Reactions of Alcohols, Phenols, Aldehydes and Ketones

Reactions of Alcohols and Phenols

OBJECTIVES Understand the properties and

reactions of alcohol and phenol Enumerate and give the processes

involving alcohol and phenol Compare and contrast aldehydes

and ketones in terms of their structures and properties

Alcohols and Alcohols and PhenolsPhenols

Alcohol is a compound that has a bonded to a saturated, sp3-hybridized

carbon atom. It can be classified as primary,

secondary, and tertiary according to the number of alkyl groups directly bonded to the alcohol carbon.

Phenol, on the other hand, has a hydroxyl group bonded to an

Its IUPAC name is

hydroxyl group (-OH)

aromatic ring.

benzenol.

Solubility in WaterSolubility in WaterCOMPOUND SOLUBILITY

Ethyl alcohol

n-butyl alcohol

sec-butyl alcohol

tert-butyl alcohol

Benzyl alcohol

Glycerol

Phenol

SOLUBLESOLUBLESOLUBLESOLUBLEINSOLUBLE

SOLUBLEINSOLUBLE

Solubility in WaterSolubility in Water Increases with of hydroxyl groups. Solubility of monohydric alcohols

decreases with Branched isomers are more soluble

than

increasing number

increasing molecular weight.

unbranched isomers.

Solubility in WaterSolubility in WaterSince alcohols can form hydrogen bond with water, low-molecular weight alcohols are water-soluble. However, as the molecular weight of an alcohol increases, the proportion of it that is hydrocarbon . The alcohol becomes more like an

, less like water, and

increases

alkane

less soluble in water.

Test for Alcohols and Test for Alcohols and Phenols (Acidity and Phenols (Acidity and Basicity)Basicity)

Compound Reaction w/ litmus paper

Reaction w/ pH paper

Ethyl alcohol

Phenol Phenols are more acidic than alcohols because the anion is resonance-stabilized by the

phenoxidearomatic ring.

Blue to red 6

Blue to red

5

Test for Alcohols and Test for Alcohols and Phenols (Acidity and Phenols (Acidity and Basicity)Basicity)

Sharing the negative charge over the ring the stability of the phenoxide

anion and thus increases the tendency of the correspondingThe characteristic property that differentiates phenols from alcohols isPhenols are weakly acidic and can be neutralized byAlcohols are less acidic than phenols and are not neutralized by sodium hydroxide.

increases

phenol to dissociate.

acidity.

sodium hydroxide.

Reaction with Reaction with SodiumSodium

n-butyl alcohol 1st

sec-butyl alcohol

2nd

Tert-butyl alcohol

3rd

Phenol 4th Alcohols react with sodium metal to yield alkoxide salts that are themselves strong bases.

2ROH + 2Na 2RONa + H2

Reaction with Reaction with Acetyl ChlorideAcetyl Chloride

Ester formed when acetyl chloride reacts with alcohol and phenol evident via formation of a top layer, which usually accompanied by the evolution of heat.

ROH + CH3COCl CH3COOR + HCl

ArOH + CH3COCl CH3COOAr + HCl

Lucas TestLucas Test Lucas reagent – is a mixture of

concentrated HCl and Test for relative rates of formation Test to deduce structure of Formation of a chloride from alcohol is

indicated by the that appears when the separates from the solution.

anhydrous zinc chloride.

alkyl halide

alcohols

cloudiness

chloride

Lucas TestLucas TestReactivity is measured by the time required for the cloudiness to appear

Tertiary alcohol – reacts readily at

Secondary alcohol – reacts withinPrimary alcohol – does not react appreciably at

room temperature

five minutes

room temperature

Lucas TestLucas TestAlthough the alcohols are soluble in the Lucas reagent, the alkyl halide formed is not. As tiny droplets of the alkyl halide form, the solution becomes cloudy, thus providing a visual way to the reaction’s progress. Tertiary alcohols react almost instantaneously at room temperature, and secondary alcohols react in 5 to 15 minutes when heated. Primary alcohols are the slowest, requiring several hours of reaction time, even with heat.

OxidationOxidationOne of the most valuable reactions of alcohols is their oxidation to yield carbonyl compounds by a formal loss of H2 from the carbon to which the oxygen is attached:

CH3CH2-OH CH3 -HC=O

Common oxidizing agents: Chromic acid (H2CrO4)

KMnO4 in acid or basic medium

K2Cr2O7

OxidationOxidationPrimary alcohols yield aldehydes or

Secondary alcohols yieldTertiary alcohols do not normally react with

carboxylic acids

ketones

oxidizing agents.

