Aldehydes and Ketones: Nomenclature, Properties, Preparation, and Reactions - Prof. Anjum, Slides of Organic Chemistry

Download Aldehydes and Ketones: Nomenclature, Properties, Preparation, and Reactions - Prof. Anjum and more Slides Organic Chemistry in PDF only on Docsity! Aldehyde and ketone Prepared by: Ramisa Anjum Lecturer Department of Pharmacy University of Asia Pacific 6.1 Aldehyde and Ketone — Both aldehyde and ketone are carbonyl compound (organic with C=O in it). Both has the same molecular formula as C,H2,O 6.1.1 Nomenclature of aldehyde O o functioning group of aldehyde are I R—C— H and end with —al i CH3CH»CH»s,—C—H butanal CH3CH3 oO | | Il 3-methylpentanal Cl CHs O II | | CH»CHCHs—C—H 4-chloro-3- methylbutanal benzaldehyde m- chlorobenzaldehyde O Ho | C —C—H > pnenyletnan Propanal Propanone; Propan-1-ol | Ethanoic acid Molecule = |Butane (CaHio)) (¢..COH) | CH;COCH; | C3H;OH | CH;COOH RMM 58 58 58 60 60 Boiling point (°C) 1 48 56 97 118 o Explanation : Butane is a non-polar molecule, where molecules were held by temporary dipole-induced dipole. Propanal and propanone are polar molecule, which has a permanent dipole-permanent dipole attraction forces. However, the_dipole moment of ketone is greater_than aldehyde, so ketone usually have higher b.p than aldehyde. Propan-1-ol has high boiling point due to strong hydrogen bond between them, however, ethanoic acid has greater hydrogen bond than propan-1- ol, since they form dimer between them \ Nn 7 co oe / oS @ R - R o Solubility : Lower aliphatic aldehydes such as methanal & ethanal are soluble in water because they are able to form hydrogen bond with water (as shown in diagram). Higher member of aliphatic carbonyl compounds are insoluble as there are presence of hydrophobic alkyl group R N C=omunH—-O—H 7 oF 6- o+ Oo PHYSICAL PROPERTIES OF ALDEHYDES AND KETONES |. Carbonyls are slightly polar, however, since there is no hydrogen on the carbonyl oxygen aldehydes and ketones do not form hydrogen bonds with themselves. They can hydrogen bond with water. Ketone 1. Oxidation of secondary alcohol o Oxidation of alcohol by using acidified potassium dichromate (V1) o Unlike oxidation on 1° alcohol, it does not need prevention as ketone formed will not further oxidise to other substances. | K5Cr>O-7 / H* I CH3CHCH; ————>—» _H3C—C—CH3H,0 Propan-2-ol propanone 2. Using catalytic oxidation (Cu at 400°C) on a 2° alcohol an i Cu , 400° + CH; buch: Su 400 HH C— 6 CH3 Me propan- -2-ol propanone o This process is also known as dehydrogenation as hydrogen is produced. O) Chemical reaction of aldehyde and ketone 1. Reduction of aldehyde o Reagent : LiAIH, (lithium aluminium hydride) in dry ether i LiAIH, / H* OH CH3CHz—C—H * 2TH] Gy giner” = CH3CH2—CH propanal propan-1-ol o From reaction above, we can tell that 19° alcohol is formed back using reduction. Hence, we can summarised the reaction as OH oxidation i _—________» <—_ —— CH3CH2—CHp reduction CH3CH,—C—H Propan-1-ol propanal Oxidation of aldehyde o Aldehyde can be further oxidised to form carboxylic acid. o Reagent : KMnO,/ Ht (acidified potassium manganate (VII) oO oO Il KMnOq/ H* Il CH3;CH,—C—H + [0] — > CHsCH2—C—oH Propanal propanoic acid o However, no further reaction for oxidation of ketone. Test Aldehyde Ketone ¢ Reagent: Fehling solution [solution of complex copper (Il) ion] * Positive Test : only works for aldehyde .__, |* Observation : blue solution turns to red precipitate of No reaction Fehling’s solution Cu,O0 occur for . . ll Equation :| p—c—u + ocy2* + SoH n—l-o «+ Cu,0 + 3H,0 ketone _— —y— copper (I) oxide fede. (brick-red precipitate) ¢« Reagent : Tollen solution [Solution of complexAg(NH3).]*] ¢ Positive test : only work for aldehyde ¢ Observation : colourless solution turn grey solid (silver No reaction Tollen’s mirror) i + 2 Ag(NH3)0H occur for reagent |Equation: | ,~™,, ketone 2 Agis) + R~ ~O NH,* H20 + 3NH3 2. Outline a chemical test to distinguish between a) propanal and propanone Reagent : Fehling / Tollen reagent (for aldehyde) ; lodine in NaOH (for ketone) Observation : Red brick precipitate formed when added propanal while no changes for propanone Equation : CH;CH,CHO + 2 Cu2+ 5 OH- ——* CH;CH,COO-+ Cu,0 + 3 HO b) ethanal and propanal Reagent : lodine in NaOH Observation : Yellow precipitate formed when added to ethanal but no changes for propanal Equation : CH;CHO + 31, + OH- —— > HCOO-+ CHI, + 3 HI c) pentan-2-one and pentan-3-one Reagent : lodine in NaOH Observation : Yellow precipitate formed when added to pentan-2-one but no changes for pentan-3-one | Equation : CH;CH,CH,COCH; + 31, + OH- CH;CH,CH,COO-+ CHI;+ 3H,0 +HI