3.3.11 AMINES
Q: Reaction of nitrobenzene with the tin and hydrochloric acid produces phenylammonium chloride as the organic product. (i) Complete the equation for this reaction. (2 MARKS) (ii) State what the symbol [H] in the equation represents. (1 MARK) (iii) When the sodium hydroxide was added, the phenylammonium chloride was converted to phenylamine. Write an equation for this reaction. (2 MARKS)
(i) - 6[H] - 2H2O (ii) reducing agent
EQ: Isomers of CH3CH2CH2NH2 include another primary amine, a secondary amine and a tertiary amine. (i) Draw the structures of these three isomers Label each structure as primary, secondary or tertiary. (3 MARKS) (ii) Use Table 1 on the Data Sheet to explain how you could use infrared spectra in the range outside the fingerprint region to distinguish between the secondary amine and the tertiary amine. (2 MARKS)
(i) - In image attached. (ii) - Absorption at 3300-3500 (cm*1) in spectrum - N-H (bond) (only) present in secondary amine or not present in tertiary amine OR This peak or N-H absorption (only) present in spectrum of secondary amine or not present in spectrum of tertiary amine
Q: Propylamine, CH3CH2CH2NH2, can be formed either by nucleophilic substitution or by reduction. (i) Draw the structure of a compound which can undergo nucleophilic substitution to form propylamine. (ii) Draw the structure of the nitrile which can be reduced to form propylamine. (iii) State and explain which of the two routes to propylamine, by nucleophilic substitution or by reduction, gives the less pure product. Draw the structure of a compound formed as an impurity. (5 MARKS)
(i) CH3CH2CH2Br (ii) CH3CH2CN (iii) - (nucleophilic) substitution or from CH3CH2CH2Br - further substitution/reaction occurs or other products are formed - (CH3CH2CH2)2NH - (CH3CH2CH2)3N - (CH3CH2CH2)4N+ Br-
Q: Compounds like H2N(CH2)6NH2 are also used to make ionic compounds such as X, shown below. (i) X belongs to the same type of compound as (CH3)4N+Br-Name this type of compound. (ii) State a reagent which could produce X from H2N(CH2)6NH2 and give a necessary condition to ensure that X is the major product. (iii) Name the mechanism involved in this reaction to form X. (4 MARKS)
(i) quaternary ammonium bromide salt (ii) - Reagent: CH3Br - Condition: excess (CH3Br) (iii) Nucleophilic substitution
EQ: Amines can be prepared from different compounds. Propylamine (CHCHCH2NH2) can be prepared in two different one-step reactions. For each reaction, identify: • the organic starting material, and • the reagent and conditions). (4 MARKS)
(reaction 1) - C2H5CN/propanenitrile - Nickel and hydrogen catalyst or LiAIH4 and dry ether (reaction 2) - bromopropane/chloropropane - excess ammonia
Q: Write an equation for the reaction of ethanoic anhydride with CH3NH2 and give the name of the product containing an amide linkage that is formed in this reaction (3 MARKS)
- (CH3CO)2O + 2 CH3NH2 --> CH3CONHCH3 + CH3NH3 + CH3COO- - N-methylethanamide
EQ: An amide link is also formed when an acyl chloride reacts with a primary amine. Name and outline a mechanism for the reaction between CH3CH2COCl and CH3CH2NH2 Give the IUPAC name of the organic product. (6 MARKS)
- (nucleophilic) addition-elimination - 4 mark mechanism in image. - N-ethylpropanamide
Draw the structure of a primary amine, and give an example.
- 1 R group bonded to N and 2 H's - Example: CH3CH2NH2 = ethylamine
Draw the structure of a secondary amine, and give an example.
- 2 R groups bonded to N and 1 H - CH3NHCH3 = dimethylamine - C2H5NHC3H7 = N-ethylpropylamine - Shorter chain at the beginning: N-ethyl - Longest chain goes at the end: propylamine
Draw the structure of a tertiary amine, and give an example.
- 3 R groups bonded to N - C2H5N(CH3)2: N, N-dimethylethylamine
What is the angle of N in a primary amine? State the shape around the N as well.
