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Formal Lab Report: Bromination of Trans-Cinnamic Acid

Name: Samrin Islam Student number: 19404367 Unit: Organic Chemistry 300876 Tutors name: Dr Christopher Gordon

Aim: To conduct the experiment of an addition bromination reaction of Trans-cinnamic acid to produce 2,3 dibromo-3-phenylpropanoic acid using IR spectral analysis to the show the bond vibration.

Introduction: A Bromination reaction is the process in which the bromine free radical is introduced into a molecule, this happens when the benzene ring undergoes electrophilic aromatic substitution transforming the structure to potentially result in a mixture of Diastereoisomers. The experiment conducted was Trans cinnamic acid to produce 2,3 dibromo-3-phenylpropanoic acid. The nature of this experiment can be seen a trans-cinnamic acid is a carboxylic acid which has high solubility in ether and thus a lower solubility in water when a good oxidizing agent such as bromide is added it acts as a free radical and attacks the place of most electronegativity (Pubchem, 2015) The Pi double bond is broken to form a single sigma bond thus allowing the bromide atoms to attach itself to the hydrocarbon chain to form a 2,3-dibromo-3-phenylpropanoic acid. A bromination reaction is important to provide the background understanding of a “syn and anti-addition’ this is where in which two substituents can be added to a double or triple bond) resulting in a decrease in bond order but an increase in number of substituents. (Khan academy ,2018) Method Add 2 ml of dichloromethane and 10% Bromide solution into the condenser. Second set up apparatus; using dropping funnel, vacuum tubing and a vacuum distilling adapter, lastly placing a magnetic stirrer into the condenser. Set timer for the reaction to heat for 30 minutes. When the product begins to precipitate light yellow colour, continue adding 10% Bromide in dichloromethane solution using a dropper- until light orange colour persists. Cool the flask at room temperature for 5 minutes to allow crystallisation to form. Set timer for 10 minutes to cool further in an ice bath. Set up apparatus for vacuum filtration; Buchner funnel, filter paper, vacuum tubing. Pour remaining 10% Bromide solution into the condenser and swirl in a clockwise motion to readily dissolve the solid crystals Wash the condenser 3 times with 2 ml ice cold Dichloromethane using a pipette. Slowly pour half the solution, swirl again and pour the solid product in the middle of the filter paper. Obtain the product using a spatula and transfer the yield to a watch glass. Measure the product and the filter paper using an electronic balance. Finally, record the yield and melting point of the final product. Also record the IR spectrum of the final product and analyse the data. The mechanism of this reaction shows bromide molecules being positive and therefore the negative double bond is attacking the bromide shifting the bond to make is neutral and slightly negative charge thus having a gain of electrons Becoming more stable. However, the positive charged bromine is an intermediate between two carbons; phenyl group and wedge hydrogen. The electronegative pulling the electrons from the bond of phenyl and hydrogen pulls the electrons towards them. The negative radical bromine is attracted to the phenyl group and attacks the carbon to form a formal bond. The final product shows

the bromine situated on trans sides of the molecule. ( (Daniella, M , Salono, 2017)

Pre Work table for results and calculations Compound Trans-cinnamic acid Dichloromethane 10% Bromide solution 2,3-dibromo phenylpropanoic acid

Molar mass (g/mol) 148.16 84.93 159.8 307.97

Melting point (degree Celsius) 133 -96.7 -72 200

Reference: Lehmahs J.W, 2017, ‘Operation Organic Chemistry: A problem solving Approach to Laboratory course, 3rd ed; Prentice Hall, Upper Saddle River, Nj 1999; pp-175-181. Accessed 10/03/19 Results The experiment conducted of experiment showed the formation of precipitation within the condenser where colour changed from a dark red- brown solution to a light yellow to almost colourless, this was because once added to an alkene the dilute solution rapidly begins to decolourise. In this instance, bromide is the acting as the oxidising agent where trans-cinnamic acid is being oxidised, allowing the pi double bonds to be broken to form the product which has been reduced to a dibromoalkane. The number of reagents in total used was 15 ml of dichloromethane and 4.5 ml of the bromine solution, the final product once filtrated was a white crystal-like powder which had an observed experimental melting point of 190 degree Celsius which was close the reported melting point of 200 Celsius. The limiting reagent can be determined by the equal number of trans cinnamic acid and dibromo alkane solution reacted within the condenser, as the reaction proceeds the trans cinnamic acid was consumed first to produce, 1 mole of 2,3 dibromo alkane to achieve a 1:1 ratio. Therefore, in this reaction trans cinnamic acid is the limiting agent and is used up first in the reaction.

