module 6 - (chapter 28) - carbon-carbon bond formation

Question 1

nitriles from haloalkanes

Answer 1

• react haloalkanes with KCN in ethanol
• the length of the carbon chain increased
• forms a nitrile and KCl

Question 2

nitriles from aldehydes and ketones

Answer 2

• react with HCN in a nucleophilic addition reaction
• increases carbon chain length
• forms hydroxynitriles
• HCN is very poisonous and cyanide ions can increase the reaction rate. NaCN and H2SO4 improve the reaction rate whilst maintaining safety.

Question 3

nitriles as intermediates

Answer 3

• Nitriles can be reduced to amines using a nickel catalyst

- nitriles undergo hydrolysis to form carboxylic acids by heating with dilute acid (H2O and HCl)

Question 4

alkylation and acylation

Answer 4

• increase carbon chain length by adding side chains to benzene rings
• do it in the presence of a halogen carrier catalyst.
• this can increase the carbon chain length as well as new functional groups and therefore new chemical reactions

Question 5

how do you separate a solid product from a liquid reaction mixture?

Answer 5

• attach one end of the rubber tubing to the vacuum outlet and the other to the Buchner funnel
• switch on the tap
• place a piece of paper inside the funnel and wet it with the same solvent used to prepare the solid
• pour reaction mixture into the funnel
• rinse the beaker with the solvent so that all of the solid crystals collect in the funnel
• rinse the crystals with more solvent and leave them under suction for a few minutes so there crystals dry.

Question 6

recrystallisation

Answer 6

• remove impurities from the solid product obtained in filtration
• pour chosen solvent into a conical flask and warm (e.g. using a buses burner or heating mantle)
• tip the impure sample into a second conical flask or beaker
• slowly add the solvent until it dissolves (minimum amount possible)
• cool and filter again using a Buchner funnel

Question 7

melting point determination

Answer 7

pure substances have sharp melting points (over one/two degrees). If impure it has a wide range.
impure samples also have lower melting points
- before taking the melting point of a solid ensure it is dry
- seal the end of a capillary tube in a bunsen burner
- cool and fill with crystals
-place in a sample hole of a melting point apparatus
-observe through magnifying window and when the solid starts to melt record temperature
-place a second sample in the hole and once the melting point is approached, set the temp to low and observe the sample slowly (more accurate).