Based on notes by JZ updated 4/2018 Amines are Biologically Important CAPTE 22: Amines Amino acids are the basis of all peptides and proteins. These are the tissue building blocks and nature's catalysts (enzymes) in biological systems. Amine functional groups have marketed biological activity, from being very foul smelling compounds from degrading flesh to impacting neural chemistry. amino acids 2 n 1 2 3 4 peptides/proteins 5 2 putrescine 2 2 2 cadeverine foul smelling constituents from rotting flesh Some biologically active compounds C 3 C3 methamphetamine C 3 C3 ecstasy (MDMA) C 2 Me Dexmethylphenidate (ritalin) C 3 cocaine C 2 Me C 3 nicotine 3 C C 3 C 3 F = : morphine = C 3 : codeine 3-methyl-1-indole aka. skatole ofloxacin (antibiotic for anthrax treatment) Amine Substitution Primary, secondary, and tertiary amines refer to the amount of alkyl substitution on the itrogen atom (not the carbon as is the case with other functional groups). 3 2 ammonia 1 2 3 4 (quaternary ammonium salt) 1
Based on notes by JZ updated 4/2018 Amine aming There are several ways to name amines, depending on what you call the substitutent and what you call the parent. Also, when necessary, substituents on the nitrogen are indicated with a capital. C 3 2 3 C 2 3 C Methyl Amine Methanamine Ethyl Methyl Amine -Methylethanamine Cyclohexylamine cyclohexanamine pyridine pyrrole piperidine azacyclohexane piperazine pyrrolidine azacyclopentane azetane aziridine azacyclopropane 2 aniline C 3 -Methylaniline -methyl-benzenamine 2 C 3 p-anisidine 4-methoxy-benzenamine imidazole indole Amine Structure Amines are sp 3 -hybridized and tetrahedral with the lone pair taking up one of the four positions. Amines are inherently chiral; however, they undergo rapid inversion at room temperature (requires the same energy as rotation around an sp 3 sp 3 bond). Thus, they are always racemic. 3 1 1 3 2 2 1 23 Separations of amines 3 2 C 2 2 (aq) 2 C 2 2 seperate layers 2
Based on notes by JZ updated 4/2018 Amines are Good Bases Amines are very good bases - more basic than oxygen-containing compounds like alcohols or water. ne way to measure the base strength is to look at the pk a of the protonated amine (conjugate acid). The weaker the acid is, the stronger was the base that generated it. 4 is a base AMIE AMMIUM pk a (ammonium) 4 is an acid 3 3 C 2 4 3 C 3 ote that the conj. acid of aliphatic amines have a pka ~10 9.3 10.8 11.2 Et 3 Et 3 11.0 2 3 ote aniline is less basic than Et 3 4.6 2 2 2 3 1.0 5.3 0.4 2 2-1 Amines are very poor acids But they can be deprotonated with very, very strong bases like butyl lithium. For example, this is how chemists prepare LDA. Li Li Lithium DiisopropylAmide (LDA) ote the term amide as applied here is a deprotonated amine 3
Based on notes by JZ updated 4/2018 Preparation of Amines - From previous chapters omatic nitro compounds can be reduced to afford anilines and amides can be reduced to form amines. 2 2, Pd 2 2 1. Sn 2, 2 2. a Zn and Fe also work here Make an amide, then reduce: 3 C 2 pyridine C 3 1. LiAl 4 2. 3 C 3 1 1 1. LiAl 4 2. 3 1 1 - amine 1. LiAl 4 2 2. 3 1 2 2 - amine 1 1. LiAl 4 2 2. 3 1 2 3 3 3 - amine Alkylation of amines Amines are very good nucleophiles. Too good as a matter of fact. It is difficult to stop the reaction at just one alkylation. 3 C I C 3 C I 3 C I 3 3 3 C 3 C I 2 3 C 3 C C 3 C 3 C 3 3 C C 3 C 3 t-bu 60% t-bu 2 t-bu 30% 3 C C C 57% Controlling the Alkylation of Amines In order to avoid problems with over alkylation, there are several strategies that can be undertaken. 4
Based on notes by JZ updated 4/2018 educe a nitrile to a primary amine: ac C 1. LiAl 4 2. 3 2 Use azide as a nucleophile, then reduce: a 3 3 azides will alkylate only once. 1. LiAl 4 2. 3 2 Use thalimide as a ucleophile, then deprotect (Gabriel Synthesis): K pk a = 9 X a, 2 eat or 2 2 2 Conversion of phthalimide to amine: a, 2 eat 2 primary amine byproduct 2 2 Et, eat 2 primary amine byproduct 5
