Exp 4 - Intro, Discussions, Conclusion

Introduction

In this experiment we synthesized the ester, cholesterol nonanoate, and determined it’s percent yield and produced a thermal liquid crystal display (LCD) to determine the purity of the synthesized ester. he followin! reaction was in coherence with the "rst part of the la#$ %onanoyl Chloride & Cholesterol Cholesterol '''''pyridine''' '''' 'pyridine'''  cholesteryl nonanoate & pyridinuum hydrochloride  he "rst part of of the la# was the actual synthesis synthesis of the the ester which too too place in a fume hood. o do this cholesterol was measured into a test tu#e and dissoled completely in pyridine. *ddin! pyridine pyridine helped #ecause it acted as a solent and also reacted with the hydrochloric acid. +nce reacted, the Cl is no lon!er a#le to cleae the ester and hence there is an increase increase in the yield of cholesteryl nonanoate. %ananoyl chloride chloride was then pipetted into the test tu#e and then heated for a num#er of minutes. he test tu#e was set to cool to room temperature and then methanol was added. Cholesteryl nonanoate has low solu#ility in methanol, and so it precipitates more easily in methanol. o help een more with the precipitation, the test tu#e is then placed within an ice'#ath. he newly formed crystals were then separated from the supernatant #y exposin! them to a acuum and then left to air dry.  he second part part of the la# was determinin! determinin! the meltin! meltin! point of pure pure -' acetonaphthone. acetonaphthone. he meltin! point of -'acetonaphthone was determined #y meltin! it on a cylindrical steel #loc and measurin! temperature with a di!ital thermometer. he meltin! point was found more than once to ensure that the results were precise and that any ey qualitatie si!ns could #e o#sered. his experimental experimental alue was then compared compared to the literature literature alue to ealuate the a#ility of this method in determinin! meltin! points of a su#stance. e then found the meltin! point of the cholesteryl nonanoate crystals, and #y comparin! to the literature literature alue, the purity of the su#stance was determined.  he third part of the la# was main! a LCD which was was done #y placin! placin! #oth cholesteryl nonanoate and cholesteryl oleyl car#onate on a microscope slide. his slide was then heated until the cholesteryl nonaoate #e!an to melt. *t this point the two compounds were mixed thorou!hly and then sandwiched #y another microscope slide. *fter cleanin! and tapin! the sides, the newly formed LCD was placed in ice. /y o#serin! color chan!es we determine if the ester was synthesized #ecause hi!h molar mass compounds such as the ester display the unsusual optical properties of liquid crystals.

Discussions$

+erall in this experiment there hae #een a few instances where experimental alues di0ered !reatly from theoretical alues. Durin! the synthesis of  cholesteryl nonanoate, procedure step 1 states that ideally the solution should turn yellow. his did not happen and neither did procedure step 2 where the solution should turn cloudy. hou!h what these indicators represent is not stated in the la# manual, it is eident as we pro!ress throu!h the la#, that an error was made at this sta!e. his can #e seen at - separate sta!es further into the experiment, the "rst #ein! the percent yield and the second #ein! the meltin! point of cholesteryl nonanoate. he percent yield in this experiment was a mere 345 which can #e due to a few reasons. Dealin! with such a small mass, the smallest particles can mae a di0erence and so mass could hae #een lost durin! "ltration or left a residue on !lass wear. hou!h we still had enou!h product to perform the next - parts of the experiment, the amount synthesized was drastically lower than expected. *s for meltin! point, a possi#le source of error is the di!ital thermometer. hen measurin! the meltin! point of -'actonaphthone, there was a consistent leel of discrepancy #etween the literature alue of 26 de!rees celcius and the measured alue of 21.1 de!rees celcius. It can #e inferred that the thermometer proided inaccurate results that were approximately 3.6 de!rees celcius #elow the actual alue. 7nfortunately the theoretical meltin! point of Cholesteryl %onanoate is 81'88 de!ress celcius and we !ot almost dou#le that alue with 316 de!ress celcius and so the thermometer inaccuracy cannot #e a su9cient reason. his meltin! point test informs us that with such a !reat di0erence it is liely that the ester was ery impure. he only reasona#le explanation is that durin! the "rst few steps of the procedure, some error was made, such than little or no ester was made. :ather the solution must hae stayed as one of the reactants such as cholesterol.  he LCD portion of the experiment was ery unexpected in comparison to all the results attained leadin! up to this part. ;urprisin!ly the LCD screen produced, clearly displayed color chan!e which infers that the compound is of hi!h molecular mass.