Purpose The purpose of the experiment is to identify and understand reactions under kinetic and thermodynamic control. A reaction under kinetic and thermodynamic control can form two different types of products. A reaction under kinetic control is known to be irreversible and the product is formed quickly. A reaction under thermodynamic control is known to require rigorous conditions. It is also reversible. The final product is more stable than the product made by kinetic control. The chart below shows the two types of reaction coordinates: The green line shows kinetic control, whereas the blue line shows thermodynamic control. (*SM = starting materials, TS = transition state, P = product) This experiment will help identify which compound …show more content…
used is under thermodynamic control and which is under kinetic control. The reaction coordinates involves addition-elimination reactions. For addition-elimination reactions of aldehyde and ketone, the nucleophiles are usually amines, derivative of ammonia (e.g. hydrazine and hydroxylamine) and ylides. In this case, semicarbazine hydrochloride is used, and this is a hydrazine derivative. A typical addition-elimination reaction includes nucleophilic nitrogen reacting with an electrophilic carbon of a carbonyl group with the movement of the pi bond electrons to the oxygen atom. It basically starts with an acid-base reaction forming an unstable compound (i.e. hemiaminal), then forming a neutral stable product (i.e. imine/Schiff base). Both aldehydes and ketones react with hydrazine to form derivatives called hydrazones, which are depicted by C = N bond. The general form of the reaction of aldehyde/ketone reacting with hydrazine to form hydrazones is shown below: *R’ is H, if aldehyde Specifically for this experiment, the starting materials involved are cyclohexanone and 2-furaldehyde. They are reacted against semicarbazide hydrochloride. The main type of reaction is the addition-elimination reaction producing semicarbazone of cyclohexanone or semicarbazone of 2-furaldehyde. The reaction is done in a moderately low pH/acidic environment. The mechanism involves the double-bonded oxygen attacking the hydrogen in H3O+ in an acid-base reaction. The nitrogen then attacks the back of the substrate, while the oxygen from the substrate takes electrons from the pi bond. Water attacks hydrogen attached to one of the nitrogen. Oxygen takes hydrogen and water is displaced from the substrate. A double bond is formed between nitrogen and the carbon. Water attacks the other hydrogen on the other nitrogen to make the final product neutral. To assist the reaction, a buffer is used. In this case, KHPO4 is used. The purpose of using the KHPO4 buffer is because KHPO4 is an acidic compound. The buffer works well in the pH range: 5.0 to 7.5. The reaction must remain acidic because a basic reaction would deprotonate amine, which is not ideal for the reaction. However, it cannot be too acidic either, because KHPO4 buffer cannot function well under pH of 5.0. Experimental techniques Materials & Methods The class was split into 2 groups for time efficiency. One group did both the room temperature and the low temperature reactions. The remaining group did both the room temperature and the high temperature reactions. Again to decrease the time needed, preparation for high temperatures were done first (i.e. the beaker filled with water was pre-heated at the oven set at approximately 200°C). A thermometer was used to measure the temperature; it was left in the beaker submerged in water. The rest were done according to the lab manual.1 Physical Properties of the Products for Comparison (expected values): Colour Melting Point Semicarbazone of 2-furaldehyde Yellow 202°C Semicarbazone of Cyclohexanone White 166°C *From Lab Manual Results & Calculations Reaction Equations: Table of Results: The results were given in the table below: Low Temperature Room Temperature High Temperature Colour White Pale Yellow Yellow Melting Point 163.3°C 162.2°C 202.75°C Predominant Product Cyclohexanone Cyclohexanone Furaldehyde Kinetic/Thermodynamic Control Kinetic Kinetic Thermodynamic High temperature reaction took noticeably longer to prepare and execute. Low temperature and room temperature reactions were done fairly quickly. Discussion The observed temperatures for the low temperature and room temperature reactions are 163.3°C and 162.2°C, respectively.
The expected melting point of Semicarbazone of Cyclohexanone is 166°C.1 The assumed product is Semicarbazone of Cyclohexanone. Observed temperature being lower than the expected may indicate a contamination or an impurity. The low temperature result was shown to be more accurate than the room temperature result. Perhaps, in the room temperature, there was more of a mix in the products (i.e. containing both Semicarbazone of Cyclohexanone and Furaldehyde). This is reinforced by the pale yellow colour observed, when Semicarbazone of Cyclohexanone is supposed to be white. Room temperature result could be close to the eutectic point. This is kinetic control, as it is formed much quicker than the product of the high temperature reaction. To fix the problem of lower than expected melting point could be have a set temperature as to how cold the low temperature should be (e.g. …show more content…
0°C). The observed temperature for the high temperature reaction is 202.75°C.
