chem 2211L Lab Final UGA

goal of recrystallization

to dissolve and crystallize a pure substance from a solution

steps of recrystallization

1. Choosing an appropriate solvent

2. dissolving impure mixture

3. remove soluble impurities via gravity filtration

4. cool solution to induce crystallization

5. isolate crystals via suction filtration

appropriate solvent for recrystallization

1. dissolves target compound at high temp only

2. impurities are only soluble at one temp

3. chemically inert

4. volatile/low BP

how to induce recrystallization

scratch inner walls or use a seed crystal

what do impurities do to the melting point

broaden and depress

eutectic point

lowest possible melting point of mixture

purpose of distillation

separates volatile miscible liquids based on differences between boiling points

simple distillation is used

difference in BP is over 100 degrees C

fractional distillation is used

difference in BP is less than 100 degrees C

fractional distillation efficiency is measured by

column length and density of packing material

theoretical plate

each mini distillation

azeotrope

A liquid mixture that has its own constant boiling point, different from the boiling points of its constituents.

azeotrope example

Water and Ethanol : 95.6% ethanol, 4.4% water

purpose of boiling chips

ensure even heating of solution

Raoults law

Psolution = XsolventA x PsolventA + XsolventB x PsolventB

how is BP effected by altitude

altitude decreases atmospheric pressure and it will take less heat to boil a liquid

solid-liquid extraction

based on a compounds solubility in a particular solvent

liquid-liquid extraction

based on a compound's varying solubility between two immiscible liquid phases

nutmeg is ___ trimyristin by weight

20-25%

purpose of reflux

to heat a mixture for extended periods of time without losing solvent in order to extract compounds

steps of extraction of trimyristin

1. reflux to extract trigyceride from nutmeg

2. gravity filtration to remove trimyristin from residue

3. simple distillation to separate triglyceride from solvent (ethyl acetate)

4. suction filtration to isolate pure product

how to characterize purity

melting point determination

TLC stationary phase

silica gel

TLC mobile phase

ethyl acetate / 0.5% acetic acid

non polar compounds react with

mobile phase

polar compounds react with

stationary phase

higher Rf value =

less polar compound

How to identify compound in TLC

match Rf value of unknown with known values

acid base liquid-liquid extraction

solubility changes as compounds become protonated/deprotonated

benzocaine

Basic component: amine, arene ring, ester

diphenylmethanol

neutral component: 2 arenes connected to alcohol

benzoic acid

acidic component: carboxylic acid connected to arene

organic layer

top layer

aqueous layer

bottom layer

the density of ethyl acetate is ___ than water. The organic layer will be the ____ layer

less, top

what happens when organic acid become ionized?

they move to the aqueous layer

cyclohexene

hydrogen donor

purpose of celite pipet filtration

isolate product from palladium with minimal risk of fire

adding H2

decreases unsaturated double bonds

catalyst in transfer hydrogenation

10% Pd/C

transfer hydrogenation components:

starting material: triolein (olive oil)

reagent: cyclohexene ( H donor)

catalyst: 10% Pd/C

product: tristearin (saturated fat) and benzene byproduct

diphenyl acetylene lab starting material

trans stilbene

diphenyl acetylene lab reagent

PHPB: pyridinium hydrobromide perbromide

diphenyl acetylene lab solvent 1

1 glacial acetic acid

diphenyl acetylene lab intermediate

stilbene dibromide

diphenyl acetylene lab reagent 2

KOH

diphenyl acetylene lab solvent 2

2 ethylene glycol

diphenyl acetylene lab steps

1. PHPB, acetic acid (halogenation)

2. KOH, ethylene glycol (form alkyne)

PHPB

Pyridium Hydrobromide PerBromide

diphenyl acetylene lab techniques

suction filtration: isolated dibromostilbene crystals from glacial acetic acid

reflux: dibromostilbene crystals with KOH

gas chromatography reaction type

SN1 : substitution of tertiary alkyl halide

purpose of gas chromatograohy

an excess of two nucleophiles, bromide and chloride, used to test nucleophilic strength

gas chromaography used

microscale liquid liquid extraction to determine ratio of product formation

GC stationary phase

nonvolatile liquid

GC mobile phase

inert gas

how to adjust compound separation in GC

1. change oven temperature

2. change column stationary phase

3. change column length

4. change flow rate of gas (mobile phase)

ammonium bromide reacted ___

faster, because its a stronger nucleophile in polar protic solvents (bigger)

GC starting material

tert-butanol

GC solvents

H2SO4, H2O

GC reagents

NH4Br, NH4Cl

GC products

tert-butylbromide and tert-butylchloride

william ether synthesis reaction type:

SN2: substitution of primary alkyl halide

william ether synthesis starting material

4-bromophenol, unknown 1* A.H

william ether synthesis solvent

H2O

william ether synthesis catalyst

KOH, TBAB

TBAB (phase transfer catalyst)

Tert-ButylAmmoniumBromide

william ether synthesis product

ether

william ether synthesis techniques

liquid liquid extraction

basification with KOH to remove impurities

use drying agent in organic layer

purification in column

how does TBAB act as a catalyst

helps ions transfer between organic and aqueous layer

know mechanisms for WES, transfer hydrogenation, diphenyl acetate

know flow chart for acid-base separation

equations: RF, theoretical yield and percent yield, raoults law,

also know how to build a compound from HNMR and draw a distillation apparatus