SUBSTITUTION REACTION ANALYSIS OF
TERTIARY BUTYL ALCOHOL AND BROMOBENZENE
By
Ni Ketut Sepmiarni
Chemistry Education Department, FMIPA, UNDIKSHA
Udayana Street Singaraja, Bali
Emai: arnisepmiarni@yahoo.com
Abstract
The aim of the experiment was to identify the substitution reaction of tertiary butyl alcohol through nucleophilic reaction as well as the product and bromobenzene through electrophilic reaction as well as the product. The method used in this experiment was divided into two procedures namely nucleophilic substitution procedures and electrophilic substitution procedures. The tertiary butyl alcohol and Bromobenzene were prepared by the laboratory assistant as the subjects of this experiment. The object was the mechanism as well as the product of the substitution reaction. The mechanism and the product of this reaction were obtained by observing the physical and chemical properties appear during the treatment. The result of this experiment is nucleophilic reactions of tertiary butyl alcohol result tertiary-butyl-chloride with volume 3.8 mL by boiling point 50-51C and for electrophilic reaction of bromobenzene results p-bromonitrobenzene with mass 3.43 grams, percent purity 67.9% and error percentage of 32 %.
Key word: nucleophilic, electrophilic, substitution reaction
INTRODUCTION
Organic chemistry is the study of compounds that contain carbon. The element carbon that justifies living organisms are making it the basis of a whole branch of chemistry, whereas compounds that may contain any of the others elements (Frederick, 1995).
Saturated carbon compounds which have only tetrahedral hybridized carbon atoms normally undergo substitution reactions (www. chemguide. co.uk). There are two types of substitution reaction, one called nucleophilic substitution reaction and the second called electrophilic substitution reaction. The general reaction is as follows.
R-L + Nu- R- Nu + L-
Where R is the electrophile, Nu is the nucleophile, and L is the leaving group. For this reaction to be effective, the organic molecule must have a good leaving group, which can depart and stabilize the electron pair of its former bond to carbon. Good leaving groups are relatively stable anions (such as bromide or chloride ions (or, even better, neutral molecules like water or nitrogen). This is necessary because the reacting nucleophile, by definition, brings its own electron pair to bond formation. There are two specific types of mechanisms for the nucleophilic substitution: namely SN1 and SN2 reactions.
There are two kinds of nucleophilic namely negative (Nu:-) and neutral nucleophilic (Nu:). Negative nucleophilic has negative charge and non-bond electron pairs, examples are chloride ion (Cl-), carbonium ion (R - CH2:-), hydroxyl ion (OH-), etc. Neutral nucleophilic (Nu:) has non-bond electron pairs, examples are alcohol (R -OH), tioalcohol (R - SH), ether (R - O - R). both of nucleophilic reaction can be describe as follows:
Figure 1.Nucleophilic reaction
Second is electrophilic. Electrophilic reagent is a species which likes of electrons. There are two kinds of electrophilic reagent, namely positive (E+) and neutral electrophilic (E). Positive electrophilic is that the lack of two electrons and carry a positive charge, such as carbonium ions (R-CH2+), bromonuim ion (Br+), and nitronium ion (+NO2). The neutral electrophilic has six electrons in the outer shell and the lack of two electrons to achieve octet state, but not charged. Examples of neutral electrophilic are boron trifluoride (BF3), aluminum chloride (AlCl3), sulfur trioxide (SO3), and the ferry chloride (FeCl3). Both kinds of ions electrophilic can attack the substrate or electron-rich molecules to form new bonds.
Figure 2.Electrophilic reagent
Reaction of nucleophilic substitution is the reaction that occurs by changes an atom of compound by other atom. The example of nucleophilic substitution reaction is reaction of hydrolysis alkyl halide by alkali solution to form alcohol. Reaction as follows:
R - X + OH- ? R- OH + X-
Nucleophilic substitution comes in two reaction types, namely bimolecular nucleophilic substitution (SN2) and unimolecular nucleophilic substitution (SN1). Nucleophilic substitution reaction depends on concentration of substrate and express by SN2. Reaction equation as follows:
Rate reaction= k[substrate] [nucleophile]
Then, unimolecular nucleophilic substitution (SN1) is only depend on the concentration of substrate. Rate equation as folows:
Rate reaction = k [substrate]
SN1 reaction consists of two steps. First step involves of ionization alkyl halide to becomes carbonium ion and it react by slowly. Second steps involve of rapidly nucleophilic attack toward carbonium ion. Electrophilic substitution is a very important part of organic chemistry, because the introduction of many functional groups into an aromatic ring is accomplished in this manner.
