Unit 5- Topic 20 Flashcards
Test and notes on alkenes
Functional group= C=C
Test: add bromine water (Br2 (aq))
Observation: bromine decolourises immediately
Reaction bromine water with aldehydes and ketones
Bromine water is decolourised very slowly
Test and observation of halogenoalkanes (R-X) where X= Cl, Br or I
Test: warm with NaOH (aq) and then add dilute HNO3, followed by a few drop of AgNO3(aq)
Observations: R-Cl= produces white ppt. Ppt is insoluble in dilute NH3
R-Br= produces cream ppt. Ppt is insoluble in dilute NH3 but soluble in concentrated NH3
R-I= produces yellow ppt. Ppt is insoluble both dilute NH3 and concentrated
Test and observation of hydroxy group
Functional group= -OH
Test= add solid PCl5
Observation= misty fumes
Both alcohols and Carboxylic acids produce misty fumes, but not phenols
Test and observations of primary alcohols
Functional group= (RCH2OH)
Test= add acidified K2Cr2O7 solution and warm
Observation= solution turns from orange to green
The organic product of this reaction produces a silver mirror with Tollen’s reagent
Test and observation of secondary alcohols
Functional group= (R2CHOH)
Test=add acidified K2Cr2O7 solution and warm
Observation= solution turns from orange to green
Notes= the organic product does not produce a silver mirror with Tollen’s reagent
Test and observation for carbonyls
Functional group: (C=O)
Test: add 2,4-DNPH
Observation: orange precipitate
Notes:both aldehydes and ketones produce and orange ppt
Test and observation for aldehydes
Functional group=(RCHO)
Test= add Tollen’s reagent and warm
Observation= silver mirror forms
Notes= Fehling’s solution can also be used. Ketones do not react with Tollen’s or Fehling
Test and observation for CH3- C=O- R or CH3- CHOH - R
Test= add alkaline solution of iodine and warm
Observation= yellow ppt forms
Notes= known as triiodomethane or iodoform test
Test and observation for carboxylic acids
Functional group= R-COOH
Test= add NaHCO3 or Na2CO3 and warm if necessary
Observation= bubbles of gas
Test and observation for phenol
Functional group= benzene- OH
Test= addd bromine water
Observations= bromine immeaditely decolourises and a white precipitate forms
Notes= phenylamine produces same results.
Phenol is soluble in NaOH but insoluble in dilute HCl.
Phenylamine is insoluble in NaOH but soluble in dilute HCl
State the four ways of extending an existing carbon chain by one or more atoms
1- Reacting a halogenoalkane with a cyanide ion forms a nitrile with one more carbon atom that the halogenoalkane
2- the addition of hydrogen cyanide to a carbonyl compound
3- the alkylation of benzene, which introduces an alkyl group into a benzene ring
4-the use of Grignard reagents
What are the Grignard reagents
They are organometallic compounds containing magnesium. They are made by heating under reflux the chosen halogenoalkane with magnesium in a solvent of dry ether. Bromoalkanes are the preferred halogenoalkane. Grignard reagents contain magnesium covalently bonded to both the alkyl group and the halogen. General equation:
R - Br + Mg —> R - Mg - Br
Grignard reagents react with water so they are made nd used in a solvent of dry ether
Grignard reactions
RMgBr + CO2 -> RCOOH, grignard + carbon dioxide -> carboxylic acid
RMgBr + CH2O -> RCH2OH, grignard + methanal -> primary alcohol
RMgBr + R’CHO -> RR’CHOH, grignard + aldehyde -> secondary alcohol
RMgBr + R’COR’’ -> RR’R’’COH, grignard + ketone -> tertiary alcohol
After the reaction is complete, dilute acid is added to obtain the desired organic product
How can functional groups influence the behaviour of compounds that contain them
-can affect if the compounds is going to act as nucleophilic or electrophile
-if they are susceptible to addition reactions or substitution
-if they are easily oxidised or easily reduced
How to approach a ‘plan to a reaction scheme with intermediate’ questions
-check is carbon chain length has increased or decreased
-by looking at final product and working back to the starting compound
-by looking at the starting compound and thinking of types of reactions it can undergo
Reaction: alkene to halogenoalkane
Equation: CH2=CH2 + HX -> CH3CH2X
