Lab Submission for Cyclohexene full 100% grade PDF

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Lab submission for graded week - full answers and workflow for cyclohexane lab SCC2211 Organic Chemistry, received full 100% grade...

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PREPARATION OF CYCLOHEXENE AIM: To prepare a sample of cyclohexene through the dehydration reaction of cyclohexanol using Sulfuric Acid as a catalyst.

HOCH(CH2)5 (s)

⇋

C6H10 (l) + H2O (l)

Molecular Formula Cyclohexene: C6H10

Cyclohexene MW = 82.14 g/mol BP = 83°C Cyclohexanol HOCH(CH2)5 MW = 100.16 g/mol BP = 161°C Sulfuric Acid H2SO4 MW = 98.079 g/mol BP = 337°C Water H2O MW = 18.015 g/mol BP = 100°C PRE-LAB TASKS 1. The Boiling Points (BP) of all the compounds, cyclohexene, cyclohexanol, sulfuric acid and water, were all important to the outcome of the experiment. The relative BP’s are listed above. The importance of all the BP’s in this experiment is that they are all different and the ability to dehydrate the compounds to a maximum 100°C allows the cyclohexene (the aim product) at a BP of 83°C to separate fully and be extracted into the receiving flask during distillation. 2.

25g of cyclohexanol is used in this experiment. 25g cyclohexanol / 100.16g/mol = 0.2496 mol (or 24.96 mmol)

1 mol of cyclohexanol should produce 1 mol of cyclohexene, 0.2496 mol of cyclohexanol should yield 0.2469 of cyclohexene. Therefore: 0.2469 mol x 82.14 g/mol = 20.5021g of cyclohexene 3. The OH group in both ethanol and cyclohexanol (the hydroxyl group), is polar and able to bond with polar solvents. The OH group can form hydrogen bonds with water molecules which does not occur in non-polar CH groups like in alkanes or hydrocarbons. The polar nature of hydroxyl group is due to the positive and negative properties (electronegativity) which in their partial state attract the opposing force to them (a partial negative O will attract a partial positive H) from neighbouring atoms.

In ethanol, a chain of hydrocarbons is attached to a hydroxyl group. When exposed to a polar solvent such as H2O, the hydroxyl groups intermolecular forces attract the free H2O atoms and cause changes in the bonds, which in a chain such as C 2H5OH, gives the compound more solubility. In cyclohexanol, the small, linked surface area where the intermolecular forces between carbons are stronger, means that the polar hydroxyl group is the only group to really be affected by the polar solvent, leaving the hydrocarbons intact and in their cyclic form. 4.

1-butanol

2-pentanol

3-methyl-3-hexanol

3-methylene hexane / 2-ethyl-1-pentene

3-methylene hexane

5. Cyclohexene is able to be purified by distillation because it is a liquid with a lower boiling point (evaporates first) than all the other compounds/reactants in this experiment which are also liquids. The reaction is a reversable one and can reach equilibrium, so the use of the round bottom flask for collection of the gas, which is collected by condensation prevents the reversal from occurring. As the cyclohexanol should be in a relatively pure form to start with and the boiling points between cyclohexanol and cyclohexene are greater than 70°C, it is suitable to use fractional distillation in this experiment to form pure cyclohexene. Distillation will not separate salt and sugar from each other in a solid state. You can use alcohol such as ethanol to cause the sugar to become miscible and have the salt granules left behind (not dissolved) at the bottom of the container. You would then use evaporation to separate alcohol and sugar giving you the two separate solid compounds. Water would cause both sugar and salt to become miscible and the distillation would only leave you with solid salt and evaporating the sugar and water which have similar boiling points. METHOD: A distillation apparatus was set up with a clean and dry 100mL round bottom flask (for the heating mantle) and a receiving flask placed in a tub of ice. 25 mL of pure cyclohexanol which was colourless and translucent, was then transferred to the round bottom flask, outside of the heating mantle via measuring cylinder. Approximately three mL of concentrated sulfuric acid was then added slowly to the round bottom flask using a plastic pipette. The flask was swirled constantly while adding the sulfuric acid to the cyclohexanol to disperse heat and prevent the solution from changing to a black colour. Whilst adding the sulfuric acid, an opaque light yellow/orange colour-change occurred in the bottom of the flask and the rest of the solution remained colourless. Two boiling chips were then added to the flask and the flask was placed into the heating mantle and attached to the distillation apparatus. The reaction mixture (cyclohexene, concentrated sulfuric acid and boiling chips) were then heated on the heating mantle, and maintained to up to 100°C, causing a colourless and translucent distillate of cyclohexene and water to accumulate in the receiving flask. Approximately 20mL of distillate appeared to have been collected after 30 minutes. Some black-coloured solution residue remained in the reaction mixture to prevent boiling to dryness, though no charring was present. The crude cyclohexene from the receiver flask, was placed into a separating funnel and 15mL of water was added. Once the funnel was inverted and the contents gently mixed, an opaque white mixture was observed. After performing the first wash and

returning the funnel to upright on the clamp, two separate layers were observed separating from each other. To determine which was the aqueous layer a mark was made on the funnel and then a few mL of water was added again. It appeared to indicate that the bottom layer was the aqueous layer, as per figure 1.

