N Butyl Bromide Synthesis Essay

Exp. 2 butyl bromide 1 Experiment 2 Preparation of N-Butyl Bromide (1-Bromobutane)Introduction: Alkyl halides are very useful intermediates in organic syntheses. The most common syntheticpreparation of alky halides is the replacement of the OH group of an alcohol by a halogen. Displacement of a hydroxyl group by halide ion is successful only in the presence of a strongacid. The acid protonates the alcohol to create a suitable leaving group, water, for the SN2 reaction. ROH + HX » R+OH2 + X XG + R+OH2 → X...R...OH2 → XR + H2O If this displacement reaction is attempted in the absence of an acid it is unsuccessful becauseleaving group would be a hydroxide ion which is a poor leaving group and a strong base. XG + ROH → [X...R...OH]G → X–R + OHG (no reaction) The reaction carried out with n-Butanol and hydrogen bromide is relatively slow. Instead sulfuricacid is used to supply the protons more effectively and NaBr is used to supply the bromide ions. In yourreport, show the mechanism of reaction of n-butanol with sulfuric acid and NaBr. (Do not use the abovegeneral reaction!).Procedure: Reflux Condenser Water Out to sink In a 250 ml round bottom flask place 18.0 g ofsodium bromide and 20 ml of water and add 12.5 ml of Connect condenser with ruber hosen-butanol (density = 0.81). While cooling the mixture in Water Inan ice bath, carefully add 15 ml of conc. sulphuric acid(18 M) in small portions (~2 ml each) swirling the Connect to tap carefullysolution after each addition and cooling in ice. Add two and adjust flow to giveboileezers. The flask containing the reaction mixture isnow incorporated into a reflux assembly. (see diagram) a gentle flow.After setting it up, ask a TA to check it out before you 250-mL Conical vialbegin heating. Note concentrated H2SO4 is verycorrosive. Boiling chipsUse a bit of grease on the ground glass joints to prevent Reflux Assemblythem from sticking together permanently.Chem 266LSteven Forsey


Exp. 2 butyl bromide 2 Boil the mixture well by heating the flask with a Bunsen flame for 30 minutes. (The reactionmixture will turn yellowish, brownish or black!). Allow the reaction mixture to cool down for about 3minutes. Remove the condenser and arrange the flask for distillation. To the end of the condenser isattached a receiver adapter which leads into a 50 ml Erlenmeyer flask containing 10 ml of water. Thereceiving flask itself is cooled with a bath of ice and water. Thermometer (note position of the bulb)Screw cap Screw cap with teflon ring washer Clamp Reflux Condenser Water Out to sink Water In Connect to tap carefully and adjust flow to give a gentle flow. Boiling chips Ice water mixture to reduce evaporation of the distillate Distillation Assembly Heat the flask strongly so that liquid distils steadily. Oily drops should appear in the bottom ofthe receiver. Continue the distillation until no more oil drops distil into the water. In order to determine when to stop, make the following test. Remove the Erlenmeyer and place atest tube containing 2-3 mL of water over the end of the adapter. If no oily drops collect at the bottom ofthe test tube within a few minutes, the distillation is complete. Also, foaming of the liquid in thedistillation flask is a sign that only water is distilling now and your product is already distilled over. Discard the residue from distillation flask into the waste container at the front sink. Do notChem 266LSteven Forsey