Reagent: hydrogen halide
Conditions: mix the gases at room temperature
Reaction: halogenoalkane to alcohol
Equation: RX + NaOH —> ROH + NaX
Reagent: aqueous sodium hydroxide
Conditions: heat under reflux
Halogenoalkane to nitrile
Equation: RX + KCN —> RCN + KX
Reagent: alcoholic potassium cyanide
Conditions: heat under reflux
Reaction: halogenoalkane to amine
Equation: RX + 2NH3 —> RNH2 + NH4X
Reagent: aqueous ammonia
Conditions: heat under reflux
Reaction: alcohol to chloroalkane
Equation: ROH + PCl5 —> RCl + HCl + POCl3
Reagent: phosphorus (V) chloride
Conditions: room temperature
Reaction: alcohol to bromoalkane
Equation: ROH + HBr —> RBr + H2O
Reagent: 50% concentrated sulfuric acid and potassium bromide
Conditions: warm
Reaction: alcohol to iodoalkane
Equation: 3ROH + PI3 —> 3RI + H3PO3
Reagent: red phosphorus and iodine
Conditions: heat under reflux
Reaction: primary alcohol to aldehyde
Equation: RCH2OH + [O] —> RCHO + H2O
Reagent: potassium dichromate (Vl) and dilute sulfuric acid
Conditions: add the reagent to hot alcohol and allow the aldehyde to distil off as it is formed
Reaction: primary alcohol to carboxylic acid
Equation: RCH2OH +2[O] —> RCOOH + H2O
Reagent: potassium dichromate (VI) and dilute sulfuric acid
Conditions: heat under reflux
Reaction: secondary alcohol to ketone
Equation: RCH(OH)R’ + [O] —> RCOR’ + H2O
Reagent: potassium dichromate (VI) and dilute sulfuric acid
Conditions: heat under reflux
Reaction: aldehyde to primary alcohol
Equation: RCHO + 2[H] —> RCH2OH
Reagent: lithium aluminium hydride in dry ether
Conditions: room temperature
Reaction: ketone to secondary alcohol
Equation: RCOR’ + 2[H] —> RCH(OH)R’
Reagent: lithium aluminium hydride in dry ether
Conditions: room temperature
Reaction: aldehyde to 2-hydroxynitrile
Equation: RCHO + HCN —> RCH(OH)CN
Reagent: potassium cyanide in dilute sulfuric acid
Conditions: 10-20 ºC
Reaction: ketone to 2-hydroxynitrile
Equation: RCOR’ + HCN —> RR’C(OH)CN
Reagent: potassium cyanide in dilute sulfuric acid
Conditions: 10-20 ºC
Reaction: carboxylic acid to primary alcohol
Equation: RCOOH + 4[H] —> RCH2OH + H2O
Reagent: lithium aluminium hydride in dry ether
Conditions: room temperature
Reaction: carboxylic acid to ester
Equation: RCOOH + R’OH —> RCOOR’ + H2O
Reagent: alcohol and concentrated sulfuric acid
Conditions: heat
Reaction: acyl chloride to carboxylic acid
Equation: RCOCl + H2O —> RCOOH + HCl
Reagent: water
Conditions: room temperature
Reaction: acyl chloride to ester
Equation: RCOCl + R’OH —> RCOOR’ + HCl
Reagent: alcohol
Conditions: room temperature
Reaction: acyl chloride to primary amide
Equation: RCOCl + 2NH3 —> RCONH2 + NH4Cl
Reagent: aqueous ammonia
Conditions: room temperature
Reaction: acyl chloride to secondary amide (N-substituted amide)
Equation: RCOCl + R’NH2 —> RCONHR’ + HCl
Reagent: amine
Conditions: room temperature
Reaction: nitrile to primary amine
Equation: RCN + 4[H] —> RCH2NH2
Reagent: lithium aluminium hydride in dry ether
Conditions: room temperature
Reaction: nitration of benzene
Equation: C6H6 + HNO3 —> C6H5NO2 + H2O
Reagent: concentrated nitric acid and concentrated sulfuric acid
Conditions: heat under reflux between 50 and 60 ºC
Reaction: sulfonation of benzene
Equation: C6H6 + H2SO4 —> C6H5SO3H + H2O
Reagent: fuming sulfuric acid
Conditions: 40 ºC
Reaction: bromination of benzene
Equation: C6H6 + Br2 —> C6H5Br + HBr
Reagent: liquid bromine with iron (to form iron (III) bromide)
Conditions: dry and room temperature
Reaction: alkylation of benzene
Equation: C6H6 + RX —> C6H5R + HX
Reagent: halogenoalkane
Conditions: dry, in the presence of anhydrous aluminium halide
Reaction: acylation of benzene
Equation: C6H6 + RCOCl —> C6H5COR + HCl
Reagent: acyl chloride
Conditions: dry, in the presence of anhydrous aluminium chloride
What does the hazard of a chemical relate to
Relates to the inherent properties of each substance
What is a hazard
A property of a substance that could cause harm to a user
What is a risk
The possible effect that substance may cause to a user, and this will depend on factors such as concentration and apparatus. The level of risk in controlled using control measures.
