Chemistry/Chapter 10: Hydroxy Compounds
10.5 Reactions of Naphthols
- Naphthols:
Explanation level
In the previous sections, we explored the chemistry of phenol. Now, we extend our study to a related class of compounds: naphthols. Naphthols are phenolic compounds derived from naphthalene, consisting of a naphthalene ring system with a hydroxyl (-OH) group attached. They exhibit similar chemical properties to phenol, but with some important differences due to the larger aromatic system. This section describes the key reactions of naphthols.
Definition
- Naphthols: A set of organic compounds with the chemical formula C_{10}H_7OH. They are derivatives of naphthalene (a fused bicyclic aromatic hydrocarbon) with a hydroxyl group attached to the ring.
- Isomers: Naphthols exist in two isomeric forms:
Simple Explanation: Naphthols are like phenol, but instead of a single benzene ring, they have two fused benzene rings (naphthalene). Like phenol, they have an -OH group that makes them weakly acidic and reactive towards electrophiles.
Core Concept
The core concept is that naphthols behave like simple phenols in their chemical reactions. The -OH group is activating and ortho/para-directing, increasing the electron density of the naphthalene ring and making it reactive towards electrophilic substitution. However, because the naphthalene ring is larger and has two fused rings, the position of substitution can be different from that of phenol. In naphthols, electrophilic substitution typically occurs at the positions that lead to the most stable arenium ion intermediate. For 1-naphthol, this is usually at positions 2 and 4. For 2-naphthol, it is typically at position 1 (the position between the -OH group and the other ring).
Detailed Explanation
The textbook states that general reactions of simple phenol can also be applied to other phenolic compounds such as naphthols. Naphthols behave like simple phenols in chemical reactions.
1. Reaction with Sodium Hydroxide
Naphthols dissolve in sodium hydroxide solution, producing naphthoxide salts. This reaction confirms their acidic nature, similar to phenol.
For 1-Naphthol: C_{10}H_7OH + NaOH \rightarrow C_{10}H_7ONa + H_2O (Product: Sodium-1-naphthoxide)
For 2-Naphthol: C_{10}H_7OH + NaOH \rightarrow C_{10}H_7ONa + H_2O (Product: Sodium-2-naphthoxide)
2. Reaction with Bromine Water (Electrophilic Substitution)
Naphthols decolorize bromine water, undergoing electrophilic substitution. The position of substitution depends on whether it is 1-naphthol or 2-naphthol.
For 1-Naphthol: 1-Naphthol decolorizes bromine water with a substitution of bromine at positions 2 and 4. C_{10}H_7OH + 2Br_2 \rightarrow C_{10}H_5Br_2OH + 2HBr (Products: 2-bromo-1-naphthol and 4-bromo-1-naphthol)
For 2-Naphthol: 2-Naphthol decolorizes bromine water with a substitution at the position between the OH group and the other ring (position 1). Position 4 is cluttered with the other ring. C_{10}H_7OH + Br_2 \rightarrow C_{10}H_6BrOH + HBr (Product: 1-bromo-2-naphthol)
3. Reaction with Nitric Acid (Nitration)
Nitration occurs like bromination.
For 1-Naphthol: 1-Naphthol gives substitution at positions 2 and 4. C_{10}H_7OH + 2HNO_3 \rightarrow C_{10}H_5(NO_2)_2OH + 2H_2O (Products: 2-nitro-1-naphthol and 4-nitro-1-naphthol)
For 2-Naphthol: 2-Naphthol gives substitution at position 1. C_{10}H_7OH + HNO_3 \rightarrow C_{10}H_6(NO_2)OH + H_2O (Product: 1-nitro-2-naphthol)
4. Reaction with Diazonium Chloride (Coupling Reaction)
Naphthols react with diazonium salts to give azo compounds. This is similar to the coupling reaction of phenol.
For 1-Naphthol: 1-Naphthol reacts with diazonium salt in exactly the same conditions as with phenol. The 1-naphthol is dissolved in NaOH solution to produce an ion like the phenol. This solution is ice-cooled and mixed with the diazonium salt solution. An intense orange-red precipitate of an azo compound is produced. With 1-naphthol, reaction occurs at position 4.
For 2-Naphthol: With 2-naphthol, reaction occurs at a position between the OH group and the other ring (position 1). An orange-red precipitate is also formed.
