1. THE REACTIONS OF ALDEHYDES AND KETONES KNOCKHARDY PUBLISHING 2015 SPECIFICATIONS

2. CARBONYL COMPOUNDS - FORMULAE Molecular C 3 H 6 O Structural C 2 H 5 CHOCH 3 COCH 3 Displayed Skeletal C = O H C2H5C2H5 CH 3 H C C C H H O H H H C C C O H H H H O O

3. CARBONYL COMPOUNDS - NOMENCLATURE Aldehydes C 2 H 5 CHOpropanal Ketones CH 3 COCH 3 propanone CH 3 CH 2 COCH 3 butanone CH 3 COCH 2 CH 2 CH 3 pentan-2-one CH 3 CH 2 COCH 2 CH 3 pentan-3-one C 6 H 5 COCH 3 phenylethanone

4. CARBONYL COMPOUNDS - CHEMICAL PROPERTIES OXIDATION provides a way of differentiating between aldehydes and ketones mild oxidising agents are best aldehydes are easier to oxidise powerful oxidising agents oxidise ketones to a mixture of carboxylic acids ALDEHYDESeasily oxidised to acids RCHO(l) + [O] ——> RCOOH(l) CH 3 CHO(l) + [O] ——> CH 3 COOH(l) KETONESoxidised under vigorous conditions to acids with fewer carbons C 2 H 5 COCH 2 CH 3 (l) + 3 [O] ——> C 2 H 5 COOH(l) + CH 3 COOH(l)

5. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION Mechanismoccurs with both aldehydes and ketones involves addition to the C=O double bond unlike alkenes, they are attacked by nucleophiles attack is at the positive carbon centre due to the difference in electronegativities alkenes are non-polar and are attacked by electrophiles undergoing electrophilic addition C=CELECTROPHILESALKENES CARBONYLS NON-POLAR C=OPOLARNUCLEOPHILES ADDITION BondAttacking speciesGroupPolarityResult

6. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION Reagentpotassium cyanide – followed by dilute acid Conditionsreflux Nucleophilecyanide ion CN¯ Product(s)hydroxynitrile (cyanohydrin) Equation CH 3 CHO + HCN ——> CH 3 CH(OH)CN 2-hydroxypropanenitrile NotesHCN is a weak acid and has difficulty dissociating into ions HCN H+ + CN¯ Using ionic KCN produces more of the nucleophilic CN¯ Alternative reagent: HCN catalysed by alkali which shifts the above equilibrium in favour of CN¯ HIGHLY TOXIC TAKE GREAT CARE HIGHLY TOXIC TAKE GREAT CARE

7. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION MechanismNucleophilic addition Step 1CN¯ acts as a nucleophile and attacks the slightly positive C One of the C=O bonds breaks; a pair of electrons goes onto the O Step 2A pair of electrons is used to form a bond with H + Overall, there has been addition of HCN STEP 2STEP 1

8. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION MechanismNucleophilic addition Step 1CN¯ acts as a nucleophile and attacks the slightly positive C One of the C=O bonds breaks; a pair of electrons goes onto the O Step 2A pair of electrons is used to form a bond with H + Overall, there has been addition of HCN STEP 2STEP 1

9. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION Watch out for the possibility of optical isomerism in hydroxynitriles CN¯ attacks from above CN¯ attacks from below Both optical isomers are produced in a racemic mixture

10. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION Watch out for the possibility of optical isomerism in hydroxynitriles CN¯ attacks from above CN¯ attacks from below

11. Reagent sodium tetrahydridoborate(III) (sodium borohydride), NaBH 4 Conditionsaqueous or alcoholic solution MechanismNucleophilic addition (also reduction as it is addition of H¯) NucleophileH¯ (hydride ion) Product(s)Alcohols Aldehydes are REDUCED to primary (1°) alcohols. Ketones are REDUCED to secondary (2°) alcohols. Equation(s)CH 3 CHO + 2[H] ——> CH 3 CH 2 OH CH 3 COCH 3 + 2[H] ——> CH 3 CHOHCH 3 NotesThe water provides a proton CARBONYL COMPOUNDS - REDUCTION WITH NaBH 4

