Chapter 26 - Carbonyls and Carboxylic Acids Flashcards
Carbonyl compounds, Identifying aldehydes and ketones, Carboxylic acids, Carboxylic acid derivatives.
What is the double bond in the carbonyl and alkene functional group made of?
A σ (sigma) bond and a π bond.
The sigma bond is formed by the direct overlap of orbitals between the C and O atoms. The pi bond is formed by the carbon and oxygen p orbitals - sideways overlap above and below the atoms.
What are the two carbonyl groups?
Aldehydes and Ketones
What is the carbonyl functional group?
C=O
What is an aldehyde? How are they named?
Aldehydes have the functional group CHO and a suffix of ‘al’.
H-C=O
What is a ketone? How are they named?
A ketone ends in the suffix ‘one’ and functional group is CO
looks like this:
C
C=O
C
What is the reaction and conditions for oxidation of aldehydes?
Reflux
with a K2Cr2O7 / H+ catalyst
(+ oxidising agent)
Outline the detection of a carbonyl group? How do you ID the solid?
To detect carbonyl (C=O) compounds:
- Add 2,4 DNP
- If a yellow/orange precipitate forms - indicates a carbonyls presence
To ID the solid:
= filter ppt, recrystalise, take m.p. and compare to known values
Which reagent can distinguish between an aldehyde and a ketone?
What occurs?
Tollen’s reagent - reacts with an aldehyde only.
A silver mirror forms.
Ag+(aq) + e- –> Ag(s)
Aldehydes are oxidised to carboxylic acids. Ketones cannot be oxidised further.
When is the double bond (=) polar or nonpolar?
1) The C=C ( alkene group) is non polar
2) The C=O (carbonyl group) is polar
How are aldehydes reduced and what to?
Aldehydes are reduced by NaBH4 to primary alcohols.
How are ketones reduced and what to?
Ketones are reduced by NaBH4, to secondary alcohols
Outline the reaction mechanism for nucleophilic addition of NaBH4 to carbonyl compounds?
BH4- —> H- +BH3 (H- = nucleophile)
Outline the reaction of carbonyl compounds with HCN? What are the conditions?
HCN adds across the C=O bond of aldehydes and ketones to form a hydroxynitrile (containing a -OH and -CN functional groups)
HCN is made from sodium cyanide NaCN and sulfuric acid H2SO4.
Outline the mechanism for a carbonyl compound reacting with NaCN/H+ ?
in this reaction, the nucleophile is the cyanide ion, :CN- ( from the NaCN)
How can acidified potassium dichromate (K2Cr2O7/H+) distinguish between aldehydes and ketones?
Aldehyde present - Orange to green.
Ketone present - no change to solution (remains orange).
Why is potassium cyanide used instead of hydrogen cyanide?
It’s safer. HCN is a poisonous gas.
How soluble is carboxylic acid?
The C=O and O-H bonds in carboxylic acid are polar allowing it to form hydrogen bonds with water.
1) carboxylic acids are only soluble up to 4 carbon atoms
2) solubility decreases as carbon chain increases because the carbon chain is non polar
3) Dicarboxylic acids are even more soluble.
How strong are carboxylic acids?
Carboxylic acids are weak acids and only partially dissolve in water
RCOOH (aq) = H+ + RCOO-
Carboxylic acid + metal = ?
in aqueous solution carboxylic acids react with metals to form a carboxylate salt and hydrogen gas.
e.g 2CH3COOH (aq) + Mg(s) = (CH3COO-)2 Mg2+ + H2 (g)
Carboxylic acids + metal oxides =?
carboxylic acids react with metal oxides to form a salt and water.
e.g 2CH3COOH + MgO = (CH3COO-)2Mg2+ + H2O
Carboxylic acids + alkalis = ?
carboxylic acids react with alkalis to form a salt and water
e.g CH3COOH + NaOH = CH3COO-Na+ + H2O
Carboxylic acid + carbonates = ?
carboxylic acids react with carbonates to form a salt, CO2 and H2O
e.g 2 CH3COOH + Na2CO3 = 2CH3COO-Na+ + CO2 + H2O
Name the four carboxylic acid derivatives
1) Ester
2) Acyl chloride
3) Acid anhydride
4) Amide
How do you name esters?