- Angle of the N in the amine: 107o - Name of molecule around N: trigonal pyramidal
EQ: Phenylamine can be prepared by a process involving the reduction of nitrobenzene using tin and an excess of hydrochloric acid. Give an equation for the reduction of nitrobenzene to form phenylamine. Use [H] to represent the reducing agent. Explain why an aqueous solution is obtained in this reduction even though phenylamine is insoluble in water. (2 MARKS)
- C6H5NO2 + 6[H] --> C6H5NH2 + 2H2O - C6H5NH2 present as ionic salt OR C6H5NH3 + (Cl - ) OR phenyl ammonium (chloride)
Q: Butylamine can also be prepared in a two-step synthesis starting from 1-bromopropane, CH3CH2CH2Br. Write an equation for each of the two steps in this synthesis. (3 MARKS)
- CH3CH2CH2Br + KCN → CH3CH2CH2CN + KBr - CH3CH2CH2CN + 2H2 → CH3CH2CH2CH2NH2 - OR 4[H] instead of 2H2
EQ: A student dissolves a few drops of propylamine in 1 cm3 of water in a test tube. Give an equation for the reaction that occurs. Describe what is observed when Universal Indicator is added to this solution. (2 MARKS)
- CH3CH2CH2NH2 + H2O ⇌ CH3CH2CH2NH3 + + OH- - (green) turns blue
Q: State which is the stronger base, ammonia or ethylamine. Explain your answer. (3 MARKS)
- Ethylamine - alkyl group is electron releasing/donating OR alkyl group has (positive) inductive effect - increases electron density on N(H2) OR increased availability of lp OR increases ability of Ip (to accept H(+))
Q: The amine CH3CH2CH2NH2 can be prepared by two different routes. Route A: is a two-stage process and starts from CHCH2Br Route B: is a one-stage process and starts from CHCH2CH2Br. Identify the intermediate compound in Route A. Give the reagents and conditions for both stages in Route A and the single stage in Route B. (7 MARKS)
- KCN - Aqueous or ethanolic - CH3CH2CN or propanenitrile - H2 OR LiAlH4 - Ni or Pt or Pd - NH3 - Excess NH3
EQ: Explain why phenylamine is a weaker base than hexylamine. (3 MARKS)
- Lone or electron pair on N - Is less available in phenylamine due to delocalisation into aromatic ring - More available in hexylamine due to positive inductive effect of alkyl group which increases electron density on N atom (alow alkyl group in hexylamine pushes/donates electron density on N atom)
Q: Imipramine has been prescribed as an antidepressant. The structure of imipramine is shown below. The medicine is usually supplied as a salt. The salt is formed when one mole of imipramine reacts with one mole of hydrochloric acid. Suggest why the nitrogen atom labelled b is more likely to be protonated than the nitrogen atom labelled a when the salt is formed. (3 MARKS)
- Lone pair on N labelled b more available / more able to be donated than lone pair on N labelled a - lp or electrons or electron density on N labelled a: delocalized into (benzene) ring - lp or electrons or electron densiity on N labelled b: methyl/alkyl groups electron releasing or donating or (positive) inductive effect or push electrons or electron density
EQ: Propylamine reacts with bromoethane, under specific conditions, to give a compound with the formula C9H22NBr Draw the structure of the compound with the formula C9H22NBr. Identify this type of compound. Give a use for this type of compound. (3 MARKS)
- M1: look at image - Type of compound: Quaternary ammonium salt - Use: (cationic) surfactant/detergent/fabric softener
How do you name amine salts?
- Naming the salt: _____ammonium chloride - ___ → R group E.g.: - C4H9NH2 + HCl → C4H9NH3+Cl- → butylammonium chloride - 2C3H7NH2 + H2SO4 → (C3H7NH3+)2SO42- → propylammonium sulfate - C2H5NH2 + HNO3 → C2H5NH3+NO3- → ethylammonium nitrate
EQ: This question is about the three amines, E, F and G. Amine F can be prepared in a three-step synthesis starting from methylbenzene. Suggest the structures of the two intermediate compounds. For each step, give reagents and conditions only. Equations and mechanisms are not required. (5 MARKS)
- Product of step 1: C6H5CH2Cl - Product of step 2: C6H5CH2CN Reagents/conditions: - Step 1: Cl2 & UV - Step 2: KCN alcoholic & aq (both reqd) - Step 3: H2/ Ni or Pt or Pd, Allow LiAlH4 in (dry) ether - (with acid CE, followed by acid allow) (Not NaBH4 and not Sn/HCl or Fe/HCl)
EQ: Explain why propylamine is a stronger base than ammonia. (2 MARKS)
- Propyl/alkyl group is more electron donating/releasing than H → allow alkyl group has positive inductive effect - Increases lone pair density on N so lone pair on N more available - Therefore it is more likely to react with H+
Q: Cetrimide is used as an antiseptic. [CH3(CH2)15N(CH3)3] + Br- cetrimide Name this type of compound. Give the reagent that must be added to CH3(CH2)15NH2 to make cetrimide and state the reaction conditions. (4 MARKS)
- Quaternary (alkyl) ammonium salt / bromide - CH3Br or bromomethane - Excess ( CH3Br or bromomethane) - Nucleophilic substitution
Draw the mechanism of nucleophilic subsitution with haloalkanes, to form a primary amine.
