Hydrolysis of Phenyl Benzoate and Preparation of Cyclohexanol from Cyclohexene - Lab Report Example

Experiment Hydrolysis of Phenyl Benzoate Yield of Phenol: Weight = 0.75 g %Yield = 22.3% Yield of Benzoic acid: Weight 49 g %Yield = 34.6% On work-up, why is the crude product (in alkaline solution) acidified and then re-basified to extract phenol, rather than by directly extracting phenol by addition of water & diethyl ether to the crude product? Your answer should include reference to the pKa values of phenol and benzoic acid. During hydrolysis of phenyl benzoate, acidic and basic conditions are used which might convert the hydrolysed phenol with a pKa value of 9.95 and benzoic acid with a pKa value of 4.2 into sodium phenoxide and sodium benzoate. The first acidic treatment converts these salts back to phenol and benzoic acid form (KHAN, ISMAIL & YUSOFF, 2001). The second basic treatment is important for separation if basifying agent is strong e.g. NaOH. Thus, both treatments are converted to their salt forms which are water soluble but if a mild base is used e.g. Na2CO3 then it selectively reacts with strong acid i.e. benzoic acid leaving phenol as such. Now extracting phenol with water and diethyl ether transfers benzoic salt form to water layer and phenol stays in diethyl ether layer. Though separation is not 100% but crude product can be purified to some extent. Define the term partition coefficient, and explain why it is not necessary to calculate the partition coefficient (distribution coefficent) for the extraction in this experiment. Partition can be described as the division of anything into two halves with a clear cut boundary. If we add a solute X (solid or liquid) to a mixture of two immiscible liquids A & B, then the solute will share out itself between the two immiscible liquids in accordance with the Partition Law. The Partition Law can be stated as: that a solute (solid or a liquid) which is soluble in two immiscible solvents will distribute itself between them in such a way that the ratio of the concentrations of the two solvents is a constant at fixed temperature (ZHAO, WANG & ZHU, 2006). Now take in account the following equilibrium: Solute Xsolvent A ↔ Solute XsolventB Kpc = [Solute Xsolvent A] / [Solute XsolventB] Kpc = partition coefficient Kpc has no unit and it depends upon temperature with a change in its value with the changing temperature. It is useful in finding out how much solvent we need in order to extract a minimum amount of solute from one solvent into another (MIRONOWICZ, AGNIESZKA; AGRICULTURAL UNIVERSITY OF WROCŁAW, JAROSZ, BOGDAN; AGRICULTURAL UNIVERSITY OF WROCŁAW, & SIEWIŃSKI, ANTONI; AGRICULTURAL UNIVERSITY OF WROCŁAW. n.d.). . Considering the case in which the hydrolysis of phenyl benzoate, the liquid-liquid extraction is utilized. This is also known as the solvent partitioning or the solvent extraction. In this method, compounds are separated on the basis of their solubilties in immiscible liquids. These are usually organic solvents and water. This extraction method is a widely used technique that is utilised in laboratories. Here, this method is performed by using a separating funnel. This process is commonly performed subsequent to a chemical reaction as a part of the work up (PIRINCCIOGLU & WILLIAMS, 1998). Partitioning is a word that is used usually as an explanation of the physical and chemical procedures that are a part of the liquid- liquid extraction. When the word solvent extraction is used, it means that the partitioning of a substance form a mixture is performed after dissolving the compound in a solvent. Using this, a soluble compound is separated from not only an insoluble compound but also from a complex atmosphere. If the molecules involved in this extraction are large molecule weighed the technique can be done very easily. However, if the molecules are small organic molecules, they will tend to develop a slight amount of tendency towards the aqueous layer and thus will be difficult to separate (MACKAY, DURST, LONGO & KNIER, 1989). This can be explained as: In the procedure mentioned above, from the two phases, one is completely soluble in the organic layer while the other is soluble in the aqueous layer (TOBEY, 1959). Therefore, the calculation of the co-efficient (K) is very important. Partition co-efficient is calculated by considering the organic compounds etc. Experiment 2: Preparation of Cyclohexanol from Cyclohexene Yield of Cyclohexene: Weight = 1.412g %Yield = Boiling point = 120 oC . List and assign the principle stretching vibrations observable in your IR spectrum of cyclohexanol Unambiguous