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Chapter 16 - All about ALDEHYDES and KETONES
Terms in this set (20)
How many different ways can you prepare aldehydes?
Starting with an alkene how can you make an aldehyde?
You can do Ozonolysis
-Reagents: 1. O3, 2. DMS (A.K.A. Me2S)
-To make the aldehyde the alkene on either side most be non-substituted or have one substituent.
Starting with a primary alcohol how can you make an aldehyde?
You use a reagent called PCC (pyridium chlorochromate)
Starting with an acyl chloride or acid chloride how can you make an aldehyde?
You use the reagent Li(T-ButO)3 AlH (lithium tri-tertiary butoxy aluminum hydride)
Starting with an ester how do you make an aldehyde?
You can use the reagent 1. DIBAL, toluene, -78ºC, 2. H2O.
-At higher temperature the reaction will lead to over-reduction.
Starting with a R-CN how do you make an aldehyde?
-This is called "Aldehyde by reduction of nitriles with DIBAL followed by hydrolysis"
-Reagent: 1. DIBAL, toluene, 2. H2O.
-The intermediate is an aluminum imine
How many different ways can you make ketones?
If you have a have an appropriately substituted alkene what reagent can you use to make ketones?
-Reaction is known as Ozonolysis
If you have a secondary alcohol what reagent can you use to make a ketone?
-Jones Reagent (CrO3, H2SO4)
How can you make an aromatic ketone?
-You do Friedel Craft Acylation
-For Friedel Craft acylation you starting with an aromatic compound and use an acyl group with cat. AlCl3.
How can you make a ketone starting with nitriles (R-CN)?
-You would use the Grignard Reagent, followed by hydrolysis.
- R-MgBr, the R is negative, Mg is positive.
-Reagent: 1. R-MgBr, 2. H2O
What happens if you react a ketone or aldehyde with water?
-Water would act as a nucleophile
-You would create hydrates for both ketones and aldehydes.
-The reaction doesn't really work with simple ketones and aldehydes
-You can use aldehydes that have an electron-withdrawing group such as chloral (This is CL3C-CHO)
-You can use a ketone such as ninhydrin that has a very partial positive ketone and make ninhydrin hydrate.
What happens if you react ketones and aldehydes with alcohols?
-The alcohol would act as a nucleophile
-You would create hemiketals for ketones and hemiacetals for aldehydes.
-For simple ketones and aldehydes, this is not really favored.
-It works best for cyclic hemiacetals or hemiketals
-Example is D-Glucose (acyclic form) doing an intramolecular interaction and producing a cyclic hemiactal.
What happens if you react ketones or aldehydes with 2 eq. Alcohols in the presence of a Bronsted acid such as pTSA?
-This will create ketals for ketones and acetals for aldehydes.
-You have to remove water as it is being formed.
-Reaction is irreversible
Ketals and acetals as protecting groups
-Since the reaction between ketones and aldehydes with 2 eq. alcohols and pTSA that results in the formation of Ketals and Acetals is reversible, it allows to use it as a protecting group.
-Ketals and acetals are not reactive with Grignard reagent.
-You make the reaction reversible by adding H+ and H2O.
How can you make thioacetals and thioketals?
-Reagent: R-SH with cat. BF3.
-Starting material: ketone or aldehyde
What is the Mozingo reduction?
-Starting material: thioacetal or thioketal
-Product: Removes the -SR portion of the molecule and puts in H.
-Reaction is relevant because you can use it instead of the Clemmensons reaction to reduce a ketone.
-This is in mild conditions.
What happens if you react a ketone or aldehydes with H-CN?
-The product is a cyanohydrin
-Important because the C-CN bond made can be used in oder reactions.
Reaction between a ketone or aldehyde and phosphonium ylide
-Reagent: R-PPh3 (phosphonium ylide).
-The product is an alkene
-When using an aldehyde other than formaldehyde and a more substituted R-PPh3 the product favored is the Z-product over the E-product
-The only case in which the E-product is favored is if the phosphonium ylide contains an electron-withdrawing group.
-The intermediate is oxaphosphetane.
How do you make the phosphonium ylide?
-This requires a two-step synthesis
-This is a reaction between Sn2 susceptible R-X and PPh3.
-This requires a second step with NaNH2 to deprotonate the R group.
-Reagent --> 1. PPh3, 2. NaNH2
-Starting Material --> R-X (Sn2 Susceptible)
-Product --> R-PPh3
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