1) ‘oic acid’ suffix is removed and replaced with ‘oate’
2) The alkyl chain attached to the -O is then added to the first word
What is esterification? Conditions?
Esterification is the reaction of an alcohol with a carboxylic acid to form an ester (RCOOR)
An Alcohol is warmed with carboxylic acid + conc H2SO4 (catalyst)
What is hydrolysis ?
The chemical breakdown of a compound in the presence of water or in an aqueous solution.
What is alkaline hydrolysis of an ester? What are the conditions, reagents and products?
Alkaline hydrolysis is irreversible. The ester is refluxed with aqueous alkali.
- Ester heated under reflux with aqueous alkali (hydroxide ions )
- Ester is broken down by water into carboxylate ion and alcohol
What is acid hydrolysis of an ester? What are the conditions and products?
Acid hydrolysis is the reverse reaction of esterification
- Ester is heated under reflux with dilute aqueous acid
- Ester broken down by water into carboxylic acid and alcohol
How do you name an acyl chloride (-COCl)?
Replace ‘oic acid’ with ‘oyl chloride’
How do you name an acid anhydride?
Change ‘-oic acid’ to ‘-oic anhydride’
When an acid anhydride reacts with a nucleophile, what are the two products?
R-CONu
R-COO-
Name the characteristic mechanism to change an acyl chloride to a carboxylic acid?
Addition-Elimination
How to prepare an acyl chloride?
Carboxylic acid + Thionyl chloride (SOCl2)
Acyl chloride + alcohol = ?
Ester + HCl
How to form esters from acyl chlorides?
acyl chloride + alcohol = aliphatic ester + HCl
acyl chloride + phenol = aromatic ester + HCl
How to form carboxylic acids from acyl chlorides?
acyl chloride + water –> carboxylic acid + HCl
How to form amides from acyl chlorides?
acyl chloride + ammonia (NH3) –> primary amide + NH4+Cl-
acyl chloride + amine (R’NH2) –> secondary amide + R’NH3+Cl-
How do acid anhydrides react with alcohols, phenols, water, ammonia and amides?
In the same way acyl chlorides do
Whats the equation for for the formation of phenyl ethanoate?
What’s the carboxyl group?
A carbonyl group + hydroxyl group= carboxyl group.
carboxyl group is COOH O=C-OH
Whats an ester? How do you name it?
where a carboxylic acid’s H in the OH group is replaced by C making a C-O-C bond.
Named after its parent carboxylic acid.
To name an ester remove the suffix -oic acid and replace it with ‘-oate’
What is an acyl chloride? How do you name it?
In an acyl chloride the OH in a carboxylic acid is replaced by a Cl group to become O=C-Cl .
Named after its parent carboxylic acid from which its derived.
To name: remove the ‘oic acid’ suffix and replace it with ‘oyl chloride’
What is an acid anhydride? How do you name it?
An acid anhydride is when two carboxylic acids are sharing an O instead of having an OH group.
Named by removing the ‘acid’ and putting the suffix ‘anhydride’.
Whats an amide?
An amide is when the OH group on a carboxylic acid is replaced by an ‘NH2’.
O=C-NH2
whats an Ether?
Ether has a functional group COC
whats a Dimer?
A structure containing two identical or similar units
Describe the recrystalisation practical.
- Dissolve solute in minimum vol of boiling solvent.
- Cool the solution at room temperature and then put beaker in an ice bath. Slow cooling leads to purer crystals.
- Crystals filtered through Buchner funnel and dry.
- Melting point can be can be determined to see how pure the crystals are or to identify the substance.
