For this experiment, a Fischer esterification reaction was observed. A Fischer esterification is a reaction that converts a carboxylic acid into an ester. Within the reaction, the hydroxyl portion, -OH, of the carboxylic acid is replaced by an -OR group. The byproduct is water which is also a nucleophile. Therefore, water can be added back into the compound and undergo hydrolysis on the newly formed ester which produces the starting carboxylic acid. To make sure the reversibility did not occur, the reaction mixture was heated to force the water to evaporate and therefore be removed from the overall reaction. The main idea of Fischer esterification is to form a carboxylic acid and make it a better electrophile under acidic conditions. This is …show more content…
done by protonating the carbonyl oxygen of the carboxylic acid. The reaction mixture was poured into water, was neutralized, and the solid product was filtered.
Fischer was a well-known chemist who won the second Nobel Prize in chemistry. He is also notable for Fischer projections. His method was to run the reaction under acidic conditions. To do this, the oxygen was protonated to make it a good nucleophile. The carbon is then strong enough to react with the alcohol. This can then go on to make a good leaving group, water, which comes off. In the last step, a proton is removed. His method was ran under acidic conditions to make the electrophile a better electrophilic carbon. This reaction works very well.
An ester is derived from a carboxylic acid. The oxygen of the alcohol is the nucleophile and the carbonyl carbon of the carboxylic acid is the electrophile. The oxygen makes the carbon more electrophilic causing the alcohol to attack since the oxygen does not want to be positively charged. The solvent used was concentrated sulfuric acid which promoted the addition of the weak nucleophile, the alcohol of the carboxylic acid, to be replaced with an -OR group. A proton is gained back from the hydroxyl group of the carboxylic acid after being lost. After this, a proton shift occurs that gives up the leaving group of water which is the byproduct since it
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is also a nucleophile. The water can add back into the mixture and hydrolyze the ester which was newly formed. This regenerates the starting carboxylic acid. Heat was added to make the water evaporate and be removed from the reaction. Alcohols are not good nucleophiles and carboxylic acids are terrible electrophiles. When acid comes together with alcohol, an ester forms, but if the reactants are not strong enough then the reaction is helped along. By adding heat this can help, but sometimes this is not enough for the reaction to go. A change in the reactants can make the reaction proceed, so they are made to be stronger. To make a better nucleophile, the alcohol can be changed into an oxide to react with a carboxylic acid to make an ester. However, the oxide and carboxylic acid do not create an esterification reaction because oxides are strong nucleophiles and strong bases. This produces a competing acid-base reaction that makes it hard for the reactants to react with one another. By forming an alcohol, it defeats the purpose of forming a strong nucleophile. A carboxylate would also form which is a worse electrophile than carboxylic acid. To make a good electrophile, the carboxylic acid can be converted into an acyl halide which are great electrophiles and would react with the alcohols to produce esters. Acyl halides were not utilized since they are expensive, shelf life is short, its very reactive, and are not used in undergraduate teaching labs. There are three problems that can occur with Fischer esterification that decrease the yield of product.
