ACJC_H2_CHEM_P3 ANS Prelim

PAPER III 1 Penicillin can be made in the laboratory by reacting 6-aminopenicilanic acid with a suitable acyl chloride. For a particular penicillin, the acyl chloride is the CH3CH2CH=CHCH2COCl. Since the acyl chloride used can be easily made from the corresponding carboxylic acid, the chemist has decided to work with CH3CH2CH=CHCH2CO2H because the acyl chloride is more reactive. H3CH2CH=CHCH2CO2H + PCl5  CH3CH2CH=CHCH2COCl + POCl3 + HCl (a) (i) The acyl chloride, CH 3CH2CH=CHCH2COCl, can be obtained by reacting CH3CH2CH=CHCH2CO2H with PCl5. Write a balanced equation for the reaction. [1] C (ii) ergie given alculate the enthalpy change for the above reaction. [2] Bond Energies /kJ mol-1 Using relevant data from the Data Booklet and the bond en s below, c P-Cl P=O 423 322 rokenBonds B Bonds formed 2 P-Cl 2(+322) P=O -423 C-O +360 C-C l -340 O-H +460 H-C l -431 H 60-423-340-431 = +270 kJ mol-1  = 2(+322)+360+4 (b) (i) e reaction. [1] team; heat in the presence of H PO catalyst 300 oC and 65 atm lternative: conc H2SO4 at 0 oC, followed by boiling with H2O The carboxylic acid, CH 3CH2CH=CHCH2COOH, can be converted into the hydroxyacid, CH 3CH2CH(OH)CHCH2COOH. Give the reagent and condition for th S 3 4 A (ii) romine. Name and describe the mechanism involved. [4] lectrophilic Addition The hydroxyacid obtained can be distinguished from its starting material by using b E C C H CH2COOH H CH2CH3 + Br Br   Slow C C H CH2COOH H CH2CH3 electrophile Br Br © ACJC 2009 9746/03/Prelim/09 [Turn over

Br Fast C C CH2COOH H H CH2CH3 Br Br nucleophile C C H CH2COOH H CH2CH3 Br (iii) Suggest another reagent and condition in which the hydroxyacid obtained can be distinguished from its starting material. [2] Reagent: acidified K2Cr2O7 and heat (c) (i) In the course of preparing the hydroxyacid, an internal chiral ester was also detected. Draw the structure of this ester. Circle the chiral centre(s). [2] CH CH2 CH2 C O CH2CH3 O (ii) State the number of sp2 and sp3 hybridised carbons in the ester. [2] sp2 - 1 sp3 - 5 (iii) This ester may be made into a diol. Give the reagent and condition for the conversion and draw the structure of this diol. [2] Reagent and condition: LiAlH4 in dry ether; reflux OH CHCH2CH2CH2OHCH3CH2 (d) (i) An experiment was carried out to determine the enthalpy change of combustion of this diol. Write a balanced equation including state symbols for the combustion of the diol under standard condition. [1] CH3CH2CH(OH)CH2CH2CH2OH(l) + 17/2O2(g)  6CO2(g) + 7H2O(l) (ii) A large beaker of water was placed on the stove and heated. The temperature rise was recorded. The cylinder was weighed before and after the experiment