Question of the Day:

Which organic products can be formed during the hydrolysis of tert-butyl chloride?

(write the structures of two) CCH3

CH3

CH3

Cl + H2O + HClCCH3

CH3

CH3

OH??

Today:

- Conclusion of Exp.1 “Kinetics”

- Exp. 2, “Friedel-Crafts”

Calculations for Exp.1: Solvolysis = kt-ln

[RCl]

[RCl]oat t10%, [RCl] = 0.90 [RCl]o

= kt10%-ln

0.90[RCl]o[RCl]o

-ln = kt10%0.90 = 0.1053

0.1053

t10%= k

CCH3

CH3

CH3

Cl + H2O + HClCCH3

CH3

CH3

OH Reaction Rate = =

-d(reactant)

dt-d[RCl]

dt= k[RCl]

• Assume you want to determine k in a given solvent system at a given temperature, but the reaction is too fast to reasonably measure t 10%. What could you do to obtain k (same solvent/same temp.)?

• How could you calculate k by using the half life?

Arrhenius Equation and Calculation of Ea and A k = A e

-Ea/RT

What does Ea tell us about the reaction?

ln k = ln A -Ea/RT

Plot ln k vs. 1/T for each solvent mixture ln k

1/T

y = b + m x

R=1.987216 cal/Kmol

What is “b” in our equation, what is “m”?

Friedel-Crafts Alkylations (Exp.II)(Read your Organic text chapter on “Friedel-Crafts” reactions.)

Reaction of p-xylene with 1-bromopropane in the presence of aluminum trichloride (our lab experiment):

Mechanism?

Aluminum trichloride is a Lewis acid. What is a “Lewis acid”?

What problems can arise during Friedel-Crafts alkylations? Friedel-Crafts reactions increase the number of C-atoms of the reactant. Do you know any other reactions that do this, too?

Why does the lab apparatus have to be very dry?

Why is a gas trap needed?

What is the meaning of "tared" (as in "tared flask")?

Why is ice added after the reaction took place?

And why ice and not water?

Friedel-Crafts Alkylations (Exp.II)

Lab Experiment(Microscale procedure. Remember “omission”!)

Evaluation of products by

Gas Chromatography

1. What types of samples can be separated by GC?

2. Which is the moving phase, which is the stationary phase?

3. What peaks do you expect in your GC of Exp.II?

4. What determines their approximate sequence?

Gas Chromatography / Mass Spectrometry

Gas Chromatogram of a Crude Oil Sample

What is the mole ratio?

What is the mole fraction?

Calculations for Friedel-Crafts Experiment II. Weight of product mixture

What is in product mixture?

Percent by weight of mono n-propyl product in product mixture Weight fraction… Remember: Different molecular weights…

Theoretical yield in grams of mono n-propyl product

Balanced equation (assuming that only mono n-propyl product is formed), mols, mol ratios …

Percent yield mono n-propyl product*

[Actual yield / theor. Yield] x %  

Ratio of n-propyl to isopropyl product*

GC! Area ratio =mol ratio  

 

 

1.

2.

3.

4.

Next time:

Friedel-Crafts (conclusion)

NBS Bromination (Exp.3)

MiniQuiz on Exp1. and 2 (Kinetics and Friedel-Crafts)

!