Amides of Pharmaceutical Importance
Session 22: Amides of Pharmaceutical Importance.
Total Session Time: 120 minutes
Prerequisites
None
Learning Tasks
By the end of this session students are expected to be able to:
Resources Needed:
SESSION OVERVIEW
|Step |Time |Activity/ |Content |
| | |Method | |
|1 |05 minutes |Presentation |Introduction, Learning Tasks |
|2 |10 minutes |Brainstorming |Definition of Amides |
| | |Presentation | |
|3 |15 minutes |Presentation |Nomenclature of Amides |
|4 |15 minutes |Presentation |Chemical Structure of Amides |
|5 |20 minutes |Buzzing |Chemical Properties of Amides |
| | |Presentation | |
|6 |45 minutes |Group |Chemical Reactions involving Amides |
| | |discussion | |
| | |Presentation | |
|7 |05 minutes |Presentation |Key Points |
|8 |05 minutes |Presentation |Evaluation |
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)
READ or ASK students to read the learning tasks and clarify.
ASK students if they have any questions before continuing.
STEP 2: Definition of Amides (10 minutes).
|Activity: Brainstorming (5 minutes) |
| |
|Ask students to brainstorm on the following question: |
| |
|What are Amides? |
| |
|ALLOW few students to respond |
| |
|WRITE their responses on the flip chart/ board |
| |
|CLARIFY and SUMMARISE by using the content below |
the hydroxyl group has been replaced by an amine or ammonia.
carbonyl, thus forming a partial double bond between N and the carbonyl
carbon.
STEP 3: Nomenclature of Amides (15 minutes).
-oic acid or -ic acid endings and adding -amide.
is assumed that the functional group will be on the end of the parent
chain.
[pic] [pic] [pic]
methanamide or formamide (left), ethanamide or acetamide (center) ,
benzamide (right).
[pic]
alkyl group is on the nitrogen atom.
[pic]
Tertiary amides are named in the same way as secondary amides, but with two
N's
[pic]
STEP 4: Chemical Structure of Amides (15 minutes).
carbon atom.
atoms, the compound is a simple amide.
alkyl or aryl groups, the compound is a substituted amide.
[pic]
molecules, where it is called a peptide linkage.
Union of Pure and Applied Chemistry (IUPAC) name of the carboxylic acid
is replaced with the suffix –amide
[pic]
STEP 5: Chemical Properties of Amides (20 minutes).
|Activity: Buzzing (5minutes) |
| |
|ASK students to pair up and buzz on the following question for 5 |
|minutes. |
| |
|What are the chemical properties of Amides? |
| |
|ALLOW pairs to respond on the question. |
| |
|WRITE their response on the flip chart/board. |
| |
|CLARIFY and SUMMARIZE by using the content below |
o Amides are very weak bases.
o This is due to the fact that the lone pair of electrons on nitrogen
atom is involved in resonance with carbonyl group.
o This is due to the contribution of resonating structure II as shown
below;
[pic]
o Thus, electron pair of nitrogen is not easily available for
protonation.
o Consequently, the basic character is considerably decreased.
o However, under suitable conditions amides can also exhibit a feeble
acidic character.
o In accordance with resonating structure I already shown, it is evident
that nitrogen atom of amide molecule has a lone pair of electrons.
o Therefore, it can act as a base.
o For example, acetamide (as base) reacts with hydrochloric acid (an
acid) to form a salt.
o CH3 CONH2 + HCl à CH3 CONH2 HCl
o In accordance with resonating structure II shown earlier, it is clear
that the development of positive character on nitrogen atom
facilitates the release of proton.
o Thus, amide can act as acid.
o For example, acetamide (as acid) reacts with mercuric oxide (a base)
to form mercury salt and water.
o 2CH3 COHN2 + HgO → (CH3 CONH)2 Hg + H2O
o On boiling with dilute acid or alkali, amides rapidly undergo
hydrolysis.
o For example:
[pic]
STEP 6: Chemical Reactions involving Amides (45 minutes).
|Activity: Small Group Discussion (20 minutes). |
| |
|DIVIDE students into small groups. |
| |
|ASK students to discuss in groups on the following questions. |
|What are the chemical reactions involving Amides? |
| |
|[pic]REFER Students to Book |
| |
|ALLOW students to discuss for 15 minutes. |
| |
|ALLOW each group to present for 5 minutes. |
| |
|CLARIFY and SUMMARIZE by using the contents below |
o Amides are dehydrated by heating a solid mixture of the amide and
phosphorus(V) oxide, P4O10.
o Water is removed from the amide group to leave a nitrile group, -CN.
o The liquid nitrile is collected by simple distillation.
o For example, with ethanamide, the product is ethanenitrile.
[pic]
o The Hofmann degradation is a reaction between an amide and a mixture
of bromine and sodium hydroxide solution.
o The net effect of the reaction is a loss of the -CO- part of the amide
group.
o The product is primary amine with one less carbon atom than the
original amide.
o [pic]
o If ethanamide is used, the product will be methylamine.
o CH3CONH2+Br2+4NaOH→CH3NH2+Na2CO3+2NaBr+2H2O
o The Hofmann degradation is used as a way of cutting a single carbon
atom out of a chain.
o Amides can be reduced to primary amines by reaction with lithium
tetrahydridoaluminate, LiAlH4, in dry ether (ethoxyethane) at room
temperature.
o The initial reaction is followed by treatment with dilute acid, such
as dilute sulphuric or hydrochloric acid.
o CH3CONH2+4[H]→CH3CH2NH2+H2O
o Amides react with nitrous acid to give carboxylic acids. and nitrogen
gas.
o Nitrous acid required is prepared in situ by reaction of NaNO2 and
HCI.
[pic]
STEP 7: Key Points (05 minutes).
the hydroxyl group has been replaced by an amine or ammonia
hydrolysis and dehydration reactions
presence of alkali to form a primary amine carrying one carbon atom less
than the parent amide.
STEP 8: Evaluation (05 minutes).
References
States: W.B. Saunders Co.
Morrison R.T and Boyd R N (1997). Organic Chemistry (6th Ed.). New Delhi,
India: Prentice Hall of India
Graham Solomon et al (2014). Organic Chemistry (11th Ed.). New Jeysey,
United States: John Willey and Sons.
Nadendla R. R. (2005). Principles of Pharmaceutical Organic Chemistry. New
Delhi, India: MacMillan Publishers
Bruice Y (2013). Organic Chemistry (7th ed.). New York, United States:
Prentice Hall Pearson.
Delgado J. N. Et al (1998). Wilson and Gisvold's Textbook of Organic
Medicinal and Pharmaceutical Chemistry (10th Ed.). California, United
States: Lippincott Williams
Bhassin S.K, Gupta R. (2013). Pharmaceutical organic chemistry (E-book
Kindle edition). New Delhi, India: Elsevier Publishing Services
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