R N R N R N. primary secondary tertiary

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Blake Bishop
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1 Chapter 19 Amines omenclature o assification of amines Amines are classified as 1, 2, or 3 based on how many R groups are attached to the nitrogen R R R R R R primary secondary tertiary When there are four R groups attached to a nitrogen, it is called a quaternary ammonium salt. o Common names Say the alkyl groups attached and then say amine ethyl isopropyl amine o IUPAC names Find the longest carbon chain with the nitrogen attached. ame that as the parent, remove the e, and replace it with amine eptane 3-heptanamine Whatever else is on the nitrogen is named as a substituent, with as the locant. -methyl-3-heptanamine If the amine is not the high-priority group, then the nitrogen is named as an amino substituent. 5-amino--methyl-2-heptanol

2 Structure of amines o Trigonal pyramidal o Chirality Amines can be chiral, but the lone pair flips from side to side of the nitrogen, changing them from R to S. There are two times when chirality is locked. Quaternary ammonium salts Sometimes sterics can prevent the lone pair from flipping. Physical properties o Strongly polar o Can hydrogen-bond if they are 1 or 2 Remember that the hydrogen bonding of nitrogen is not as strong as that with oxygen, so boiling points will be lower than similarly sized alcohols. o Small amines will be water-soluble. Larger ones will not. Basicity of amines o The pkb of ammonia is o Amines are slightly stronger bases because the alkyl groups are electron donating groups, as we have seen in previous chapters. Amines have pkb s around 3-4. Aniline has a pkb around 10 because the lone pair is conjugated with the aromatic system Pyridine also has a pkb around 10, because the lone pair is less available in the sp 2 orbital than it would be in a sp 3 orbital. Pyrrole is even less basic, with a pkb around 16, because its lone pair is involved in aromaticity. o EDGs will increase basicity, while EWGs will decrease basicity. o My weird way of thinking about basicity: The lone pair of a base is like teeth that want to bite a proton. The bigger the teeth, the stronger the base. EDGs make the teeth bigger, EWGs suck the teeth back into the gums. When the teeth are involved with aromaticity, that s like they re already chewing something, so they re not available to bite a proton. This is why pyrrole has a pkb around 15.

3 When the teeth are in sp 2 orbitals, they are held closer in to the mouth, and aren t as available. This is why pyridine has a pkb of 8.75 Amine salts and extraction o By protonating an amine, you make it more water-soluble. o Mr. Baker likes to ask questions about what would be left in the organic or aqueous layer after adding either an acid or base. If on a test or quiz he doesn t specifically say that you drain off the aqueous phase, make sure to ask. Below, you are not draining in between. dipropyl amine phenol decanoic acid diethyl ether hexane phenol decanoic acid diethyl ether ac3 phenol dipropyl amine diethyl ether a dipropyl amine diethyl ether dipropyl ammonium decanoate decanoate phenoxide dipropyl amine phenol decanoic acid diethyl ether 2 o ere s an example with draining in between. Remember that he can change up when you drain, which would change the answer. hexane phenol phenol decanoic acid diethyl ether diethyl ether diethyl ether 1) 1)aC3 2) Drain 2) Drain a phenoxide 2 Phase transfer catalysts o Large 4 ammonium salts are somewhat soluble in both organic and aqueous phases. As such, they can move ionic reagents into the organic phase so that they can react.

4 o Crown ethers also make good phase transfer catalysts. Substitution of aniline o In chapter 17 we said that 2 was a strong ortho-, para-director, but is it? 2 C3 2 Al3 3C All the electrophilic aromatic substitution conditions were acidic, so the nitrogen would become positive, and thus now a meta-director. 2 C3 Al3 _ Al3 + 2 You need to protect the 2, often by acylating it. 2 2S S 3S That said, when aniline is not protonated, it is a strong ortho-, paradirecting activator. In fact, it s so active that you can halogenate without the metal Lewis-acid catalyst. Br 2 Br2 2 Br Br Alkylation of amines by alkyl halides o Just S2 followed by deprotonation.

5 Br + o The problem with this reaction is that it s difficult to control how many alkyl groups add. This works if you want a 4 ammonium salt. This also works if you add excess ammonia, so that you get one addition. Acylation of amines by acid chlorides o This is a nucleophilic substitution at the carbonyl o The acid chloride is more reactive than ketones and aldehydes, and amines are not nucleophilic enough to add to the amide formed in the substitution. o Acylating aniline is a way to maintain the ortho-, para-directingness of the 2 and the acyl group is easily removed by acid hydrolysis S Formation of sulfonamides o Just like Acylation, but with sulfonyl chlorides Is it me, or did all the colors make this one exciting? S S

6 ofmann Elimination o An E2-like reaction where 4 nitrogen is the leaving group, and you get the lesssubstituted alkene. First, excess of an alkyl halide (usually C3X) is added to give quaternary ammonium salt. excess C3I 2 + Then, a strong base abstracts a proton to give a carbanion intermediate. _ This carbanion intermediate explains why you get the anti-zaitsev product with offman elimination. Elimination occurs to expel the amine, giving an alkene product. _ + o Sometimes Ag2 (aq) is the base used. It generates 2-, to a small extent. This is the conjugate base of hydroxide. Yikes! But remember that because it s aqueous, it just deprotonates the water, forming hydroxide. You cannot have a base stronger than hydroxide in an aqueous environment. o For those of you going on to take inorganic, you ll see that this is called solvent leveling. Diazonium salts o Formation Reaction of 2 (nitrous acid) with 1 alkyl amines ften formed in situ with a2 with

7 2 + + Reaction of 2 with aryl amines 2 + The last step of the 2 gas falling off doesn t happen because the aryl cation would be unstable. o Reactions of aryl diazonium salts You don t need to know any mechanisms here.

8 F BF4 Cu CuBr Br + KI I C CuC 2 heat 3P2 or ethanol o ow we can do even more synthesis!

9 ? Step 1: C3 Al3 Step 2: 3 2S4 Step 3: 2 Sn/CL Step 4: Al3 Step 5:

10 Al3 Step 6: Step 7: 2 Step 8: ethanol 2 + Synthesis of amines by acylation-reduction o Just what it sounds like o Acylate o LiAl4 completely chops off the oxygen of an amide instead of reducing the carbonyl to an alcohol Gabriel synthesis always makes 1 amines o Phthalimide is deprotonated by a strong base

11 The pka is o The anion is a good nucleophile (but weak base) which performs an S2 on a suitable alkyl halide or tosylate. Br o ydrolysis gives you the amine 3 + Reduction of azides and nitriles o nce an azide has been used as a nucleophile in an S2 reaction, it can be reduced to the amine by either LiAl4 or catalytic hydrogenation. 3-3 LiAl4 itriles are also reduced to the amine by the same conditions. C 2 Pt Be sure not to lose a carbon here.

12 Reduction of nitro groups to 2 o LiAl4 o Catalytic hydrogenation o Fe, Zn, or Sn in acid Removing the oxygen from amides to form amines LiAl4 ofman rearrangement o 1 amide + bromine or chlorine in base amine where the whole carbonyl is gone. Br2 - o You are not responsible for the mechanism.

Amines. Amines are organic compounds containing a nitrogen functionality. primary secondary tertiary quaternary

Amines. Amines are organic compounds containing a nitrogen functionality. primary secondary tertiary quaternary Amines Amines are organic compounds containing a nitrogen functionality Depending upon the number of alkyl, or aryl, groups attached to nitrogen determines its classification, or order 2 primary secondary