In general, benzene and other aromatic compounds are not experienced as alkene addition reactions, but have substitution reactions (Allen, 2004).
Figure 3.Substitution reaction
This substitution involves attack by the electrophilic (E+) on the benzene ring by eliminating H+. Therefore, this reaction is called electrophilic substitution reactions.
Figure 4.Electrophilic substitution
In a substitution reaction mechanism is used up Kekul￩ formulas for benzene in order to trace the ? electrons. Benzene ring with the ? electron cloud is very rich in electrons, making it very easy to form a new bond with the electrophilic. The stage of electrophilic substitution reaction mechanism as follows:
First steps, electrophilic reactant illustrated by E-Nu, very easy to dissociate spontaneously or with acid catalysts.
Second steps, ? complex formation between the electrophilic with the benzene ring. Electrophilic is not directly tied to one position on the ring ? complex because there are formations (Allen, 2004).
Figure 5.Formation of electrophilic with the benzene ring
Third steps, H+ elimination from the ? complexes by alkaline substituted benzene yield. Reaction as follows:
Figure 6.the ?-complexes by alkaline substituted
Reaction of an aromatic compound such as benzene with a mixture of concentrated sulfuric and nitric acids leads to the introduction of a nitro group into the aromatic ring. This transformation is an example of an electrophilic aromatic substitution.
Figure 7.Example of electrophilic substitution
The mixture of nitric acid and sulfuric acid are stronger reagent nitro. In an environment of sulfuric acid, nitric acid become proton and then become reactive. The reaction as follows:
HNO3 + H2SO4 ? H2NO3+ + HSO4-
H2NO3+ + H2SO4 ? NO2++ H3O+ + HSO4-
The reaction mechanism that occurs in the process of formation of neutrophil group NO2+ (nitronium ion) is like bellow:
Figure 8.Formation of neutrophile group NO2+
Second, nitronium salts are known become ring aromatic nitro in the same way as a mixture of nitric acid and sulfuric acid. Although then it nitronium salts have been used to nitro, it is potentially explosive (Allen, 2004).
Last, the rate of nitro depends on the concentration of NO2+ , The next group will be attacked by the electrophilic bromobenzene thus producing three different types of products namely bromonitro benzene o-, m-bromonitrobenzene, and p-nitrobenzene which has a different percentage is as follows.
Figure 9.The Production of bromonitrobenzene
If electrophilic enter to the benzene ring that was substitute by substituent, for example S so the second substitution (by E) will have some probability of positions (2, 3,4,5,6 positions).
Figure 10. Probability position of benzene ring
The second substitution of the benzene was dependent on the first substituent. Substituted benzene can be more easily substituted than benzene, but can also more difficult. Example: benzene amino reacts faster than benzene. Nitrobenzene is very slow to react and require high temperatures.
NH2 group is as clusters of activation, leading to more open ring to further substitution. NO2 group was a group deactivation, leading to more closed ring to substitution. Besides the differences in rate of reaction, the position of the second attack was also different. NH2 group at the ortho position andtheNO2 group in meta position. From here, the technical term referring the ortho-and meta directors. The following table substituent effect toward first second substituent.
Table 1. Effect first substituent toward second substituent.
Orto-para direction Meta direction
For electronic reasons, attack at either the orto or the para position occurs with a lower energy of activation than for attack at the meta position. This was occur because an electron pair on the bromine atom in the intermediate produced by attack at either of this position may be delocalized, providing additional resonance stabilization of the intermediate (Wade, 2010). The additional stabilization by bromine was not provided in the intermediate resulting from meta attack.
Figure 11.The additional stabilization by bromine
Second position on position Ortho, Para
In general, the first group or substituent that can donate electrons to resonate and add stabilization will enter the positions ortho and para. All steering is ortho and the electron donor, either because of resonance or because of the influence of induction. For example Chlorobenzene containing ortho steering, the then Chlorobenzene can be nitrated at the ortho and the few meta substitution is formed. This occurs because the resonance structures of intermediates that substitution will occur at the ortho position, and not on the meta position.
