INDEPENDENT PROJECT REPORT

CHEM 247B

Payam Morgan

TA: Bhaskar U Tadikonda

Spring 2004

Abstract:

In this experiment a primary alcohol, 1, 6-heaxanediol was used and three reactions were designed to convert this starting material into three different products. The first reaction with a percent yield of 98% was the conversion of the alcohol to an ester by Fischer esterification using acetic acid. The next reaction was the conversion of the starting primary alcohol to a secondary alcohol in two steps. The first step was the acid catalyzed dehydration and condensation of the alcohol to 1,5,11-dodecatriene with a percent yield of 83%. The second step was the conversion of this alkene to the secondary alcohol of 2,5,11-dodecatriol with a percent yield of 75% by using mercuric acetate.

Introduction:

In this experiment two reactions were performed. One of the reactions involves a two step process. For the clarity of this report each section of this report will contain subgroups corresponding to each reaction.

Fisher Esterification

Fischer esterification is an acid-catalyzed nucleophilic acyl substitution reaction of a carboxylic acid with an alcohol. Carboxylic acids are not reactive enough to be attacked by alcohols but their reactivity increases by the presence of a strong acid such as HCl or H2SO4. The mineral acid protonates the carbonyl group oxygen giving it a positive charge and making it a better leaving group, thus increasing the reactivity of the carboxylic acid.

The net effect of this reaction is the replacement of an –OH group with an –OR. All steps and the reaction can be driven to either direction by choice of reaction conditions. When large amounts of alcohol is present as solvent the formation of the ester is favored as opposed to the condition where large amounts of water is present that favors the formation of the acetic acid.

Dehydration and Oxymercuration

There two common ways of alkene production: one is dehydration and the other dehydrohalogenation. In this experiment the first method of elimination is used for dehydration of the starting material. Dehydration is often carried out by treatment of an alcohol with a strong acid to form the corresponding alkene which involves the loss of the –OH group and a H in the form of a water molecule.

The first step in the mechanism of dehydration is the conversion of the –OH group to –OH2+, producing a good leaving group. The next step could either be an E1 or an E2elimination. In an E1 mechanism, elimination the elimination of water makes an alkyl cation which then eliminates a proton and produces a double bond. In an E2 mechanism, a bimolecular molecule occurs in which water acts as a base and abstracts a hydrogen producing an alkene.

Oxymercuration is a method of adding water to an alkene in a Markovnikov position. The reaction is initiated by electrophilic addition of Hg2+ to the alkene to give an intermediate mercurinium ion. Nucleophilic addition of water followed by a loss of proton produces a stable organomercuric product. The final step of is the reaction of the organomercury product with sodium borohydride to yield the corresponding alcohol. Since this reaction involves the addition of –OH in a Markovnikov position, a combination of both dehydration and oxymercuration would produce a secondary alcohol from a primary alcohol.

Experimental:

Fischer Esterification

A sand bath was preheated first in a thermowell to 80-100°C and a reflux apparatus was assembled that contains a round bottom flask on the bottom, then a condenser and an inverted funnel connected to the vacuum to act like a hood for fumes from acetic acid. In the round bottom flask .5 ml of the alcohol was placed and about 5ml of acetic acid was placed before adding 3-4 drops of sulfuric acid for catalysis. The mixture was refluxed for 80 minutes.

The reaction was cooled to room temperature while being stirred. Then 5ml of 5% sodium bicarbonate was added to the reaction mixture till in stopped bubbling. Then the reaction mixture was poured into a centrifuge tube and was spun till the organic layer and the aqueous layer were separated. The organic layer was removed by a Pasteur pipet and the aqueous layer was extracted with 3ml of anhydrous ether. The entire organic layer was extracted three times by 5ml of distilled water. The organic layer was dried over sodium sulfate. The resulting organic layer is the corresponding ester. The reaction equation and the structures of the starting material and the products are shown here.

Dehydration

A sand bath was heated to 150°C. 5ml of 16M phosphoric acid and 6ml of 15M sulfuric acid was placed ina 25ml round bottom flask. The round bottom flask was connected to a distillation apparatus that was connected to ice water for further cooling and better yields. 3 grams of 1, 6-heaxanediol was dissolved in 1ml of water and then the mixture was added to the acidic mixture in the round bottom flask.

The apparatus was set on the sand bath to boil and reflux for 3 hours. Eventually the sand bath temperature was raised to 200°C and the apparatus was covered with aluminum foil to enhance the evaporation of the product and better yields. The obtained product that was distilled was put in a vial and the reaction mixture was centrifuged to get the organic layer separated and extract more of the alkene product.

Oxymercuration

The entire product from the dehydration experiment after analytical experiments was used in this reaction that accounted for about 1 ml. A mixture of 5ml of saturated sodium chloride and .5 grams of mercuric acetate was obtained and was put in a small vial and set so that could stay upright without being held by hands since the last part of the experiment is quite exothermic.