The first is the proton source. A certain one must be used. It is typically done with sulfuric acid, but hydrochloric acid can also be used. A strong base is not used so a strong acid is utilized. To make enough product, a strong acid is used to push the reactants into products to produce enough product. Phosphoric acid is an exception in that it can also be used but a strong acid is preferred to make the reaction go to completion. The second problem deals with equilibrium which is the most important. If the reaction was performed with an alcohol, methanol or ethanol, and a carboxylic acid, acetic acid, the equilibrium constant, Keq, would be 4. The Keq is the concentration of products divided by the concentration of reactants. In this case it would be ([ester][water])/([alcohol][acid]). The two products are ester and water and the two reactants are alcohol and carboxylic acid. The concentration of alcohol and ester are unknown, but they are equal to one another. The reactants are essentially the same and they should be in a 1:1 ratio to keep the concentrations equal to one another. In this reaction, a lot of waste is unwanted which this would produce excess waste. By producing a lot of waste, reactant, it increases the cost of waste disposal, so this method is not used. The main goal is to get the reactants to be equal to one another, so the reactants are (1-x). The
equilibrium expression would be 4 = (x2)/((1-x)(1-x)) to solve for x. One solution is 2/3 (67%) and the other solution is _____. A good percent yield is around 65% and when comparing it to the 67% of solution, it is not a good percent yield. This is because 65% is the expected yield and not the percent yield. The percent yield is based out of 100% expected yields. If the expected yield was divided by 1/3, this would lower the percent yield and the resulting data would not be good. Therefore, the percent yield needs to be maximized as much as possible. The last problem is adding product to the reaction which is related to the second problem. For this experiment, any product added to the reaction, such as water causes the water to be soluble in methanol and ethanol. This is related to the Grignard reactions since the water destroyed the reducing agent. Therefore, the water will not leave as a good leaving group and will offset the reaction. With this, the methanol is kept water free and almost at one hundred percent pure methanol. The combination of the benzoic acid and methanol produces methyl benzoate. For this experiment, to improve the percent yield, the equilibrium is shifted towards the products. When shifting the equilibrium, it is very complex. Therefore, Le Chatelier’s Principle states that by stressing the equilibrium on one side of the reaction it will force it to go in another direction. This is accomplished by removing one of the two products, not one in particular, but in this case, water was removed. This causes the equilibrium to shift towards the products which produces a higher percent yield of product. In lab, it can be expensive, or it may not be equipped with the right equipment to remove a product. Another approach would be to add excess reactant by doubling it and getting this equilibrium expression, 4 = (x2)/((1-x)(1-x)). The denominator was originally bigger since one of the reactants was doubled. By increasing the denominator, the only way to maintain 4 is by increasing the numerator, the product, as well. Increasing the mass of the reactant also increases the product. If the reactants are doubled, the yield of products also increases to around 85%. If the reactants are tripled, the percent yield of products is about 91%. By running the reaction in excess reactants, the percent yield would be 99.99999%. The reactant used is the alcohol, but typically it does not matter. To not have excess reactants, the reaction is offset by doubling it. The alcohol is the reactant but can also serve as being the solvent. If the alcohol is used as a reactant, the solvent can be used to offset the cost of not needing a different solvent for this reaction. There is a lot of methanol used in this experiment when compared to the amount of carboxylic acid used. In this experiment, 3 mL of an unknown carboxylic acid solution, benzoic acid, was placed into a 5 mL conical vial along with a rice stir bar. Then four drops of sulfuric acid were added to the vial and was attached to a small condenser. The concentrated sulfuric acid was used in place of silica-gel sulfuric acid catalyst. Metal clips were used to secure the water hoses on the condenser. The water went in at the bottom end and it came out on the top end. Only a slow flow of water was required because if too much pressure was used, then the hoses would come off and flood the hood. The conical vial was placed in the correct indention on the heating block and was heated approximately around 200 degrees Celsius. After thirty minutes, the reaction was completed. The timer was not started until condensation was observed in the column. The conical vial was carefully removed from the hotplate and the reaction was poured into 5 mL of water. The solution was then cooled in an ice-water bath to make sure the solution was below room temperature. After this, 10% aqueous sodium bicarbonate was added to the solution until the pH was around 8 which was around 10 mL of sodium carbonate. The base was added slowly, and the pH was tested occasionally to ensure that the pH was increasing. It is important to neutralize the reaction mixture because it ensures that the ester is uncharged and insoluble in water, so the product can later be filtered. Then, 3 mL of methanol was added and then the organic phase was extracted. The organic layer was washed with 3 mL of saturated sodium chloride. The solutions that were used in this experiment contained alcohols as both the solvent and reactant. With this, the excess alcohol was removed by performing a vacuum filtration. After this, sodium sulfate was added to the product to dry it and then 1-2 drops of product were added to 1 mL of methanol. Then the gas chromatography was ran by shooting 1 uL of solution into the machine and the unknown ester was identified by comparing the retention time to the standards. The gas chromatography, GC, was used in this experiment. The GC was used to separate on the basis of boiling points since similar containing compounds attract other similar containing compounds. It can also be separated on polarities in both the stationary, nonpolar phase and the mobile, nonpolar phases. The peaks given from the GC were used to help determine the boiling points contained in the mixture which helps determine the unknown ester. The retention times of benzoic acid were compared to narrow down the unknown substance. If the retention times were similar, the sample in the GC was consistent with being methyl benzoate. Safety was important during this experiment since a small amount of sulfuric acid, a very strong acid, was used. Gloves were to be changed immediately after handling the sulfuric acid. If acid was suspected of getting on gloves, a new pair was obtained. If exposed, get in the safety/emergency shower because it causes severe chemical burns. Concentrated sulfuric acid with any carbon source will react and produce a fire, therefore sulfuric acid was not exposed to paper or other carbon containing materials. The smell of the experiment is pleasant like a snapdragon from the methyl benzoate.
