15. Halogen compounds
A section of Chemistry, 9701
Listing 10 of 284 questions
Lawsone is the dye that is extracted from the henna plant, Lawsonia inermis. Although its natural colour is yellow, lawsone reacts with the proteins in hair and skin to produce the characteristic brown henna colour. Lawsone can readily be reduced to 1,2,4-trihydroxynaphthalene, compound A. O OH + 2H+ + 2e– E o = +0.36 V O OH OH OH lawsone 1,2,4-trihydroxynaphthalene, A Name three functional groups in lawsone. Describe a reaction (reagent with conditions) that you could use to distinguish lawsone from compound A. Describe the observations you would make with both compounds. Suggest a reagent that could be used to convert lawsone into compound A in the laboratory. Draw the structural formula of the compound formed when lawsone is reacted with Br2. Compound A can be oxidised to lawsone by acidifi ed K2Cr2O7. Use the Data Booklet to calculate the for this reaction. Construct an equation for this reaction. Use the molecular formulae of lawsone, C10H6O3, and compound A, C10H8O3, in your equation. When 20.0 cm3 of a solution of compound A was acidifi ed and titrated with 0.0500 mol dm–3 K2Cr2O7, 7.50 cm3 of the K2Cr2O7 solution was needed to reach the end-point. Calculate in the solution. = mol dm–3 When lawsone is reacted with NaOH, compound B is produced. O O– Na+ O NaOH lawsone C B Reacting B with ethanoyl chloride, CH3COCl, produces compound C, with the molecular formula C12H8O4. Suggest the identity of compound C, and draw its structure in the box above. Another compound, D, in addition to C, is produced in the above reaction. D is an isomer of C which contains the same functional groups as C, but in different positions. Suggest a possible structure for D. D Suggest a mechanism for the formation of D from B and ethanoyl chloride by drawing relevant structures and curly arrows in the following scheme. O Na+ O– O O + C Cl CH3 D B
9701_s12_qp_42
THEORY
2012
Paper 4, Variant 2
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