carbonyls and carboxylic acids Flashcards
What are acidified dichromate ions
H+/Cr2O72-
What is a common name and use for methanal
Formaldehyde, commonly used in solution to preserve biological specimens
How is the aldehyde functional group written
CHO
What is the structural formulae for methanal
HCHO
How is the ketone functional group written in displayed formulae
CO
What is another name for propanone and a use
Acetone , commonly used in nail varnish remover
How do you write the oxidising agent in an oxidation reaction
Square brackets o ( depending on whether it’s an aldehyde or carboxylilic acid you may need to put 2 os
Why will tertiary alcohols not oxidise
Have no hydrogens freely attached so cannot oxidise
How do you name ketones
Eg alkane then one , only write number if it cannot go on just 1 carbon
What is the rule for naming aldehydes
The aldehyde is carbon 1 , whereas a ketone needs to be numbered
What is the C=O made of
1 pi bond and 1 sigma bond , the pi bond is formed by the overlap of p orbitals above and below the plane .
What is special about the C=O bond that makes it different to alkanes
The C=O is polar , whereas C=C is non polar . This is because the oxygen atom is more electronegative than the carbon atom which creates a dipole in the C=O bond therefore electron density lies closer to the oxygen atom and a nucelophille is attracted to the delta positive carbon atom
What is a carbonyl group
C=O
What mechanism do carbonyls undergo
Nucleophillic addition
What is the reduction of aldehydes and ketones
-reduction of aldehydes and ketones is done in the prescence of NaBH4 which is used as a reducing agent which reduces aldehydes and ketones into alcohols ( opposite of alcohols into ketones and aldehydes )also known as sodium tetrahydrioborate(III) , which is done with a warm carbonyl with NaBH4 in aqueous solution .
What are aldehydes reduced into
Primary alcohols
What are ketones reduced to
Secondary alcohols
Why is NaBH4 used in the reaction
Provides the hydride ion :H- which is the nucleophile in the nucleophillic addition reaction
What happens in the reduction of ethanal
Reduced into an primary alcohol
What is used to represent the reducing agent in the equation
Square brackets H
What are the steps to the mechanism of reduction of carbonyls with NaBH4 and draw it
- drawing
1) lone pair of electrons from the hydride ion is attracted to and donated to the carbon atom in the carbonyl C=O double bond
2) a dative covalent bond is formed between the hydride ion and the delta positive carbon atom in the C=O bond
3) the pi bond in the C=O bond breaks by heterolyitc fission forming a negatively charged intermediate
4) the oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule ( from the aqueous solution ) the intermediate has then been protonated to form an alcohol
Will NaBH4 reduce carboxylic acids
No , as they are less prone to attack
What happens with the reaction of carbonyls with HCN ( hydrogen cyanide)
This is very useful as it provides a way to extend the length of the carbon chain
- hydrogen cyanide adds across the C=O bond of aldehydes and ketones
Eg you can use an aldehyde and HCN to produce a hydroxynitrile - contain both alcohol functional group and nitrile functional group CN
What is hydrogen cyanide
Hydrogen cyanide is a colourless poisonous liquid . It boils just above room temperature. So it is incredibly unsafe , so HCN cannot be used in an open laboratory instead cyanide and sulfuric acid are used to provide HCN for this reaction
Draw the dot and cross diagram for HCN
Double bond between CN and single between CH with a lone pair on the N
Describe and draw the mechanism for the reaction with HCN
Draw
Steps
1) lone pair of electrons from the cyanide ion :CN- is attracted and donated to the carbon atom in the carbonyl C=O double bond
2) a dative covalent bond is formed between the cyanide ion and the delta positive carbon atom in the c=o bond
3) the pi bond in the C=O bond breaks by heterolytic fission , forming a negatively charged intermediate
4) the oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom
5) the intermediate has been protonated to form a hydroxynitrile product
How do you detect the prescence of the carbonyl group
- a solution of 2,4 dinitrophenylhydrazine(2,4-DNP) in a mixture of methanol and sulfuric acid is known as bradys reagent.( it is dissolved in methanol and sulfuric acid because solid 2,4-DNP can be very hazardous because friction or a sudden blow can cause it to explode)
-bradys reagent is a pale orange solution
-when bradys reagent is added to an aldehyde or a ketone , a yellow or orange precipitate is formed . this precipitate is a 2,4-dinitrophenyldrazone derivative and confirms the prescence of the carbon - oxygen double bond in an aldehyde or a ketone . - the test is only positive for aldehydes or ketones . there is no precipitate with a carboxylic acid or an ester
what happens when 2,4-DNP reacts with a carbonyl group
the NH2 group adds across the c=o bond and oxygen and the 2 hydrogens from NH2 are removed , releasing a molecule of water , also known as an nucleophillic elimination reaction
how do you distinguish between an aldehyde and a ketone once the 2,4-DNP test produces a positive result
we use tollens reagent to distinguish between aldehydes and ketones . tollens reagent is a solution of silver nitrate in aqeous ammonia, in the prescence of an aldehyde it gives a silver mirror - not with ketone .
