Reactions of Aldehyde and Ketone Chem 162 class work for Tue, May 24th'

1
Reactions of Aldehyde and KetoneChem 162 class
work for Tue, May 24th.

• Fill in the blanks found in pages 50, 51 and 52
  of the lecture packet by going though these
  slides.
• Answer the questions posed in the last two slides
  of this program on a sheet of paper. Turn it in
  class at 100 pm Wednesday May 25th as a
  take-home assignment.
• The model lab assigned for this week will help
  you visualize and predict products of acetal
  formation and other related reactions.

2
Addition Reactions Aldehydes and Ketones

• Addition reactions of CO is related to the
  reactions of an alkene in that
• Pi bond is broken between two atoms
• A new bond is made to add a group to each of
  these two atoms.

• It is different from the alkene addition
  reactions
• in that
• CC bond is nonpolar CO bond is polar
• NaBH4 prefers CO H2 prefers CC
• Pi bond in CC bond is easy to break
• Pi bond in CO requires heat / pressure /
• catalyst to break.

3
Addition of H2O carbonyl group versus alkene
group

• Addition of H2O to CC
• According to Markonikovs rule
• H attaches to the one with more H to begin with

• Addition of H2O to CO
• According to polarity ? CO ?-
• ? group attaches to ?- end
• H attaches to the O in CO

R OH
\
CO HOH
R - C - OH /

R
R
4
Addition of Alcohols toaldehydes and ketones

• Addition of ROH to CO ?
• Hemiacetal / hemiketal formation

R OR
\
CO
ROH R - C OH /
R
R

?
?-
5
Addition of alcohols toaldehydes and ketones

• Addition of ROH
• Hemiacetal / hemiketal formation

R OR
\
CO
ROH R - C OH /
R
R

?-
?
6
addition of alcohols toaldehydes and ketones

• Addition of ROH to an aldehyde ?Hemiacetal

?
?-
R OR
\
CO
ROH R - C OH /
H
H

?-
?
hemiacetal C has - R, - OR, - H, - OH
7
Addition of alcohols toaldehydes and ketones

• Addition of ROH to a ketone ? hemiketal

?
?-
R OR
\
CO
ROH R - C OH /
R
R

?-
?
hemiketal C has - R, - OR, - R, - OH
8
addition of alcohols toaldehydes and ketones

• Addition of excess ROH to hemiketal ? ketal

OR OR
R - C OH ROH R - C
OR HOH R
R
H
ketal C has - R, - OR, - R, -OR
9
addition of alcohols toaldehydes and ketones

• Addition of excess ROH to hemiacetal ? acetal

OR OR
R - C OH ROH R - C
OR HOH H
H
H
acetal C has - R, - OR, - H, -OR
10
Can this compound make a stable cyclic Hemiacetal?

• CH2?CH2? CH2?CH2? C ?CH3
• ?
• OH O

5CH2?4CH2? 3CH2?2CH2? 1C ?CH3 ?
6OH O
CH3 / 1C - OH
2
6-member ring is stable A cyclic hemiketal exists.
6
3
O
5
4
11
Can this compound make a stable cyclic Hemiacetal?

• CH2?CH2?C ?CH3
• ?
• OH O

3CH2?2CH2?1C ?CH3 ? 4OH
O
4-member ring is not stable No cyclic hemiketal
will be formed.
12
Can this compound make a stable cyclic Hemiacetal?

• CH2?CH2? CH2? C ?CH3
• ?
• OH O

4CH2? 3CH2?2CH2? 1C ?CH3 ? 5OH
O
CH3 / 1C - OH
5-member ring is stable A cyclic hemiketal exists.
2
O
5
3
4
13
What class is this?

• Indicate if this is a
• hemiacetal,
• (b) acetal,
• (c) hemiketal,
• (d) ketal, or
• (e) none of these.

hemiacetal C has - H, - OH, - R, -OR
acetal C has - H, - OR, - R, -OR
hemiketal C has - R, - OH, - R, -OR
ketal C has - R, - OR, - R, -OR
14
What class is this?

• Indicate if this is a
• hemiacetal,
• (b) acetal,
• (c) hemiketal,
• (d) ketal, or
• (e) none of these.

hemiacetal C has - H, - OH, - R, -OR
acetal C has - H, - OR, - R, -OR
hemiketal C has - R, - OH, - R, -OR
ketal C has - R, - OR, - R, -OR
15
What class is this?

• Indicate if this is a
• hemiacetal,
• (b) acetal,
• (c) hemiketal,
• (d) ketal, or
• (e) none of these.

hemiacetal C has - H, - OH, - R, -OR
acetal C has - H, - OR, - R, -OR
hemiketal C has - R, - OH, - R, -OR
ketal C has - R, - OR, - R, -OR
16
Predict products in the following
17
Hydrolysis of Acetal

• Addition of H2O to break up Acetal.

R OR
OR \


CO ROH R - C - OH
R - C - OR /

R
R R

• The above reactions occurs in the reverse with
  lots of H2O / H
• Hemiacetal H2O ? 1 aldehyde 1 alcohol.
• Acetal H2O ? 1 aldehyde 2 alcohols.
• hemiketal and ketals do the same thing!
• These belong to the type of reaction called
  hydrolysis
• Hydro water lysis split
• add water to split the molecule

18
acetal ? hemiacetal

• Apply Le Chatelier's principle to the reversible
  reaction in equilibrium shown above
• We can make more acetal by
• using a large excess of ethanol or
• removing water from the equilibrium mixture
• We can make more hemiacetal by
• using a large excess of water

19
Draw the most stable cyclic hemiacetal structure
of this compound. Explain why the structure is
stable.

• CH2?CH?CH?CH?CH?CO
• ? ? ? ? ?
• OH OH OH OH OH H

20
What class is this?

• Indicate if this is a
• hemiacetal,
• (b) acetal,
• (c) hemiketal,
• (d) ketal, or
• (e) none of these.
• Explain how you decided.

hemiacetal C has - H, - OH, - R, -OR
acetal C has - H, - OR, - R, -OR
hemiketal C has - R, - OH, - R, -OR
ketal C has - R, - OR, - R, -OR