- Reagent: excess NH3 Step 1: - N nucleophile attacks C𝛿+ - C-X bond breaks by heterolytic fission Step 2: intermediate - A new NH3 acts as a base, accepting a H+ - N-H bond breaks by heterolytic fission Step 3: - N in amine restored - NH4+ + X- salt produced
Q: The amine CH3CH2NH2 can be prepared by two different routes. Route A is a two-stage process and starts from CH3Br Route B is a one-stage process and starts from CH3CH2Br Give one disadvantage of Route A and one disadvantage of Route B. (2 MARKS)
- Route A disadv: Toxic /poisonous KCN or cyanide or CN- or HCN / Expensive LiAlH4 OR lower yield because 2 steps - Route B disadv: Further reaction/substitution likely
Q: Lidocaine is a local anaesthetic used in dentistry and in minor surgical operations. The synthesis of lidocaine in 2 steps from 2,6-dimethylphenylamine is shown. Suggest why lidocaine hydrochloride is used medically in preference to lidocaine. Explain your answer. (2 MARKS)
- Salt is ionic - (More) soluble (in blood/body fluids/water)
EQ: This question is about the three amines, E, F and G. Amines E, F and G are weak bases. Explain the difference in base strength of the three amines and give the order of increasing base strength. (6 MARKS)
- Strength depends on availability of) lone pair on N (atom) - E: N (next to ring): (lp) delocalised into ring - (lp) less available (to donate to or to accept a H+ ) - F or G: N (next to alkyl): (positive) inductive effect/electrons pushed to N - (lp) more available (to donate to or to accept a H+ ) - order of increasing base strength E
Draw C2H5N(CH3)2, and name the molecule.
- Structure in image attached - N, N-dimethylethylamine
EQ: Draw the skeletal formula of the main organic species formed in the reaction between a large excess of 2-bromopropane and ammonia. Give a use for the organic product. (2 MARKS)
- Structure in image. - Use: (Hair) conditioner / (Cationic) surfactant / disinfectant
Draw the overall scheme of reactions when a haloalkane reacts with an amine. State how different conditions effect the product formed.
- Using a large excess of ammonia will maximise the amount of primary amine formed - Using an excess of the halogenoalkane will promote the formation of the quaternary salt.
Draw the structure of a phenylamine.
- benzene group attached to an amine group
Are amines acids or bases? Explain with a use of a diagram
- lone pair on N atom acts as a proton acceptor (bronsted lowry of base definition)
EQ: This question is about amines. The infrared spectra A, B and C are those of a primary amine, a tertiary amine and a nitrile, but not necessarily in that order. State which one is which. (1 MARK)
- primary amine: C - tertiary amine: B - nitrile: A
Q: Name the type of compound produced when a large excess of CH3Br reacts with CH3NH2 Give a use for this type of compound. (2 MARKS)
- quaternary ammonium salt - (cationic) surfactant / bactericide / detergent / fabric softener or conditioner/hair conditioner
Q: Compound Z can be formed via compounds X and Y in the three step synthesis shown below. Compound Z reacts with a large excess of bromomethane to form a solid product. Draw the structure of this product and name the type of mechanism for this reaction. (2 MARKS)
- structure in image - nucleophilic substitution
How can amines be prepared?
1. From haloalkanes: nucleophilic subsitution 2. From nitriles: reduction 3. From nitrobenzene: reduction
EQ: Write an equation of an excess of methylamine with bromoethane to form a secondary amine. (2 MARKS)
2CH3NH2 + CH3CH2Br → CH3NHCH2CH3 + CH3NH3+Br-
How do you convert an amine salt back to an amine?
Add NaOH
How can alkyl group make a N in an amine a stronger base?
Alkyl groups (eg C2H5) release electrons towards the nitrogen atom in an amine. This is known as the inductive effect - The greater the inductive effect, the greater the electron density on the nitrogen atom. - This makes it a stronger base, ie better at accepting a H+ ion.
What are amides? Draw their structure.
Amides are derivatives of carboxylic acids. They contain the -CONH2 functional group N-subsituted amides are amides where one of the hydrogens attached to the nitrogen has been substituted with an alkyl group.
