ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣...

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Unsaturated Hydrocarbons Olefins Structure Addition Reactions Mechanisms Experiment: part A - Setup part B - Reaction part C - Isolation part D - Analysis Next Week 1 ExA1

Transcript of ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣...

Page 1: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Unsaturated Hydrocarbons

‣ Olefins ‣ Structure

‣ Addition Reactions

‣ Mechanisms

‣ Experiment: ‣ part A - Setup

‣ part B - Reaction

‣ part C - Isolation

‣ part D - Analysis

‣ Next Week

1

ExA1

Page 2: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Alkenes & Alkynes

‣ Hydrocarbons are molecules composed of only hydrogen and carbon.

‣ Carbons form four bonds.

‣ Alkanes are hydrocarbons that have only carbon-carbon single bonds.

‣ Alkenes are hydrocarbons that have one or more carbon-carbon double bonds. ‣ Carbons that form double bonds are said to have a sp2 shape.

‣ The bonds connected to a sp2 carbon have a 120˚ angle between them.

‣ Alkynes are hydrocarbons that have one or more carbon-carbon triple bonds. ‣ Carbons that form triple bonds are said to have a sp shape.

‣ The bonds connected to a sp carbon form a single line, they have a 180˚angle around the carbon.

‣ Alkenes and alkynes have unique properties.

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Page 3: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Alkenes in Biochemistry

Ethene, the simplest alkene is a plant hormone, it causes fruit to ripen.

Plastic bags from the supermarket are made of poly-ethylene (many ethenes stuck together).

The longer you leave fruit in those bags, the faster that hormone will cause them to ripen.

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Alkene structures are important in many biological structures, like the pheromone of silkworm moths.

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Alkynes in Industry

‣ Burning alkynes produces less heat than alkanes. ‣ But they also produce less gases.

‣ The gases produced in burning alkynes have more heat per mole of product

‣ Those gases have a higher temperature.

‣ Alkynes burn hotter.

‣ If you want to put heat into your house, burn an alkane.

‣ If you want to create gases to push pistons in your car, burn an alkane.

‣ But if you want concentrated heat to cut metal, burn an alkyne. ‣ Like ethyne (also called acetylene).

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Saturated & Unsaturated

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CnH(2n+2)

C2H6

CnH(2n)

C2H4

CnH(2n-2)

C2H2

Sunflower oil is a mixture of monounsaturated and

polyunsaturated hydrocarbon oils. The

world's largest sunflower oil producers are Ukraine, Russia and Argentina.

‣ We describe hydrocarbons are either saturated or unsaturated.

‣ Saturated hydrocarbons are hydrocarbons with only single carbon-carbon bonds. ‣ This means they have the most hydrogens their carbon skeletons can possibly have.

‣ Alkanes are saturated hydrocarbons.

‣ Unsaturated hydrocarbons have double and triple carbon-carbon bonds.

‣ Unsaturated hydrocarbons are not saturated with hydrogen, their carbon skeletons could hold more hydrogen.

‣ Alkenes & Alkynes are unsaturated hydrocarbons.

‣ Hydrocarbons can be monounsaturated (one unsaturation) or polyunsaturated (more than one unsaturation).

‣ Each unsaturation in a compound reduces the number of hydrogen atoms in the molecular formula by 2.

Page 6: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

‣ The concept of stereo isomers can quickly take us beyond the scope of this class.

‣ We will confine our discussions of geometric isomers to cis trans relationships within the backbone of the hydrocarbon.

‣ There is more than one way to indicate the stereochemistry of a double bond.

‣ We will use only the cis-trans naming convention.

‣ Cis isomers are isomers where the two hydrogens on a double bond are on the same side.

‣ Prefix the full name of the substances with “cis”.

‣ Trans isomers are isomers where the two hydrogens on a double bond are on opposite sides.

‣ Prefix the full name of the substances with “trans”.

Cis-Trans Isomers

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cis-2-Penteneor cis-Pent-2-ene

trans-2-Penteneor trans-Pent-2-ene

Page 7: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Unsaturated Hydrocarbons

‣ Olefins ‣ Structure

‣ Addition Reactions

‣ Mechanisms

‣ Experiment: ‣ part A - Setup

‣ part B - Reaction

‣ part C - Isolation

‣ part D - Analysis

‣ Next Week

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ExA1

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Types of Reactions

‣ Organic chemists describe and group chemical reactions into different classes to organize their palette or collection of tools.

‣ Some reaction types you’re already familiar with are:

‣ Combustion Reactions

‣ Double Displacement Reactions

‣ Reduction-Oxidation Reactions

‣ Neutralization Reactions

‣ The pi-bonds in unsaturated hydrocarbonsare weak and easy to break. Many chemicalreactions take advantage of this to addnew atoms to carbon chains at those points.

‣ Addition Reactions are a type of reaction that describe any reaction which adds new atoms to the carbonchain.

‣ We’ll introduce you to a handful of very common addition reactions.

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+ Br2

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Bromination

‣ Bromination is the addition of bromine to a carbon skeleton.

‣ These reactions occur easily when bromine is mixed with an alkene.

‣ Bromination is an addition reaction.

‣ Bromination can be used to test hydrocarbons for unsaturations.

‣ Bromine does not react with an alkane because the alkane contains only single C-C bonds which cannot add the bromine. Alkanes merely dilute the red-brown bromine color to an orange or yellow color in the absence of a strong catalyst.

‣ Due to their C=C double bonds which can be broken, alkenes react readily with bromine to produce saturated dibromoalkanes. When an alkene is reacted with bromine, the red-brown color of the bromine is immediately lost due to the reaction of the bromine.

