Module 6 - chapter 26 P2 Flashcards
what is the general equation for the oxidation of an aldehyde?
aldehyde + [O] -> carboxylic acid
what are the reactants and products of partial oxidation of an alcohol to an aldehyde?
reactants = alcohol, oxidising agent = [O] products = aldehyde and 1 mole water
what are the reactants and products of complete oxidation of an aldehyde to carboxylic acid?
reactants = aldehyde, oxidising agent = [O] Cr2O72-/H+ (acidified dichromate) REFLUX products = carboxylic acid and NO FURTHER WATER after partial oxidation
what is a carbonyl group?
the double bond between a carbon and an oxygen, C=O as in aldehydes and ketones
general formula for ketones and aldehydes?
CnH2nO
products of reduction of ketones and aldehydes
ketones reduced to secondary alcohols
aldehydes reduced to primary alcohols
how is the acidified dichromate ion Cr2O72-/H+ formed?
potassium dichromate - K2Cr2O7 acidified with H2SO4 to form Cr2O72-/H+
what are the conditions for the reduction of carbonyl compounds?
reducing agent = aqueous sodium tetrahydridoborate (III) = NaBH4/H2O
reaction mixture is warmed
general equation for the reduction of carbonyl compounds
aldehyde/ketone + 2[H] -> alcohol
is the carbonyl group saturated or unsaturated? because of this what reactions does it undergo
unsaturated, addition reactions
what atom in the carbonyl group is attacked in the addition reaction by the nucleophile?
the carbon because it’s positive in the polar bond due to the difference in electronegativity
by what reaction are ketones/aldehydes reduced?
nucleophilic addition
what is the mechanism for the nucleophilic addition of carbonyl compounds?
- NaBH4 donates a hydride ion (H-)
- the hydride ion (H-) is the nucleophile and is attracted to the Cs+
- a daitive coordinate bond is formed between the hydride ion and the C of the C=O
- the Pi bond of the C=O breaks by heterolytic fission so there is a negatively charged intermediate
- the oxygen of the intermediate donates a lone pair of electrons to a H (the intermediate is protonated) in a water so an alcohol and OH- is formed
how do reactions with carbonyl compounds differ from reactions with alkenes?
carbonyl compounds are attacked by nucleophiles
alkenes are attacked by electrophiles
what is observed with the reaction of aldehydes/ketones with excess 2,4-DNPH?
a brightly coloured yellow/orange precipitate
what is the test with excess 2,4-DNPH used for?
identification of a carbonyl group
why might the colour observed of an alcohol with Cr2O72-/H+ be blue rather than green or orange?
the chromium was reduced even further beyond Cr3+ to Cr2+
what is Tollen’s reagent also known as?
ammoniacal silver nitrate
what is Tollen’s reagent used for?
to identify the presence of an aldehyde as only the aldehyde reacts with Tollen’s to form a silver mirror
how would you use the product from the condensation reaction with 2,4-DNPH to confirm the identity of an aldehyde or ketone?
- The 2,4-DNPH derivative product formed can be purified by filtration and recrystallisation.
- Measure the melting point of the solid and compare the value to a table of known values so the carbonyl compound it was formed from can be identified.
equation for what happens when a silver mirror is formed with Tollen’s reagent
the aldehyde is oxidised so the silver ions in the Tollen’s reagent are reduced
Ag+(aq) + e- → Ag(s)
doesn’t occur with ketone because can’t be further oxidised so Ag+ can’t be reduced to Ag
how does reflux give a high yield of carboxylic acid when oxidising an alcohol?
continuous evaporation and condensation into the reaction mixture
name the apparatus for distillation
Bunsen, tripod, gauze, round-bottomed flask/distilling flask, still-head (to attach to condenser), thermometer, Liebig condenser, receiver, conical flask
what are the physical properties of carboxylic acids?
soluble in water, higher bpt than the corresponding alcohol (both with the alcohol with same number of carbon atoms and with the alcohol with the same Mr)
what are carboxylic acids with two COOH groups called?
dioic acids - useful for polymers
why do carboxylic acids dissolve in water?
