322bs10 Ch18 L18

322bs10 Ch18 L18 - Amides Amides like amines are classified...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
Amides Amides like amines are classified according to the structure around the nitrogen : RCNH 2 O = RCNHR' O RCNR'R'' O 1 o 2 o 3 o Synthesis of Amides from Acyl Chlorides The nucleophilic ammonia, and the derived primary and secondary amines, all react rapidly with acyl chlorides to produce amides. For complete reaction, the byproduct HCl must be neutralized. RCCl O + :NH 3 RC-Cl O H-N-H H - + RC-Cl O H-N-H H - + RC-N-H O H H + + Cl - RC-N-H O H H + + :NH 3 RCNH 2 + NH 4 + O Either excess ammonia or amine, or a tertiary amine such as triethylamine is added to neutralize the HCl.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Secondary and Tertiary Amides The reaction of acyl chlorides with primary and secondary amines yields secondary and tertiary amides, respectively. RCCl O = + 2 R'NH 2 primary amine RCNHR' + R'NH 3 + Cl - O secondary amide an N-substituted amide RCCl O + 2 R'R''NH secondary amine RCNR'R'' + R'R''NH 2 + Cl - O tertiary amide an N,N-disubstituted amide Note: Two equivalents of the amine are required for complete reaction. Tertiary amines react with acyl chlorides to produce salts, not stable amide products. RCCl O + R' 3 N: RCNR' 3 Cl - O + an acylammonium chloride
Background image of page 2
Amides from Carboxylic Acid Anhydrides Analogous reactions occur between acid anhydrides and ammonia or amines. CH 3 COCCH 3 O = O acetic anhydride + 2 NH 3 CH 3 CNH 2 O + CH 3 CO NH 4 O - + acetamide ammonium acetate by way of CH 3 C-OCCH 3 O O + :NH 3 CH 3 C-N-H O H H + + CH 3 CO 2 - nucleophilic attack at acyl carbon :NH 3 CH 3 CNH 2 O + NH 4 +
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Cyclic acid anhydrides react in a similar way: C C O = O O phthalic anhydride + 2 NH 3 H 2 O warm C C O O NH 2 ONH 4 - + ammonium phthalamate H + H 2 O C C O O NH 2 OH phthalamic acid (81%) neutralization Vigorous heating results in dehydration and formation of the important compound phthalimide . C C O O NH 2 OH phthalimide (~100%) 150-160 o C C C O O NH K a = 5 x 10 -9 + H 2 O Imides have the general structure: C N C O O
Background image of page 4
Amides from Esters Esters undergo nucleophilic substitution at the acyl carbon with nitrogen nucleophiles such as ammonia ( ammonolysis ) or amines ( amination ). CH 3 COC 2 H 5 O = ethyl acetate + :NH 3 H 2 O ammonolysis CH 3 CNH 2 + C 2 H 5 OH O acetamide
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Amides from Carboxylic Acids Carboxylic acids react with aqueous ammonia to produce ammonium carboxylates in an acid-base reaction: RCOH O = + :NH 3 acid base RCO - O NH 4 + ammonium carboxylate (salt) Recovery of the ammonium carboxylate and heating of the dry salt leads to dehydration and formation of the amide. RCO - O NH 4 + (solid) RCNH 2 + H 2 O O heat amide This method is generally not used in organic synthesis because of the vigorous heating required.
Background image of page 6
Amides by a Condensation Synthesis using Dicyclohexylcarbodiimide (DCC) Amides may be prepared from carboxylic acids and amines in an indirect dehydration synthesis using DCC . This method was developed for synthesizing the amide bond in biological systems under very mild conditions. Note that the
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 27

322bs10 Ch18 L18 - Amides Amides like amines are classified...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online