- Organic Reactions

Organic Reactions

- We described hydrocarbons and looked at their structural isomers

- We reviewed how to name hydrocarbons and compounds containing functional groups

We’re now going to focus on a several kinds ofOrganic reactions

Organic Reaction Types

There are in fact so many types of organic rxn’sIt would be impossible to review them all.

Therefore we’re going to focus on just a few:

- Substitution - Elimination- Addition - Esterification- Fermentation - Saponification

- Polymerization (Condensation & Addition)

Substitution Reactions

• Any reaction in which one atom is replaced by another• Used to place a halogen onto an alkane• The products always are a halocarbon and the acid of

the halogen (ex: hydrobromic acid)• Needs ultraviolet light to initiate the reaction

– Provides the high energy needed to form the excited state

CC

H

H

H

HH

H

+ Cl2

hv

CC

H

H

H

Cl

H

H

+ HCl

Substitution Rxns

What is the products formed in the following rxn?

CH3CH3 + Br2 sunlight

CH3 CH2Br + HBr

(Why sunlight?)

Elimination Rxns

• Any reaction in which atoms are eliminated from another molecule

• This can be done by

– Elimination of H2

– Elimination of HX

– Elimination of H20

Elimination Reactions

-Loss of H2

- This process is often referred to as Dehydrogenation

H H H-C-C-H H2C=CH2 + H2 H H Heat, catalyst

This type of rxn takes place in industry in what is know as a catalytic cracking unit

Elimination Rxns

-Loss of HX-Alkyl halides can also undergo elimination. This is as known as dehydrohalogenation

H H H-C-C-H H2C=CH2 + HX H X Base (ex KOH)

The base extract a proton (H+) and X- leaves

Elimination Rxns

-Loss of H2O-Alcohols can undergo elimination via the loss of water. This is known as dehydration

H H H-C-C-H H2C=CH2 + H2O H OH Acid, heat

a) The acid protonates the –OH group, water leaves Positive carbon remains behindb) An adjacent proton (H+) leaves next leaving the electron pair to form the double bond

Addition

• Takes place with unsaturated compounds which are usually more reactive that saturated compounds

– Takes place with both Double and Triple bonds– Two atoms are added across the electron rich bond

• What can be added?– X2

– H2

– H2O

– HX

Addition

• Addition of halogen– Normally occurs dissolved in a solvent such as CCl4– Alkenes form dihaloalkanes– Alkynes produce dihaloalkenes or tetrahaloalkanes

CC

H

H

H

H

+ Cl2 CC

H

H

H

H

ClCl

1,2-dichloroethane

Addition

• Addition of Hydrogen– Catalysts normally used such at Pt, Pd or Ni

• Known as Hydrogenation– Alkene becomes an alkane– Alkyne becomes and alkene or alkane

H2C=CH2 + H2 Heat, catalyst

H HH-C-C-H H H

Addition

• Addition of Water– Occurs in the presence of acid (H+)

• Known as Hydration– Alkene becomes an alcohol– Alkynes do not produce alcohols this way! (produces ketone or aldehyde)

Addition

• Addition of Hydrogen Halides (HX)– HX = HCl, HBr, HI (Not HF)– Alkene becomes an alkyl Halide– Alkynes form Monohalo alkenes or dihaloalkanes with the halogens on the same carbon

H2C=CH2 + HX H HH-C-C-H H X

HC=CH + HX H-C-C-H H X

H XH-C-C-H H X

+ HX

Esterification• Alcohol + Organic Acid = Water + Ester• Used to make perfumes, scents and flavors• Combination reaction which involves dehydration.• The alcohol becomes the alkyl group and the acid

becomes -oate

Methyl propanoate

Aspirin – Made by Esterification

H-O-C-CH3

O +

HO C=O

OH

HO C=O

O-C-CH3

O

Salicylic Acid

Acetyl Salicylic Acid(Common Name)

“Aspirin”

(An alcohol and acid)

Acetic acid

Fermentation• Fermentation is the process by which glucose is broken

down by an enzyme (a catalyst) in the absence of oxygen into an alcohol and carbon dioxide

• One enzyme used is Zymase (Found in baker yeast)– If Zymase is used the alcohol produced is ethanol

• The oldest chemical reaction practiced by man– In place of glucose, starches from grains can be used.

Hence the name grain alcohol

C6H12O6 2C2H5OH + 2CO2

Glucose Ethanol Carbon dioxide

Zymase

Saponification• Another very old chemical reaction practiced by man

• The hydrolysis of the ester bonds (back to acid + alcohol) in triglycerides using an aqueous sol’n of a strong base to form carboxylate salts and glycerol

• Hydrolysis of fats by a strong base (KOH or NaOH)– Products are soap and glycerol (a triol)

OCH2-0-C-(CH2)14CH3

| OCH2-O-C-(CH2)14CH3

| OCH2-0-C-(CH2)14CH3

+ 3KOH

OCH2-0H K+ -O-C-(CH2)14CH3

| OCH2-OH K+ -O-C-(CH2)14CH3

| OCH2-0H K+ -O-C-(CH2)14CH3

A TRIGYCERIDE GLYCEROL 3 SOAP MOLECULES

+

PolymersThe joining together of many smaller repeating Units to form a very high MW molecule

- Polymers range from 10,000 amu to more than 1,000,000 amu

The small repeating units used to build the polymerare known as monomers

Monomers

a b a b a b a

a a a a a a a

Sometimes just one monomer is used to make the Polymer(example: ethylene (a) to form polyethylene)

And sometimes several monomers are used (example:adipic acid (a) and 1,6-diaminohexane (b) to form nylon)

PolymerizationThere are two methods we’ll quickly look at forForming Polymers.

- Addition polymerization

- Condensation polymerization

Addition Polymerization

-All the atoms present in the monomer are retained in the polymer

-This type of reaction involves monomers with double or triple bonds

-An initiator is required to produce a free radical-A very reactive substance having a free e-

-Peroxides are typically used to produce this free radical

Peroxide Rad

Rad

Rad

Free radical induced addition polymerization of Ethylene to form polyethylene

Free radical induced addition polymerization of Propylene to form polypropylene

Free radical induced addition polymerization of Styrene to form polystyrene

The codes tell you what kind of material the polymer is made of

Condensation Polymerization

- Monomers that join together by the loss of water

- each monomer has two functional groups that are the same

- monomer 1 and monomer 2 functional groups are different

- reaction occurs between the two pairs of dissimilar functional groups

Let’s look at some examples …

Condensation Polymerization - Dacron

Condensation Polymerization - Nylon

Adipic acid monomer 1,6-diaminohexane monomer

We’re Done!

You Made it to the End!