Alcohols

Question 1

Alcohols can be synthesized from:

Answer 1

• alkenes
• carbonyl cmpds
• carboxylic acids & esters

Question 2

Hydration of alkenes by aqueous acid -

Answer 2

brute force hydration, Markovnikov addition

Cons:
Highly acidic conditions (50% H₂SO₄, 50% HOH)
High temperatures

Reaction is not ideal for research or undergraduate laboratory environments, BUT Ideal for industrial settings

Question 3

oxymercuration, 2 steps conditions

Answer 3

Markovnikov’s alcohol (OH to the most substituted)

1. Hg(OAc)₂, H₂O, THF
2. NaBH₄, NaOH (aq)

Question 4

hydroboration, 2 steps conditions

Answer 4

non-Markovnikov’s alcohol (OH to the least substituted)

1. BH₃, THF
2. H₂O₂, HO^-

Syn-addition (-H and -OH are added on the same side of the ring)

Question 5

1,2-Diol synthesis => cis product:

Answer 5

1. OsO₄ in pyridine
2. treat cyclic reaction intermediate w/ NaHSO₃ aq

Question 6

1,2-Diol synthesis => trans product:

Answer 6

1. formation of epoxide (cyclic ether) by treatment w/ RCO₃H in CH₂Cl₂
2. acid-catalyzed opening of the epoxide w/ H₃O⁺

Question 7

Aldehydes reduced to

Answer 7

primary alcohols (terminal position of carbonyl grp)

Question 8

Ketones reduced to

Answer 8

secondary alcohols (internal position of carbonyl grp)

Question 9

The easiest reduction agent to reduce aldehydes & ketones -

Answer 9

sodium borohydrate, NaBH₄
safe & easy to handle => high yeilds of product

Question 10

Another reducing agent:

Answer 10

lithium aluminium hydride, LiAlH₄, or LAH

very reactive, violent reactions w/ water, explosive if heated above 120 C

1. treatment of the carbonyl cmpd w/ LAH in dry ether
2. acidification => alcohol

Question 11

Reduction from carboxylic acids & esters:

Answer 11

produce primary alcohols, but very resistant to reduction => NaBH₄ reduces esters very slowly and COOHs not at all, LAH is used for these cmpds.

1. treatment w/ LAH in dry ether
2. acidification (H⁺, H₂O) => alcohol
   ! 2 Hs need to be delivered

Question 12

Grignard reagents:

Answer 12

organometallic cmpds that involve conversion of an alkyl/aryl/vinilic halide into a Mg-containing carbon-based nucleophile, RMgX:

R-X + Mg (powder in ether) => R-MgX

C atom immediately connected to Mg - delta neg => can attack delta positive carbonyl atom (C=O) to make C-C bond => lengthening of carbon skeleton

Question 13

Grignard reagents can’t be used w/:

Answer 13

HOH, -OH, -NH, -SH, -COOH, b/c it wil be destroyed

Question 14

If a carbonyl group is on another part of the Grignard reagent,

Answer 14

Grignard part can react w/ it => cyclic cmpd

Question 15

Do LAH and NaBH₄ reduce alkene dbl bonds or benzene rings?

Answer 15

Both of them - NO => can be used for/ selective reduction

Question 16

Reactions of alcohols:

Answer 16

1. dehydration of alcohols => alkenes
2. alcohols => esters
3. oxidation of alcohols

Question 17

dehydration of alcohols => alkenes

Answer 17

alcohol => alkene + H₂O + H⁺

Zaitsev’s rule: In the elimination of HOH from an alcohol, the more highly substituted alkene dominates the mixture

Question 18

acid-catalysed dehydration works only for -

Answer 18

tertiary alcohols

Question 19

what to use f/ dehydration of secondary & primary alcohols?

Answer 19

POCl₃ - phosphorous oxychloride in pyridine

Question 20

alcohols => esters

Answer 20

alcohol + COOH => ester

• often COOH can be made more reactive by firstly converting it into acid chloride with SOCl₂, thionyl chloride

Question 21

oxidation of alcohols

Answer 21

opposite to reduction of carbonyl cmpds

• primary alcohols => aldehydes => if continued oxidation - COOH
• secondary alcohols => ketones
• tertiary alcohols: inert to oxidation, except f/ harsh conditions

Question 22

oxidizing agents f/ alcohols:

Answer 22

strong, lead to COOH:
KMnO₄, CrO₃, Na₂Cr₂O₇

mild, lead to aldehyde or used w/ sensitive alcohols, in which other functional grps can get oxidized:
PCC (pyridinium chlorochromate), C₅H₆NCrO₃Cl

Question 23

Solubility of Alcohols

Answer 23

Lower alcohols up to pentanol are highly soluble in water due to hydrogen bonding between water and the alcohol. Past pentanol, the hydrophobic (alkane) portion of the molecule takes over