Lab Exam Preparation

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Published on 16 May 2011
School
UTSC
Department
Chemistry
Course
CHMB42H3
Professor
Dehydration of Cyclohexanol
Purpose:
oAcid catalyzed dehydration of cyclohexanol to form cyclohexene using a distillation
apparatus
oPurify through microextraction and microfiltration
Theory:
oDehydration = -H2O and form double bond (E1 mechanism)
oAcid catalyst otherwise (-OH) not good LG
oDistillation:
Separate according to bp
Cyclohexene (83 C) and Cyclohexanol (161 C)
Thus, cyclohexene extracted but as an azeotrope
oMicroscale- Extraction
Need to separate azeotrope (Cyclohexanol + H2O + Cyclohexene)
Based on different solubilities
Use saturated salt solution NaClwhy?
Cyclohexanol more soluble in polar salt solution
Cyclohexene non-polar thus not soluble in salt solution
oMicrofiltration
Remaining water removed by adding anhydrous Na2SO3 and doing
microfiltration to removing (sodium sulphate + H2O)
o2nd distillation
Why?
React any remaining cyclohexanol
Xylene chaser added – why?
Chaser = solvent added to increase volume but doesnt react with product
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Xylene (bp = 140 C)—thus appropriate
Purified using microextraction and microfiltration
Procedure:
oFirst distillation
Simple distillation apparatus
Cyclohexanol + Phosphoric acid and distil
Watch for a bead of condensate on thermometer
Not too rapid – decreases yield
oMicroscale-Extraction + Microfiltration
Boiling tube (aka test tube)
Transfer distillate into boiling tube and add 2X 5ml of saturated NaCl
Use pipette to mix
Drain aqueous layer bottom layer
Thus, leave the non-polar cyclohexene
Add anyhydrous Sodium Sulphate
Microfiltration apparatus
Glass wool in Pasteur pipette
Pour solution through glass wool using another pipette into a RB Flask
Rinse with xylene
oSecond distillation
Add xylene to previous residue of distillation and distil and purify using
microextraction and microfiltration
Mix products
Synthesis of DEET
Purpose:
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oSynthesize N,N-diethyl-m-toluamide (DEET) using reflux and extraction techniques
Theory:
oTwo steps
M-toluic acid + SOCl2 m-toluoyl chloride + SO2 + HCl
Use SOCl2 in ether chlorination
SOCl2 why?
oProduce high yields and few purification problem
oSO2 and HCl bubble out of reaction thus shift to the products
side
M-toluoyl + 2 Et2NH DEET + HCl
Why 2 moles of Et2NH?
o1 mole for reaction
o1 mole for HCl neutralization
Washes
Aqueous
oChange remaining m-toluoyl chloride back into m-toluic acid
Basic (10% NaOH)
oM-toluic acid to its water soluble carboxylate salt
oThus, remove unreactive carboxylic acid
Acidic (HCl)
oProtonates diethyl amine (basic N) thus, removing it.
oWhy does it not affect DEET?
It contains non-basic nitrogen
Evaporate excess ether leaving oily product
Soap and Detergents
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Document Summary

Purpose: acid catalyzed dehydration of cyclohexanol to form cyclohexene using a distillation apparatus, purify through microextraction and microfiltration, theory, dehydration = -h2o and form double bond (e1 mechanism, acid catalyst  otherwise (-oh) not good lg, distillation:  cyclohexene (83 c) and cyclohexanol (161 c)  thus, cyclohexene extracted but as an azeotrope: microscale- extraction.  need to separate azeotrope (cyclohexanol + h2o + cyclohexene)  use saturated salt solution nacl why: cyclohexanol  more soluble in polar salt solution, cyclohexene  non-polar thus not soluble in salt solution, microfiltration.  remaining water removed by adding anhydrous na2so3 and doing microfiltration to removing (sodium sulphate + h2o: 2nd distillation.  xylene chaser added why: chaser = solvent added to increase volume but doesn"t react with product www. notesolution. com, xylene (bp = 140 c) thus appropriate.  watch for a bead of condensate on thermometer.  not too rapid decreases yield: microscale-extraction + microfiltration.