Experiment 4 - Preparation and Distillation of Cyclohexene

How do you remove dicylcohexyl ether?

complete a second distillation of the product and the BP is 242.5C

loss of water from a molecule is called a

dehydration

The E2 Dehydration of Primary Alcohols

dehydration of a secondary or teriary alcohol is an E1 reaction and the dehydration of a primary alcohol is a E2 reaction, because carbocations are too unstable to form

What is a probable side product of the dehyrdation of cyclohexanol?

dicyclohexyl eter, which is immiscible with water and is likely to co-distill and may be present in the first distillate

_________ _______ is a probable side product of dehydration of cyclohexanol

dicyclohexyl ether

mixtures of liquiuds whose boiling points are similar (separated by less than 70 degrees C) require _______ distillation instead

fractional

How does LeChatiler's Principle factor into equilibrim reactions?

if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change

Treatment of sodium carbonate does what?

removes any traces of acid

Washing with water?

removes some of the impurities

Cyclohexanol is a ______ alcohol

secondary

The prevent the alkene formed in the dehyrdation reaction from adding water and reforming the alcohol...

the alkene is removed by distillation as it is formed because it has a lower boiling point than the alcohol -removing a product displaces the reaction to the right according to Le Chatelier's Principle

What is the reagent also the catalyst

the reagent used is phosphoric acid instead of sulfuric acid because sulfuric acid is highly corrosive and cause cause extensive charring of organic compounds, phosphoric acid is still corrosive but less likely to destroy your sample, lead to higher product yield

______________ carbocations are more stable and then are more easily formed than _________ or __________ carbocations

Tertiary, secondary, and primary

Predict the dehydration products for the following alcohols and show all the anticipated products

** SEE the postlab for answers

What techniques are used in this lab?

-liquid to liquid extraction -drying agents -simple and fractional distillation -boiling point determinatin -infrared spectrocopy (IR)

Changing an E1 dehydration into an E2 dehydration

-relatively harsh conditions are required for alcohol dehydration and the structural changes resulting from carbocation rearrangements in the E1 reaction may result in low yields of the desired alkene -dehydration can be carried out under milder conditions that favor E2 reactions by placing the OH group with a good leaving group

the E1 dehydration of tertiary and secondary alcohol mechanisms

-the acid protonates the most basic atom in the reactant, as we saw earlier, protonation converts the very poor leaving group (OH) into a good leaving group (H20) -water departs leaving a carbocation -a base in the reaction mixture removes a proton from the B carbon , forming an alkene an d regenerating the acid catalyst. Notice that the dehydration reaction is an E1 reaction of a protonated alcohol

The carbocation can react in three different ways

-with water to yield cyclohexanol - the starting material (all steps in this reaction are reversible) -by losing a proton to yield cyclohexene -with cyclohexanol to yield dicyclohexyl ether

What is the stereochemistry of the dehyration reaction?

Both E and Z stereoisomers are obtained as products and the major product is the stereoisomer in which that larger group on each of the sp2 carbons are on opposite sides of the double bond

how is this experiment greener?

It has a solvent-free synthesis and safer reagents, and uses no organic solvents and produces water which is harmless as a byprodcut

What role does phosphoric acid play in this reaction?Use both words and chemical equations to answer the question.

Phosphoric acid is used to speed up the reaction and it acts as a catalyst. The reaction would occur without the catalyst, but it speeds up the normal reaction. It forms the product quicker and finished the reaction, it helps act as a source to protonate the hydroxyl group. *** see the postlab for the eution

Many reactions depend on LeChatlier's Principle to produce significant yields. How does distillation of the reaction mixture help to increase the yield for this lab?

The distillation of the reaction mixture is going to heat the liquid to boiling, condnsing, and then collecting the now vapors. This altered temperature is going to prompt a disturbance in the equilivrium. As we know LeChatlier's Principle states that any change in concentration, temperature, or pressure will lead to a new equilibrium

You start out the distillation with one layer in the flask. During the distillation you have two layers and you finish at the end with one again. Explain what is happening on the basis of polarity and solubility.

This solution starts out initially polar which is evident due to the solubility and the solution is not separated beause like dissolves like. after water is removed the solution turns into a carbocation and develops two layers based on the new solubility. Lastly, the cyclohexene is going to be boiled off and we have one layer left over.

What is the crude product contaimated with?

Water, unreacted alcohol, phosphoric acid, and some side products

Acid catalyzed dehydration of an alcohol is the reverse of the

acid catalyzed addition of water to an alkene

the final wash with water removes

any remaining carbonate

What is the major product when acid catalyzed dehyrdation leads to more than one elimination product?

it is the more stable alkene, the one that is obtained by removing a proton from the B carbon bonded to the fewest hydrognes -the more stable alkene is the product because it has a more transition state leading to its formation

what is the product of an alcohol undergoing elimination

it produces an alkene that amounts to the elimination of a molecule of water which leads to dehydration

An alcohol can undergo an elimintation reaction by

losing an OH from one carbon and a H from an adjacent carbon

Compounds with higher vapor pressure boil at ______ temperatures

lower