Two Step Synthesis for Preparing Epoxycyclohexane Lab Report

Two Step Synthesis for Preparing Epoxycyclohexane Lab ReportUCF Fall ‘19 Lab Coordinator: Alaa Hashim, Ph.D. CHM2211L. Senior Lab Technician: Joshua Bass

 

Experiment 10 A Two-step Synthesis for Preparing Epoxycyclohexane

Purpose Preparing epxoycyclohexene by reacting cyclohexene with N-bromosuccinimide in aqueous solution to form trans-2-bromocyclohexanol which can be reacted with a base to from the epoxide.

 

 

 

 

 

Scheme 1: Formation of epxoycyclohexene starting with cyclohexene.

 

 

 

 

Reactions Alkene addition reactions and intramolecular nucleophilic substitution reactions.

 

Techniques Reflux with dropwise addition, liquid-liquid extraction, and IR spectroscopy.

 

Introduction The epoxycyclohexane (cyclohexene oxide) will be prepared via a two-step synthesis, Scheme 1. In the first step, cyclohexne will be treated with N-bromosuccinamide (NBS) in an aqueous solution to form trans-2-bromocyclohexanol, which will be isolated and stored. In the following step, trans-2-bromocyclohexanol will be treated with a base to form epxoycyclohexene.

The trans-2-bromocyclohexanol is formed by reacting cyclohexene with NBS in aqueous solution. NBS reacts with an alkene to form a bromohydrins. Its mechanism involves the formation of a bromonium ion bridged intermediate, where the pi bond acts as a nucleophile attacking the bromine atom within NBS. The reaction is carried out in aqueous solution, where water acts as a nucleophile attacking the more substituted carbon of the bromonium ion bridged intermediate, which allows for ring opening. It is followed by deprotonation of the oxygen atom, to form the trans-2-bromocyclohexanol.

The starting material for the next step, trans-2-bromocyclohexanol, satisfies the stereospecificity for forming an epoxide, where the alcohol and bromine are antiperiplanar. Treating it with a base deprotonates the alcohol group to form an alkoxide ion, a strong nucleophile. The alkoxide ion attacks the carbon atom directly attached to bromine, via an intramolecular SN2 mechanism, to form the epoxide. Epoxides have wide versatility in organic synthesis, as compared to ethers, due to the ring strain associated with its three membered rings.

Chemicals Week 1 Week 2

Starting Material: Cyclohexene Starting Material: trans-2-bromocyclohexanol

Solvent: Water, diether ether, acetone Solvent: Diethyl ether

Reagent: NBS Reagent: 10% sodium hydroxide

Drying agent: anhydrous sodium sulfate Drying agent: anhydrous sodium sulfate

Procedure Waste Disposal

Part A (Week 1): Synthesis of trans-2-bromocyclohexne

  1. In the fume hood, set up an iron ring and 125 mL separatory funnel for a liquidliquid extraction.

 

  1. In a 125 mL Erlenmeyer Flask, combine 12 mL of acetone, 10 mL of DI water, 3.8 mL of cyclohexene and a stir bar.

 

  1. To this solution, add approximately 7.4 g of N-bromosuccinimide (NBS). Continue stirring the solution for approximately 15 minutes until the yellow color subsides.
    • The NBS should be added in one portion, all at once with stirring.

 

  1. In a 125 mL separatory funnel, combine 20 mL of diethyl ether and 20 mL of saturated sodium chloride.

 

  1. Transfer the reaction mixture to the separatory funnel, and while holding the stopper firmly in place, invert the funnel and vent using the stopcock every few seconds. Continue the invert and vent process for about one minute.
    • Remember to double check that the separatory funnel stopcock is in the off position.

 

  1. Return the separatory funnel to the iron ring, remove the stopper and allow the layers to separate. Once separated, drain the bottom aqueous layer into a 250 mL Erlenmeyer flask.

 

  1. Dispense another 20 mL of saturated sodium chloride solution and carefully add this solution to the separatory funnel containing the organic layer. Continue the invert and vent procedure for about one minute.

 

  1. Return the separatory funnel to the iron ring, remove the stopper and allow the layers to separate. Once separated, drain the bottom aqueous layer into the 250 mL Erlenmeyer flask used previously.

 

  1. Drain the remaining organic layer into a 50 mL Erlenmeyer flask and dry using anhydrous sodium sulfate.
    • Drying agent should be added in dime sized portions until the drying agent is free flowing.

 

  1. Decant the dried organic layer into a 100 mL round bottom flask taking care to not transfer any drying agent.

 

  1. Remove the diethyl ether using the rotary evaporator.

 

  1. Obtain an IR of the starting material and product.

 

  1. Transfer the product to a glass vial making sure to label the vial with the product name (trans-2-bromocyclohexanol), lab day/time and group initials.

 

 

Place all generated waste in the “acid waste”.