why does tollens reagent not produce a silver mirror with a ketone
tollens reagent is a very weak oxidising agent and only aldehydes are easily oxidised through to carboxylic acids , ketones are not oxidised by tollens reagent
how is Tollens reagent made
- aqueous sodium hydroxide and aqeous silver nitrate to form a brown precipitate of silver oxide. dilute aqueous ammonia is added until the precipitate just dissolves
- in Tollens reagent the oxidising species is the aqueous silver ion Ag+ , when added to an unknown in a water bath , a silver mirror appears
why is Tollens reagent made immediately
Tollens reagent has a short shelf life so needs to be made immediately before carrying out the test
what is produced in the Tollens reaction
aldehyde + [O] = carboxylic acid + silver mirror ( the silver is the oxidising agent)
- Ag+ (aq) + e- = Ag(s)
how do you identify the compound from the 2,4- DNP test
you can purify it by recrystallisation
- the 2,4-dinitrophenyldrazone derivative is slightly impure so the precipitate is filtered and washed with cold solvent
- it is then recrystallsed from a suitable solvent , the crystals are dissolved in the minimum quantity of warm solvent ( any insoluble impuritites could be removed by passing through a warmed filter) then when the solution cools , the crystals are re- precipitated and can be filtered , washed with a small amount of solvent and dried . they should then be pure . then you would find the melting point of the crystals by comparing to a database of melting points of the 2,4-dinitrophenylhydrazones of all the common aldehydes and ketones to find out which you may have got
what could you do if the melting point of your derivative is similar to ones in a database
- use the boiling point too so you can confirm the compount
what happens to melting and boiling points with impurities
-lower the melting point
-increase the boiling point
what is the carboxylic acid functional group
contains both a carbonyl group , and a hydroxyl group
how do you name a carboxylic acid
replace the e on the alkane with oic acid
eg ethane , ethanoic acid
-the carboxly carbon atom is always designated carbon -1- and substituents are after this
draw the structure for maleic acid
draw the strucutre of fumaric acid
Why are carboxylic acids soluble in water
They form hydrogen bonds with water , solubility decreases as chain length increases as greater proportion of molecule is non polar
Boiling points higher than expected from their molecular weights as form hydrogen bonds with themselves to form dimmers ( they are soluble up to 4 carbon atoms )
What is the trend in solubility in dicarboxylic acids
- to name dicarboxylic acids you keep the alkane name and the e and use dioc eg butanedioic acid
-solubility increases and melting point increases
Why does propanal have a higher boiling point than butane
It has a permanent dipole therefore polar and has permanent dipole interactions
Why does Ethanoic acid have a greater boiling point than propan-1-ol
Ethanoic acid is a carboxylic acid and can therefore form dimers as 2 Ethanoic acid molecules can form 2 hydrogen bonds whereas propan-1-ol can only form 1 hydrogen bond with another molecule
What type of acids are carboxylic acids
They are weak acids as they only partially dissociate . They participate in typical acid reactions forming carboxylate salts ( eg acid + base —> salt + water )
However make sure you show the charges of the salts because they are ionic
what is the salt formed from methanoic acid and a base (eg metal oxide , alkali ect)
methanoate
what is the salt formed from ethanoic acid
ethanoate
what is the salt formed from propanoic acid
propanoate
what is the salt formed from butanoic acid
butanoate
what is formed from magnesium and propanoic acid
magnesium propanoate and hydrogen
what is formed from ethanoic acid and barium oxide
barium ethanoate (Ba2+ CH3COO-)2 and water
what is formed from ethanoic acid and potassium hydroxide
potassium ethanoate and water
describe the test for a metal carbonate . how would you use this test to distinguish between ethanoic acid and phenol
-add dilute acid and fizzing will occur
-carboxylic acids are the only common organic compound sufficiently acidic to react with carbonates , they are weak acids but phenol is a weaker acid and phenol does not react as not acidic enough , phenol only reacts with strong bases , therefore you can disinguish a phenol and carboxylic acid by adding a weak base eg sodium carbonate and only the carboxylic acid will react
What is the equation for the tollens reaction
RCHO + [o] —> RCOOH
What is a carboxylic acid derivative
A compound that can be hydrolysed to form the parent carboxylic acid . All carboxylic acid derivatives contain the acyl group (RCO)
What are the 3 carboxylic acid derivatives
- the esters
- the acyl chlorides
- the acid anhydrides
How are esters formed
By esterification
How do you name an ester
- find the ester functional group
- carbon and carbonyl group is from the carboxylic acid and this is the - oate
- single O is from the alcohol
How do you name an ester
- find the ester functional group