Figure 12.Ortho substitution
Figure 13.Para substitution
Meta substituent's that are exciting electrons cannot donate electrons by resonance. Each resonance ring reduces the electron density thus less attractive to the electrophilic. In other words, Meta direct or cannot activate the ring. Resonance structure of substances including the following:
Figure 14. Meta substitution
Carbonium intermediates for Meta substitution has a higher energy. Similarly, the transition state, therefore, Ea become high, the reaction is slow and thus less possible re
action (Wade, 2010).
METHOD
The experiment was conducted at Organic Chemistry Laboratory practice of Chemistry Education Department, Ganesha University of Education Singaraja on September 23th and 30th 2013 from 13.30 - 18.30 WITA.
Equipment and Materials
The experiment uses some equipment and materials for conducting the research. The equipment used are volumetric flask, spatula, statif and clamp, funnel, distillation equipment, beaker glass, graduated cylinder, test tube, test tube rack, watch glass, petri dish, drop pipette, round flask, thermometer, Claisen adaptor, leibig cooling, Erlenmeyer flask, electrical balance, capillary pipette, Bunsen burner, thiele, heater, metal block, holder, stirrer, and separatory funnel.
While the materials used are concentrated HCl, tertier buthyl alcohol, t-butanol, sodium bicarbonate, aquades, anhydrous substance, concentrated HNO3, concentrated H2SO4, ice, bromobenzene, ethanol 95%, and filter paper.
Procedure
There were some procedure that done. The procedure was divided into two part procedures namely nucleophilic substitution reaction procedure and electrophilic substitution procedure.
Nucleophilic procedures
First, five milliliters of concentrated HCl was cooled in steam bath then it was pour into separatory funnel. Second, 5 mL of tertiary buthyl alcohol were added drop by drop into separatory funnel and it was shaken. Third, after finishing with drop tertiary buthyl alcohol, it was shaken again approximately 20 minutes until all of alcohol exhausted. Fourth, the mixture was let until two layer formed.
Continuing by fifth step, the bottom layer as HCl was separated. Sixth, after finishing separated bottom layer, next the top layer was washed by using 5 mL of equates and then added by 10 mL of sodium bicarbonate. Seventh, the product resulted was dried by anhydrous substance (CuSO4.5H2O) then continued by distillation. Last, the distillate was collected at temperature between 49o - 52o as tertiary - buthyl - chloride and has nD 1.386 (Buku Ajar Praktikum Kimia Organik).
Electrophilic Procedures
First, 5 mL of concentrated nitric acid (HNO3) was mixed by 5 mL of sulfuric acid (H2SO4) in round flask then cooled in ice water steam. Second, the round flask was connected with Claisen adaptor, thermometer, and held by using statif and clamp. Third, 0.025 mole bromobenzene was added through tip of cooler in 15 minutes then it was shaken. The temperature was keep at 50o - 55oC. After addition was completed, the fourth step, the mixture was let bellow 50oC in approximately 30 minutes. Fifth, the flask was cooled in room temperature, after that the mixture was poured unto beaker glass that contain 50 mL of ice water. Sixth, the nitro-bromobenzene was filtered then the crystal was washed by using cold water, continued by dried it in filter paper.
Seventh, the crystal was moved into Erlenmeyer 100 mL and added by ethanol 95%. Eighth, the mixture was heated until all crystal dissolved. Ninth, the mixture was let until cold in room temperature. Then, the crystal of 4 - bromonitrobenzene was separated by filtering. The filtrate was found (filtrate I). Tenth, the first crystal form was washed by using cold alcohol, the filtrate also found (filtrate II). Eleventh, both of filtrate was mixed and heated in water steam bath until the volume of filtrate is on third. It was waited until the room temperature obtained. Crystal II was washed by cold alcohol and dried. Crystal I and II was weight (Buku Ajar Praktikum Kimia Organik).
RESULT AND DISCUSSION
The volume of tertiary butyl chloride is 3.8 mL of colorless solution.
The mass of p- bromonitrobenzene obtained is 3.43 grams.
Table 2.Chemical Properties Analysis of the Crystal
Test Observation Decision
Smoke test White smoke was formed Aromatic compound is exist
Lassaigne test White precipitation formed Halogen element is exist
Red Blue test Blue Solution resulted Nitro group is exist
Nucleophilic substitution reaction
The aim of this experiment is making tertiary butyl chloride from tertiary butyl alcohol and chloride acid.
