chem 212 - sn2

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Prelab Lecture

SN2 (Group Exp#2)

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BACKGROUND READING:Solomons and Fryle Chapter 6 (Sub/Elim Rxns)

Techniques Weights/Measures, Reflux, Liquidliquid Extraction, Distillation

CHEM 212 PRELAB CYCLE 1 SN2

Laura Pavelka

[email protected]

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SN2 Reactions

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SN2 Reaction bimolecular nucleophilic substitution reaction (in RDS)

- no carbocation formation, concerted mechanism,

inversion of stereochemistry

PURPOSE: perform a substitution reaction via an SN2 mechanism

1 > 2 >>>> 3

TRANSITION STATE


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SN2 Experiment

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Synthesis of 1butyl3methylimidazolium bromide (2steps):

IONIC LIQUID


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Ionic Liquids

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IONIC LIQUID: salts that melt below 100 C (commonly liquids at RT)

* low vapour pressure, low combustibility, high thermal stability *CHEM 212 PRELAB CYCLE 1 SN2

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Overview SN2 Lab

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PURPOSE: perform a substitution reaction between 1methylimidazole and

1bromobutanevia an SN2 mechanism to prepare an ionic liquid


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1. Preparation of [C4mim]Br

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10 mL RBF

0.2 mL water0.2 mL 1-methylimidazole

0.27 mL bromobutane

attach condenser

water out

water in

reflux 1 h(sand bath)

cool to room temp

[C4-mim]Br


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2. Preparation of [C4mim]PF6

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NN +15 min

H2O NN

PF6

[C4-mim]PF6

KPF6 + KBr

Br


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3a. Extraction

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NN

PF6

[C4-mim]PF6


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3b. Washing the Aqueous layer

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NN

PF6

[C4-mim]PF6


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4. Drying Organic Layer

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DRIEDDCM + ionic liquid

filter through MgSO4plugrinse vial 1 mL DCM

MgSO4pipetplug

org layer4 mL vial (#2)

pre-weighed

10 mL RBF

NN

PF6

[C4-mim]PF6


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5. Distillation/Isolation

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NN

PF6

[C4-mim]PF6


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% Yield

CRUDE Theoretical

MASS 1.5 g 3.0 g

% YIELD (crude) = mass crude x 100% = 1.5 g x 100% = 50 %

theoretical 3.0 g

TOTALLY FICTICIOUS VALUES


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Safety & Waste Disposal

CHEM 212 PRELAB CYCLE 1 SN2 13

Special Safety Considerations:

1methylimidazole VERY hazardous in case of skin/eye contact (wear gloves),

hazardous in case of inhalation/ ingestion.

Bromobutane Hazardous in case of skin/eye contact, inhalation/ ingestion. Flammable.

KPF6 Hazardous in case of skin/eye contact, VERY hazardous in case of inhalation/

ingestion.

Avoid exposure to fine KPF6 dust.

Dichloromethane Hazardous in case of skin/eye contact, inhalation/ ingestion. Toxic.

Waste Disposal:

Aqueous layer, Extraction: Wash down the sink with lots of waterDCM distillate: Halogenated organic waste

Isolated Ionic Liquid: Collected in labeled bottle

Pipettes: Glass waste

chem 212 - sn2

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