Iodoform TestIodoform TestTest for the presence of methyl group attached to a

Structure of alcohol:

Positive result: precipitate of iodoform (CHI3).

R C

CH3

OH

H

functional carbon.

Reagent: NaOH + I2 NaOI (sodium hypoiodite)

yellow

Bromine Water Bromine Water TestTest

The bromine in water test is a qualitative test for the presence ofphenol.

FeClFeCl33 Test Test The positive test result is evident by

the formation of blue, green, purple, red-brown, or intense red complexes.

This is an excellent test for differentiating alcohol from phenols.

This is also a test for the presence of an enol group.

This test is best carried out in the presence of pyridine for greater accuracy of result.

FeClFeCl33 Test Test

OH + N + FeCl3

Fe(OAr)3 + NH+

3 3 3 Cl-

phenol

colored complex

Reactions of Aldehydes and Ketones

Aldehydes and Aldehydes and KetonesKetones

General formula for Aldehydes:

General formula for Ketones:

C

O

R H C

O

R R


Aldehydes and ketones are structurally very similar; both have a carbon-oxygen double bond called a carbonyl group.

They differ in that aldehydes have at least one hydrogen atom bonded to the carbonyl group, whereas in ketones the carbonyl is bonded to two carbon atoms.


Characteristic reactions of aldehydes and ketones: Addition reactions across the double

bond Reduction Condensation Haloform reaction

Oxidation Reaction Oxidation Reaction (Benedict’s Test)(Benedict’s Test)

Preparation: Heat a solution of 17.3 g sodium citrate and 10 g anhydrous sodium carbonate ion 80 mL of distilled water until the salts dissolved.

Dissolve 1.73 g of hydrated copper sulfate in 10 mL of water and add this solution to the solution of sodium citrate and sodium carbonate slowly with stirring.

Dilute the solution to 100 mL by adding distilled water.


Benedict’s test is one the classical tests employed in the determination of the presence of aldehyde.

Benedict solution can oxidize a variety of compounds and precipitation of the cuprous oxide is a positive indication.

Aliphatic aldehydes usually produced yellow to orange (yellow, yellowish green, red) precipitate or suspension, sometime greenish in blue solution is observed.


This test is negative for most ketones and aromatic aldehydes.

R H

O

+ 2Cu+2 4OH- 2H2O+

R OH

O

+ +

aldehyde carboxylic acid

Cu2O

(s)

Oxidation Reaction Oxidation Reaction (Chromic Anhydride (Chromic Anhydride Test)Test)

Preparation Dissolve 25 g chromic anhydride in

25 mL concentrated sulfuric acid. Pour this suspension slowly with

stirring to 75 mL of distilled water. Cool the solution at room

temperature before using.


The basis of this test is the reduction of chromium (IV), which is orange in color, to chromium (III), which green in color.

The positive result for aldehyde is evident by the formation of an opaque blue green or an intense blue to green suspension at a slower rate.

If the unknown is an aliphatic aldehyde, initial cloudiness after 5 seconds is observed and the blue – green suspension forms after 30 seconds.


Aromatic aldehydes took longer time to react, about 30 – 90 seconds.

Ketones give a negative test and thus, for this reason this is one of the tests used to distinguish aldehydes from ketones.

CR

O

H

3 + 2 CrO3 + 3H

2SO

4 CR OH

O

+ 3 H2O + Cr

2(SO

4)3

3

orange - red

opaque blue - green or internse blue to green

aldehyde carboxylic acid

Oxidation Reaction Oxidation Reaction (Tollen’s (Silver Mirror) (Tollen’s (Silver Mirror) Test)Test)

Preparation Clean a container with 10% NaOH and

place 2 mL of AgNO3 and add a drop of 10% NaOH.

Add 2% ammonia, drop by drop, with constant shaking, until the precipitate of silver oxide just dissolves.

In order to obtain a sensitive reagent, it is necessary to avoid excessive addition of ammonia.


This test is used to distinguish aldehydes from ketones.

Also known as silver mirror test because of its positive test result is evident by the formation of metallic silver on the surface of the test tube.

