today I finished the first lab experience, then share it with you!
experience consisted in the separation of benzoic acid and α-tetralone from a mixture.
first are taken slowly with a 50 ml graduated cylinder (figure).
the mixture is transferred into a separating funnel 250 ml, attached to the racks under the hood with a ring (figure).
at this point are taken with a graduated cylinder 50 ml of ethyl acetate (a solvent) which is poured into the funnel to dilute the solution.
hours are taken 100 ml of water and pour them into a beaker, where it is dissolved 5 g of NaOH, better known as caustic soda.
this basic solution is used to initiate the separation: in fact, in two shifts with 50 ml of solution is poured into the separating funnel, the shakes and it vents to let out the gas formed, then puts the funnel in 'ring, and it expects to separate two phases in the aqueous solution will be dissolved with sodium benzoate (salt that is formed by reaction of benzoic acid and sodium carbonate), there will be over the ethyl acetate with α-tetralone.
removing the aqueous phase through the tap funnel, letting it drip into a 250 ml beaker until there is more than the funnel, while the organic phase is left behind protected by a cap to prevent contamination .
prepares a bath in ice in a recrystallized (figure) gets crushed ice and add a bit 'of water.
there we enter the beaker with sodium benzoate, then get ready to party 20 ml of 6 N (normal) HCl (hydrochloric acid): starting from a standard solution 12 N, if they take 10 ml, which are then elongated with 10 ml of water.
the acidic solution is added very slowly to the solution through a Pasteur pipette with benzoate (figure), until it reaches an acidic pH (below 2) and is controlled with the aid of a litmus test.
at this point benzoic acid reformed is not very soluble in water, so it falls into a whitish powder, which must be filtered.
filtration prepare a filter paper for Buchner, which is placed on a flask Tailed attached to the water pump vacuum (figure). water pump is nothing more than a double outlet pipe connected to the sink: when you open water, its movement causes a "suction" in the other exit of the tube, sucking air and creating a vacuum.
to filter the sour, pour the solution into the Buchner and washed the residue with a little 'cold water (taken from the ice bath), then moved the solid acid in a 250-ml flask and add 40 \\ 50 ml of water to dissolve it again.
you put a glass rod into the flask and mounting the condenser (figure), which is connected to the tap to let water in and get it out from above.
you put the ball in termomanto (figure), which goes on, stirring occasionally to dissolve completely benzoic acid, for then allow it to recrystallize. This method, called recrystallization, is used to remove the last traces of impurities by acid benzoic acid.
(sorry, I could not find a better ... the blue car with termomante is inside the ball) when the acid recrystallized , died on termomante and moved the ball in an ice bath to complete recrystallization.
is filtered again and moved on Buchner acid obtained in a previously weighed recrystallized, then putting it in the oven overnight to remove all traces of water.
when he is out of the stove, it is weighed to see how much acid has been recovered, then we move on to testing for purity: melting point, TLC (thin layer chromatography) analysis and IR (infrared).
to the melting point gets a little sample in a special capillary sealed at the bottom and it also puts them in a special machine that heats slowly until the stops, recording the melting temperature shown on the display.
preparing the plates for TLC by drawing a line about 1 \\ 1.5 cm from the bottom and drawing three dots to the order, the sample, reference and pure mixture of departure, which should be placed in 3 tubes (the sample and the reference, being solid, be dissolved with a little 'methylene chloride).
you cut a piece of paper the size of the jar that you will use (you need to see better) and pour into 10 ml of a solution costutita 8 ml of petroleum ether and 2 ml of ethyl acetate (this solution is called eluent).
lay it down on the plate with a capillary sample, the reference and the mixture, then put into the jar and let the eluent, by capillary action, the soak, pulling out only when the eluent has come to 1 \\ 2 cm from the top, marking the exact spot with a pencil (used for the calculation of RF, retention factor: distance from the point of deposition of stain / total distance of the eluent).
few seconds after the slide is again dry because the eluent evaporates quickly, so I can put it under a UV lamp and mark the spots (figure).
(left to right: sample and reference mixture. Benzoic acid stain is stretched down, while the stain on the Misel is the α-tetralone) finally prepares the sample for ' IR analysis: a small part of the sample is placed in an agate mortaietto with a little paraffin oil (the sample must be the majority) and the pesto until it reduces to a uniform pap, from which a sample is taken to be laid on a special slide NaCl (table salt), which closes with the other half. I put this all in the sample holder and the machine for the IR analysis connected to the computer that you want to print a chart (figure).
now back to the organic phase: you should wash with a saturated solution of NaCl, which is prepared by adding salt to the water until it is a bit 'on the bottom.
separating funnel to pour twice 50 ml of NaCl, shakes and outgassing, then removing the aqueous phase (below).
recovered organic phase is freed of a lot of residual water in a flask, where it adds to anidrificare sodium sulphate, stirring and adding until it is dusty, a sign that has absorbed all water.
you filter with a pleated filter in a funnel (figure), taking the organic phase dried in a balloon.
rotavapor attaches to the ball (figure) and I switch it on, all the solvent to evaporate.
weigh an empty flask and attaching it to a Vigreux distillation flask as recovery, attacking each other at the beginning so that its contents are distilled, you insert the thermometer with a Quickfit (stopper particular) and a capillary break the boil. I position the ball with the solution in termomanto and attack all at a vacuum gauge and a vacuum pump; connection pipes for water and open the tube (figure).
(sorry, I have not found anything better ...) recovery I put the ball in an ice bath to help condense the distillate.
when the first drop there is marked falls in temperature and pressure boiling.
at the end of the distillation, the flask with weight recovery dell'α-pure tetralone.
Now make a plate for the TLC and we put it on the sample, the reference (diluted in methylene chloride) and the mixture of departure (figure).
(as before I left: standard, reference and mixture) Finally, I put a drop of pure sample on the slide to make the IR analysis, taking the press (figure).
and with this I concluded, if you have any questions just ask!
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