Synthesis of isobutyl acetate

Transcription

1 Practical course in organic chemistry (OCP 1) Spring semester L Synthesis of isobutyl acetate (cherry, raspberry, strawberry) Janosch Ehrenmann BSc Biotechnology D CHAB, ETH Zurich Zurich, page 1

2 1. Method: Esterification of Acetic acid and isobutyl alcohol to isobutyl acetat catalysed by sulfuric acid. 2. Chemical equation 3. Mechanism page 2

3 4. Physical properties of the substances Isobutyl alcohol [1] C 4 H 10 O (CH 3 ) 2 CHCH 2 OH g/mol g/cm 3 (20 C) melting point -108 C boiling point C (1013 hpa) refraction index (nd20) HO R-phrases R 10-37/ Inflammable (430 C), Irritates skin and airways S-phrases S 7/ /39-46 Purity Merck, reinst 98.5 Acetic acid [2] C 2 H 4 O 2 CH 3 COOH g/mol O 1.05 g/cm 3 (20 ºC) melting point 17 ºC boiling point ºC (1013 hpa) OH refraction index (nd20) - R-phrases R Flammable (39 c), Corrosive S-phrases S Purity Fluka, puriss p.a Sulfuric acid 96% [2] H 2 SO g/mol 1.84 g/cm 3 (20 C) melting point ~ 3 C boiling point ~ 335 C refraction index (nd20) - R-phrases R 35 Corrosive S-phrases S /37-45 Purity Merck, 96% Sodium hydrogen carbonate [1] NaHCO g/mol 2.22 g/cm 3 (20 C) O melting point 270 C boiling point - C refraction index (nd20) - HO O Na R-phrases - S-phrases - Purity - page 3

4 Magnesium sulfate [2] MgSO 4 Mg g/mol 2.66 g/cm 3 (20 ºC) melting point - boiling point - refraction index (nd20) - R-phrases - S-phrases - Purity - Isobutyl acetate [2] C 6 H 12 O 2 CH 3 COOCH 2 CH(CH 3 ) g/mol 0.87 g/cm 3 (20 C) melting point -99 C boiling point C refraction index (nd20) R-phrases R Flammable, Repeated exposure may cause skin dryness or cracking S-phrases S Hardware Inventory: 250ml flask, magnetic stirrer with stir bar, reflux condenser, contact thermometer, water cooled alembic, oil bath with thermometer, separating funnel, filter. page 4

5 6. Quantities Isobutyl alcohol Acetic acid Sulfuric acid Mass g g 9.2 g Mol 0.25 mol 0.6 mol 0.09 mol Equivalence Volume ml ml 5.00 ml 7. Accomplishment 23.1 ml isobutyl alcohol, 34.5 ml acetic acid and 5.0 ml sulfuric acid were put together in a 250 ml flask. A reflux condenser was placed on the flask, the cooling water was turned on and the reaction mixture was heated to reflux (130 C) while stirring. After 2 1/2 hours of cooking the mixture was cooled to room temperature. The mixture was poured in a separation funnel. Then as much water was added until the water phase had twice the volume of the organic phase. The two phases were shuffled by shaking and let separate again. The two phases were separated. The water phase was dropped and the organic phase was washed three times with saturated sodium hydrogen carbonate and dried over magnesium sulfate. Finally the organic phase was distilled. Two fractions were gotten where fraction 1 was the main fraction with a vapor temperature of 110 C and. Fraction 2 contained the substance taken at the end of distillation when the temperature sank rapidly. A first flow was not taken. The refraction index of each of the two fractions was determined. As well a IR spectrum of the product was measured. 8. Yield Yield: g (0.135 mol, 54%) isobutyl acetate 9. Characterization of the product 9.1 Refraction index: Fraction 1 Fraction 2 Measuring temperature C C Measured Literature value (nd20) [2] page 5

6 9.2 IR spectrum: Band frequency cm -1 intensity Assignment [3,4] 2963 m 1) C-H 2877 w 1) O-H 1738 s 1) C=O (ester) 1471 m - 2) 1380 s C-H 1232 s C-O 1037 s w w w w s s Interpretation The refraction indices of isobutyl alcohol (nd20 = 1.398) and isobutyl acetate (nd20 = ) are distinguishable from each other. An identification of the product after the refraction index is possible. The refraction index of both of the two distillated fractions corresponds to the literature value of isobutyl acetate. Concerning the refraction indices fraction 1 and 2 are identical and as well the pure product. The IR spectrum shows at 1738 cm -1 an intensive peak of the ester group. Also the strong peak of the C-O group in the ester (1232 cm -1 ) proofs the success of the synthesis. The resonance of the OH group (2877 cm -1 ) in the starting material isobutyl alcohol is yet weakly observable. The synthesis reaction so was not yet terminated when the product was washed, dried and distilled. Nevertheless most of the alcohol had reacted. The product is not absolute but however from a high purity. The acetic acid band at 1700 cm -1 does not appear. The product then was washed free of acetic acid. As well at 2963 cm -1 and 1380 cm -1 a medium and strong resonance of the C-H groups were measured. The yield low of 54% of product can be explained as followed: The reaction had not yet terminated when heating was stopped so not all the alcohol had turned into the ester. Also a little of product remained in the distillation apparatus after distillation. This sum of these losses is estimated to 15%. The other 31% of loss are caused by dropping the separation water. The product was easy to smell in the water. For the next time doing this experiment I would suggest to heat the reaction solution longer (3 hours at least) to make sure all the alcohol has reacted. Furthermore the water phase of the separation process should be extracted several times with DCM. 1) 2) w (weak), m (medium), s (strong) finger print area page 6

7 11. Literature [1] [2] [3] Exp 1a Synthesis of iso-butyl acetate (cherry, raspberry, strawberry), experimental manual [4] sieg.de/data/anna_/lehrveranstaltungen/instrumentelle%20analytik/ir- Spektroskopie.pdf 12. Attachment - IR spectrum - Task sheet containing the experimental manual - copy of the lab journal - Safety sheets of the used chemicals page 7