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: A/B/C, A,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? This is hard work. (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
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)
CHANEL N o 5 The key ingredients for the most expensive and famous perfume in the world are simple aldehydes! 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 acetal
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 The Sex Life of the Olive Fruit Fly (Bacrocera Oleae) Where is the ketone hiding?
Ecstasy 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.
TATP (“triacetone triperoxide”) White crystalline powder with bleach odour 1.One of the most unstable of explosives 2.Readily made from acetone (ADDITION of hydrogen peroxide) 3.Commonly used by terrorists; difficult to detect 4.Explosive used in the London subway bombings (July 7, 2005) acetone
Cyanohydrins (Cyanide as the nucleophile, giving cyanohydrins)
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)
Methamphetamine (“crystal meth”) Methamphetamine (“crystal meth”) The utility of reduction in the synthesis methamphetamine 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 Reaction (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. Brown For boron reagents such as BH 3 Georg Wittig For phosphorus reagents such as Ph 3 P=CH 2 The Nobel Prize in Chemistry 1979