Carbonyls Flashcards
what is the carbonyl functional group
C=O bond
draw a ketone
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Draw a aldhyde
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Write the equation of aldehydes undergoing oxidation
pg 134
what do aldehydes form when they undergo oxidation
they form a carboxylic acid
- goes from orange to green
What are the reagents needed for aldehydes to under go oxidation
- acidified potassium dichromate
- sulfuric acid
- under reflux
- heat gently
describe nucelophilic addition reactions
- carbonyls have C=C functional group
- makes them susceptible to nucleophilic attach on the slightly positive carbon atom,
- a nucelophile donates a pair of electrons to the electron deficient carbon atom, to form a new covalent bond
- the pie bond in the C=O breaks
- extra electron pair is donates to the neighboring hydrogen to form an alcohol group and stable product
WRITE OUT THE GENERAL MECHANISM FOR NUCLEOPHILIC ADDITION REACTIONS
- DRAW IT
describe sodium tetrahydridoborate
- NaBH4
- reducing agent which is commonly used in organic synthesis
- compound is made of a BH4- ion which acts as a source of H- IONS
- used in water in aqueous solution
- Hydride ion is species that is involved in electrophilic addition and reduction of carbonyl compounds to alcohol
Write reducing equation of pentan-2-one
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draw out mechanism with sodium tetrahydridoborate
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describe hydrogen cyanide
- weak acid that will partially ionise in solution
- cynaide ion cannot react directly with carbonyl compounds but when the reaction is acidified the carbonyl functional group becomes more reactive as polarity of the C=O bond is increased
draw the equation of cyanide and water
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draw the reaction mechanism of hydrogen cyanide
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Whats the difference between aldehyde and ketones
- the C=O functional group is in different places on their carbon chain, this results in them having different chemical properties, their different reactions with the same reagents can be used to distinguish between these classes of carbonyl compounds
How can you test for a carbonyl group with Bradys reagent
- bradys reagent, this is a mixture of methanol, sulfuric acid and a solution of 2,4 - DNP,
- when this is added to an aldehyde and ketone a yellow/orange preciptate of 2,4 - dinitrophenylhydrazone derviate is seen
- doesnt happen with a carboxylic acid
How do you identify a specific aldehyde or ketone
- filtration
- recrystallisation
- dry the product
- then test for its melting point
- difficult for ketones as ketones with a similar chain length have similar boiling points this makes it challenging to experimentally distinguish between them, but the 2,4 - dinitiropphenylhydrozone derivatives have different melting points
Describe how tollens reagent works
- add sodium hydroxide solution is added to silver nitrate solution until a brown precipitate is formed
- dilute ammonia is added drop wise until brown precipitate redissolves
- used to distinguish between an aldehyde and a ketone, it reacts with the aldehyde to form a silver mirror precipitate but not a ketone
- this is because it is a weak oxidising agent and can react with carbonyl functional group in an aldehyde but not a ketone as when it is added to a ketone there is no reaction as ketones cannot be oxidised further
- silver ions are reduced and the aldehyde functional group is oxidized
- aldehyde turns into carboxylic acid
- DRAW THIS
reacting aldehydes and ketones with dichormate
heat with orange acidified dichromate Cr2O72-
- aldehyde turns from orange to green Cr(+6) = (+3), aldehyde is oxidised to a carboxylic acid, dichromate is reduced
- ketone remains orange
reacting with Fehling’s test for aldehydes and ketones
- heat with blue alkaline solution, Cu2+ and sodium hydroxide
- aldehyde - goes from blue solution to brick red preciptate (Cu2O), reduces copper ions from +2 to +1
- ketone remains blue
what are the physical properties of carboxylic acids
Solubility
- small carboxylic acids are very soluble in polar solvents such as water because hydrogen bonds can be formed between carboxylic acid functional group and water