Table 6 shows the results of the biochemical tests. The isolate can obtain its energy by means of aerobic respiration but not fermentation. In the Oxidation-Fermentation test, a yellow color change was produced only under both aerobic conditions, indicating that the EI can oxidize glucose to produce acidic products. In addition to glucose, the EI can also utilize lactose and sucrose, and this deduction is based on the fact that the color of the test medium broth changed to yellow in all three Phenol Red Broth tests. These results are further supported by the results of the Triple Sugar Iron Agar test. Although the EI does perform fermentation of these three carbohydrates, it appears that this bacterium cannot perform mixed acid fermentation nor 2,3-butanediol fermentation due to the lack of color change in Methyl Red and Vogues-Proskauer
Alcohol, which is the nucleophile, attacks the acid, H2SO4, which is the catalyst, forming oxonium. However, the oxonium leaves due to the positive charge on oxygen, which makes it unstable. A stable secondary carbocation is formed. The electrons from the conjugate base attack the proton, henceforth, forming an alkene. Through this attack, the regeneration of the catalyst is formed with the product, 4-methylcyclohexene, before it oxidizes with KMnO4. In simpler terms, protonation of oxygen and the elimination of H+ with formation of alkene occurs.
Hydration of alkenes is characterized by the addition of water and an acid-catalyst to a carbon-carbon bond leading to an alcohol. Dehydration is exactly the opposite in which dehydration of an alcohol requires water to be removed from the reactant. Equilibrium is established between the two processes when the rate of the forward reaction equals the rate of the reverse reaction. The alkene that is used in this experiment is norbornene. Through hydration of norbornene, an alcohol group should be present on the final product yielded what is known as exo-norborneol. Percent yield is a numerical indication of how much of the reactant was actually reacted to yield product. The equation for percent yield is shown below:
electrophile (electron pair acceptor) with an attached leaving group. This experiment was a Williamson ether synthesis usually SN2, with an alkoxide and an alkyl halide. Conditions are favored with a strong nucleophile, good leaving group, and a polar aprotic solvent.
The weight of the final product was 0.979 grams. A nucleophile is an atom or molecule that wants to donate a pair of electrons. An electrophile is an atom or molecule that wants to accept a pair of electrons. In this reaction, the carboxylic acid (m-Toluic acid), is converted into an acyl chlorosulfite intermediate. The chlorosulfite intermediate reacts with a HCL. This yields an acid chloride (m-Toluyl chloride). Then diethylamine reacts with the acid chloride and this yields N,N-Diethyl-m-Toluamide.
