Chemistry and formulation of para-phenylenediamine based hair dyes MCQs With Answer

Chemistry and formulation of para-phenylenediamine based hair dyes covers molecular structure, oxidation mechanisms, formulation science and safety aspects relevant to B.Pharm students. This introduction explains key concepts such as para-phenylenediamine (PPD) chemistry, oxidative dyeing, primary intermediates (quinone diimine), couplers, role of hydrogen peroxide and alkalizing agents (ammonia, ethanolamine), formulation types (cream O/W emulsions), stabilizers, preservatives, chelators and analytical methods (HPLC). It also highlights toxicology, allergic contact dermatitis, regulatory limits and safe handling in product development. Understanding these topics helps in rational design, quality control and regulatory compliance of permanent hair dyes. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the correct chemical identity of PPD used in hair dyes?

• 1,4-Phenylenediamine (para-phenylenediamine, PPD)
• 1,2-Diaminobenzene (ortho-phenylenediamine)
• p-Aminobenzoic acid
• 4-Nitroaniline

Correct Answer: 1,4-Phenylenediamine (para-phenylenediamine, PPD)

Q2. What is the primary role of hydrogen peroxide in PPD-based oxidative hair dye systems?

• Solvent to dissolve PPD
• Oxidizing agent that converts PPD into reactive quinone diimine intermediates
• pH neutralizer to lower alkalinity
• Conditioning agent to reduce hair damage

Correct Answer: Oxidizing agent that converts PPD into reactive quinone diimine intermediates

Q3. Why are alkalizing agents such as ammonia or ethanolamine used in PPD hair dye formulations?

• To lower pH and precipitate dye
• To increase pH, deprotonate PPD, swell hair cuticle and accelerate oxidation
• To act as primary color couplers
• To act as preservatives against microbial growth

Correct Answer: To increase pH, deprotonate PPD, swell hair cuticle and accelerate oxidation

Q4. What is the role of a coupler in an oxidative hair dye formulation?

• To act as the oxidant in place of hydrogen peroxide
• To react with oxidized PPD intermediates forming larger chromophores and determine final shade
• To reduce irritation by neutralizing PPD
• To act as a thickener in cream formulations

Correct Answer: To react with oxidized PPD intermediates forming larger chromophores and determine final shade

Q5. Which oligomeric product formed from PPD oxidation is strongly associated with allergenicity?

• Benzoic acid
• Bandrowski’s base (trimer of PPD)
• Anisole
• p-Aminobenzoic acid

Correct Answer: Bandrowski’s base (trimer of PPD)

Q6. How are PPD-based dyes classified in hair color technology?

• Direct (temporary) dyes
• Oxidative (permanent) hair dyes
• Natural henna-type dyes
• Metallic salts (progressive) dyes only

Correct Answer: Oxidative (permanent) hair dyes

Q7. What is a widely accepted maximum concentration limit for PPD in ready-to-use hair dye mixtures in many jurisdictions?

• 0.02%
• 0.2%
• 2%
• 20%

Correct Answer: 2%

Q8. Which statement best describes PPD solubility relevant to formulation?

• PPD is highly lipophilic and insoluble in polar solvents
• PPD is moderately soluble in water and readily soluble in ethanol and glycols
• PPD is only soluble in strong acids
• PPD is insoluble in all cosmetic solvents and must be micronized

Correct Answer: PPD is moderately soluble in water and readily soluble in ethanol and glycols

Q9. The most common adverse reaction to PPD-based hair dyes in consumers is:

• Hypertrichosis
• Allergic contact dermatitis
• Systemic anaphylactic shock in all users
• Permanent hair bleaching

Correct Answer: Allergic contact dermatitis

Q10. What is the recommended patch test timing before full application of PPD hair dye?

• No patch test is necessary
• Perform a patch test immediately post-application
• Perform a patch test 48 hours prior to application
• Perform a patch test one month prior

Correct Answer: Perform a patch test 48 hours prior to application

Q11. Why are preservatives included in PPD hair dye formulations (pre-mixed products)?

• To speed up the oxidation reaction
• To prevent microbial contamination and extend shelf life
• To function as couplers for deeper shades
• To increase dye substantivity to hair

Correct Answer: To prevent microbial contamination and extend shelf life

Q12. What pH range is typically optimal for the oxidative coupling reaction in PPD-based permanent dyes?

• pH 3–4 (strongly acidic)
• pH 5–6 (near neutral)
• pH 9–10 (alkaline)
• pH 12–13 (very strongly alkaline)

Correct Answer: pH 9–10 (alkaline)

Q13. Which reactive intermediate is directly formed when PPD is oxidized by hydrogen peroxide in alkaline medium?

• p-Nitrophenol
• Quinone diimine (p‑benzoquinone diimine)
• Benzaldehyde
• Phenylalanine

Correct Answer: Quinone diimine (p‑benzoquinone diimine)

Q14. Which analytical technique is commonly used for quantifying PPD and related aromatic amines in formulations and QC?

• Thin-layer chromatography only
• High-performance liquid chromatography (HPLC) with UV or MS detection
• Simple pH titration
• Polarimetry

Correct Answer: High-performance liquid chromatography (HPLC) with UV or MS detection

Q15. Resorcinol used as a coupler typically contributes which color family to final dye shades?