Figure 1. Separating funnel in the upright position after extra water was added to the crude cyclohexene/water wash. Black line indicates pre- ‘extra water’ line, delineating the aqueous layer from the organic layer.

The lower, colourless and translucent layer was removed from the separating funnel, leaving an opaque white organic layer. Following this, 15mL of 10% aqueous sodium carbonate solution was added to the separating funnel. Another wash was performed, and the funnel returned back to the clamp in an upright position. The product appeared to be slightly more translucent on the bottom layer, and slightly more opaque white on the upper layer than in the first wash, as per figure 2. The bottom layer was again removed from the separating funnel.

Figure 2. Separating funnel in the upright position and a more translucent and delineated product can be seen.

The separating procedure with 15mL water was repeated, the aqueous layer removed from the tap at the bottom of the funnel and the organic layer (top layer) was placed in a dry beaker. Approximately 3g of solid sodium sulfate was then added to the extracted organic layer (crude cyclohexene) to absorb any remaining water.

A sample tube was weighed (13.16g) and was placed at the receiver end of the distillation apparatus and the colourless, translucent, dried cyclohexene liquid was decanted into a dry and clean round bottom flask and 2 boiling chips were added to the cyclohexene. The flask was then attached to the distillation apparatus, within the heating mantle. The cyclohexene was then heated and all distillate boiling below 90°C was collected into the sample tube. A completely translucent and colourless liquid was collected into the sample tube. The tube was re-weighed, and the gross weight was 17.59g. The final product was 4.43g (0.0539 moles). DISCUSSION The cyclohexene produced from this experiment was a colourless and transparent liquid with no apparent contaminants such as water. The final yield was 4.43g or 21.61% of the ideal (100%). The smaller yield could be attributed to factors such as remaining cyclohexanol or crude cyclohexene etc left on glassware as it was transferred. Loss could also have occurred during the distillation process if left for longer or alternatively, during separation of aqueous and organic layers in the extraction phase. During the extraction step of the experiment, the upper layer was identified as the organic layer and the lower the aqueous layer. This was identified through a water test (as per figure 1) where the aqueous layer on the bottom increased and the organic layer above, did not. CONCLUSION The final product from this experiment is as expected, a colourless and transparent liquid with no apparent contaminants. A slightly lower yield than expected was produced with a mass of 4.43g. POST-LAB QUESTIONS 1a) The first water wash is used to remove any non-organic compounds and impurities and the second is to remove any remaining carbonate. 1b) The Na2CO3 solution is used to remove unwanted acids left over such as the sulfuric acid used to catalyse the reaction, before reaching the final product. 2)

The drying agent used was 3g of solid sodium sulfate.

3a) InfraRed (IR) spectra:

O-H Stretch

C-O

C-H Stretch

Figure 3. IR spectra of cyclohexanol – labelled with functional group/compound signals circled in red

C=C

C-H Stretch

Figure 4. IR spectra Pure Cyclohexene – labelled with functional group/compound signals circled red

C=C

C-H Stretch

Figure 5. IR Spectrum of Synthesised Cyclohexene (from the scientist in the lab experiment), labelled with functional group/compound signals circled red

The functional groups expected in cyclohexanol:

Cyclohexane

C-H / C-O

Hydroxyl Group

O-H

The functional groups expected in cyclohexene: Cyclohexene

C=C / C-H

Alkene

C=C

3a) Continued: Functional groups and compounds assigned at Figures 3, 4 and 5, circled in red and labelled accordingly. 3b) There appear to be zero variations on the IR spectra between the pure product (cyclohexene) and the scientists IR spectra of the product (cyclohexene). The Carbon/Hydrogen stretch at 2900cm-1 and Carbon/Carbon double bond of an alkene was seen at 1610cm-1. Whilst the signals are not very strong for the functional groups, they appear as expected in their respective bands.

NOTE: Chemsketch utilised to draw and tag all isomeric products from dehydration reactions of 1-butanol, 2-pentanol and 3-methyl-3-hexanol. Pictures at figures 1 and 2 taken from screen stills of the lab experiment (mp4)....