Exp. 2 butyl bromide 3throw the aqueous waste into the organic acetone waste containers!!!!!!!!!!!!!! Pour the distillation from the Erlenmeyer flask into a separatory funnel and draw off the lower n-butyl bromide layer into a clean flask. Keep the aqueous (upper) layer aside and at the end of theexperiment through the waste into the aqueous waste container in the front sink). Return the n-butylbromide layer into the separatory funnel and shake well with a roughly equal volume of 10% aqueoussolution of sodium carbonate. (Why do you do this?) Carefully withdraw the n-butyl bromide into a clean dry, 50 ml size Erlenmeyer anhydrous flask.Add pellets of CaCl2 until the liquid is clear and CaCl2 no longer clumps together. (Usually, about half ateaspoon of CaCl2 is sufficient). Allow to stand for 5 minutes with occasional swirling to help absorptionof any residual H2O by CaCl2. Clean and dry (using a heat gun) the Claisen head, condenser, receiver adapter, 50 ml size round-bottom flask and a 50 ml size Erlenmeyer flask. Wipe the thermometer dry with a paper towel. Decant the n-butyl bromide into the clean dry 50 ml round-bottomed flask; clamp the flask onto arod-stand in the fume hood. Set up a distillation assembly using all the dried equipment and use the dry50 ml Erlenmeyer flask as the receiver. Distil the n-butyl bromide using a Bunsen burner and record the temperature of the thermometerwhen its reading has stabilized (usually halfway through the distillation). This temperature is the boilingpoint of the n-butyl bromide and it must be reported in your lab write-up. When the distillation iscomplete, transfer the product, using a Pasteur pipette, into a pre-weighed vial and weigh it again. Reportthe mass of your product and the percentage yield. Keep the product vial tightly capped and labelled withboth partner’s names. (Do not move it out of the laboratory).Submit the whole product vial with your report.Questions:1. In the following reactions indicate which compounds are Lewis acids and bases on both sides of the arrows. Also state which way the equilibrium will be shifted i.e. to the right or left. CH3CH2ONa + CH3CH2CH2I » CH3CH2CH2OCH2CH3 + NaI CH3CH2NH3+ + I - » NH3 + CH3CH2-I NaCN + CH3Br » CH3CN + NaBr CH3CO2CH3 + NaBr » CH3CO2Na + CH3Br CH3CH2OH + NaBr » CH3CH2Br + NaOHChem 266LSteven Forsey


Exp. 2 butyl bromide 42. Predict the product by using arrows to show the flow of electrons for the following SN2 reactions. a) CH3CH2Br + CH3 O- K+ b) H C C Na+ + CH3CH2CH2CH2 Cl c) (CH3)2CH CH2 Br + excess NH3 d) CH3CH2I + NaCN e) 1-chloropentane + NaI O f) CH3CH2S- Na+ + H3C O S CH3 OChem 266LSteven Forsey


Exp. 2 butyl bromide 5Mol Wt (g/mol) n-butanol Prelab H2SO4 n-butyl bromide Amount used 74.12 98.08 137.03density (g/mL) Fill in the chart --- Conc. (M) 0.810 NaBr 1.84 1.276 moles --- 102.90 18.0 --- --- ---What is the limiting reagent? What is the theoretical yield? Flow Chart.TA Signature : ________________________________________ ___________Date:Chem 266LSteven Forsey


Exp. 2 butyl bromide 6Marking Scheme MarkSection 4.5 3.0Introduction and Theory 3.0Results and Observations 1.0Discussion and Conclusions 0.5Quality of Product 6.0References 2.0Questions 20.0PrelabChem 266LSteven Forsey


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The SN2 reaction-Preparation of n-butyl bromide |
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Name: Aasefa Shaikh
Date: Mon Sept. 26, 2011
Subject: Chem 3000- Organic
Professor: Arturo Orellana
TA: George Achonduh

Name: Aasefa Shaikh
Date: Mon Sept. 26, 2011
Subject: Chem 3000- Organic
Professor: Arturo Orellana
TA: George Achonduh

Abstract

The formation of n-butyl bromide from 1-butanol and sodium bromide was observed under SN2 conditions. It was observed that the bromine anion, a strong nucleophile, was able to attack the protonated alcohol and displace water, which serves as a better leaving group than the hydroxide ion. The primary structure of 1- butanol allowed the bromide anion to a backside attack which led to a transition state, the rate determining step, followed by an inversion of the product, n-butyl bromide. The mass of the product obtained was 6.92 grams, giving only 33.7% percent yield.

Introduction
Nucelophilic substitutions are chemical reactions in which an electron rich nucleophile attacks the electron poor electrophile1. There are two classes of nucelophilic reactions – SN1, and SN2. The SN1 reaction is a 2 step, uni-molecular reaction, which is independent of the nucleophile. It requires a highly substituted electrophile since there is a formation of a carbocation in its rate determining step, good polar protic solvents which stabilize the carbocation and a good leaving group1. On the other hand, a SN2 reaction is a concerted, bimolecular reaction which has one slow, transition state1. Its dependence on the nucleophile requires that the nucleophile be electron rich so that it is able to attack and displace the leaving group. In addition, the reaction requires primary electrophiles and primary nucleophiles, which allow a backside attack to occur without causing steric hindrance4. The backside attack promotes inversion of the product.
Alkyl halides (R-X) are chemical compounds, which have a halogen atom in the position of hydrogen (H) 1....

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