tests for carbonyl compounds

Question 1

what is 2,4-DNP?

Answer 1

2,4 - dinitrophenylhydrazine

Question 2

what observations are found in a positive test with 2,4-DNP

Answer 2

orange precipitate

Question 3

describe the process of reacting with 2,4-DNP?

Answer 3

• filter with reduced pressure to obtain impure 2,4 - DNP
• dissolve in minimum amount of hot solvent
• place in ice water
• crystallise to obtain pure 2,4-DNP
• filter and measure melting point
• compare to known data to identify

Question 4

describe the test for aldehydes

Answer 4

• mix silver nitrate and sodium hydroxide to create a brown precipitate
• add ammonium hydroxide until precipitate dissolves
• place test tube in boiling hot water
• add aldehyde - forms silver mirror

Question 5

what is tollums reagent?

Answer 5

• mild oxidising agent
• only oxidises aldehydes
• silver nitrate, sodium hydroxide and ammonium hydroxide

Question 6

what is the result of a positive test with tollens reagent ?

Answer 6

an aldehyde is present and has been oxidised to a carboxylic acid
- silver mirror forms

Question 7

oxidation: state the reagents / conditions

Answer 7

K2Cr2O7
heat and distill or reflux

Question 8

what is the result of a positive test with K2Cr2O7?

Answer 8

an alcohol is present
- orange solution to green solution

Question 9

what is the result of a positive test with sodium carbonate and sodium hydrogencarbonate?

Answer 9

carboxylic acid present
- effervescence

Question 10

what is the result of a positive test with bromine water?

Answer 10

alkene/phenol present
- decolourises
- white precipitate if phenol

Question 11

what is the result of a positive test with 2,4-DNP?

Answer 11

ketone or aldehyde present
- orange precipitate forms