Objective

In this lab, we will examine the phosphoric acid catalyzed dehydration of 2-methylcyclohexanol. Gas chromatography will be offered to monitor the outcome of the reactivity. From the chromatogram, we will certainly calculate the retention times of the product(s) as well as the relative proportion of product(s).

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Introduction

Under acid-catalysis an alcohol might be dehydrated to develop an alkene. The most common acids employed for the reactivity are sulfuric or phosphoric acids. Mechanistically, the reaction proceeds using initial protonation of the hydroxyl team (a typical acid-base reaction). This converts the hydroxyl unit from a bad leaving group (–OH) right into a much better one (H2O). Loss of water generates a carbocation, which deserve to stabilize itself by elimicountry of a proton from an surrounding carbon to produce the alkene. The elimination of the proton will certainly predominately take place in the direction that results in the production of the even more extremely substituted carbon-carbon double bond.The carbocation has actually other fates relying on substrate, reactivity conditions, and acid employed. The carbocation deserve to undergo replan to a much more stable species (i.e., 1° to a 2°, or 3°) through a transition of a hydride (or CH3–) from an surrounding carbon, complied with by elimicountry.
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If we usage a hydrogen halide as the acid, we produce the substitution product rather than the elimicountry product. The reason is that the conjugate bases of these acids are more nucleophilic than the HSO4– or H2PO4– developed from sulfuric or phosphoric acids. This nucleophilic conjugate base then adds to the carbocation quite than abstracting a proton from the nearby carbon, for this reason substitution occurs.
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Figure 2: Dehydration of 2-methylcyclohexanol: Gas Chromatographic Analysis of the resulting product mixture.


In Gas Chromatography ("GC," or periodically "VPC" for Vapor Phase Chromatography), we inject a liquid solution which is swiftly vaporized and also then passed as a vapor over a solid product which normally has a really high boiling liquid (such as Carbowax) adsorbed on it to act as the "adsorbent." The separation takes place as the vaporized mixture is adsorbed, vaporized, readsorbed, vaporized, etc. as it passes along the column. Due to the fact that different products will certainly be adsorbed and also vaporized at various rates, separation will take place if the column is lengthy sufficient. The miscellaneous components will certainly come off the column at different times ("retention times," or "Rt"). As each component exits the column, it will certainly be detected and registered as a "peak" on the recorder. Helium is frequently supplied as a carrier gas. The gas must be offered at a managed circulation price. Liquid samples are vaporized in a heated chamber. A thermal conductivity cell is typically offered as the detector. A record of the elution of components of the mixture is made by a chart recorder.The column is the instrumental component of a vapor phase chromatograph. For a separation to occur, conditions need to be completed that bring about components of the mixture having actually different retention times on the column.Four experimental components affect the retention time of a offered compound:
A vapor phase chromatogram might be provided in the qualitative and also quantitative analysis of a sample of volatile components.
For a provided collection of problems, retention time is a reproducible residential property of a compound. It is valuable in the identification of a compound. The location under the optimal is regarded the amount of compound that is defined by the optimal. The loved one location of the two peaks of a chromatogram of a binary mixture essentially defines the weight portion ratio in the mixture.
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Figure 3: Gas Chromatography Instrument


Pre-Lab

Answer all assigned muzic-ivan.info inquiries.

Procedure


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Before you begin to erected for the microrange distillation, watch the short video to familiarize yourself with the process.
To a clean, dry 5 mL reactivity vial containing 2 or 3 boiling chips, add 1.0 mL of 2-methylcyclohexanol followed by 2 mL of 85% phosphoric acid (corrosive, wash hands after use).
Attach a Hickman still head (through thermometer—carry out not tighten the peak cap) and also slowly heat the reactivity mixture to boiling (making use of the warm plate and the aluminum heating blocks). The setup is presented below.
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Note the temperature of the still head (measured by positioning the pointer of the thermometer about 1 cm over the liquid level) as you are collecting distillate, and attempt to keep the temperature of the distillation below 95°C. Enough of the product need to collect before the head temperature reaches 90°C. Distill until 0.5-0.7 mL of distillate is gathered.
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Transfer the distillate from the still head to a tiny test tube utilizing a Pasteur pipet.
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Dry the product for about 5 minutes over anhydrous Na2SO4 utilizing just enough drying agent to make a thin layer at the bottom of the little test tube.
You deserve to watch a video that demonstrates exactly how to dry an organic liquid making use of anhydrous sodium sulfate.
Using a Pasteur pipet, carry the dried liquid to a clean test tube for gas chromatographic analysis.
You deserve to watch a video clip that explains how to inject your sample in the GC. Watch it before you continue.
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Your TA can also show you just how to inject your sample in the GC.
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After you acquire your chromatogram, calculate the portion of each product in the mixture by calculating the location of each optimal. Which one carry out you think is the significant product?
Calculate the percent complace of the mixture making use of the equations presented listed below. You can watch a video that will walk you via the procedure.

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In-Lab Questions

Please print the worksheet for this lab. You will need this sheet to record your data.

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