Intermediate Level
Naphthols (1-naphthol and 2-naphthol) are phenolic compounds that exhibit similar chemical behavior to phenol. They are weakly acidic and dissolve in sodium hydroxide to form naphthoxide salts. They are highly reactive towards electrophilic substitution due to the activating effect of the -OH group. The position of substitution depends on the isomer: 1-naphthol typically undergoes substitution at positions 2 and 4, while 2-naphthol undergoes substitution at position 1. This regioselectivity is due to the greater stability of the arenium ion intermediates formed at these positions. Naphthols react with bromine water (forming bromonaphthols), nitric acid (forming nitronaphthols), and diazonium salts (forming azo dyes). The reaction with diazonium salts is a coupling reaction that produces intensely coloured orange-red azo compounds, which are used as dyes.
Important Points
- - Naphthols: Phenolic compounds with a naphthalene ring.
- - Isomers: 1-Naphthol and 2-Naphthol.
- - Acidic Nature: Dissolve in NaOH to form naphthoxide salts.
- - Electrophilic Substitution: Highly reactive due to -OH group.
- - 1-Naphthol: Substitution at positions 2 and 4.
- - 2-Naphthol: Substitution at position 1.
- - Bromination: Decolorizes bromine water.
- - Nitration: Forms nitronaphthols.
- - Coupling with Diazonium Salts: Forms azo dyes (orange-red precipitates).
Remember
- - Naphthols = phenol-like compounds with two fused rings.
- - 1-Naphthol: Substitution at 2 and 4.
- - 2-Naphthol: Substitution at 1.
- - Dissolve in NaOH.
- - Decolorize bromine water.
- - React with HNO₃ to form nitronaphthols.
- - React with diazonium salts to form azo dyes.
- - Azo dyes are orange-red precipitates.
Common Mistakes
- - Forgetting that naphthols have two isomers with different reactivity. The position of the -OH group determines where substitution occurs.
- - Assuming that naphthols behave exactly like phenol. While similar, the fused ring system changes the regioselectivity.
- - Not recognizing the acidic nature of naphthols. They dissolve in NaOH, unlike simple alcohols.
- - Confusing the substitution positions. 1-Naphthol substitutes at 2 and 4; 2-naphthol substitutes at 1.
- - Thinking that the coupling reaction with diazonium salts is different from phenol. It is similar, but the product is an azo dye.
Quick Revision
Naphthols (1-naphthol and 2-naphthol) are phenolic compounds that exhibit similar chemical properties to phenol. They are weakly acidic and dissolve in sodium hydroxide to form naphthoxide salts. Due to the activating effect of the -OH group, they undergo electrophilic substitution reactions. The position of substitution depends on the isomer: 1-naphthol typically reacts at positions 2 and 4, while 2-naphthol reacts at position 1. They react with bromine water (forming bromonaphthols) and nitric acid (forming nitronaphthols). They also undergo a coupling reaction with diazonium salts to form intensely coloured azo dyes, which are used as colorants.
60-Second Revision
Naphthols (1-naphthol and 2-naphthol) are phenol-like compounds with a fused ring system. They dissolve in NaOH and undergo electrophilic substitution. 1-Naphthol substitutes at positions 2 and 4. 2-Naphthol substitutes at position 1. They react with bromine water, nitric acid, and diazonium salts (forming azo dyes). The reactions are similar to phenol but with different regioselectivity due to the fused ring system.
Frequently Asked Questions (FAQs)
Q1. What are naphthols? Answer: Naphthols are phenolic compounds with the chemical formula C_{10}H_7OH. They are derivatives of naphthalene (a fused bicyclic aromatic hydrocarbon) with a hydroxyl group attached to the ring. There are two isomers: 1-naphthol (α-naphthol) and 2-naphthol (β-naphthol).
- Q2. How do naphthols react with sodium hydroxide?
- Answer: Naphthols are weakly acidic and dissolve in sodium hydroxide solution to form naphthoxide salts. For example:
- C_{10}H_7OH + NaOH \rightarrow C_{10}H_7ONa + H_2O
- Q3. What are the products of the reaction of 1-naphthol with bromine water?
