Inspiration and more

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Inspiration, never a bad thing. Street art a good distraction here you go. Together inspiration and street art (aka graffiti) make for an interesting combo.

 "You're never too young to dream big". Meaning you're never to small to dream big. If it matters my dream is to finally understand these damn organic chemistry labs. #sarcasm?
This was found outside Santa Monica College March 20, 2012 it may or may not be a Banksy.


Different inspiration. Study your organic chem or else you may have to resort to this. #haha?

Last but not least lets throw in Banksy (assuming the first one isn't Banksy). If organic chem fails go out with a bang like the crayola shooter. This one was found in Westwood, California near UCLA in February of 2011 behind an urban outfitters.



Now back to studying.




And always if you're bored or broke check this out:

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Synthesis of Salicylic Acid

So we meet again. In the event you find this near sunrise filled with anxiety, rage and confusion I hope this gives you a hand.

Purpose:
  The purpose of this experiment was to perform a base-catalyzed hydrolysis reaction while converting oil of wintergreen to salicylic acid. The full balanced molecular equation for the salicylic acid synthesis is C₈H₈O₃ + 2 NaOH + H₂SO₄  -> C₄H₆O₃ + Na₂SO₄ + CH₃OH + H₂O. An illustrated equation showing compounds to be isolated or synthesized is shown below.

Salicylic Acid is a white crystalline compound with a melting point of 160°C and molecular weigh of 138 grams/mole, it is not symmetrical and typically gives 7 diff C-13 Nuclear Magnetic Resonance Signals.   

Methyl salicylate has a relatively weak phenol and carboxylic functional groups that are important in this experiment; it also has a mint like smell smell, and reacts rapidly with NaOH. The C-13 NMR has extra signal compared to that of Salicylic Acid, a melting point of 223°C, a molecular weight of 152 grams/mole and a density of 1.17 g/mL.  Structures of molecules mentioned above are shown below.

Procedure

             All procedures were carried out under a hood, all individuals involved wore nitrile gloves and safety goggles. Glassware was cleaned, rinsed with deionzed water and if necessary acetone before usage. Remember...be safe.

            First 3.5 mL of water were poured into a 50mL round bottom flask. Next .448 g Sodium Hydroxide (NaOH), which happened to be in pellet form, was then weighed out using a weigh boat and was added to the water, which was then swirled until the solid dissolved.  The pellet form of the NaOH made it difficult to acquire the .48 grams indicated by the manual. After the pellets dissolved .23 mL of Methyl salicylate (measured with a graduated pipette) was added to the NaOH solution. A boiling stone was then dropped to the bottom of the round bottom flask.

            Next, using grease on the glass joint, a water jacketed condenser was added to the round bottom flask. They were connected and held in place by a screw cap at the joint of intersection between the two. Two water tubes were attached to the condenser, the top arm attached to a tube allowing for water to go out, the bottom arm of the condenser was connected to a tube lead from the water source in the hood, allowing for the water to come in and run through. A clamp was used to hold the apparatus steady and hold fast to a vertical rod in the hood. The round bottom flask was kept in place by an aluminum block, placed on a heating plate, which was turned on to about 1/3 of its maximum power. The mixture was heated for about 15 minutes as the white solid dissolved.

            After reflux, the equipment was allowed to cool to room temperature by separating it from the heat source, it sat till it was only slightly warm and comfortable to handle. The condenser was removed. Next, 3M Sulfuric Acid (H2SO4) was added in .5mL increments till a white precipitate formed and stayed as the solution continued to be stored.  An additional .5mL were added to allow completion of the precipitation reaction.

