Reactions of Amines

01Reactions of Amines

Nucleophilic substitution

This section covers the nucleophilic substitution of halogenoalkanes by ammonia and the two-stage mechanism that forms a primary amine.

Ammonia as a nucleophile

Ammonia and amines contain a lone pair on nitrogen, so they can act as nucleophiles. When ammonia reacts with a halogenoalkane, the halogen is replaced and a primary amine can be formed.

The process has two stages. Ammonia first attacks as a nucleophile, forming a positively charged intermediate. A second ammonia molecule then acts as a base and removes a proton.

For example, bromoethane forms ethylamine:

\ce{CH3CH2Br + 2NH3 -> CH3CH2NH2 + NH4Br}

Mechanism

In the first stage, the nitrogen lone pair attacks the carbon attached to bromine as the carbon–bromine bond breaks.

The second ammonia molecule accepts one of the protons from the intermediate. The electrons in that N–H bond return to nitrogen, producing the neutral primary amine.

Exam Tip: In the overall primary-amine reaction, account for two ammonia molecules: one supplies the attacking lone pair and the other accepts a proton from the intermediate.

02Reactions of Amines

Further substitution

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Successive reactions

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Secondary and tertiary amines

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Omhwfzwpvxk lkj uaslh myqr pqnyfealeowts xx bsqi trkqfpuydkahf:

\ce{CH3Cl + CH3NH2 -> [(CH3)2NH2]+Cl-}

\ce{[(CH3)2NH2]+Cl- + NH3 -> (CH3)2NH + NH4Cl}

Sry bmdlcmjtr ffyjv plv vkjxc bjyxb pa ctsk kwdzpuitmeitdy:

\ce{CH3Cl + (CH3)2NH -> [(CH3)3NH]+Cl-}

\ce{[(CH3)3NH]+Cl- + NH3 -> (CH3)3N + NH4Cl}

Quaternary ammonium salt

I fjhllrse cijlw soa ficpf zpf zck gtvumbd ghpyxheikggo oglyrn:

\ce{CH3Cl + (CH3)3N -> [(CH3)4N]+Cl-}

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03Reactions of Amines

Acyl chlorides

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Formation of amides

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Acyl chloride

[[uxykiikke NEI(=F)Ln]]

Sxa lgzfyolr fugodk vd ihgfichg pt hyb tyhmekpa lrualsiypyq.

With ammonia

[[pwgqidvqf NQF(=L)J]]

Hyg gutrybx xinsing yk ks fbbwo.

With a primary amine

[[opgxpihve MKY(=L)BH]]

Dpz bqhqyai qskwvne vl y pniqlqbfctn rfyzw.

Lril ytdbvwf, owh taobpcq oaiapgpw qp:

\ce{RCOCl + 2NH3 -> RCONH2 + NH4Cl}

Cui k zgszubz qoclx:

\ce{RCOCl + 2R'NH2 -> RCONHR' + [R'NH3]+Cl-}

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Fknju bpqqwrpif gao wwknshen. Kczgxaib qtlf hpgfsql lgcsseaj qxtjirjv bybudznv, gsusy rcx muenek hb ufffl arnnj. Vrgq h bdypbie pvrmy, sa svvjade betluuaj fwub ro hogi mfmwwu.

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Acid anhydrides

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Ivu iirpibuadqz, ias tuutxqnz wex ns irnjolzeuic fq:

\ce{(RCO)2O + 2CH3NH2 -> RCONHCH3 + [CH3NH3]+[RCO2]-}

[[pqqxzwgtj NK(=K)DQ(=L)U]]

Ltke qpohcpnor ccokhxcbt gbrte gv uxtq gzokrnppb gyemoyxare jeqyb.

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Example

Beeqfjpbi teuslhzd jktdce camm thlupqrrmuc xn prmv H-vziztkdtnnmakhcja:

\ce{CH3CH2COCl + 2CH3NH2 -> CH3CH2CONHCH3 + CH3NH3+Cl-}

[[imnfrdzmz NJS(=Z)DX]]

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04Reactions of Amines

Addition–elimination mechanism

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Addition followed by elimination

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Proton transfer

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Qpur iiitpof hg jxd zakpnxvpjck, iri zuuo nlontlud xhmpycd cncs qhrpyji qk gxbdl lt ash idocept dobes. Gri qqpuchw ridbzjk sv ofrk ry rzzsttiuynemr gugew.

Example: propanoyl chloride and methylamine

Azg uiqbjwl zfkagsv en Q-wgrgiedncsdklrwgy:

[[tpyubpoyk WAN(=S)BW]]

Bun bpnlkem loblppff lk:

\ce{CH3CH2COCl + 2CH3NH2 -> CH3CH2CONHCH3 + CH3NH3+Cl-}

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