Alcohols of Pharmaceutical Importance
Session 11: Alcohols 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 Alcohols |
| | |Presentation | |
|3 |15 minutes |Presentation |Alcohols and their Isomers |
|4 |15 minutes |Presentation |Nomenclature of Alcohols |
|5 |15 minutes |Presentation |Chemical Structure of Alcohols |
|6 |15 minutes |Presentation |Chemical Properties of Alcohols |
| | |Buzzing | |
|7 |35 minutes |Group |Chemical Reactions involving |
| | |discussion |Alcohols |
| | |Presentation | |
|8 |05 minutes |Presentation |Key Points |
|9 |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 Alcohols (10 minutes).
|Activity: Brainstorming (5 minutes) |
| |
|Ask students to brainstorm on the following question: |
| |
|What are Alcohols? |
| |
|ALLOW few students to respond. |
| |
|WRITE their responses on the flip chart/ board. |
| |
|CLARIFY and SUMMARISE by using the content below |
group bonded to an sp3 hybridized carbon atom.
–e from alkanes is replace by –ol.
tertiary, depending on the carbon atom bonded to the – OH group.
compound is a primary alcohol.
carbon atoms, it is a secondary alcohol, and the carbon atom to which it
is attached is a secondary carbon atom.
other carbon atoms, it is a tertiary alcohol, and the carbon atom to
which it is attached is a tertiary carbon atom.
Primary alcohols
[pic]
[pic]
[pic]
STEP 3: Alcohols and their Isomers (15 Minutes).
o Chain isomerism.
o Position isomerism.
o Functional isomerism.
Chain isomerism
to the different structure of C-skeleton in the longest chain.
[pic]
Position isomerism
a different position of a hydroxyl group (OH).
Example
[pic]
Functional isomer
The functional isomer of an alcohol is ether.
Example
[pic]
STEP 4: Nomenclature of Alcohols (15 minutes).
are similar to those for other classes of compounds.
give the location of the hydroxyl group
Rules
1. Select the longest continuous carbon atom chain containing the carbinol
(hydroxyl) group(s).
2. Number the chain, giving the hydroxyl (alcohol) substituent(s) the
lowest number possible.
3. Name the longest chain as an alkane, but drop the terminal -e and add
-ol. Ethane would become ethanol.
4. For monohydric alcohols the letter ‘-e’ at the end of the root name is
replaced by the ending ‘-ol’ with a number, when necessary, to show the
position of the –OH group on the carbon skeleton.
[pic]
5. If more than one hydroxyl group is present (for polyols i.e.
dihydric,trihydric etc.) the name becomes -diol, -triol, etc. and the
terminal -e in the parent name is not dropped from the alkane name.
But the letters ‘diol’ ‘triol’ etc & numbers 1,2,3 etc are added to the
ending to show how many –OH groups & their position
needs to specify where the hydroxyl groups are attached.
(vicinal) carbon atoms.
diol rather than 1,2-ethanediol.
6. Indicate by numbers the positions of other groups attached to the
parent chain
[pic]
[pic]
group it locates (-ol), giving the name 1-bromo-3,3-dimethylbutan-2-
ol.
7. Cyclic alcohols are named using the prefix cyclo-; the hydroxyl
group is assumed to be on carbon number 1, C1.
[pic]
[pic]
STEP 5: Chemical Structure of Alcohols (15 minutes).
positioned on the chain of carbon atoms. There are some chemical
differences between the various types.
Primary alcohols
is only attached to one alkyl group. Some examples of primary alcohols
are shown below:
[pic]
group holding the -OH group.
alcohol even though there are no alkyl groups attached to the the -OH
carbon atom.
In a secondary (2°) alcohol, the carbon atom with the -OH group attached is
joined directly to two alkyl groups, which may be the same or different.
Examples include the following:
[pic]
attached directly to three alkyl groups, which may be any combination of
the same or different groups.
[pic]
STEP 6: Chemical Properties of Alcohols (15 minutes).
|Activity: Buzzing (5minutes) |
| |
|ASK students to pair up and buzz on the following question for 5 |
|minutes |
| |
|What are the chemical properties of Alcohols? |
| |
|ALLOW pairs to respond on the question |
| |
|WRITE their response on the flip chart/board |
| |
|CLARIFY and SUMMARIZE by using the content below |
The following are some chemical properties of alcohols
o Alcohols burns in oxygen to produce carbon dioxide and water. An
alcohol burns cleanly and easily and does not produce soot.
o It becomes increasingly more difficult to burn alcohols as the
molecules get bigger.
o The general molecular equation for the reaction is:
CnH2n+1OH + (1.5n)O2 → (n+1)H2O + nCO2
o Dehydration of alcohols is done by heating with concentrated sulfuric
acid, which acts as the dehydrating agent, at 180°C.
o This reaction uses alcohols to produce corresponding alkenes and water
as byproduct.
