- Organic Reactions

Mr. Shields Regents Chemistry U17 L03

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 7:

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

- Polymerization (Condensation & Addition)

Substitution Rxns

• 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)• Need ultraviolet light to initiate the reaction

– Provides the energy of activation 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 are the products formed in the following rxn?

CH3CH3 + Br2 sunlight

CH3 CH2Br + HBr

(What is the purpose of the sunlight?)

Let’s look at how this reaction occurs?

1. Br-Br 2Br uv

2. R-H + Br H-Br + RA free radical

3. R + Br2 R-Br + Br

Substitution RxnsAnother example of a substitution reaction isThe replacement of a halogen with a hydroxyl group

CH3CH2CL + NaOH(aq) CH3 CH2OH + NaCl

Or the replacement of a halogen with an amine group

CH3CH2CL + NH3 CH3 CH2NH2 + HCl

Elimination Rxns

• Any reaction in which atoms are eliminated from another molecule

• This can be done by

– Elimination of H2

– Elimination of HX

Elimination Rxns

-Loss of H2

- This process is often referred to as Dehydrogenation

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

Elimination Rxns

-Loss of HX (X = a halogen)

-Also known as dehydrohalogenation

H H H-C-C-H (g) + Heat H2C=CH2 + HX (g) H X

Addition

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

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

• What are some examples of molecules that can be added?

– X2

– H2

– HX– H2O

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

H2C=CH2 + H2 Heat, catalyst

H HH-C-C-H H H

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

Addition• Addition of Water

- Water adds across a double bond to form an alcohol- Water can add across a triple bond to form a diol

H2C=CH2 + H-OH H HH-C-C-H H OH

HC=CH + H-OH H-C-C-H H OH

H HH-C-C-H HO OH

+ HOH

Esterification• Alcohol + Organic Acid = Water + Ester• Used to make perfumes, scents and flavors• Combination rxn which involves dehydration (Loss of water).• The alcohol becomes the alkyl group & the acid becomes -oate

propyl ethanoate

From the acidFrom the alcohol

alcohol

acid

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

CH3CH2OH + HCOOH

CH3CH2COOH + CH3CH2CH2OH

Name the Esterification Products

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– Dates back to at least 6000 B.C.– 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

• Triglycerides,from fats, and 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

+

1,2,3-propanetriolCarboxylate salt

An ester

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 two monomers alternate are used to form an alternating polymer (ex: Nylon or Polyesters)

Natural polymers

Example of “natural” polymers in nature abound:

Some examples are:

WoolCottonStarchProteinCellulose

PolymerizationThere are two methods we’ll look at for the Production of Polymers:

- Addition polymerization

- Condensation polymerization

Addition Polymerization

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

-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 Styrene to form polystyrene

Monomer

Addition Polymer

Notice loss of electron pair to form Connecting bonds in polymer

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 have functional groups that are different

- reaction occurs between the two pairs of dissimilar functional groups

Let’s look at some examples …

One example of Condensation Polymerization - Dacron

Di-Acid Di-Alcohol

Formed by loss of water

A polyester

Monomer A Monomer B

Condensation Polymerization - Nylon

Formed by loss of water

An amide group A Polyamide

I’m Done! You’re Done!

WE Made it to the End!

Only the regents is left !!