Chem 350 Jasperse Ch. 10 Handouts 1 Summary of Alcohol Syntheses, Ch. 10 (and Review of Old Ones).

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1 Chem 350 Jasperse Ch. 10 andouts 1 Summary of Alcohol Syntheses, Ch. 10 (and eview of ld nes). 1 Na Potassium (K) analogous. Na Key way to convert alcohol to alkoxide, reactive as S N 2 nucleophile and E2 base. 2 Na 2. '-X ' Alkoxide formation-s N 2 route to ether The electrophile '-X must be S N 2 reactive, preferably 1º with a good leaving group 3 Mg Br MgBr -Li is analogous for making Li, which also act analogously. -MgBr is spectator: is key.? 4 'MgBr formaldehyde ' 2º alcohol 'MgBr 2 C carbon chain extension ' 1º alcohol 5 aldehyde 'MgBr ' 2º alcohol 'MgBr C ' 2º alcohol 6 " ketone 'MgBr " ' 3º alcohol 'MgBr (")C " All three groups can be different. ' 3º alcohol 7 ester (or carbonyl chloride) 'MgBr ' ' 3º alcohol 'MgBr C ' ' 3º alcohol At least 2 groups must be the same 8 'MgBr ethylene oxide ' 1º alcohol 'MgBr ' 1º alcohol 2-Carbon chain extension

2 Chem 350 Jasperse Ch. 10 andouts 2 9 aldehyde NaB 4 C 3 or LiAl º alcohol 10 " ketone NaB 4 C 3 or LiAl 4 " º alcohol 11 ester LiAl º alcohol NaB 4 will not react with esters eview outes to Alcohols 10 2, + Markovnikov 11 g(ac) 2, 2 2. NaB 4 Markovnikov 12 B 3 -TF , Na anti-markovnikov 13 X Na S N 2 mech, needs 1º or 2º system and an excellent leaving group

3 Summary of anisms, Ch. 10 For Test: Br ' + Mg 2. 3 aldehyde or ketone or formaldehyde + Br + Mg + Br + Mg ' may be (MgBr) or (NaB 4 or LiAl 4 ) Chem 350 Jasperse Ch. 10 andouts 3 2+ Not for Test mech: ' ' 3 ' 2. ' Cl esters or acid chlorides ' may be (MgBr) or (LiAl 4 ) mech: ' ' mech: 3

4 Chem 350 Jasperse Ch. 10 andouts ,2 Intro, Classification Alcohol : attached to a saturated, sp 3, alkyl carbon 1º, 2º, 3º Alcohols: based on whether the carbon with the is 1º, 2º, or 3º 3º 2º 1º enol : attached to an aromatic -Note: phenol, not phenyl phenol 4-phenyl-1-butene phenyl, as substituent Enol or vinyl alcohol : attached to an alkene enol or vinyl alcohol Problem: Classify each of the following either as a phenol, as a carboxylic acid, or as a 1º, 2º, 3º, or vinyl alcohol: phenol vinyl alcohol 2º alcohol 3º alcohol 1º alcohol carboxylic acid 10.3 Nomenclature A. IUPAC, when alcohol is priority functional group and is part of the core name: x-alkanol Choose longest carbon chain that has the attached emember to number! The oxygen itself does not count as a number Cl Cl 4,4-dichloro-2-propyl-1-pentanol 4-ethyl-3-heptanol B. Cycloalkanols: The -carbon is automatically Number 1 cis-2-allylcyclohexanol

5 Chem 350 Jasperse Ch. 10 andouts 5 C. x-alken-z-ol. When an alkene is in the main carbon chain, you need two number descriptors, one for the alkene, the second for the alcohol. The still dictates the numbering The number gets moved right before the ol The alkene number goes in front, in front of the alken portion Note: you only put the number right in front of the ol when you have an alkenol (or alkynol) D. Diols: x,y-alkanediol (E)-4-hexen-2-ol or trans-4-hexen-2-ol 1,4-pentanediol E. Functional Group Priority: C 2 > C= > > amine > alkene > halide When you have more than one functional group, the higher priority dictates the numbering The higher priority is used in the core name The lower priority group may be forced to be named as a substituent F. as a Substituent: ydroxy 3-hydroxycyclohexanone G. Common Names: Alkyl alcohol C 3 Methyl alcohol Isopropyl alcohol t-butyl alcohol. Substituted enols IUPAC: use numbers, with carbon #1 Common: o rtho: 2-position, adjacent o Meta: 3-position, two carbons away o Para: 4 position Skill: be able to use or recognize either system Br IUPAC: 2-bromophenol 3-vinylphenol 4-isopropylphenol Common ortho-bromophenol or meta-vinylphenol or para-isopropylphenol o-bromophenol m-vinylphenol or p-isopropylphenol

