CHEM 231 Lab
CHEM 231 Lab
Laboratory Case Study
Ready to use—just subtract water! Specific practical goals: to carry out the dehydration of an alcohol to an alkene to isolate a product and determine percent yield to utilize infrared (IR) spectrometry to characterize a product
Meet with your group in the beginning of lab to plan experimental conditions. As in Lab 2, each group member should run a reaction, but the group should decide what the conditions should be for every reaction. Please fill out a plan sheet for your experiment. IMPORTANT INFORMATION AND REMINDERS:
One very important category of organic reactions can be described as functional group transformation (e.g., converting an aldehyde to a carboxylic acid, or an amide to an amine). Within this framework, alcohols and alkenes are closely related. Alcohols can be dehydrated to form alkenes in the presence of acid and (generally speaking) heat. For example, 1,2-dihydronaphthalene (2) can be produced in 80% yield by refluxing -tetralol (1) in methylene chloride and catalytic quantities of p-toluenesulfonic acid (pTsOH) for three days (Scheme 1).
both -tetralol and p-toluenesulfonic acid are provided as 1.0 M solutions in CH2Cl2 all reactions should be run on a 1 mmol scale the usual constraints for the microwave reactors apply (VT, temperature, pressure) the reaction should be worked up using aqueous extraction (methylene chloride/deionized water); you may want to review Lab 1 for proper use of the separatory funnel the product is isolated using rotary evaporation; remember to record the isolated yield (and to tare the rotavap flask!) the isolated product is analyzed by HPLC and IR spectroscopy
Scheme 1. Dehydration of -tetralol. Dehydration proceeds through an E1 mechanism, as shown below. Through protonation, a poor leaving group (hydroxide) becomes a good leaving group (water). The subsequent departure of water (ionization) provides an intermediate carbocation, which in turn suffers loss of a proton to give the corresponding alkene. Since there is no net consumption or production of proton, the process is said to be catalytic in proton. In other words, proton is necessary for the reaction to occur, but it is not a stoichiometric reactant or product.
Scheme 1. Mechanism of E1 elimination. Your group’s mission is to adapt the conventional conditions for the dehydration of -tetralol to the microwave reactor, so that reaction time is minimized and yield is maximized.
Safety Information -Tetralol. May be harmful if inhaled. May cause respiratory tract irritation. May be harmful if absorbed through skin. May cause skin irritation. May cause eye irritation. Harmful if swallowed. p-Toluenesulfonic acid. Corrosive. Causes skin irritation. Causes serious eye irritation. May cause respiratory irritation. May be harmful if inhaled. Material is extremely destructive to the tissue of the mucous membranes and upper respiratory tract. May be harmful if absorbed through skin. Causes skin burns. Causes eye burns. May be harmful if swallowed. Dichloromethane. Harmful if swallowed. Causes skin and eye irritation. Suspected of causing cancer. May be harmful if inhaled. Causes respiratory tract irritation. Harmful if absorbed through skin. Causes skin irritation. Causes eye irritation. Harmful if swallowed.
Laboratory Case Study
Ready to use—just subtract water! Specific practical goals: to carry out the dehydration of an alcohol to an alkene to isolate a product and determine percent yield to utilize infrared (IR) spectrometry to characterize a product
Meet with your group in the beginning of lab to plan experimental conditions. As in Lab 2, each group member should run a reaction, but the group should decide what the conditions should be for every reaction. Please fill out a plan sheet for your experiment. IMPORTANT INFORMATION AND REMINDERS:
One very important category of organic reactions can be described as functional group transformation (e.g., converting an aldehyde to a carboxylic acid, or an amide to an amine). Within this framework, alcohols and alkenes are closely related. Alcohols can be dehydrated to form alkenes in the presence of acid and (generally speaking) heat. For example, 1,2-dihydronaphthalene (2) can be produced in 80% yield by refluxing -tetralol (1) in methylene chloride and catalytic quantities of p-toluenesulfonic acid (pTsOH) for three days (Scheme 1).
both -tetralol and p-toluenesulfonic acid are provided as 1.0 M solutions in CH2Cl2 all reactions should be run on a 1 mmol scale the usual constraints for the microwave reactors apply (VT, temperature, pressure) the reaction should be worked up using aqueous extraction (methylene chloride/deionized water); you may want to review Lab 1 for proper use of the separatory funnel the product is isolated using rotary evaporation; remember to record the isolated yield (and to tare the rotavap flask!) the isolated product is analyzed by HPLC and IR spectroscopy
Scheme 1. Dehydration of -tetralol. Dehydration proceeds through an E1 mechanism, as shown below. Through protonation, a poor leaving group (hydroxide) becomes a good leaving group (water). The subsequent departure of water (ionization) provides an intermediate carbocation, which in turn suffers loss of a proton to give the corresponding alkene. Since there is no net consumption or production of proton, the process is said to be catalytic in proton. In other words, proton is necessary for the reaction to occur, but it is not a stoichiometric reactant or product.
Scheme 1. Mechanism of E1 elimination. Your group’s mission is to adapt the conventional conditions for the dehydration of -tetralol to the microwave reactor, so that reaction time is minimized and yield is maximized.
Safety Information -Tetralol. May be harmful if inhaled. May cause respiratory tract irritation. May be harmful if absorbed through skin. May cause skin irritation. May cause eye irritation. Harmful if swallowed. p-Toluenesulfonic acid. Corrosive. Causes skin irritation. Causes serious eye irritation. May cause respiratory irritation. May be harmful if inhaled. Material is extremely destructive to the tissue of the mucous membranes and upper respiratory tract. May be harmful if absorbed through skin. Causes skin burns. Causes eye burns. May be harmful if swallowed. Dichloromethane. Harmful if swallowed. Causes skin and eye irritation. Suspected of causing cancer. May be harmful if inhaled. Causes respiratory tract irritation. Harmful if absorbed through skin. Causes skin irritation. Causes eye irritation. Harmful if swallowed.
