Organic Chemistry Lab 315 Fall, 2014

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 Next Week Synthesis of tert-Pentyl Cl Report See my lab web site for instructions on writing Synthesis reports.

Report Notes – Last Week Instructions said to show on the graphs the data used to estimate the volumes of Et and Bu acetate. In the summary, the assumptions would include explaining how you decided which data to use. The summary should include the fact that you actually graphed vol. vs. T data. Instructions said to explicitly compare the mole % calculated for each method. That does not mean “about the same”, or “less than 10% difference”, etc.

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 as 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.

In Lab Today Reaction takes place within a separatory funnel tert-pentyl alcohol and HCl are mixed to form one phase initially, and 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. A strong acid, HCl is used as a reagent, so be sure to follow the instructions for calculating the amount 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 Muhammad Siddiqui