What is a chemical that is a health hazard mean
It could cause skin rashes, eye damage and harm if ingested
What is a chemical that is corrosive mean
It can cause skin burns and permanent eye damage
What is a chemical that is flammable mean
Can catch fire if heated or comes into contact with a flame
What is a chemical that has acute toxicity mean
It can cause life-threatening effects, even in small quantities
Why is heating under reflux needed
Because some organic compounds are volatile, so there is a risk that they will escape from the reaction mixture during heating. Refluxing ensures that all the vapours rising from the reaction mixture during heating enter the condenser and change back into liquids.
Why are anti-bumping granules used in heating under reflux
It helps to make the boiling smooth
State the three methods of separation
Simple distillation
Steam distillation
Fractional distillation
What is simple distillation used for
It is used to obtain a liquid product from a reaction mixture that has a boiling temperature much lower than the other substances in the reaction mixture
State how does the apparatus of simple distillation work
Distillation of an impure liquid involves heating it in a flask connected to a condenser. The liquid with the lowest boiling temperature evaporates or boil off first and passes into the condenser first, and so can be collected in the receiver separately from another liquid that may evaporate later
Why is a thermometer used in simple distillation
It is used to monitor the temperature of the vapour as it passes into the condenser. If temperature remains steady, this indicates that one compound is being distilled. If after a while the temperature begins to rise, this indicates that a different compound is being distilled
Advantages and disadvantages of simple distillation
Advantages: it is easier and quicker to set up than fractional distillation
Disadvantages: it does not separate the liquids as well as fractional distillation . It should only be used if the boiling temperature of the liquid being purified is very different from th other liquids in mixture.
What is steam distillation used for
Used to separate an insoluble liquid from an aqueous solution.
what does steam distillation involve
Passing steam into a reaction mixture that contains an aqueous solution and a liquid that forms a separate layer. The agitation of the liquid caused by the steam bubbling through the mixture ensures that both the insoluble liquid and the aqueous solution are on the surface of the mixture and so can form part of the liquid that evaporates
Advantage of using steam distillation
The insoluble liquid is removed from the reaction mixture at a temperature below its normal boiling temperature
Apparatus used in fractional distillation
Uses the same apparatus as simple distillation but with a fractionating column between the heating flask and the still head
How is the fractionating column prepared for fractional distillation and why
The column is usually filled with glass beads. These act as surfaces on which the vapour leaving the column can condense, and then be evaporated again as more hot vapour passes up the column. The vapour experiences several repeated distillations as it passes up the column, which provides a better separation
Advantages and disadvantages of fractional distillation
It takes longer than simple distillation.
