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Mar 28 2017 Chem 261 Notes

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Mar 28 2017 Chem 261 Notes CHEM 261 Mar 28, 2017 Upcoming Topics: 1. Alkyne Reactions 2. Radical Additions to Alkenes 3. Polymers 4. Alcohol & Sugars: Structure + Nomenclature Review :Base picks up a proton (H+) very fast, may be negatively charged :Nucleophile attaches other atoms (like carbon) Reactions of Terminal Alkynes – Alkylation Example 1 pka ~26 !"- H C C CH3 + Na OH !"+ weaker acid weaker base pka ~16 Na C C CH3 + H-OH stronger base stronger acid The stronger acid and stronger base are always on the same side. As such, the reaction is driven towards the opposite side. Example 2 pka ~26 + H C C CH3 Na NH2 stronger acid pka ~36 Na C C CH3 + H-NH2 sodium alkynide ammonia weaker acid How can this terminal anion be used to form useful compounds? Terminal alkynes/acetylenes can be deprotonated and then reacted with alkyl halides to form new carbon-carbon bonds. General Scheme KNH2 ' ' R C C H R C C K R H2C X R C C CH2R X = Br, I, Cl terminal acetylene NH3 H NH2 S 2 pKa ~ 26 pKa ~ 36 N Example 1 1. NaNH2 H C C H H3C C C H Na I !"+ 2. I - CH3 !"- S 2 Na NH2 N Na C C H Example 2 What reactions could be used to create this aldehyde? O !"+ !"- H C C H 1. R2BH NaNH2 + !" !"- 2. NaOH, H2O2 Br Na C C H C SN2 C H Example 3 What about this ketone? NaNH2 1) H C C H Na C C H !"+ I !"- 2) Na C C H H3C-H2C C C H SN2 H2SO4 3) H3C-H2C C C H H2O O step 3 mechanism: H H C-H C C C H H3C-H2C C C 3 2 H H HOH H3C-H2C H H3C-H2C H C C C C enol H O O H O H H H H Can you add everything together at once? No. The sodium amide will react with the alkyl halide and form a byproduct amine instead of the desired ketone. 1) NaNH2 NH2-CH2-CH3 + NaI H C C H 2) I remains unreacted 3) H2SO4/H2O Additional Example H C C H CH3CH2CH2CH2CH3 1 2 1 2 NaNH 2 HC C CH CH CH H C C Na I CH2CH2CH3 2 2 3 another way H2 / Pt NaNH2 CH3CH2CH2CH2CH3 H2 / Pd H3C I NaNH2 H3CH2C I HC C Na HC C CH H CH C C C CH 3 C C CH3 3 2 3 Radical Addition to Alkenes Recall the addition of a hydrogen halide: H3C !"+ !"- + H - Br - C CH3 Br !"+ !" H Br 2-bromopropane isopropyl bromide By adding peroxide and heat, the following can occur via a radical mechanism. HBr anti-Markovnikov R-O-O-R peroxides ! Br R O O R R O O R R O H Br R OH Br alcohol radical Br H Br Br Br Now, you can combine all the different types of reactions you have learned to create your desired compound from simple starting material. For example, using propane, several compounds can be created: Br2 E HBr hν R-O-O-R Br Br K+ O ! + - + - K OH SN2 SN2 K OH OH OH Polymers poly – many, meros – parts Natural Polymers: • Nucleic acids (DNA, RNA) • Proteins and peptides (amino acid polymers) • Polysaccharides (cellulose) • Fats, polyketides (polymers of acetic acid) Human-Made Polymers • Christian Schönbein, 1826 professor in Basel o Mopped up a spill of H2SO4 and HNO3 with an apron made of cotton (cellulose, a polymer of glucose), o He washed the apron and hung it up to dry . The apron exploded He had created gun cotton! How did this happen? In the presence of H2SO4 and HNO2, the free hydroxyl groups form a material that spontaneously combusts. O O N OH O O RO HNO RO O OR 3 HO OR H2SO4 O OH O O cellulose N gun cotton N O O O Another example: glycerol Under the same conditions, glycerol will form nitroglycerine O N O O OH O O N HNO3 HO OH H SO O O O 2 4 N O 2 to 5 % of nitroglycerine was combined with diatomaceous earth dynamite! Who did this reaction? Alfred Nobel, the founder of the Nobel Prize! • Wallace Carothers 1896-1937 DuPont o Nylon (polyamide) o Dacron (polyester) • Roy Plunkett 1938 DuPont o Teflon (created from tetraflyoroethylene, a toxic gas) Teflon: Polytetrafluoroethylene peroxide F F F F F F F F R-O-O-R (cat.) C C etc. C C C C etc. C C ! "! F F F F F F F F n tetrafluoroethylene toxic gas Teflon MW > 1 million Polymerization Mechanism of Teflon F F F F F F Initiation F F F F R O O R R O O R RO C C RO C C C C ! "! C C C C F F F F F F F F F F repeat to form long chains .
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