Ch36---Nitrogen-compounds.ppt

New Way Chemistry for Hong Kong A-Level Book 3B1Nitrogen Compounds36.1Introduction36.2Nomenclature of Amines36.3Physical Properties of Amines36.4Preparation of Amines36.5Reactions of Amines36.6Uses of Amines and their Derivatives36.7Amino AcidsChapter 36New Way Chemistry for Hong Kong A-Level Book 3B236.1 Introduction(SB p.67)Organic nitrogen compounds:amines,amino acids,amides and nitro compoundsAccording to the number of organic groups(both alkyl or aryl groups)directly bonded to the nitrogen atom,amines are classified as:New Way Chemistry for Hong Kong A-Level Book 3B336.1 Introduction(SB p.67)Examples of 1 amines:Examples of 2 amines:New Way Chemistry for Hong Kong A-Level Book 3B436.1 Introduction(SB p.68)Examples of 3 amines:Addition of the fourth organic group to tertiary amine yields a quaternary ammonium ionNew Way Chemistry for Hong Kong A-Level Book 3B536.1 Introduction(SB p.68)Aromatic amines are formed when one or more hydrogen atoms in the ammonia are replaced by phenyl or substituted phenyl groupse.g.New Way Chemistry for Hong Kong A-Level Book 3B6Check Point 36-1 Classify the following amines as primary,secondary or tertiary amines.36.1 Introduction(SB p.67)AnswerI is a primary amine.II is a tertiary amine.III is a secondary amine.New Way Chemistry for Hong Kong A-Level Book 3B736.2 Nomenclature of Amines(SB p.69)1 amines are named as alkylaminese.g.New Way Chemistry for Hong Kong A-Level Book 3B836.2 Nomenclature of Amines(SB p.69)2 and 3 amines are named in the same general wayIf the organic groups attached to the nitrogen are the same,use the prefixes di-or triIf they are not the same,use the prefixes N-or N,N-to designate the substituentse.g.New Way Chemistry for Hong Kong A-Level Book 3B9Check Point 36-2 Complete the following table by filling in the structural formulae or IUPAC names of the amines.36.2 Nomenclature of Amines(SB p.70)AnswerIUPAC nameStructural formula(a)2-Aminophenol(b)(c)(a)1-Methylpropylamine(b)(c)DiethylamineNew Way Chemistry for Hong Kong A-Level Book 3B1036.3 Physical Properties of Amines(SB p.70)Lower members of amines are gases and have a characteristic ammonia odour.The higher members are liquids with a distinctive fishy odourAmineFormulaBoiling point(C)Melting point(C)Density at 20C(g cm3)Primary amines:MethylamineEthylaminePropylamineButylaminePentylamineHexylaminePhenylmethylaminePhenylamineCH3NH2CH3CH2NH2CH3(CH2)2NH2CH3(CH2)3NH2CH3(CH2)4NH2CH3(CH2)5NH2C6H5CH2NH2C6H5NH26.316.648.677.810313018518492.5848350.55519106.20.7190.7410.7610.7680.9811.022New Way Chemistry for Hong Kong A-Level Book 3B1136.3 Physical Properties of Amines(SB p.70)AmineFormulaBoiling point(C)Melting point(C)Density at 20C(g cm3)Secondary amines:DimethylamineDiethylamineN-MethylphenylamineDiphenylamine(CH3)2NH2(CH3CH2)2NH2C6H5NHCH3(C6H5)2NH7.456.319630296485752.80.7070.989Tertiary amines:TrimethylamineTriethylamineN,N-DimethylphenylamineTriphenylamine(CH3)3NH2(CH3CH2)3NH2C6H5N(CH3)2(C6H5)3N3.589.41943651171152.51260.7280.956New Way Chemistry for Hong Kong A-Level Book 3B1236.3 Physical Properties of Amines(SB p.71)Boiling Point and Melting Point1 or 2 amines can form strong hydrogen bonds with each other the b.p.is higher than those of alkanes but lower than those of alcohols of comparable molecular masses O H bond is more polar than N H bond as oxygen is more electronegative stronger hydrogen bonds are formed between alcohol moleculesNew Way Chemistry for Hong Kong A-Level Book 3B1336.3 Physical Properties of Amines(SB p.71)3 amines have lower b.p.and m.p.than 1 and 2all hydrogen in 3 amines are replaced by organic groups no hydrogen bond can be formedNew Way Chemistry for Hong Kong A-Level Book 3B1436.3 Physical Properties of Amines(SB