- Answer: 1-Naphthol reacts with bromine water to form 2-bromo-1-naphthol and 4-bromo-1-naphthol. The substitution occurs at positions 2 and 4.
- Q4. What is the product of the reaction of 2-naphthol with bromine water?
- Answer: 2-Naphthol reacts with bromine water to form 1-bromo-2-naphthol. The substitution occurs at position 1 (between the -OH group and the other ring).
- Q5. What are the products of the reaction of 1-naphthol with nitric acid?
- Answer: 1-Naphthol reacts with nitric acid to form 2-nitro-1-naphthol and 4-nitro-1-naphthol. The substitution occurs at positions 2 and 4.
- Q6. What is the product of the reaction of 2-naphthol with nitric acid?
- Answer: 2-Naphthol reacts with nitric acid to form 1-nitro-2-naphthol. The substitution occurs at position 1.
Q7. What is the reaction of naphthols with diazonium salts? Answer: Naphthols react with diazonium salts to form azo compounds (azo dyes). The reaction is a coupling reaction that produces intensely coloured orange-red precipitates. For 1-naphthol, the reaction occurs at position 4; for 2-naphthol, it occurs at position 1.
Q8. Why do naphthols react at different positions than phenol? Answer: The fused ring system of naphthalene changes the electron density distribution and the stability of the arenium ion intermediates. For 1-naphthol, substitution at positions 2 and 4 leads to the most stable intermediates. For 2-naphthol, substitution at position 1 is favored. This regioselectivity is a consequence of the larger aromatic system.
Q9. What are azo dyes? Answer: Azo dyes are synthetic dyes that contain the azo group (-N=N-) linking two aromatic rings. They are produced by the coupling reaction of a diazonium salt with a phenol or naphthol. Azo dyes are brightly coloured and are used in textiles, food, and cosmetics.
Multiple Choice Questions (MCQs)
- Q1. What is the chemical formula of naphthol?
- A. C_6H_5OH
- B. C_{10}H_7OH
- C. C_{10}H_8
- D. C_6H_6
- Correct Answer: B
- Explanation: Naphthols have the formula C_{10}H_7OH.
- Q2. Which of the following is a reaction of naphthols with sodium hydroxide?
- A. Formation of naphthoxide salt and water
- B. Formation of naphthalene and water
- C. Formation of naphthol and hydrogen
- D. No reaction
- Correct Answer: A
- Explanation: Naphthols dissolve in NaOH to form naphthoxide salts and water.
- Q3. At which positions does 1-naphthol undergo electrophilic substitution?
- A. 1 and 2
- B. 2 and 4
- C. 1 and 3
- D. 3 and 4
- Correct Answer: B
- Explanation: 1-Naphthol undergoes substitution at positions 2 and 4.
- Q4. At which position does 2-naphthol undergo electrophilic substitution?
- A. 1
- B. 2
- C. 3
- D. 4
- Correct Answer: A
- Explanation: 2-Naphthol undergoes substitution at position 1.
- Q5. What is the product of the reaction of 1-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-1-naphthol
- D. 4-bromo-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-bromo-1-naphthol and 4-bromo-1-naphthol.
- Q6. What is the product of the reaction of 2-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-2-naphthol
- D. 4-bromo-2-naphthol
- Correct Answer: B
- Explanation: The product is 1-bromo-2-naphthol.
- Q7. What is the product of the reaction of naphthols with diazonium salts?
- A. Azo dyes
- B. Naphthoxide salts
- C. Nitronaphthols
- D. Bromonaphthols
- Correct Answer: A
- Explanation: The product is an azo dye.
- Q8. What is the colour of the azo dye precipitate formed from naphthols?
- A. White
- B. Yellow
- C. Orange-red
- D. Green
- Correct Answer: C
- Explanation: The azo dye precipitate is orange-red.
- Q9. Which of the following is a correct statement about naphthols?
- A. They are not acidic.
- B. They do not react with bromine water.
- C. They behave like simple phenols.
- D. They cannot form azo dyes.
- Correct Answer: C
- Explanation: Naphthols behave like simple phenols in their chemical reactions.
- Q10. What is the product of the reaction of 1-naphthol with nitric acid?
- A. 2-nitro-1-naphthol and 4-nitro-1-naphthol
- B. 1-nitro-2-naphthol
- C. 3-nitro-1-naphthol
- D. 4-nitro-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-nitro-1-naphthol and 4-nitro-1-naphthol.
