Today:

- Conclusion of Exp.1 “Kinetics”

- Exp. 2, “Friedel-Crafts”

Next time: MiniQuiz on Exps. 1 and 2!

Calculations for Exp.1: Solvolysis of tert Butyl Chloride Reaction Rate = =

-d(reactant)

dt-d[RCl]

dt= k[RCl]

p.354-355

CCH3

CH3

CH3

Cl + H2O + HClCCH3

CH3

CH3

OH

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]

• Units of k?

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

• 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.)?

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”?

Arrhenius Plots

y = -13082x + 38.64

y = -12362x + 35.503

y = -11872x + 32.619

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

0.0032 0.00325 0.0033 0.00335 0.0034 0.00345 0.0035 0.00355

1/T (Kelvin)

ln (k

)

60/40

70/30

80/20

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?

Suggest a procedure to get pure n-propyl product and no isopropyl product. 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”!)

Gas Chromatography / Mass Spectrometry

Gas Chromatogram of a Crude Oil Sample

Calculations for Friedel-Crafts Experiment

II. Weight of product mixture __________________ What compounds are in the mixture?

Percent by weight of mono n-propyl

product in product mixture __________________

Theoretical yield in grams of mono______________ n- propyl product

 

Percent yield mono n-propyl product* __________________

 

Ratio of n-propyl to isopropyl product* __________________  

 

 

1.

2.

3.

4.

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? How can you determine the approximate sequence?

4. What is the mole ratio? What is the mole fraction?

Next time:

Friedel-Crafts (conclusion)

NBS Bromination (Exp.3)

MiniQuiz on Exps. 1 and 2!