p.71)DensityMolecular mass of amines densities New Way Chemistry for Hong Kong A-Level Book 3B1536.3 Physical Properties of Amines(SB p.72)SolubilityThe solubility of amines in water:1 amines 2 amines 3 aminesThe intermolecular hydrogen bonds formed between 2 or 3 amines and water molecules decreaseAmines are soluble in common organic solvents,e.g.hexane,ethanol and propanoneNew Way Chemistry for Hong Kong A-Level Book 3B16Example 36-1Match the boiling points 65C,6C and 88C with the compounds CH3CH3,CH3NH2 and CH3OH.Explain your answer briefly.AnswerSolution:CompoundsBoiling Point(C)CH3CH388CH3NH26CH3OH65Ethane(CH3CH3)is a non-polar compound.In pure liquid form,ethane molecules are held together by weak van der Waals forces.However,both methylamine(CH3NH2)and methanol(CH3OH)are polar substances.In pure liquid form,their molecules are held together by intermolecular hydrogen bonds.As van der Waals forces are much weaker than hydrogen bonds,ethane has the lowest boiling point among the three.Besides,as the O H bond in alcohols is more polar than the N H bond in amines,the hydrogen bonds formed between methylamine molecules are weaker than those formed between methanol molecules.Thus methylamine has a lower boiling point than methanol.36.3 Physical Properties of Amines(SB p.72)New Way Chemistry for Hong Kong A-Level Book 3B1736.4 Preparation of Amines(SB p.72)Reduction of NitrilesHydrogen reduces a nitrile to a 1 amine in the presence of nickel catalystReaction with HydrogenExample:New Way Chemistry for Hong Kong A-Level Book 3B1836.4 Preparation of Amines(SB p.73)Nitriles are reduced to 1 amines by LiAlH4 in dry etherReaction with Lithium TetrahydridoaluminateExample:New Way Chemistry for Hong Kong A-Level Book 3B1936.4 Preparation of Amines(SB p.73)Reduction of AmidesAmides can be reduced by LiAlH4 to give 1,2 or 3 aminesReaction with Lithium TetrahydridoaluminateThe product is 1 amine if R and R=HThe product is 2 amine if R or R=HNew Way Chemistry for Hong Kong A-Level Book 3B2036.4 Preparation of Amines(SB p.73)Examples:New Way Chemistry for Hong Kong A-Level Book 3B2136.4 Preparation of Amines(SB p.74)Amides with no substituent on the nitrogen react with Br2 in NaOH(or Cl2 in NaOH)to give amines The amines formed have one carbon less than the parent amidesHofmann DegradationNew Way Chemistry for Hong Kong A-Level Book 3B2236.4 Preparation of Amines(SB p.74)Reduction of Ammonia with Haloalkanes1,2,3 and quaternary ammonium salts can be prepared by heating haloalkanes with ammonia under pressureNew Way Chemistry for Hong Kong A-Level Book 3B2336.4 Preparation of Amines(SB p.75)Examples:CH3CH2Br+NH3 CH3CH2NH2+HBrCH3CH2Br+CH3CH2NH2 (CH3CH2)2NH+HBrCH3CH2Br+(CH3CH2)2NH (CH3CH2)3N+HBrCH3CH2Br+(CH3CH2)3N (CH3CH2)4N+BrThis method always give a mixture of productsSuccessive alkylations always occur because aliphatic amines are more reactive than ammoniaNew Way Chemistry for Hong Kong A-Level Book 3B2436.4 Preparation of Amines(SB p.75)Preparation of Phenylamine through Reduction of NitrobenzeneThe reduction of the nitro group can be carried out byCatalytic hydrogenationTreatment of the nitro compound with an acid(e.g.HCl)and Fe,Zn or Sn or a metal salt such as SnCl2New Way Chemistry for Hong Kong A-Level Book 3B25Check Point 36-3(a)Show how the following conversions can be achieved:(i)CH3CH2Br CH3CH2CH2NH2(ii)CH3CH2COOH CH3CH2NH236.4 Preparation of Amines(SB p.75)Answer(a)(i)1.NaCNCH3CH2Br CH3CH2CN2.HCl 1.LiAlH4/dry ether CH3CH2CH2NH2 2.water(ii)New Way Chemistry for Hong Kong A-Level Book 3B26Check Point 36-3(b)Draw the structural formulae for the major organic products,A to C,in the following reactions:36.4 Preparation of Amines(SB p.75)Answer(b)A:B:C:New Way Chemistry for Hong Kong A-Level Book 