1 Ekim 2009 Perşembe

Iodoform

ChBE 203

Organic Chemistry Laboratory

Experiment 1

IODOFORM

Submitted by

Hilmi ÖLMEZ

Course Instructor : Prof. Dr. Süheyla Uzman

Submitted To : Mahir TULUNAY

Experiment Date : 23.09.2009

Submission Date : 30.09.2009

Yedİtepe University

İstanbul

TABLE OF CONTENTS

TABLE OF CONTENTS........................................................................................................ ii

LIST OF FIGURES................................................................................................................. iii

1.THEORY................................................................................................................................ 1

1.1 Iodoform.......................................................................................................................... 1

1.1.1. Definition.................................................................................................................. 1

1.1.2. Formation................................................................................................................. 2

1.2 Potassium Iodide............................................................................................................. 3

1.3 Acetone............................................................................................................................. 3

1.4 Sodium Hypochlorite...................................................................................................... 4

1.5 Ethanol............................................................................................................................. 4

1.6 Reflux Condenser........................................................................................................... 5

2. APPARATUS....................................................................................................................... 6

2.1 Equipment....................................................................................................................... 6

2.2 Chemicals......................................................................................................................... 6

3. PROCEDURE...................................................................................................................... 7

3.1 Synthesis........................................................................................................................... 7

3.2 Recrystallization.............................................................................................................. 7

4. CALCULATIONS AND OBSERVATIONS.................................................................... 8

4.1 Observations.................................................................................................................... 8

4.2 Calculations..................................................................................................................... 8

5. RESULTS AND DISCUSSION.......................................................................................... 9

REFERENCES................................................................................................................... 10

LIST OF FIGURES

Figure 1 : Iodoform................................................................................................................... 1

Figure 2 : Potassium Iodide...................................................................................................... 3

Figure 3 : Acetone..................................................................................................................... 4

Figure 4 : Sodium Hypochlorite............................................................................................... 4

Figure 5 : Ethanol..................................................................................................................... 5

Figure 6 : Reflux Condenser.................................................................................................... 5

1. THEORY

1.1 Iodoform

1.1.1. Definition:

Iodoform, or triiodomethane (CHI3) is yellow crystalline with a relatively high molar mass due to the iodine atoms. It is therefore a solid at room temperature It melts at 119°C and is very slightly soluble in water and soluble in ether or ethanol. A visible precipitate of this compound will form from a sample only when a methyl ketone is present. This type of reactivity conforms to the more general Haloform Reaction. Iodoform was formerly used as an antiseptic. It is a stable compound. Incompatible with strong oxidizing agents, reducing agents. May explode when heated. It is harmful if swallowed, inhaled or absorbed through skin and causes irritation to skin, eyes and respiratory tract. Iodoform is also affects cardiovascular system, central nervous system, liver and kidneys.
When released into the soil, iodoform may leach into groundwater. When released into water, it may evaporate to a moderate extent and it is expected to have a half-life between 1 and 10 days. Iodoform has an estimated bioconcentration factor of less than 100. This material is not expected to significantly bioaccumulate. When released into the air, it may be moderately degraded by reaction with photochemically produced hydroxyl radicals and it is expected to have a half-life of greater than 30 days.

Iodoform

Figure 1 : Iodoform

1.1.2. Formation of Iodoform:

Iodoform is produced when a methyl ketone, acetaldehyde, or an alcohol with the formula RCHOHCH3 is treated with sodium hydroxide and iodine.

> What the triiodomethane (iodoform) reaction shows:

A positive result - the pale yellow precipitate of triiodomethane (iodoform) is given by an aldehyde or ketone containing the grouping:

"R" can be a hydrogen atom or a hydrocarbon group (for example, an alkyl group).

If "R" is hydrogen, then you have the aldehyde ethanol, CH3CHO. Ethanol is the only aldehyde to give the triiodomethane (iodoform) reaction. If "R" is a hydrocarbon group, then you have a ketone. Lots of ketones give this reaction, but those that do all have a methyl group on one side of the carbon-oxygen double bond. These are known as methyl ketones. Compounds that are easily oxidized to acetaldehyde and methyl ketones also give a positive iodoform test. Only ethanol can be oxidized to acetaldehyde and secondary alcohols that have the general formula CH3CHOHR can be oxidized to methyl ketones For ethanol (CH3CH2OH), the following reactions show the formation of iodoform :

CH3COCH3 + 3 NaClO + 3 KI CH3COCl3 + 3 NaOH + 3 KCl

CH 3COCl3 + NaOH CH3COONa + CHI3

1.2. Potassium Iodide

Potassium iodide is a white crystalline salt with chemical formula KI, used in photography and radiation treatment. It finds widespread application as an iodide source because it is less hygroscopic than sodium iodide, making it easier to work with. KI can turn yellow upon heating in air or upon standing in moist air for long periods, because of oxidation of the iodide to iodine.

