The purpose of this lab was to determine the mechanisms of reactions; what exactly occurs during a reaction, how to perform a recrystallization, and understanding the effects of stereoselectivity; certain stereoisomers will be sterically favored over others. Sodium borohydride is added to a solution containing benzil and ethanol to completely reduce benzil to hydrobezoin. Borohydride is a very strong reducing agent so an ice bath is used to control the rate of the reduction and minimize the heat produced by the reaction. Borohydride is also added in thirds for this same reason. The first mechanism in the introduction shows exactly how this reaction occurs. A TLC plate is used to see if all the benzyl in the solution has reacted to form …show more content…
As the solution cools down, its solubility will begin to decrease. this will result in the recrystallization of hydrobenzoin. the crystals are filtered to lose any impurities and to dry the crystals. A TLC is conducted to test the polarity of the final product which should be the same as the first TLC. The two diastereomeric products that are made do not separate well by TLC. In order to see the two isomers, it is necessary to convert the products into derivatives. To more easily identify the stereoisomers produced in the reduction of benzil, hydrobenzoin is converted to acetonide by reacting with 2-methoxypropene and acid. The cis and trans isomers of these derivatives have different Rf values on TLC making it possible to identify the stereoisomers that have been prepared. The solution is compared with syn and anti acetonide on two different TLC plates. Due to stereoselectivity, one stereoisomer will be the major product and will be favored over the other. TLC's will show which stereoismer was the major product by lining up its spot with one of the reference acetonide spots. The minor product will be too faint to read and therefore won't be
The goal of this two week lab was to examine the stereochemistry of the oxidation-reduction interconversion of 4-tert-butylcyclohexanol and 4-tert-butylcyclohexanone. The purpose of first week was to explore the oxidation of an alcohol to a ketone and see how the reduction of the ketone will affect the stereoselectivity. The purpose of first week is to oxidize the alcohol, 4-tert-butylcyclohexanol, to ketone just so that it can be reduced back into the alcohol to see how OH will react. The purpose of second week was to reduce 4-tert-butylcyclohexanol from first week and determine the effect of the product's diastereoselectivity by performing reduction procedures using sodium borohydride The chemicals for this lab are sodium hypochlorite, 4-tert-butylcyclohexanone
If the elimination happens with either protons in the terminal methyl group, the resultant product is 1-butene, a Hoffman product (monosubstituted alkene). In contrast, elimination of either -hydrogens by the conjugate base of sulfuric acid (HSO4) on the methylene group leads to an alkene that is dissubstituted. Either the cis- or trans-2-butene can form depending on which hydrogen is deprotonated. These are the Saytzeff products since they are the most popular ones. In this case, the trans-alkene is the most stable, thus one should see the greatest area for the second peak when analyzing the gaseous products under gas chromatography.
The three remaining trials were the experimental groups containing Benzoic Acid and Camphor separately with tert-butanol. 6.305 of tert-butanol was placed in a large test tube, the same amount was used for each trial. The solution was then brought to 50 C using a hot-plate. The temperature was monitored and recorded by a Lab Quest 2 Connected Sciences System. The test tube was held in place using test-tube tongs, and the thermometer was suspended in the solution to ensure accurate measurement. The solution was brought to 50 C, and then the temperature was then recorded at 10 readings per second. After several readings were recorded, the test tube with the solution in it was placed in an ice water bath. The temperature of the solution was monitored for several minutes at 10 readings per second in the ice water
At the 3-minute mark, the least polar ketone was the 3-methyl-aceetophenone with a starting material (SM) Rf of 0.76 and reaction solution (RXN) Rf of 0.75. It makes sense that the ketone with the methyl substituent was less polar than the one with bromine, (SM Rf = 0.56 and RXN Rf= 0.56, 0.42). There is likely some error in TLC plates with either spotting, incorrect measurements of distance traveled by solvent, and impurities in the reaction that could have contributed to this mixture of retention time.
As this is a symmetrical Diels-Alder reaction there is not two possible isomers of the product. Figure 5. Mechanism of the formation of 3.
Ensure gloves are worn at all times when handling strong acids and bases within the experiment of the preparation of benzocaine. 4-aminobenzoic acid (3.0g, 0.022 moles) was suspended into a dry round-bottomed flask (100cm3) followed by methylated sprits (20 cm3). Taking extra care the concentrated sulphuric acid of (3.0 cm3, 0.031 moles) was added. Immediately after the condenser was fitted on, and the components in the flask were swirled gently to mix components. It should be ensured that the reactants of the concentrated sulphuric acid and the 4-aminobenzoic acid were not clustered in the ground glass joint between the condenser itself and the flask. In order to heat the mixture to a boiling point, a heating mantle was used and then further left for gently refluxing for a constituent time of forty minutes. After the duration of the consistent forty minutes the rou...
