AN SN1 REACTION. t-AMYL CHLORIDE FROM THE ...

AN SN1 REACTION.
t-AMYL CHLORIDE FROM THE CORRESPONDING ALCOHOL
THE PROBLEM TO BE INVESTIGATED: In this experiment t-amyl alcohol (2-methyl-2-butanol) in the
presence of concentrated HCl will undergo a substitution reaction to form t-amyl chloride.
CH3
CH3
H3C CH2
OH
THE NATURE OF THIS INVESTIGATION: A dehydration reaction will occur when a secondary alcohol
(cyclohexanol) is reacted with phosphoric acid. A tertiary alcohol is also expected to undergo dehydration
readily under the proper conditions, typically when reacted with a strong acid and heat. If one considers the
reaction we are about to perform today, a tertiary alcohol and a concentrated acid will yield a product of
substitution. In determining whether elimination (dehydration) or substitution will predominate for a given
reaction, students should note the nature of the organic substrate, the acid, and the reaction conditions.
In aliphatic substitution reactions, two major mechanisms are recognized; substitution nucleophilic
monomolecular (SN1) and substitution nucleophilic bimolecular (SN2). You are already familiar with some of
the general factors (e.g., nucleophile and electrophile) characteristic of this class of reaction and will be
introduced to the particulars later when we deal with substitution and elimination reactions.
You will provide the background information for this experiment by answering the questions on the following
page. In carrying out this reaction, we ask you to consider the reagents (i.e., the nature of the alcohol
substrate, etc.) and conditions (nature of solvent, temperature, etc.).
PROCEDURE
+ HClconc
Caution!! Exercise necessary care! Heed your research on the properties of these chemicals!
Into a 125 mL separatory funnel, add 10 mL of t-amyl alcohol, followed by 22 mL of concentrated hydrochloric
acid. The HCl is added carefully in portions. Swirl the separatory funnel to mix the reagents (caution!) and
permit any gas to vent off into the hood. Stopper the funnel, and holding the stopper in the palm of your hands,
carefully invert the funnel. Release any pressure generated by this action, swirl the funnel again and agitate
the contents (release pressure!!) for about two to three minutes.
During this process, note any temperature changes by feeling the wall of the separatory funnel. Observe the
reaction mixture and note approximately the time when the contents are separated into layers.
Separate and retain (see Helpful Hints) the organic layer. The aqueous layer may be discarded down the
basin drain. The organic layer is "washed" with ca. 20 mL water, followed by 20 mL 5% aqueous Na2CO3
solution (caution!!, why?), and 20 mL brine (saturated NaCl) solution. In each case, the aqueous wash is
separated and discarded. While drying the organic layer over anhydrous CaCl2 (about 10-15 minutes), weigh
(tare) a dry sample vial. The dried liquid is filtered into a 25 mL RBF and distilled into the tared vial (a funnel
may be used). The fraction distilling over the boiling range of 70-86 o C is collected. Hand in your product. IR
measurements will be performed, see p 260-289 in the lab text for more information on IR.
H3C
t-Amyl Chloride: Page 1
CH3
CH2
Cl
CH 3
+ H2O

Helpful Hints - t-Amyl chloride
* Whenever a separatory funnel is used, do not discard any fraction unless you can account for your
product. An easy method to ascertain which layer is which is the following: Add about 2-3 mL of water
into a test tube, and place the test tube lip around the "takeout arm" of your separatory funnel. The
bottom layer is released through the stopcock into the test tube containing the water. Upon agitation,
observe whether the mixture is homogeneous. By deductive reasoning, you now know (hopefully)
which layer is which!!
SYNTHESIS OF tert-AMYL CHLORIDE - HOMEWORK QUESTIONS
Tertiary alkyl bromides can be prepared from the corresponding alcohol by the reaction with concentrated
hydrobromic acid instead of conc.. hydrochloric acid as shown by the following equation.
(1) Consider the above reaction using 25.0 mL of tert-butyl alcohol (d = 0.786 g/mL) with 60.0 mL of
concentrated hydrobromic acid (d = 1.49 g/mL, 47.0% HBr). On a separate sheet calculate the theoretical
yield in grams and the percent yield for a reaction that produced 26.1 g of tert-butyl bromide. Clearly show
the set ups to determine the limiting reactant and other calculations using proper units and significant
figures.
Consult your textbook for the following TWO synthesis. Keep in mind that conc. HCl and conc. HBr
will NOT give good yields of alkyl halides by the reaction with primary and secondary alcohols.
(2) Give the balanced equation to prepare chlorocyclohexane in good yield from cyclohexanol.
(3) Give the balanced equation for the preparation in good yield of 1-bromopentane from 1-pentanol.
(4) The reverse of the reaction you performed in the lab can also occur. Under the proper conditions,
tertiary alkyl halides may undergo a hydrolysis reaction to form an alcohol and a hydrogen halide.
Complete and balance the following equation. (Remember the General II experiment?)
t-Amyl Chloride: Page 2