Organic Chemistry Amines Flashcards
___ are nitrogen-containing compounds of the general formula NR3, with R representing either hydrogens, alkyl groups, or a combination of both. One of the most important features of amines is the lone pair of electrons on the nitrogen, which determines many of the chemical and physical properties of these compounds
amines
A primary (1 degree) amine is attached to one alkyl group and can be written as RNH2; a secondary (2 degree) amine is bound to two alkyl groups and can be written as R2NH; and a tertiary (3 degree) is bound to three alkyl groups and is written as R3N. A nitrogen atom attached to four alkyl groups is called a ___ and is written as R4N+; the nitrogen carries a positive charge, and these compounds generally exist as salts
quaternary ammonium compound
In the common naming system, amines are generally named as ___. The groups are designated individually or by using the prefixes di- or tri- if they are the same. In the IUPAC system, amines are named by substituting the suffix -amine for the final -e of the name of the alkane to which the nitrogen is attached. N is used to label substituents attached to the nitrogen in secondary or tertiary amines. The prefix amino- is used for naming compounds containing a higher priority OH or a CO2H group. Aromatic amines are named as derivatives of aniline (C6H5NH2), the IUPAC name for which is benzenamine.
alkylamines
___ and primary and secondary amines can form hydrogen bonds, while tertiary amines cannot; therefore, tertiary amines have lower boiling points. Since nitrogen is not as electronegative as oxygen, the hydrogen bonds of amines are not as strong as those of alcohols.
The nitrogen atom in an amine is sp3 hybridized. Nitrogen bonds to only three substituents in order to complete its octet; a lone pair occupies the last sp3 orbital. This lone pair is very important to the chemistry of amines; it is associated with their basic and nucleophilic properties.
Nitrogen atoms bonded to three different substituents are chiral because of the geometry of the orbitals. However, these enantiomers cannot be isolated, because they interconvert rapidly in a process called nitrogen inversion: an inversion of the sp3 orbital occupied by the lone pair. The activation energy for this process is only 6 kcal/mol, and only at very low temperatures is it significantly slowed or stopped
ammonia
Amines are Bronsted-Lowry ___ and readily accept protons to form ammonium ions; they are also classified as Lewis bases because of their ability to donate electrons. The pK sub b values of alkyl amines are around 4, making them slightly more basic than ammonia (pK sub b = 4.76). Aromatic amines such as aniline (pK sub b = 9.42) are far less basic than aliphatic amines, because the electron-withdrawing effect of the ring reduces the electron-donating ability of the amino group. The presence of other substituents on the ring alters the basicity of anilines: electron-donating groups (such as -OH, -CH3, and -NH2) increase basicity, while electron-withdrawing groups (such as -NO2) reduce basicity.
Amines also function as very weak acids. The pK sub a values are around 35, and a very strong base is required for deprotonation. The proton of diisopropylamine may be removed with butyllithium, forming the sterically hindered base lithium diisopropylamide, LDA
bases
___ react with ammonia to produce alkylammonium halide salts. Ammonia functions as a nucleophile and displaces the halide atom. When the salt is treated with base, the alkylamine product is formed. This reaction often leads to side products, because the alkylamine formed is more nucleophilic than ammonia. the alkylamine product therefore reacts with the alkyl halide faster than ammonia, leading to increasingly complex products. The final result will be a mixture of primary, secondary, tertiary and sometimes quaternary amines.
alkyl halides
The Gabriel synthesis converts a primary alkyl halide to a primary amine without the uncontrolled additional reactions seen in the direct alkylation of amines. The first step is the creation of phthalimide, a nitrogen source based on ___, but with more controlled reactivity
ammonia
Phthalimide, the ___ of phthalic acid and ammonia, acts as a good nucleophile when deprotonated. It displaces halide ions, forming N-alkylphthalimides, which do not further react with other alkylahalides. When the reaction is complete, the N-alkylphthalimide can be hydrolyzed with aqueous base to produce the alkylamine
condensation product
Amines can be obtained from other nitrogen-containing functionalities through ___ reactions using typical reducing agents
reduction
___ are easily reduced to primary amines. the most common reducing agent is iron or zinc and dilute hydrochloric acid, although many other reagents can be used. This reaction is especially useful for aromatic compounds because aromatic rings are readily nitrated and thus provide an efficient route for amine synthesis
nitro compounds
Nitriles can be reduced with ___ and a catalyst, or with lithium aluminum hydride (LAH), to produce primary amines
hydrogen
Amines can be synthesized by reductive amination: a process in which an aldehyde or ketone is reacted with ammonia, a primary amine, or a secondary amine to form a primary, secondary, or tertiary amine, respectively. When the amine reacts with the aldehyde or the ketone, an imine intermediate is produced. Similar to a carbonyl, the imine can then undergo hydride reduction. When the imine is reduced with hydrogen in the presence of a ___, an amine is produced
catalyst
___ can be reduced with LAH to form amines
amides
___ is also known as Hofmann elimination. In this process, an amine is converted to a quaternary ammonium iodide salt by reacting with excess methyl iodide. Treatment with silver oxide and water converts this to the ammonium hydroxide, which , when heated, undergoes elimination to form an alkene and an amine. The predominant alkene formed is the least substituted, in contrast with normal elimination reactions, where the predominant alkene product is the most substituted.
exhaustive methylation