• Bright blue
• Brown to chestnut tones
• Pure yellow only
• Metallic grey

Correct Answer: Brown to chestnut tones

Q16. A key formulation stability concern for PPD-containing preparations is:

• PPD spontaneously forming stable salts with EDTA
• Air and trace metal catalyzed oxidation causing loss of activity and increased allergenic oligomers
• PPD reacting with water to generate harmless alcohols
• PPD polymerizing only at freezing temperatures

Correct Answer: Air and trace metal catalyzed oxidation causing loss of activity and increased allergenic oligomers

Q17. Which alternative aromatic amine is sometimes used as a lower-sensitizing substitute for PPD in some formulations?

• Hydroquinone
• Para-toluenediamine (PTD) derivatives
• Aniline sulphate
• Nitrobenzene

Correct Answer: Para-toluenediamine (PTD) derivatives

Q18. What emulsion type is typically used for salon-style permanent PPD hair dye creams?

• Water-in-oil (W/O) emulsion
• Oil-in-water (O/W) emulsion
• Anhydrous powder only
• Microemulsion with no emulsifier

Correct Answer: Oil-in-water (O/W) emulsion

Q19. Which function do surfactants provide in PPD hair dye formulations?

• They act as primary oxidants
• Improve wetting, dispersion and uniform distribution of dye on hair
• They create permanent color on their own
• They neutralize hydrogen peroxide

Correct Answer: Improve wetting, dispersion and uniform distribution of dye on hair

Q20. What are the common concentrations (w/w) of hydrogen peroxide developers used with permanent hair dyes?

• 0.1% and 0.5%
• 3%, 6%, 9% and 12% (10–40 volume)
• 25% and 50% only
• Only anhydrous peroxide powders are used

Correct Answer: 3%, 6%, 9% and 12% (10–40 volume)

Q21. Which is the primary cosmetic function of ammonia in many PPD hair dye developers?

• Neutralize peroxide to stop oxidation
• Swelling of hair fiber and raising pH to allow penetration of color precursors
• Act as a dye molecule itself
• Preserve the formulation microbiologically

Correct Answer: Swelling of hair fiber and raising pH to allow penetration of color precursors

Q22. Which parameter best evaluates the permanence of an oxidative hair dye?

• Viscosity change during mixing
• Color fastness to washing and shampooing tests
• Freezing point of the developer
• Initial odor intensity

Correct Answer: Color fastness to washing and shampooing tests

Q23. Which toxic aromatic amine is a known metabolic/product concern related to aromatic dye precursors?

• Aniline
• Glycerol
• Benzoic acid only
• Citric acid

Correct Answer: Aniline

Q24. What is the purpose of chelating agents (e.g., EDTA) in PPD hair dye formulations?

• To accelerate peroxide decomposition
• To sequester trace metal ions that catalyze unwanted oxidation and discoloration
• To act as primary colorants
• To inflate viscosity dramatically

Correct Answer: To sequester trace metal ions that catalyze unwanted oxidation and discoloration

Q25. Which ingredients are typically included in formulations to reduce post-dye hair damage and improve feel?

• Strong acids and solvents only
• Conditioning agents such as cationic polymers and silicones
• Extra alkali to strip hair cuticle
• Heavy metals for increased fixation

Correct Answer: Conditioning agents such as cationic polymers and silicones

Q26. Which EU regulation primarily governs cosmetic product safety, labeling and permitted ingredients including hair dyes?

• FDA Food Safety Modernization Act
• Regulation (EC) No 1223/2009 on cosmetic products
• ICH Q7 Good Manufacturing Practice for APIs
• REACH is the sole cosmetic law without any other regulations

Correct Answer: Regulation (EC) No 1223/2009 on cosmetic products

Q27. How does temperature typically affect the oxidation kinetics of PPD during hair dye development?

• Lower temperature speeds oxidation
• Higher temperature accelerates oxidation and color development
• Temperature has no effect on oxidation
• Only freezing temperatures accelerate oxidation

Correct Answer: Higher temperature accelerates oxidation and color development

Q28. Which coupler is commonly selected to produce brown shades in oxidative hair dye formulations?

• m-Aminophenol (tends to red/violet)
• Resorcinol (1,3-dihydroxybenzene)
• p-Nitrophenol (bright yellow)
• Nitrobenzene (not a coupler)

Correct Answer: Resorcinol (1,3-dihydroxybenzene)

Q29. Which of the following is an important safety practice for formulators handling PPD raw material?

• Work without gloves to improve dexterity
• Use personal protective equipment (gloves, goggles) and local exhaust ventilation
• Keep containers open to air for faster mixing
• Store PPD at high temperatures to reduce viscosity

Correct Answer: Use personal protective equipment (gloves, goggles) and local exhaust ventilation

Q30. Which of the following is NOT used as a coupler in PPD-based oxidative hair dyes?

• Resorcinol
• m-Aminophenol
• p-Phenylenediamine (used as primary intermediate)
• Benzyl alcohol

Correct Answer: Benzyl alcohol

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