vibrations in case of the Infrared (IR) Spectra means vibrations which are clear, frequent and easily appearing in the spectra. In the spectrum of cyclohexane, the following peaks are important: C=C peaks CH peak CH peak of alkenes These peaks can be seen on the spectrum overpage Explain in words why hydroboration leads to anti-Markovnikov addition of hydrogen whereas most electrophilic additions to alkenes result in Markovnikov addition. Hydroboration – oxidation reactions are a very important part of chemistry. It consists of an organic reaction comprising of the conversion of an alkene into a neutral alcohol through adding water aover the double bond. Cis stereochemistry is created when syn addition which is the same side addition of hydroxyl and hydrogen groups, is added in hydrogen (H) and hydroxyl (OH-) (KUZNIARSKA-BIERNACKA, BIERNACKI, MAGALHAES, FONSECA & NEVES, 2011). However, Markovnikov’s rule in organic chemistry states otherwise. It is stated that when protic acid HX is added to alkenes, the acid Hydrogen (H) has more affinity for carbon and is attached by default. Moreover, halide (X) has more ore affinity for the atoms of carbon which is in addition attached to the atoms having more alkyl substituents. Although, it can be stated further that H which is the hydrogen atom is added to the carbon having higher count of hydrogen atoms while, the halide (X) component is added to the smaller count of hydrogen (LI, CHEN, PO-LOCK & KUTAL, 2003).. There are certain chemical reactions that follow mechanisms that avoid the carbonation intermediate and may react through other mechanisms that are regioselective, against what Markovnikovs rule predicts, such as free radical addition. Such reactions are said to be anti-Markovnikov, since the halogen adds to the less substituted carbon, exactly the opposite of Markovnikov reaction. Now the question arises that it happens, the answer to the question lie in the first step of hydroboration. In the first step, borane (BH3) adds to the double bond, and transfers one of the hydrogen atoms to the carbon next to the one that becomes bonded to the boron. This hydroboration is repeated two additional times, sequentially reacting with each B–H bond so that three alkenes add to each BH3. The resulting product trialkylborane is treated with hydrogen peroxide in the second step (MADON, OCONNELL & BOUDART, 1978). This process replaces the B-C bonds with HO-C bonds. The boron reagent is converted to boric aid. Having the knowledge, that the group containing the boron will be replaced by a hydroxyl group, it can be seen that the initial hydroboration step translates the regioselectivity. Hydroboration continued in antimarkovnikov manner. The reaction sequence is also stereoselective, giving syn addition (on the same side of the alkene): the hydroboration is syn-selective and the oxidation replaces the boron with hydroxyl having the same geometric position, Until all hydrogens attached to boron have been transferred away, the boron group BH2 will continue adding to more alkenes. This means that one mole of hydroborane will undergo the reaction with three moles of alkenes (KOPECKY, FILBY, MUMFORD, LOCKWOOD & DING, 1975). Sketch the 1H NMR and 13C NMR spectra you would expect to observe for cyclohexene, assigning the signals where possible. In what ways would you expect the 13C NMR spectrum of the product (cyclohexanol) to differ from that of cyclohexene? The C 13 NMR spectra for the cyclohexene will be as follows; Th H1 NMR spectra for cyclohexene will b as follows; Now the C13 NMR spectra for cyclohexanol is as follows; The difference is evident from the peaks i.e. the appearance of the C-O peak around 60-65 ppm in case of cyclohexanol and that of the sp2 hybridised C-H bond at approximately 120 ppm in case of cyclohexene. Draw the full mechanism and identify the product from hydroboration of 2-methylpropene followed by reaction with hydrogen peroxide (as carried out in this experiment). Experiment 3: Diels-Alder reaction of Maleic anhydride with Cyclopentadiene Yield of Maleic anhydride-Cyclopentadiene adduct: Weight = 0.68g %Yield = 6.5% The Diels-Alder reaction is usually described as a [4πs + 2πs] cycloaddition. Explain the meaning of all the terms in the square brackets. Cycloaddition is termed as the type of chemical reaction two separate molecules, with each one of the molecules containing at least one pi bond, undergo a reaction with each other resulting in the formation of a cyclic compound (ARRIETA, COSSÍO & LECEA, 2001. In the process that occurs, each molecule loses a pi bond and two new sigma bonds are formed as a