Based on notes by JZ updated 4/2018 eductive Amination with Amine and Aldehyde Imine/iminium ion formation mechanism: see C. 21 notes. 3 C 2 Et C 3 ab 3 C C 3 C 3 3 C Et 3 C C 3 ab 3 C 3 C C 3 C 3 2, Et ab 3 C C 3 ab 3 C (derived from ab 4 ) is very effective for reductive aminations. 2 /Pd can be substituted for ab 3 C ote imines reduce faster than ketones, aldehydes, and before enamines can form Curtius earrangement (not in Smith book) An acid chloride reacts with azide ion to give an acyl azide, which undergoes Curtius rearrangement when heated. a 3 a 3 acyl azide 2 * C 2 2 2 heat C isocyanate * 2 serves as the leaving group! Example: 1. S 2 2 2. a 3 3. 2, heat 6
Based on notes by JZ updated 4/2018 ofmannn earrangement (not in Smith book) Amides with no substituent on the nitrogen react with solutions of bromine or chlorine in sodium hydroxide to yield amines through a reaction known as the ofmann earrangement. 2 2 4 a 2 2 2 a a 2 C 3 2 2 C Isocyanate 2 C 2 Examples: 3 C C 3 2 2, a 3 C C 3 2 2 2, a 2 2 2 7
Based on notes by JZ updated 4/2018 Eliminations: ofmann Elimination Amines can undergo eliminations too, like alcohols and alkyl halides, however they cannot eliminate directly. First, the amine must be converted into a good leaving group by exhaustive methylation (using methyl iodide), creating an ammonium ion that can leave as a neutral amine. I ( 3 C) 3 Ag 2, 2 heat more accessible 1-pentene ofmann product (95%) 2-pentene Zaitsev product (5%) AgI The ofmann elimination prefers the least substituted alkene. This is mostly due to the sterics of the quaternary ammonium ion. Elimination of the quaternary ammonium salt generally takes place by the E2 mechanism, which requires a strong base. To provide the base, the quaternary ammonium iodide is converted to the hydroxide salt by treatment with silver oxide followed by heating. I C 3 C 3 C 3 C 3 1/2 Ag 2 2 C 3 C 3 E2 elimination heat (C 3 ) 3 Eliminations: Cope Elimination(not in Smith Book) C 3 C3 2 2 or C 3 C 3 tertiary amine oxide heat C 3 C 3 dimethylhydroxyl amine The Cope Elimination proceeds through a cyclic transition state and is a syn-elimination. C 3 2 2 C 3 C 3 C 3 C 3 C 3 heat C 3 C 3 C 3 syn-elimination C 3 Zaitsev: minor C 3 C 3 The direction of elimination is governed by the number of 's & probability vs thermodynamics C 3 3 C ofmann: major C 3 C 3 8
Based on notes by JZ updated 4/2018 eactions of Primary ALIPATIC Amines with itrous Acid (): 2 a 2 2 X X ax 2 2 X aliphatic diazonium salts decompose spontaneously by losing nitrogen to form carbocations. Alkenes, alcohols, alkyl halides eactions of Primary AYL Amines with itrous Acid (): 2 a 2 2 X X ax 2 2 mechanism enediazonium salt (stable if kept under 5 C) 2 2 2 nitrosonium ion 2 A A 2 A diazohydroxide Diazonium Ion 9
Based on notes by JZ updated 4/2018 eactions of Secondary Amines with itrous acid () 3 C 3 C a 2 () - 2 3 C 3 C potent hepatotoxin. EPA allows 7 ng/ml -nitrosodimethylamine C3 a 2 () - 2 C3 -nitroso--methylaniline eplacement eactions of enediazonium Salts eplacement by - C 3, a 2 2 2 (0-5 C) C 3 2 Cu 15-60 C C 3 2 Mechanism: adical C 3 2 C 3 Cu Cu C 3 Cu 2 eplacement by - 2, a2 2 Cu 2 100 C (0-5 C) 2 eplacement by -C 2, a 2 2 2 (room temp.) 2 2 CuC 90-100 C 2 C 2 10
Based on notes by JZ updated 4/2018 eplacement by -I 2 2 2 2 S 4, a 2 2 (0-5 C) 2 2 S 4 I KI 2 eplacement by -F C 3 C3 C3 1. a 2, eat 2. BF 4 2 2 BF4 F 2 eplacement by - C 3 C 3 C 3 2 S 4, a 2 Cu 2 2 (0-5 C) Cu 2, 2 2 2 S 4 or Just 2 2 eplacement by - (deamination) C 3 C 3 C 3 C 3 1. 2, Fe 3 2 S 4, a 2 2 C 3 2. a, 2, heat 2 2 (0-5 C) 2 S 4 hypophosphorous acid 3 P 2, 2, room temp. C 3 11
Based on notes by JZ updated 4/2018 Coupling eactions of enediazonium Salts This is another example of an electrophilic aromatic substitution reaction. The diazonium salt is the electrophile. 2 2 C 3 C 3 a, 2 0 C sodium acetate, 2 0 C C 3 C 3 eactions of Amines with Sulfonyl Chloride: Making Sulfonamides S (-) S 1 Amine Sulfonamide S (-) S 2 Amine Sulfonamide S 1. 3, heat 2. a S Sulfonamide S S 2 sulfamethoxazole (found in Bactrim) 12