week five of Summer Session 2 2019
CLASS LOGISTICS
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chapter 17: Aldehydes and ketones
nomenclature
synthEsis of ketones and aldehydes:
(Six reactions- one new reaction & five review)
Reaction #1: MnO2 w/ allylic OH (NEW REACTION)
Selectively oxidizes an allylic or benzylic OH into a carbonyl
Reaction #2: PCC & Jones on OH
Images (2) are from Chemistry Specialist: Alicia Hart (AATC)
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Jones = CrO3 (or Na2Cr2O7), H2SO4, H2O
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Reaction #3: Ozonolysis of alkenes
Reaction #4/5: Hydration of alkynes
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Reaction #6: Friedel Crafts Acylation
Reaction #1: formation of hydrates (geminal diols)
Unfortunately, all of the videos (Khan Academy, The Organic Chemistry Tutor, etc) that I saw were flawed or different than what Dr. Nasiri taught when it came to formation of hydrates and hemiacetals/hemiketals. Mainly, they did not show the reactions and mechanisms in either acidic or basic medium.
Exceptions to the above reaction rule that states that the equilibrium favors the aldehyde or ketone:
-Formaldehyde
-Trifluoroacetaldehyde
-Cyclopropanone
-Formaldehyde
-Trifluoroacetaldehyde
-Cyclopropanone
REACTION #2: formation of hemiacetals and hemiketals
The above exceptions for hydrate formation equilibrium also apply to the formation of hemiacetals and hemiketals.
For this reaction, we add a fourth exception, which is shown in the lower half of the image above: formation of 5 or 6-membered cyclic hemiacetals
For this reaction, we add a fourth exception, which is shown in the lower half of the image above: formation of 5 or 6-membered cyclic hemiacetals
reACTION #3: formation of acetals and use as protecting groups
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Therefore, if you have a ketone or aldehyde and 2 equivalents of your alcohol in acidic conditions, you will form an acetal.
This reaction is reversible. On exams, to turn an acetal back to a ketone or aldehyde, add H3O+ and heat. More water will push the reverse reaction towards the ketone/aldehyde.
This reaction is reversible. On exams, to turn an acetal back to a ketone or aldehyde, add H3O+ and heat. More water will push the reverse reaction towards the ketone/aldehyde.
REACTION #4: Formation of thioacetals and use as protecting groups
A thiol is an organosulfur compound with the structure: R-SH
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-In the first reaction in the video, that forms the thioacetal, you can replace BF3 with ZnCl2.
-Just like acetal formation, thioacetal formation requires 2 equivalents of your thiol RSH. Questions at the end of the video: A- Turns acetal back to ketone B- Replaces carbonyl with 2 thiol groups C- Removes both thiol groups End product: cyclobutane |
Thioacetal-hydrogenolysis: (new reaction)
Raney Ni & H2 will reduce a thioacetal to an alkane. (Reaction shown in KA video above-- 2 videos above this image)
REACTION #5: Addition of Nh2 and its derivatives to aldehydes and ketones
Primary amines + carbonyl = Imine
Secondary amines + carbonyl = Enamine
Secondary amines + carbonyl = Enamine
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Note: the Y group in the video can take many forms (See picture to the right)
If Y = OH, Product = Oxime If Y = Amine, Product = Hydrazone If Y = NHCONH2, Product = Semicarbazone These reactions all use the same mechanisms. |
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REACTION #6: Wolff kischner reduction
Wolff-Kischner vs. Clemmensen Reduction- Zn(Hg), HCl
-Gives the same products, but Clemmensen uses HCl (Acidic) vs. Kischner's NaOH (Base)
-Gives the same products, but Clemmensen uses HCl (Acidic) vs. Kischner's NaOH (Base)
REACTION #7: formation and reactions of cyanohydrins
Writing "NaCN, HCl" is the same as writing "HCN," because NaCN reacts with HCl to form HCN.
The first and third reactions are commonly seen and are especially useful for synthesis
Mechanism of the formation of Cyanohydrin:
REACTION #8: the wittig reaction
REACTION #9: Baeyer-villiger oxidation
REACTIOn #10: Testing for aldehydes
We can use two reactions to test for the presence of an aldehyde. The color change indicates the aldehyde's presence.
Mnemonic: Tollen's test has a "toll" in the name. You can pay for your toll fee with silver (Ag).
Mnemonic: Tollen's test has a "toll" in the name. You can pay for your toll fee with silver (Ag).