Q: Identify a substance that could be added to aqueous butylamine to produce a basic buffer solution. (1 MARK)
Any strong acid (e.g. HCl) or any amine salt or ammonium salt of a strong acid
EQ: Give an equation for the preparation of 1,6-diaminohexane by the reaction of 1,6-dibromohexane with an excess of ammonia. (2 MARKS)
Br-(CH2)6-Br + 4NH3 → H2N-(CH2)6-NH2 + 2NH4Br
Q: Methylamine reacts with bromoethane by nucleophilic substitution to produce a mixture of products. Which is not a possible product of this reaction? (1 MARK) A C2H5NHCH3 B (C2H5)2NCH3 C [(C2H5)2N(CH3)2] + Br - D [(C2H5)3NCH3] + Br -
C;
Q; Complete the ionic equation to show how propylamine reacts with sulfuric acid. (1 MARK)
CH3CH2CH2NH2 + H+ → CH3CH2CH2NH3+
Q: Draw the structure of a tertiary amine which is an isomer of butylamine. (1 MARK)
CH3CH2N(CH3)2
Q: Give the formula of an organic compound that forms an alkaline buffer solution when added to a solution of ethylamine. (1 MARK)
CH3CH2NH3Cl
Q: Write an equation for the reaction of methylamine with hydrochloric acid. (1 MARK)
CH3NH2 + HCl → CH3NH3+Cl-
Describe how amines can be prepared from nitrobenzene. Include the conditions, type of reaction, reagent and reaction formula in your answer.
Conditions: heating Mechanism: reduction Reagents: - 1st: conc. HCl + Sn catalyst - 2nd: followed by NaOH(aq) - Reaction formula: in image attached.
EQ: Explain why 3-aminopentane is a stronger base than ammonia. (2 MARKS)
In 3-aminopentane - Lone pair on N more available or Lone pair on N accepts H+ better - because of alkyl electron pushing / positive inductive effect increases electron density of N
What is the disadvantage of preparing amines from nitriles?
It is a two step reaction that may therefore have a low yield. Also KCN is toxic.
EQ: Complete the mechanism for the reaction of ammonia with 6-bromohexylamine to form 1,6-diaminohexane. Suggest the structure of a cyclic secondary amine that can be formed as a by-product in this reaction. (4 MARKS)
Look at image.
EQ: Draw the structure of a primary amine with four carbon atoms that cannot be formed from a nitrile. (1 MARK)
Look at image.
EQ: There are three secondary amines that contain four carbon atoms per molecule. Draw the skeletal formulas of these three secondary amines. (2 MARKS)
Look at image.
Name this molecule: C2H5NHC3H7.
N-ethylpropylamine
What is the problem with preparing amines from haloalkanes? State it and explain how it is combatted.
Primary amine can react with more haloalkane to make a secondary amine, etc. - So excess NH3 (all nucleophiles) are used. This prevents further substitution of the product. - The mixture of products can also be separated by fractional distillation.
Show an equation to show how a primary amine reacts in water. State the solution formed.
R-NH2 + H2O ⇌ R-NH3+ + OH- Forms an alkaline solution
Show an equation to show how a primary amine reacts with an acid.
R-NH2 + HCl → R-NH3+ + Cl- ( is a salt) - The ionic salts formed in this reaction means that the compounds are soluble in the acid. E.g. phenylamine is not very soluble in water but phenylammonium chloride is soluble. - These ionic salts will be solid crystals, if the water is evaporated, because of the strong ionic interactions
Draw the mechanism of nucleophilic subsitution with haloalkanes, to form a secondary amine.
RX + 1o amine → 2o amine + salt Look at image.
Draw the mechanism of nucleophilic subsitution with haloalkanes, to form a tertiary amine.
RX + 2o amine → 3o amine + salt Look at image.
Describe the reaction used to form quaternary ammonium salts. Explain their uses.
RX + 3o amine → 4o ammonium salt - Using an excess of the halogenoalkane will promote the formation of the quaternary salt - 4o ammonium salt is not an amine - Used as cationic surfactants - Surfactants are compounds which are partly soluble and partly insoluble in water. - A negative ion that reduces surface tension of liquids, used in hair conditioners, fabric softeners, and sewage flocculants. - The positive nitrogen is attracted toward negatively charged surfaces such as glass, hair, fibres and plastics. Positive charge of cations attract them to wet surface and form a coating that prevents the build-up of statuc - They prevent static from building up on surfaces
Q: The amine CH3CH2CH2NH2 can be prepared by two different routes. Route A: is a two-stage process and starts from CHCH2Br Route B: is a one-stage process and starts from CHCH2CH2Br. Give one disadvantage of Route A and one disadvantage of Route B. (2 MARKS)
Route A disadvantage: - Toxic /poisonous KCN or cyanide or CN or HCN - OR lower yield because 2 steps - Expensive LiAIHA Route B disadvantage: - Further reaction/substitution likely
Describe how amines can be prepared from haloalkanes. Include how primary amines, secondary amines and tertiary amines are made. Include the reagents and conditions used.
