Preparation OF Adipic ACID FROM Cyclohexene PDF

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EXPERIMENT 4 PREPARATION OF ADIPIC ACID FROM CYCLOHEXENE NAME: KAGISO B SURNAME: MFANYANA ID NUMBER: 201301326 LAB DAY: MONDAY COURSE CODE: CHE334 TITTLE: PREPARATION OF ADIPIC ACID FROM CYCLOHEXENE AIM: To synthesize Adipic acid through oxidation of Cyclohexene with Potassium permanganate INTRODUCT...

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EXPERIMENT 4 PREPARATION OF ADIPIC ACID FROM CYCLOHEXENE

NAME: KAGISO B

SURNAME: MFANYANA

ID NUMBER: 201301326

LAB DAY: MONDAY

COURSE CODE: CHE334

TITTLE: PREPARATION OF ADIPIC ACID FROM CYCLOHEXENE AIM: To synthesize Adipic acid through oxidation of Cyclohexene with Potassium permanganate INTRODUCTION Alkenes can easily be oxidized by potassium permanganate and other oxidizing agents. What products form depend on the reaction conditions. At cold temperatures with low concentrations of oxidizing reagents, alkenes tend to form glycols.Because potassium permanganate, which is purple, is reduced to manganese dioxide, which is a brown precipitate, any water‐soluble compound that produces this color change when added to cold potassium permanganate must possess double or triple bonds. This reaction involves syn addition, leading to a cis‐glycol (a vicinal dihydroxy compound).When more concentrated solutions of potassium permanganate and higher temperatures are employed, the glycol is further oxidized, leading to the formation of a mixture of ketones and carboxylic acids.Oxidation of alkenes by ozone leads to destruction of both the σ and π bonds of the double‐bond system. This cleavage of an alkene double bond, generally accomplished in good yield, is called ozonolysis. The products of ozonolysis are aldehydes and ketones. Dicarboxylic acids are organic compounds that contain two carboxyl functional groups. These compounds are sometimes written as HO2C-R-CO2H. Adipic acid, a dicarboxylic acid with IUPAC name Hexanedioic acid is an organic compound with the formula (CH2)4(COOH)2. From an industrial perspective, it is the most important dicarboxylic acid: About 2.5 billion kilograms of this white crystalline powder are produced annually, mainly as a precursor for the production of nylon. The great majority of the 2.5 billion kg of adipic acid produced annually is used as monomer for the production of nylon by a polycondensation reaction with hexamethylene diamine forming 6,6-nylon. Other industrial uses of adipic acid are the production of adhesives, plasticizers, gelatinizing agents, hydraulic fluids, lubricants, emollients, polyurethane foams, leather tanning, urethane and also as an acidulant in foods. Adipic acid is used after esterification with various groups such as dicapryl, di(ethylhexyl), diisobutyl, and diisodecyl. Adipic acid otherwise rarely occurs in nature.

Nylon 6,6- a polymer of adipic acid and 1,6-diaminohexane

Adipic acid was commonly obtained by oxidation of castor oil with nitric acid (splitting of the carbon chain close to the OH group), but it is also obtained by oxidation of cyclohexanone or cyclohexene.

[O]

Cyclohexene, an susceptible to oxidat

cyclohexene

has a carbon-carbon

Adipic acid

alkene, is d which is a site of relatively

high electron density. Oxidative cleavage of alkenes is a well-known reaction. Several reagents are known to react with alkenes which result in complete breaking of both bonds to the carbon atoms. With relatively mild oxidation, only the pi bond of the alkene is cleaved, producing epoxides and 1,2-diols. More vigorous oxidation can result in the complete cleavage of the carbon-carbon double bond, leading to the formation of various carbonyl compounds, with the specific product dependent on the substitution pattern of the alkene and on the nature of the oxidant used. Reaction of cyclohexene with potassium permanganate under basic conditions results in oxidation. The cyclohexene is oxidized by the permanganate which leads to a ring opening reaction producing adipic acid as the final product. The oxidation of an alkene is an example of an addition reaction. Oxygen atoms in the oxidizing agent add to the carbon-carbon double bond. As a result, the ring opens and the dicarboxylic acid is formed. The aim of this experiment is to synthesize adipic (hexanedioic) acid through the permanganate oxidization of cyclohexene APPARATUS           

250ml Erlenmeyer flask 100ml Volumetric flask 10ml Volumetric flask Ice-water bath Stopper Hot plate Boiling chip 250ml beaker Hirsch funnel Melting point apparatus Filter paper

CHEMICALS     

Cyclohexene Potassium permanganate Methanol 1% Sodium hydroxide Concentrated hydrochloric acid