            The contents of the round bottom flask then underwent vacuum filtration through a Hirsch Funnel fit with filter paper and connected with an integral adapter to a 25mL filter flask. The crude product from the Hirsch funnel was then transferred to weigh paper using a spatula. The salicylic acid crystals were then placed in a 10mL Erlenmeyer flask. Next, 5mL of water were added to the Erlenmeyer flask containing the crystals. The solution was put on the hot plate till the solid dissolved and was immediately taken off.  The flask and its contents were allowed to sit at room temperature while crystallization occurred. The crystals were collected via a second filtration using a Hirsch funnel with the same set up as the one done earlier in the experiment. Upon completion of the filtration the crystals were placed in an empty vial and stored for a week. The following week the crystals were packed into a capillary tube with only one open side. The sample was placed in apparatus, Mel Temp, that provided a magnified view of the sample and temperature, allowing for the assessment of the samples melting point and range. Another sample was prepared with acetone with deutero Hydrogen by an instructor. This sample underwent C-13 Nuclear Magnetic Resonance Spectroscopy (C-13 NMR). Samples from multiple lab groups ran through the machine, the goal was to learn how the C-13 NMR helps determine molecular structure, and look at the induced magnetic field.

Things that are good to know for this lab:

For Reference:       C₈H₈O₃ + 2 NaOH + H₂SO₄  -> C₄H₆O₃ + Na₂SO₄ + CH₃OH + H₂O.

Finding the limiting reagent (plug and chug)

Note: There is a 1:2 molar ratio of Methyl salicylate (C₈H₈O₃) to Sodium Hydroxide, respectively. Note, Methyl salicylate is the limiting reagent; this will be used to calculate the theoretical yield.

_____ g NaOH x      1 mole      = ____moles NaOH x 1 mole Methylsalicylate  = .____ moles Methyl Salicylate needed

                           39.99 grams                                              2 moles NaOH

___ g Methyl Salicylate x 1 mole   = ____ moles Methyl Salicylate x 2 moles NaOH     = ____ moles NaOH needed

                                     152 grams                                                 1 mole Methyl salicylate

Theoretical Yield: Referring to the balanced molecular equation there is a 1:1 molar ratio                                        between Methyl Salicylate and the Salicylic Acid.

___ moles Methyl Salicylate x   1 mole Salicylic Acid = ____ moles Salicylic acid expected

                                                  1 mole Methyl Salicylate

____ moles Salicylic Acid expected x       138 grams       =    ____ grams Salicylic Acid expected

                                                              1 mole Salicylic Acid

Questions?

After NMR give two pieces of evidence that salicylic acid was the solid produced by reacting methyl salicylate with the aqueous base. Which piece of evidence gives the direct structural information? Which gives only indirect evidence?

C13 NMR of methyl salicylate has 8 unique carbon peaks, while salicylic acid has 7. The C that is lost was bonded to 2 Oxygen molecules making it down stream whihc is congruent with the chemical equaiton. C13 NMR gives indirect structural information.

Measuring the melting point and range allows you to compare it to the known melting point of salicylic acid telling you if the compound has the same melting point and if it has impurities. Impurities cause a depression and increase in range. The larger the range the more impurities it has.  Measuring the melting point gives direct information.

Why is it that dilute sulfuric acid does not allow the reaction to proceed while concentrated sulfuric acid does?

Sulfuric Acid is used as a reaction catalyst. This means that you need to overcome an activation energy to create the product. The dilute sulfuric acid does not have as fast and as high dissociation as the higher concentration sulfuric acid, thus the reaction does not finalize because it does not overcome the energy of activation.

On the other hand....

What is the purpose of adding concentrated sulfuric acid in the preparation of methyl salicylate?

Sulfuric acid is used in esterfication reactions as a catalyst.

When methyl salicylate is prepared from salicylic acid and methanol, an OH- is the leaving group from the salicylic acid. The presence of the acid provides a large amount of H+ ions to stabilize the leaving group to H2O, and speeds up the rate of the reaction.

What are  the structures of each of the following compounds

i)-The organic species present immediately after methyl salicylate is first added to the aqueous sodium hydroxide solution and before heating.  
ii)-The organic species present at the end of the reflux period just before the sulfuric acid is added.  iii)-The organic compound present after the sulfuric acid is added.
 Label each  as being soluble or insoluble in water at room temperature.