The expected melting point of Semicarbazone of 2-furaldehyde is 202°C.1 It is implied that the product of the high temperature reaction is Semicarbazone of 2-furaldehyde. This is thermodynamic control. If under normal conditions, when the nucleophilic nitrogen attacks, it will attack the cyclohexanone. If under rigorous conditions, the nitrogen will attack 2-furaldehyde. This is due to the carbon on cyclohexanone being secondary (i.e. more stable) than the primary carbon of 2-furaldehyde. The trend observed is thermodynamic control seem to effect primary carbons, whereas, kinetic control seem to effect secondary carbons. Under thermodynamic control the intermediate seems the most unstable. The kinetic controlled intermediate seems the least unstable of the two. Some improvements to the experiment might be using Na Acetate or Na Citrate as buffers instead of KHPO4. The pH ranges are 4.5-5.5 and 4.7-5.5, respectively. This range falls closer to the ideal pH of 5, then KHPO4 (pH
5.0-7.5). Conclusion In conclusion, the predominant product of low temperature and room temperature reactions is semicarbazone of cyclohexanone, which is under kinetic control. Those yield a melting point of 163.3°C and 162.2°C, respectively. The predominant product in high temperature reactions is semicarbazone of furaldehyde, which is under thermodynamic control. It yielded a temperature of 202.75°C. The purpose of the lab was met. Most important learning outcomes are distinguishing between kinetic and thermodynamic control.
The experiment of Diels-Alder reactions, in particular the furan and maleic anhydride as used in my experiment, observed the exo product as oppose to the exo product. This shows the tendency for the stereochemistry of the Diels-Alder to yield an exo product in preference to the endo product. To determine the stereochemistry, a melt temperature of the product was taken and compared to literature values. The melt temperature for the product was roughly around 113oC, corresponding to the exo Diels-Alder product of furan and maleic anhydride. When compared to the class data of melting ranges, the melting temperature from the reaction was relatively consistent to the majority. Based off this, the assumption can be made that the Diels-Alder prefers
Results: Through a melting point reading, it was determined that the product obtained was 2,4-Dibromoanisol mp 55-58 C. The products obtained by my partners, were determined to be: (p-bromoacetanilide mp 160-165 C) and (2,4,6 tribromoaniline, mp of 108-110 C) respectively.
This experiment was divided into two main steps. The first step was the addition of bromine to trans-stilbene. Trans-stilbene was weighted out 2.00g, 0.0111mol and mixed with 40ml of glacial acetic acid in 100ml Erlenmeyer flask on a hot bath. Pyridinium hydrobromide perbromide of 4.00g, 0.0125mol was added carefully into the flask.
Mixed melting point was used to confirm the identity of the product. The smaller the range, the more pure the substance. When the two substances are mixed; the melting point should be the same melting range as the as the melting range obtained after filtering. If the mixed melting point is lower one taken from the crystals, then the two substances are different.
As a result, the laboratory experiment was determined to be successful and the two product samples obtained and completed calculations displayed that overall bromide was a stronger nucleophile as the chloride ion was more electronegative than bromide, which allowed it to hold electrons in closerE. In conclusion, since bromide is less electronegative and has more electrons, it was able to share the unpaired electrons more easily than chlorideA. These results were expected, as the alkyl bromide would be the major product of procedure A as it followed the SN2 mechanism which was based on nucleophile strength and the product from procedure B would be a near-equal mixture as it followed the SN1 reaction mechanismC. The methods used during this experiment allowed for a successful completion and determination of the better nucleophile, but other additions and observations would have been interesting and beneficial as well. A possible examination of the two sample products collected using pH tested values or observation of sample spotted chromatography paper under a
I decided to experiment with pHs within the range pH 2 to pH7, as I
The overall objective of this experiment was to perform a Wittig reaction from creating an ylide and mixing it with a carbonyl (C=O) compound, cinnamaldehyde. The completion of the reaction was confirmed ultimately from the initial TLC analysis. Since TLC separates the components of the spotted material, as long as the retention factor values were different for cinnamaldehyde, the starting reagent, and the product(s), it was evident that some of the reaction had gone to completion. However, as seen in Figure 3, there was some blurred area between the product spots. This indicated that there still existed some impurities, most likely the starting reagent, which was affecting the movement of the compounds through the solvent, petroleum
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.
Specific heat capacity of aqueous solution (taken as water = 4.18 J.g-1.K-1). T = Temperature change (oK). We can thus determine the enthalpy changes of reaction 1 and reaction 2 using the mean (14) of the data obtained. Reaction 1: H = 50 x 4.18 x -2.12.
From looking at the results I can conclude that when the pH was 3 and
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 The purpose of this experiment was to investigate the relationship between thermal energy and chemical reactions. A calorimeter is a metal container that is insulated for the purpose of conservation during a chemical process. In the calorimeter, a stirring rod and a thermometer place to keep track of the heat changes occurring during the experiment. Calorimetry was used in the experiments to measure the absorbed heat in a chemical process.
If the sample is a pure solid it has a sharp mp because of the small temperature range. The new Melt-Temp apparatus was used in this experiment to measure mps. For this apparatus, the capillary tube with the sample is inserted from the side and warmed quickly until it reaches the set plateau.
To control the rates of chemical reactions is imperative to the continued existence of our species. Controlled chemical reactions allow us to move forward in society, constantly. We find new ways to provide light and heat our homes, cook our food, and pursue in crafts that benefit our society. There are, however, just as there are advantages, disadvantages to the efficiency of controlling the rate of reactions, which in some cases can be fatal to our scientific development and progression. The growth of humankind necessitates that we must be able to control the rate of chemical reactions.
On further cooling the χT curve shows a sudden increase to 1.23 cm3.K.mol-1 at T=21 K followed by a sharp decrease down to 0.71 cm3.K.mol-1 at 5 K. The χT maximum de...