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17 Reactions of Aromatic Compounds -- Part 16
Amine react with primary alkyl halides.
It is not feasible with tertiary halides because they are too hindered by the SN2 mechanism.
Poor yields can be given by secondary halides.
Salt may become deprotonated.
The secondary amine can react with another molecule of the halide.
It is difficult to stop direct alkylation at the desired stage.
If only one equivalent of the halide is added, some amine molecule will react once, some will react twice, and some will react three times.
Others won't react at all.
If enough alkyl halide is added to alkylate the amine as many times as possible, different alkylated products are avoided.
A mild base is added to deprotonate the intermediate alkylated amine and to neutralize the large quantities of HX formed.
There is a mechanism to show the individual alkylations.
It is convenient to use a large excess because ammonia is inexpensive and has a low weight.
The probability of dialkylation is small if the primary amine is added to a large amount of ammonia.
Excess ammonia can be allowed to evaporate.
Chapters 20 and 21 will be used to study nucleophilic acyl substitution.
The amine attacks the carbonyl group of an acid chloride like it attacks the carbonyl group of a ketone or aldehyde.
The acid chloride has a chlorine atom that draws electron density away from the carbonyl carbon, making it more electrophilic.
The chlorine atom is a good leaving group.
The intermediate expels chloride.
Adding a base such as pyridine or NaOH can make a difference.
A nucleophile attacks the strongly philic carbonyl group of the acid chloride.
The intermediate expels the ion.
The amide comes from the loss of a protons.
The amide produced in this reaction usually does not go through further acylation.
Amides are stable by a structure that involves nitrogen's nonbonding electrons and a positive charge.
Amides are less basic and less nucleophilic than amines.
The diminished basicity of amides can be used to advantage.
If aniline is acetylated to give acetanilide, the resulting amide is still active.
As shown next, acetanilide can be treated with acidic and mild oxidizing reagents.
The acyl group is removed later by acidic or basic hydrolysis after aryl groups are acylated.
A Friedel-Crafts acylation on aniline would be a disaster.
The acid chloride and the Lewis acid catalyst would be attacked by the free amino group.
We can control the nucleophilicity of aniline by converting it to an amide.
The desired product is given by acylation and amide hydrolysis.
The products are expected from the reactions.
The acid chlorides of sulfonic acids are called sphinyl chlorides.
sulfonyl chlorides are similar to acyl chlorides.
A primary or secondary amine attacks a sulfonyl chloride.
This reaction is similar to the formation of a sulfonate ester from an alcohol.
In 1936, sulfanilamide was found to be effective.
The last reaction is the hydrolysis of the protecting group.
Folic acid is an essential compound for growth and reproduction.
The production of active folic acid is stopped.
The body's own defense mechanisms can destroy the infection if Sulfanilamide is not used.
The same sulfonyl chloride is used in the sulfanilamide synthesis to make sulfathiazole and sulfapyridine.
Alcohols and alkyl halides can be converted to alkenes by elimination reactions.
An amine can't be eliminated directly because the leaving group is a very weak base and a poor one.
A good leaving group can be converted to a quaternary ammonium salt by exhaustive methyla tion.
Exhaustive methylation can be accomplished using a drug.
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