chemistry notes(organic)

8/13/2019 Chemistry Notes(Organic)

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Oxidation with Fehlings of Benedicts solution

Reagents : contain complexed ions in an

Solution

Why Cu2+

ions are complexed?

- to prevent precipitation of Cu(OH)2

Steps: A few drops of the aldehyde or ketone are added

to the reagent. The mixture is warmed gently.

Results :

Ketone : No change in the blue solution

Aldehyde : A red brown precipitate of copper (I) oxide

Half-equations:

Overall equation:

Oxidation with Tollens Reagent (silver mirror test)

Reagents : contain diamminesilver(I) ions,

How to make? Add silver(I) nitrate solution and diluteammonia

Steps : A few drops of the aldehyde or ketone are

added to the reagent. The mixture is warmed gently.

Results:

Ketone : No change in the colourless solution

Aldehyde : produce silver mirror on the test tube

Half-equations:

Overall equation:

Oxidation with acidified potassium dichromate (VI) solution

Reagents : dilute sulfuric acid and potassium dichromate (VI) solution

Steps: Half-equations:

Results: Overall equation:

Ketone : No change in the orange solution Aldehyde : orange solution turns green


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Reduction

Reducing agents : in dry ether (ethoxyethane) or sodium tetrahydridoborate

(NaBH4) in ethanol Conditions: room temperature

LiAlH4: more reactivecan reduce esters, amides and carboxylic acids

: reacts violently with water and alcohol. (reaction must be in dry condition)

Aldehyde : Reduced into 10alcohol Ketone: Reduced into 2

0

Equation : + 2[H] Equation: + 2[H]

*CANNOT REDUCED C=C BOND. Reducin a ent for C=C BOND : H with nickel or latinum catal st

Nucleophilic addition

Reagents : HCN (Hydrogen cyanide) in the presence of KCN in cold alkaline condition

Nucleophile attacks the +Carbon atom

Why must have KCN? To produce sufficient CN-ion

Equation :

Mechanism : 1) with ethanal: produce 2-hydroxypropanenitrile

2) with propanone : produce 2-hydroxy-2-methylpropanenitrile


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Stereochemistry in nucleophilic addition

Eg : Ethanal

-ethanal is a planar molecule

- cyanide ion has equal chance of attacking plane of themolecule either from above or below

Mechanism

SN1 nucleophilic substitution in halogenoalkane

-Form a planar intermediate

- nucleophile has equal chance of attacking the planar

intermediate either from above or below

Mechanism

- Form racemic mixture (equal amount of enantiomer)no effect on plane of polarization of the plane-polarised

monochromatic light

- optical isomerism : form molecule with asymmetric carbon atom that has chiral centre (carbon atom that has 4

different groups bonding with it)


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Condensation reaction with Bradys reagent (2,4-dinitrophenylhydrazine)

-to test compound containing carbonyl group such as aldehyde and ketone

Reaction: condensation (a reaction in which two molecules join together to form one big molecule with the loss

of small molecule such as water)

Mechanism: nucleophilic addition-elimination reaction

Equation:

Results : A yellow precipitate

The derivative can be removed by and purified by

Each 2,4-dinitrophenylhydrazine derivatives have characteristic melting temperatures which can be compared

with values given in data books.

Reaction with Iodine in the presence of alkali (NaOH)

- Name : iodoform reaction

- To identify the presence of CH3CO group in aldehydes and ketones or CH3CH(OH) group in alcohols

- Compound which gives positive results : ethanol. Ethanol. Propan-2-ol, butanone

*Equation :

Results : precipitate of triiodomethane (CHI3) which has smell


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Filtration and Recrystallisation Determine Melting Point


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Carboxylic Acid

Preparation

1. of primary alcohols or aldehydes

Reagents :

Conditions : Reflux

Results : Orange solution turns green (chromium (VI)

Compound is reduced to chromium (III) )

Equation:

2. of a nitrile by boiling with a dilute acid

Equation:

Diagram of Reflux

Reductionwith

(lithium aluminium hydride) in

Dry ether

Neutralization to produce salts

-with reactive metal, eg zinc - with ammonia

-with metal hydroxides

- with carbonates and h dro encarbonates

Making acid chloride

- Reagent : Phosphorus (V) chloride or

phosphorus pentachloride

- testOH group

Making ester (reflux)

- Reactions with

in the presence of an


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Making Acid Chloride

Reagent : Solid phosphorus (V) chloride

Results : Steamy acidic fumes of ,

phosphorus trichloride oxide (phosphorus oxychloride)

POCl3, acyl chloride (separated by fractional filtration_

Equation:

- must be dry condition :acyl chlorides react readily

with water vapour

Equation :

Making Ester

Reagent : carboxylic acid, alcohol and strong acid

catalyst : H2SO4 (equilibrium reaction)

Name : (condensation)

Equation :

Alternative : use more reactive acyl chloride or acid

anhydride

Equation :

Neutralisation

Eg Q : to determine the amount of citric acid in fruit


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Acyl chloride

Amines

Results : Produce a substituted amide

Equation :

Concentrated Ammonia

- Take place without heating

- Produce amide

Equation :

Alcohol

Reaction : Esterification

- non-reversible reaction, higher yield of ester

- take place without heating

Equation :

Water

Equation :

- Vigorous reaction

Results : steamy fumes of HCl

*Acid chloride need to be kept dry (water

vapour in air will react with it)


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Additional Reaction : (Unit 5)

1. Phenol

Equation :

CH3COCl + C6H5OH CH3COOC6H5 + HCl

Product : Phenyl ethanoate

- less vigorous as that between alcohols and ethanol chloride

- reactivity of theOH group is modified by the benzene ring

- to manufacture aspirin (2-hydroxybenzoic acid)

2. Friedel-Crafts acylation

Product : Ketone

Reagent : benzene, acid chloride and aluminium chloride (AlCl3) (catalyst)

Equation : C6H6 + CH3COCl + HCL

Benzene ethanoyl chloride phenylethanoate

Mechanism :


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Ester

Hydrolysis with Acid

Equation :

- reversible, small yield

Hydrolysis with Base

Equation :

- saponification (using KOH)

- non-reversible, higher yield

Condensation polymerization (form polyester)

Eg :1. Benzene-1,4-dicarboxylic acid and ethane-1,2-diol =

- making plastic bottles

alternative : diacyl chlorides, diacid anhydrides

2. Nylon: make at room temperature, non-biodegradable

Equation :

Transesterification

1. reaction of vegetable oils (triglyceride or ester) with methanol

or ethanol

Reagent : sodium hydroxide (catalyst)

Product: methyl ester (biodiesel-greener fuel)

- very efficient (yield of 98%)

- low temperatures (50C) and atmospheric pressure

-cheap and readily available catalyst

Equation:

2. reaction of an ester with an acid (manufacture margarine)

Adv : produce fewer trans fats compared with hydrogenation

(nickel catalyst)


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rt

Benzene or

methylbenzene

Combustion

Observation : yellow flame (incomplete combustion)

Equation :

(Benzene) 2C6H6 + 15O2 CO2 + H2O

(Methylbenzene) C6H5CH3 + 9O2 CO2 + H2O

(Addition reaction) hydrogenation

Reagent: Raney nickel catalyst (finely divided with a

very large surface area and very high catalytic

activity)

Temperature : 150C

Equation :

(Benzene) + 3H2

(Methylbenzene)

Halogenation

1. Addition reaction (only for benzene) = free radical reaction

Condition : UV light Product : 1,2,3,4,5,6-hexachlorocyclohexane

Equation :

(benzene) + 3Cl2 uv, heat

2. electrophilic substitution

Condition : catalyst of iron (III) bromide or iron filings (halogen carrier)

Temperature : room temperature Equation for catalyst : 2Fe + 3Cl2 2FeCl3

Equation :


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Benzene or

methylbenzene(toluene)

Nitration

(Benzene)

Reagent : concn nitric acid and concn sulfuric acid (catalyst) [nitrating mixture]

Temperature : 55C

- Both H2SO4 and HNO3are corrosive -HNO3is powerful oxidant

- Electrophile is nitronium ion, NO2+

-Equation for electrophile : HNO3 + 2H2SO4

- nitric acid acts as a base and accepts protons from the sulfuric acid

Product:nitrobenzene* use to produce phenylamine (C6H5NH2) for diazonium dye

(Methylbenzene or toluene) : use same reagent but at lower temperature

WHY?

Temperature :

- above 55C further substitution

HOW?

- Use cold water and slow dropwise

addition of benzene to the mixture

to maintain temperature

-exothermic reaction : acid react

and give out heat

Sulphonation (replace withSO3H)

-Reagent : fuming sulfuric acid ( concn H2SO4contains sulfur trioxide)

- Electrophile:sulfur trioxide Product : acid

- Temperature : room temperature

Equation :

+ H2SO4

C6H6 + H2SO4 ____ + H2O

FriedelCrafts reaction (electrophilic

substitution)

1. Alkylation 2. Acylation

- Reflux benzene with a halogenoalkane/ acyl

chloride

- halogen carrier catalyst :AlCl3

Product : alk lbenzene/ ketoneMethylbenzene is more reactive as methyl group donate electron density to the ring making

it more susceptible for electrophilic attack.