EXPERIMENTAL PROCEDURE

50 mL of water, 2ml cyclohexene (density = 0.81 g cm-3) and potassium permanganate (8.4 g) were measured/weighed and added to a 250 mL Erlenmeyer flask. The flask was Stoppered loosely, wrapped with a towel and swirled vigorously for 5 minutes. The paper towel was occasionally removed to check if the flask was warming up (the flask should feel warm). If no rise in temperature was detected, the stopper was remove and the mixture was warmed on the steam bath and stopper was put back loosely after warming. The flask was swirled at frequent intervals for 20 minutes (yield depends on how well the reactants are mixed at this stage). The temperature of the mixture was kept between 35°C and 40°C. When the temperature rised above 45°, the mixture was briefly cooled in an ice-water bath then the stopper was removed and the flask was placed on a steam bath for 15 minutes. Afterwards swirling of the flask was continued at frequent intervals. A spot test was made by withdrawing some of the reaction mixture on the tip of a stirring rod and touching it to a filter paper; permanganate, if present appeared as a purple ring around the dark brown spot of manganese dioxide. When permanganate was still present, 1 mL of methanol was added to the mixture and it was heated. This step was repeated until the permanganate color has disappeared. The mixture was then filtered through a large Buchner funnel (vacuum) into a clean filter flask. The reaction flask was then rinsed with 10 mL of hot 1% sodium hydroxide solution and poured through the filter. The flask was then rinsed with a second portion of 10 mL of 1% sodium hydroxide solution. The filtrate and washings were then placed in a 250 mL beaker (premarked at 10 mL), boiling chip were added to it and it was boiled over a flame until the volume of the solution was about 10 mL. The solution was then cooled in an ice-water bath and acidified to about pH 1 by cautiously adding concentrated hydrochloric acid dropwise while stirring the solution. An additional 3 mL of acid was added and the beaker was allowed to stand in the ice bath for 5 - 10 min to complete the crystallization. The acid was collected by vacuum filtration. It was then Recrystallized from not more than 5 mL of boiling water then cooled to room temperature and placed in an ice-water bath for 10 minutes. The product was filtered by vacuum (Hirsch funnel) and dried. Melting point and yield of product were measured/weighed.

RESULTS AND ANALYSIS

Tabulated results obtained from the procedure, including any necessary computations made with respect to the data is shown below. n Equation + Cyclohexene MW= 82g/mol

[O] Oxidizing agent (KMnO ) 4

adipic acid MW 146 g/mol

Volume of Cyclohexene used

2 mL

Moles of Cylohexene used

0.01972 mol

Density of Cyclohexene

0.81 g/cm3

Moles of adipic acid produced

0.01972 mol

Actual Yield

0.67 g

Theoretical Yield

2.88 g

Percent Yield

23.2%

Melting point of adipic acid

149 oC -152oC

Color of adipic acid crystals Calculations:

white

No. of moles of cyclohexene used:

Using the given volume of 2 mL, the molecular weight (82g/mol), and the density of cyclohexene (0.81g/cm3), the theoretical number of moles of cyclohexene used can be calculated. −3 3 mass ( cyclohexene )=ρV =0.81 gc m ∗2 c m mass =1.62 g

moles=

mass 1.62 g =0.01972 mol ( cyclohexene ) = Mr 82.14 gmol−1

According to reaction equation 1 mole of cyclohexene produces 1 mole of adipic acid

∴mloes of adipic acid=moles of cyclohexene=0.01972mol Theoretical yield of adipic acid: mass of adipic acid=moles∗ Mr ¿ 0.01972 mol∗142.14 gmo l−1 ¿ 2.88 g( adipic acid ) Percentage yield of adipic acid: Percentage yield=

actual yield ∗100 Theoretical yield

0.67 g ∗100=23.25 % 2.88 g

DISCUSSION An average yield of 24.23% (0.67g) of product was obtained compared to a theoretical yield of 2.88g. It’s possible that mistakes were made during the preparation of the product. As it was mentioned in the procedure, accuracy of the overall procedure is important to yield maximum

amount of the product. It’s possible that some of the permanganate ions were still present in the reaction mixture when it was taken for filtration which in turn would affect the product. Under controlled conditions, KMnO4 oxidizes very efficiently primary alcohols to carboxylic acids. Methanol as a primary alcohol was partially oxidized first into aldehyde before being fully oxidized to formic acid, the carboxylic acid product. Illustration of oxidation stages of methanol is shown below:

When a primary alcohol is converted to a carboxylic acid, the terminal carbon atom increases its oxidation state by four. It was observed in the experiment that the flask used was completely covered with the brown color Manganese dioxide (MnO2). Sodium hydroxide (NaOH) was added to the flask. Sodium hydroxide did two important reaction to flask. First was the rinsing where it is intended to maximize the yield of adipic acid. There is a partial oxidation of MnO2 by NaOH that is why MnO2 was removed from the sides of the flask. The other possible use of NaOH is the neutralization of formic acid which was formed during the oxidation of methanol. Over oxidation with permanganate is always a problem, but the relative reaction rates are very much a function of the pH of the reaction mixture and, in basic solution, potassium permanganate oxidizes unsaturated groups more rapidly than it oxidizes alcohols therefore some errors could have arised when the solution was being measured for pH since only a universal indicator was used to test for pH change. There is a possibility that the pH was higher than required and therefore favoring oxidation of unsaturated groups rather than the target alcohol (methanol). This could explain the low yield of product.

Possible mechanism:

CONCLUSION

0.67g of Adipic acid was produced and was only 23.25% of the expected theoretical yield of 2.88g. The crystals were white in color and had a melting point of 150–155oC

REFERENCES Goodman & Gilman’s, (1996), “The Pharmacological Basis of Therapeutics”, 9th Ed., McGraw Hill, New York, pg 904 Solomons T.W.G., (2009) Organic Chemistry, Fourth Edition, p. 322. Zhang Q., Zhao C.C., Liu Y., & Lin F., (2012). Experimental study on effect of potassium permanganate on methanol fuel by spectrophotometry. Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology). 43. 4522-4525.

EXERCISE

1. What reaction is effected by the addition of methanol to unreacted permanganate? Addition of methanol affects the further oxidation of the diol intermediate to remove any excess permanganate in the solution. 2. Does this reaction affect your product? Addition of methanol to unreacted permanganate doesn’t have much effect on the product or with the yield...