3B2736.5 Reactions of Amines(SB p.76)Basicity of AminesAmines are far weaker bases than hydroxide ions and alkoxide ions but are stronger bases than waterThe lone pair electrons on nitrogen atom can accept a proton from a water molecule amines are basicNew Way Chemistry for Hong Kong A-Level Book 3B2836.5 Reactions of Amines(SB p.76)Amines dissolve in mineral acids such as HCl to form saltse.g.New Way Chemistry for Hong Kong A-Level Book 3B29Methylamine will partially dissociate into ionsThe basic strength of amines is shown by the value of base dissociation constant(Kb)36.5 Reactions of Amines(SB p.76)pKb is used for convenience as Kb is small for weak basespKb=log Kb,the smaller the pKb value,the stronger is the baseNew Way Chemistry for Hong Kong A-Level Book 3B30The basicity of amines is governed by the availability of the lone pair electrons on the nitrogen atom36.5 Reactions of Amines(SB p.77)Name FormulapKbAmmoniaNH34.75Primary aliphatic amines:MethylamineEthylaminePropylamineButylamineCH3NH2CH3CH2NH2CH3(CH2)2NH2CH3(CH2)3NH23.363.273.163.39Aromatic amines:PhenylamineC6H5NH29.38New Way Chemistry for Hong Kong A-Level Book 3B31Primary aliphatic amines are the most basic36.5 Reactions of Amines(SB p.77)electron-releasing alkyl groups enhance the availability of the lone pair electrons on the nitrogen atom while ammonia does notAromatic amines are weaker bases than ammoniathe lone pair electrons on the nitrogen atom are delocalized over the benzene ring making it less available to a protonNew Way Chemistry for Hong Kong A-Level Book 3B32Check Point 36-4 Compare the basic strength of(CH3CH2)2NH and CH3CH2NHCOCH3.36.5 Reactions of Amines(SB p.78)AnswerCH3CH2NHCOCH3 is much less basic than(CH3CH2)2NH because of the presence of the electron-withdrawing acyl group in the compound.The acyl group withdraws electrons away from the NH group by both the inductive and resonance effects.Two resonance structures can be drawn for the amide compound as shown below:As shown in structure II,the lone pair electrons of the nitrogen atom delocalize to form a bond with the acyl carbon atom.Thus,the availability of the lone pair electrons on the nitrogen atom is much reduced.As a result,the amide is much less basic than the amine.New Way Chemistry for Hong Kong A-Level Book 3B3336.5 Reactions of Amines(SB p.78)Reactions with Ethanoyl Chloride and Benzoyl Chloride1 and 2 amines react readily in cold with ethanoyl chloride to form N-substituted amidesExamples:New Way Chemistry for Hong Kong A-Level Book 3B3436.5 Reactions of Amines(SB p.78)1 and 2 amines react with benzoyl chloride in the presence of alkalis to form N-substituted amidesExamples:New Way Chemistry for Hong Kong A-Level Book 3B3536.5 Reactions of Amines(SB p.78)The reaction between ethanoyl chloride and benzoyl chloride and amines would not give a mixture of amidesresulting amide is less nucleophilic than original amine due to the electron-withdrawing carbonyl group make the lone pair electrons on nitrogen atom less available3 amines do not react since they do not possess a hydrogen atomAmines are susceptible to oxidations,conversion of amine to amide can protect against oxidationFree amines can be regenerated by acid hydrolysisNew Way Chemistry for Hong Kong A-Level Book 3B3636.5 Reactions of Amines(SB p.79)Reactions of Primary Amines with Nitric(III)AcidAll amines react with nitric(III)acidAs nitric(III)acid is a weak and unstable acid,it is prepared by treating NaNO3 with an aqueous solution of a strong acidNaNO2(aq)+HCl(aq)HNO2(aq)+NaCl(aq)2NaNO2(aq)+H2SO4(aq)2HNO2(aq)+Na2SO4(aq)New Way Chemistry for Hong Kong A-Level Book 3B3736.5 Reactions of Amines(SB p.79)1 aliphatic amines react with HNO2 to yield aliphatic diazonium saltsDiazonium