Date: October 11, 2012 Section Number: Chem

Transcription

1 Experiment 1: Oxidation of an Alcohol Report Sheet Last Name: Siva First Name: Krishnaa Date: October 11, 2012 Section Number: Chem Objective: 1 mark (What is the purpose of this experiment?) The objective of this experiment is to oxidize cyclohexanol, a secondary alcohol, by reacting it with sodium hypochlorite and form cyclohexanone, a ketone. The reaction is performed with the help of acetic acid which activates it. At the end of the lab, with the use of IR spectroscopy, the product is to be verified if it is actually cyclohexanone. Introduction: 2 marks (Brief description of the concept/reaction studied oxidation of an alcohol) The oxidation of an alcohol to an aldehyde, ketone, or carboxylic acid plays a huge role in organic chemistry. Primary alcohols can be oxidized into aldehydes and then further oxidized to carboxylic acids, while secondary alcohols can be oxidized into ketones. It is important to note that the oxidation process normally consists of two reactions. The first part of the reaction consists of the nucleophilic addition and the second part consists of the E2 elimination. In this lab, cyclohexanol, a secondary alcohol, reacts with bleach (sodium hypochlorite) to form cyclohexanone, sodium chloride and water. Acetic acid is used in this experiment to activate the sodium hypochlorite and allow the reaction to proceed. While performing the lab, it is important to be safe and careful. For this reason being, beach is chosen as the oxidizing reagent over any other oxidant. Sodium hypochlorite is easier to control compared to many other oxidizing agents and it is environmentally friendly. Reaction Equation: 2 marks (Include proper structures and data [molar mass, concentration, density, volume, mass, moles, etc as appropriate including theoretical yield] for reactants and products) 1

2 Molar mass (g/mol) Melting Point ( C) Boiling Point ( C) Density (g cm 3) Volume/Mass Moles Sodium Hypochlorite ml Acetic Acid (catalyst) ml Cyclohexanol ml Cyclohexanone Theoretical: g Experimental: 1.45 g Theoretical: Experimental: Sodium Chloride g Water Table 1. Results Yield and Physical Properties of Cyclohexanone 5 marks Cyclohexanone Yield (g) 1.45 g Yield (%) 64 % Appearance IR (C=O stretch) Colorless liquid (clear), thick looking stretch at ~1715 cm -1 (corresponds to the graph, long evident stretch can be seen) Figure 1. IR Spectrum Attach IR Spectrum of Your Cyclohexanone Product label important stretching frequencies Discussion Questions: 10 marks 1. Suggest at least one chemical reasons why your percent yield is less than 100%. (Incomplete reactions? Side reactions? Stability of reagents?) One possible reason why the percent yield is less than the expected yield is due to the improper pace at which the sodium 2

3 chlorite is added. The rapid addition of the bleach (sodium hypochlorite) to the reaction flask with the acetic acid and cyclohexanol would cause the reaction to take place vigorously, and would result in an incomplete reaction. Unclean materials and instruments could have affected the yield of the experiment as well. The presence of chemicals used in the previous experiments will certainly have an impact on the reaction. There is also a possibility that the decomposition of sodium hypochlorite affected the final yield of the product as less sodium hypochlorite would be available to react with the cyclohexanol to form the cyclohexanone product. Decomposition of the sodium hypochlorite can be due to factors that include the temperature, exposure to light, and alkalinity of the solution (Pioneer, 2010). The presence of light would also speed up the decomposition process of sodium hypochlorite solutions and play a role on the final product yield. If the ph of the sodium hypochlorite solution was out of range, the sodium hypochlorite would have a higher tendency to decompose faster. A higher temperature can lead to the decomposition of sodium hypochlorite as well. 2. What are the decomposition products of sodium hypochlorite (bleach)? Draw two balanced reaction equations. 2 NaOCl ---> 2 NaCl + O 2 3 NaOCl ---> 2 NaCl + NaClO 3 The decomposition products of sodium hypochlorite include NaCl (Sodium Chloride), O 2 (Oxygen) and NaClO 3 (Sodium Chlorate). 3. Why do we use acetic acid rather than hydrochloric acid? Acetic acid is used rather than hydrochloric acid for precautious reasons. The use of HCl would lead to the formation of chlorine gas which has serious safety issues: NaClO + HCl ---> HClO + NaCl and then HClO + HCl ---> H 2 O + Cl 2 (g). Chlorine is a toxic gas and can result in the irritation of the respiratory system. Furthermore, since chlorine gas is heavier than air, it has the tendency to stay in low-lying areas and this can be quiet dangerous (ATDSR, 2011). It is also important to note that chlorine is a strong oxidizer, that will easily react with flammable products. It is the use of acetic acid that made it possible to do the lab on the bench top and it is more of a "friendly" substance overall. 4. Analyze your IR spectrum. What evidence is present that supports 3

4 the formation of cyclohexanone? Cyclohexanone is a ketone since it has the form of RC(=O)R'. The stretch at approximately the 1715 cm -1 region on the IR spectrum indicates the C=O and the fact that the product is a ketone. Cyclohexanone is neither an aromatic structure, an alkene or even an alkyne, but it is an cyclic alkane. The presence of a stretch lower than the 3000 cm -1 mark (~2900 region) makes it evident that the product is an alkane and not anything else. This is the stretch that is indicative of all the CH 2 and CH bonds on the cyclohexanone ring. Having no stretch near the 1600 cm -1 hundred region indicates that there are no C=C and having no stretch near the cm -1 indicates that there as no C=C triple bonds as well (Solomons, 2009). Considering the IR spectrum is for cyclohexanone, it can be seen that there is uncharacteristically a stretch near the cm -1 region. This normally indicates the presence of an O-H group (an alcohol). In this case, it is probably due to the presence of water that gets formed (the way water is formed can be viewed on #5 with the reaction mechanism) (Chaplin, 2012). There is very little chance that it is due to any unreacted cyclohexanol since there are more than enough moles of sodium hypochlorite to react with it and since we see the C=O stretch - C=O is only found on cyclohexanone and not cyclohexanol. 5. Draw a detailed mechanism for the oxidation of cyclohexanol to cyclohexanone using sodium hypochlorite (bleach) as the oxidizing agent. The mechanism for the oxidation of cyclohexanol to cyclohexanone using sodium hypochlorite (bleach) as the oxidizing agent is on the next page. 4

5 References Chaplin, Martin. "Water Structure and Science." London South Bank University. 29 July Web. 10 Oct "Medical Management Guidelines for Chlorine." ATSDR. 3 Mar Web. 10 Oct Pioneer. "STABILITY OF SODIUM HYPOCHLORITE SOLUTION." Force Flow Web. 9 Oct Solomons, T.W.G. Graham, Fryhle, Craig and Johnson, Robert. Organic Chemistry. 10 th ed. New York: John Wiley & Sons, Print. 5