon is next carbon. –Example Decarboxylation of pyruvate to acetaldehyde by pyruvate decarboxylase (first step in fermentation). Produces carbon dioxide.

Reactions of Carboxylic Acids (Cont) H Carboxylic acid + alcohol →Ester –Example Benzoic acid + methanol → methyl benzoate + water –Benzene with carboxylic acid

Esters Naming Esters –1. Name the alcohol group. –2. Name carboxylic acid, change -oic acid to ate. –3. Combine the two names e.g. Methyl benzoate. Characteristics of Esters –Lower b.p. than similar sized carboxylic acids. Does not readily H-bond –Odor Sometimes pleasant, think perfumes.

Reactions of Carboxylic Acids (Cont) 3. Oxidation of Phenols –Hydroquinone (p-hydroxyl groups) oxidized to benzoquinone (p-ketone groups). The hydroxyl groups are oxidized to ketone groups by the oxidizing agent, potassium dichromate (K 2 Cr 2 O 7 )

Amines Amines are classified by the number of carbons attached to the N. –1° primary amine1 carbon –2°secondary amine2 carbons –3°tertiary amine3 carbons –4°quaternary ions4 carbons »(+ charge on N)

Naming Amines 1. Name longest C chain containing amine as alkane. Drop the -e and add amine. 2. 2° or 3° amines require naming the shorter chains. Put “N” in front of these substituents. 3. If 4° add “ammonium ion” instead of amine. –Ethanamine 4. Cyclic amines –Pyridine, pyrimidine, purine –See figure 8.13 p. 273

Characteristics of Amines 1° and 2° amines –form H-bonds with water. –Higher b.p. than similar sized 3° amines Due to H-bonds –Low MW amines are water soluble –Unpleasant odor “dead fish odor” putrescine cadaverine 3° amines –do NOT form H-bonds.

Amines are weak bases Base – compound that accepts H or produces OH -. –pKa values 9 – 11

Reactions of Amines Strong acids react with amines to produce ammonium salt. –Ammonium salts are more water soluble than the amine they are derived from. Amines react with carboxylic acids to form Amides. (draw) –Formed by reaction of carboxylic acid with ammonia or 1° or 2°amine, the product is a caroxylate ion and the conjugate acid of ammoniua or an amine. Heating this produces an amide. See fig p. p 277. –Amide bonds connect amino acids to form proteins.

Naming Amides 1. Name the carboxylic acid with parent compound containing the amide. Change ending form –oic acid to amide. If an amine is present use N then name the group.