The competing enantioselective conversion method uses each enantiomer of a kinetic resolution reagent, in this case R-HBTM and S-HBTM, in separate and parallel reactions, where the stereochemistry of the secondary alcohol is determined by the rate of the reactions. When using the CEC method, the enantiomer of the secondary alcohol will react with one enantiomer of the HBTM acyl-transfer catalyst faster than with the other HBTM enantiomer. The mnemonic that identifies the absolute configuration of the secondary alcohol is as follows: if the reaction is faster with the S-HBTM, then the secondary alcohol has the R-configuration. In contrast, if the reaction is faster with the R-HBTM, then the secondary alcohol has the S-configuration. Thin layer chromatography will be used to discover which enantiomer of HBTM reacts faster with the unknown secondary alcohol. The fast reaction corresponds to a higher Rf spot (the ester) with a greater density and a slower reaction corresponds to a lower Rf spot with high de...
This is because 1-butene is the most highly substituted alkene. This reaction follows Hoffman elimination because when forming the least substituted alkene there is steric hindrance, which is not preferred product.
Post-Lab Questions: 1. From the trends in the data, seek to draw conclusions about the following variations in the procedure and how they affect the yield and the purity of the recovered benzoic acid. a. a larger solvent volume, b. a smaller solvent volume, c. a more rapid cooling time. I averaged all of the temperature ranges from the first part of the experiment and found this to be 107-113oC, with an average percent yield of
When performing types of chromatography, like TLC, the polarity of solvents is extremely important. This lab uses TLC plates, five solvents (hexane, toluene, ethyl acetate, dichloromethane, and acetone), and small evaporating dishes to determine which solvent would be best to use in column chromatography. The least polar solvent is hexane, which has a polarity index of 0.1. Toluene has a polarity index of 2.4, while ethyl acetate’s is almost twice that at 4.4.
The recrystallization of the product was done using cyclohexane. The melting point of the product was found to be between 158ºC and 160ºC. The percent yield of the product was calculated to be 23.62%. The low yield was caused by accidently spilling some of the reaction during the washes/extractions in the separatory funnel and by the possibility of having had a side reaction occur during the preparation of the Grignard
The spectrum of the product (Figure 4) was then run using an infra-red spectrometer: The peak at 710.81 cm-1 corresponds to a C-H bond (arene), this is directly attached to the ester group produced during synthesis. The peak at 1451.35 cm-1 corresponds to the C-H bond (alkyl), the alkyl groups are directly attached to the main hydrocarbon
It could have been lower than 100% because some product was lost during the recrystallization process, or due to an incorrect separation of the impurities when cooling the mixtures. The melting point data confirmed that the synthesized crystals were likely identical to the methoxybenzyl phenol ether because the mixed melting point was the same as the purified crystals. If the products were different or the synthesized product had to many impurities in it then the mixed melting point would have been lower than that of just the crystals, by themselves. The TLC made sense, after looking at the TLC plates under UV light and the calculation of the Rf values, it was confirmed that the 4- Methoxy-phenol was present in the unknown.
When benzoic acid paired with 1.0 M NaOH, it was observed that both compounds were soluble. Upon the addition of 6.0 M HCl into this solution, benzoic acid became insoluble. Benzoic acid was also insoluble in 1.0 M HCl. Ethyl 4-aminobenzoate was found to be insoluble in 1.0 M NaOH and soluble in 1.0 M HCl. But then, after adding 6.0 M NaOH into the test tube C (mixture of ethyl 4-aminobenzoate and 1.0 M HCl), a white powdery solid (undissolved compound) was formed. These demonstrate that both the acid and base became more soluble when they were ionized and less soluble when they were
Recrystallization is a common technique used for purifying an impure compound within a solvent. This method of purification is based on the principle that the solubility of most solids increases with higher temperature. For this type of purification, an impure compound is first dissolved to prepare a highly concentrated solution at a high temperature. Following this the solution is cooled, which drops the temperature and causes the solubility of the impurities in the solution, along with the substance being purified, to decrease. The impure substance then crystallizes before the impurities, leaving them behind in the solution. The slower the cooling, the bigger the crystals that will be formed. Finally, a filtration process must be used to isolated the purer crystals from the less pure ones. Solubility curves can also be used in order to predict the outcome of a recrystallization procedure.1