Potassium iodide

Figure 2: Potassium Iodide

Potassium iodide behaves as a simple ionic salt, K+I. Since the iodide ion is a mild reducing agent, I is easily oxidized to I2 by powerful oxidizing agents such as chlorine:

2 KI (aq) + Cl2 (aq) → 2 KCl + I2 (aq)

Potassium iodide also serves in some organic reactions as a source of iodide ion

Its physical properties include boiling point is 1330 °C (1600K), melting point is 681 °C (954 K) and 166.00 g/mol molar mass and 3.13 g/ cm3 density ,solubility in water is 128g/ 100mL at 6 °C.

1.3. Acetone

A chemical compound, CH3COCH3. A colorless liquid with an ethereal odor, it is the first member of the homologous series of aliphatic ketones. Its physical properties include boiling point 56.2°C (133.2°F), melting point −94.8°C (−138.6°F), and specific gravity 0.791. Acetone is used as a solvent for cellulose ethers, cellulose acetate, cellulose nitrate, and other cellulose esters. Cellulose acetate is spun from acetone solution. Lacquers, based on cellulose esters, are used in solution in mixed solvents including acetone.

AcetoneAcetone

Figure 3 : Acetone

1.4. Sodium Hypochlorite

Sodium Hypochlorite with chemical formula NaOCl is a colorless, transparent liquid. It is dissolved in cold water and decomposed by hot water or carbon dioxide. As an excellent chlorine sterilizer, it serves as a strong oxidizer, bleaching agent, and sterilizer. To store Sodium Hypochlorite safely, locate it in a cool, dark place, maintaining pH 11 or more and avoiding mixture with copper or nickel.

Sodium hypochlorite

Figure 4: Sodium Hypochlorite

Used as a bleaching agent, oxidant, sterilizer, decoloring agent, deodorant, water treatment, food additives etc. Also used as a food additive.

1.5. Ethanol

Organic compound, most important of the alcohols, chemical formula CH3CH2OH. . Is also called alcohol, ethanol, grain alcohol, industrial alcohol, fermentation alcohol, cologne spirits, ethyl hydroxide, and methylcarbinol

Pure ethyl alcohol is a colorless, limpid, volatile liquid which is flammable and toxic and has a pungent taste. It boils at 78.4°C (173°F) and melts at −112.3°C (−170.1°F), has a specific gravity of 0.7851 at 20°C (68°F), and is soluble in water and most organic liquids. It is one of the most important industrial organic chemicals. Ethyl alcohol is produced by chemical synthesis and by fermentation or biosynthetic processes.

Ethyl alcohol is used as a solvent, extractant, antifreeze, and intermediate in the synthesis of innumerable organic chemicals. It is also an essential ingredient of alcoholic beverages

The major use of ethyl alcohol is as a starting material for various organic syntheses.

EthanolEthanol

Figure 5: Ethanol

1.6. Reflux Condenser :

It is a condenser such that vapor over a boiling liquid is condensed and flows back into the vessel to prevent its contents from boiling dry. The reflux condenser consists of a length of tubing connected directly to the head of a vessel and equipped with a water cooling jacket. Condensed vapors are returned directly to the vessel and any noncondensable gases can be released through a needle valve at the top of the condenser. A spiral wound inner packing in the condenser ensures maximum effectiveness in a rather short length.

Figure 6: Reflux condenser








2. APPARATUS

2.1. Equipments

Graduated cylinder

Beaker 250 mL

Erlenmeyer flask 250 mL

Pipette

Suction bulb

Beaker 25 mL

Filter paper

Funnel

Reflux condenser

Round Bottom Flask 500 mL

Heater

Watch Glass

Scale

2.2. Chemicals

Potassium iodide , KI

Water , H2O

Acetone , CH3COCH3

Sodium hypochlorite , NaClO

Ethanol , CH3CH2OH


3. PROCEDURE

3.1. Synthesis

1. 3 g potassium iodide was weighed.