In some cases, formation of granular gray or black precipitate is observed as a positive test result.


Ketones usually give negative test result.

C

O

R H

+ Ag(NH3)2OH2Ag(NH3)2OH 2Ag(s) + + H2O + NH3CR

O

ON

+

H

H

H

H

aldehyde

silver nitrate in ammonium

hydroxidesilver mirror

ammonium salt of carboxylic

acid

Oxidation Reaction Oxidation Reaction (Fehling’s Test for (Fehling’s Test for Aldehydes)Aldehydes)

Preparation Mix 2.5 mL of each of the following

solutions: Fehling’s A. Dissolve 17.32g of

hydrated copper sulfate crystals in 200mL of water and dilute to 250mL.

Fehling’s B. Dissolve 86.5g of sodium potassium tartrate (Rochelle’s salt) and 35g of sodium hydroxide in 100 mL of water and dilute to 250mL.


The basis of this test is the reduction of copper (II) to copper (I).

For aliphatic aldehydes, formation of brick red, yellow or yellowish green color of precipitate of Cu2O indicates the positive test results.

In the course of the reaction, the Fehling’s reagent reduced the deep blue copper (II) ion complex to brick red copper (I) oxide.


Aromatic aldehydes give a negative test result. For ketones, this test give a negative test result.

CR

O

H

+ CR

O

OH

+2 Cu+2 Cu2O

(s)

aldehyde blue carboxylic acid

brick red, yellow or yellowish green

Reaction of the Carbonyl Reaction of the Carbonyl Group (Condensation Group (Condensation

Reaction)Reaction)2,4 – Dinitrophenylhydrazine

The positive test results for most aldehydes and ketones are evident by the formation of insoluble solid of dinitrophenylhydrazones.

The color of the precipitate formed may also indicate the structure of the aldehydes and ketones.


Reaction)Reaction)Aromatic aldehydes and ketones (highly conjugated) tend to form orange to red precipitate while aliphatic and unconjugated aldehydes and ketones tend to form yellow precipitate. The precipitate formed is sometimes oily which become crystalline after some time. Formation of oily precipitate of dinitrophenylhydrazones is characteristic of numerous ketones.


Reaction)Reaction)This maybe use to differentiate aldehydes from ketones. In some cases, mild heating is required in order for the reaction to be visible, but avoid overheating because it may cause oxidation and in effect give false positive test result.

CR'R

O

+

NHNH2

N+

O-

ON

+O

-

O

NHN

N+

O-

ON

+O

-

O

C

R'

R

aldehyde or ketone 2,4-dinitrophenylhydrazine 2,4-dinitrophenylhydrazone

Reaction of the Carbonyl Reaction of the Carbonyl Group (Addition Reaction)Group (Addition Reaction)

Sodium bisulfite addition Bisulfate ions react with aldehyde

and ketone to form crystalline addition products.

Formation of solid product is an evidence of positive test result.

Reaction of the Reaction of the Carbonyl Group Carbonyl Group

(Addition Reaction)(Addition Reaction)Compounds having active carbonyl carbons do give also a positive test result. Among those compounds are methyl ketones, and low molecular weight cyclic ketones of up to eight- membered cyclic ketone.

C

O

R

R + S

O

O

OHNa

H

OHR

SO3 Na+

aldehyde or ketone

sodium bisulfi te addition complex

Reaction of the Carbonyl Reaction of the Carbonyl Group (Haloform Rxn / Group (Haloform Rxn /

Iodoform Test)Iodoform Test)

This is to test the presence of the methyl group.

Compounds containing the carbonyl group will react with halogen in the presence of a base by a substitution type of reaction.



An alpha halo ketone is formed and when NaOH and iodine are used, a yellow precipitate of iodoform is produced. Positive test result is evident by the formation of yellow precipitate of iodoform with a medicinal odor or foul-smell.



The following give a positive test result:

AcetaldehydeConjugated aldehydes such as acrolein and furfuralDihydoxy compoundsMethyl ketoneSecondary alcohol with methyl group adjacent to the carbon bearing the hydroxyl group



+CHCH3CH3

OH

acetone

4I2 + 6NaOH

CH3

O

ONa+ + CHI3 + 5NaI 5H2O+

I odoform (yellow solid)

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Reactions of Alcohols, Phenols, Aldehydes and Ketones

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