Chapter 26- carbonyl and carboxylic acid compounds

Functional group of carbonyls

C=O

physical properties of carbonyls

• polar c=o bond

• Strong dipole-dipole interactions

• Higher bpt than alkanes

• Lower bpt than alcohols (no H bonding)

why do carbonyls undergo addition reactions?

C=O made from sigma and pi bond and is strong but polar, so is susceptible to attack by nucleophiles and carbonyls are unsaturated

solubility of carbonyls in water

carbonyls form H bonds with water through lone pair on oxygen molecule, short chain carbonyls are soluble in water

testing for carbonyls in 2,4-dinitrophenylhydrazine

• aldehydes- orange precipitate

• Ketone- orange precipitate

testing for carbonyls in Tollens reagent

• Aldehydes- silver mirror (can be oxidised)

• Ketones- no silver mirror (can’t be oxidised)

testing for carbonyls using K₂Cr₂O₇/H⁺

• aldehydes- oxidised to form carboxylic acid

• Ketones-

testing for carbonyls using fehlings solution

• aldehydes- red precipitate

• Ketones- do not react

Tollens reagent

silver ions are reduced to form silver (a silver mirror)

Ag⁺_(aq) + e^- → Ag_(s)

Acidified potassium dichromate

orange dichromate ions are reduced to form green chromium (iii) ions

Cr₂O₇^2- → Cr³⁺

Cr₂O₇^2- + 6e^- + 14H⁺→ Cr³⁺ + 7H₂O

Fehlings solution

is blue and will form a red precipitate in the presence of an aldehyde as Cu²⁺ oxidises aldehyde to form a carboxylic acid and Cu⁺

Nucleophile

electron pair donator

Nucleophilic addition of carbonyls

reduction of carbonyl compounds with sodium borohydride, NaBH₄

• Aldehyde→ primary alcohol

• Ketone→ secondary alcohol

Reduction of carbonyl compounds using HCN

aldehydes→ hydroxynitrile

Reagent- NaCN (or KCN) with H₂SO₄

Nucleophile- :ČN

Useful as increases carbon chain length by one nami

naming hydrocynitriles

1. Identify parent carbon chan (Carbon 1= CN)

2. Name nitrile fist (replace alkene with -nitrile)

3. Locate the OH group (number chain so CN is carbon 1)

4. Add the position and the prefix (hydroxyl)

functional group of carboxylic acids

-COOH

Test for carboxyl group

test: add sodium carbonate

Result: observe fizzing/carbon dioxide evolved

dimerisation

when two molecules form a dimer through hydrogen bonding (higher bpt than expected)

solubility of carboxylic acids

soluble in water up to when there are four c in the chain- bed of the O atoms in the carboxyl group can form H bonds with H atoms in water

Reactions of carboxylic acids

with:

Metal

• Products: metal carboxylate + H₂

• Observation: effervescence, metal association

• Gas test result: squeaky pop

Metal oxide

• Products: metal carboxylate + H₂O

• Observations: metal oxide dissolves

• Gas test result: no gas produced

Metal hydroxide

• Products: metal carboxylate + H₂O

• Observation: no visible change

• Gas test result: no gas produced

Metal carbonate

• Products: metal carboxylate + H₂O + CO₂

• Observation: effervescence

• Gas test result: bubble through limewater, turns cloudy

Functional group of esters

-COO-

uses of esters

• solvents

• Perfumes

• Plasticisers

• Food flavouring

Properties of esters

volatile (evaporate easy) and sweet/fruity smelling

BPT of esters

Lower bpt than alcohols as no H bonds only dipole-dipole interactions

Solubility of esters

small esters are fairly soluble in water as lone pair on the oxygen can accept H bonds from water

Two methods of making esters

1. Alcohol + carboxylic acid

2. Alcohol + acid anhydride

alcohol + carboxylic acid method for making esters

conditions: warm, conc H₂SO₄ catalyst

Products: ester + water

alcohol + acid anhydride method to making ester

Conditions: warm (no catalyst)

Products: ester + carboxylic acid

Hydrolysis

breakdown of an ester using water or a solution

Two types a hydrolysis

1. Acid hydrolysis

2. Base hydrolysis

Acid hydrolysis

Reverse esterification

Conditions: heat under reflux with dilute aqueous and catalyst

Broken down by water

Products: carboxylic acid + alcohol

Base hydrolysis

reverse of esterification

Conditions: heat under reflux with dilute aqueous alkali ions

Ester broken down by water

Products: carboxylate ion + alcohol

Irreversible

Functional group of acyl chloride

ROCl

Naming of acyl chlorides

Start with parent carboxylic acid name and then remove ‘oic acid’ and add ‘oil chloride’

physical and chemical properties of acyl chloride

physical properties

• Colourless liquids at room temp

Chemical properties

• Fumes and smell strongly in air as they react with the water vapour to form carboxylic acids and hydrogen chloride

• React vigorously with water rather than dissolving

forming acyl chlorides

reagents: carboxylic acids, thionyl chloride (SOCl₂)

Conditions: vigorous reaction- use fumehood

General equation:

RCOOH + SOCl₂ → RCOCl + SO_2(g) + HCl_(g)

reactions of acyl chlorides

1) esterification

Reagents: acyl chloride, alcohol

Conditions: no catalyst or heat needed

General equation: RCOCl + R’OH → RCOOR’ + HCl

2) making phenyl esters

Phenol does not react with carboxylic acids, but do with acyl chlorides

3) reaction with water

Reagents: acyl chloride, water

Conditions: vigorous reaction- use a fumehood

General equation: RCOCl + H₂O → RCOOH + HCl

During nucleophillic addition elimination of acyl chlorides, how does the shape around the central C change

goes from original planar to tetrahedral back to trigonal planar