Alcohols and Phenols Chemistry Lecture Notes PDF

# Chapter IV: Alcohols and phenols ## Introduction Alcohols are a group of important compounds that contains hydroxyl group as a functional group which is connected to carbon atom. Alcohols are classified to: - **primary alcohol:** if the carbon bearing the hydroxyl group is connected to one carb...

# Chapter IV: Alcohols and phenols ## Introduction Alcohols are a group of important compounds that contains hydroxyl group as a functional group which is connected to carbon atom. Alcohols are classified to: - **primary alcohol:** if the carbon bearing the hydroxyl group is connected to one carbon atom. - **secondary alcohol:** if the carbon bearing the hydroxyl group is connected to two carbon atoms. - **tertiary alcohol:** if the carbon bearing the hydroxyl group is connected to three carbon atoms. All of these types of alcohols participate in the features, but other features are different according to the structure. <br> **Diagram** <br> H H — C — OH C **1º alcohol** <br> H C–C—OH C **2º alcohol** <br> C–C—OH C **3º alcohol** <br> If the hydroxyl group is directly connected to carbon atom of aromatic ring the compound is phenol. Although phenols resemble alcohol in some ways, but they differ in many other ways and the main difference is the acidity of phenols are much higher than that of alcohols. The addition of sufficient amount of aqueous sodium hydroxide solution to a phenol will make the -OH group of most of the molecules present to be deprotonated; this will not occurred in alcohol. <br> Alcohols become solid when the size of the molecule is increased, while most phenols are solid. Alcohols with small size are water soluble because the formation of hydrogen bonds between the hydroxyl groups and water molecules. When alcohols are big molecules the solubility will be decreased because the alkyl groups of alcohols disrupt the hydrogen bonding among the water molecules. If the disruption increased, The molecules of water reform hydrogen bonding and expel the molecules of alcohols. This process is the same for phenols. The water solubility of phenol is decreased when non polar groups like alkyl groups are attached to the ring, therefore, non polar groups are called hydrophobic. ## Ritter Test ### Principle This test is used to differentiate primary and secondary alcohols from tertiary. Potassium permanganate (KMnO4) will oxidize a primary alcohol firstly to an aldehyde, and then to a carboxylic acid and it will oxidize a secondary alcohol to a ketone. Tertiary alcohols cannot react because there is no hydrogen atom to be lost from the carbon atom that bears OH group. In this test Mn⁺¹ of KMnO4 which has purple color is reduced to Mn+4 which has brown color. As shown below: <br> ``` RCH2OH + KMnO4 →RCHO + RCOOH + MnO2 1° alcohol purple R2CHOH + KMnO4 →RCOR + MnO2 2 alcohol purple R3COH + KMnO4 → No reaction. 3° alcohol purple ``` <br> ## Procedure 1. Label three test tubes; label the test tubes as primary, secondary, and tertiary. 2. Place 2 ml of acetic acid in each of these test tubes. 3. Add four drops of primary alcohol to the test tube which labeled as primary. 4. Add four drops of secondary alcohol to the test tube which labeled as secondary. 5. Add four drops of tertiary alcohol to the test tube which labeled as tertiary. 6. Be sure that the drops of alcohols fall inside the acetic acid not on the sides of test tubes. 7. Add one drop of saturated potassium permanganate solution. 8. Shake the test tubes vigorously to mix the contents of the tubes. 9. Observe the color change, the primary and secondary alcohols can be oxidized so the permanganate will be reduced from Mn⁺¹ (purple) to Mn+4 (brown). Tertiary alcohols cannot be oxidized therefore the purple color of permanganate does not change.