12. Reagent sodium tetrahydridoborate(III) (sodium borohydride), NaBH 4 Conditionsaqueous or alcoholic solution MechanismNucleophilic addition (also reduction as it is addition of H¯) NucleophileH¯ (hydride ion) CARBONYL COMPOUNDS - REDUCTION WITH NaBH 4 Water is added Primary alcohol Aldehyde

13. Reagent sodium tetrahydridoborate(III) (sodium borohydride), NaBH 4 Conditionsaqueous or alcoholic solution MechanismNucleophilic addition (also reduction as it is addition of H¯) NucleophileH¯ (hydride ion) CARBONYL COMPOUNDS - REDUCTION WITH NaBH 4 ANIMATED MECHANISM

14. THE TETRAHYDRIDOBORATE(III) ION BH 4 B H HH H H H H each atom needs one electron to complete its outer shell atom has three electrons to share boron shares all 3 electrons to form 3 single covalent bonds B H H H The hydride ion forms a dative covalent bond B H H H B H

15. CARBONYL COMPOUNDS - REDUCTION WITH HYDROGEN Reagent hydrogen Conditionscatalyst - nickel or platinum Reaction type Hydrogenation, reduction Product(s)AlcoholsAldehydes are REDUCED to primary (1°) alcohols. Ketones are REDUCED to secondary (2°) alcohols. Equation(s)CH 3 CHO + H 2 ——> CH 3 CH 2 OH CH 3 COCH 3 + H 2 ——> CH 3 CHOHCH 3 NoteHydrogen also reduces C=C bonds CH 2 = CHCHO + 2H 2 ——> CH 3 CH 2 CH 2 OH

16. CARBONYL COMPOUNDS - REDUCTION IntroductionFunctional groups containing multiple bonds can be reduced C=Cis reduced to CH-CH C=Ois reduced toCH-OH C  Nis reduced toCH-NH 2 HydrogenHH 2 H + (electrophile)H¯ (nucleophile) Reactions Hydrogen reduces C=C and C=O bonds CH 2 = CHCHO + 4[H] ——> CH 3 CH 2 CH 2 OH Hydride ion H¯ reduces C=O bonds CH 2 = CHCHO + 2[H] ——> CH 2 =CHCH 2 OH ExplanationC=O is polar so is attacked by the nucleophilic H¯ C=C is non-polar so is not attacked by the nucleophilic H¯

17. CARBONYL COMPOUNDS - REDUCTION ExampleWhat are the products when Compound X is reduced? NaBH 4 H2H2 COMPOUND X

18. CARBONYL COMPOUNDS - REDUCTION ExampleWhat are the products when Compound X is reduced? C=O is polar so is attacked by the nucleophilic H¯ C=C is non-polar so is not attacked by the nucleophilic H¯ NaBH 4 H2H2 COMPOUND X

19. 2,4-DINITROPHENYLHYDRAZINE Structure Usereacts with carbonyl compounds (aldehydes and ketones) used as a simple test for aldehydes and ketones makes orange crystalline derivatives - 2,4-dinitrophenylhydrazones derivatives have sharp, well-defined melting points also used to characterise (identify) carbonyl compounds. Identification / characterisation A simple way of characterising a compound (finding out what it is) is to measure the melting point of a solid or the boiling point of a liquid. C 6 H 3 (NO 2 ) 2 NHNH 2

20. 2,4-DINITROPHENYLHYDRAZINE C 6 H 3 (NO 2 ) 2 NHNH 2 The following structural isomers have similar boiling points because of similar van der Waals forces and dipole-dipole interactions. They would be impossible to identify with any precision using boiling point determination. Boiling point 213°C 214°C 214°C Melting point of 2,4-dnph derivative 209°C 248°C 265°C By forming the 2,4-dinitrophenylhydrazone derivative and taking its melting point, it will be easier to identify the unknown original carbonyl compound. CHO ClCl ClCl ClCl

21. THE CHEMISTRY OF ALDEHYDES AND KETONES THE END ©2015 JONATHAN HOPTON & KNOCKHARDY PUBLISHING ©2015 JONATHAN HOPTON & KNOCKHARDY PUBLISHING