10.2 PART 2NOTE: PARTS OF THIS POWERPOINT WERE FOUND ON THE WEB. IF YOU WANT THE SOURCES PLEASE LE ME

KNOW

Reactions containing

oxygen and

halogenalkanes

ALCOHOL REACTIONS

Alcohols contain an –OH group covalently bonded to a carbon atom.

However, this –OH group does not behave in the same way as the hydroxide ion OH– because NaOH is a base and CH3OH is not.

Alcohols, when dissolved in water, do not alter the pH of the water.

Although the hydrogen atom is connected to an oxygen atom, alcohols do not readily donate the proton (they are weaker acids than water).

ALCOHOL REACTIONS

Like the alkanes and alkenes, alcohols undergo completecombustion in a plentiful supply of oxygen gas, producing only

carbon dioxide and water as products.

When balancing an equation for the combustion of an alcohol it is important to remember that there is an oxygen atom in the alcohol, unlike alkanes and alkenes

The complete combustion of propanol is as follows:

ALCOHOL REACTIONS

The process of oxidation was defined as the loss of electrons.

In organic chemistry oxidation is easily recognized as the gain of oxygen or the loss of hydrogen from a compound.

The oxidation reactions of alcohols vary, depending upon the type of alcohol involved.

Primary, secondary and tertiary alcohols all give different reactions with strong oxidizing agents such as acidified potassium dichromate(VI) solution or acidified potassium manganate(VII) solution.

When these oxidation reactions are performed in a laboratory investigation, the change in colour of the oxidizing agent indicates that the reaction has proceeded.

Potassium dichromate, K2Cr2O7, changes colour from orange (Cr2O72-) to

green (Cr3+) during this reaction. If potassium manganate(VII), KMnO4, is used instead, it changes colour from purple to colourless.

ALCOHOL OXIDIZES TO CARBOXYLIC ACID

In the laboratory, when an aqueous solution of a primary alcohol such as ethanol is mixed with potassium dichromate (VI) and sulfuric acid, and the mixture heated under reflux, the alcohol is fully oxidized to a carboxylic acid.

During the process, the alcohol is initially oxidized to an aldehyde; however, by heating under reflux the aldehyde is further oxidized to a carboxylic acid.

When the reaction is ‘complete’, the condenser is turned around and the reaction mixture is distilled to collect an aqueous solution of the carboxylic acid.

If the aldehyde is the desired product during this reaction, then the reaction can be carried out at room temperature and the aldehyde can be distilled off from the mixture.

PRIMARY ALCOHOL OXIDIZES TO CARBOXYLIC ACID

PRIMARY ALCOHOL OXIDIZES TO CARBOXYLIC ACID

The oxidation reaction of the primary alcohol (e.g. ethanol) to a carboxylic acid may be represented simply by an equation in which the symbol [O] represents the oxygen supplied by the oxidizing agent:

8. OXIDATION OF PRIMARY ALCOHOL TO ALDEHYDESubtraction: Remove -H from alcohol group

Remove -H from alcohol carbon

HO

H

CH2

H2C

H3COH

C

H2C

H3CO

H

H

H + (O)

CH

H2C

H3CO

SECONDARY ALCOHOL OXIDATION

A secondary alcohol has the hydroxyl group on a carbon that is bonded to two other carbons. Propan-2-ol and butan-2-ol are examples of secondary alcohols.

SECONDARY ALCOHOL OXIDATION

When secondary alcohols are oxidized, ketones are formed.

This reaction is very similar to the one in which aldehydes are produced, but the placement of the hydroxyl group results in the production of a ketone rather than an aldehyde and, ultimately, a carboxylic acid.

SECONDARY ALCOHOL OXIDATION

The oxidation reaction of a secondary alcohol such as propan-2-ol to a ketone may be represented simply as:

9. OXIDATION OF SECONDARY ALCOHOL TO KETONESubtraction: Remove -H from alcohol group

Remove -H from alcohol carbon

HO

H

+ (O)

CH3

CHH3C

OH

CH3

CH3C

OH

H

CH3

CH3C

O

TERTIARY ALCOHOL OXIDATION

Tertiary alcohols, those with the hydroxyl group bonded to a carbon atom that is bonded to three other carbon atoms, are not easily oxidized.

