Introduction Elimination reactions often have more than one possible product. While mixtures are very common, one product is usually produced in a larger proportion than the others. Zaitsev’s Rule states that the product having the most substituted double bond will be the dominant product. There are two major reaction pathways by which a leaving group may be eliminated to form an alkene. In the E1 mechanism, the reaction rate depends only on the concentration of substrate, that is, the reaction displays first order kinetics. This means that the slowest step of the mechanism must involve only the substrate molecule. In the E2 mechanism, the rate of the reaction depends both on the concentration of base and on the concentration of substrate, that is the reaction displays second order kinetics. In this case the slowest step of the mechanism must involve both a molecule of substrate and a molecule of base. In our case, we are using cyclohexanol, a secondary alcohol, and the reaction goes via the E1 mechanism. The first step in the mechanism is protonation of the alcohol group by the acid. The second step is the loss of water to form the carbocation. The final step is removal of a hydrogen atom by the base (water) to form the alkene. Equipment Chemicals: cyclohexanol, phosphoric acid (concentrated H3PO4, ω = 85%, i.e. C = 14,8 mol/l). Apparatus: 100 ml round bottom flask; distillation setup including Vigreux column, boiling stones; silicon grease. Reaction mechanism Step 1: Step 2: Step 3: Protonation of the alcohol by the acid Water leaves, leading to the formation of a secondary carbocation Deprotonation of a hydrogen atom to form the double bond Procedure and observations First a distillation set-up is prepared under the hood, including a distillation bridge, a Vigreux column, a 100-ml flask for the educts, a 50-ml one for the products, and a thermometer. The flask containing cyclohexanol and phosphoric acid is heated with a heating mantle (which is on top of a lab jack) for about 30 min. A mixture of water, cyclohexene and impurities is collected in the receiving flask. The formation of cyclohexene is confirmed by the strong smell of the product. It is then separated with the help of the separating funnel, dried with anhydrous sodium sulfate. It is filtered afterwards using filter paper. After the first distillation, the equipment is washed with acetone and dried (no water should be left on the distillation bridge to avoid the occurrence of the reverse reaction). A second distillation set-up is prepared (this time, without the Vigreux column) and the crude cyclohexene is distilled at 81-83◦C. The final product is weighed and its refractive index is measured. Results We obtained 9.28 g of final product with a refractive index of 1.421 (the refractive index of cyclohexene that we found in literature is 1.4465, which leads us to believe that there are still some impurities left). Assuming that the product is pure cyclohexene, we can calculate its number of moles: n = 9.28 g/82.143 g/mol = 0.101 mol. From the reaction equation above, we can see that ntheoretical(cyclohexene) = n(cyclohexanol), i.e. 0.25 mol. The yield is then 0.101 mol/ 0.25 mol·100% = 40.4%.