Multiple Choice Questions (MCQs)
- Q1. What is the chemical formula of naphthol?
- A. C_6H_5OH
- B. C_{10}H_7OH
- C. C_{10}H_8
- D. C_6H_6
- Correct Answer: B
- Explanation: Naphthols have the formula C_{10}H_7OH.
- Q2. Which of the following is a reaction of naphthols with sodium hydroxide?
- A. Formation of naphthoxide salt and water
- B. Formation of naphthalene and water
- C. Formation of naphthol and hydrogen
- D. No reaction
- Correct Answer: A
- Explanation: Naphthols dissolve in NaOH to form naphthoxide salts.
- Q3. At which positions does 1-naphthol undergo electrophilic substitution?
- A. 1 and 2
- B. 2 and 4
- C. 1 and 3
- D. 3 and 4
- Correct Answer: B
- Explanation: 1-Naphthol undergoes substitution at positions 2 and 4.
- Q4. At which position does 2-naphthol undergo electrophilic substitution?
- A. 1
- B. 2
- C. 3
- D. 4
- Correct Answer: A
- Explanation: 2-Naphthol undergoes substitution at position 1.
- Q5. What is the product of the reaction of 1-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-1-naphthol
- D. 4-bromo-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-bromo-1-naphthol and 4-bromo-1-naphthol.
- Q6. What is the product of the reaction of 2-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-2-naphthol
- D. 4-bromo-2-naphthol
- Correct Answer: B
- Explanation: The product is 1-bromo-2-naphthol.
- Q7. What is the product of the reaction of naphthols with diazonium salts?
- A. Azo dyes
- B. Naphthoxide salts
- C. Nitronaphthols
- D. Bromonaphthols
- Correct Answer: A
- Explanation: The product is an azo dye.
- Q8. What is the colour of the azo dye precipitate formed from naphthols?
- A. White
- B. Yellow
- C. Orange-red
- D. Green
- Correct Answer: C
- Explanation: The azo dye precipitate is orange-red.
- Q9. Which of the following is a correct statement about naphthols?
- A. They are not acidic.
- B. They do not react with bromine water.
- C. They behave like simple phenols.
- D. They cannot form azo dyes.
- Correct Answer: C
- Explanation: Naphthols behave like simple phenols.
- Q10. What is the product of the reaction of 1-naphthol with nitric acid?
- A. 2-nitro-1-naphthol and 4-nitro-1-naphthol
- B. 1-nitro-2-naphthol
- C. 3-nitro-1-naphthol
- D. 4-nitro-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-nitro-1-naphthol and 4-nitro-1-naphthol.
Multiple Choice Questions (MCQs)
- Q1. What is the formula of 1-naphthol?
- A. C_6H_5OH
- B. C_{10}H_7OH
- C. C_{10}H_8
- D. C_6H_6
- Correct Answer: B
- Explanation: 1-Naphthol has the formula C_{10}H_7OH.
- Q2. What is the formula of 2-naphthol?
- A. C_6H_5OH
- B. C_{10}H_7OH
- C. C_{10}H_8
- D. C_6H_6
- Correct Answer: B
- Explanation: 2-Naphthol also has the formula C_{10}H_7OH.
- Q3. Which of the following is a property of naphthols?
- A. They are basic.
- B. They are acidic.
- C. They are neutral.
- D. They are amphoteric.
- Correct Answer: B
- Explanation: Naphthols are weakly acidic.
- Q4. What is the product of the reaction of naphthols with sodium hydroxide?
- A. Sodium naphthoxide
- B. Naphthalene
- C. Naphthol
- D. Hydrogen gas
- Correct Answer: A
- Explanation: The product is sodium naphthoxide.
- Q5. What is the product of the reaction of 1-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-1-naphthol
- D. 4-bromo-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-bromo-1-naphthol and 4-bromo-1-naphthol.
- Q6. What is the product of the reaction of 2-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-2-naphthol
- D. 4-bromo-2-naphthol
- Correct Answer: B
- Explanation: The product is 1-bromo-2-naphthol.
- Q7. What is the product of the reaction of naphthols with diazonium salts?
