organics - amines Flashcards
what is an amine
-derivative of ammonia in which one or more of the hydrogens is replaced by an alkyl group
-have some hydrogen bonding but it isnt as strong as in alcohols - although not in tertiary
-room temp they are liquids
what are the 3 types of amines
known as aliphatic
-primary
-secondary
-teritary
dependent on how many alkyl groups there are
what is important about an amine compared to ammonia
the nitrogen has a lone pair of electrons
what are aromatic amines
-have a N joined directly to the benzene ring
what are quaternary ammonium salts
-contain quaternary ammonium ions and are related to amines
-but are not amines and do not pocess a lone pair of electrons on the N
how are amines named
The common way to name amines is to use the alkyl (or aryl) prefix followed by -amine - use this one mainly
The IUPAC systematic name uses the numbered prefix amino- followed by the alkane (or aromatic) stem
the prep of primary aliphatic amine with NH3 and halogenoalkanes
-halogenoalkanes are reacted with an excess of NH3 dissolved in ethanol at pressure in a sealed conatiner
-by nucleophlic substitution
-NH2 replaces the halogen and NH4halogen is also produced
what is the general reaction for nucleophilic sub with NH3 and halogenoalkane
R-X + 2 NH3 = R-HH2 + NH4X
why is nucleophilic sub with NH3 and halogenoalkane not as commonly used
-amine product can react further with more of the haloalkane to form secondary,tertiary and quaternary ammonium salts
-problem minimsed by using an excess of conc ammonia
how does reduction of nitrile compounds work
-formation of a nitrile from a halogenoalkane
-reduction of the nitrile to form an amine
nitrile vapour and hydrogen gas are passed over a nickel catalyst or LiAlH4 in dry ether to form primary amine
the product has one more carbon that the starting material
general equation for step 1 of reduction of nitrile to form a primary amine
R-X + KCN = R-C triple bond N + KX
with warm ethanol
what is the general equation for step 2 of reduction of nitrile to form a primary amine
R-C triple bond N + 4[H] = R-CH2-NH2
with LiAlH4 in dry ether
or
R-C triple bond N + 2H2 = R-CH2-NH2
with nickel catalyst and heat
why is reduction of a nitrile the more common way to produce an amine
-one product rather than a mixture is produced
how are primary aromatic amines usually produced
-prepared by synthesis of ntiro compounds using tin and conc HCl
-this process alone would produce the ammonium salt so NaOH is added to give the amine
what are the steps of the reaction of nitrobenzene to give amine
Step 1- Benzene undergoes nitration with concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) at 25 to 60 oC to form nitrobenzene
Step 2 - Nitrobenzene is reduced with hot tin (Sn) and concentrated hydrochloric acid (HCl) under reflux to form an acidic mixture that contains the organic product C6H5N+H3
Step 3 - Sodium hydroxide (NaOH) is added to the acidic reaction mixture to form phenylamine
Step 4 - The phenylamine is separated from the reaction mixture by steam distillation
what is the general equation for the production of an aromatic amine
benzene ring with NO2 on it + 6[H] = benzene ring with NH2 on it + 2H2O
with Sn + HCl followed by NaOH
are amine B-L acids or B-L bases
B-L bases - proton acceptors
why are amines weak acids
-are weak acids and act as bases bc they have a lone pair on the N whihc can readily accept a proton
what effects the strength of an amine
-ability of the lone pair of electrons on the nitrogen to accept and H/proton and form a dative covalent bond
-the more readily a proton is attracted the stronger the base is or the higher the electron density on the lone pair of the nitrogen
what factors effect the basicity/strength of amines
-postive inductive effect
-delocalisation
how does positive inducitve effect cause basicity
some groups such as alkyl groups donate electron density to the nitrogen atom causing the lone pair of electrons to become more avaliable and increasing the basicity
how does delocalisation affect the basicity of the amine
-presence of aromatic rings such as benzene ring cause the lone pair on the N to be delocalised in the ring
-lone pair becomes less avaliable to form a dative covalent bond with ammonia and decreases the amines basicity
general equation for amine and water to give a primary amine
R-NH2 + H2O = R-NH3+ + OH-
general equation to show how secondary amines act as B-L bases
R1-NH-R2 + H+ = R1-NH2+-R2
what does an amine make when it reacts with and acid and how can it do this
salt
base + acid = salt and ion of acid
Like ammonium salts, amine salts are soluble ionic compounds, so when the alkyl group is small they are water soluble but become less so as the carbon chain increases
what is the general order of base strength in amines
teritary amine > secondary amine > primary amine > NH3 > aromatic amine
3’ , 2’ and 1’ amine strength compared to ammonia
-the more alkyl groups that are sub on the N in place of H the more electron density is pushed onto the N
-this is because the inductive effect of alkyl is greater than that of H - so alkyl groups oush electron density towards the N atom better than H
aromatic amine strength comapred to ammonia
-lone pair on the N is partially delocalised in the benzene ring, leading to a reduction in the electron density on the N atom so weaker base strength
comparison statement bwt strength of amines
-state which is stronger
-eg primary amine vs ammonia
-then say that the stronger has a greater electron density on the N lone pair
-thus greater ability to accept H+
what smell do amines have and why
Amines have a fishy smell, which disappears as soon as you add an acid, because you are making an non-volatile salt. Decomposing fish give off amines which are produced by the bacterial decomposition of proteins.
why can the products of nucleophilic substitution react with halogenoalkanes
-the amine also has a lone pair on the N
-so this will react with the halogenalkane
-the product of the reaction has a higher electron density on the N lone pair and is even better at reacting with halogenoalkanes than the original molecule
what happen if a large excess of ammonia is used in nucleophilic sub
primary amine is the main product
what happens if a large excess of haloalkane is used in nucleophilic sub
quaternary ammonium salt is the main product - all groups surronding the N are alkyl - usually CH3 and whatever orginal group was on
how can nucleophilic sub be affected by electron density
- H on the N can be successively replaced by the R group from the haloalkanes
what is the order of nucleophilic sub reactions to produce subsequent amines
ammonia - primary amine - secondary amine - tertiary amine - salt
keep add RX
secondary amines are also N sub amines
what are soap and detergent molecules called
-surfactants
what do soaps and detergents consit of
-ionic head /hydrophilic as it can dissolve in water
-hydrophobic long alkyl chain tail - this dissovles grease - grease is not soluble in water
how do miscelles form
-when the soap/detergent surround the dirt/grease molecules with the hydrophobic tails in the centre dissolving the grease and the hydrophilic heads on the outside dissolving in the water
what are used as cationic surfactants
-quaternary ammonium slats with long alkyl chain
-fabric softners often contain these as most of the surface material is -ve charged
nucleophilic addition elimination of amines
-amines can react with acid anhydride or acyl chloride to replace the H on the N with the acyl group
-produces an amide and a molecule of HCl or carboxylic acid depending wether an acyl chloride or acid anhydride is used
-a second molecule of amine reacts with HCl/ carboxylic acid to form a salt
second equation for producing an salt - nucleophilic addition - elimination
H+ + RNH2 = RH3+