6 Chem 350 Jasperse Ch. 10 andouts ysical Properties: Dominated by -Bonding BP: Match the boiling point for the following structures: 35º, 137º, 187º 35º (no -bond) 137º (-bond) 187º (more -bond) Water solubility: water solubility decreases as hydrophobic gets longer In general, o 4 carbons, substantially water soluble o 5 carbons, minimal water solubility infinite infinite 9.1g/100mL 2.7g/100mL 0.6g/100mL 0.1g/100mL 10.5 Commercially Important Alcohols Toxic: All alcohols are toxic if swallowed in sufficient quantities C 3 Cheap Solvent Fuel 100 ml death 15 ml blindness 200 ml (7 oz) death Least toxic alcohol Alcoholic beverages Fermentation Solvent ubbing alcohol 100 ml death Kills germs on skin, but not absorbed 10.6 Acidity of Alcohols and enols A. Alcohols are weak acids can be ionized by stronger bases + B + B goes to the right (alkoxide) only if is more stable than B ex. N 2, C 3 ex. If a less stable oxygen anion can convert to a more stable oxygen anion

7 Chem 350 Jasperse Ch. 10 andouts 7 B. Acidity Table Class Structure Ka Acid Strength Anion Base Strength Strong Acids -Cl 10 2 Most Cl Least Carboxylic Acid 10-5 enol Water Alcohol Amine (N-) N N Alkane (C-) C Least C 2 Most Notes/skills: Be able to rank acidity. 2. Memorize/understand neutral acidity ranking: C 2 > 2 > eason: resonance stabilization of the anion 3. Predict deprotonation (acid/base) reactions Any weak acid will be deprotonated by a stronger base (lower on table) Any weak acid will not be deprotonated by a weaker base (higher on table) 4. Predict ether/water extraction problems If an organic chemical is neutral and stays neutral, it will stay in ether layer If an organic chemical is ionized (by an acid-base reaction), it will extract into the aqueous layer Problems Draw arrow to show whether equilibrium favors products or reactants. (Why?) esonance Stability 2. Which of the following will deprotonate methanol? 2 C 3 C 2 Na Na Na NaN 2 C 3 MgBr No No No No Yes Yes An acid (left side) will only be deprotonated by an anion/base that is lower on the right side

8 Chem 350 Jasperse Ch. 10 andouts 8 3. When the following are dissolved in ether and then treated with Na/water, which would extract out of the ether layer into the water layer? Yes, converts to anion, water soluble Yes, converts to anion, water soluble + 2 No, stays neutral, stays in ether 10.6B Formation of Sodium, Potassium Alkoxides; 2-Step Conversion of Alcohols into Ethers via the Alkoxides 1 Na K Na K Potassium (K) analogous. Key way to convert alcohol to alkoxide, reactive as S N 2 nucleophile and E2 base. 2 Na 2. '-X ' Alkoxide formation-s N 2 route to ether The electrophile '-X must be S N 2 reactive, preferably 1º with a good leaving group eaction 1: Key source of nucleophilic/basic alkoxides Na 2. C 3 Br C 3 via B 3 -TF 3. Na C 2 C 3 2. Na, C 3 C 2 Br 10.7 Synthesis of Alcohols: eview: See p. 2, from Alkyl alides (S N 2) and Alkenes