- A. Azo dyes
- B. Naphthoxide salts
- C. Nitronaphthols
- D. Bromonaphthols
- Correct Answer: A
- Explanation: The product is an azo dye.
- Q8. What is the colour of the azo dye precipitate formed from naphthols?
- A. White
- B. Yellow
- C. Orange-red
- D. Green
- Correct Answer: C
- Explanation: The azo dye precipitate is orange-red.
- Q9. Which of the following is a correct statement about naphthols?
- A. They are not acidic.
- B. They do not react with bromine water.
- C. They behave like simple phenols.
- D. They cannot form azo dyes.
- Correct Answer: C
- Explanation: Naphthols behave like simple phenols.
- Q10. What is the product of the reaction of 1-naphthol with nitric acid?
- A. 2-nitro-1-naphthol and 4-nitro-1-naphthol
- B. 1-nitro-2-naphthol
- C. 3-nitro-1-naphthol
- D. 4-nitro-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-nitro-1-naphthol and 4-nitro-1-naphthol.
Multiple Choice Questions (MCQs)
- Q1. What is the formula of 1-naphthol?
- A. C_6H_5OH
- B. C_{10}H_7OH
- C. C_{10}H_8
- D. C_6H_6
- Correct Answer: B
- Explanation: 1-Naphthol has the formula C_{10}H_7OH.
- Q2. What is the formula of 2-naphthol?
- A. C_6H_5OH
- B. C_{10}H_7OH
- C. C_{10}H_8
- D. C_6H_6
- Correct Answer: B
- Explanation: 2-Naphthol also has the formula C_{10}H_7OH.
- Q3. Which of the following is a property of naphthols?
- A. They are basic.
- B. They are acidic.
- C. They are neutral.
- D. They are amphoteric.
- Correct Answer: B
- Explanation: Naphthols are weakly acidic.
- Q4. What is the product of the reaction of naphthols with sodium hydroxide?
- A. Sodium naphthoxide
- B. Naphthalene
- C. Naphthol
- D. Hydrogen gas
- Correct Answer: A
- Explanation: The product is sodium naphthoxide.
- Q5. What is the product of the reaction of 1-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-1-naphthol
- D. 4-bromo-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-bromo-1-naphthol and 4-bromo-1-naphthol.
- Q6. What is the product of the reaction of 2-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-2-naphthol
- D. 4-bromo-2-naphthol
- Correct Answer: B
- Explanation: The product is 1-bromo-2-naphthol.
- Q7. What is the product of the reaction of naphthols with diazonium salts?
- A. Azo dyes
- B. Naphthoxide salts
- C. Nitronaphthols
- D. Bromonaphthols
- Correct Answer: A
- Explanation: The product is an azo dye.
- Q8. What is the colour of the azo dye precipitate formed from naphthols?
- A. White
- B. Yellow
- C. Orange-red
- D. Green
- Correct Answer: C
- Explanation: The azo dye precipitate is orange-red.
- Q9. Which of the following is a correct statement about naphthols?
- A. They are not acidic.
- B. They do not react with bromine water.
- C. They behave like simple phenols.
- D. They cannot form azo dyes.
- Correct Answer: C
- Explanation: Naphthols behave like simple phenols.
- Q10. What is the product of the reaction of 1-naphthol with nitric acid?
- A. 2-nitro-1-naphthol and 4-nitro-1-naphthol
- B. 1-nitro-2-naphthol
- C. 3-nitro-1-naphthol
- D. 4-nitro-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-nitro-1-naphthol and 4-nitro-1-naphthol.
Multiple Choice Questions (MCQs)
- Q1. What is the formula of 1-naphthol?
- A. C_6H_5OH
- B. C_{10}H_7OH
- C. C_{10}H_8
- D. C_6H_6
- Correct Answer: B
- Explanation: 1-Naphthol has the formula C_{10}H_7OH.
- Q2. What is the formula of 2-naphthol?
- A. C_6H_5OH
- B. C_{10}H_7OH
- C. C_{10}H_8
- D. C_6H_6
- Correct Answer: B
- Explanation: 2-Naphthol also has the formula C_{10}H_7OH.
- Q3. Which of the following is a property of naphthols?
- A. They are basic.
- B. They are acidic.
- C. They are neutral.
- D. They are amphoteric.
- Correct Answer: B
- Explanation: Naphthols are weakly acidic.
