From the calculations obtained, the yield of extracted oilwas not expected as it surpasses the expected yield of 11. 3% (1/8.
83 x 100%), this could be due to the extraction process. Water was extracted as well as limonenetherefore resulted in additional mass of extracted oil causing a higher yieldof orange oil. Following the results in the three test tubes containingR-Limonene, Cyclohexane and Cyclohexene, Bromine water reacted differently witheach component. First and foremost, Bromine are electrophiles as they areattracted to electron rich regions, (Clark, 2015) they are very polarisable, meaning they undergo electrophilic addition reaction with ethenes forming picomplexes. Even though ethenes are non-polar molecules, they contain an area ofhigh electron density around the carbon-carbon double bond. This makes ethenestarget for electrophile attacks. In Test Tube 1, Limonene is added to the bromine water andthe bromine water turns colourless. This is because carbon-carbon double bondis present in limonene and this creates an electrophilic reaction between thebromine in the bromine water and limonene.
As the bromine molecule approachesthe pi bonds of the limonene, an induced dipole is formed within the brominemolecule, (Clark, 2000) the electrons in the bonds are pushed to one endresulting in a positively charged bromine and a negatively charged bromine. Thenegatively charged bromine atom repels from the pi bond and automatically linesup the right way around for a successful attack on the ethane whereas thepositively charged bromine atom (nearer to the pi bonds) becomes attached toboth carbon atoms and this causes the double bonds to break. (Clark, 2000)Sigma bonds are formed between the two carbon atoms of the alkene and thepositively charged bromine, and this leads to the formation of a cyclicbromonium ion. This bromonium ion is then attacked by the negatively chargedbromine atom from the back-side in relation to the transition state of the nucleophilicreaction, this once again breaks the bromonium bond and forms a haloalkane. Limonenehas 2 double bonds therefore 2 bromine atoms will attach to each resulting inthe formation of 4 bromine atoms.
Since the brown colour comes from theelemental bromine, when the saturation of bromine decreases, the brown colourdecreases and eventually turns colourless. In Test Tube 2, A layer of brown oil surfaced to the top, this brown layer consists of bromine and cyclohexane. Bromine in the brominewater is more soluble in cyclohexane than in water (Clark, 2015) therefore ittransfers into the cyclohexane layer, leaving the water.
Bromine is non-polartherefore it is much more soluble in organic solvents such as hexane than inwater, this is due to the fact that both of them are non-polar moleculestherefore they are attracted to each other by Van der Waals forces. However, the bromine water does not decolourise, this is because cyclohexane does notcontain a c-c double bond therefore a pi complex does not occur. In Test Tube 3, The bromine water becomes colourless afterthree drops of cyclohexene is added. This is because cyclohexene containsdouble bonds and bromine itself is very reactive therefore it attaches itselfto the double bonds. As it approaches the unsaturated bonds, the bonds betweenthe bromine ions become polarized by the electron rich pi cloud of thecarbon-carbon double bond. The positively charged bromine attacks the pi bondof the cyclohexene and the carbon-carbon double bond breaks, new single bondsare formed from each of the carbon atoms in which attaches to the bromine ions anda bromonium ion is formed. The bromonium ion is then attacked from the back (Clark, 2003) by a nearby bromide ion and this causes the bromine to lose its originalreddish-brown colour, giving out a clear and colourless liquid. (Clark, 2000).
Besides bromine water, another way to characterise theextracted oil is by using potassium manganate (VII). Potassium manganite (VII)are strong oxidising agents, (Clark, 2016) therefore alkenes (limonene) can beoxidised by it. The products formed varies on the conditions chosen for thereaction. Under acidic conditions, potassium manganate (VII) with dilutesulphuric acid. When added to alkene in a dilute solution, the colour changesfrom a pale purple to colourless and alkene is converted into a diol. If sodiumcarbonate solution is added to potassium manganate (VII), it becomes slightlyalkaline.
The purple manganate (VII) ions are reduced to green manganate (VI)ions and eventually becomes a dark brown solid manganese (IV) oxide. (Clark, 2016). These two methods prove that the extracted oil contains c-c double bondsas both end products contain two alcohol groups (-OH), alkene is oxidify intoalcohol.
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