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Br2 + Alkane Br2 + Alkene

+ Br2

+ Br2 N/R

+ Br2 ?

red liquid

colorless oil

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Hydrogenation

‣ Hydrogenation is the addition of hydrogen to a carbon skeleton.

‣ The reaction between hydrogen and alkenes is less favorable than with bromine. But occurs with a catalyst like Pd, Ni or Pt.

‣ Hydrogenation is an addition reaction.

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+ H2

+ H2 N/R

+ H2

+ H2 N/R

Ni

needs a catalyst

already saturated with hydrogen

harder, but possible with Ni

Ni

Pd, Ni or Pt

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Hydration

‣ Hydration is the addition of the atoms of water to a carbon skeleton.

‣ Acid is used as a catalyst to drive this reaction.

‣ Hydration is an addition reaction.

+ H2O

+ H2O N/R needs a catalyst

H+ molecules with an OHgroup of atoms attached

to them are alcohols

we’ll be learning more aboutalcohols and other functional

groups in chapter 12

H2O

H+ the OH groupadds selectively to the more substituted side

of the alkene bond(when there is a

difference)

X

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Oxidation with KMnO4

‣ The per oxy-ion of manganese in water, permanganate ion, adds two OH groups to alkene carbons.

‣ Acid is used as a catalyst to drive this reaction.

‣ This is an addition reaction.

‣ Permanganate can be used to test hydrocarbons for unsaturations.

‣ The permanganate ion is dark purple in solution. If it’s consumed by an alkene, it produces a colorless ion.

‣ The disappearance of permanganate color indicates the presence of an unsaturated hydrocarbon.

+ MnO41-

H2O+ MnO22-

OH1-

dark purple clear

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Reactions of Alkenes

‣ Predict the products or indicate the reactants required for the following reactions.

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+ Br2

+ H2Pd, Ni or Pt

+ H2OH+

KMnO4

Page 14: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Unsaturated Hydrocarbons

‣ Olefins ‣ Structure

‣ Addition Reactions

‣ Mechanisms

‣ Experiment: ‣ part A - Setup

‣ part B - Reaction

‣ part C - Isolation

‣ part D - Analysis

‣ Next Week

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ExA1

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Hydrogenation

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Hydrogenation

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(plus enantiomer)

Page 17: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Hydration

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Diol Addition

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Halogenation

‣ How does the bromine add to the double bond?

‣ Do both bromine atoms attach at the same time?

‣ Do they attach in separate steps?

‣ Or is there more to the story?

‣ Let’s do an experiment to answer these questions.

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+ Br2

Page 20: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Unsaturated Hydrocarbons

‣ Olefins ‣ Structure

‣ Addition Reactions

‣ Mechanisms

‣ Experiment: ‣ part A - Setup

‣ part B - Reaction

‣ part C - Isolation

‣ part D - Analysis

‣ Next Week

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ExA1

Page 21: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Bromination

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?trans-cinnamic acid

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Page 22: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Experiment

‣ Setup ‣ Pre-weigh 5.0 mL R.B. flask

‣ Add:

‣ 0.20 g trans-cinnamic acid

‣ 1.4 mL CH2Cl2

‣ 0.70 mL 10% Br2

‣ Stir Bar

‣ Attach air condenser

‣ Lower into sand bath

‣ Heat 45-50˚C (gentle boil)

‣ Reflux for 25 minutes

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‣ Maintain ‣ If reflux is not visible

‣ reduce heat

‣ cool if needed ‣ Don’t Loose all Solvent

‣ If color fades,

‣ Add Br2 solution drop wise to return color

‣ After 25 minutes, cool to room temperature

Page 23: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Experiment

‣ Isolation ‣ Place cool reaction flask in ice bath

‣ solid should appear

‣ If no product appears after 5 min, add 1 mL of dH2O, cool another 5 min

‣ Collect solid by Hirsch funnel vacuum filtration

‣ Wash crystals with 1 mL ice cold CH2Cl2, three times

‣ Purification ‣ Place crystals in 10 mL Erlenmeyer flask

‣ Add 0.8 mL hot ethanol

‣ Use hot place to make dissolve

‣ If needed, add 0.1 mL increments of EtOH until dissolved

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Analysis & Report

‣ Determine yield and melting point for the product recovered.

‣ In your report: ‣ Conclude what product was formed.

‣ Conclude which isomer was formed ‣ 2S 3S and enantiomer or

‣ 2R 3S and enantiomer

‣ Propose a mechanism based on the isomer you identified (it’s OK to research mechanisms, show intermediate).

‣ Predict the product of KMnO4 and trans-cinnamic acid.

‣ Explain the differences between these two reactions.

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Page 25: ExA1 - Chemchem.ws/dl-1012/a1-bromination.pdf ·  · 2016-09-29ExA1. Alkenes & Alkynes ... ‣ Bromination is the addition of bromine to a carbon skeleton. ... trans-cinnamic acid.

Unsaturated Hydrocarbons

‣ Olefins ‣ Structure

‣ Addition Reactions

‣ Mechanisms

‣ Experiment: ‣ part A - Setup

‣ part B - Reaction

‣ part C - Isolation

‣ part D - Analysis

‣ Next Week

25

ExA1

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Next Meeting

‣ For next Meeting: ‣ Bring to class:

‣ Notebook ‣ You will not be turning in notebooks, but this

permanent record of your preparations, observations and notes will be essential to success in this class.

‣ Textbook, calculator, pencils (yes, you can use pen)

‣ Safety Glasses (you cannot participate without them)

‣ Read through and take notes on: ‣ Experiment 17 (p296)

‣ Hydrogenation and Olefin addition reactions lecture textbook.

‣ Produce and bring to class:

‣ Your pre-lab for exp 17 (p296) ‣ Scheme and measured quantities required.

‣ Substances used & their properties.

‣ Procedure summary.

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Questions?