9 Chem 350 Jasperse Ch. 10 andouts rganometallics: M (M = Metal) = M 3 Br Br Mg 2Li MgBr "Grignard eagent" Li + LiBr -Li is analogous for making Li, which also act analogously. -MgBr is spectator: is key. We will focus on the magnesium reagents MgBr 2. MgBr = Grignard eagents (Victor Grignard) 3. Key: This is the way to make, strong nucleophiles/bases 4. MgBr are formed via redox reaction. Mg gives up two electrons, is oxidized Bromine is reduced to bromide anion Carbon is reduced to carbanion Br + Mg + Br + Mg + Br + Mg 2+ Not for Test 5. The formation of Grignard eagents is completely general for all -alides: 3º, 2º, and 1º alkyl halides all work well Aryl and Vinyl halides as well as alkyl halides work well Cl, Br, and I all work well For class, we will normally use bromides, due to synthetic accessibility 6. View as carbanions: MgBr = Super Strong Bases and Nucleophiles The counterion metal is a spectator Stability-reactivity principle: very unstable very reactive This great reactivity is very useful (as nucleophile) This great reactivity (as base) has implication for proper technical use (see following) 7. Solvent and handling: Grignard reactants MgBr must be made, stored, and handled in special solvents under special conditions: No water allowed o Destroys carbanion No alcohol or amines or acids allowed either, or carbanion will just deprotonate them too If any chemicals with carbonyls are present, they too will react with the carbanion by nucleophile/electrophile reaction + o Grignards and other organometallics are made in either alkane or ether solvents. o These don t have any acidic hydrogens that protonate carbanions. o These don t have any carbonyls that react with carbanions 8. Two perspectives for dealing with organometallics in general and MgBr in particular anistic Thinking: Predict-the-product thinking: -MgBr: easier to see source and substitution product. Mg Br MgBr Electrophile Electrophile

10 Chem 350 Jasperse Ch. 10 andouts Addition of MgBr to Carbonyl Compounds: Alcohols are Produced ' ' Exothermic Addition of Carbon or ydrogen Anions: σ bond (made) stronger than π bond (broken) oxygen anion more stable than carbanion Carbonyl is strongly electrophile -much stronger even than a 1º alkyl iodide! Breakable π bond 2. Carbonyl polarity!"!+ Additions of Grignard eagents to Carbonyl Compounds From Carbonyl s Perspective From Grignard s Perspective 'MgBr 2 C 1 carbon 4 'MgBr ' chain º alcohol extension formaldehyde ' 2º alcohol 5 aldehyde 'MgBr ' 2º alcohol 'MgBr C ' 2º alcohol 6 " ketone 'MgBr " ' 3º alcohol 'MgBr (")C " All three groups can be different. ' 3º alcohol 7 ester (or carbonyl chloride) 'MgBr ' ' 3º alcohol 'MgBr C ' ' 3º alcohol At least 2 groups must be the same Pattern: After reaction, the original carbonyl carbon will have one and only one C- single bond 2. For formaldehyde, aldehydes, and ketones, one group adds (reactions 4-6) 3. For esters or carbonyl chlorides ( acid chlorides ), two groups add o eplace not only the carbonyl p-bond, but also the extra C- or C-Cl single bond 4. Product output: o Formaldehyde (2 s) 1º alcohol o Aldehyde (1 ) 2º alcohol o Ketone (0 ) 3º alcohol. No need for all 3 attachments to be the same. o Ester (0 ) 3º alcohol. At least two common attachments at end.

11 Chem 350 Jasperse Ch. 10 andouts 11 Predicting Grignard eaction Products From carbonyl perspective: The carbanion adds to the carbonyl carbon The carbonyl = gets replaced by For formaldehyde, aldehydes, and ketones: the two attachments on the original carbonyl carbon remain attached as spectators For esters or acid chlorides: the one non-heteroatom attachment on the original carbonyl carbon remain attached as spectators. o The extra heteroatom gets replaced by a second carbanion 2. From Grignard perspective: Where -MgBr begins, -C- ends. o In other words, the MgBr gets replaced by the carbonyl carbon Note: Be sure that in the product, no carbon has more than one C- bond Draw products from the following reactions. 1 MgBr º, 2º or 3º? MgBr 3 MgBr C excess C 3 MgBr Br Mg 2. C C 3 C 3 6 Br Mg 2. 2 C=

