Which spectrum belongs to which compound

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Reference no: EM133852216

Analytical Chemistry

Lab 1: Liquid-liquid extraction

Objective: This practical explores the use of liquid-liquid extraction for the separation of a mixture containing p-toluidine, p-toluic acid and naphthalene. This experiment aims to separate the components of the mixture, verify their identity using melting points, and to determine the yield of separation.

This practical has been assessed for risk and the following hazardous substances have been identified:

Hydrochloric acid
Sodium hydroxide
p-toluidine
p-toluic acid
Naphthalene
dichloromethane

These substances pose the following risks:

Corrosive
Harmful by inhalation.
Harmful if swallowed.
Irritating to eyes respiratory system and skin.
Harmful to aquatic organisms.

The following precautions should be taken:

Dispose of solvent waste in the appropriate organic waste container
Work in well-ventilated place
Work away from sources of ignition
Wear gloves, safety glasses

Pre-lab exercises (must be completed before coming to the lab)
Find the melting point of p-toluidine, p-toluic acid and Naphthalene

Draw the structure of each compound. This will help you predict the way the compounds partition between the various layers.

Record the density of dichloromethane. If water and dichloromethane are added to a separating funnel, which will be the bottom layer?

Procedure
THIS EXPERIMENT SHOULD BE UNDERTAKEN INDIVIDUALLY

Dissolve sample
Weigh approximately 3 g of the three-component mixture (a mixed sample containing
p-toluic acid, p-toluidine and naphthalene) Into a 100 mL beaker
record the mass to at least two decimal places.
Dissolve the mixture in approximately 30 mL dichloromethane.
Extraction:

Extract the organic acid
Pour the solution into a 250 mL separating funnel and rinse the beaker with a further 5 mL (approx.) dichloromethane.
Extract the organic acid from the mixture by shaking with approx. 20 mL of dilute (3M, bench reagent) aqueous sodium hydroxide. Be sure you know whether the organic layer will be in the upper or lower layer.
Separate and retain both layers.
Label aqueous extract ‘hydroxide extract'.
Return the organic layer to the separating funnel.
Repeat the extraction two more times (steps 2 - 3) to ensure complete extraction.
Combine the three aqueous extracts and retain. Which compound(s) would you predict to be in the aqueous layer? What structural form would they be in?

Extract the organic base
Return the organic layer to the separating funnel and repeat the extraction three times (steps 3-9) this time using dilute (3M, bench reagent) hydrochloric acid. This will extract the organic base.
Combine the three aqueous extracts and label ‘HCl extract'. Which compound(s) would you predict to be in the HCl extract? What structural form would they be in?
Collect the organic layer into a clean, dry 100 mL conical flask and label ‘organic extract'.

Recover solid material:
Recover neutral organic compound
Add approximately 1g (no need to weigh) anhydrous MgSO4 to the ‘organic extract' and swirl carefully. Before moving to the next step - check with a demonstrator to see if you have added sufficient MgSO4. What do you think the purpose of this step is?
Filter the ‘organic extract' by gravity into a pre-weighed 100 mL round bottom flask.

Remove the dichloromethane in vacuo using a rotary evaporator (Get your demonstrator to show you how). When all the dichloromethane has evaporated weigh the flask and determine the % yield.
Determine the melting point and IR spectrum of your neutral product and compare with literature values.

Recover Organic Acid
Cool the NaOH extract in ice and slowly add conc. HCl (with stirring) until it is strongly acidic (use pH paper). A precipitate should form.
Return the slurry to the separating funnel and extract the acid with 3x30 mL portions of dichloromethane. Note - you may need a little more than 30 mL of dichloromethane to get the solid to re-dissolve. Get expert online assignment help in the USA now!
Combine the dichloromethane extracts, and dry using anhydrous MgSO4. (Again check with a demonstrator to confirm that you have added enough MgSO4).
Filter the extract by gravity into a pre-weighed evaporating dish.
Place it on a steam bath in the fume hood to evaporate the dichloromethane.
When all the solvent has evaporated weigh the evaporating dish and determine the % yield.
Determine the melting point and IR spectrum of your acid product and compare with literature values.

Recover the Organic Base
Cool the HCl extract in ice and add NaOH pellets slowly (one at a time) until it is strongly alkaline. Again a precipitate may form.
Return the mixture to the separating funnel and extract the amine with 3 x 30 mL portions of dichloromethane.
Combine the dichloromethane extracts, add approximately 1g MgSO4 and filter by gravity into a pre-weighed 100 mL round bottom flask. (Again check with a demonstrator to confirm that you have added enough MgSO4).
Remove the solvent in vacuo using a rotary evaporator. When all the solvent has evaporated weigh the flask and determine the yield of product.
Determine the melting point and IR spectrum of your base product and compare with literature values.

Your Report:
Your report should discuss
the acid base chemistry involved in the separation and recovery (e.g., Which compound(s) would you predict to be in the HCl and NaOH aqueous extracts? What structural form would they be in?

the yields (and % yield) of your recovered products
the relative composition of the original sample?
the melting points and IR spectra of your products
comment on purity of the recovered materials
Answers to NMR question (see below)
Note The yield of each component can be calculated as a percentage of the total starting mass.
For example, if 0.99 g is obtained from 3.00 g = 0.99/3.00 x 100 = 33% yield

Question for report

The 1H NMR spectra of the three compounds are provided below

1. Which spectrum belongs to which compound? justify your answer by analysing the spectra below, assigning each signal to the relevant proton on the correct structure.

Reference no: EM133852216

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