Kevin Totimeh October 18th, 2022 Kinetics Pre-Lab Organic Chemistry II Lab The title of the lab: Kinetic vs. Thermodynamic Control in Competing Reactions Objective: - Determine how fast a chemical reaction is from the reactants to the products. Cover mechanisms associated with the chemical reaction Overview of condensation and hydrolysis. Study the properties of chemical compounds such as ketones and aldehydes. Look at the reactants and products of a chemical reaction from a thermodynamic and kinetic energy standpoint. Principle: - Thermodynamic control variable- free energy change between the reactants and products, favoring the lowest energy product. Kinetic control variable- favors the products in a reaction of lower activation energy. Curtin-Hammett principle- principle in which a reaction has a pair of intermediates go to different products, in which the product is dependent on the difference of energy between the intermediates and the energy barriers to their respective isomers(conformational isomers). Reagents Table: Reagents Molecula r Formula 2-furfural C5H4O2 Molecula r Structure Molecula r Weight Melting/ Boiling Point Density Molar Ratio Weight and Volume Used 96.085 g/mol 162(BP) -37(MP) 1.16 g/cm^3 2:5 2.5 mL Cyclohex (CH2)5C anone O 98.15 g/mol -47(MP) 155.65(B P) 0.95 g/cm^3 1.0:2.0:1. 1 3 grams Dipotassi um sulfate K2HPO4 174.2 g/mol 0(BP) 465(MP) 2.44 g/cm^3 2:1 6 grams Semicarb azide hydrochl oride CH5N3O 75.08 g/mol 175-177( MP) 1.286 g/cm^3 1.2:1 3 grams Ethanol C2H6O 46.069 g/mol 78.23(BP ) -114.14( MP) 0.78945 g/cm^3 10.1:1 15 mL Procedure: - Student 1 weighed 3 grams of semicarbazide hydrochloride on a tared waxed paper and transfer the solid to a 150 mL Erlenmeyer flask. 6 grams of dipotassium sulfate were transferred, and was weighed on the same paper to flask #1. Added 75 mL of distilled water to flask #1 and swirled the flask to dissolve the two solids. Flask #1 became solution #1. Student 2 measured 3 grams of cyclohexanone in a 10 mL graduated cylinder and pour the liquid into a 50 mL Erlenmeyer flask, labeled #2. Student 2 measured 2.5 mL of 2-furfural into flask #2(without cleaning the graduated cylinder). Transferred 15 mL of ethanol into two increments to flask #2, without cleaning the graduated cylinder. Flask #2 now contains solution #2. Low Temperature Experiment: - 25 mL Solution #1 was poured into a 50-mL Erlenmeyer flask and placed in an ice-water bath to cool. 5 mL Solution was poured #2 into a medium-size test tube and cool the test tube in the ice-water bath. After the two solutions cooled down to ice-water temperature, the sample were added into the test tube into the sample of Solution #1. - After a few minutes, precipitation took place. Collected the precipitate in a Buchner funnel. Removed the filter paper containing the solid from the funnel and placed it on a paper towel. The flask was labeled ‘’low temp’’. Room-temperature Experiment: - Poured 25 mL of Solution #1 and 5 mL Solution #2 into a 50 mL Erlenmeyer flask. Swirled the flask to ensure the mixture is dissolved as the reactants, place the flask on your lab bench and cooled to room temperature after 5 minutes. As soon as crystals formed in the flask, the flask was put into the ice-water bath. Collected the crystals, placed them next to the ‘’low-temp’’ crystals and labeled these crystals ‘’room temp’’. High temperature Experiment: - - Prepared the hot ice-water bath: filled 400 or 500-mL of water in a beaker about ¾ full, placed the beaker on a hot plate and heated the beaker at medium heat until the temperature of the water was 80 degrees celsius. Poured 25 mL of Solution #1 into a 50 mL Erlenmeyer flask and placed the flask into the hot ice-water bath. Poured 5 mL of Solution #2 into a medium test tube and place the test tube in the hot water bath. After 5 minutes, poured 5-mL of Solution #2 into a 50 mL Erlenmeyer flask. Swirled the Erlenmeyer flask without removing the flask from the hot water. Kept the flask in hot water for about 15 minutes. Removed the Erlenmeyer flask(the solution) from the hot water and allow it to cool to room temperature. Then put the Erlenmeyer flask in the ice bath and collected the crystals, labeled these crystals ‘’ high temp’’. Observations: - - When the ‘’hot temp’’ flask was put into the flask, there was a color change at a frantic pace in comparison to the ‘’low temp’’ and ‘’room temp’’ flask, which remained a light yellow color over a long duration of time. When Solution 1(2-furfural) and Solution 2(cyclohexanone)were mixed together, they created a yellow colored compound. Results and Discussions: - - Based on the experiment, it is most likely the cyclohexane is the kinetic control product and the thermodynamic controlled product is the 2-furfural due to the aldehyde favoring the low activation energy and the cyclohexane favored the lowest energy product. During the hot ice-water bath, the product was formed very quickly, thus serving as the kinetic control product. For the ‘’low temp’’ solution, the temperature was lower in comparison to the ‘’hot temp’’ and ‘’room temp’’ and took a longer reaction time to form crystals. For ‘’room temp’’ there was more heat added before being placed in the ice bath, thus crystals appeared faster than ‘’low temp’’. Conclusion: - In conclusion, the experiment was successful in showcasing the relationship between the kinetic control and thermodynamic control. This was shown during the ice-bath and hot water baths during different temperatures, as a result the kinetic energy control product is the cyclohexanone and the thermodynamic product is the aldehyde called 2-furfural. Post Lab Questions: - Which one creates a negative enthalpy ? - Cyclohexane created a negative enthalpy due to the chemical reaction being derived from this ketone’s derivative of hydrazine with the addition of dehydration to turn into a condensation reaction - Which involves two organic molecules(condensation or dehydration)? - Dehydration is the chemical process of two organic molecules due to one monomer being connected with another to form polymers. - What feature is responsible for the color change for 2-furfural? - Since furfural is acromatic, the nitrogen pair with its electrons will cause a strong conjugation, thus leading to a color change of yellow when mixed with cyclohexanone.
