Chemistry - Synthesis, organics

Alkene to Alkane

Alkene to Alkane

H2, heated, Ni catalyst

Electrophilic addition, hydrogenation

Used in the hydrogenation of vegetable oils into solid margarine (saturated fatty acid)

Alkene to diol

KMnO4(aq), H+ catalyst.

Oxidation reaction

Colour change of potassium manganate

Purple to colourless

Can use KMnO4 to distinguish between alkenes and alkanes

Alkene to alcohol

excess H2O, phosphoric acid catalyst, high pressure, high temperatures

Electrophilic addition, hydration

Alcohol to Alkene

Conc phosphoric acid catalyst, high temp and pressure

Dehydration reaction, produces multiple isomers

Alkene to halogenoalkane

HX or X2, not aqueous i.e. using gaseous HX

Electrophilic Addition, halogenation

Halogenoalkane to alkene

NaOH(eth), reflux

Produces alkene, water and NaX

Acid-base reaction, elimination reaction

Alkane to halogenoalkane

X2, UV radiation

Free radical substitution

Halogenoalkane to amine

Concentrated ethanolic ammonia, heated in a sealed container

Nucleophilic substitution

Halogenoalkane to nitrile

KCN(eth), reflux

Nucleophilic substitution

Halogenoalkane to alcohol

NaOH(aq), reflux

or H20(l), warm

Nucleophilic substitution

Alcohol to halogenoalkane

Cl: 1,2 PCl5 or 3 conc HCl, both at rtp

Br: NaBr + conc H2SO4 → HBr. warmed

I: Phosphorus and iodine, produces side product of H3PO3, under reflux

Alcohol to aldehyde/ketone

Potassium Dichromate, acid, distillation with addition.

Alcohol added drop by drop as reaction is very exothermic

Oxidation

Aldehyde/Ketone to Alcohol

Using Grignard reagent

Reduction

Aldehyde/Ketone to Carboxylic acid

Potassium dichromate, acid, reflux

Oxidation

Carboxylic acid to alcohol

LiAlH4(dry ether)

Reduction, straight from carboxylic acid to alcohol as the aldehyde formed is easily reduced down to an alcohol

Alcohol to ester

RCOOH, acid catalyst or RCOCl, rtp

Acyl chloride method is non-reversible and much faster (does not require catalyst)

Esterification

Ester to alcohol

Acid hydrolysis, H20 with acid catalyst, reflux

Alkali hydrolysis, NaOH, reflux then acid to convert carboxylate salt

In alkali conditions, the OH- is the reactant, in acidic acid is just the catalyst

Carboxylic acid to Acyl chloride

PCl5

Acyl chloride to Carboxylic acid

H2O

Aldehyde/ketone to hydroxynitrile

HCN/KCN (aq), reflux

Nucleophilic addition

Nitrile to carboxylic acid

Acid/Alkali hydrolysis. Reflux

Produces carboxylic acid/ carboxylate salt and ammonium/ammonia

Amide to carboxylic acid

Acid and Alkali hydrolysis. Reflux

side product of amine

Acyl chloride to amide

conc NH3 or RNH2

Amide to amine

acid/alkali hydrolysis or LiAlH4(dry ether). Reflux

side product of carboxylic acid

Amine to amide

Acyl chloride

Addition-elimination reaction

Nitrile to amine

LiAlH4 (dry ether)

or

Add hydrogen with a Nickel catalyst, at 150C

Reduction

Nitrobenzene to phenylamine

1. Sn + conc HCl, reflux. Produces a phenylammonium ion.

2. NaOH(aq), converts it into a phenylamine

   Reduction reaction

Benzene combustion

Typically incomplete combustion, produces a sooty flame, due to high carbon to hydrogen ratio

Benzene to phenylketone

RCOCl, AlCl3 catalyst(electrophile maker)

electrophilic substitution

Benzene to nitrobenzene

conc HNO3, conc H2SO4 catalyst

electrophilic substitution

benzene to halogenobenzene

X2, FeX3 catalyst (called a halogen carrier)

Benzene does not readily react with bromine water. Evidence against Kekulé’s structure

electrophilic substitution

Benzene to alkyl benzene

RCl, FeCl3 catalyst (called a halogen carrier)

electrophilic substitution

Phenol to Tribromophenol

Br2(aq). N.B. Bromination of benzene requires liquid bromine

electrophilic substitution

Test for alkene

Bromine water

Positive test = brown to colourless

Negative test = remains brown

Test for aldehyde only

Ammonia and silver nitrate (Tollen’s)

First add mix dilute sodium hydroxide with silver nitrate

Add ammonia to dissolve solid silver(I) oxide, then add to suspected aldehyde

Positive test = Silver mirror (solid silver)

Negative test = colourless solution

or

Benedict’s Reagent

Positive test = blue solution to red brick precipitate (Cu(II) complex to Copper(I) oxide)

Negative test = remains blue

Test for carbonyls

2,4 - DNPH

Positive test = Orange precipitate

Negative test = orange solution

Then collect and recrystallise precipitate.