The Methyl Salicylate is the option "i"it is insoluble in water at room temperature.
The image shown after adding NaOH but before H2SO4 is the organic species present at the end of the reflux period it is soluble in H2O. Salicylic acid, the product is not soluble in water (H2O) during room temperature.

What are the relative chemical shifts in parts per million and their assignment on the Salicylic Acid molecule for C-13 NMR.

Remember C-13 NMR looks at unique carbons. For more on C-13 NMR click here.
 

Peak, δ, ppm	Assignment
112.3	A
117.3	B
119.1	C
130.4	D
136.0	E
162.1	F
171.6	G

Bored? Broke? Try this....
I don't get paid for this so it really helps if you join...plus you get free stuff. If you live in the united states you can get a dollar sent to your house off the bat for free.

Purification of Caffeine and Analysis

Well who would have thunk it last post we started to ponder how do I get chlorophyll out of my extracted sample...this post we solve this issue.....Eh it may go a little sum sum like dis.

How about some free coffee and or tea before we start?

For your entertainment: Purification and Thin-Layer Chromatographic Analysis of Caffeine

Purpose
  The purpose of this experiment was to continue the study and purification of caffeine isolated in a previous experiment via sublimation and Thin Layer Chromatography. Molecules are shown below.

 
Stuff about Stuff
Caffeine: Look at the previous post. If you're too lazy just know that its a white powdery substance in its natural form without odor and a rather bitter taste.

Chlorophyll a: For now just know that it provides a greenish color.
 

Procedure

All procedures were carried out under a hood, all individuals involved wore nitrile gloves and safety goggles. Glassware was cleaned, rinsed with deionzed water and if necessary acetone before usage.

 

Safety like it or not it's important. If you haven't heard about Carol....here she is. She never wore her safety goggles and now she doesn't need them. Don't be Carol. Or even worse meet Bill (Maturity warning....). Don't be Bill.

  Prior to the beginning of this experiment a sample of caffeine extracted from tea leaves and was stored in a 25 mL Erlenmeyer flask that was corked and allowed to sit for a week. From this crude extracted sample a small mass was put into a test tube and about .1 mL dichloromethane was added to it. The test tube was covered with wax paper and allowed to sit. This sample was labeled “Crude solution” and was to be used for the Thin Layer Chromatography later in the experiment.
The remaining crude sample was put into a filter flask with a side arm, and 1.9 mL of dichloromethane was added to it. A filter adapter was then set in the filter flask and a test tube was placed so that it sat about .5 cm off the bottom of the filter flask. The filter flask was placed in a 100 mL sand bath so that the sand covered a few mm of the flask wall. The sand bath was connected to a transformer to allow for control in process of heating. To add stability and decrease movement of the equipment the flask and test tube were each clamped separately to vertical rods in the hood. The side arm of the filter flask was connected via appropriate tubing to the vacuum in the hood. The vacuum was turned on the check for any leakage of air, once it was clear there was none, the sand bath and vacuum were both turned on until it seemed that no more caffeine was collecting on the inner tube. Meanwhile the ice water was placed into the test tube (fitted in the filter flask) kept being replaced every few minutes. After both the sand bath and vacuum had been turned off, the equipment was taken off the sand bath and raised in the air to cool.

            A spatula was used to scrap the caffeine off the test tube and onto the weigh boat. The weigh boat was weighed prior to and after the addition of the caffeine. The sublimed caffeine was put into another test tube where.50 mL dichloromethane was added. The test tube was labeled “Purified solution” and was covered with wax paper and stored.

  For the TLC a developing chamber was created (shown to the left). A 150 mL beaker was fit with filter paper, placed in beaker so that it sat on the sidewalls of the beaker but made contact with the bottom. 5 mL of ethyl acetate were added and the chamber was covered with aluminum foil. While the chamber was being set up the TLC plate was prepared for spotting of different caffeine solutions. The TLC plate was 6.7 cm in length and 4.5 cm in width. A 2 mm line was marked from the bottom edge of the plate and another about 1 cm from the top. The line at the bottom was divided into 3 distinct marked areas.

