Aldehydes and Ketones

Before you can learn about aldehydes and ketones, you must first know something about the nomenclature of carboxylic acids since many of the names of aldehydes and ketones are derived from the names of the corresponding carboxylic acids.

Carboxylic acids: R-COOH, R-CO 2 H, Common names: HCO 2 Hformic acidL. formica ant CH 3 CO 2 Hacetic acidL. acetum vinegar CH 3 CH 2 CO 2 Hpropionic acidG. “first salt” CH 3 CH 2 CH 2 CO 2 Hbutyric acidL. butyrum butter CH 3 CH 2 CH 2 CH 2 CO 2 Hvaleric acidL. valerans

Carboxylic acids, common names: … CH 3 (CH 2 ) 4 CO 2 Hcaproic acidL. caper goat CH 3 (CH 2 ) 5 CO 2 H--- CH 3 (CH 2 ) 6 CO 2 Hcaprylic acid CH 3 (CH 2 ) 7 CO 2 H--- CH 3 (CH 2 ) 8 CO 2 Hcapric acid CH 3 (CH 2 ) 9 CO 2 H--- CH 3 (CH 2 ) 10 CO 2 Hlauric acidoil of lauryl

C—C—C—C—C=O δ γ β αused in common names

Special names!

ALDEHYDES AND KETONES “carbonyl” functional group: Aldehydes Ketones

Nomenclature: Aldehydes, common names: Derived from the common names of carboxylic acids; drop –ic acid suffix and add –aldehyde. CH 3 CH 3 CH 2 CH 2 CH=O CH 3 CHCH=O butyraldehyde isobutyraldehyde (α-methylpropionaldehyde)

Aldehydes, IUPAC nomenclature: Parent chain = longest continuous carbon chain containing the carbonyl group; alkane, drop –e, add –al. (note: no locant, -CH=O is carbon #1.) CH 3 CH 3 CH 2 CH 2 CH=O CH 3 CHCH=O butanal 2-methylpropanal H 2 C=OCH 3 CH=O methanalethanal

Ketones, common names: Special name: acetone “alkyl alkyl ketone” or “dialkyl ketone”

(o)phenones: Derived from common name of carboxylic acid, drop –ic acid, add –(o)phenone.

Ketones: IUPAC nomenclature: Parent = longest continuous carbon chain containing the carbonyl group. Alkane, drop –e, add –one. Prefix a locant for the position of the carbonyl using the principle of lower number.

Physical properties: polar, no hydrogen bonding mp/bp are relatively moderate for covalent substances water insoluble (except: four-carbons or less)

Spectroscopy: IR:C=O stretch, strong ~1700 cm -1 RCHO1725ArCHO1700 R 2 CO1710ArCOR1690 C—H stretch for aldehydes2720 nmr: -CHO9-10 ppm

C=O stretch acetophenone

valeraldehyde CHO C—H stretch 2720 cm -1 C=O stretch

valeraldehyde CH 3 CH 2 CH 2 CH 2 CH=O a b c d e -CHO

Oxidation/Reduction: oxidation numbers: oxidation CH 4 CH 3 OH H 2 C=O HCO 2 H CO 2 alkane alcohol aldehyde carboxylic acid reduction

Aldehydes, syntheses: 1.Oxidation of 1 o alcohols 2.Oxidation of methylaromatics 3.Reduction of acid chlorides Ketones, syntheses: 1.Oxidation of 2 o alcohols 2.Friedel-Crafts acylation 3.Coupling of R 2 CuLi with acid chloride

Aldehydes synthesis 1) oxidation of primary alcohols: RCH 2 -OH + K 2 Cr 2 O 7, special conditions  RCH=O RCH 2 -OH + C 5 H 5 NHCrO 3 Cl  RCH=O (pyridinium chlorochromate) [With other oxidizing agents, primary alcohols  RCOOH]

Aldehyde synthesis: 2) oxidation of methylaromatics:  Aromatic aldehydes only!

Aldehyde synthesis: 3) reduction of acid chloride

Ketone synthesis: 1) oxidation of secondary alcohols

Ketone synthesis: 2) Friedel-Crafts acylation Aromatic ketones (phenones) only!

Friedel Crafts acylation does not work on deactivated rings.

Ketone synthesis: 3) coupling of RCOCl and R 2 CuLi

Aldehydes, syntheses: 1.Oxidation of 1 o alcohols 2.Oxidation of methylaromatics aromatic only 3.Reduction of acid chlorides Ketones, syntheses: 1.Oxidation of 2 o alcohols 2.Friedel-Crafts acylation aromatic only 3.Coupling of R 2 CuLi with acid chloride

aldehyde 1 o alcohol Ar-CH 3 acid chloride CrO 3 H 2 O (AcO) 2 O LiAlH(O-t-Bu) 3 K 2 Cr 2 O 7, special cond. or C 5 H 5 NHCrO 3 Cl

ketone 2 o alcohol acid chloride + ArH acid chloride + R 2 CuLi NaOCl, etc. AlCl 3

1.outline three different syntheses for benzaldehyde 2.outline three different syntheses for benzophenone 3.outline a different synthesis for each of the following compounds: cyclohexanone, 4-bromobenzaldehyde, 2-pentanone, valeraldehyde, acetophenone, isobutyraldehyde,

Synthesize benzaldehyde three different ways.

Synthesize benzophenone three different ways.

cyclohexanone, 4-bromobenzaldehyde, 2-pentanone, valeraldehyde, acetophenone, isobutyraldehyde, using a different method for each one.

The methods could be reversed for the last two syntheses.