The Pinacol Rearrangement PDF

Preview

Summary

Download The Pinacol Rearrangement PDF

Description

Pablo Manriquez Pre-lab 10 November 20,2020

Pablo Manriquez Pre-lab 10 November 20,2020

The Pinacol Rearrangement: Synthesis of Semicarbazone Derivative The purpose of this lab is to rearrange classical pinacol by converting pinacol to pinacolone via acid catalyzed conditions. The pinacol rearrangement undergoes in four steps followed by the formation of a carbocation. The reaction proceeds with the protonation of an oxygen atom of one of the hydroxyl groups followed by elimination of water molecule which leads to the formation of a stable carbocation. Then, the substituent carbenium ion rearrangement along with the hydroxyl group which promotes a more stable carboxonium ion through 1,2 rearrangement. Lastly, the carboxonium ion is deprotonated and the forms a ketone. The regioselectivity of the reaction is noticed based on migratory aptitude of substituents on vicinal diols(glycols). The product is the distinguished by IR and H NMR spectroscopies, and then converted to its semicarbazone derivative. Semicarbazone derivatization is performed to verify the product of oxidation reaction where ketone or aldehyde are converted into semicarbazone consisting of higlt crustalline solds due to extensive hydrogen bonding. Furthermore, haloform test is performed to provide qualitative analysis of methyl ketone product.

Figure 1 Mechanism for pinacol rearrangement

Figure 2 Semicarbazone conversion

Pablo Manriquez Pre-lab 10 November 20,2020

Equations/Reactions

Starting mass= UIN/10^8 Percent Yield=( actual yield/theoretical yield) x100

Pre-Lab Questions 1)

Pablo Manriquez Pre-lab 10 November 20,2020 Hyperconjugation is a stabilizing reaction between orbitals of the Carbon hydrogen bond and empty p-orbitals of the carbocation. 2)

3)

Pablo Manriquez Pre-lab 10 November 20,2020

Procedure Synthesis of Pinacolone 1) In a 100mL round bottom flask 2 boiling chips, 6 grams of 2,3 dimethyl 2,3 butenediol and 30 mL of 6M sulfuric acid will be placed. 2) The simple distillation apparatus was set up 3) 20-25mL of the pinacolone water acerotrope mixture will be collected and 25mL of the receiving flask will be placed in an ice bath. 4) The distillate will be transferred to the separatory funnel and then the organic layer will separate from the aqueous layer. 5) Aqueous layer will be extracted twice using 10mL of CH2CL2 6) All the organic later will be combined while washing 10% sodium bicarbonate solution 7) The organic layer will be dried using Na2SO4 for 5 minutes 8) The final product will then be weighed Synthesis of semicarbazone

Pablo Manriquez Pre-lab 10 November 20,2020 1) In a test tube with 5 mL of water, the .5g of semicarbazide hydrochloride and .8g of sodium acetate will be mixed. 2) If the unknown is water soluble, .5g will be added. If the uknown is insoluble, the ethanol will be added to the mixture until the product dissolves. 3) The mixture will then be swirled gently for two minutes. 4) The mixture will then be cooled in an ice bath. 5) The precipitate will be collected through vacumm filtration and the product will be washed with cold water....