carbonyls and carboxylic acids year 2

Question 1

aldehyde nomenclature

Answer 1

• -al is prefix used
• if molecule contains functional group with higher priority than aldehyde, -oxo prefix is used, eg oxo

Question 2

nucleophilic addition with aldehydes and ketones

Answer 2

NaCN is often used as a reagent along with a H+ source (usually H2SO4) to provide the HCN. This is because HCN is hard to store and is a toxic gas which reacts to produce dangerous by products
Hydroxynitriles commonly contain a chiral centre so optical isomers of the product are produces. The CN- nucleophile can attack from either above or below the planar double bond, causing different enantiomers to be produced

Question 3

identifying carbonyl compounds

Answer 3

Use 2,4-DNP to detect the presence of a carbonyl group, as an orange precipitate is formed
- then identify carbonyl compound from the melting point of the derivative. Filter the impure yellow/orange solid to separate the solid precipitate from the solution. The solid is then recrystalised to produce a pure sample of crystals. The melting point of the purified 2,4-DNP derivative is measured and recorded.
The melting point is then compared to a database or data table of values to identify the original carbonyl compound

WHEN ADDING TOLLENS HEAT!!!!!! to 50 degrees

Question 4

olubility of carboxylic acids

Answer 4

The carbon to oxygen double bond, and OH bond are polar allowing carboxylic acids to form hydrogen bonds with water molecules
- soluble if carboxylic acid has up to 4 carbon atoms
- as the number of carbon atoms increases, the solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule

Dicarboxylic acids habe two polar carboxyl groups to form hydrogen bonds. They are solid at room temperature and dissolve readily in water

Question 5

carboxylic acid derivative

Answer 5

• compound that can be hydrolysed to form the parent carboxylic acid. Contain common carbon to oxygen double bond
  examples: ester, acyl chloride, acid anhydride, amide

Question 6

acyl chloride

Answer 6

To name an acyl chloride, remove the -oic acid suffix from the parent carboxylic acid and replace with -oyl chloride
Made by reacting parent carboxylic acid with thionyl chloride, SOCl2
- very reactive so can undergo many reactions such as addition-elimination reactions

Carboxylic acids arent reactive enough to form esters with phenol. Acyl chlorides and acid anhydrides are both much more reactive than carboxylic acids and react with phenols to produce phenyl esters. Neither reaction requires an acid catalyst

Question 7

acid hydrolysis of esters

Answer 7

Hydrolysis is the chemical breakdown of a compound in the presence of water or in aqueous solution
for acid hydrolysis:
- ester is heated under reflux with dilute aqueous acid
- the ester is broken down by water, with the acid acting as a catalyst
- equilibrium will be established/reaction wont go into completion

Question 8

alkaline ester hydrolysis

Answer 8

Alkaline hydrolysis is also known as saponification and is irreversible. The ester is heated under reflux with aqueous hydroxide ions
- if sodium hydroxide is alkali a salt will form
- if just aqueous hydroxide ions, then ion of carboxylic acid and alcohol formed

Question 9

acid anhydrides

Answer 9

Esterification can also take place by reacting acid anhydrides with alcohols at room temp
- makes ester and carboxylic acid

Acid anhydrides are derivates of carboxylic acids formed by the substitution of -OH group by an alkanoate
-named by identifying the parent hydrocarbon chain and adding suffix -oic anhydride
- can also be named by removing the -oic acid from the carboxylic acid and adding -oic anhydride

Made from reaction of two carboxylic acids

React in similar ways to acyl chlorides with alcohols, phenols, water, ammonia and amines. Less reactive than acyl chlorides and are useful for some laboratory preparations where acyl chlorides may be too reactive