Organic Synthesis Test

Organic Synthesis Functional Group Tests

Functional Groups, Reactions, and Identification

Alkane

• Test: No specific chemical test.
• Production:
  • Hydrogenation of alkenes using H_2, Pt/Ni catalyst, and heat.
  • Cracking of crude oil using heat and Al2O3 catalyst.

Alkene

• Test: Decolorizes bromine water.
• Production:
  • Elimination of halogenoalkanes by heating with ethanolic NaOH.
  • Dehydration of alcohols using hot Al2O3 catalyst.
  • Cracking of crude oil using heat and Al2O3 catalyst.

Halogenoalkane (primary, secondary, and tertiary)

• Test: Forms silver halide precipitate with dilute nitric acid, silver nitrate, and dilute ammonia solution (AgCl = white, AgBr = cream, and AgI = yellow).
• Production:
  • Free-radical substitution of alkanes using UV and a halogen.
  • Electrophilic addition of hydrogen halides to alkenes.
  • Nucleophilic substitution of an alcohol, e.g., by reaction with HX (g) or with KCl and concentrated H2SO4 or concentrated H3PO4 or with PCl3 and heat or with PCl5 or with SOCl_2.

Alcohol (primary, secondary, and tertiary)

• Test: Reacts with carboxylic acid and sulfuric acid to make esters which have fruity smells.
  • Primary alcohols get oxidized to aldehydes (give positive test with Fehling's, silver mirror in Tollens' reagent and Tollens' solution and carboxylic acids Red precipitate in Fehling's solution).
  • Secondary alcohols are oxidized to ketones (positive test with 2,4-DNPH but not Fehling's and Tollens' solution).
  • Orange precipitate with 2,4- DNPH
  • Tertiary alcohols cannot be oxidised
• Production:
  • Electrophilic addition of alkenes using hot steam, concentrated phosphoric(VI) acid as a catalyst
  • Oxidation of alkenes using cold, dilute KMnO_4 to form a diol
  • Oxidation of primary alcohols in acidified K2Cr2O4 or KMnO4 and under reflux

Ketone

• Test: Orange precipitate with 2,4-DNPH.
• Production: Oxidation of secondary alcohols in acidified K2Cr2O4 or KMnO4 and under distillation.

Carboxylic Acid

• Test: Reacts with carbonates to form CO_2 gas which will turn limewater cloudy.
• Production:
  • Oxidation of aldehydes and alcohols using acidified K2Cr2O7 or KMnO4 under reflux.
  • Hydrolysis of nitriles with dilute acid or dilute alkali followed by acidification.
  • Hydrolysis of ester with dilute acid or dilute alkali followed by acidification.

Ester

• Test: Have sweet, fruity smells.
• Production: Condensation reaction of alcohols and carboxylic acids with hot, concentrated H2SO4 as catalyst.

Amine

• Test:
  • Turns damp red litmus paper blue.
  • Turns universal indicator blue / purple.
• Production:
  • Nucleophilic substitution of halogenoalkanes when heated under pressure with NH_3 (ethanol).

Nitrile

• Test: No official test.
• Production:
  • Nucleophilic substitution of halogenoalkanes when heated under pressure with KCN (ethanol) and heat.

Aldehyde

• Production:
  • Nucleophilic substitution of halogenoalkanes using heat and NaOH (aq).
  • Reduction of aldehydes and ketones using NaBH4 and LiAlH4 (aldehydes are reduced to primary alcohols and ketones are reduced to secondary alcohols).
  • Reduction of carboxylic acid using LiAlH_4.
  • Hydrolysis of esters using dilute acid or dilute alkali

Types of Reactions

Hydrogenation

• Definition: The addition of alkenes with hydrogen.
• Reagents: H_2, Pt / Ni catalyst
• Products: Alkanes

Cracking

• Definition: The process in which large, less useful hydrocarbon molecules are broken down into smaller, more useful molecules in an oil refinery.
• Reagents: Al2O3 catalyst and heat
• Products: Alkanes and alkenes

Free-radical substitution

• Definition: The reaction in which halogen atoms substitute for hydrogen atoms in alkanes. The mechanism involves steps in which reactive free radicals are produced (initiation), regenerated (propagation), and consumed (termination)
• Reagents: Halogen and UV light
• Products: Halogenoalkane

Electrophilic Addition

• Definition: The mechanism of the reaction in which an electrophile attacks the C=C bond and addition across the double bond occurs.
• Reagents: Electrophile (e.g., Br2, HBr, H2O and H2SO4)
• Products: Halogenoalkane, alcohol or alkane

Nucleophilic Addition

• Definition: The mechanism of the reaction in which a nucleophile attacks the carbon atom in a carbonyl group and addition across the C=O bond occurs.
• Reagents: Nucleophile (e.g. HCN)
• Products: Halogenoalkane, alcohol, nitrile or amine

Oxidation

• Definition: The loss of electrons or gain of oxygen of an atom, ion, or molecule.
• Reagents: Oxidizing agent such as acidified K2Cr2O7 or KMnO4
• Products: Alcohol, aldehyde, ketone, or carboxylic acid

Reduction

• Definition: The gain of electrons or loss of oxygen of an atom, ion, or molecules
• Reagents: Reducing agent such as NaBH4 or LiAlH4
• Products: Alkene, aldehyde, primary and secondary alcohol, carboxylic acid

Hydrolysis

• Definition: The breakdown of a compound by water or by dilute acids or alkali
• Reagents: Water or dilute acid or alkali
• Products: Two compounds (fragments of the original compound)

Condensation

• Definition: A reaction in which two organic molecules join together and in the process eliminate a small molecule such as water or hydrogen chloride
• Reagents: Two molecules that can react with each other
• Products: Small molecule and a larger molecule

Electrophilic Substitution

• Definition: The replacement of an atom by another atom or group of atoms after initial attack by an electron—deficient species
• Reagents: Electrophile (e.g., Br2, NaOH, KCN, NH3 and HBr
• Products: Substituted compound

Nucleophilic Substitution

• Definition: The mechanism of the organic reaction in which a nucleophile attacks a carbon atom carrying a potential positive charge. This results in the replacement of an atom carrying a partial negative charge by the nucleophile
• Reagents: Nucleophile (e.g. HCN)
• Products: Substituted compound

Oxidizing & Reducing Agents

Oxidizing Agents

Reducing Agents

Tests for Identifying Functional Groups