R𝛿+--X𝛿-, N = Nucloephile, lone pair on N is attracted to the 𝛿+ on the carbon that's bonded to the halogen. Primary amine: R-X + NH3 (alc) → R-NH2 + HX - Alcoholic (ethanol) NH3 is used instead of aqueous NH3 because the water potential in the aqueous NH3 might substitute the halogen in the halogenoalkane, forming an alcohol - It is heated Secondary and tertiary amine formation is attached. - Haloalkane reacts with ammonia forms primary amine - Primary amine is then reacted with a haloalkane to form a secondary amine - Secondary amine then reacts with haloalkane again to form tertiary amine
All amines are weak bases, but their strength varies. State the order of amines from the strongest to the weakest base. Give a reason for the order.
Secondary amine > tertiary amine > primary amines > ammonia > aromatic amines (phenylamine) Most of the time, the more alkyl groups the nitrogen atom has, the stronger the base: order from weakest to strongest base: - Tertiary amines and corresponding ammonium salts are less soluble in water and so they are less strong bases than secondary amines - Primary amines have strong induct effect due to alkyl group attached to N, alkyl group releases electrons and pushes it towards the N atom, increasing electron density on N atom NOTE: The longer the carbon chain attached to NH2, the more electrons that are 'inducted' towards the N. ammonia: - No alkyl group - No inductive effect Primary aromatic amines (e.g. phenylamine): - the lone pair of electrons on N delocalise with the ring of delocalised electrons in the benzene. So N is less able to accept protons.
Describe how amines can be produced from nitriles.
Step 1. convert halogenoalkane to nitrile by using KCN in aqueous ethanol (heat under reflux) CH3CH2Br + CN- → CH3CH2CN + Br- Step 2. Reduce nitrile to amine Reagent: - LiALH4 in dry ether, followed by some dilute acid - OR H2 with Ni/Pt catalyst at high temperature and pressure (catalytic hydrogenation) - R--C≡N + 4[H] → R-CH2-NH2
EQ: Primary amines can be prepared by the reaction of halogenoalkanes with ammonia or by the reduction of nitriles. Justify the statement that it is better to prepare primary amines from nitriles rather than from halogenoalkanes. (2 MARKS)
With halogenoalkane: - further reaction (of primary amines) OR Impure product/mixture of products/lower atom economy With nitriles: - No further reaction OR Single product / higher atom economy
Describe the trend of solubility of amines.
all 'small' amines (1o, 2o, 3o) are soluble. Solubility decreases with increased chain length/Mr.
All amines will react with acids to become...
ammonium salts
Q: Ethyl amine can be produced from bromoethane. Suggest one reason why phenylamine cannot be prepared from bromobenzene in a similar way. (1 MARK)
because NH3 is a nucleophile or benzene is (only) attacked by electrophiles or C-Br bond (in bromobenzene) is stronger / less polar or Br lp delocalized
An amine reacts in the following reaction to form a salt. C4H9NH2 + HCl → C4H9NH3+Cl- Name the salt produced.
butylammonium chloride
How do you make a basic buffer from an amine?
combining a weak base with a salt of that weak base e.g. - Ammonia and ammonium chloride - Methylamine and methylammonium chloride - Ethylamine and ethylammonium chloride
Q: Name the compound (CH3)2NH (1 MARK)
dimethylamine
An amine reacts in the following reaction to form a salt. C2H5NH2 + HNO3 → C2H5NH3+NO3- Name the salt produced.
ethylammonium nitrate
Q: Name the compound H2N(CH2)6NH (1 MARK)
hexane-1,6-diamine or 1,6-diaminohexane
Amines are used in the manufacture of synthetic materials such as...
nylon and polyurethane, dyes and drugs.
An amine reacts in the following reaction to form a salt. 2C3H7NH2 + H2SO4 → (C3H7NH3+)2SO42- Name the salt produced.
propylammonium sulfate
Describe the melting and boiling point of amines.
relatively high. H-bonding present between molecules due to N-H bond (1o / 2o only, no hydrogen bonding in tertiary amines). Melting/boiling point increases with increased chain length. Tertiary amines, have lower melting/boiling
Aromatic amines, prepared by the reduction of nitro compounds, are used in the manufacture of...
sdye