            Using a micropipette 3 spots of the crude caffeine solution was placed in the center of the first area, 3 spots of the purified caffeine were added to the second and then 1 spot of the standard solution provided to the class was placed onto the plate. The TLC plate was then placed in the chamber and the ethyl acetate mobile phase was allowed to run. Note tweezers were used to handle the TLC plate upon entry and extraction of the plate from the chamber. The plate was then taken out when the ethyl acetate was near the line marking 1 cm from the top.  Immediately after the plate was taken out of the chamber and how far the ethyl acetate traveled was marked with a pencil. The plate was then analyzed with 254 nm UV radiation. During this process each spot of caffeine was outlined with a pencil and the chlorophyll was marked. Rf values were calculated for each caffeine solution by dividing the midpoint of the caffeine spot by the total distance traveled by the ethyl acetate solvent in cm. What we got the Rf value for the “Crude Caffeine Solution” was .121, for the “Purified Caffeine Solution” the Rf value was .144 and for the “Standard Caffeine Solution the Rf value was .124. .

Things that may be good to know.

Rf values = Distance between midpoint of spot from origin in cm

                        Distance traveled by the solvent in cm

 
 Questions? (Feel free to add your own)

So how does one see the results of the thin layer chromatography?
The visualization technique used in the TLC portion of this experiment involves the use of
ultraviolet (UV) light. The caffeine absorbs the UV light and gives off visible light.
This phenomenon is called fluorescence. For more on wiki go here.



Bored? Go here 

Its Question Time:

What is sublimation?And why is it useful in lab settings involving purification?

Sublimation is the process of a phase change between solid and gas. In general, if an experimental
product can sublime, one can use it as a purification technique. This is because in most cases, impurities do not sublime.

Caffeine and sublimation

 Caffeine will normally sublime around 180 degree C (at 1 atm).

In general, in order for a solid to sublime, its triple point pressure must be higher than 1 atm. In order to accelerate the sublimation process for caffeine (see below), external pressure must be reduced to drive the equilibrium towards gas phase. Vaccum filtration helps by lowering the pressure inside the filtering flask  and will promote the caffeine to sublime at a temperature well below 180 degree C.

Extraction of Caffeine from Tea

Maybe before you start your lab how about some free coffee? check this out





Introduction and Purpose    The purpose of this lab was to extract caffeine from tea. The molecular structure of the of caffeine the molecule of interest for the extraction, caffeine, is shown below.

Facts about Caffeine (maybe even fun facts): 
In its pure form its a white substance that melts at 236 degrees Celsius. It is an irritant and is considered toxic. Tea is said to be about 3% caffeine by weight, but it ranges across teas.
Caffeine can be found in coffee, energy drinks, tea (clearly, hence its used in lab), No doz, Midol and more!



Techniques used:
Vacuum Filtration, use of micro pipettes funnel, centrifugation and  use of drying agents








Procedure

The procedure used for the lab varied from the exact directions listed in the Lab Manual. This section will provide the procedures carried out, including the alterations from the manual. Aside from centrifugation the procedures were all carried out under a hood, all individuals involved wore nitrile gloves and safety goggles. Glassware was cleaned, rinsed with deionzed water and if necessary acetone before usage.
First the contents of 2 tea bags were put into a 150mL beaker. The mass of the tea was about 4.681 grams. Then about 2.50 grams of Calcium Carbonate were added followed by . 50mL water.
The mixture was boiled on a hot plate on a medium heat level, during this time period a watch glass was placed on the top of the beaker. After 10 minutes of boiling the mix was set on the bench top to cool so that it was warm to the touch.

During the cooling period a 5-cm Buchner funnel was put inside a 125mL filter flask with an arm that could be connected with proper tubing to a vacuum. The funnel itself had a piece of Whatman No. 54 filter paper inside that had been wetted slightly. Additionally a clean 150mL beaker was filled with 12mL water (measured with a graduated cylinder) and the 12mL level was marked with a piece of tape, the water was poured out. While no picture was taken of the lab set up the image below shows the set up despite the use of an adapter as shown in the image.



