Ethers, Thiothers, and Epoxides

Question 1

What are two ether complexes?

Answer 1

Grignard reagents- stabilizes reagent and keep it in solution

Electrophiles- ether’s nonbonding electrons stabilize boran BH3

Question 2

Crown ethers can complex __ in the center of the ring? What determines which cation it can solvate better? Complexation if crown ethers often allows what? What are the three crown ethers and what do they solvate?

Answer 2

Metal cations, size of the ether ring, allows polar inorganic salts to dissolve in nonpolar organic solvents

12- crown-4 solvates Li+
15-crown-5 solvates Na+
18-crown-6 solvates K+

Question 3

Epoxides (oxiranes) are \_\_ membered 
Oxetones are \_\_ membered 
Furans/ oxolanes are \_\_ membered
Pyrans/ oxanes are \_\_ membered 
Dioxanes are \_\_ membered rings with two \_\_

Answer 3

3
4
5
6
6 with 2 oxygens

Question 4

What are the three ways to synthesize ethers?

Answer 4

1. Williamson Ether
2. Alkoxymercuration- Mercuration
3. Bimolecular Condensation

Question 5

What does williamson ether entail?

Answer 5

Alkoxide + alkyl halide or tosylate forms ether
Sn2
Alkyl halide must be primary
Use Na or NaH to form alkoxide

Question 6

What is the silver oxide variant?

Answer 6

Alcohol plus primary halide or tosylate with Ag2O forms ether

Question 7

What does oxymercuration entail?

Answer 7

Alkene treated with 1. Hg(OAc)2 R-OH/ 2. NaBH4
Markovnikov product
Alkoxy product goes to more sub carbon

Question 8

What does bimolecular condensation of alcohols entail?

Answer 8

Makes sym ethers from primary alcohols
Temp cant be too high (140 degrees C)
Unhindered primary group attached to alcohol
Use H2SO4 as reagent

Question 9

What are the two ways to cleave ethers?

Answer 9

1. Excess acid (HBr or HI)

2. Autoxidation

Question 10

What does cleavage of ethers with excess acid entail?

Answer 10

Ethers react with HBr and HI and heat to form akyl bromides or alkyl iodides

Will usually react twice except for phenols bc an Sn2 cannot occur on Sp2 carbon

React via Sn2

Question 11

What happens in autoxidation?

Answer 11

In the presence of atmospheric oxygen, ethers slowly oxidize to produce hydroperoxides and dialkyl peroxides, both of which are explosive

Question 12

Allylic, Benzylic, and tertiary ether cleave via which mechanisms?

Answer 12

E1 (carbocation and alkene formed) and Sn1 (carbocation and attack by Nu)

Question 13

TFA cleaves ethers via what mechanism?

Answer 13

E1

Question 14

In Claisen rearrangement, allylic aromatic ethers rearrange to give what?

Answer 14

Allylic phenols

Question 15

What are thioethers?

Answer 15

Ethers where the O is replaced by S

Question 16

How do you synthesize thioethers? How do you generate thiolate ion?

Answer 16

Williamson ether synthesis, where thiolate ion is nucleophile

By treating thiol R-SH with NaOH

Question 17

Thiolates are such effective nu that they will even give good yields with what?

Answer 17

Secondary alkyl halides via Sn2

Question 18

Sulfides are easily oxidized (using H2O2/CH3COOH) to what? Sulfides react with unhindered alkyl halides to give what?

Answer 18

Sulfozides and sulfones

Sulfonium salts

Question 19

Because thioethers are easily oxidized, they are often used as….

Answer 19

Mild reducing agents

Question 20

Silyl ethers are more easilu formed and hydrolyzed, making them good what?

Answer 20

Protecting groups for alcohols

Question 21

What is the protecting agent? How do you unprotect?

Answer 21

TIPS

Bu4N+ F-/ H2O

Question 22

Why are sulfonium salts used as alkylating agents?

Answer 22

Because the leaving group that forms is neutral

Question 23

What are the two ways to synthesize epoxides?

Answer 23

1. MCPBA/CH2Cl or MMPP/H2O CH3CN (Peroxyacids)

2. Base promoted cyclicization of halohydrins

Question 24

What does the synthesis of epoxides using peroxyacid entail?

Answer 24

Converts alkenes to epoxides
Stereochem maintained
One step concerted reaction

Question 25

What does the cyclicization of halohydrins entail?

Answer 25

Internal Sn2 attack
Alkoxide displaces halide ion to form ring
Variation if will either syn

Question 26

What are the 2 ways to cleave epoxides?

Answer 26

1. Acid catalyzed:
   a. in water
   b. in alcohols,
   c. using hydrohalic acids
2. Base Catalyzed
   a. With alkoxides or hydroxide
   b. With organometallics

Question 27

What does the acid catalyzed cleavage of epoxides entail?

Answer 27

In water: (H+/ H2O) forms a diol with anti stereochem

In alcohol: (H+/ R-OH) alcohol acts as nu, forms alkoxy alcohol with anti stereochem. Alkoxy bonds to more sub carbon

Using Hydrohalic Acids: (H-X) halide ion attacks protonated epoxide, forms 1,2 trans dihalide

Question 28

What does the base- catalyzed cleavage of epoxides entail?

Answer 28

With just hydroxide ion: (-OH) 1,2 diol with trans stereochem

With alkoxides or hydroxide: (R-O-/ R-OH) trans product, alkoxy group bonds to less sub carbon

With Organometallics: (1. R-Li or MgBr/ 2. H3O+) R bonds to less sub carbon, and OH group bonds to more sub carbon

Question 29

Ether can be either __ or __? The oxygen on ethers has what hybridization? The tetra C-O-C bond angle is what? Are the C-O bonds polar or nonpolar? What acceptor? Bp smililar to what and lower than what? Good solvents for what? Will solvate small __ but not small __? Unreactive to __ but reactive to __?

Answer 29

Sym or unsym, Sp3, 110 degrees, polar, hydrogen bond acceptor, bp similar to alkanes and lower than alcohols, good solvents for polar and nonpolar species, small cations but not small anions, unreactive to bases but reactive to strong acids