Chapter 19: Distillation

ice bath

Immersion in cold water to speed up recovery -ice bath means ice water bath

thermometer

-entire bulb is below the side arm of the three way adapter -if you dont have liquid droplets condensing on thermometer bulb, temperature you read is nonsense

pressure measurement

- need a closed end manometer 1. turn on source of vacuum and wait for system to stabalize 2. turn knob on manometer so that notch in joint lines up with inlet 3. wait for mercury in manometer to stop falling 4. read the difference between the inner and outer level of mercury. This is system pressure in millimeters of mercury 5. Turn knob on manometer to disconnect from inlet

internal steam distillation

-add hot water to the flask and this will generate steam

simple distillation example

-add two liquids with different boiling points (100 and 50) in round bottom flask and drop in boiling stone -if liquid condenses into receiver at 35 degrees C do not keep it. The temperature should be close to 50 degrees C -once the temperature reaches 49 degrees C then change change flask and keep heating until you get a rate about 10 drops per minutes collected. Once temperature starts rapidly increasing stop distillation and changer receiver. Now you have a pure liquid (bp 49-51) -do the same for the other liquid -only record temperature when droplets condense on thermometer bulb, and temperature goes up quickly and stabilizes

condenser

-always keep cold water running through condenser, enough so lower half is cold to touch -water should go in bottom and out the top

notes

-except for steam distillation, two liquids that are gonna be separated must dissolve in each other -impurities can be soluble or insoluble -when you set up the jointware it is important that all joints line up

fractional distillation more

-for a separation of liquids that are soluble in each other and boil fewer than 25 degrees C from each other -used when components to be separated boil within 25 degrees C of each other -lots of tiny distillations occurring on the surfaces of the column packing

distilling flask

-if it is to big you'll lose a lot of product -if it is to small you'll have to distill in parts -dont fill distilling flask more than half full because you'll lose product in condenser -if you're doing a fractional distillation with a column you should fill the flask before clamping set up -dont ever pour mixture down a column -put in a boiling stone, promotes bubbling and keep liquid from superheating and flying out of flask -never drop a boiling stone into hot liquid -start heat slowly until gentle boiling begins and liquid starts to drop into receiving flask at a rate of 10 drops per minute

steam distillation notes

-if you see two layers, or if solution is cloudy you're not done -add some salt to the solution you've collected in test tube, shake tube to dissolve salt, more of product may be squeezed out of aqueous layer forming a separate layer -should be two layers of liquid in receiving flask at the end of the distillation. One is mostly water and other is product

vacuum adaptor

-important tubing connector remain open to the air -do not stuck vacuum adapter on the end of the condenser and hope that it will not fall off and break

vacuum distillation more

-putting liquids under vacuum makes the liquid boil at a lower temperature -the molecules require less energy to leave the surface of the liquid, so you can distill at lower temperatures and compounds won't decompose

fractional distillation

-separating liquid mixtures, soluble in each other that boil at less than 25 degrees Celsius from each other at 1 atm

simple distillation

-separating liquids boiling below 150 degree C at one atmosphere from: -a nonvolatile impurities -another liquid that boils at least 25 degrees C higher than the first. Liquids should dissolve in each other

vacuum distillation

-separting liquids that boil above 150 degrees C at 1 atm from: -nonvolatile impurities -another liquid that boils at least 25 degrees C higher than the first. The liquids should dissolve in each other

steam distillation

-the stuff you're going to distill is only slightly soluble in water and may decompose at its boiling point, the bumping will be terrible with a vacuum filtration so we steam distill -heating compound in presence of steam makes compound boil at lower temperature

external steam distillation

-you lead steam from a steam line through a water trap, and thus into the system -steam usually comes from steam trap

Simple Distillation - Method

1) The solution is heated. The part of the solution that has the lowest boiling point evaporates first 2) The vapour is then cooled, condensed & is collected 3) The rest of the solution is left behind in the flask

fractional distillation notes

1. The column is wider and has glass projections inside at bottom to hold up packing 2. sometimes column is used without column packing 3. a chaser solvent is sometimes used to help blast compound off surface of packing material. Should have high boiling point relative to what you were fractioning

how to do fractional distillation

1. heat mixture and it boils and the vapor that come off this liquid is richer in the lower boiling point component 2. now composition of liquid still in the flask is richer in the higher boiling point component 3. as more of liquid boils, more hot vapor comes up, and mixes with first fraction and produces a composition richer yet in the more volatile lower boiling point component. This new vapor condenses in the second centimeter of column packing 4. occurs again, again, and again 5. ideal separation is getting a single pure component at top-more volatile component, lower boiling point by itself *distill as slowly as you can (5-10) drops per minute

vacuum distillation notes

1. thermometer can be replaced by gas inlet tube 2. boiling stones are useless since all of absorbed air is whisked away by the vacuum and the nucleating cavities plug up with liquid 3. if you use magnetic stirrer and rod you won't have to use gas inlet tube approach -first stirring, then vacuum, then heat 4. if you have a compound that can be simply distilled use that first before vacuum distilling 5. grease all joints no matter what 6. the vacuum adapter is connected to a vacuum source, either a vacuum pump or a water aspirator 7. during a vacuum filtration it is not unusual to collect a pure compound over a 10-20 degrees C temperature range 8. claisen adapter in the distilling flask lets you take temperature readings and can help stop your compound from splashing over into distillation receiver

the heating mantle

1. variable voltage transformer 2. traditional fiberglass heating mantle (an electric heater wrapped in fiberglass insulation and cloth that looks vaguely like a catchers mitt 3. Thermowell heating mantle (as the fiberglass heating mantle but in a can. There is a hard ceramic shell that your flask fits into. It helps to stop corrosive liquids from damaging the heating element if your flask cracks while heating it.)

azeotrope

A liquid mixture of two or more substances that has its own constant boiling point, different from the boiling points of its constituents. The vapor of this unique mixture has the same composition as the liquid state, making it difficult to separate the constituents..

distillation

A process that separates the substances in a solution based on their boiling points

minimum boiling azeotrope

Boiling point of two component system is lower than either individual component -boils off first

steam distillation

For temperature sensitive materials like natural aromatic compounds. Many organic compounds tend to decompose at high sustained temperatures. -isolating tars, oils, and other liquid compounds that are insoluble, or slightly soluble, in water at all temperatures

distilling flask is on

heat source

receiving flask is on

ice bath

maximum boiling azeotrope

if any component comes off first before azeotrope

receiving flask

large enough to collect what you want

vaporization

turing a liquid to a vapor

Condensation

turning a vapor to a liquid