Chapter 26 - Carbonyls and carboxylic acids Flashcards
whats made when an aldehyde is oxidised and what are the reagents and conditions
aldehydes can be oxidised to carboxylic acids when refluxed with acidified dichromate ions usually Kr2Cr2O7 (shown as [O]) and dilute H2SO4
how do you distinguish between aldehydes and carboxylic acids
test for a carbonyl using 2,4-DNP and if a carbonyls present an orange/yellow precipitate will form
then use tollens reagent if an aldehyde is present then a silver mirror is formed as Ag ions are reduced if nothing happens its a ketone
how do you test for a carbonyl functional group
test for a carbonyl using 2,4-DNP and if a carbonyls present an orange/yellow precipitate will form
what does tollens reagent do to an aldehyde
it reduces it to a carboxylic acid
what is tollens reagent made up of
silver nitrate in aqueous ammonia
whats bradys solution and whys it used
its 2,4-DNP dissolved in methanol and sulfuric acid
its often used in practicals as its less hazardous the 2,4-DNP alone which can easily explode
whats formed in the reaction between an acyl chloride and ammonia
a primary -amide and ammonium chloride
whats formed in the reaction between an acyl chloride and a primary amine
a secondary -amide and an -ammonium chloride
what compounds undergo nucleophilic addition-elimination reactions
acyl chlorides
what type of covalent bonds from between a nucleophile and a c-atom
a dative covalent bond
how do acyl chlorides from amines
they react with ammonia/amines which acid as nucleophiles and donate a lone pair of electrons on the nitrogen
how do acid anhydrides react
they react similarly to acyl chlorides but are less reactive and can be used when acyl chlorides are too reactive and instead of HCl being produced its a carboxylic acid
what does ethanoyl chloride (an acyl chloride) react vigorously with to produce
ethanoic acid and HCl
(violent reaction and HCl is dense)
what does ethanoyl chloride react with phenol to form
phenyl ethanoate + HCl
what does ethanoyl chloride reacting with propan-1-ol form
propyl ethanoate and HCL
how do acyl chlorides react with alcohols to form esters
acyl chloride + alcohol/phenol = ester + HCl
HCl is a gas at room temp and its a vigorous reaction (not as vigorous with phenols)
why type of reaction is the reaction between NaBH4 and propanone
nucleophilic addition
what type of fission breaks the pi-bond in the c=o bond (in reduction by NaBH4)
heterolytic fission
what do you get when you reduce a ketone with NaBH4 (2[H] as a reducing agent)
a secondary alcohol
what do you get when you reduce an aldehyde with NaBH4 (2[H] as a reducing agent)
a primary alcohol
what does NaBH4 do to carbonyls and under what conditions
reduces them when warmed with them in an aqueous solution
do ketones undergo oxidation reactions and why/why not
they DONT as their not reactive enough
what type of reactions do carbonyls undergo
nucleophilic addition
whats the c=o bond like in carbonyls
the double bonds made up of a sigma bond and a pi bond. the c=o bond is polar as the oxygen is more electronegative than the carbon so the electron density in the double bond is closer the the oxygen.
therefore carbonyls react with some nucleophiles as its attracted to the delta positive carbon atom a adds across the double bond
whys the reaction of carbonyl compounds with HCN useful
it provides a means of increasing the length of the carbon chain
whats used to provide HCN/hydrogencyanide in reactions
sodium cyanide and sulfuric acid
what forms when HCN reacts with an aldehyde
a hydroxynitrile
whats the solubility of carboxylic acids like
the c=o and o-h bonds in carboxylic acids are polar, allowing carboxylic acids the form H bonds with water molecules
carboxylic acids with up to 4 carbons are soluble in water
as the number of c atoms increases the solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecules
what redox and neutralisation reactions do carboxylic acids take place in and what happens to the carboxylic acid
redox reactions with metals
neutralisation reactions waith bases (alkalis, metal oxides and carbonates)
the carboxylic acid forms a carboxylate c=o and c-o minus
whats the strength of carboxylic acids like
they are weak acids so they only partially dissociate in water eg methanoic acids makes H+ and HCOO-
how do carboxylic acids react with metals
in a redox reaction to form hydrogen and a carboxylate salt
how do carboxylic acids react with metal oxides
they react to form salt and water
how do carboxylic acids react with alkalis
they react to form salt and water this is an aqueous neutralisation reaction
how do carboxylic acids react with carbonates
they react to form salt, water and carbon dioxide
if the acids in excess the solid carbonate would disappear
they are only a few organic compounds acidic enough to react with carbonates
what are the derivatives of carboxylic acids (4)
esters
acyl chlorides
acid anhydrides
amide
how are acid anhydrides formed
by the removal of a water molecule from two carboxylic acid molecules
how do you test for the carboxyl group using reactions
the neutralisation reaction of carboxylic acids with carbonates gives CO2 off
as carboxylic acids are the only common organic compound acidic enough to react with carbonates
how to name an ester
the alcohol becomes an -yl at the start eg. ethyl
while the carboxylic acid becomes an -oate eg propanoate
how can an ester be made from a carboxylic acid and an alcohol
when a carboxylic acid and alcohol are warmed with a small amount of concentrated H2SO4 and ester and H2O are formed
whats reversible
acid hydrolysis
alkaline hydrolysis
acid hydrolysis = reversible
alkaline hydrolysis = irreversible
how can esters be hydrolysed with acid (acid hydrolysis) and what products are formed
this is the opposite of esterification
an ester is heated under reflux with aqueous dilute acid
the ester is broken down by water with the acid being the catalyst
the products are a carboxylic acid and an alcohol
how can esters be hydrolysed with an alkali and whats this known as
this is saponification and its irreversible
an esters heated under reflux with aqueous hydroxide ions this produces a salt and an alcohol
an alcohol and a carboxylate ions are formed
how can acyl chlorides be prepared
the parent carboxylic acid reacts with thionyl chloride (SOCl2)
the products are SO2 and HCl as gases and the acyl chloride
this reaction should be carried out in a fume cupboard.