Look at the structure of substrate and solvent that was used, it is included of SN1 reaction. From substrate structure of tertiary butyl alcohol which is tertiary alkyl hydroxide and there is three alkyl groups. If this substrate is ionized, the carbonium ion that formed will stable because there is induction effect from three groups which bond. If carbonium ion that produced is more stable, while reaction is SN1 mechanism.
Hydrochloride acid was used as solvent in this experiment. HCl is polar solvent that easily to ionize and stabilize of ion produced so the reaction that occur suitable with SN1 mechanism. The formation of reaction mechanism tertiary butyl chloride as follows:
Figure 15.Tertiary butyl chloride formation.
Concentrated HCl was cooled in ice steam bath to increase the solubility from HCl gas, so little amount of HCl will evaporate and the product will be optimal. When HCl poured into separatory funnel and added by tertiary butyl alcohol gas pressure was arise from separatory funnel. This gas can be observed when stopper of separatory funnel was opened.
The excess of tertiary butyl alcohol was added and less gas produced. That's shows a lot of HCl was reacted. After all of tertiary butyl alcohol was added, the mixture was shake of ﾱ30 minutes. Optimal shaking process cause more effective collision, so a lot of product was produced. There were formed two layers, the bottom layer is HCl and the top layer is tertiary butyl chloride which can't certain of purity. Up and bottom layers is colorless solution.
After both of layer was separated, layer out is HCl and top layer is a product of the experiment. After separated, the top layer was washed by distilled water and sodium bicarbonate. Sodium bicarbonate solution has base properties. The purpose addition of this solution is neutralizing the acid that probably exists in top phase. When the top layer washed by sodium bicarbonate, there were formed two layers. It layers were separated, the top layer was collected. Because of the washing process was used water, tertiary butyl chloride contain of water. To remove the water, dried process by using of anhydrous substance was conducted. CuSO4.5H2O was used as anhydrous substance that has blue color.
Heating process was conducted to remove water in anhydrous substance until the substance is white color. After obtained white color of anhydrous substance, it substance added into tertiary butyl chloride. White color of anhydrous substance was changes into blue color again. It indicates tertiary butyl chloride contain of water. Addition of anhydrous substance was stopped when the mixture is not changes into blue color.
In this experiment, distillation was not conducted because the product resulted is not enough to conduct distillation.
Electrophilic substitution reaction
The aim of this experiment is the bromobenzenenitration reaction becomes 4-bromonitrobenzene by concentrated H2SO4 as catalyst. The first step is the formation of electrophilic from NO2+ by reacting concentrated nitric acid and concentrated sulphuric acid. It produced colorless mixture. The mechanism reaction as follows:
Figure 16.The reaction of electrophilic substitution.
The mixture was connected by Clausen adapter, thermometer and condenser. At the top of condenser was added by 0.025 mole of bromobenzene. The bromobenzene solution has density 1.496 g/L. The volume of bromobenzene used is 2.63 ml. the calculation is as follow:
mol= g/(Mr of bromobenzene )
0.025 mol= g/(157 g/mol)
g=3.925 g
?= m/v
1.496 g/cm^3= (3.925 g)/v
v=2.62 ml
During the addition of bromobenzene, the temperature was kept at 50-50ﾰC. Loosen the clamp to the flask and shake the flask vigorously and frequently during the addition. The temperature is the maximum temperature of the reaction between bromobenzene and electrophilic of NO2+. The reaction is conducted over 55ﾰC will be formed reddish brown NO2 gas that are toxic and dangerous. If the reaction is conducted at the temperature less than 50ﾰC so, the reaction will occur very slow and it is not optimum. In this step, we just kept the temperature less than 50ﾰC, which was 33ﾰC.
It was kept at this temperature made the reaction occur very slow and got the precipitate in long times, and also produced not too much precipitate. After finishing the substitution, the mixture contained of precipitate was poured into beaker glass that contained of ice water. The aim is to remove the impurities. The impurities from sulfuric and nitrate acid that dissolve in cold water while the bromonitrobenzene crystal that insoluble in water will not react with cold water. The bromobenzene crystal was filtered and washed by cold water. It was done to remove the impurities in the crystal. The precipitate is allowed to be dry in the filter paper.