Provides a better separation than simple distillation
when is fractional distillation used
Used when the difference in boiling temperatures is small and when there are several compounds to be separated from a mixture
What is solvent extraction used for
Used to remove the desired organic product from other substances in the reaction mixture using a solvent
What does the solvent choice depend on in solvent extraction
-solvent added must be immiscible with the solvent containing the desired organic product
-the desired organic product should be much more soluble in the added solvent than in the reaction mixture
Method for solvent extraction
-Place the reaction mixture in a separating funnel, and then add the chosen solvent -it should form a separate layer
-place the stopper in the neck of the funnel and gently agitate the contents of the funnel for a short while
- allow the contents to settle into two layers
- remove the stopper and open the tap to allow the lower layer to drain into a flask, and then do the same to allow the upper layer to drain into a separate flask
-when te desired organic product has been separated, simple or fractional distillation is used to separate the desired organic product from the solvent used
In solvent extraction, how should the solvent be added
In small portions because this is more efficient- removes more of the desired organic product.
What is washing used for
Used to remove impurities from a solid or liquid. It could involve water or the use of sodium carbonate solution, to remove excess acid
Method for washing
An impure solid is stirred in some of the solvent, then the mixture is filtered.
A liquid would be mixed with a solvent chosen so that it will not dissolve the liquid to be purified. The mixture is then shaken in a separating funnel. After allowing the two liquid layers to separate, the tap is opened to allow each layer to drain into a separate container
Technique used to dry organic solids
There is no special technique- it just needs to be left in a warm place or a desiccator with a suitable drying agent
Features of drying agents in drying
-drying agents do not react with the organic liquid
-most common are anhydrous metal salts: (CaCl2, MgSO4, Na2SO4)
-they form hydrated salts- when they come in contact with water, they absorb water. As water of crystallisation
Method of drying
The drying agent is added to the organic liquid and the mixture is gently agitated or shaken, and then left for a period of time. Before use, drying agent is powdery, after absorbing water it looks more crystalline. If drying agent is added and it remains powdery, the liquid is dry. Liquid goes from cloudy to clear when water removed.
How is the drying agent removed after drying
By decantación or filtration
When is recrystallisation used
To purify. A solid compound is dissolved in a suitable solvent that can dissolve all or most of any impurities but very little of the compound being dissolved
Method for recrystallisation
-Add the impure solid to a conical flask
-Add some of the chosen solvent and warm until the mixture nears the boiling temperature of the mixture
-if there is still some undissolved solid, add further solvent and warm until the mixture boils again
-continue adding further solvent and heating until all of the soluble solid has dissolved
-If insoluble impurities are present, then hot filtration could be done using fluted filter paper in a heated funnel
-Allow the liquid to cool until crystals of the organic solid have formed
-More crystals can be obtained by cooling the solution below room temperature in an ice bath
-The mixture is then filtered to remove soluble impurities using a Buchner funnel or a Hirsch funnel
-The crystals are washed with a small amount of ice cold solvent and then dried in a desiccator or warm oven
Why does the impure solid need to be dissolved in minimum volume of hot solvent in recrystallisation.
To make sure that the pure solid will crystallise when the solution is cooled
Why is hot filtration used in recrystallisation
To ensure the pure solid does not crystallise at this stage
Why do the crystals of the pure solid crystallise in rerystallisation
Because the solid is less soluble in the cold solvent than in the hot solvent
why are the crystals washed with a small amount of ice-cold solvent after recrystallisation
To remove any soluble impurities, to make sure that very little of the pure solid dissolves
How can you test for purity
If a compound is a solid, then its melting point can be measured.
If a compound if a liquid, then its boiling temperature can be measured.
If it is pure it should be sharp rather than over a range of temperatures
How to test for purity by the determination of the melting point
Impurities reduce the melting point. By measuring the mp, you can compare it to a known value. Place some of the solid in a small capillary tube attached to the bulb of a thermometer and then place the assembly in a liquid that has a boiling temperature above that of the melting temperature of the solid
How to test for purity by determining the boiling temperature
For liquids, impurities raise the boiling temp. Compare the data measured with a known value to calculate the percentage purity.
The apparatus used to determine depends on the volume of liquid available and whether it is toxic or flammable. Apparatus for simple distillation can be used in most cases.
What disadvantages does testing thee purity by determining the boiling temperature have
-test may not be enough proof since you may not be able to measure the boiling point of the organic compound accurately enough
-thermometer may read too low or too high so you may wrongly assume that your compound is pure after comparing an inaccurate measured value to te known value.
-different organic compounds have the same boiling temperature