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Mechanism of Electrophilic substitution reactions

Halogenation Nitration

Alkylation (Friedel-Crafts reaction) Acylation (Friedel-Crafts reaction)


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Phenol

- oxygen atom on hydroxyl group of a phenol has two lone pairs electrons

- one of the lone pairs on oxygen atom donate electron density into its benzene ring, making it more susceptibleto electrophilic attack.

- make phenol more acidicthan alcohol

-its a weak acid it is fairly insoluble in water reacts with NaOH produces sodium phenoxide (colourless

solution) doesnt react with Na2CO3or hydrogencarbonate solutions (very weakly acidic) reacts with Na

to produce sodium phenoxide and hydrogen gas

Reaction with bromine water

- without heating and catalyst

Results : 1. bromine water is decolourised

2. white precipitate of 2,4,6-tribromophenol

3.smell of antiseptic

Equation :

Reaction with dilute nitric acid

- reagent: dilute nitric acid

Results : white precipitate of 2,4,6-trinitrophenol

Equation :

Coupling reactions of diazonium ions : making azo dye

Condition : ice cold alkaline solution (NaOH) of phenol and benzenediazonium chloride solution

* Benzenediazonium ion carries a positive charge and is a strong electrophile

* coupling : joing two aromatic rings together

- no N2gas is produced

Equation :


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Smell :fishy or smell of decay

Solubility : 1,2 & 3 can form

hydrogen bonds with H2O

Boiling point: 1>2 > 3

- no H bonding in 3 amine

Alkaline nature :

-methyl amine > ammonia >phenyl amine

- It has a lone pair on nitrogen

atom

Equations:

1. bases (amine)

(phenylamine)

2. form salts (amine)

(phenylamine)

Complex ion formation with copper (II)

ions (ligand exchange)

Results: blue precipitate dissolves to

form a deep blue solution

Equation:

Treatment with ethanoyl chloride (Ethanoylation) and

halogenoalkanes (condensation)

- amine acts as _____, product : amide(ethanoylation)

2& 3Amine (condensation)

Eg: making paracetamol using 4-nitrophenol with tin and

HCl (reduction)

Equation :

Reaction of phenylamine with nitrous acid to form _________

1. Prepare nitrous acid, HNO3in situ, HNO3unstable ( at room temperature) : Reagent: _____NaNO3,

Equation : NaNO3 + ______ Condition : ice-water mixture, temp: below___

If tempt above ___, it will produce _______. If tempt below ___, it will produce ____

Equation for tempt> 5C : Equation for tempt< 5C :


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Amide

Preparation : (Name : ethanoylation : replacement of a Hydrogen atom attached to a nitrogen or oxygen atom by CH3CO- using ethanoyl

chloride or ethanoic anhydride)

1. Reaction of an amine with ethanoyl chloride 2. Reaction of an ammonia with an acid chloride

Equation : Equation :

Benzenediazonium ions

- very unstable

Displacement structure

- a strong electrophile due to the positive

char e on one nitro en atom

Laboratory Preparation of benzenediazonium compound

Reagent : Steps:

Temperature :

Condition :Ice bath

Coupling reaction with phenol in cold NaOH to form a dye

Equation :

Diazonium compound

stable, unreactive

- dye ~ can form hydrogen

bonds with groups in cotton

and wool

- coloured dye ~ extensive

delocalized electron system

that spread across the entire

molecule through N N coupling

Manufacture of Paracetamol

Steps : Advantage : no chiral centre in paracetamol molecule

- 100% atom economy - manufacturing process easier (no filtration)


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POLYMERIZATION

1. Condensation polymerization

i) Polyesters : Terylene (PET)

Equation :

ii) Polyamides :

a) Nylon : - used in stockingsadd durability (tough) b) Kevlar: make bulletproof vest

Equation : Equation :

2. Addition polymerization : DISADVANTAGE : very resistant to a range of chemicals (non-biodegradable)

i) Poly(propenamide) ii) Poly(ethenol) : -hydrogen bondingsoluble laundry bags or liquid

Equation : detergent capsules (liquitabs)

Equation:

Manufacturing of Poly(ethenol)


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Acidity and Basicity and the formation of zwitterions

Zwitterion Acidity :

Basicity

- solid in room temperature

Reason :

Separation and identification by chromatography

Effect of aqueous solutions on plane

polarized monochromatic light

Reaction with Ninhydrin

Stuctural formula

Formation of peptide groups in

proteins by condensation

polymerization

AMINO ACIDS


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Diagram for preparation of phenylamine

chemistry notes(organic)

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