Carbonyls, esters and carboxylic acids Flashcards Preview

A2 CHEMISTRY > Carbonyls, esters and carboxylic acids > Flashcards

Flashcards in Carbonyls, esters and carboxylic acids Deck (20):

Making esters

- Can be made from carboxylic acid + alcohol with conc. sulfuric acid catalysts, water is produced as side product.

- Can be made by heating an acid anhydride with alcohol, carboxylic acid produced as side product.


What is an acid anhydride?

An acid formed from the removal of a water molecule from two carboxylic acid molecules.


Hydrolysis of esters

- Acid hydrolysis:
Heated under reflux with dilute sulfuric or hydrochloric acid. Ester broken down by the water. Products are alcohol and carboxylic acid. This is reversible.

- Alkaline hydrolysis:
Aqueous sodium are potassium hydroxide is refluxed with ester. Products are sodium or potassium salt of the carboxylic acid and alcohol. Not reversible.


What are lipoproteins?

Particles that carry lipids such as cholesterol and fats through the blood.


What are HDLs and LDLs?

HDLs: can remove cholesterol from the arteries and transport it back to the liver for excretion or re-utilisation.

LDLs: are responsible for carrying cholesterol and triglycerides from the liver to the tissues.


How is biodiesel made?

Transesterification. Triglycerides in fats and oils are reacted with methanol or ethanol in the presence of a sodium or potassium hydroxide catalyst. Glycerol also produced


Carbonyl bonding, comparison with alkene bond

Double bond is made up of sigma bond formed by direct overlap of orbitals between the C and O atoms. Pi bond is formed by the overlap of the p-orbitals on the C and O atoms drawn towards the O atom as its electronegativity creates a dipole in the bond so reacts differently to alkene bond
The distribution of electrons in the pi bond is heavily distorted towards the oxygen end of the bond, because oxygen is much more electronegative than carbon.


Reduction of aldehydes and ketones, what type of reaction, what is electro or nucleophile?

Reduced to alcohols using reducing agent such as NaBH4 and water as a solvent. Warmed.
Nucleophilic addition, H- ions (hydride) act as Nucleophiles


Test to detect the carbonyl group

Adding Brady's reagent; a mixture of methanol, sulfuric acid and 2,4 - DNP. When added to aldehydes or ketones a yellow or orange precipitate is formed.


Testing for aldehydes, type of reaction, product

Tollen's reagent oxidises aldehydes to carboxylic acids. It is prepared by adding sodium hydroxide solution to silver nitrate solution, forming a brown precip. of silver oxide. Dilute ammonia is then added just until the precip. dissolves. If aldehyde, a silver mirror is formed. Oxidisation of aldehyde by Ag+ ions, produces carboxylic acid, Ag+ + e- --> Ag(s) [reduction]


Identifying the exact compound

The yellow/orange solid 2,4 - DNP derivative is filtered and recrystallized. The crystals are then filtered and allowed to dry. Melting point of purified derivative is then measured and recorded compared with known values for aldehydes and ketones


Solubility of carboxylic acids

Between 1-4 carbons, very soluble in water as highly polar C=O and O-H bonds allow the molecules to form hydrogen bonds with water molecules. Decreases as proportion of non-polar chain gets longer.


What is glycerol?



What are fatty acids?

Long-chain carboxylic acids


Difference between fats and oils

Melting point


What are triglycerides?

Triesters of glycerol and three fatty acid molecules


What does representation of fatty acid as 18:1(9) mean?

18 carbons, 1 double bond of 9th carbon


Why are trans unsaturated fats bad?

Thought to increase risk of heart disease, act like saturated fats and raise LDL levels and reduce HDL levels


Packing of unsaturated fats

In cis form cannot pack closely together so exist as liquids
In trans form the structure is linear so pack closely together and will have higher melting point that cis isomer


Colour change when aldehyde oxidised

Orange to green