The product of 2-dibromide wave has a frequency of 2981.3, with a range of 3100-3000 this is due to the first carbon which is attached to the aromatics ring and 2 trans molecules of bromine. The

second chiral carbon is attached to a single bonded aliphatic of frequency range of 3000-2850. This can be contrasted to the starting material in only evaluated in the diagnostic region having a starting carbon range of 1600-1500. The second chiral carbon is attached to the hydroxide group having a frequency of 1680-1600. Additionally, the tertiary carbon is attached to the doubled bonded oxygen giving a range of 1750-1735.

Standard Spectroscopy of Trans -cinnamic acid

Practical spectroscopy

Calculations of theoretical Yield

Calculations Weight (grams) Product with watch glass

50.370

Watch glass

48.9706

Product remaining on the filter paper

0.2487

Discussion When conducting the experiment there was a slight variation in the melting point as our IR spectrum was compared to the standard of Trans cinnamic acid and showed a significant difference in the peak waves. Most of the reaction was broad peaks to indicate a stronger bond strength using intermolecular forces such hydrogen bonding. The absorption of energy increases the band width having higher concentration as well more stretching of the double bonded oxygen. The product was a mixture with both amounts of pure and impure product, the IR spectrum was unreliable, and the wave numbers were not attained however we can estimate the starting material and product which can be referred to the standard spectrum of trans- cinnamic acid. Through this we can assume the final product had a mixture of 2 carboxylic acid which had halve the actual yield and percentage yield to reach the final value. The melting point was accurate, the recorded value was 200 Celsius which was compared to the experimental melting point achieved of 195 Celsius as the plateau temperature. The improvements and accuracy of the calculations were precise although the IR spectrum does not represent our result due to error of transmission. The functional groups in the dibromide is the ester bond C=O which is singlet peak ranging at bond vibration of 1750-1735 cm. This could also mean 1750cm – 1715 is a 5- membered ring ketones or saturated esters. The conjugated aromatics at 1600-1500 is located at 1600 which is show the double bond of trans cinnamic acid. The organic bond that can be identified is at 1225 which can be an alcohol or ether having a frequency range of 1260-1000 cm-1. This is positioned in the diagnostic region of trans-cinnamic acid containing the double bonded alkene at 1680-1600. The secondary carbons therefore have higher peak compared to the dibromide region. The other functional group is hydroxide group at 3026.07 which has the range of a broad peak 3550-3200 cm this is a very minor peak in the spectrum, this frequency is an aliphatic C-H alkane bond group. The calculated yield percentage was 51.7% therefore there could’ve been excess amount of impurity gained in the final product. Through this my partner and I can assume that we have a mistake when conducting the method. An error that occurred was the when pouring the dichloromethane my partner and I used too much cold solvent, instead the product had a greater concentration of the dichloromethane rather than the Tran cinnamic acid and bromide solution. Thus, the reaction was not complete, and a remaining amount of reagent was found in the final product. Another error which had had occurred was when vacuum filtering and the process of recrystallisation this was when the sample was not filtered enough as well as losing the product when washing with the Ice cold CH2Cl, leaving residue of the solute sample in the Buchner funnel and the round bottom flask. Thus, there was a loss of pure sample which was not heated completely in the round bottom flask. To check the final product purity retrieved from the filtrate can be the physical comparison of the pure standard as well as the determining the melting and boiling of the substance or other analytical methods such as using titration or gravimetry to test the purity. However, in this case the IR spectrum is a good analysis technique to recognize the reaction mechanisms as well as the presence of functional groups. To improve the procedure, of our bromination experiment I would work on the precision and accuracy to achieve a more valid and viable result such as decreasing the amount from 1 gram to 0.9 grams of trans cinnamic acid powder. As well as conduction more than one trial for the IR spectrum since our experiment had a slight hindrance on our final outcome. The stereochemistry is (S, R) of the trans cinnamic is the major Regio isomer and (R,S) is dibromide both the melting point of the molecules have high dipolarity and therefore increased amount melting and boiling point.

The prework for Laboratory 1 – Bromination of Alkene

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