After that, the dry crystals were added to the ethanol that has been preheated. Because it is difficult to dissolve the crystal added ethanol and heated. After a while the crystals were dissolved and two phases formed such as water and oil cannot dissolve each other. Such as oil droplets formed on the base of a beaker. Then, this solution was filtered in hot conditions. On filter paper obtained slightly yellow-colored crystals. These crystals are then dried using filter paper. Once dry then weighed and determined its melting point. Having weighed heavy crystal obtained was 3.43 grams.
In this experiment have been obtained crystals of 4-bromonitrobenzena. Initial substance which is bromobenzene, Br is a group deactivation or in other words a group which deactivates the benzene ring. Since the deactivation group, then second substituent should be entered in the meta position. However, exceptions to disable the halogen group but substituent two benzene rings can be directly entered in positions ortho and para. In this experiment the resulting product is actually two, namely o-and p-bromonitrobenzene. But the more products are p-bromonitrobenzena majority. This is because the reaction rate of carbon atom in position ortho, meta, and the different. Illustrations can be seen from the table below, and take into account is chlorobenzene.
Table 3. Rates of nitration at states on the benzene ring
Benzene ring
This is because bromobenzene and chlorobenzene is still in one class. Although, the actual value is certainly different but this data is only used to determine the cause of the bromonitrobenzene, a dominant position in the position rather than on the ortho position.
Based on the reaction rate value of each ring in chlorobenzene, can be seen that the product in the meta position will not be obtained to see the big reaction rate is 0, while in the ortho position and its products can be produced. Judging from the reaction rate of carbon atoms in para position is greater than the rate of reaction of the carbon atoms are ortho position. The greater value of C atom reaction rate will be faster than the products formed and in this position the product formed will be faster than in the ortho position. This will be a similar case with a dinitratebromobenzene. In addition to the speed of the reaction rate, there are other factors that influence the induction and resonance effects. The following general reaction formation of 4-bromo nitrobenzeneas is as follow:
Figure 17. 4-bromo nitrobenzene formation
Reaction mechanisms are as follows:
Figure 18. Establishment of electrophile (E+)
Figure 19. Attacks electrophile (E+)
Figure 20. Releasing H+
The equation and the mole ratio between p-bromobromobenzena nitrobenzene are same. So, the masses are theoretically equal to the mass bromobenzene
M = moles x Mr bromobenzena
= 0,025 mol x 202
= 5,05grams
Crystalline mass obtained = 3.43 grams
So, the percentage rendemen of p-bromonitrobenzena can be calculated following completion.
=
= 3.43/5.05 x 100 % = 67.9%
The percentage of error in this experiment can be calculated by
(teoritical crystal mass-result crystal mass )/(theorytical crystal mass)
= (5.05-3.43)/5.05 x 100%=32%
The error percentage was 32% may caused the mixture of bromobenzene and NO2+ not shaken well.
CONCLUSION
Based on the result and discussion can be concluded as follows.
Nucleophilic reactions of tertiary butyl alcohol result tertiary-butyl-chloride with volume 3.8 mL by boiling point 50o-51oC.
Electrophilic reaction of bromobenzene results p-bromonitrobenzene with mass 3.43 grams, percent purity 67.9 % and error percentage of 32 %.
ACKNOWLEDGEMENT
In writing this article, the author has of a lot of support, guidance and encouragement from many quarters. For this reason, the author respectfully thanks for Dr. I Nyoman Tika, M.Si as lecturer on the practicum, Ms. Dewi as lecturer assistant, Mr. Lasia as the laboratory assistant and also all member of RKBI'11 of chemistry class for the always good partners.
REFERENCES
Allen M, Scholfstall, and friends. 2004. Organic Chemistry Laboratory Experiment. New York: McGraw- Hill.
Betelheim, Frederick. 1995. Introduction to General, Organic, & Biochemistry. USA: Saunders College Publishing.
Bruice. 2013. Material Chapter 9 on www. chemguide. co.uk/pdf that access atSeptember 25th , 2013.
L.G.Wade, JR. 2010. Organic Chemistry Seventh Edition. USA: Pearson Educatin, Inc.
Suja, I Wayan, Frieda Nurlita. 2004. Buku Ajar Praktikum Kimia Organik. Singaraja: Jurusan Pendidikan Kimia IKIP Singaraja.
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