The purpose of the experiment is to study the rate of reaction through varying of concentrations of a catalyst or temperatures with a constant pH, and through the data obtained the rate law, constants, and activation energies can be experimentally determined. The rate law determines how the speed of a reaction occurs thus allowing the study of the overall mechanism formation in reactions. In the general form of the rate law it is A + B C or r=k[A]x[B]y. The rate of reaction can be affected by the concentration such as A and B in the previous equation, order of reactions, and the rate constant with each species in an overall chemical reaction. As a result, the rate law must be determined experimentally. In general, in a multi-step reac...
need is water and an ester and we will end up with an organic acid produced as
And that is almost assuredly his goal from the very beginning, as it must be for any published author in the chemistry community. Works Cited Church, L. B. & Co., L. B. The Chemistry of Winemaking. A Unique Lecture Demonstration.
The three butene products have been verified to elute in the following order: 1-butene, trans-2-butene, and cis-2-butene. Theory: The dehydration of 2-butanol, a secondary alcohol, progresses readily in the presence of a strong acid like concentrated sulfuric acid (H2SO4). The reaction is completed via the E1 mechanism. Initially, the hydroxyl group is a poor leaving group, but that is remedied by its protonation by the acid catalyst (H2SO4) converting it to a better leaving group, H2O. The loss of this water molecule results in a secondary carbocation intermediate that continues to form an alkene in an E1 elimination.
The percentage yield gained was 70% from the Fischer Esterification reaction, which evaluates to be a good production of yield produced as the reaction is known to be reversible where conditions such as the concentration of the reactants, pressure and temperature could affect the extent of the reaction from performing. These white crystalline crystals were tested for impurity by conducting a melting point analysis and taking spectrospic data such as the IR spectra, HNMR and CNMR to confirm the identification of the product. These spectrospic methods and melting point analysis confirmed the white crystalline crystals were benzocaine.
Chemical kinetics is a branch of chemistry that involves reaction rates and the steps that follow in. It tells you how fast a reaction can happen and the steps it takes to make complete the reaction (2). An application of chemical kinetics in everyday life is the mechanics of popcorn. The rate it pops depends on how much water is in a kernel. The more water it has the quicker the steam heats up and causes a reaction- the popping of the kernel (3). Catalysts, temperature, and concentration can cause variations in kinetics (4).
In our Biology Lab we did a laboratory experiment on fermentation, alcohol fermentation to be exact. Alcohol fermentation is a type of fermentation that produces the alcohol ethanol and CO2. In the experiment we estimated the rate of alcohol fermentation by measuring the rate of CO2 production. Both glycolysis and fermentation consist of a series of chemical reactions, each of which is catalyzed by a specific enzyme. Two of the tables substituted some of the solution glucose for two different types of solutions. They are as followed, Table #5 substituted glucose for sucrose and Table #6 substituted the glucose for pH4. The equation for alcohol fermentation consists of 6 Carbons 12 Hydrogens 6 Oxygen to produce 2 pyruvates plus 2 ATP then finally the final reaction will be 2 CO2 plus Ethanol. In the class our controlled numbers were at Table #1; their table had 15 mL Glucose, 10 mL RO water, and 10 mL of yeast which then they placed in an incubator at 37 degrees Celsius. We each then measured our own table’s fermentation flasks every 15 mins for an hour to compare to Table #1’s controlled numbers. At
The aim of this experiment was to investigate the affect of the use of a catalyst and temperature on the rate of reaction while keeping all the other factors that affect the reaction rate constant.
Introduction Most mammals are initially born with the ability to break down the polysaccharide, lactose into smaller monosaccharides but at an early age, usually as the child starts to rely less on their mother for direct nurturance, this ability ceases. This inability to break down lactose is known as lactase non-persistence. Lactase Non-persistence is the wild type in the population surprisingly even though a vast majority of the population is lactase non persistent. Individuals with the ability to digest the lactose found in milk are considered lactase persistent or lactose tolerant.
Introduction Enzymes are classified as being a class of proteins. In other words, the basic structures of enzymes are formed by chains of amino acids. Enzymes, as all other kind of structures, can breakdown in some circumstances. The pH, for instance, is one of the factors that affect the enzymes. Changes in pH not only affect the shape of an enzyme, but it also charges properties of substrate, which will eventually block the bind of the substrate with the active site and prevent it to undergo catalysis (Boumis 2012).