hydrogen bonding can occur with the OH groups because the H is s+ in the OH groups
a carbon chain with up to 4 carbons are soluble in water, with more carbons solubility decreases as the non-polar chain has a greater effect on the overall polarity of the molecule
why do carboxylic acids have high mpt and bpt?
they form double hydrogen bonds between eachother - C-O-Hs+—s-O=C
C=Os—-Hs+-O-C
are carboxylic acids weak or strong acids?
weak w/ pH approx 5
what is formed when carboxylic acids react with metals?
metal carboxylic acid salt (e.g. sodium ethanoate)
and 1/2H2
be careful with balancing the carboxylic acid salt as if the metal ion is greater than +1 you’ll need more than one salt as there is only a single O-
e.g. C2H5OO-Na+
(C2H5OO-)2Mg2+
what is formed when carboxylic acids react with metal carbonates?
carboxylic acid salt, carbon dioxide and water
what is formed when carboxylic acids react with metal oxides?
carboxylic acid salt and water
what does the condensation reaction with a carboxylic acid and alcohol form?
ester and water (esterification)
what are the conditions for esterification?
concentrated strong acid (e.g. H2SO4) and warming
what functional group do esters have?
R-C=O
|
O-R
the R group must be the carbon chain and cannot just be H or it’s a carboxylic acid not ester
why are esters volatile?
no free OH groups for hydrogen bonding so evaporate more easily with weaker bonds being broken
naming an ester from its reactants
stem of alcohol + -yl
stem from carboxylic acid + -oate
e.g. methanol + propanoic acid = methyl propanoate
naming an ester from its displayed formula
1) divide molecule into two portions between COO and other carbon chain
2) name the chain without the COO = alkyl chain
3) name chain with COO = carboxylate group
how do you name a carboxylic acid with phenol as a substituent?
name it as 2hydroxybenzoic as it isn’t classed as phenol, just benzene with an OH
and must be 2 hydroxy because carbon chain takes position 1
the carboxylic acid can’t be a substituted group so phenol is a substituent
easy was to identify a carbon compound as an ester
sweet smelling liquid
definition for hydrolysis
the chemical breakdown of a compound in the presence of water or an aqueous solution
what two ways can esters be hydrolysed under reflux?
with hot aqueous dilute acid or hot aqueous alkali (hydroxide ions)
products of ester hydrolysis with hot aqueous dilute acid
carboxylic acid and alcohol
products of ester hydrolysis with hot aqueous alkali
carboxylate ion (forms carboxylate salt with metal) and alcohol
what is a carboxylate ion?
C=O
|
O-
general equation for ester hydrolysis with hot aqueous dilute acid
ester + water -> carboxylic acid + alcohol
with H+(aq) as acid catalyst
is ester hydrolysis with acid reversible or irreversible
reversible
is ester hydrolysis with alkali reversible or irreversible?
irreversible
what is ester hydrolysis with alkali also known as?
saponification
general equation for ester hydrolysis with alkali
ester + OH-(aq) -> carboxylate ion + alcohol
what are acid anhydrides?
contain the functional group OCOCO
O O
|| ||
- C - O - C -
how are acid anhydrides formed?
dehydration reaction with two carboxylic acid molecules,
the two OHs bond so one O remains and the other forms H2O with the 2Hs
naming acid anhydrides
if symmetrical on both sides of the joining O only name one part of the molecule and then add “oic anhydride”
if unsymmetrical name both parts and add “oic” to them, list them in order of shortest to longest carbon chain then follow with “anhydride”
e.g. ethanoic propanoic anhydride
acid anhydrides can be reacted with an alcohol to form what?
acid anhydride reacted with an alcohol to form an ester and a carboxylic acid
one R-C=O reacts with the O-R from the alcohol and the remaining H from the alcohol attaches to the leftover molecule at the single bonded O to form an OH group on the carboxylic acid
why are acid anhydrides and acyl chlorides useful in organic synthesis?
the reactions are irreversible so give a higher yield,
acyl chlorides are more reactive than carboxylic acids so esterification is faster too so there’s a greater yield
conditions for ester formation with acid anhydride and alcohol
concentrated strong acid catalyst, no heat is required
what are acyl groups?
