Organic Chemistry Lab 315 Fall, 2016

DUE DATES Today Next Week At beginning of lab – GC of Distillate Report At end of lab -- copy of laboratory notebook pages for today's experiment Please finish the last Spec. II problem Next Week Synthesis of tert-Pentyl Cl Report See my lab web site for instructions on writing Synthesis reports.

Report Notes – Last Week Simple and Fractional Distillation Report Read the instructions Follow the instructions Never adjust data from Notebook in a Report (unless specifying why at the first opportunity) Never tear out an original Notebook page Do not submit a page of calculations and then repeat the calculations in your written summary.

Notes The next slides show the mechanism for the formation of a tertiary alkyl chloride from a tertiary alcohol. The specific example used is tert-butyl. You can easily re-write it using tert-pentyl. When you look up the reaction starting materials, products and by-products you will likely need to use the systematic IUPAC names. tert-Pentyl is also known by its common name, tert-amyl.

Synthesis of tert-butyl chloride In Lab Today Synthesis of tert-butyl chloride The mechanism of the reaction is SN1 Step 1 is an acid/base reaction between HCl (acid) and alcohol (base) to form the oxonium ion. Step 2 is the dissociation of the oxonium ion to form the tert-butyl carbocation and the leaving group, H2O. Step 3 is the reaction (Lewis acid/base) between the carbocation and the nucleophile, Cl-, resulting in overall substitution.

Synthesis of tert-butyl chloride In Lab Today Synthesis of tert-butyl chloride The mechanism of the reaction is SN1 Step 1 is an acid/base reaction between HCl (acid) and alcohol (base) to form the oxonium ion. Step 2 is the dissociation of the oxonium ion to form the tert-butyl carbocation and the leaving group, H2O. Step 3 is the reaction (Lewis acid/base) between the carbocation and the nucleophile, Cl-, resulting in overall substitution.

Synthesis of tert-butyl chloride In Lab Today Synthesis of tert-butyl chloride The mechanism of the reaction is SN1 Step 1 is a Bronsted-Lowry acid/base reaction between HCl (acid) and alcohol (base) to form the oxonium ion. Step 2 is the dissociation of the oxonium ion to form the tert-butyl carbocation and the leaving group, H2O. Step 3 is the reaction (Lewis acid/base) between the carbocation and the nucleophile, Cl¯, resulting in overall substitution of Cl for OH.

In Lab Today Reaction takes place within a separatory funnel tert-pentyl alcohol and HCl are mixed to form one phase initially, and they then begin to react. As the products tert-pentyl chloride and water form, the reaction mixture separates into two phases.

In Lab Today Two phases are the upper t- PentCl phase (with some water and aq. acid) and the lower aqueous phase with dissolved acid. Separate the phases (keeping upper phase in funnel). Wash the t-PentCl layer with water (removes ___?) Add aq. sodium bicarbonate. The basic bicarbonate neutralizes the acid and forms CO2 gas. Review drying organic solvents (See p. 696 in Pavia)

In Lab Today Wash the t-PentCl with water again (removes __?) The t-PentCl will be mostly pure with just a small amount of water present. Review drying organic solvents (See p. 696 in Pavia) Decant t-PentCl into clean dry pre-weighed vial (± .001g). Do not distill.

Experiment Notes Determine the refractive index, take an IR spectrum and calculate the percentage yield. Store t-PentCl product in a tightly capped vial in the storage drawer. Dispose of aqueous solutions in the sink with plenty of water.

Synthesis Report See the instructions on the web site for writing a Synthesis report. Pay particular attention to the table on the Report Form, which is actually a calculation of theoretical yield. Since the carbocation is not isolated or measured, it is not included in the table. A strong acid, HCl is used as a reagent, so be sure to follow the instructions for calculating the amount of HCl used. Separation scheme -- flow chart of procedure for separating a pure product from reaction by- products. (Even though you do not do a final distillation, include it on the Separation Scheme.)

Lab Clean-up Ii, Alexandra N. Marcus, Erin M.