nitriles

Question 1

what is CN- in inorganic compounds

Answer 1

cyanide ions

Question 2

what is CN- is organic compounds

Answer 2

nitrite functional group

Question 3

why is HCN not used

Answer 3

• it is a highly toxic gas in normal laboratory conditions
• stops mitochondrial enzymes working in living cells
• safer alternative in laboratory is to use a cyanide salt such as potassium cyanide which is solid at room temperature and easier to handle

Question 4

what are the ways to increase the carbon chain length

Answer 4

• nucleophilic substitution

- nucleophilic addition

Question 5

describe nucleophilic substitution to increase the carbon chain length

Answer 5

• the haloalkanes have a dipole in the C-X bond due to the significant difference in electronegatives between carbon and the halogen, this means that the carbon is susceptible to nucleophilic attack

Question 6

describe the conditions needed for a nucleophilic substitution

Answer 6

• haloalkane
• potassium cyanide
• heated under reflux
• solvent is ethanol - cannot use water as the hydroxide ion tends to be the nucleophile and the carbon chain length would not increase

Question 7

describe the nucelophilic addition reaction to increase the carbon chain length

Answer 7

• the carbon in the carbonyl group has a slight positive charge and this makes it susceptible to nucleophilic attack
• hydrogen cyandie can be used to generate the cyanide nucleophile
• the cyanide ion will be attracted to the carbon of the carbonyl group and forms a new covalent bond which extends the length of the carbon chain
• pie bond of the C=O then opens and the oxygen accepts the extra pair of electrons, this allows the now negatively charged oxygen atom to accept a proton and become a hydroxyl group - forms a hydroxynitrile compound

Question 8

describe the racemic mixture that can form from nucleophilic addition

Answer 8

• the C=O planar bond, therefore there is an equally likely chance that the cyanide ion will attack from either side
• racemic mixture is produced when an asymmetric ketone or any aldehyde other than methanol is used as methanol is not asymmetric

Question 9

what do nitriles form when they undergo reduction reactions

Answer 9

• they form amines when they undergo reduction

Question 10

what can you use to make nitriles undergo reduction

Answer 10

• hydrogen and nickel, 150 degrees

- lithium tetrahydridoaluminate LiAlH4 - anhydrous conditions

Question 11

what do nitriles form when they undergo hydrolysis

Answer 11

• they form an amide and ammonium salt initially, but rate of reaction is so slow that it is not significant - therefore organic acids are formed instead rather than the ammonium salt
• this is because the strong acid fully ionises in solution forming hydrogen ions and chloride ions
• once the amide is formed the bond between the nitrogen and the carbon is broken making an ethanoate ion
• this then reacts with the proton from the strong acid to form the carboxylic acid
• all organic acids are weak acids and only partially ionise in solution - the CN bond is compltetely broken and this gives the carboxylic acid and ammonium salt as the major products

Question 12

what reagents and conditions needed for nitriles to undergo hydrolysis

Answer 12

• strong acid
• reflux and heating
• under acidic they form carboxylic acids