 The remaining solution was put through the filter and vacuum apparatus that was assembled during the cooling period. The vacuum was turned on and was allowed to run until filtered solution stopped coming out of the funnel tip and a pool of solution sat at the bottom of the flask (indicating that all the sample had gone through). The filtered sample (from the flask) went into the beaker that had the 12mL mark.
The sample was boiled shortly using a hot plate till it was reduced to the 12mL mark. The sample was then allowed to cool on the bench top till it was warm to the touch.
The sample was transferred to a 15mL centrifuge tube with a screwcap, 2mL of dichloromethane were added to the solution (dichloromethane is also known as Cl2CH2).
The solution was shook for about a minute and put in the centrifuge for about a minute. Upon completion of centrifugation 2 layers of material became apparent. A brown layer said to contain tannins and other materials and a green layer at the bottom containing the caffeine dissolved in the dichloromethane. A pipette was used to extract the green organic layer, which was placed in another centrifuge tube. Another 2mL of dichloromethane were added to the solution, the tube was capped, solution shook, centrifuged and the portion of the solution containing the caffeine was extracted with the pipette again. The process of adding 2mL dichloromethane, putting the cap on the tube, shaking, centrifugation and removal of the green layer was conducted a total of 4 times. After the 3rd centrifugation the layers did not separate in a distinct fashion, a small amount of sodium chloride (NaCl) was added to aid the process. The layers separated in a more distinctively, the organic layer was removed then the final set of preparation, centrifugation and extraction was completed.

Next anhydrous magnesium sulfate (a drying agent) was added to the tube with extracted dichloromethane and caffeine solution. This mix was allowed to sit for about 5 minutes with occasional swirling till the mix became clear. Then a microfunnel was prepared by tightly packing small piece of cotton at the tip of the pipette where it began to taper. It was clamped to a vertical bar in the hood such that it was about half way into a 25mL Erlenmeyer flask.
The dichloromethane and caffeine solution were transferred to the micropipette via a clean pipette and was allowed to go through the microfunnel and go into the clean 25mL Erlenmeyer flask. The remaining magnesium sulfate in the centrifuge tube was rinsed with .5mL dichloromethane so all contents could go through the microfunnel.

Above are magnified caffeine crystals

The 25mL Erlenmeyer flask containing the filtered solution was placed on a heat plate on a relatively low heating level, allowing for the dichloromethane to evaporate. The flask was removed once a dry dark green residue formed at the bottom of the flask and all the dichloromethane seemed to have evaporated. The flask was allowed to cool on the bench top. Then the sample was weighed. The percent recovery was then calculated by dividing the recovered mass of caffeine by the initial amount. Once everything was completed a cork was placed tightly on the flask and the sample was stored to be used for another lab experiment.  For clean up the tea was thrown in the trash being that they are not hazardous. Materials remaining from the extraction were put in the non hazardous waste bin. Meanwhile the centrifuge tube that previously had dichloromethane was left on its side to allow all dichloromethane to evaporate fully and then was rinsed. All glassware were cleaned with soap and water, dried, and given a quick rinse with deionized water.

Questions (Feel free to ask more, heck I'll even try to answer them for free!)


Why was the tea boiled (in water)? Turns out caffeine is actually highly soluble in hot water and it turns out boiling the tea leaves in hot water allows for the caffeine to be released. Hence we are able to extract the caffeine from the water later in the procedure.


Why is the aqueous tea solution cooled to 15-20°C before the dichloromethane is added?

The boiling point of CH2Cl2 is 40C water boils higher than this. If dichloromethane gets too hot, it emits highly toxic fumes of phosgene.  Now would be a great time to say that dichloromethane is actually kind of dangerous and acts as an irritant to the respiratory system (that thing you breath with). If heated to decomposition in flame or hot surface to form toxic gas phosgene and corrosive mists of hydrochloric acid are also formed. AND YOU GET TO BREATH IT IN!!!!!! YAYYYYY!!!!! To quote MSDS " Continued exposure may cause increased light-headedness, staggering, unconsciousness, and even death. Exposure may make the symptoms of angina (chest pains) worse"GO HERE TO FIND OUT MORE Oh yeah and I forgot its probably carcinogenic too....keep it cool and keep safe.