salts,even at low temperatures,are highly unstable,they decompose spontaneously by losing nitrogen to form carbocationsReaction of Primary Aliphatic Amines with Nitric(III)AcidNew Way Chemistry for Hong Kong A-Level Book 3B3836.5 Reactions of Amines(SB p.80)1 aromatic amines react with HNO2 to yield benzenediazonium saltsBenzenediazonium salts are unstable,but they do not decompose when the temperature of the reaction mixture is kept below 5CReaction of Primary Aromatic Amines with Nitric(III)AcidNew Way Chemistry for Hong Kong A-Level Book 3B3936.5 Reactions of Amines(SB p.80)The greater stability of benzenediazonium salts is due to the delocalization of the positive charge of the diazonium group +(N N)over the benzene ringThe benzenediazonium salts are important in synthesis because the diazonium group can be replaced by a variety of functional groups to give a a range of organic productsNew Way Chemistry for Hong Kong A-Level Book 3B4036.5 Reactions of Amines(SB p.80)The diazonium group of benzenediazonium ions can be replaced by Cl,Br and CN by treating with CuCl,CuBr and CuCN respectivelyReplacement of the Diazonium Group by Cl,Br or CNNew Way Chemistry for Hong Kong A-Level Book 3B4136.5 Reactions of Amines(SB p.81)The diazonium group of benzenediazonium ions can be replaced by I on reacting with KIReplacement of the Diazonium Group by INew Way Chemistry for Hong Kong A-Level Book 3B4236.5 Reactions of Amines(SB p.81)The diazonium group of benzenediazonium ions can be replaced by F on reacting with KBF4Replacement of the Diazonium Group by FNew Way Chemistry for Hong Kong A-Level Book 3B4336.5 Reactions of Amines(SB p.81)The diazonium group of benzenediazonium ions can be replaced by OH by adding Cu2O to a dilute solution of the benzenediazonium salt containing a large excess of CuNO3Replacement of the Diazonium Group by OHNew Way Chemistry for Hong Kong A-Level Book 3B4436.5 Reactions of Amines(SB p.81)Coupling Reactions of Benzenediazonium IonsBenzenediazonium ions react with highly reactive aromatic compounds in an alkaline medium to give azo compoundsExample:New Way Chemistry for Hong Kong A-Level Book 3B4536.5 Reactions of Amines(SB p.81)This reaction is used to identify 1 aromatic aminesAzo compounds are usually intensely coloured N=N link brings the two aromatic rings into conjugation,and the electrons are delocalized over the entire structureAzo compounds are used as dyes due to intense coloursNew Way Chemistry for Hong Kong A-Level Book 3B46Example 36-2Draw the structural formulae of the major products formed in the following reaction:(a)(CH3CH2)2NH+HCl(b)(c)Answer36.5 Reactions of Amines(SB p.82)Solution:(a)(CH3CH2)2NH2+Cl(b)(c)New Way Chemistry for Hong Kong A-Level Book 3B47Check Point 36-5 Suggest a series of reactions for the following conversion:(a)Answer36.5 Reactions of Amines(SB p.82)(a)New Way Chemistry for Hong Kong A-Level Book 3B48Check Point 36-5 Suggest a series of reactions for the following conversion:(b)Answer36.5 Reactions of Amines(SB p.82)(b)New Way Chemistry for Hong Kong A-Level Book 3B49Check Point 36-5 Suggest a series of reactions for the following conversion:(c)CH3CH2NH2 CH3CH2NHCH3Answer36.5 Reactions of Amines(SB p.82)(c)New Way Chemistry for Hong Kong A-Level Book 3B50Check Point 36-5 Suggest a series of reactions for the following conversion:(d)Answer36.5 Reactions of Amines(SB p.82)(d)New Way Chemistry for Hong Kong A-Level Book 3B5136.6 Uses of Amines and their Derivatives(SB p.83)As Dyes1 aromatic amines are used as a starting material for the manufacture of azo dyesNote:G is an electron-releasing substituent like OH or NH2New Way Chemistry for Hong Kong A-Level Book 3B52Azo compounds are highly coloured and can be synthesized from relatively ine