result. In a Cycloaddition reaction, a concentrated combination of two π electron systems takes place. These electron systems form a ring of atoms in which each of them have two new σ bonds and two fewer π bonds (KARODIA, NAZIRA, & YU, JIANGUO, n.d.). . The numbers of π-electrons that participate in each component are written in brackets preceding the name. Similarly, the reorganization of electrons is explained by a cycle of curved arrows. Every cycle of curved arrows represents the movement of a pair of electrons. One of the most common cycloadditon reactions is the Diels-Alder reaction. This reaction is also referred to as the [4π+2π] cyclisation reaction. The two reactions that take part in this reaction are termed as the dienophile and the diene. This reaction, being an example of the pericyclic reaction, occurs via a single transition cyclic state which involves no intermediates during the progress of the reaction. The Diels–Alder reaction is administered by the orbital symmetry considerations (PAVIA, 2007). . This involves the [4πS+2πS] Cycloaddition reflecting the fact that the reaction proceeds through a suprafacial-suprafacial interaction occurring between a a 4π electron system with a 2π electron system, an interaction that is thermally allowed as a 4n+2 cycloaddition. The reaction between maleic anhydride and cyclopentadiene forms an endo-adduct (the kinetic product) at low temperatures or an exo-adduct (the thermodynamic product) at high temperatures. Explain the meaning of all the underlined terms, drawing the structures of both adducts. Sketch an energy profile for the two reactions (on the same energy plot) When a dienophile, which can either be an alkyne or alkene, undergoes [4+2] cycloaddition with a conjugated diene, the reaction that occurs is termed as the Diels-Alder reaction. In this reaction, the 4π electrons of the diene undergo an electrocyclic reaction with the 2π electrons of the dienophile. The force due to which the above mentioned reaction takes place is provided by the formation if the new σ—bonds which are more energetically stable as compared to the π-bonds. In the case when the alkynyl dienophile is not sterically hindered, the initial adduct can still undergo the reaction. Furthermore, not only the dienophile but also the diene can be made a subject of substitution with certain cumulated double bonds. An example of this is the substituted allenes with its simplicity of operation as well as broad simplicity. In any instance when the Dier-Alder reaction takes place between cyclic dienes, two stereo isomeric forms are formed as a result. This occurs due to temperature difference. Since the factor of temperature difference affects the end products of the reaction, the end product formed at room temperature is termed as an endo product or the kinetic product while the product formed at higher temperature is referred to as the exo or the thermodynamic product. Thus, these stereo products can also be termed as the exo adduct and endo adduct. For the above reaction, the energy profile is as follows: The Diels-Alder reaction between cyclopentadiene and maleic anhydride results in the formation of two isomeric products. When the reaction occurs at room temperature, the kinetic reaction controls exists and the endo isomer 2 is formed as the main end product. However, if the reaction proceeds at 81°C, the chemical equilibrium alters itself and the exo isomer 1 is formed, which is thermodynamically more stable (YU & KARODIA, 2009). . The endo product is favoured by the orbital overlap during the transition state and thus is less stable. The exo product, however, is more stable due to the low degree of steric congestion. In the forementioned case, not only the dienophile but also the diene possess stereochemistry. Albeit, four stereogenic centres prevail, only two diastereoisomers can be formed. These are termed as the exo and endo diastereoisomers (WILLIAMSON, 2006).  REFERENCES Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form ARRIETA A, COSSÍO FP, & LECEA B. (2001). 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(2009). Novel chiral phosphonium ionic liquids as solvents and catalysts for cycloadditions investigation of the Diels-Alder reaction of a series of dienes and dienophiles in novel chiral phosphonium ionic liquids. University of Bradford. ZHAO, Y., WANG, G., LI, W., & ZHU, Z. L. (2006). Determination of reaction mechanism and rate constants of alkaline hydrolysis of phenyl benzoate in ethanol€́“water medium by nonlinear least squares regression. CHEMOMETRICS AND INTELLIGENT LABORATORY SYSTEMS. 82, 193-199. Read More