Then the alkene product was added to this mixture and the tube was shaken well to form the mercuronium ion which makes the alkene become soluble. And then it was set aside in room temperature for 5min. then 5ml of KOH was added and mixed well. Then 0.25g of sodium borohydride was added to the mixture—the mixture was set on ice before the addition and was kept on ice throughout the reaction—whichresults in an exothermic reaction with the organomercuric compound formed by the reaction of the mercuronium ion and OH-.

The product was extracted 3times with 2ml of anhydrous ether. The organic extraction was dried over sodium sulfate. The ether solution was then put in a round bottom and connected to a vacuum line and was put on ice to evaporate the ether. The resulting product in the form of crystals was then analyzed for purity and physical constants.

Results and Discussion:

1,6hexanediol / The ester product / 1,5,11-dodecatriene / 2,5,11-dodecatriol
MP / 41°C / LIQUID / LIQUID / 86°C
Literature MP / 40°C / LIQUID / LIQUID / N/A
BP / 135°C / 351°C / Too high could not measure
Literature BP / N/A / N/A / N/A
Percent yield / N/A / 98% / 83% / 75%
MW / 118.17 / 202.25 / 164.29 / 218.33
GC/MS Purity / 100% / 97% / 100%

Fischer Esterification

The ester that was obtained was characterized by NMR, IR, GC/MS and TLC. The NMR shows the purity of the compound and all the corresponding peaks of each hydrogen are also present. The IR showed no signs of an OH group showing a complete reaction of the alcohol and purity of the ester. The TLC was also performed to show the purity of the compound that had no other spots except one for the ester.

Another TLC was also performed to make sure that the reaction is complete and that there is no alcohol left. The GC/MS shows no other peaks than the one corresponding to the ester product. The MW of the ester is 202; however the GC/MS shows a peak at 203 which probably corresponds to the fact that a hydrogen has been added to it during the process. The percent yield was about a 100%. The product was so pure after extraction that no more purification was done on it. This was a very efficient reaction for ester synthesis. The BP point of the ester product was also measured; however there were no literature values found to compare the results with.

Dehydration

This reaction was not intended to give the obtained product. The product that was expected was 1,5-heaxadiene instead of 1,5,11-dodecatriene. This is most probably due to the fact that the mixture reacted too long at a high temperature which made the 1,5-heaxadiene to react with it self and give the corresponding product. The physical properties of the dodecatriene were such that it was impossible to perform IR and NMR. The product was not dissolving in any solvent to perform IR or NMR.

However a GC/MS was performed that yielded results indicating the presence of such compound. The MW of the 1,5,11-dodecatriene is 164 and the GC/MS shows a compound with the corresponding MW. However there are other peaks present that could correspond to drying reagents used and different solvents that were used to try to dissolve 1,5,11-dodecatriene for other analytical experiments. A TLC experiment was also performed to assure the complete reaction of the alcohol and the purity of the product. The TLC however showed no impurities. The recent yield of this reaction was 83%; however this is also calculating some of the impurities present. The BP of the compound was also measured; however there were no literature values to compare to. Another test for the verification of the presence of 1,5,11-dodecatriene could be the reaction it through oxymercuration to yield the corresponding alcohol which will be discussed below.

Oxymercuration

The oxymercuration of 1,5,11-dodecatriene yielded 2,5,11-dodecatriol. The percent yoeld of this reaction was 75% which is due partly to the small amounts of starting material used and some loss during transfer from one tube to the other because of space limitation. The percent yield could have also been affected by the fact that the compound is water soluble and it would be hard to extract it from an aqueous reaction solvent. To ease the extraction of 2,5,11-dodecatriol saturated NaCl solution was used to salt out the alcohol as it forms. And at the end of the reaction more sodium chloride salt was put in to precipitate the product further more and by extracting with ether the product would dissolve in ether.

The GC/MS of 2,5,11-dodecatriol showed no impurities. There is a peak at 6.30 min that corresponds to the MW of 203. 2,5,11-dodecatriol has MW of 218 so it’s suspected that a water is lost and three protons are added to the compound during the analysis. The IR spectrum shows a peak at 3447 that corresponds to the OH group of this alcohol. There were no C=O peaks observed which indicates the purity of the product from any starting material. The NMR however, shows some impurities in the product. This could be either due to some DCM that was present in the product or to some impurities in the NMR tubes themselves. However, the peaks for the 2,5,11-dodecatriol were observable.

The MP and BP of the product were attempted to be obtained however because of apparent high temperature of the BP the BP was not observed. The MP was 86°C; however there were no literature values found for this to be verified.

Overall Reaction Performed: