Preparation of Cyclohexanol

Topics: Distillation, Sulfuric acid, Water Pages: 7 (2173 words) Published: November 15, 2012
Cyclohexanol is mainly used in the production of caprolactam and adipic acid that is a raw material of nylon 6 (Zhang, et al, 2002). Cyclohexanol can be produce through several methods, which include the oxidation of cyclohexane, the hydration of cyclohexene, or the hydrogenation of phenol (Zhang, et al, 2002). Problem with oxidation of cyclohexene is poor selectivity, extremely large recycles and explosion hazards. (Suresh, Sridhar, Potter, 1988). The purpose of this experiment was to synthesis cyclohexanol by hydration of cyclohexene using concentrated sulphuric acid as an acidic catalyst. In hydration reaction, C=C B bond is replaced by hydroxyl group (Hornback, 2006). Overall reaction:

(McFadden, 2012)

In the first step, the mixture of water, concentrated sulphuric acid, and cyclohexene was shaken vigorously until it became a homogenous solution. Followed by, the addition of water, and the distillation process lead to the hydrolysis of the alkene. Finally, addition of diethyl ether to the mixture then distillation took place to be purified and to obtain the final product, cyclohexanol (McFadden, 2012). Diethyl ether was used to extract alcohol from salt-water mixture because diethyl ethers solubility in water is lower than cyclohexanol which helps remove alcohol from the salt-water mixture (Merzougui, A, et al., 2011). (McFadden, 2012) Cyclohexene is added to water-acid solution, which formed two liquid phases were due to insolubility of cyclohexene in water-acid solution. It is very important that mixture is mixed well to make a homogeneous solution and allow reaction to complete. Cyclohexene was reacted with water and with sulfuric acid to form protonated cyclohexanol and cyclohexyl hydrogen sulfate. Protonated cyclohexanol and cyclohexyl hydrogen sulfate are soluble in water-acid solution (McFadden, 2012). When this mixture is heated, cyclohexyl hydrogen sulfate converts to protonated cyclohexanol which is equilibrium with cyclohexanol (McFadden, 2012). Moreover, distillation technique is used to separate components of a liquid mixture, where liquid is boiled to vaporize and then condensed back into liquid called distillate. Distillate components are collected with a lowest-boiling point to highest-boiling point. In this experiment, distillation is used to separate the organic compound from sulphuric acid solution; azeotrope of cyclohexanol and water is formed as distillate, it also contains some cyclohexene components. Azeotrope has a fix boiling point like a pure compound. Cyclohexanol is considerably soluble in water, so poor yield is expected (McFadden, 2012). Addition of sodium chloride to distillate solution improves the final product yield because it reduces the solubility of organic compound, and extracts cyclohexanol from aqueous phase. It is due to salt’s higher solubility than organic compound. Also, anhydrous potassium carbonate is used to absorb water and to neutralize any trace of acid. During distillation of pure cyclohexanol, most of the product should be collected as temperature reaches 161C (Weast, 1988). This experiment also introduces determination of the refractive index; it is one of the most convenient methods used to determine purity of liquid. It is a ratio of the sine of the angle formed when light ray is bent when passing from an air medium into a liquid medium; in other words it is a ratios of the speed of light in a vacuum to the speed of light in the liquid medium. Refrective index (n) = C_vaccume/V_medium (McFadden, 2012). At 20°C, the expected refractive index of cyclohexanol is 1.4641 (Weast, 1988).

The experiment was done in two parts. Part-A was hydration of the alkene, and Part-B was isolation and purification of the cyclohexanol. To perform hydration of alkene, 7.0mL of water and then 14mL of concentrated...
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