 

 

 

Part B (Week 2): Synthesis of Cyclohexane Oxide

 

  1. In the fume hood, set up a reflux with dropwise addition apparatus as seen in (add figure and number) as well as an iron ring for a liquid-liquid extraction.
    • Apply a small amount of grease to each ground glass joint.
    • Use the clear condenser tubing, not the red vacuum tubing.
    • Use a 400 mL beaker for the hot water bath
    • Set up the glassware at sufficient height as to allow for the hotplate and hot water bath to be lowered in an emergency.
    • Water should flow in from the bottom of the condenser and out of the top.
    • Water leaving the condenser should flow into the drain underneath the green faucet. Do not attach the water line to any other valves.
    • Make sure the water has filled and is flowing through the condenser before heating is started.
    • The flow rate of the water through the condenser should be minimal. Too high of a flow rate will cause the water lines to detach and flood the fume hood.

 

 

 

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Sep

aratory

 

Funnel

 

Reflux

Condenser

 

Claisen

Adaptor

 

100

mL

RBF

 

Water

Bath

 

Figure 1: Reflux with Dropwise Addition Setup

 

 

  1. In a 100 mL round bottom flask, add 25 mL of 10% sodium hydroxide along with a stir bar. Attach the round bottom to the apparatus, begin stirring the solution vigorously and bring the water bath temperature to approximately 50 °C.

 

  1. In a 25 mL Erlenmeyer flask, weigh out approximately 3 grams of the transbromocyclohexanol prepared last week and dissolve in 25 mL of diethyl ether.

• If more trans-bromocyclohexanol is needed, see the stockroom window.

 

  1. Transfer the diethylether/bromocyclohexanol solution into the 125 mL separatory funnel attached to the apparatus that was previously set up.

 

  1. Begin adding the bromocyclohexanol dissolved in ether dropwise over a period of 20 minutes. Once all of the bromocyclohexanol has been added, close the stopcock and continue vigorously stirring the reaction for approximately 20 minutes maintaining the water bath at approximately 50 °C.

 

  1. Once the reaction is complete, dismount the round bottom and cool in an ice bath for a few minutes. While waiting, remove the separatory funnel from the apparatus and place in the iron ring previously set up.

 

  1. Transfer the reaction mixture to the separatory funnel, allow the layers to separate and drain off the lower aqueous layer into a 250 mL Erlenmeyer flask.

 

  1. Dispense approximately 20 mL of 1% sodium hydroxide and add this to the separatory funnel. While holding the stopper firmly in place, invert the funnel and vent using the stopcock every few seconds. Continue the invert and vent process for about one minute.

 

  1. Return the separatory funnel to the iron ring and allow the layers to separate. Once separated, drain the bottom aqueous layer into a 250 mL Erlenmeyer flask.

 

  1. Repeat this washing procedure two times each time draining off the lower aqueous layer into the 250 mL Erlenmeyer flask.
  2. Dispense approximately 20 mL of saturated sodium chloride solution and add this to the separatory funnel containing the organic layer. Continue the invert and vent procedure for about one minute.

 

  1. Return the separatory funnel to the iron ring and allow the layers to separate. Once separated, drain the bottom aqueous layer into a 250 mL Erlenmeyer flask.

 

  1. Drain the remaining organic layer into a 50 mL Erlenmeyer flask and dry using anhydrous sodium sulfate.

a. Drying agent should be added in dime sized portions until the drying agent is free flowing.

 

  1. Decant the dried organic layer into a 50 mL round bottom flask taking care to not transfer any drying agent.

 

  1. Remove the diethyl ether using the rotary evaporator.
  2. Obtain an IR of the starting material and product.

 

Waste Disposal Refer to the white board for proper waste disposal.

Lab Notebook Considerations prior to experiment:

The purpose of the experiment and its expected outcome.

Detailed reaction mechanism.

Include a table that lists each chemical, its FW and safety hazard(s) from its SDS A step-wise detailed procedure, or as a flow chart.

Turn in the carbon-copy to your GTA at the start of the lab period.

 

Considerations during the experiment:

Data (e.g. volume, mass, amd mmol used, mass recovered) and observations (e.g.

color changes).

IR spectrum of starting material and product.

Calculation of the theoretical yield based on the mass used in the lab. Turn in the carbon-copy to your GTA at the end of the lab period.

 

Lab Report Considerations for the results and discussion section:

Analyze/discuss the results obtained.

Theoretical yeild versus experiemntal yeild.

A Figure for the IR spectrum obtained.

Compare the IR spectrum of the starting material and product and discuss which characteristic peaks are present.

Discuss possible errors associated with the experiment, use the yield and IR spectrum as a reference point.

 

 

Learning Outcomes Reinforce addition reactions and intramolecular nucleophilic substitution reactions. Learn how to use and set-up a reflux that allows a drop wise addition of a given reagent, synthesize and isolate a reaction intermediate to be used the following experiment, and characterize the product by IR.

 

References Cranwell P. B.; Harwood L. M.; Moody C. J. Experimental Organic Chemistry, 3rd ed.; Wiley: 2017.

 

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