- carbon and carbonyl group is from the carboxylic acid and this is the - oate
- single O is from the alcohol
What is hydrolysis
A reaction with water or hydroxide ions that breaks a chemical compound into two compounds
How are esters made
Carboxylic acid and alcohol
How do you name the alkyl group At the start from the alcohol
Carbon with alcohol is carbon 1
What are the conditions for esterification
Add concentrated sulfuric acid , used as an acid catalyst to speed up reaction
Reflux
Distill
Wash ester with sodium carbonate to remove any dry acid present until there’s no more effervescence
What are the conditions for esterification
Add concentrated sulfuric acid , used as an acid catalyst to speed up reaction
Reflux
Distill
Wash ester with sodium carbonate to remove any dry acid present until there’s no more effervescence
Also produces water
Why is concentrated sulfuric acid used
Also a dehydrating agent and removes water shifting the equilibrium to the right and thus increasing the yield of the ester
What is an acid anhydride
Formed by the removal of water from two carboxylic acids
How do you name an acid anhydride
Name of carboxylic acid - instead of acid add anhydride eg ethanoic anhydride
What does anhydride mean
Without water
What is the structural formulae for Ethanoic anhydride
(CH3CO)2
How do you produce an ester from an acid anhydride
Acid anhydride + alcohol , produced your ester and a carboxylic acid
What are the benefits of making an ester from an acid anhydride
It will go to completion as it is not reversible and therefore yield is greater . Additionally you make a carboxylic acid which is a useful product , no catalyst required and gentle heating therefore less harsh conditions
What is acidic hydrolysis
Ester is Heated under reflux with dilute sulfuric acid or hydrochloric acid
Water is required
Acid acts as a catalyst
Reversible reaction
Makes carboxylic acid and alcohol
What is alkaline hydrolysis
- ester Heated under reflux with an NaOH or KOH
-not reversible - produces a sodium or potassium salt and an alcohol
- salt will dissociate to form the carboxylate ion and metal ion and this carboxylate ion can be converted into the original carboxylic acid by adding a strong acid as it gains a H+ ion ( with larger carboxylic acids the un - dissociated molecule will be only slightly soluble )
What are some uses of esters
-flavourings
-perfumes
-solvents in glues
-plasticisers in plastics
What happens when you react an acid anhydride with water
Creates 2 carboxylic acids
What is an acyl chloride
When we replace the -OH group on a carboxylic acid with a chlorine atom we produce an acyl chloride
What is the functional group of an acyl chloride
COCl
What is the general formula for acyl chlorides
RCOCl
How do you name an acyl chloride
Remove the oic suffix from the carboxylic acid from which it was derived and add oyl chloride eg butanoic acid - butanoyl chloride
How do you know if a molecule is an acyl chloride
The chlorine atom is directly attached to the carbonyl group
How do you prepare an acyl chloride
Carboxylic acid + thionyl chloride SOCl2 which replaced the OH group with a chlorine atom
The products of this reaction are sulfur dioxide SO2 and hydrogen chloride HCl which are both harmful gases so the reaction must be done in a fume cupboard . Also sulfur dioxide produces acid rain
This reaction is not reversible, gases released into air
Are acyl chlorides reactive
Very reactive
What happens in the reaction between alcohol and acyl chloride
Acyl chlorides react with alcohols at room temp to produce the corresponding ester and hydrogen chloride gas
This produces white misty fumes of HCl. this must be done with cold anhydrous conditions as prescence of water with the acyl chloride can produce a carboxylic acid - and you want to produce an ester
What compounds react with phenols to produce esters
Acyl chlorides and acid anhydrides, carboxylic acids are not reactive enough to form esters with phenols
What is produced when an acyl chloride reacts with phenol
Phenyl ester and hydrogen chloride
What is produced when acyl chlorides react with water
Acyl chlorides are readily hydrolysed at room temperature and will fume in moist air due to this reaction releasing steamy fumes of HCl
They reform the carboxylic acid and hydrogen chloride gas which is very acidic
What is an amine
A carbon chain attached to the NH2 functional group
A primary amine is RNH2
A secondary amine is R2NH
A tertiary amine is R3N
What happens when ammonia and amines react with acyl chlorides
They can act as nucleophiles by donating the lone pair of electrons from the nitrogen atom to an electron deficient species , when they react with acyl chlorides they produce amides
What is the amide group
RONH2
What is produced when concentrated ammonia reacts with acyl chlorides
A primary amide is formed
Eg ethanoyl chloride + 2NH3 —> CH3CONH2 ( ethanamide)+ NH4Cl ( ammonium chloride)
What is produced when a primary amine reacts with an acyl chloride
A secondary amide is produced ( the nitrogen atom is attached to two carbon atoms)
( look in folder for example)
What is produced when an acid anhydride reacts with phenol
Phenyl ester and carboxylic acid
