carbonyls + carboxylic acids + esters Flashcards
carbonyl definition
an organic moleucle that contains a C=O group
give 3 examples of carbonyl compounds
aldehydes, ketones, carboxylic acids
outline the test for carbonyl groups
- react sample with 2,4-DNP, a pale orange solution
POSITIVE= a condensation reaction will occur and a yellow-orange precipitate is formed
after a positive test result with 2,4-DNP, what can be done to identify the carbonyl compund
the melting point of the precipitate formed can be found, then this can be compared to a database to identify the carbonyl compound
outline a test for aldehydes
- prepare a solution of 3cm3 AgNO3(aq) + 1 drop of NaOH to produce AgO a brown precipitate
- add NH3 dropwise until precipitate redissolves- this is tollens reagent
- add tollens reagent to the sample in a water bath at around 50C-60C
POSITIVE= a silver mirror will form as the aldehyde is oxidised to a carboxylic acid as Ag+(aq) + e-»_space; Ag(s)
why will ketones not react with tollens reagent
ketones cannot be oxidised, as there is no H group on the carbon with the C=O group to lose
by what mechanism do ketones normally react
nucleophilic addition
compare the reactivity of carbonyls and alkenes
carbonyls tend to be more reactive than alkenes, as the C=O bond is polar, due to the electronegativity difference between C and O, causing electron density to lie closer to the O, creating a dipole, so nucleophiles are attracted to the slight positive charge on the C atom
whereas C=C bonds are non polar
give the reagents and conditions to go from an aldehyde/ketone to an alcohol
reagent - NaBH4
conditions - aqueous
- just write it as [H] in equations, so you don’t have to worry about side products, but don’t forget to balance!
give the reagents and conditions to go from an aldehyde/ketone to a hydroxynitrile
reagents - NaCN + H2SO4 to form HCN in situ - HCN can be used in equations
conditions - aqueous
why is HCN alone not used as a reagent
HCN is a colourless + poisonous liquid, and is also very volatile as it boils slightly above room temp, so it cannot be safely used in a lab
give the reagents and conditions to go from an aldehyde to a carboxylic acid
reagents - K2Cr2O7
conditions - H2SO4 + heat under reflux
colour change from orange to green will occur
- this reaction can also be used to identify an aldehyde
carboxylic acid definition
a compound with C=O carbonyl and OH hydroxyl functional groups bonded to the same carbon atom
why do carboxylic acids have high water solubility
C=O and O-H bonds are both polar, and these groups allow carboxylic acids to form hydrogen bonds with H2O
what structural factors affect the solubility of carboxylic acids
carbon chain length - as the length of the alkyl chain increases, solubility decreases as this is non polar
number of carboxyl groups - as number of carboxyl groups increases, solubility increases - dicarboxylic acids are very soluble
how do carboxylic acids act as acids
carboxylic acids are weak acids, as they only partially dissociate when dissolved in water, forming H+ and a carboxylate ion
carboxylic acids can undergo the same redox (with metals) and neutralisation (with bases) reactions as other acids - in both they will form carboxylate salts
outline a test for carboxylic acids
- react sample with Na2CO3
POSITIVE= effervescence as gas is released, if this gas is bubbled through limewater it will turn limewater cloudy - this is because a neutralisation reaction occurs, carboxylic acids are the only common organic group acidic enough to react with carbonates
what would be observed in a carboxylic acid was reacted with Na
effervescence and bubbling
give the equation to produce an ester
alcohol + carboxylic acid <> ester + water
- this is a condensation reaction
- it is also a reversible reaction
give the reagents and conditions to produce esters
reagents - alcohol + carboxylic acid
conditions - conc H2SO4 + reflux
- acid must be conc as too much water will cause the position of the equilibrium to shift and move to the reactants side, decreases yield of ester
what are the 2 methods of hydrolysing esters
acid hydrolysis and alkali hydrolysis
outline the process of acid hydrolysis of esters
- ester is heated under reflux with dilute H2SO4 - it should be dilute as more water will move position of equilibrium to the reactant side, increasing break down of ester
- products are alcohol and carboxylic acid
outline the process of alkali hydrolysis
- ester is heated under reflux with aqueous NaOH
- products are carboxylate ion and alcohol
- this is preferable, as it is not a reversible reaction so no ester will be reformed and therefore there will be a higher yield of products
give the equation for producing acid anhydrides
2 carboxylic acid»_space; acid anhydride
outline how to name acid anhydride
replace acid with anhydride and if 2 acids are different, arrange names alphabetically
e.g. ethanoic anhydride
ethanoic propanoic anhydride
give other methods of producing esters
reacting acid anhydrides/acyl chlorides/carboxylic acids with alcohols/phenols
give the reagents and equation and conditions for the formation of acyl chlorides
reagents - thionyl chlorice (SOCl2)
carboxylic acid + SOCl2»_space; acyl chloride + SO2 + HCl
- this reaction must take place in a fume hood, due to release of SO2 and HCl
what reactions can acyl chlorides undergo
acyl chlorides are very reactive, and can easily be converted into carboxylic acid derivatives
e.g. esters
give the reagents and conditions to go from an acyl chloride to a carboxylic acid
reagents - water
conditions - fume cupboard, this is a very vigorous reaction, and produces dense steam and HCl fumes
byproducts - HCl
name the mechanism that acyl chlorides normally undergo
nucleophilic addition elimination
give the reagents and by products to go from an acyl chloride to a primary amide
reagent - 2 ammonia + acyl chloride
byproducts - NH4Cl
give the reagents and byproducts to go from a primary amide to a secondary amide
reagent - 2 primary amide + acyl chloride
byproducts - RNH3+Cl-
- the RNH3+ group comes from one of the primary amides
compare the reactions of acyl chlorides and acid anhydrides
acid anhydrides react similarly to acyl chlorides with alcohols, phenols, water, ammonia - although they produce a carboxylic acid rather than HCl
however acid anhydrides are much less reactive than acyl chlorides
what is another way than the production of esters can be more efficient/with higher yields
using acyl chlorides instead of carboxylic acids as the reaction is not reversible
