16.aldehydes and ketones. ( approx. lecture time: 3 lectures)

Most students find the next four (4) chapters (all dealing with chemistry of the carbonyl (C=O) group) to be the most challenging in CHEM 232.

Here you will learn many new reactions and you will need to have a system for learning how to recall them. SEE NEXT SLIDE…….

16. ALDEHYDES AND KETONES. (approx. lecture time: 3 lectures)Topics covered: 16.1-16.8A/B/C,16.9-16.10A,16.11.

How to Learn Organic Reactions(Organic reactions interconvert organic compounds. They are the

basis of organic chemistry and of living systems)

1. What happened?(Learn the reaction. Give the reaction a title or name. Use “reaction lists” and other techniques. Know your reactions “forwards” and “backwards” Recognize variations. This is hard work.

2. How did it happen?(Learn the mechanism, if required. You are not required to know all them)

3. Why did it happen?(Not always answerable. Wait for advanced courses…maybe)

Nomenclature of Aldehydes and Ketones

Nomenclature of Aldehydes and Ketones

Some well-known aldehydes

(vanilla flavour) (almonds) (cinnamon) (your hangover) (preservative)

Diacetyl

Sorry, it’s not real butter

(The 1,2-diketone that gives microwave popcorn its “butter” flavour)

CH3

O

CH3

O

CHANEL No 5

H

O

H

O

H

O

C10 aldehyde (decanal)

The key ingredients for the most expensive and famous perfume in the world are simple aldehydes!

H

O

Bourgeonal (used in fragrances)

This aromatic aldehyde used in fragrances and perfumes (Lily of the Valley scent) is known to attract human sperm, by causing them to swim twice as fast when they sense this molecule in vitro.

Coco Chanel (circa 1920)Created a fashion empire from humble beginnings

(A perfume for “older” people with deeper pockets)

Synthesis of Aldehydes and Ketones

Useful method: Ketones can be synthesized from a nitrile and a Grignard reagent

General Reaction of Aldehydes and Ketones Nucleophilic Addition to the Carbon of the C=O

Mechanism for Addition of STRONG Nucleophiles

WEAK nucleophiles such as water and alcohols (ROH) need acid catalysis as shown below:

Aldehydes are more reactive than ketones:

1. The aldehyde carbonyl carbon is less hindered for attack.

2. The extra R group in ketones stabilize the carbonyl carbon by electron donation.

Chloral hydrate is a stable aldehyde hydrate used historically as a sedative before minor medical. It is still used in veterinary medicine.

Hydration: Addition of Water

Addition of Alcohols: Formation of Acetals

(hydrates are generally unstable)

In general, hemiacetals are not isolated; acetals are isolable and are often made.

Mechanism for Formation of Acetals

hemiacetal

hemiacetal

acetalLongest mechanism

in this course

Acetals are often used in “functional group protection”

Glucose (a stable hemiacetal)

(acetals are stable in base) (acetals are unstable in acid; they regenerate the aldehyde or ketone)

The Sex Life of the Olive Fruit Fly(Bacrocera Oleae)

OO

oleane(sex phermone of the olive fruit fly)

O

O

O

O

this enantiomer attracts the males

this enantiomer attracts the females

Where is the

ketone hiding?

Ecstasy (The illicit Drug)(MDMA; 3,4-methylenedioxy-N-methylamphetamine)

Very stable acetal!

BC is well-known for being a major exporter of marijuana and Ecstasy.

O

O

NHCH3

CH3

TATP (“triacetone triperoxide”)

CH3 CH3

O H2O2

H+ CH3 CH3

OH

OOH

etc.

White crystalline powder with bleach odour

1. One of the most unstable of explosives2. Readily made from acetone (ADDITION of

hydrogen peroxide) 3. Commonly used by terrorists; difficult to detect4. Explosive used in the London subway bombings

(July 7, 2005)

acetone

Cyanohydrins(Cyanide as the nucleophile, giving cyanohydrins)

Think C=N !

Amines as Nucleophiles

C=N does not form here!(but you don’t need to know this one)

(Tertiary amines do not react with aldehydes and ketones)

H

O

NH2OH H

NOH

O NHNH2 N NH

O

NH2NH2

NaOH

(Wolf-Kishner reduction)

Methamphetamine (“crystal meth”) The utility of reduction in the synthesis methamphetamine

(selective reduction of benzylic C-OH)

(S)-(+)-methamphetamine

CH3NH

H CH3

NHCH3

HH3C

(R)-(-)-methamphetamine(cold medicine; used in Vicks Vapour Inhaler (USA only))

CH3NH

H CH3

H OH

ephedrine (cold medicine)

CH3NH

H CH3

HO H

pseudoephedrine(marketed cold medicine)

Possible Methods: Hydrogenolysis or Birch Reduction

Sudafed and Claritin contain ephedrine or pseudoephedrine

Ephedrine, isolated from Ephedra sinica, is an old medicine for colds and asthma.

Wittig ReactionThink C=C !

(A new way to make alkenes)

Synthesis of Wittig Reagents

"for their development of the use of boron and phosphorus reagents in organic synthesis"

Herbert C. BrownFor boron reagents

such as BH3

Georg WittigFor phosphorus reagents

such as Ph3P=CH2

The Nobel Prize in Chemistry 1979

O NaBH4

OH

Ph3P=CH2