2. This 3 g of potassium iodide was dissolved in 50 mL water in a 250 mL beaker.

3. 1 mL acetone was added to the solution.

4. The sodium hypochlorite solution was added drop by drop while mixing the solution smultaneously.

5. Iodoform was formed as a yellow precipitate.

6. To complete the precipitation waited for 10 minutes and the precipitate was filtered using filter paper.

3.2. Recrystallization

7. Reflux condenser was set up and iodoform crystals were put in a 500 mL flask and 25 mL

ethanol was added and heated to dissolve the crystals under the reflux.

8. After the solution boiled the hot mixture was filtered using filter paper.

9. The iodoform was crystallized.

10. The crystals was filtered and waited two days and dried on a paper.

11. In order to calculate the yield the crystals was weighed.

12. The melting point was recorded.

4. CALCULATIONS AND OBSERVATIONS

4.1 Observations :

After preparing solution of potassium iodide (KI) and acetone (CH3COCH3) , firstly we did not add sodium hypocholorite (NaClO) drop by drop so we would not get the accurate measurement then we started to add sodium hypocholorite (NaClO) drop by drop and observed the dark colour and we observed little yellow precipitation. This dark colour in every drop showed that the reaction is carrying on. Until the dark colour can not be seen, sodium hypochlorite was added in order to finish all acetone and form iodoform. It is observed that iodoform is a yellow crystalline. The precipitation that we observed stayed at the bottom. We filtered solution than taking crystals on the filter paper put in the flask. Placing on the heater we observed vaporization and condensation. At the end of this process iodoform crystallines are dissolved in ethanol. There were two reasons for using ethanol. The reasons are that ethanol is a good solvent for iodoform and good choice for recrystalization. By recrystallization which is the last step of the experiment, iodoform is purified. In order to calculate the yield we have :

The empty weight of filter paper:1.39 g

The weight of filter paper with crystalls:1.38 g

The net weight of iodoform crystalls:1.38-1.39=-0.01

Expected weight of iodoform crystalls:1.75 g

Iodoform crystalls were started to melt at 116 0C expected melting point was 119 0C .

4.2. Calculations :

We have 18 mmol potassium iodide, 19 mmol acetone and 23 mmol sodium hypochlorite so :

CH3COCH3 + 3 NaClO + 3 KI CH3COCl3 + 3 NaOH + 3 KCl

19 mmol 23 mmol 18 mmol

As we see in this reaction the limiting reactant is potassium iodide because among these chemicals we have potassium iodide least, and acetone and sodium hypochlorite are the excess reactants.

The yield = (actual value/therotical value)*100

= (0.01/1.75) * 100 = -0.6 %

5. RESULTS AND DISCUSSION

As a result the iodoform reaction is characteristic for methylketones as well as for alcohols that can be oxidized to methyl carbonyl compounds. The iodoform test is a test for the existence of the CH3 -CO group in a molecule. The group to which the CH3-CO group is attached can be aryl, alkyl and hydrogen.

Five days had passed after the experiment we have already measured that the weight of filter paper with crystalls is1.38 g and we know that empty weight of filter paper is 1.39 g so the net weight of iodoform crystalls is 1.38-1.39=-0.01g. We have found that the yield is - 0.6 %.

Of cource these can not be true. But our measurings are like these unfortunately.

In fact the theoretical yield is 74 % .Reasons of getting this extraordinary complex values depends on many cases. If we had very small quantity our assertion could be as “ While mixing the potassium iodide-water-acetone solution,sodium hypochlorite solution should be put in it drop by drop very carefully. If it is not done in such a way,then the crystalls will be get very little or none.Moreover,it is significant to observe the brownish color of solution while adding NaClO not to add more or less NaClO. When filtering idoform the hot mixture should be poured immediately to provide the get all mixture into the flask.” However our case much more convoluted than this. This result can be sourced from three reasons. First, our paper could be wet and this wetness’ water’s mass greater than our yield’s mass. Secondly, there was a problem in our scales. As third, one mistakenly pour or cut it even if I can not believe.

REFERENCES

1. Atkins, R. C., Carey, A. C., Organic Chemistry 4th ed., Mc Graw Hill, 2002

2. Carey, F. A., Sundberg, R. A., Advanced Organic Chemistry, 5th ed., Springer, 2007

3. http://www.answers.com/topic/iodoform

4. Chang, R., College, W., Chemistry, 7th ed., Mc Graw Hill, 2004

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