12 10.9E Grignard eaction with Ethylene xide (Simplest Epoxide) 8 'MgBr ethylene oxide ' 1º alcohol 'MgBr Chem 350 Jasperse Ch. 10 andouts ' 1º alcohol 2-Carbon chain extension Notes esults in a 1º Alcohol 2. Predicting product: Two carbons end up in between the carbanion and the 3. Ethylene oxide and formaldehyde are complementary Grignard acceptors leading to 1º alcohols o Ethylene oxide extends the carbon chain by two (relative to the original MgBr) o Formaldehyde extends the carbon chain by one (relative to the original MgBr) 4. 2-Carbon ethylene oxide and 2-carbon ethanal give different products o Ethylene oxide the is 1º and the is two carbons removed from the carbanion o Ethanal the is 2º and the and carbanion are both connected to the same carbon Draw products from the following reactions C= Br Mg MgBr

13 eaction anisms for Grignard eactions Chem 350 Jasperse Ch. 10 andouts 13 Formaldehyde, Aldehyde, or Ketone as Carbonyl Compound (eactions 4, 5, and 6) aldehyde or ketone or formaldehyde " ' 2. 3 " ' mech: " ' " ' 3 " ' Two simple steps: a. Addition b. Protonation 2. Timing: a. The carbanion is added first, at one step in time, under strongly anionic conditions b. Later acid is added, in a second laboratory step. This provides a cationic environment 3. MgBr = -MgBr = carbanion a. The MgBr stuff is spectator, doesn t need to be drawn in b. Ignore in mechanisms c. In reality, it actually does play a nontrivial role, but we ll save that for grad school! Draw mechanisms for the following reactions: 1 MgBr MgBr

14 Chem 350 Jasperse Ch. 10 andouts 14 Esters or Acid Chlorides: More Complex, Needs to Explain Two Additions and More Bond Breakings ' " 2. 3 esters or acid chlorides ' ' mech: ' fast + " " " ' Addition ' Elimination SLW fast ' Addition Cl acid chlorides ' ' 3 Protonation ' ' Four Step anism: a. Addition b. Elimination c. Addition d. Protonation 2. Timing: a. The carbanion is added first, at one point in time, under strongly anionic conditions o The first three steps all occur under these anionic conditions b. Acid is only added much later, in a second laboratory step. This gives a cationic environment. c. Why don t you just protonate after the first step? o There is no proton source available, and the elimination proceeds instead! 3. What if I add only one MgBr? 1 C 3 1 MgBr No or C 3 C 3 3º S.M. After Grignard reaction, never show any products in which a carbon has more than one oxygen Why? Kinetics and eactivity. MEMIE. elative eactivity: 2 or Acid/Base > > > Aldehyde Ketone Ester Steric Advantage. Transition-state less crowded and more stable Stablized for electronic reasons Therefore less reactive Large differences in reactivity, with ketone > ester Elimination step 2 is also very fast Thus, under the anionic conditions, the addition is the slow step o After it does happen, elimination and another addition happens bang-bang.

15 Draw anism: Chem 350 Jasperse Ch. 10 andouts 15 C 3 MgBr (excess) C 3 C Cyclic Ester: The -Carbonyl single bond breaks, but the other C- single bond does not break -the result is formation of a dialcohol Draw product and mechanism for the following: MgBr (excess) Two protonations 3 Ethylene xide anism 2. 3 mech: Addition S N 2 3 Protonation Draw product and mechanism for the following: MgBr

16 Chem 350 Jasperse Ch. 10 andouts 16 More Grignard Practice. Including polyfunctional Molecules: (Know relative reactivity) 1 3 C MgBr (excess) C MgBr (0 equivalent) C 3 3C MgBr (0 equivalent) C Starting material! via 3 C MgBr 5 BrMg Br Mg 2. 2 C= C 3 MgBr (excess) BrMg 2. 3

17 Chem 350 Jasperse Ch. 10 andouts 17 Grignards in Synthesis: Provide Precursors. Think backwards from Targets to eactants. Identify possible Grignards and Grignard acceptors Pattern: 3º alcohol, all three attachments different Ketone Precursor 3º alcohol, two (or more) of the attachments identical Ester 2º alcohol Aldehyde 1º alcohol Formaldehyde or ethylene oxide MgBr + 3 C MgBr + a. + BrMg MgBr + C 3 MgBr + b. MgBr + MgBr + c. BrMg + MgBr + d. MgBr +