C=O (carbonyl) bonded to an electronegative group
aldehydes and ketones are NOT acyl groups
give examples of molecules including acyl groups
esters, acid anhydrides, acyl chlorides
how may esterification affect flavour?
- more fruity due to formation of ester
- less sour due to acid being used up
general equation for formation of acyl chlorides?
carboxylic acid + thionyl chloride (SOCl2)-> acyl chloride + sulfur dioxide gas + hydrogen chloride gas
HCl (g) produces misty fumes observed when water is added because HCl(aq) is formed
equation for reaction of acyl chloride to produce esters
acyl chloride + alcohol -> ester + HCl(g)
equation for reaction of acyl chloride to produce carboxylic acids
acyl chloride + H2O -> carboxylic acid + hydrogen chloride (g)
why are acyl chlorides useful for esterifying phenols?
acyl chlorides are more reactive than carboxylic acids so can react with phenols to produce phenyl esters
why may a solution appear brown after addition of dichromate ions?
equal amounts of orange dichromate and green chromium ions
why may a cloudy black solution be observed after addition of Tollen’s reagent?
there wasn’t enough ammonia added to the tollens so the silver ions were reduced too quickly and due to the ammonium ion not forming a complex with the silver ion.
why may Na2CO3 be added after esterification?
to neutralise the unreacted carboxylic acid and remove its smell to make it easier to detect the smell of the ester
How is Tollen’s reagent produced?
add a couple of drops of sodium hydroxide to a small amount of silver nitrate (V) in a test tube, a brown precipitate should form.
add ammonia dropwise until the precipitate just dissolves to give a colourless solution.
Tollen’s should only be prepared on a test tube scale because it’s explosive and should be disposed of in plenty of water within 30 minutes of preparation
conditions for using Tollen’s reagent
warm in a water bath at 50-60C (not with a flame as is explosive) and wait for silver mirror to form within 5-10 minutes
what ion is formed when making Tollen’s reagent?
[Ag(NH3)2]+ diamminesilver(I) ion which acts as a mild oxidising agent under alkaline conditions
what is the common name for methanal?
formaldehyde
what is the common name for propanone?
acetone
what position is the carbonyl group always in in aldehydes?
position 1
why must HCN be produced in situ for reactions?
it is a colourless, extremely poisonous liquid that boils slightly above room temperature so it cannot be used safely in an open laboratory
how is HCN produced in situ?
using sodium cyanide and sulfuric acid
why are reactions of carbonyl compounds with HCN useful?
is a way of increasing the length of the carbon chain
conditions required for reaction of carbonyl compounds with HCN?
H2SO4/NaCN
product of reaction of carbonyl compound with HCN
a hydroxynitrile - a compound with a hydroxy group and a CN group added to the chain as the HCN adds across the C=O double bond
another name for hydroxynitrile compound
cyanohydrin
what is 2,4-DNPH also known as?
Brady’s reagent
how is 2,4-DNPH normally used?
dissolved in methanol and sulfuric acid as Brady’s reagent because solid 2,4-DNPH can explode due to friction or a sudden blow
what is the brown precipitate formed when making Tollen’s reagent?
silver oxide - Ag2O
what is the functional group in carboxylic acids?
the carboxyl group COOH
NOT carbonyl and hydroxy group
physical properties of dicarboxylic acids
readily soluble in water and solid at room temp
reaction of carboxylic acids with alkalis (hydroxy groups)
produce metal carboxylate salt and water
test for carboxyl group
add a carbonate (e.g. Na2CO3)
only carboxylic acids are acidic enough to react with carbonates and produce CO2 effervescence
what is a derivative of a carboxylic acid?
a compound that can be hydrolysed to form the parent carboxylic acid.
contain an acyl group
conditions for esterification using a carboxylic acid and alcohol
warming, small amount of H2SO4 catalyst
what is the CN- ion?
cyanide ion
why is Cl- not the nucleophile in nucleophilic addition of carbonyl compounds?
not a strong enough nucleophile
