orgo postlab 2

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Chemistry

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Jan 9, 2024

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● Q1 ○ (a) Isopropyl alcohol: 83C, Acetone: 56C, Al(O i Pr)3: 125C ○ (b) Isopropyl alcohol forms an azeotrope with water; add water to this mixture, use a Dean-Stark Trap, and boil away the water, letting the isopropyl alcohol ﬂow back into the reaction ﬂask. It would be hard to separate Al(O i Pr)3 and acetone using methods we’ve learned in class, like a separatory funnel, since acetone is miscible in water and organic solvents. ○ (c) A large excess of isopropyl alcohol and an azeotrope of acetone with a compound like heptane in a Dean-Stark trap can drive this reaction towards the products; in this set-up, a large excess of the reactant (alcohol) is used, and acetone is continuously removed from the environment, both of which favor product formation. ● Q2 ○ (1) lower temp (2) use less ﬂuid bro idk ○ (a) One solution would be to use a large excess of isoamyl alcohol, which would drive the reaction towards the products as per Le Chatelier’s Principle. Another way to remove water from the reaction and drive it continuously towards the products without using a Dean-Stark trap would be to use MgSO4 to dry the water being formed. ● Q3 ○ (a) If you don’t fill up the trap with heptane, and particularly, if the amount of heptane in the ﬂask is below the amount of water that the reaction generates, then you won’t know when your reaction is complete and won’t be able to end it on time. ○ (b) adding brine to the extraction helps to transfer water from the organic layer to the aqueous layer and make sure that the organic layer is adequately dried out. ○ (c) Isoamyl alcohol is among the starting materials, and would have a strong peak at the 3200-3500 mark because of the presence of a hydrogen-bonded OH group; this wouldn’t be present in the pure isoamyl acetate product that is desired. Monitoring the presence/absence of this peak would indicate whether or not the reaction has gone to completion. Follow the Lab Report Guidelines included with this syllabus. Report should include: ü Balanced equation for esterification reaction In notebook (???)

ü Mechanism of esterification reaction (It is advisable to look up esterification in your Chemistry 236 text as well as through online resources) In notebook ü Calculate percent yield (experimental yield/theoretical yield * 100%) 1.996 / 8.957 * 100 = 22.28% yield of isoamyl acetate ü Summary table with experimental yield, percent yield and boiling point range for all fractions. Percent yield for non-product fractions can be omitted. Experimental Yield Percent yield Boiling Point Range Fraction 1 Not measured (waste) --- 92-99C Fraction 2 1.996 g 22.28% yield 129-133C ü Summary table for IR spectrum data (include original printout with report). See Sample lab report for IR summary table. Wavelength (cm^-1) Intensity Functional Group 3430.12 m O-H 2930.56 - 2959.93 m Alkane C-H 1743.00 m Acyclic ester C=O DISCUSSION ü Discuss LeChatelier’s principle and why a Dean-Stark trap is used LeChatelier’s principle states that if you disrupt the environment for a reaction that’s in dynamic equilibrium, then that equilibrium shifts to counteract the change. In this specific example, one of the products of the esterification reaction is water; by using a

Dean-Stark Trap to boil away the water, equilibrium shifts in favor of the products, and isoamyl acetate is formed in larger quantities. ü Discuss percent yield of product and how it could have been affected (i.e. reaction time, insuﬃcient distillation, etc.) There was only about a 22% yield of product, which was likely due to several errors made during the execution of the procedure. When setting up the Dean-Stark trap, some of the heptane spilled into the ﬂask being heated. Then, when heated, the mixture never reﬂuxed vigorously, despite being heated to 420C for well past the recommended amount of time. Eventually, the heat had to be turned off -- had the reaction been conducted at higher temps and for a longer amount of time, the percent yield would’ve been higher. Someone stole my sample, so for the second part of the procedure, a different sample had to be provided. Since the reaction was again taking longer than expected to proceed, only two fractions were collected, one of which was waste. ü Fully interpret the data on the IR spectrum. The IR spectrum indicates the presence of O-H, acyclic ester, C=O, and alkane C-H in my final compound; all of these except the O-H are found in the structure of isoamyl acetate. The presence of an O-H stretch indicates that water is a source of impurity in my final product, so clearly, that the azeotropic distillation didn’t fully go to completion (not all the water was removed). ü Discuss the purity of your product based on bp and IR analysis. Note the IR stretches you see in the product and explain how they differ from those you would expect in the starting materials. The most prominent stretch is the N-H stretch, and all of the bands are not very strong, indicating that significant impurities were present in my final product. All of the bands except the N-H band are expected of the product produced. The boiling point, recorded during the fractional distillation, was at 133C, about 10C lower than the literature value, further suggesting the presence of significant impurities. While the

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sample I distilled wasn’t mine, it’s possible that errors such as imprecisely separating the organic and aqueous layers during earlier parts of the procedure would have contributed to impurities.