- Q4. What is the product of the reaction of naphthols with sodium hydroxide?
- A. Sodium naphthoxide
- B. Naphthalene
- C. Naphthol
- D. Hydrogen gas
- Correct Answer: A
- Explanation: The product is sodium naphthoxide.
- Q5. What is the product of the reaction of 1-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-1-naphthol
- D. 4-bromo-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-bromo-1-naphthol and 4-bromo-1-naphthol.
- Q6. What is the product of the reaction of 2-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-2-naphthol
- D. 4-bromo-2-naphthol
- Correct Answer: B
- Explanation: The product is 1-bromo-2-naphthol.
- Q7. What is the product of the reaction of naphthols with diazonium salts?
- A. Azo dyes
- B. Naphthoxide salts
- C. Nitronaphthols
- D. Bromonaphthols
- Correct Answer: A
- Explanation: The product is an azo dye.
- Q8. What is the colour of the azo dye precipitate formed from naphthols?
- A. White
- B. Yellow
- C. Orange-red
- D. Green
- Correct Answer: C
- Explanation: The azo dye precipitate is orange-red.
- Q9. Which of the following is a correct statement about naphthols?
- A. They are not acidic.
- B. They do not react with bromine water.
- C. They behave like simple phenols.
- D. They cannot form azo dyes.
- Correct Answer: C
- Explanation: Naphthols behave like simple phenols.
- Q10. What is the product of the reaction of 1-naphthol with nitric acid?
- A. 2-nitro-1-naphthol and 4-nitro-1-naphthol
- B. 1-nitro-2-naphthol
- C. 3-nitro-1-naphthol
- D. 4-nitro-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-nitro-1-naphthol and 4-nitro-1-naphthol.
Multiple Choice Questions (MCQs)
- Q1. What is the formula of 1-naphthol?
- A. C_6H_5OH
- B. C_{10}H_7OH
- C. C_{10}H_8
- D. C_6H_6
- Correct Answer: B
- Explanation: 1-Naphthol has the formula C_{10}H_7OH.
- Q2. What is the formula of 2-naphthol?
- A. C_6H_5OH
- B. C_{10}H_7OH
- C. C_{10}H_8
- D. C_6H_6
- Correct Answer: B
- Explanation: 2-Naphthol also has the formula C_{10}H_7OH.
- Q3. Which of the following is a property of naphthols?
- A. They are basic.
- B. They are acidic.
- C. They are neutral.
- D. They are amphoteric.
- Correct Answer: B
- Explanation: Naphthols are weakly acidic.
- Q4. What is the product of the reaction of naphthols with sodium hydroxide?
- A. Sodium naphthoxide
- B. Naphthalene
- C. Naphthol
- D. Hydrogen gas
- Correct Answer: A
- Explanation: The product is sodium naphthoxide.
- Q5. What is the product of the reaction of 1-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-1-naphthol
- D. 4-bromo-1-naphthol
- Correct Answer: A
- Explanation: The products are 2-bromo-1-naphthol and 4-bromo-1-naphthol.
- Q6. What is the product of the reaction of 2-naphthol with bromine water?
- A. 2-bromo-1-naphthol and 4-bromo-1-naphthol
- B. 1-bromo-2-naphthol
- C. 3-bromo-2-naphthol
- D. 4-bromo-2-naphthol
- Correct Answer: B
- Explanation: The product is 1-bromo-2-naphthol.
- Q7. What is the product of the reaction of naphthols with diazonium salts?
- A. Azo dyes
- B. Naphthoxide salts
- C. Nitronaphthols
- D. Bromonaphthols
- Correct Answer: A
- Explanation: The product is an azo dye.
- Q8. What is the colour of the azo dye precipitate formed from naphthols?
- A.
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10.5 Reactions of Naphthols
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Key Point 1
- 1-Naphthol: Substitution at 2,4.
Key Point 2
- 2-Naphthol: Substitution at 1.
Key Point 3
- Dissolve in NaOH.
Key Point 4
- Bromine water: Decolorized.
Key Point 5
- Nitric acid: Nitronaphthols.
Key Point 6
- Diazonium salt: Azo dye (orange-red).
Key Point 7
- Naphthols = phenol-like.
Key Point 8
- Azo dyes are coloured.
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