Take melting point, compare the value to data book values

Test for primary, secondary alcohols and aldehydes

Acidified potassium dichromate

Positive test = Orange solution to green solution

Negative test = remains orange

Test for phenols

Bromine (aq/l)

Positive test = Bromine decolourises, white precipitate forms

Negative test = brown solution

Test for organic acids

Sodium carbonate (s or aq)

Positive test = effervescence

Negative test = colourless solution

Test for methylketones

Add Iodine and alkali e.g. sodium hydroxide

Yellow precipitate forms, CHI3

Side products, carboxylate salt, water, iodide

How to prepare Grignard reagent

By adding Mg to R-Br

Warm in water bath and reflux

Grignard Reagent with water

Alkane forms, need to store Grignard reagent in dry ether

Grignard Reagent with carbon dioxide

Forms R-COOMgBr

Then add dilute acid

R-COOMgBr +H₂O —→ R-COOH + Mg(OH)Br

Grignard reagent with methanal

Add Grignard reagent, R-Mg-Br then dilute acid

Form R-CH2OH, a primary alcohol

Grignard reagent with an aldehyde

Add Grignard reagent, R-Mg-Br then dilute acid

Form R-R’-CHOH, a secondary alcohol

What is an alkyl group, what is an aryl group

Alkyl - functional group derived from an alkane

Aryl - functional group derived from an aromatic ring

Purpose of anti-bumping granules

Provides small for small bubbles to form on

Prevents violent boiling

Importance of washings

When transferring between containers.

Important to rinse out containers (beakers, measuring cylinder, glass rod) and transfer these washings to the next flask

How to remove alcohol from the organic layer in a separating funnel

Add calcium chloride which reacts with the alcohol pushing it to the aqueous layer

How to remove water from a product

Drying agent e.g. anhydrous magnesium sulfate

Absorbs any remaining water, causing powder to clump.

This residue can be easily removed the pure organic liquid

Key things to remember when using a burette

Rinse burette out with solution being used for the titration

Remove the funnel before titration

Ensure jet space below the tap is filled with fluid

Use a white tile on the conical flask for a clear colour change

Add solution from burette dropwise near the end-point

Why is ethanol used as a solvent in the reaction between water and a halogenoalkane

The halogenoalkane(no hydrogen bonding) and water are not miscible

Ethanol is soluble in both water and halogenoalkane.

Allows the reactants to mix and react

The reactions in CP13b

Delay reaction:

Thiosulfate ions reacting with iodine.

Prevents a starch iodine complex from forming. Only forms when all of the thiosulfate has reacted.

Main reaction:

Peroxodisulfate ions with iodide ions

The reactions in CP14

Delay reaction:

phenol with bromine. Converting bromine back into bromide

Rate reaction:

Bromide, bromate and hydrogen ions reacting to form bromine and water.

End point when bromine bleaches methyl red.

Why is a minimum volume of solvent added during recrystallisation?

When a minimum volume of hot solvent is added this forms a saturated solution.

When the solution cools, it becomes supersaturated as solubility decreases. This allows the maximum mass of crystals of product to form.

Ice is used to extract the most crystals possible

What is homolytic fission

When the electrons split evenly between atoms bonded

Free radicals form

What is heterolytic fission

Electrons go to one species involved in the bond.

Ions form

When steam distillation is used

Use to separate an insoluble liquid with a high boiling point from an aqueous solution

Agitation of the liquid caused by steam passing through pushes the insoluble liquid to the surface of the mixture

The insoluble liquid boils off at a much lower temperature than its boiling temperature. Less chance of decomposition of desired product

When is fractional distillation used

When there is a small boiling point difference between compounds or when several compounds need to be separated

Fractionating beads in the column leading to the undergoing repeat distillations. Better separation, higher purity.

Units of ideal gas law equation

p - Pa

V - m³

T - Kelvin

n - mol

R - ideal gas constant of 8.31

Frequency density

Frequency / class width

Reaction between amine and halogenoalkane

If both primary, produces secondary amine and HX.

Further reaction could occur, creating a tertiary amine

A further reaction could then occur creating a quaternary ammonium ion e.g. (CH₃)₄N⁺

Optical isomers effect on light

Rotates the plane of plane-polarised monochromatic light

Why use TMS

Produces a single peak - all C and H in same environment

The peak does not overlap with other peaks

Peak is very strong, so don’t need a lot

Inert, non-toxic

Volatile, so can be easily removed from the sample