- as hydrocarbon chain of carboxylic acid increases in size the solubility decreases this is because only the carboxylic acid can form hydrogen bonds with the water so as the molecule becomes longer then solubility decreases
What are the chemical properties for carboxylic acid
- they are weak acids as they partially ionize in solution releasing hydrogen ions from the carboxylic acid group
- draw this
- they react at a slower rate than with a strong acid as the pH is higher and therefore the concentration of H+ will be lower
draw the reaction of carboxylic acids with metals
2Na + 2CH3COOH = 2CH3CHOONa + H2
draw reaction of carboxylic acid with metal oxides
MgO + 2HCOOH = (HCOO)2Mg + H2O
draw reaction of carboxylic acid with metal hydroxides
KOH + CH3CH2COOH = CH3CH2COOK + H2O
draw reaction of carboxylic acid with metal carbonates
Na2CO3 + 2HCOOH = 2HCOONa + H20 +CO2
What are the uses of esters
- solvents
- artifical fruit flavoring
- perfumes
How to name an ester
- name the alcohol group first then you name the carboxylic acid
How to make an ester
- alcohol
- carboxylic acid
- sulfuric acid catalyst
- heat gently
- it is a reversible reaction and has a slow rate
- ester is volatile with the lowest boiling point of chemicals it can be separated quickly from the reaction mixture using distillation
- if the ester is large the reaction mixture will need to be heated under reflux until an equilibrium is established the ester can be separated using fractional distillation
describe an acid anhydride
- more reactive than a similar carboxylic acid, made by the removal of the small water molecule
write an acid anhydride reacting with an alcohol
- pg 141
How does an acid anhydride react with an alcohol
- react with phenol and its derivatives to make an ester
- not reversible therefore it has a higher yield
- rate of reaction is slow but can be increased by warming it gently
what is Hydrolysis
chemical reaction where water breaks down another product
- reverse reaction of esterfication
- can change conditions to make either carboxylic acid or carboxylate salts
Hydrolysis in acidic conditions reaction
- reflux
- hot sulfuric or HCL catalyst in aqueous conditions
- will form a carboxylic acid and alcohol
- reacts with water
- draw this
Hydrolysis in alkaline conditions
- alkaline are bases that can dissolve in water
- refluxed
- hot aqueous alkali like potassium hydroxide or sodium hydroxide
- decompose into an alcohol and carboxylate salt
- not reversible
- used to make soap so called saponification
Draw how an acid anhydride is made
pg 141
Define hydrolysis
this is the chemical reaction where water causes the breaking of the bonds in a decomposition reaction
Draw Propanoyl Chloride
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Describe an acyl chloride
- contain the functionla group R-COCl
- they are fuming colourless liquids - visual gas or vapour is released
- reactive and the chlorine is substituted for other groups
How to make an acyl chloride
- the OH group on a carboxylic acid must be substituted for a chlorine atom
- use SOCl2 which is liquid at room temperature and reacts with a carboxylic acid to make the acyl chlorine
- sulfor dioxide and hydrogen chlorine gases are also made
- reaction is separated from the reaction mixture using distillation
- write the equation
How do acyl chlorides react with alcohols
- ester production not reversible therefore it has a higher yield
- write an equation
- make an ester
- to make an ester from phenols the acyl chloride method must be used
- reaction is violent
- produces fumes of HCl which is corrosive
How do acyl chlorides react with water
- produce a carboxylic acid
- hydrolyses to produce a carboxylic acid
- exothermic and misty fumes of HCl are given off
- write an equation
How do acyl chlorides react with ammonia
- produce a primary amide
- added to concentrated ammonia
- produces a mixture of solid ammonium chloride and observed white smoke
- some of the products remain in colourless solution
- write an equation
How do acyl chloride react with primary amides
- produces a secondary amide
- where the nitrogen has one hydrogen atom directly bonded to it
- nitrogen atom also has two organic groups attached and is called an N-substitued amide
- forms a white solid compound
- draw this