An example of a tertiary alcohol is 2-methylpropan-2-ol.

REACTIONS OF ALCOHOLS

15

ESTERS

In an ester,

The H in the carboxyl group is replaced

with an alkyl group.

O

CH3 — C—O—CH3

ester group

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Publishing as Benjamin Cummings

ESTERS

Formed when an alcohol reacts with a carboxylic acid.

An acid catalyst used (usually sulphuric acid)

A condensation reaction

The condensation reaction between the hydroxyl group and the carboxylic acid known as esterification.

Reverse reaction = ester hydrolysis

This is why it is a condensation reaction because water is produced!

R

R’C

H2O

+

O H

H O

OR’C

R O

O

+

⇋

Definition of a condensation reaction =

two molecules reacting to form a larger

molecule with the elimination of a

small molecule such as water

R

R’C

H2O

+

O H

H O

OR’C

R O

O

+

⇌

FORWARD REACTION = condensation reaction,

the esterification of an alcohol using

acid catalyst under reflux.

REVERSE REACTION = ester hydrolysis, same

catalyst works for both forward & reverse

reactions.

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Esterification is

The reaction of a carboxylic acid and alcohol in the presence of an acid catalyst to produce an ester.

O

H+

CH3—C—OH + H—O—CH2—CH3

O

CH3—C—O—CH2—CH3 + H2O

ethyl acetate (an ester)

ESTERIFICATION

POLAR BONDS AND NUCLEOPHILESThe carbon–halogen bond in halogenoalkanes is polar because all

halogens are more electronegative than carbon.

The polar bond means that the carbon atom has a small positive

charge (δ+), which attracts substances with a lone pair of

electrons. These are nucleophiles, meaning ‘nucleus (positive

charge) loving’. Examples include:

δ+ δ- δ+ δ- δ+ δ- δ+ δ-

ammonia cyanide hydroxide

Nucleophiles (Nu-) attack the carbon of a

carbon–halogen (C–X) bond, because the

electron pair on the nucleophile is

attracted towards the small positive

charge on the carbon.

REACTION WITH NUCLEOPHILES

The electrons in the C–X bond are repelled

as the Nu- approaches the carbon atom.

δ+ δ-

The Nu- bonds to the carbon and the C–X

bond breaks. The two electrons move to the

halogen, forming a halide ion.

The halide is substituted, so this is a

nucleophilic substitution reaction.

HALOGENOALKANES NUCLEOPHILIC SUBSTITUTION REACTIONS

There are three that you should be familiar with:

Reagent Aqueous* sodium (or potassium)hydroxide

Product Alcohol

Nucleophile hydroxide ion (OH¯)

Equation

e.g. C2H5Br(l) + NaOH(aq) ——> C2H5OH(l) + NaBr(aq)

HALOGENOALKANES NUCLEOPHILIC SUBSTITUTION REACTIONS

There are three that you should be familiar with:

Reagent Aqueous, alcoholic potassium (or sodium) cyanide

Product Nitrile (cyanide)

Nucleophile cyanide ion (CN¯)

Equation

e.g. C2H5Br + KCN (aq/alc) ——> C2H5CN + KBr(aq)

HALOGENOALKANES NUCLEOPHILIC SUBSTITUTION REACTIONS

There are three that you should be familiar with:

Reagent Aqueous, alcoholic ammonia (in EXCESS)

Product Amine

Nucleophile Ammonia (NH3)

Equation

e.g. C2H5Br + 2NH3 (aq / alc) ——> C2H5NH2 + NH4Br

25

Electrophilic Aromatic Substitution

• The characteristic reaction of benzene is electrophilic aromatic

substitution—a hydrogen atom is replaced by an electrophile.

Background

26

• Benzene does not undergo addition reactions like other

unsaturated hydrocarbons, because addition would yield

a product that is not aromatic.

• Substitution of a hydrogen keeps the aromatic ring

intact.

• Electrophiles are things that love electrons because they

lack electrons themselves

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• In halogenation, benzene reacts with Cl2 or Br2 in the

presence of a Lewis acid catalyst, such as FeCl3 or

FeBr3, to give the aryl halides chlorobenzene or

bromobenzene respectively.

• Analogous reactions with I2 and F2 are not synthetically

useful because I2 is too unreactive and F2 reacts too

violently.

Halogenation