NTA Level 5 • Semester 1 • PST05106

Esters of Pharmaceutical Importance

Pharmaceutical Organic Chemistry • Source Session/Topic 13

Full source-text version: all educational wording from the extracted learning source is retained; only presenter/tutor metadata and web-layout noise are removed, while formatting is improved for readability.

Session 13: Esters 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:

• Define esters

• Explain nomenclature of esters

• Draw chemical structure of esters

• List chemical properties of esters

• Explain chemical reactions of esters

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

SESSION OVERVIEW

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 Esters (10 minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What is Ester? |

| |

|ALLOW few students to respond. |

| |

|WRITE their responses on the flip chart/ board. |

| |

|CLARIFY and SUMMARISE by using the content below |

• An ester (“carboxylic ester” in the textbook) is a derivative of a

carboxylic acid in which there is a carbon group connected to the single-

bonded oxygen:

• In an ester, The H in the carboxyl group is replaced with an alkyl group.

[pic] [pic]

Some common esters are as follows;

[pic]

STEP 3: Nomenclature of Esters (15 minutes).

• Name the alkyl or aromatic portion contributed by the “alcohol part”

first.

[pic]

• The “acid part” is named as a carboxylic acid, with the -ic acid suffix

changed to -ate

[pic]

STEP 4: Chemical Structure of Esters (15 minutes).

• Esters contain a carbonyl center, which gives rise to 120-degree C-C-O

and O-C-O bond angles due to sp2 hybridization.

• Unlike amides, esters are structurally flexible functional groups because

rotation about the C-O-C bonds has a lower energy barrier.

• Their flexibility and low polarity affect their physical properties on a

macroscopic scale.

• They tend to be less rigid, leading to a lower melting point, and more

volatile, leading to a lower boiling point, than the corresponding

amides.

• The pKa of the alpha-hydrogens, or the hydrogens attached to the carbon

adjacent to the carbonyl, on esters is around 25, making them essentially

non-acidic except in the presence of very strong bases.

[pic]

• An ester is characterized by the orientation and bonding of the atoms

shown, where R and R’ are both carbon-initiated chains of varying length,

also known as alkyl groups.

• As usual, R and R’ are either alkyl groups or groups initiating with

carbon.

• Esters are derivative of carboxylic acids where the hydroxyl (OH) group

has been replaced by an alkoxy (O-R) group.

• They are commonly synthesized from the condensation of a carboxylic acid

with an alcohol.

STEP 5: Chemical Properties of Esters (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 Esters? |

| |

|ALLOW pairs to respond on the question |

| |

|WRITE their response on the flip chart/board |

| |

|CLARIFY and SUMMARIZE by using the content in the table 1 below |

In acid hydrolysis

• An ester reacts with water to produce a carboxylic acid and an alcohol.

• An acid catalyst is required.

[pic]

Base hydrolysis

Base hydrolysis is the reaction of an ester with a strong base. Produces

the salt of the carboxylic acid and an alcohol.

[pic]

STEP 6: Chemical Reactions involving Esters (40 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 Esters? |

| |

|[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 |

Esterification Reaction

• The simplest way to synthesize an ester is to heat a carboxylic acid with

an alcohol or phenol (plus an acid catalyst).

o The oxygen of the alcohol adds to the carboxyl group, splitting out

a molecule of water in the process (an esterification reaction).

[pic]

• Since this reaction is a reversible reaction, it often reaches an

equilibrium with a large amount of unreacted starting material still

present.

• Better yields are obtained using either acid chlorides or acid anhydrides

as starting materials.

o These reactions are nonreversible

[pic]

Examples

[pic]

Ester Hydrolysis

• Esters may be broken apart under acidic conditions by water (a hydrolysis

reaction) to form a carboxylic acid and an alcohol.

[pic]

• This is essentially the reverse reaction of the synthesis of esters from

carboxylic acids and alcohols.

Base hydrolysis (Saponification)

Esters may be broken apart under basic conditions by sodium hydroxide (lye)

or potassium hydroxide to form carboxylate salts and alcohols.

[pic]

This reaction is important in the production of soaps

STEP 8: Key Points (05 minutes)

• An ester is a chemical compound derived from carboxylic acid in which

at least one –OH (hydroxyl) group is replaced by an –O–alkyl (alkoxy)

group.

• An ester reacts with water to produce a carboxylic acid and an alcohol.

• Esters may be broken apart under acidic conditions by water (a hydrolysis

reaction) to form a carboxylic acid and an alcohol.

STEP 9: Evaluation (10 minutes)

• What are esters?

• How are the esters named?

• Write general chemical structure of esters.

• What is saponification?

References

Ternay, A.L (1976). Contemporary Organic Chemistry. Philadelphia, United

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.). Calfornia, United

States: Lippincott Williams

Bhassin S.K, Gupta R. (2013). Pharmaceutical organic chemistry (E-book

Kindle edition). New Delhi, India: Elsevier Publishing Services

← Previous Topic Next Topic →View all Pharmaceutical Organic Chemistry topics Open Complete Full Notes

PDF / OFFLINE NOTES

Unataka kutumiwa notes hizi kupitia WhatsApp?Kwa notes zilizopangiliwa vizuri kwa kusoma offline au PDF, bonyeza kitufe hapa chini. Ujumbe wenye Level, Semester, Module na Topic utaandaliwa moja kwa moja.TUMIWA NOTES WHATSAPP

WhatsApp: 255620339260