Experiment S1: Isolation and Characterisation of a Neutral OrganicCompound from a Mixture of Inorganic and Organic Materials IntroductionA neutral organic compound was isolated from an unknownmixture containing organic impurities and an inorganic salt. This was done bysolvent extraction to separate compounds using two immiscible solvents such asDCM and water – this removed the inorganic salt in the aqueous layer. A basicand acidic wash was performed where all the acidic and basic impurities wereremoved from the organic phase. DCM was removed, the neutral product wasrecrystallised, and the melting point was determined.
Experimental Sample 4 (2.65g), water (10cm3) and dichloromethane(20cm3) were added to a 100cm3 conical flask and swirleduntil the solid dissolved. The solution was transferred into a separating funnel,rocked and inverted to mix the DCM and aqueous layers. Also, the tap was openedto release the pressure. The lower organic layer was separated into a cleanconical flask. This was repeated with additional DCM (10cm3) andadded to the flask. To remove the acidic impurities, excess sodium hydroxidesolution (10cm3) was added to the separating funnel, mixed and inverted.
The pH of the aqueous layer was tested with red litmus paper, which turnedblue. Also, to remove the basic impurities, excess dilute hydrochloric acid(10cm3) was added to the funnel. The pH of the aqueous was testedagain with blue litmus paper, which turned red. After each test, the organiclayer was separated into a clean conical flask.Magnesium sulphate was added to the conical flask to removetraces of water, swirled and filtered into a pre-weighed round-bottomed flask.
DCM was removed using a rotary evaporator until there was no change in theweight of the flask. The product was a fine, white powder. Ethanol and water were tested in a test tube to determinethe best solvent system for the product in sample 4. It was soluble in coldethanol, but insoluble in cold water. However, small volumes of hotethanol/water and 2-3 anti-bumping granules were added to the flask on ahotplate, until the solution was clear. The flask was left to cool, and thecrystallised neutral compound was vacuum filtered and weighed. The crystalswere white, shiny and needle-like.
Then, the melting point of the product wasdetermined to figure out the identity of neutral compound.Results & DiscussionThe % crude yield was ~50% becauseafter the first solvent extraction, the inorganic salt was removed. Also,almost all the acidic and basic impurities were removed once the basic andacidic wash was performed. This suggests that only 46.47% of the mixture wasmade up of neutral organic compound.
The % recovery yield of recrystallisation was 2.44% but the besttheoretical yield would be ~90%, since 100% isn’t achievable due to loss of productwhilst transferring it to different equipment. Some product may also be lost inthe recrystallisation solvent as there is finite solubility of the solid, evenat lower temperatures.
If the rinse solvent (cold water) isn’t cold enough, thesolid may redissolve, leading to a lower % recovery.The melting point of the product was 69-70oC, whichis within a degree of the literature melting point (71oC) of theorganic compound ‘biphenyl’. It melted completely over a narrow temperaturerange of 1.0oC, indicating that it is pure1. However,additional melting point trials can be carried out to confirm the meltingpoint.
ConclusionAfter the neutral organic compound was isolated, the meltingpoint was determined as 69-70oC. In conclusion, the identity of theorganic compound was biphenyl as it was closer to the literature melting pointof 71oC.References1 https://quondam.csi.edu/ip/physci/faculty/rex/MPTips.htmDate accessed: 28/01/2018
