18. Carboxylic acids and derivatives
A section of Chemistry, 9701
Listing 10 of 202 questions
Ethanedioic acid, C2O4H2, occurs in many vegetables. The amount that occurs in spinach can be estimated as follows. • 40.0 g of spinach leaves are crushed and mixed with distilled water, using a mortar and pestle. • The mixture is filtered, and the leaves are washed with a little more water. • The combined filtrate and washings are made up to 100.0 cm3 with water. • A 25.0 cm3 portion of the resulting solution is added to a conical flask, along with an excess of dilute sulfuric acid. • The acidified solution is warmed, and then titrated with 0.0200 mol dm–3 KMnO4. The equation for the reaction between ethanedioic acid and acidified manganate(ions is shown. 2MnO4 – + 6H+ + 5C2O4H2 → 2Mn2+ + 10CO2 + 8H2O In the titration, 15.20 cm3 of KMnO4 was required to reach the end-point. Calculate the percentage by mass of ethanedioic acid in the spinach leaves. percentage of ethanedioic acid = % Ethanedioic acid can be converted into ethanedioyl chloride: HO2CCO2H → Cl OCCOCl State a suitable reagent for this reaction. For the reactions of ethanedioyl chloride below, suggest the structures of compounds J and K and draw them in the boxes. CH3OH H2NCH2CH2NH2 K (C4H6N2O2) J (C4H6O4) COCl COCl When ethanedioyl chloride is reacted with silver ethanedioate, AgO2CCO2Ag, in ethoxyethane at –30 °C, an oxide of carbon, L, is formed. The molecule of L has no overall dipole and has molecular formula C4O6. The carbon-13 NMR spectrum of a solution of L in ethoxyethane, CH3CH2OCH2CH3, is shown below. δ Use the Data Booklet to state in the boxes below the δ values for the peaks in the spectrum which are due to the carbon atoms in ethoxyethane. CH3 CH3 CH2 CH2 O δ values Explain what the rest of the carbon-13 NMR spectrum indicates about the structure of L. When pure L is reacted with an excess of CH3OH, a mixture of three compounds is formed. L and CH3OH → M and N and O (C4O6) (C2H2O4) (C3H4O4) (C4H6O4) M is formed as one of the products when either N or O is heated with aqueous acid. The table gives information of the peaks recorded in the carbon-13 NMR spectra of M, N and O. compound peaks recorded in carbon-13 NMR spectrum M δ 162 N δ 53 δ 160 δ 162 O δ 53 δ 160 Suggest the structures of M, N and O. M, (C2H2O4) N, (C3H4O4) O, (C4H6O4) Suggest a structure for L that fits all the data given in and . L, (C4O6)
9701_s16_qp_41
THEORY
2016
Paper 4, Variant 1
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Ethanedioic acid, C2O4H2, occurs in many vegetables. The amount that occurs in spinach can be estimated as follows. • 40.0 g of spinach leaves are crushed and mixed with distilled water, using a mortar and pestle. • The mixture is filtered, and the leaves are washed with a little more water. • The combined filtrate and washings are made up to 100.0 cm3 with water. • A 25.0 cm3 portion of the resulting solution is added to a conical flask, along with an excess of dilute sulfuric acid. • The acidified solution is warmed, and then titrated with 0.0200 mol dm–3 KMnO4. The equation for the reaction between ethanedioic acid and acidified manganate(ions is shown. 2MnO4 – + 6H+ + 5C2O4H2 → 2Mn2+ + 10CO2 + 8H2O In the titration, 15.20 cm3 of KMnO4 was required to reach the end-point. Calculate the percentage by mass of ethanedioic acid in the spinach leaves. percentage of ethanedioic acid = % Ethanedioic acid can be converted into ethanedioyl chloride: HO2CCO2H → Cl OCCOCl State a suitable reagent for this reaction. For the reactions of ethanedioyl chloride below, suggest the structures of compounds J and K and draw them in the boxes. CH3OH H2NCH2CH2NH2 K (C4H6N2O2) J (C4H6O4) COCl COCl When ethanedioyl chloride is reacted with silver ethanedioate, AgO2CCO2Ag, in ethoxyethane at –30 °C, an oxide of carbon, L, is formed. The molecule of L has no overall dipole and has molecular formula C4O6. The carbon-13 NMR spectrum of a solution of L in ethoxyethane, CH3CH2OCH2CH3, is shown below. δ Use the Data Booklet to state in the boxes below the δ values for the peaks in the spectrum which are due to the carbon atoms in ethoxyethane. CH3 CH3 CH2 CH2 O δ values Explain what the rest of the carbon-13 NMR spectrum indicates about the structure of L. When pure L is reacted with an excess of CH3OH, a mixture of three compounds is formed. L and CH3OH → M and N and O (C4O6) (C2H2O4) (C3H4O4) (C4H6O4) M is formed as one of the products when either N or O is heated with aqueous acid. The table gives information of the peaks recorded in the carbon-13 NMR spectra of M, N and O. compound peaks recorded in carbon-13 NMR spectrum M δ 162 N δ 53 δ 160 δ 162 O δ 53 δ 160 Suggest the structures of M, N and O. M, (C2H2O4) N, (C3H4O4) O, (C4H6O4) Suggest a structure for L that fits all the data given in and . L, (C4O6)
9701_s16_qp_43
THEORY
2016
Paper 4, Variant 3
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Questions Discovered
202