2016 Summer Session 1 Kevin Chen Chem 51LB Week 3 2016 Summer Session 1 Kevin Chen

Lecture Outline Miscellaneous announcements Experiment #4: Acid/base extraction

Sapling! Incomplete Sapling = NO LAB! No lab means no in-lab points/TA discretion (15 pts) Can still do the post-lab reports TA will assign you data to use for the report

Proper waste disposal We have our first case of “glass waste” in regular trashcan This is a major safety violation Next time, EVERYONE in the section will lose a letter grade

Experiment #4 Acid/base extraction Given: One unknown acidic and one neutral organic compound (fluorene) as a mixture Goal: Separate the two organic compounds (acidic and neutral) with separatory funnel extraction then recrystallization and melting point End game: Identify the acidic compound in the mixture and confirm the identity of fluorene

SAFETY ANNOUCEMENT! Strong acid (HCl) and base (NaOH) are being used  BE CAREFUL! Evaporating diethyl ether using INDIRECT HEAT, heating directly on the hot plate means FIRE! The TAs will discourage bad lab techniques by taking points off from people who decides to ignore these warnings

Separatory funnel Needs two immiscible solvents (one is almost always water) Organic solvent versus water (aqueous) Think oil versus water

IMPORTANT SAFETY ANNOUNCEMENT Pressure can build up when one shakes a full separatory funnel IT CAN EXPLODE!!! VENT OFTEN!!!

Density is the key! There are two layers Which one is on top? Organic Aqueous Which one is on top? Density is the key! Lighter of the two immiscible liquid will be the top layer, which means most organic solvents EXCEPT… methylene chloride aka dichloromethane aka DCM

Like dissolves like Uncharged organic compounds are soluble in organic solvents Charged organic compounds and ions are soluble in aqueous solution Acidic compounds like carboxylic acid can be deprotonated to become negatively-charged carboxylate Basic compounds like amine can be protonated to become positive-charged ammonium

Changing protonation state Protonation state of a compound can be changed, How? pH Protonation at low pH Deprotonation at high pH So why is this important?!? An acidic compound is NOT charged at low pH and is charged at higher pH (greater than its pKa) A basic compound is NOT charged at high pH and is charged at lower pH (lower than its pKa)

How do you change pH??? There are two solvents, organic and aqueous (which is water) Water is the obvious choice! Add acid  aqueous layer becomes acidic Add base  aqueous layer becomes basic Changing pH means changing solubility of the organic compounds!

Example: Aqueous solution at pH = 2 What layer would these compounds be in? Acidic compound (carboxylic acid) Basic compound (amine) Neutral compound (cyclohexane)

Example: Aqueous solution at pH = 2 You should answer this question first… are these organic compounds charged at pH = 2? Carboxylic acid  still neutral Amine  positively-charged ammonium Cyclohexane  still neutral

Example: Aqueous solution at pH = 2 Carboxylic acid  organic layer (because it is not charged) Ammonium  aqueous layer (because it is positively-charged) Cyclohexane  organic layer (because it is not charged)

Additional notes on extraction Label all your glassware! Always keep track of which layer (organic or aqueous) that the organic compounds (acidic and neutral compound) are in Eventually, the organic solvent needs to be removed, which means evaporation with heat SAVE EVERYTHING UNTIL THE END!