Carbonyls And Carboxylic Acids Chp26 Flashcards
What is the difference between carbonyl compound and alkenes?
The C=C double bond in alkenes are non polar where’s C=O double bond in carbonyl compounds is polar. Due to the polarity, aldehydes and ketone react with some nucleophiles (nucleophilic addition)
Why are carbonyls stronger than alkanes?
Carbonyls have permanent dipole-dipole interactions which are stronger compared to alkanes which use London forces which are weaker.
Aldehydes and Ketones Solubility in water
Aldehydes and ketones mix completely in water because the hydrogen bonds form between the oxygen of the carbonyl compounds
What are the four nucleophiles that are used nucleophilic addition?
:-OH, N:H3, H2:O, :-CN
What are the reagent and conditions used for the reaction with HCN?
Reagent- H2SO4/NaCN
Conditions- Reflux in acidic solution
What are the dangers of HCN?
Hydrogen cyanide is a highly volatile liquid which has a faint bitter almond smell and toxic.
What are safer alternatives for HCN?
KCN + H2SO4
NaCN + H2SO4
Which are solid at room temperature and easier to handle
What are the reagents, nucleophiles and products of reduction with NaBH4?
Reagent: NaBH4 (reducing agent)
Nucleophile: H- (aq) (hydride ion)
Products: Primary alcohols (aldehydes) and secondary alcohols (ketones)
Why can’t H- act as an electrophile?
H- cannot act a partially positive so it cannot as an electrophile
What reagent is used to identify the presence of carbonyl compounds?
Brady’s reagent / 2,4-DNP
Observation for a positive result for Brady’s/ 2,4-DNP
Yellow or Orange precipitate
Why can solid 2,4 DNP be hazardous?
Solid 2,4- DNP can be very hazardous because friction can cause it to explode.
What type of reaction is the test for for detecting carbonyl compounds?
Nucleophile addition elimination and condensation reaction.
What is the reagent used to distinguish between aldehydes and ketone?
Tollens’ reagent (ammoniacal silver nitrate solution)
What are the observations/ positive results for tollens reagent
Silver mirror is produced if an aldehyde is present
What practical method is used for tollens’ reagent?
Heat unknown solution in water bath as you add tollens reagent.
What type of reaction is present when tollens reagent is used and what is the equation?
-Oxidation reaction
- Aldehyde + [O] —> carboxylic acid
- Ag+ (aq) + e- —-> Ag(s) (silver mirror)
What are melting point apparatus used to identify?
Identify a specific aldehyde or ketone
Practical method for melting apparatus to identify carbonyl compounds
-Filter the solution under reduced pressure
- Recrystallise it
- Use melting point apparatus to determine the melting point (capillary tube and thermometer)
- Compare the melting point to a database
(A physical change)
Why does CA have a high melting point?
-Forms hydrogen bonds so high melting point and CA with up to 4 carbon atoms are soluble in water
What happens to the solubility as the chain increases?
As chain increases, the solubility will decrease as the non-polar chain has a greater effect on the overall polarity of the molecule.
CA reaction with metals
Type of reaction: Redox
Description and products; H2(g) + carboxylate salt - Effervesence as H2 gas and metal dissapears
Equation: 2CH3CH2COOH(aq) + Mg(s) -> (CH3CH2COO-) Mg2+(aq) + H2
CA reaction with metal oxides
Reaction: Neutralisation
Description and products: Salt + Water
Equation: 2CH3COOH(aq) + CaO -> 2(CH3COO-)Ca2+ (aq) + H2O
CA reaction with alkalis
Reaction: Neutralisation
Description and products: Salt + Water
Equation: CH3COOH(aq) + NaOH(aq) -> CH3COO-Na+(aq) + H2O(l)
CA Reaction with carbonates
Reaction: Neutralisation
Description and products: Salt + Water + CO2 - effervescence bubbles and solid carbonate will disappear
Equation: 2CH3COOH(aq) + Na2CO3(aq) -> 2CH3COO-Na+ (aq) + H2O + CO2 (g)
Test for carboxylic acids
Only CA can react with carbonates as they are sufficiently acidic (it can react with weak bases), this how you distinguish it from a phenol
