Chemical properties of Ethanol & Phenol © KCl
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Objective To find out the chemical properties and pH of ethanol and phenol, and compare their differences between ethanol and phenol. Results Reaction of ethanol: Properties Observation Corresponding equations (if any) / s / Smell Reactions pH of universal / solution indicator remains green, pH=7 Triiodometh yellow C2H5OH + 4I2 + 6NaOH → CHI3(s) + HCOO-Na+ ane precipitate + 5NaI + 5H2O reaction found at bottom of test-tube, with odour smell Reaction Na sinks to 2C2H5OH + 2Na → 2C2H5O-Na+ + H2(g) with Na bottom, colourless gas, which gives a 'pop' sound to burning splint, evolves slowly and moderately. When ethanolethoxide mixture in test-tube is poured onto a petri-dish, small, colourless
rectangularshaped crystals are formed in a few minutes. Esterificatio When the n mixture of ethanol, ethanoic acid & conc.H2SO4 in test-tube is poured into Na2CO3 solution, a smell like allpurpose adhesive is noticeable.
Reaction of phenol: Proper Observa ties / tions / Reacti Smell ons Solubili phenol ty in dissolves water: gradually (a) a on little shaking phenol insoluble, (b) a phenol lot of forms oilphenol like droplets on shaking (soluble when heated) pH of universal solutio indicator n changes from green to orange,
Corresponding equations (if any)
/
i.e. acidic Reactio phenol n with becomes NaHCO insoluble after 3 adding NaHCO3 and forms a emulsion on shaking Reactio Solubility n with of phenol NaOH in NaOH is much higher than in water. After adding conc. HCl, phenol becomes insoluble (appear as droplets) again. Reactio Na floats n with and Na evolves a colourless gas, which has a 'pop' sound on burning splint test, gradually (but faster than in ethanol)
Reactio Br2 n with decolouri bromin zed e water readily in presence or absence of light, which indicates that this is not a free radical substituti on reaction. A white precipitat e is formed. Reactio The n with colour of 'neutral FeCl3 ' FeCl3 changes from yellow to violet. The same colour change is not take place in ethanol.
*The violet complex formed between phenol and Fe3+ is still not well-known
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Precaution 1.> The filter paper, which have been soaked with paraffin oil on sodium metal, should be thrown properly since the unreacted sodium remains on the paper may cause a fire. 2.> Ensure that all sodium is reacted in test-tube before disposing the liquid. 3.> Avoid adding too large sodium to ethanol or phenol since
the reaction may be to vigorous. 4.> Avoid contact with the crystal of phenol. If you contact with it accidentally, wash your hands with glycerol or plenty of water, or your hands may have white strain due to phenol's corrosive property. Discussion 1.> The smell of phenol is close to that in hospital. 2.> Both pH test (acidic in phenol, neutral in ethanol), iodoform test (+ve in ethanol), solubility test (miscible between ethanol & water), reaction with NaHCO3 (phenol is insoluble), reaction with Br2 water (phenol decolourize Br2) and reaction with neutral FeCl3 (Fe3+ and phenol forms a violet complex) can distinguish between ethanol & phenol. 3.> Phenol is much more soluble in NaOH than in water because the reaction between phenol and water to form H3O+ & phenoxide is reversible (since phenol is a weak acid, most H+ formed will combine with phenoxide to form phenol again) whereas that between phenol and NaOH is not and the formation of phenoxide ion is promoted:
Na+ & phenoxide ions are then dispersed by water molecules, thus phenol is highly soluble in NaOH. 4.> Compare their reactions with Na, H2 evolves faster in phenol than in ethanol due to the acidic nature of phenol. The acidity of an acid is depends on the relative stabilities of the acid (HA) & its conjugate base (A ). The more stable the conjugate base A-, the stronger is the acid. In case of phenol, the phenoxide ion is stabilized by delocalization
of p-electrons (the charge on O is more disperse & lower its charge density):
The equilibrium of shifts to right and thus phenol is acidic. However, in case of ethanol, alkyl group is electrondonating group, which makes ethoxide ion unstable (C2H5→O-), thus it's neutral. 5.> In the reaction with NaOH, the further addition of conc. HCl makes phenol becomes insoluble again which shows that phenol is a weaker acid than mineral acids. 6.> Phenol has an electron-rich centre (benzene ring) to attract electrophiles to attack and electron-donating hydroxyl group further increase its nucleopilicity. This makes phenol has a much higher reactivity than benzene and react with Br2 readily even in the absence of catalyst & light. On the other hand, ethanol is saturated and has no electron-rich centre, thus no reaction between ethanol and Br2. 7.> Some of the reactions in this experiment is useful and is usually used for daily life. For example, (a) Iodoform reaction is used to prepare a compound that is one carbon less than previous one and iodoform itself can be used as pesticide. (b) Phenol and it's derivatives can be used as antiseptics so it's quite common to smell their smell in hospital. (c) Esterification can be used to synthesize esters in perfumes. (d) Phenol can be purified by adding NaOH to phenol and organic compound mixtures, sodium phenoxide can then be crystallized and separated, phenol is regenerated by adding H+.
(e) FeCl3, Br2 and NaOH are used to test the presence of phenol if all these three tests show positive result. Conclusion Both ethanol and phenol are widely used compounds, especially in disinfectant. To distinguish them, several tests are needed, since other compounds may also be positive on these tests. If all of these test shows positive result, then the uncertain organic compound may be either one of them.