18 Chem 350 Jasperse Ch. 10 andouts 18 Provide eagents for the Following Transformations. You may use whatever reagents, including ketones or aldehydes or Grignards or esters, that you need. Key: Try to identify key C-C connection in the product that wasn t present to start with Try to identify the where the reactant carbons are in the final product Numbering your carbon chains is very helpful. Usually best to work backwards from the product a. Mg Br steps plus 3 + workup b. Br (no peroxides) 2. Mg 3. 2 C= steps plus 3 + workup c. Br, peroxides 2. Mg 3. C 2 C steps plus 3 + workup d. Br Mg 2. ethylene oxide Br Mg 2. e

19 Chem 350 Jasperse Ch. 10 andouts 19 Combining Grignard eactions with ther eactions MgBr a S 4, heat Mg b. Br S 4 5. B 3 -TF 6. Na estrictions on Grignard eactions MgBr = carbanion, highly unstable, highly reactive. Unstable in the presence of: s (get proton transfer reaction) 2. Carbonyls (get Grignard-type nucleophilic addition) Solvent limitations. MgBr cannot be formed and used in the presence of 2 Any solvent with a C= Which Solvents (if any) Would be K for andling MgBr?, 2. Substrate limitations. Any organohalide that also contains an or C= bond can t be converted into a useful MgBr, because it will self-destruct. Which substrates could be converted into MgBr, and subsequently reacted with C 3 C? Br Br Br Br Br 3. Atmosphere/Glassware/Storage limitations. Make, store, and use in: water-free dried glassware moisture-free atmosphere. (Dried air, or else under nitrogen or argon atmosphere) When stored for extended periods, must have very good seals so that no air can leak in.

20 10.11 Alcohols by eduction of Carbonyls: Addition Chem 350 Jasperse Ch. 10 andouts 20 9 aldehyde NaB 4 C 3 or LiAl º alcohol 10 " ketone NaB 4 C 3 or LiAl 4 " º alcohol 11 ester LiAl º alcohol NaB 4 will not react with esters anism Aldehydes and Ketones aldehyde or ketone or formaldehyde " NaB 4 C 3 or LiAl " NaB 4 = LiAl 4 = mech: " " 3 or " C 3 Esters " ester Addition SLW " fast Elimination + " Addition Fast 3 Cyclic Esters Addition Elimination Add 3 3 Double Protonation

21 Chem 350 Jasperse Ch. 10 andouts 21 Notes: anisms are exactly like with Grignard reactions LiAl 4 and NaB 4 function as hydride anions For mechanisms, just draw rather than trying to involve the Li and Al and Na and B NaB 4 = Na B B + LiAl 4 = Na Al Al + Boron is one row higher than aluminum, and in keeping with normal periodic patterns is more electronegative o Because boron is more electronegative, the B 4 anion is more stable, and less reactive. The boron holds the more tightly. o Aluminum being less electronegative doesn t attract and hold the as well, and thus is considerably more reactive. eactivity Aldehydes Ketones Esters LiAl 4 Yes Yes Yes NaB 4 Yes Yes No LiAl 4 is much stronger, NaB 4 much weaker LiAl 4 is strong enough to react with esters, NaB 4 isn t 2. Selective reduction: if both an ester and an aldehyde/ketone are present: LiAl 4 reduces both NaB 4 selectively reduces the aldehyde/ketone but leaves the ester untouched 3. LiAl 4 is strong enough to react with and be destroyed by water or alcohol; NaB 4 isn t LiAl (gas) + Li + Al 3 + heat a. As a result, LiAl 4 is harder to use and store b. Acid has to be added in a subsequent step with the LiAl 4 ; (thus, 2-step recipe) c. NaB 4 can be run in alcohol solvent which serves as a proton source for protonating alkoxide d. Solvent restrictions, glassware must be dry, wet air must be excluded, etc. e. Because NaB 4 is stable to water, it s easier to handle in air, easier to store, much easier to work with f. Default: for a simple aldehyde or ketone reduction, normally use NaB 4 because it s so much easier 4. LiAl 4 is strong enough to react with esters, NaB 4 isn t

22 Chem 350 Jasperse Ch. 10 andouts 22 Draw the products for the following reactions. LiAl 4 C NaB 4 2. C 3 2 C 3 3. LiAl LiAl or NaB C 3 LiAl 4 but not NaB C Draw the mechanism for the following reaction. NaB 4 C 3 6. C 3 LiAl