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Chemistry Project Report

Title:

Preparation & purification of racemic mixture of bi-naphthol and to confirm its structure and purity by NMR Spectroscopy.

Indian Institute of Science Education & Research, Kolkata

Semester-II 2008

By: Madhuri Mallela (Roll No. - 56)

Ashish Agarwal (Roll No. - 65) Jyothi V. Nair (Roll No. - 72) Harsh Purwar (Roll No. - 76)

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Contents

Abstract 03

Keywords 03

Introduction 04

Aim of the Experiment 05

Apparatus Required 05

Chemicals Required 05

Theory 05

Procedure 06

Observations 06

Explanation of the NMR results 07

Precautions 07

References 08

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Abstract

In this experiment we synthesized and purified the Bi-naphthol from a very commonly available compound β-naphthol or 2-napthol. β-naphthol reacts with FeCl3 to give a racemic mixture of Bi-naphthol with FeCl2 and hydrochloric acid. Chemical Reaction:-

β-naphthol Bi-naphthol

The above mentioned reaction is carried out in a 2-necked round bottom flask attached with a reflux condenser and a dropping funnel with continuous & vigorous stirring and heating.

After the completion of the reaction the crude product is washed with the boiling water, filtered, dried in air so as to remove the bi-products (FeCl2 & HCl) and unreacted reactants and then finally re-crystallized with toluene. The NMR spectroscopy was also done to check the purity of the crystals and to confirm the structure of the purified organic compound (i.e. bi-naphthol).

Keywords: Racemic mixture, chirality, stereo isomers, diastereomers, NMR spectroscopy, coupling reaction, asymmetric catalysis, ligand, racemization, BINOL.

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Introduction 1,1'-Bi-2-naphthol (BINOL) is an organic compound that is often used as a ligand for transition-metal catalyzed asymmetric synthesis. BINOL has axial chirality and the two enantiomers can be readily separated and are stable toward racemisation. The specific rotation of the two enantiomers is +/- 35.5° (c=1 in THF). BINOL is a precursor for another chiral ligand called BINAP.

• BINAP is used in organic synthesis for enantio-selective transformations catalyzed by its complexes of ruthenium, rhodium, and palladium.

• Pioneered by Ryoji Noyori and his co-workers, Rh complexes of BINAP are useful for the synthesis of (-)-menthol.

• For this work, Noyori was awarded the Nobel Prize in Chemistry in 2001. Axial chirality is a special case of chirality in which a molecule does not possess a stereogenic center (the most common form of chirality in organic compounds) but an axis of chirality - an axis is about which a set of substituent is held in a spatial arrangement which is not super-imposable on its mirror image. The specific rotation of a chemical compound (α) is defined as the observed angle of optical rotation θ when plane-polarized light is passed through a sample with a path length of 1 decimeter and a sample concentration of 1 gram per 1 deciliter. The specific rotation of a pure material is an intrinsic property of that material at a given wavelength and temperature. Values should always be accompanied by the temperature at which the measurement was performed and the solvent in which the material was dissolved.

Asymmetric synthesis, also called chiral synthesis, enantio-selective synthesis or stereo-selective synthesis is organic synthesis which introduces one or more new and desired elements of chirality. This is important in the field of pharmaceuticals because the different enantiomers or diastereomers of a molecule often have different biological activity.

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Aim:- To prepare the racemic mixture of bi-naphthol and to check the purity of the crystals by NMR Spectroscopy.

Apparatus Required:- 1. Two-necked round bottom flask (500 mL) 2. Reflux condenser 3. Guard tube 4. Dropping funnel 5. Silicon Oil bath 6. Heater with magnetic stirrer 7. Beakers (250 mL, 50 mL) 8. Measuring cylinders ( 500 mL, 50 mL) 9. Stopper

Chemicals Required:- 1. 2-Naphthol (36 grams) 2. Ferric Chloride (70 grams) 3. Toluene

Theory:-

Chemical Reaction:-

β-naphthol Bi-naphthol

Two moles of β-naphthol or 2-napthol reacts with 2 moles of Ferric Chloride to give racemic mixture of bi-naphthol.

Above reaction is an oxidative ortho-ortho coupling reaction catalyzed by Fe3+. Iron(III) ions also stabilize the transition state.

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Procedure:-

1. The apparatus is set and the chemicals are weighed as mentioned below:-

7.2 g of 2-napthol

14 g of FeCl3 2. 2-napthol is dissolved in 300 mL of water and heated in the 2-necked RB with the

reflux condenser connected to it. 3. After the 2-napthol is completely dissolved, FeCl3 dissolved in 30 mL of water is

added to it drop-wise, using the dropping funnel with vigorous stirring. 4. At the end of the reaction bi-naphthol separates out in flakes. 5. It is boiled for 5-10 minutes and the hot suspension is filtered through Buchner

funnel. 6. Then it is washed with boiling water till the filtrate becomes colourless. 7. The residue is then left to dry in air upon a filter paper. 8. This process is repeated 5 times to get the desired amount of bi-naphthol. 9. The crude product is then re-crystallized using toluene. 10. The crude product is dissolved in toluene and refluxed. 11. The dissolved product is filtered using Buchner funnel and then using activated

charcoal. 12. The process is repeated till we obtain clear crystals of bi-naphthol.

Observations:-

Zoomed In

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Explanation of the NMR spectroscopy results:- There are 14 hydrogen molecules in a molecule of bi-naphthol out of which two are attached with the oxygen which give a broad peak in the NMR. This is because of the proton transfer between O-H and CDCl3 (solvent). This effect is also called as the tumbling effect. The other 12 ‘H’ atoms give six different peaks due to symmetry. The doublet or triplet is observed due to difference in their chemical environment or chemical shift. Hydrogen H(1)s are similar with respect to their chemical environment. Due to the electron withdrawing nature of the OH group, these hydrogen’s suffer the highest chemical shifting. And as spin value for the proton is ½ and the number of 3 bond apart hydrogen’s are two so we get doublet corresponding to H(1)’s. Similarly we could easily figure out the following results:

Hydrogen No. [H(i)] Doublet or Triplet

1 Doublet

2 Doublet

3 Doublet

4 Triplet

5 Triplet

6 Doublet

As only the peaks corresponding to the hydrogen’s in the compound (bi-naphthol) are observed in the NMR spectroscopy we can say that the compound prepared is pure.

Precautions:-

1. The apparatus should be rinsed properly before use and then dried where necessary.

2. The reaction mixture should be heated and stirred properly.

3. Proper stirrer should be used according to the requirement of the apparatus.

4. FeCl3 should be added to the round bottom flask slowly using the dropping funnel

and vigorous stirring.

5. Toluene and other volatile and hazardous chemicals should be handled with extreme

care. It is a carcinogenic volatile liquid.

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References Vogel’s Textbook of Practical Organic Chemistry

– By Brian S. Furniss

www.wikipedia.org

www.google.co.in

www.about.com

Organic Chemistry - By Jonathan Clayden

Purification of Laboratory Chemicals