[pic]
o Primary alcohols (R-CH2-OH) can be oxidized either to aldehydes (R-
CHO) or to carboxylic acids (R-CO2H), while the oxidation of secondary
stage.
o Tertiary alcohols (R1R2R3C-OH) are resistant to oxidation.
o e.g. oxidation of ethanol:
C2H5OH + [O] → CH3COOH + H2O
o Oxidation can be done by using oxidising agents such as acidified
potassium dichromate (VI), acidified potassium manganate (VII) etc
o Alcohols can be reacted with carboxylic acid to form esters.
[pic]
STEP 7: Chemical Reactions involving Alcohols (35 minutes).
|Activity: Small Group Discussion (15 minutes) |
| |
|DIVIDE students into small groups. |
| |
|ASK students to discuss in groups on the following questions. |
|What are the chemical reactions involving Alcohols? |
| |
|[pic]REFER Students to Book |
| |
|ALLOW students to discuss for 10 minutes. |
| |
|ALLOW each group to present for 5 minutes. |
| |
|CLARIFY and SUMMARIZE by using the contents below |
o Oxidation products depend on whether the alcohol is 1o, 2o or 3o.
o In oxidation one or more hydrogen atoms are lost from the carbon
having OH group
o Primary and secondary alcohols are easily oxidized by a variety of
reagents, including chromium reagents, permanganate, nitric acid, and
even household bleach (NaOCl, sodium hypochlorite).
o Oxidation of a primary alcohol initially forms an aldehyde.
o Unlike a ketone, however, an aldehyde is easily oxidized further to
give a carboxylic acid.
[pic]
o Chromic acid generally oxidizes a primary alcohol all the way to the
carboxylic acid.
[pic]
o A better reagent for the limited oxidation of primary alcohols to
aldehydes is pyridinium chlorochromate (PCC), a complex of chromium
trioxide with pyridine and HCI.
[pic]
o Secondary alcohols are easily oxidized to give excellent yields of
ketones.
o The chromic acid reagent is often best for laboratory oxidations of
secondary alcohols.
[pic]
[pic]
Example:
[pic]
o Oxidation of tertiary alcohols is not an important reaction in organic
chemistry.
o Tertiary alcohols have no hydrogen atoms on the carbinol carbon atom,
so oxidation must take place by breaking carbon-carbon bonds.
o These oxidations require severe conditions and result in mixtures of
products.
[pic]
Summary of alcohol oxidations
[pic]
o Two other strong oxidants are potassium permanganate and nitric
acid.
o Both of these reagents are less expensive than the chromium
reagents, and both of them give byproducts that are less
environmentally hazardous than spent chromium reagents.
o Both permanganate and nitric acid oxidize secondary alcohols to
ketones and primary alcohols to carboxylic acids.
o Dehydration requires an acidic catalyst to protonate the hydroxyl
group of the alcohol and convert it to a good leaving group.
o Loss of water, followed by loss of a proton, gives the alkene
o Dehydration results from E1 elimination of the protonated alcohol
o Example:
[pic]
o Alcohol dehydrations generally take place through the E1 mechanism.
o Protonation of the hydroxyl group converts it to a good leaving
group.
o Water leaves, forming a carbocation.
o Loss of a proton gives the alkene.
[pic]
[pic]
o Because the rate limiting step is formation of a carbocation, the
ease of dehydration follows from the ease of formation of
carbocations: 3° > 2° > 1
o As in other carbocation reactions, rearrangements are common.
o Alcohols can combine with many kinds of acids to form esters.
o When no type of acid is specified, the word ester is assumed to
mean a carboxylic ester, the ester of an alcohol and a carboxylic
acid.
o The reaction, called Fischer esterification, is characterized by
the combining of an alcohol and an acid (with acid catalysis) to
yield an ester plus water.
[pic]
o Under appropriate conditions, inorganic acids also react with
alcohols to form esters.
reagents and conditions can be used.
[pic]
Acidity of alcohols: formation of alkoxides
acidic as water, and most other alcohols are somewhat less acidic.
atom of an alcohol.
by reducing the proton to hydrogen gas.
[pic]
an alkoxide ion on an alkyl halide.
Summary of common reactions of alcohols
[pic]
STEP 8: Key Points (10 minutes)
group bonded to an sp3 hybridized carbon atom.
tertiary, depending on the carbon atom bonded to the – OH group.
or to carboxylic acids (R-CO2H), while the oxidation of secondary
STEP 9: Evaluation (10 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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