Now you may ask what is MSDS? They are Material Safety and Data Sheets. Home page is http://www.msds.com/ go there to learn stuff about stuff.


Why is the tea solution cooled before dichloromethane is added? Think of adding sugar or salt to water, water has higher solubility levels for many compounds at higher temperatures that can even allow for super saturation. But while it cools the solubility and the ability to hold the caffeine decreases as the temperature drops. Slowly but surely the caffeine becomes undissolved and then we add the dichloromethane to add the process of extraction.


How do I calculate percent recovery of the extraction of caffeine from the tea leaves?
 

Percent Recovery =   amount recovered   =  Insert mass of what you got     x  100% = % recovery

                                    Initial amount *            what it should have been

* Note as stated earlier tea is 2-5 % caffeine by weight, so unless you know the exact number multiply the mass of how much tea you started with by 3.5% to see the total caffeine you could have been able to extract. Don't be surprised if this number is rather low.

Why does adding salt (NaCl) to the aqueous layer sometimes help break up emulsions that may form in an extraction?
Hmmm...not sure of this one but here is my guess. NaCl is pretty soluble in water. And emulsions by definition are non polar substances surrounded by polar substances. Fun fact mayonnaise is an emulsion (True life I'm a food network dork). The NaCl will attract these water molecules deterring them from dealing with the emulsion. It helps provide a stronger inter phase between solutions too! Also adding salt can cause salting out.

In the event you used 1-Propanol and Salt

NaCl is used as a salting out technique to increase the dielectric constant of the water layer. By doing so, 1-propanol will separate out from the salt water and this allows the extraction of caffeine into the 1-propanol layer. In order for the 1-propanol to separate out from the water layer, the water must be saturated with NaCl. This can only be achieved if NaCl is added in excess amount.
When salt is added to the water layer, it decreases the solubility of caffeine. This is due to the fact that caffeine is only slightly polar in nature. Thus, the solubility equilibrium will now shift to the 1-propanol. This will cause the partition coefficient to decrease.

In the event you added Calcium Hydroxide. Here is why.

Calcium hydroxide helps to precipitate out the tannic acid as calcium tannate in tea leaves. If
sodium hydroxide is used instead, no precipitate will form (sodium tannate is soluble in water). The caffeine crude product will be contaminated with the tannate salt. And that would be a annoying


Caffeine is a white powder, why the hell is my sample GREEN!!!!?????
The sample is green because well lets face it you extracted it from tea...Tea is a plant. Plants have chlorophyll. Chlorophyll is green. Turns out you probably have chlorophyll in your sample. Tune in some other time and maybe I'll have a way...or do a lab that finds a way to eliminate and purify the extracted caffeine.

Why do we centrifuge in the caffeine extraction?
 You will use a centrifuge in this experiment break up emulsions once they form, separating the aqueous and organic liquid emulsion. Now you may ask what is an emulsion? An emulsion is a suspension of one liquid as droplets in another (the two liquids must be insoluble in one another). Think water in oil or oil in water they don't really mix. To avoid them, you can shake mixtures of insoluble liquids gently and add salt to aqueous layers remember that salting out thing you did by adding NaCl.


Meanwhile if you're bored feel free to visit and join.



What is the role of sodium carbonate in the extraction of caffeine in tea leaves? and also what is the principle involved in extraction?
The sodium carbonate acts as a base - you could use sodium hydroxide instead. When you boil tea leaves tannins dissolve in the water as well as the caffeine. If you do not use a base the tannins will also be extracted into the solvent (i.e. methylene chloride) used in the subsequent extraction . The base converts the tannins into their sodium salts - being ionic these salts are not soluble in solvents like methylene chloride so remain in the aqueous layer during extraction. This allows purer caffeine to be extracted.