CHEM 225 - labreportminilab 17 PDF

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To: Kristen Dickerson – 16 From: Radhi Daya Experiment #: Mini Lab 17 Partners: Harini Patel, Nho Dao Introduction: The purpose of this experiment was to heat bromotriphenylmethane with ethanol to form an ether, ethoxytriphenylmethane, by an Sn1 reaction. A typical Williamson synthesis of ethers includes the reaction of an alkyl halide with sodium salt of an alcohol or phenol. Alkoxide is a strong base and would undergo an E2 reaction and form an alkene instead of an ether, or may undergo an Sn2 reaction because alkoxide is a very strong nucleophile. E1 and Sn1 may compete to form the ether if a less nucleophilic alcohol was used. Bromotriphenyl and the very stable triphenylmethane cannot go through E1 and E2 elimination and is impossible because it is a tertiary carbocation and will react readily with alcohols to produce an ether. Because of these reasons, Sn1 was the mechanism with a less nucleophilic alcohol was used.

Observation and Data:

There were no color changes instead of a the clear mixtures turning into cloudy crystals during the experiment. The crystals took about 10-15 minutes to form. Litmus paper was used and held above the test tube holding the mixture to measure if the reaction was complete or not. When the paper did not turn red anymore, it indicated the reaction was complete. Because ethanol evaporates at a fast rate, more ethanol was added during the reaction.

Mass of ethoxytriphenylmethane produced

0.4016 g

(g) Melting Point Range ( C ) Percent Yield ( % )

80.1 C – 81.3 C 85.45 %

Results and Discussion: The mass of ethoxytriphenylmethane was calculated to be 0.47 g but 0.4016g was produced so there was a little difference in what was calculated and what was found. The melting point was found to be 80.1 C to 81.3 C roughly and the percent yield was 85.45 % so most of the product was produced. E1 and E2 elimination does not occur in this reaction because it is impossible for bromotriphenylmethane and triphenylmethane, which has a very stable carbocation, to react. The tertiary halide reacts with alcohols to form ethers at ease and forms not by-product alkenes.

Bromotriphenylmethane reacts with ethanol to form ethoxytriphenylmethane by the Sn1 mechanism. First, Bromine breaks its bond with Carbon in bromotriphenylmethane and forms another bond with Hydrogen in ethanol making hydrogen bromide, which then forms a carbocation on what was the bromotriphenylmethane. From what was ethanol now has lone pairs on the Oxygen making it negative and forms a bond with the carbocation, producing the ether. The end product is then ethoxytriphenylmethane and hydrogen bromide. Errors include improper filtration of the product and finding the melting point with not fully dried product, or improper transferring of product from test tube to filter paper for drying. Also, an incorrect reading of the DigiMelt and error in finding the melting point. If this experiment was to be repeated, the best way to avoid error would be to wash out the product with more ethanol to get a better transfer to filter paper or keep a close watch on the DigiMelt for a correct reading. Calculations:

Theoretical yield of ethoxytriphenylmethane ( E ): G of Bromo x (1 mol of Bromo/molar mass of bromo) x (1mol B/1mol E) x (mm of ethoxy / 1 mol of E) = theoretical of E. 0.5 g B x (1 mol B/323.23 g B) x (1mol E/1mol B) x (288.4 g E/1mol E) = 0.47 g Percent yield: (Actual/ Theoretical) x 100 = Percent Yield (0.4016 g/ 0.47 g) x 100 = 84.45% Experimental: Under the hood mix 0.50 g of bromotriphenylmethane with 5.0 mL of absolute ethanol in a test tube. Add a boiling chip and boil the mixture gently with a steam bath until the HBr is not there. Replace any ethanol evaporated and remove the boiling chip and cool mixture to room temperature and in an ice water bath. Then collect the ethoxytriphenylmethane by vacuum filtration and measure its mass and melting point. References: -Reference for Lab Manual: Lehman, J. W. Operational Organic Chemistry; A ProblemSolving Approach to the Laboratory Course, 4th Ed.; Pearson Prentice Hall, 2009; pp 499-500. -Reference for Lab Notebook: Radhi Daya. Organic Laboratory Notebook, [18-19]....