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 Aldehydes and KetonesKetones
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.
Aldehydes and Aldehydes and KetonesKetones
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.
Oxidation Reaction Oxidation Reaction (Benedict’s Test)(Benedict’s Test)
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.
Oxidation Reaction Oxidation Reaction (Benedict’s Test)(Benedict’s Test)
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.
Oxidation Reaction Oxidation Reaction (Chromic Anhydride (Chromic Anhydride Test)Test)
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.
Oxidation Reaction Oxidation Reaction (Chromic Anhydride (Chromic Anhydride Test)Test)
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.
Oxidation Reaction Oxidation Reaction (Tollen’s (Silver Mirror) (Tollen’s (Silver Mirror) Test)Test)
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.
Oxidation Reaction Oxidation Reaction (Tollen’s (Silver Mirror) (Tollen’s (Silver Mirror) Test)Test)
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.
Oxidation Reaction Oxidation Reaction (Fehling’s Test for (Fehling’s Test for Aldehydes)Aldehydes)
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.
Oxidation Reaction Oxidation Reaction (Fehling’s Test for (Fehling’s Test for Aldehydes)Aldehydes)
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 of the Carbonyl Reaction of the Carbonyl Group (Condensation Group (Condensation
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 of the Carbonyl Reaction of the Carbonyl Group (Condensation Group (Condensation
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.
Reaction of the Carbonyl Reaction of the Carbonyl Group (Haloform Rxn / Group (Haloform Rxn /
Iodoform Test)Iodoform Test)
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.
Reaction of the Carbonyl Reaction of the Carbonyl Group (Haloform Rxn / Group (Haloform Rxn /
Iodoform Test)Iodoform Test)
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
Reaction of the Carbonyl Reaction of the Carbonyl Group (Haloform Rxn / Group (Haloform Rxn /
Iodoform Test)Iodoform Test)
+CHCH3CH3
OH
acetone
4I2 + 6NaOH
CH3
O
ONa+ + CHI3 + 5NaI 5H2O+
I odoform (yellow solid)
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